THE 


AMERICAN 


SYSTEM  OF  DENTISTRY. 


IN  TREATISES  BY  VARIOUS  AUTHORS. 


EDITED    BY 

WILBUR   F.  LITCH,  M,D.,  D.D.S., 

PROFESSOR  OF   PROSTHETIC    DENTISTRY,  THERAPEUTICS,  AND   MATERIA   MEDICA   IN  THE 
PENNSYLVANIA   COLLEGE  OF   DENTAL  SURGERY,   PHILADELPHIA. 


VOLUME    I. 

REGIONAL  AND  COMPARATIVE    DENTAL  ANATOMY, 
DENTAL  HISTOLOGY,  AND  DENTAL  PATHOLOGY. 


WITH    FIVE    HUNDRED  AND   THIRTY-SEVEN    ILLUSTRATIONS   AND   SIX    PLATES. 


'..55% 


PHILADELPHIA  : 

LEA    B E^ecXH lEi3f)P-v^    CO, 


Si 


'^//j 


Entered  according  to  Act  of  Congress,  in  the  year  1886,  by 

LEA    BROTHERS    &    CO., 

in  the  Oflfice  of  the  Librarian  of  Congress  at  Washington.     All  rights  reserved. 


Westcott  &  Thomson,  William  .J.  Dornan, 

Stereotypers  and  Electrotypem,  Philada.  Printer,  Philada. 


\ 


PREFACE.    V.I 


No  fact  is  now  more  fully  recognized  than  that  a  clear,  intelligent, 
and  comprehensive  knowledge  of  any  subject  can  best  be  communicated 
by  one  who  has  a  working  acquaintance  with  it  or  has  made  it  an 
object  of  special  research.  To  secure  for  the  several  departments  of 
this  work  writers  thus  informed,  and  willing  to  take  from  needed  rest 
and  give  to  toil  the  time  necessary  for  the  systematic  presentation  of 
their  specialized  knowledge,  was  not  the  least  of  the  difficulties  which 
attended  the  inception  of  this  undertaking.  How  well  those  who 
assumed  this  labor  have  accomplished  their  several  tasks  these  pages 
must  testify. 

In  judging  of  their  work,  the  fact  must  be  borne  in  mind  that 
those  textual  abridgments  which  are  essential  in  a  compend  or  man- 
ual would  fall  far  short  of  the  obvious  requirements  of  a  systematic 
treatise.  Throughout  the  preparation  of  these  volumes  this  distinction 
has  been  recognized,  and,  while  prolixity  and  useless  verbiage  have 
been  avoided,  space  has  been  given  for  the  fullest  possible  exposition 
of  the  subjects  taught.  Above  all,  it  has  been  desired  that  each  con- 
tribution should  be  a  teaching  paper;  hence  no  detail  necessary  to 
make  clear  the  meaning  of  the  writer  has  been  spared. 

This  particularity  of  method  has  been  specially  emjjiiasized  in  the 
sections  devoted  to  technical  processes  and  manipulative  procedures ; 
and  as  a  full  comprehension  of  their  intricate  details  can  rarely  be 
attained  through  so  imperfect  an  agency  as  a  merely  verbal  descrip- 
tion the  text  has  been  lavishly  furnished  with  illustrations  largely 
made  from  original  drawings  and  models  prepared  by  the  various 
contributors. 

Upon  certain  points  in  histology,  pathology,  and  therapeutics  some 
divergence  of  views  will  be  noted.  The  Editor  has  not  sought  to 
enforce  absolute  harmony  of  doctrine,  or  assumed  to  commit  this  work 
to  a  partisan  advocacy  of  either  side  of  questions  which  are  still  i<ub 
judice.  Recognizing  the  fact  that  the  profession  at  large  still  differ 
upon  many  questions  of  great  although  not  vital  importance,  and  that 

3 


4  PREFACE. 

ill  practice  the  same  end  may  often  be  attained  by  widely  different 
means,  he  has  deemed  it  the  wiser  course  to  allow  freedom  of  state- 
ment to  all,  sure  that  at  last  the  truer  knowledge  will  prevail. 

It  has  been  found  impossible  in  a  work  of  this  character  to  define 
the  limitations  of  each  paper  so  sharply  and  rigidly  as  to  avoid 
all  duplication  of  matter.  It  Avill,  however,  be  found  that  if  writers 
traverse  for  short  distances  the  same  field,  they  do  it  from  diflPerent 
directions  and  survey  it  from  varying  standpoints,  often  to  the  reader's 
profit ;  so  that  within  reasonable  limits  this  defect  in  the  method  of 
literary  collaboration  is  not  an  unmixed  evil.  It  has,  however,  been 
restricted  to  the  narrowest  possible  bounds. 

The  Editor  cannot  close  this  preface  without  extending  to  the  con- 
tributors his  heartfelt  thanks  for  their  generous  co-operation.  He 
trusts  and  believes  that  they  will  find  abundant  reward  for  their 
unselfish  labors  in  that  satisfaction  which  ever  comes  from  a  good 
M'ork  well  wrought,  and  in  the  approval  of  their  professional  brethren 
everywhere. 

His  special  thanks  are  due  to  Dr.  James  W.  White,  Editor  of  the 
Dental  Cosmos,  and  also  to  Professors  C.  N.  Peirce,  T.  C.  Stell- 
WAGEN,  Henry  Leffmann,  and  Albert  P.  Brubaker,  for  counsel 
and  help  which  have  been  of  the  highest  value  in  the  editorial  super- 
vision of  this  work. 

THE  EDITOR. 

June,  1886. 


CONTRIBUTORS  TO  VOLUME  I. 


BLACK,  G.  v.,  M.D.,  D.D.S., 

Professor  of  Pathology  in  the  Chicago  College  of  Dental  Surgery,  Chicago. 

BRUBAKER,  ALBERT  P.,  A.M.,  M.  D.,  D.  D.  S., 

Professor  of  Physiology  aud  Pathology  in  the  Pennsylvania  College  of  Dental 
Surgery ;  Demonstrator  of  Physiology  in  the  Jefferson  Medical  College,  Phila- 
delphia. 

CRYER,  M.  H.,  M.D.,  D.  D.  S., 

Chief  of  Clinic  of  Oral  Surgery,  Medico-Chirurgical  College  of  Philadelphia. 

DALL,  W.  H., 

Curator  of  the  Department  of  Mollusks,  National  Museum,  Washington,  D.  C. 

SUDDUTH,  W.  XAVIER,  M.  D.,  D.  D.  S.,  F.  R.  M.  S., 

Demonstrator  of  Dental  Histology  in  the  Philadelphia  Dental  College,  Phila- 
delphia. 

TRUMAN,  JAMES,  D.  D.  S., 

Professor  of  Dental  Pathology,  Therapeutics,  and  Materia  Medica  in  the  Dental 
Department  of  the  University  of  Pennsylvania. 

WORTMAN,  JACOB  L.,  M.D., 

Anatomist  to  the  U.  S.  Army  Medical  Museum,  Washington,  D.  C. 


V 

CONTENTS  OF  VOLUME  I. 


PAGE 

PREFACE    3 

PART   I. 
REGIONAL  ANATOMY. 

REGIONAL  ANATOMY,  Etc.    By  M.  H.  Cryer,  M.D.,  D.  D.S 35 

LYxMPHATIC  VESSELS  OF  THE  HEAD  AND  NECK.      By  Albert  P. 

Brubaker,  a.  M.,  M.  D.,  D.  D.  S 325 

*  PART  II. 

DENTAL   ANATOMY. 

THE  TEETH  OF  THE  INVERTEBRATES.     By  W.  H.  Dall 337 

THE  TEETH  OF  THE  VERTEBRATES.     By  Jacob  L.  Wortman,  M.D.  .    351 

PART  III. 

EMBRYOLOGY   AND   DENTAL   HISTOLOGY. 

EMBRYOLOGY  AND  DENTAL  HISTOLOGY.     By  W.  Xavier  Scdduth, 

M.D.,  D.D.  S 519 

PART  IV. 

GENERAL  AND  DENTAL  PATHOLOGY. 

GENERAL  PATHOLOGY.     By  G.  V.  Black,  M.  D.,  D.  D.  S 661 

DENTAL  CARIES.     By  G.  V.  Black,  M.  D.,  D.  D.  S 729 

PATHOLOGY  OF  THE  DENTAL  PULP.  By  G.  V.  Black,  M.  D.,  D.  D.  S.  829 
DISEASES  OF  THE  DENTAL  PULP,  AND  THEIR  TREATJNIENT.     By 

James  Truman,  D.  D.  S 888 

DISEASES    OF    THE    PERIDENTAL   MEMBRANE.      By   G.  V.  Black, 

M.D.,  D.D.S 918 

ABRASION  AND  EROSION  OF  THE  TEETH.     By  G.  V.  Black,  M.  D., 

D.D.S 993 


INDEX 1011 

7 


ILLUSTRATIONS. 


FIGURE 

1.  Section  of  a  Sound  Adult  Femur  . 

2.  Structure    of    the    Neck    of    the 

Femur 

3.  Fibula  tied  in  a  Knot  after  Mace- 

ration in  a  Dilute  Acid  .... 

4.  Transverse    Section    of    Compact 

Tissue  of  Humerus  .... 

5.  Section    Parallel    to  the    Surface 

from  the  Shaft  of  the  Femur  .    . 

6.  Lamellfe  torn  off  from  a  Decalci- 

fied Human  Parietal  Bone     .    . 

7.  Transverse  Section  of  Decalcified 

Human  Tibia 

8.  Lacuufe  of  Osseous  Substance    .    . 

9.  The  External  Periosteum  .... 
10.  Cells  from  the   Marrow  of  Bone 

during  their  Period  of  Develop- 
ment    

IL  Three    Mnltinuclear    Giant-cells 
(Osteoclasts) 

12.  Section  of  Part  of  One  of  the  Limb- 

bones  of  a  Fcetal  Cat 

13.  Imperfectly     and      Ill-developed 

Upper  Jaw , 

14.  Occipital  Bone,  outer  surface    .    . 

15.  Occipital  Bone,  inner  surface    .    . 

16.  Development  of  Occipital  Bone    . 

17.  Left  Temporal  Bone,  outer  surface 

18.  Left  Temporal  Bone,  inner  surface 

19.  Petrous  Portion  of  Temporal  Bone, 

inferior  surface 

20.  Development    of   the    Temporal 

Bone  by  Four  Centres 

21.  Sphenoid  Bone,  superior  surface  . 

22.  Spiienoid  Bone,  anterior  surface  . 

23.  Spiienoid  Bone,  posterior  surface  . 

24.  Foetal  S[ihenoid  Bones 

25.  Left  Parietal  Bone,  external  sur- 

face   

26.  Left  Parietal   Bone,  internal  sur- 

face   

27.  Frontal  Bone,  outer  surface  .    .    . 

28.  Frontal  Bone,  inner  surface   .    .    . 

29.  Frontal  Bone  at  Birth,  developed 

by  two  lateral  halves 

30.  Ethmoid    Bone,  outer   surface   of 

right  lateral  mass 

31.  Perpendicular   Plate  of  Ethmoid 

Bone 

32.  Ethmoid    Bone,   inner  surface  of 

right  lateral  mass 

33.  The  Vomer  Bone    ....... 


PAGE 

FIG 

36 

34. 

36 

35. 

38 

36. 

37. 

38 

38. 

39 

39. 

40. 

40 

41. 

41 

42. 

41 

42 

43. 

44. 

44 

45. 

46. 

44 

47. 

48. 

46 

49. 

49 

50 

50. 

52 

54 

55 

51. 

57 

52. 

58 

53. 

61 

63 

54. 

64 

66 

55. 

68 

56. 

69 

57. 

70 

58. 

72 

74 

59. 

76 

60. 

61. 

76 

62. 

77 

63. 

78 

64. 

80 

65. 

iURF.  PAGE 

.  Left    Superior    Maxillary   Bone, 

outer  surface 82 

.  Left    Superior    Maxillary    Bone, 

inner  surface 83 

.  The  Anterior  Palatine  Fossa  .  .  86 
.  Alveoli  of  Permanent  Teeth  .  .  87 
.  Development     of     the     Superior 

Maxillary  Bone 89 

,  Left  Palate  Bone,  internal  view  .  91 
Left  Palate  Bone,  posterior  view  .  92 
Right  Inferior  Turbinated   Bone, 

internal  surface 94 

.  Right  Inferior  Turbinated  Bone, 

outer  surface 94 

Left   Lachrymal   Bone,   external 

surface 95 

Right  Nasal  Bone 96 

Left  Nasal  Bone 96 

Left  Malar  Bone,  outer  surface  .  98 
Left  Malar  Bone,  inner  surface  .  98 
Inferior    Maxillary    Bone,   outer 

surface 100 

Inferior    Maxillary   Bone,   inner 

surface 102 

Internal  Face  of  the  Right  Maxilla 
of    Human    Embryo    of  Three 

Months 105 

The  Inferior  Maxilla  of  a  Fcetus 

of   Nine  Months  .    , 105 

Appearance  of  Lower  Jaw  with 

Deciduous  Teeth 106 

Lower  .Jaw  with  Permanent  Teeth 

in  position      106 

Partial   Absorption    of    Alveolar 

Process    .    .    , 106 

Complete  Absorption  of  Process  .  106 
Absorption  of  Alveolar  Process  in 

Old  Age 107 

Hyoid     Bone,    anterior     surface 

(enlarged) _  ....    108 

Temporo-maxillary   Articulation, 

internal  view 113 

Vertical     Section    of     Temporo- 
maxillary  Articulation    ....    114 

Side  View  of  Skull 116 

Anterior  and  Posterior  Fontanelles 

at  Birth 119 

The  Lateral  Fontanelles  at  Birth  119 
Base  of  the  Skull,  inner  or  cerebral 

surface 121 

Base  of  the  Skull,  external  surface   125 
Anterior  Region  of  Skull  ....    131 
9 


10 


ILLUSTRATIONS. 


FIGURE  PAGE 

66.  Roof  of  the  Mouth 137 

67.  Vertical  Section  of  Articular  Car- 

tilage     139 

68.  White  Fibro-cartilage    from    an 

Intervertebral  Disc 139 

69.  Fibro-cartilage  of  an  Interverte- 

bral Ligament 140 

70.  Multiplication  of  Cartilage-cells    141 

71.  Vertical  Section  of  the  Skin  of 

the  Thumb 143 

72.  Section  of  Skin      ....    '   .    .  146 

73.  Tactile  Corpuscle 146 

74.  Section  of  Hair-follicle      ....  147 

75.  Lower   portion    of    Hair-pouch, 

fi'om  the  lip  of  a  kitten     .    .    .  148 

76.  Duct  of  the  Sweat-gland  .    .    .    .  151 

77.  Section  of  Coil  of  a  Sweat-gland  152 

78.  Sebaceous  Gland    from  the  Alse 

Nasi      153 

79.  Tendon  of  Mouse's  Tail   ....   159 

80.  Transverse    Section    from    the 

Sterno-mastoid 161 

81.  Muscular  Fibre 161 

82.  Muscular  Fibres  (highly  magni- 

fied)   161 

83.  A   Branched  Muscular  Fibre  of 

Frog's  Tongue 162 

84.  Fragments    of    an    Elementary 

Fibre  of  the  Skate 162 

85.  Magnified     Human     Muscular 

Fibre 163 

86.  Nuclei  of  Muscular  Fibre    .    .    .   164 

87.  Involuntary  Muscular  Fibre-cells 

from  Human  Arteries    ....    164 

88.  The  ^Muscles  of  Expression     .    .    167 

89.  Muscles  of  the  Head,  Face,  and 

Neck 170 

90.  Muscles  of  the  Right  Orbit  ...    175 

91.  Position  and  Attachment  of  the 

Muscles  of  the  Left  Eveball    .   176 

92.  The  Temporal  Mus.-le  .■ .    .    .    .180 

93.  The  I'terygoid  Muscle 181 

94.  Muscles   of    the   Neck,  anterior 

view      184 

95.  Muscles  of  the  Tongue,  left  side  187 

96.  Muscles  of  the  Pharynx,  external 

view      192 

97.  Muscles  of  the  Soft  Palate   ...   195 

98.  Vertical     Section    through     the 

Mucous  Membrane  of  the  Large 
Intestines  of  a  Dog 202 

99.  Submaxillary  Gland  of  the  Dog  .    204 

100.  Section  of  Human  Submaxillary 

Gland 205 

101.  Alveoli  of  a  Serous  Gland   ...  206 

102.  Tiie  Salivary  Glands 207 

103.  View  of  the  Right  Submaxillary 

and    Sublingual    Glands,  from 
the  inside 210 

104.  The  Meibomian  Glands,  etc.  from 

the  inner  surface  of  the  eyelids  211 

105.  The  Lachrvmal  A|)paratus,  right 

side    .    .■ \    .   212 

106.  The  Arch  of  the  Aorta  and  its 

Branches      215 


FIGURE  PAGE 

107.  Anatomy  of  the  Arteries  of  the 

Neck,  right  side      217 

108.  The    Arteries   of  the    Face   and 

Scalp 223 

109.  The   Internal   Maxillary  Artery 

and  its  Branches 231 

110.  The  Internal  Carotid  and  Verte- 

bral Arteries,  right  side    .    .    .   236 

111.  Arteries  of  the  Orbit,  from  the 

outer  side 238 

112.  Veins  of  the  Head  and  Neck  .    .    250 

113.  Vertical   Section  of    the    Skull, 

showing  the  sinuses  of  the  dura 
mater 257 

114.  The  Sinuses  of  the  Dura  Mater, 

seen  in  horizontal  section  of  the 
skull 260 

115.  Veins  of  the  Diploe,  as  displayed 

bvthe  removal  ofthe  outer  table 

of  the  skull 262 

116.  Ganglion-cell  of  a  P^rog    ....   264 

117.  A  Ganglion-cell  within  itsSheath 

from  the  Human  Sympathethic    264 

118.  Nerve-cell    from    vSpinal  Cord  of 

Ox ••....  265 

119.  Section  of  the  Saphenous  Nerve   265 

120.  Diagram  of  Structure  of  Nerve- 

fibVe       266 

121.  Nerve-substance   from   the    Eel, 

magnified 266 

122.  Tubular  Nerve-fibres 267 

123.  Nerve-fibres 267 

124.  Portions    of    Two    Nerve-fibres 

from  a  Young  Rabbit    ....   268 

125.  Nerve-fibre    from     the     Sciatic 

Nerve  of  the  Rabbit 268 

126.  Portion  of  the  Network  of  Fibres 

of  Remak 269 

127.  Division  of  a  Nerve-fibre,  from 

pulmonary  membrane  of  frog  .    269 

128.  Division   of  a  Nervous    Branch 

into  its  Ultimate  Fibres  .    .    .    .   269 

129.  Plexus  of  Fine  Non-meduUated 

Nerve-fibres  of  the  Cornea    .    .    270 

130.  Intra-ei)ithelial    Nerve-termina- 

tion in  Cornea 270 

131.  End-bulb  from  the  Human  Con- 

junctiva     271 

132.  Termination  of  the  Nerves  in  the 

Salivary  Cilauds 272 

133.  Termination  of  Nerves  in  Non- 

striped  j\Iuscular  Tissue    .    .    .272 

134.  Muscular  Fibres  of  Lacerta  viri- 

dis,  with    the    terminations   of 
nerves 273 

135.  Dissection  of  the  Sinuses  of  the 

Skull  and  Cranial  Nerves     .    •   274 
1-36.  Base  of  the  Brain  .    ......   275 

137.  Semi-diagrammatic   View    of    a 

Deep  Dissection  of  the  Cranial 
Nerves  on  left  side  of  head  .    .   276 

138.  The  Nervous  Distribution  of  the 

•     Head 278 

139.  Nerves   of    the   Septum   of   the 

Nose 277 


ILL  USTRA  TIONS. 


n 


FIGURE  1 

140.  Diagramof  the  Optic  Nerves  and 

Tracts  in  Man 

141.  Nerves  of  the  Orbit,  seen  from 

above    

142.  Nerves  of  the  Orbit  and  Ophthal- 

mic Ganglion      

143.  Distribution   of  the  Second  and 

Third  Divisions  of  the    Fifth 
Nerve  and  Submaxillai'v  Gan- 


144. 
145. 
146. 
147. 
148. 
149. 
150. 


151. 
152. 


153. 

154. 
1 55. 

156. 
157. 

158. 


159. 
160. 
161. 
162. 
163. 

164. 
165. 
166. 

167 
168 
169 
170, 
171, 
172 
173, 
174, 
175, 
176, 
177. 


A  Diagram  of  the  Distribution  of 
the  Fifth  Nerve 

Pterygo-maxillary  Region  and 
Fifth  Nerve 

The  Spheno-palatine  Ganglion 
and  its  Branches 

The  Otic  Ganglion  and  its 
Branches      

Diagram  of  the  Facial  Nerve  and 
its  Distribution 

Middle  Fo.ssa  of  tlie  Base  of  I  he 
Skull 

Ganglia  and  Communications  of 
the  Divisions  of  the  Ninth, 
Tenth,  and  Eleventh  Pairs  .    . 

Tympanic  Nerve 

Distribution  of  the  Ninth.  Tenth, 
and  Eleventh  Pairs  of  Nerves 
on  the  left  side 

Origin  and  Connections  of  the 
Glosso-pharyngeal,  Pneumo- 
gastric,  and  Spinal  Accessory 
Nerves      

Dissection  of  the  Side  of  the  Neck 

Section  of  Small  Lymphatic 
Gland 

Portion  of  the  Medullary  Sub- 
stance of  the  Mesenteric  Gland 
of  an  Ox 

Superficial  Lymphatics  and 
Glands  of  the  Head,  Face,  and 
Neck 

The  Deep  Lymphatics  and 
Glands  of  the  Neck  and  Tho- 


279 
280 

282 

283 
285 
296 
300 
303 
304 
306 


JRE 

■1 


311 
312 


314 

317 
321 

328 
329 


331 


Head  of  Nereis  margaritacea  .  . 
Cephalic  Region  of  the  Leech  .  . 
Oral  Apparatus  of  Echinus  .  . 
Dental  System  of  Echinus  .  .  . 
Sectional  Diagram  of  Molluscan 

Radular  Apparatus 

Jaw  of  Tritonium 

Teeth  of  Bela . 

Teeth  of  Conus 


y  Rhachiglossate  Teeth 

>  Tsenioglossate  Teeth   . 

Ptenoglossate  Teeth 

1 


Rhiphidoglossate  Teeth     .    .   <^ 


332 

338 
338 
339 
340 

342 
343 
346 
346 

346 

347  1 

347 
347 
348 


FIGUF 

178. 

179.  . 

180.  }-  Jaws  of  Pulmonates 349 

181. 
182. 
183. 
184. 
185. 
186. 
187. 


1 


Teeth  of  Pulmonates 349 


Docoglossate  Teeth 348 


Section  through  the  Skin  of  an 
Embryonic  Shark 353 

188.  Third  Lower  Premolar  of  a  Dog  355 

189.  Three  Stages  in  the  Develop- 
ment of  a  Mammalian  Tooth- 
germ     362 

190.  Skull  of  the  Codfish 367 

191.  Teeth  of  Notidanus 372 

192.  Lower  Jaw  of  Port  Jackson 
Shark 373 

1 93.  Teeth  of  Rays 374 

194.  Ceratodus,  and  Teeth  of  Same  .   376 

195.  Vertical  View  of  the  Upper  Jaw 

of  a  Dog 397 

196.  Vertical  View  of  the  Lower  Jaw 
of  a  Dog 398 

197.  Side  View  of  the  Skull  of  a  Dog  402 

198.  Side  View  of  the   Skull  of  an 

Armadillo 409 

199.  Side  View  of  the  Skull  of  Zeu- 

glodon  cetoides 415 

200.  Mandible  of  Mesonyx  ossifragus  418 

201.  Skull  of  Mesonyx  ossifragus,  an- 

terior to  post-glenoid  process  .   419 

202.  Right    Mandibular    Ramus    of 

Dissacus  navajovius 420 

203.  Skull  of  Hvaenodon  horridus  .    .   421 

204.  Skull  and  Part  of  the  Posterior 

Foot    of    two    individuals    of 
Stypolophus  whitise 422 

205.  Left  Mandibular  Ramus  of  Tri- 

isodon  quivirensis 423 

206.  Skull  of  Leptictis  haydeni  ...   424 

207.  Parts  of  Upper  and  Lower  Jaws 
of  Esthonyx  burmeisteri  .    .    .    425 

208.  Side  View  of  a  Portion  of  a 
Skull  of  Blarina  talpoides  .    .   426 

209.  Vertical  View  of  Grinding  Sur- 
face of  Same 426 

I  210.  View  of  the  Grinding  Surface  of 
an  Unworn  Molar  Tooth  of 
Dasyurus 428 

211.  Two  Incisors  of  the  Lower  Jaw 
of  Galeopithecus,  external 
view 429 

212.  Vertical  View  of  Upper  and 
Lower  Jaws  of  European 
Hedgehog 429 

213.  Fragment  of  the  Lower  Jaw  of 
a  species  of  Miacis 430 

214.  Ui)per  and  Lower  Jaw  of  two 
species  of  Didymictis   ....   430 

215.  Superior  Maxillarv  Bone  of  Man  438 

216.  Inferior  Maxillary 439 

217.  A  Left  Upper  Central  Incisor  .   440 
i  218.  A  Lower  Incisor 440 


12 


ILLUSTRATIONS. 


FIGURE  PAGE 

219,  Left  Sniierior  Human  Canine  .   441 

220.  FirstUpper  Bicuspid  or  Premolar  442 
2'il.  Second  Lower  Human  Bicuspid  443 

222.  First  Lower  Human    Molar  .    .  443 

223.  First  Superior  Human  Molar  .  445 

224.  Occlusion  of  the  Teeth  ....  446 

225.  Deciduous  Teeth 446 

226.  Dentition  in  Childhood    ....  447 

227.  Vertical  View  of  the  Lpper  Jaw 

of  aSeal  (Phoca  vitulina)     .    .   449 

228.  Vertical  View  of  the  Lower  Jaw 

of  a  Seal 450 

229.  Skull  of  Amphicvon  cuspigerus  452 

230.  Portions  of  Skull"  of  Oligobunus 

crassivultus 453 

231.  Part  of  Right  Mandibular  Ra- 

mus of  Temnocvon  altigenis  .   453 

232.  Skull  of  Ailurodon  ssevus  ...   454 

233.  Superior  Dental  Series  of    Icti- 

therium  robustum 455 

2.34.  Skull  of  Hya?na    .......   455 

235.  Superior  Sectorial  and  First  Mo- 

lar of  Hysenictis  grseca  ....   456 

236.  Fragment- of  Lower  Jaw  of  Hy- 

senictis  grseca 456 

237.  Skull  of  Prorelurus  julieni  .    .    .   458 

238.  Portions   of  Jaw   of   Proselurus 

julieni 459 

239.  Skull  of  Archwlurus  debilis    .    .  459 

240.  Skull  of  Nimravus  goraphodus  .  459 

241.  Skull  of  Dinictis  cyclops     .    .    .  460 

242.  Skull  of  Pogonodon   platycopis  461 

243.  Cranium  of  Smilodon  necator  .  462 

244.  Upper  and  Lower  Jaw  of  Amer- 

ican Pine  Marten 

245.  Cranium  of  Common  Rat  .    .    . 

246.  Grinding   Surface   of  the   First 

Lower  Molar  of  a  Muskrat    . 

247.  Teeth  of  Fox  Squirrel 467 

248.  First  Lower  Premolar  of  Porcu- 

pine   

249.  Last  Molar  of  Capybara  .... 

250.  Dentition  of   Periptychus  rhab- 

dodon    

251.  Dentition    of    Ectoconus    ditri- 

gonus    

252.  Skull  of  Phenacodus  priniijevus  . 

253.  Parts  of  Cranium  of  Meniscothe- 

rium  terrserubne 

254.  Lower  Jaw  of  Meni.scotherium 

terrserubne      474 

255.  Molar   Teeth    of    Dendrohyrax 

arboreus 475 

256.  Skull  of  Hyracotherium  augus- 

tidens 477 

257.  Skull  of  Aphelops  megalodus  .   479 

258.  Superior     Molar    Dentition     of 

Rhinoceros 480 

259.  Upper  and  Lower  Molar  Teeth 

of  Lambdotherium 481 

260.  Upper   and    Lower    Molars    of 

Right    Side    of    a    species    of 
Ancliithorium 481 

261.  A  Superior  Molar  Tooth  of  spe- 

cies of  Hippotheriura   ....   482 


465 
466 

467 


468 
469 

470 

471 
473 

474 


273. 


274. 


275. 


278. 
279. 

280. 

281. 


286. 

287. 
288. 


497 
532 


533 


535 
536 


FIGURE  PAGE 

262.  Lower  Molar  of  Same 482 

263.  Skull  of  Hippotherium  seversum  483 

264.  Molar    Tooth    of    a   species    of 

Horse .483 

265.  Upper  and  Lower  Jaw  of  Vir- 

ginia Deer 487 

266.  Molar    Teeth    of    Indian    Ele- 

phant     490 

267.  Skull  of  Loxolophodon  cornutus  492 

268.  Dentition  of  Virginia  0[)Ossum  .   495 

269.  Dental  Series  of  Kangaroo  .    .    . 

270.  Human  Blood-corpuscles     .    .    . 

271.  Fibrin-filaments  and  Blood-tab- 

lets     

272.  Epithelial    Cells    in    the    Oral 
Cavity  of  Man 

Columnar  Ciliated  Epithelium 
Cells 

Epithelium-cells  of  Salamander 
Larva  in    Different    Phases   of 
Division 536 

Connective-tissue  Corpuscles  .    .   537 

276.  Preparation  of  the  Omentum  of 

Guinea-pig 537 

277.  Bundles  of  the  "White  Fibres  of 

Areolar  Tissue       537 

Elastic  Fibres  of  Areolar  Tissue  537 
Articular  Cartilage  from   Head 

of  Metatarsal  Bone 538 

Frog's  Egg,  Early  Stage  of  De- 
velopment     544 

Egg  of  Frog  in  Process  of  De- 
velopment     544 

282.  Egg  of  Frog,  farther  advanced  .   544 

283.  Tadpole,  fully  developed     .    .    . 

i^n-'  r  Cross-section  of  Frog's  Egg  .    . 

[  Cross-section  of  Tadpole   .    .    . 

Three  Stages  in  the  Segmenta- 
tion of  the  Rabbit's  Ovum  .    . 

289.  Optical  Section  of  Rabbit's  Ovum 

at  the  Close  of  Segmentation    . 

290.  Rabbit's  Ovum  between  Seventy 

and  Ninety  Hours  after  Im- 
pregnation    546 

Diagi'ammatic  Views  of  the  Blas- 
todermic Vesicle  of  a  Rabbit 
on  the  Seventh  Day 547 

Embryonic  Area  of  a  Rabbit's 
Ovum  on  the  Seventh  Day    .    547 

Rabbit  Embryos  of  about  the 
Nintii  Day,  seen  from  the  dor- 
sal side .   548 

294.  Rabbit    Embryo    of    about    the 

Twelfth  Day 549 

295.  Figures  illustrtiting  the  Forma- 

tion of  a  Face  in  the  Human 
Eml)ryo 550 

Face  of  an  Embryo  of  Twenty- 
tive  to  Twenty-eight  Days  .    . 

Embryo  removed  from  the  Ovum 

298.  Aleckel's  Cartilage  from  Human 

Embryo  of  Forty  to  Forty-two 

Days 


544 
544 

544 

545 
545 


291. 


292. 
293. 


296. 
297. 


551 
551 


552 


ILLUSTRATIONS. 


13 


FIGURE  PAGE 

299.  Embryo  Pig  an  inch  and  a  third 

long  ;  side  view  of  Mandibular 
and   Hyoid  Arches 552 

300.  Meckel's  Cartilage,  from  jaw  of 

two-and-a-half  months'  human 
foetus  undergoing  ossification  .   553 

301.  Transverse    yection    through   a 

Blastoderm  of  Chick,  about  the 
eighth  hour  after  incubation    .   554 

302.  Porcine  Embryo 555 

303.  Growth  of  Jaw  from  the  Blasto- 

derm      556 

304.  Embryotic  Hairs  and  Hair-fol- 

licle   558 

305.  Longitudinal    Section   of  Hair- 

follicle      559 

30G.  Commencing     Replacement    of 

Old  by  New  Hair 559 

307.  Sebaceous  Gland  and  Hair  .    .    .    561 

308.  Vertical  Section  of  the  Skin  of 

the  Thumb 562 

309.  Three     Stages     in    Developing 

Enamel-organ 563 

310.  Porcine  Embryo 564 

311.  Deposition  of  Fat  in  Connective- 

tissue  Cells 565 

312.  Jelly  of  Wharton 566 

313.  Porcine  Embryo 567 

314.  Surface  View,  from  below,  of  a 

small  portion  of  the  posterior 
end  of  the  pellucid  area  of  a 
thirty-six  hours'  chick  ....   568 

315.  Osseous  Lamellte 572 

316.  Transverse  Section   of  Compact 

Tissue  (of  Humerus)    ....   576 

317.  Section  of  a  Haversian  Canal  .    577 

318.  A  Small  Mass  of  Bone-substance 

in  the  Periosteum  of  Lower 
Jaw  of  a  Human  Fcetus   .    .    .    578 

319.  Osteoblasts    from    the    Parietal 

Bone  of  a  Human  Embryo 
thirteen  weeks  old     .    .        .    .   579 

320.  Inferior  Maxilla  of  Porcine  Em- 

bryo    _ 580 

321.  Developing    Lamella   of   Bone, 

Porcine    Embryo 581 

322.  Forming  Bone  in  Human  Fretus, 

two  months 582 

323.  Developing  Parietal  Bone  of  a 

Foetal  Cat 583 

324.  Transverse  Section  of  a  Bf)ne  .    .   584 

325.  Section  of  Phalangeal  Bone  of 

Human   Fcetus,  five   months  .   585 

326.  Longitudinal     Section    through 

the  Upper  Half  of  the  Decal- 
cified Humerus  of  a  Foetal 
Sheep  .    .    .    .    : 586 

327.  Section   of  Part  of  One   of  the 

Limb-bones  of  a  Foetal  Cat    .   588 

328.  Section    of    Femur    of    Human 

Foetus  of  five  months  ....   589 

329.  Section  of  Fang  parallel  to  the 

Dentinal  Tubules 591 

330.  Section  of  Developing  Tooth  of 

Young  Rat 592 


FIGURE  PAGE 

331.  Interglobular  Spaces 595 

332.  Transverse  Section  of  Shell  of 

Pinna 596 

333.  Membranous    Basis   of  Shell  of 

Pinna 596 

334.  Longitudinal  Section  of  Shell  of 

Pinna 598 

335.  Oblique    Section    of    Prismatic 

Shell-substance 598 

336.  Enamel-prisms 601 

337.  Section  of  Hinge-tooth  of  Myo- 

arenaria 603 

338.  Longitudinal  Vertical  Section  of 

the  LTpper  Small  Incisor  of  a 
Rabbit      607 

339.  Diagraunnatic  Section  of  Enamel 

and  Dentine 608 

340.  Connective  Tissue  of  Mesoblast ; 

Epiblast,  formed  of  one  layer 

of  cells '.    .   612 

341.  Infant  Layer  of  Epithelium  and 

Embryonal  Connective  Tissue  .   613 

342.  Epithelium,   infant  layer;    Em- 

bryonal Connective  Tissue    .    .614 

343.  Mucous  Membrane  of  Mouth  .    .   615 

344.  Inferior  Maxilla,  first  stage  in  the 

formation  of  band  .    .    .    •    •    •    617 

345.  Vertical  Section  of  Band  of  Por- 

cine Emljryo 618 

346.  Epithelium  with   Iniant   Layer, 

Connective  Tissue,  Band,  and 
Lamina 619 

347.  Longitudinal  Transverse  Section 

of  Inferi(jr  Maxilla 620 

348.  Longitudinal  Transverse  Section 

of  both  sides  of  the  Inferior 
Maxilla 621 

349.  Vertical   Section  through   Band 

from  Jaw  of  Porcine  Embryo  .    621 

350.  Same  as  349,  only  more  highly 

magnified 622 

351.  Vertical  Section  through   Band 

and  Cord  of  3'  cm.  Porcine  Em- 
bryo .    .    .    . " 623 

352.  Vertical      Transverse      Section 

through  Jaw  of  Porcine  Em- 
bryo '. 623 

353.  Illustration  of  Invagination    .    .   624 

354.  Inner   Tunic    Enamel-organ   of 

Porcine  Embryo 626 

355.  Vertical  Transverse   Section  of 

Jaw  of  Porcine  Embryo  .    .    .   629 

356.  Vertical  Transverse   Section  of 

Jaw  of  Porcine  Embryo,  show- 
ing differentiation  of  perios- 
teum   630 

357.  Vertical   Transverse   Section  of 

Jaw  of  Porcine  Embryo  .    .    .    632 

358.  Vertical   Transverse   Section  of 

Jaw  of  Porcine  Embryo,  in- 
jected    633 

359.  Vertical  Transverse  Section  of  9 

cm.  Bovine  Embryo 635 

360.  Section  of  Jaw  of  Eight  Months' 

Human    Foetus,    showing   ver- 


14 


ILLUSTRATIONS. 


367. 
368. 

369. 


FIGURE  PAGE 

tical  transverse  section  of  cen- 
tral insisor 636 

361.  Temporary  Molar  (Eabbit),  with 

permanent  molar  developing 
underneath 637 

362.  Vertical  (Section  of  Jaw  of  Por- 

cine Embryo 638 

363.  Vertical  Transverse  Section  Cen- 

tral Incisor  of  Porcine  Embryo  639 

364.  Stellate  Reticulum,  Inner  Tunic, 

and  Odontoblastic  Layer    .    .    .   640 

365.  Circle  showing   Dental  Papilla, 

Odontoblasts,  Dentine,  Auielo- 
blasts,  and  Stellate  Reticulum  .   641 

366.  Vertical   Section  through  Apex 

of  Central  Incisor  of  10  cm.  Por- 
cine Embryo 642 

Calcification  and  Decalcification 
of  the  Teeth    ........   647 

Comparative  Stages  of  Calcifica- 
tion of  the  Temporary  and  Per- 
nuinent  Teeth 651 

Vertical  Section  of  a  Tooth  in.  situ  657 

370.  Sphygmographic  Tracings  illus^ 

trating  Difierent  Characters  of 
the  Pulse 668 

371.  Nornuil  Capillary 679 

372.  Capillaries  after  Passive  Hyper- 

semia 679 

373.  jSatural  Hsemostasis 681 

374.  Ligatured  End  of  the  Crural  Ar- 

tery of  a  Dog 682 

375.  Section  of  a  Thrombus,  after  mod- 

ified ligation    ........   682 

376.  Diagram  of  the  Conditions  fol- 

lowing Embolism  of  an  End- 
artery    .   684 

377.  Diagram  of  a  Hemorrhagic  In- 

farct   685 

378.  Ceils  containing  Blood-corpuscles 

from  the  neighborhood  of  a 
hemorrhage 686 

379.  Crystals  of  ILTmatoidin  ....   686 

380.  Crystals  of  Hivniin 687 

381.  Crystals  of  IliKinatoidin  from  a 

Uterine  Blood-clot  ......   687 

382.  Blood  in  Pernicious  An,iemia  .    .   688 

383.  From  Red  Medulla  of  Bone  in 

Pernicious  Anaemia 689 

384.  Inflamed  Capillary  of  the  Mesen- 

tery of  a  Frog 691 

385.  Ama'boid    Movement  of   White 

Blood-corpuscles 691 

386.  Inflamed  Human  Omentum     .    .    692 

387.  Infiamed  Iris 695 

388.  Cornea  of  the  Krog,  excised  three 

ihours  after  irritation  .   .        .    .   697 

389.  Corpuscles  of  the  Cornea,  eight 

hours  after  irritation 698 

390.  Cornea,  sixteen  hours  after  irri- 

taticm 698 

391.  Cornea,  about  twenty-four  hours 

after  the  insertion  of  a  line  lig- 
ature   698 

392.  Pus-cells 701 


393. 
394. 
395. 


396. 

397. 

398. 

399. 
400. 
401. 

402. 

403. 
404. 
405. 
406. 

407. 
408. 
409. 
410. 
411. 
412. 
413. 
414. 
415. 

416. 
417. 
418. 

419. 
420. 
421. 
422. 
423. 
424. 
425. 
426. 
427. 
428. 
429. 
430. 
431. 
432. 
433. 
434. 
435. 
436. 
437. 
438. 
439. 
440. 
441. 

442. 

443. 
444. 


Pus-corpuscles 

Granulation-cells 

Section  through  the  Border  of  a 
Healing  Surface  of  Granula- 
tions   

New  Formation  of  Blood-vessels 

in  a  Granulating  Wound  .    .    . 

Formation  of  the  Ducts  in   the 

Sprouting  of  a  Grain  of  Corn  . 

Eegenei'ation  of   Epithelium   in 

Cornea  of  a  Rabbit 

)  Sections  showing  Absorption  of 

)      Blood-clot 

Cross-section  of  Arterial  Throm- 
bus of  Three  Months     .... 

Carious  Dentine 

Represent  the  number  of  cari- 
ous cavities  observed  in  one 
hundred  persons,  and  the  po- 
sition of  these  cavities  on  the 
individual    surfaces     of    the 

teeth 782- 

Damp  Chamber 

Forms  of  Fungus  from  the  Saliva 

>  Lactate-of-Zinc  Crystals     .    .   -| 

Cocci  and  Diplococci 

Fungus  of  Caries 

Tubules  of  Dentine  united  .  .  . 
Tubules  from  Natural  Caries  .  . 
Outline  of  Epithelial  Scale  from 

Human  Mouth 

Fungus  Growth  in  Starch  .  .  - 
Fungus  from  Carious  Dentine  . 
Apparatus  for  Experiment  with 

Tobacco 

Fungus  Growths 


Ig, 


owths  in  Gelatin-tubes  .    . 


Fungus  Growths 


Tissue  of  Dental  Pulp 

Odontoblasts  clinging  to  Imper- 
fectly-developed Dentine  .    .    . 

Point  of  the  Pidp  of  an  Incisor 
injected  with  Beale's  Blue    .    . 

Hypersemia  of  the  Dental  Pulp 

Dilated  Blood-vessels  from  the 
Dental   Pulp  in    Hyiiersemia  . 


701 

704 


705 
706 

707 

708 

709 

710 
766 


-785 
792 
795 
798 
800 
802 
802 
803 
804 

804 
804 
804 

809 

814 

814 
814 
814 
815 
817 
823 
824 
824 
825 
825 
825 
825 
826 
826 
826 
827 
827 
827 
829 

830 

831 
843 

845 


n.L  USTRA  TIONS. 


15 


FIfiURE 

445.  A 


PAGE  1  FIGURE 


Hyper- 


446. 

447. 
i48. 


Small  Vein  from 

semic  Pnlp  .... 
Dilated  V^essels  from  the  Dental 

Pulp 

Section  of  Hyper.iemic  Pulp  .    . 
InHammation  of  Dental    Pulp  . 

449.  Section  of  Dental  Pulp,  showing 

the  invasion  of  the  inflamma- 
tory process 

450.  Minute      Inflammatory      Focus 

within     the    Tissues     of    the 
Pulp 

451.  Lower   Molar  with    Caries,  and 

microscopical    section    of   the 
same 

452.  Progressive  Suppuration  of  the 

Pulj)   ol'  an  Incisor 

453.  Abscess  within   the   Tissues   of 

the  Pulp 

454.  Carious  Tooth  and  Microscopical 

Section 

455.  Chronic    Inflammation    of    the 

Pulp 

456.  Deposit  of  Calcoglobulin  witJiin 

the    Tissues    of   an    Inflamed 
Pulp 

457.  A  Small  Pulp-nodule 

458.  Section   of  a   Pulp-nodule  .    .    . 

459.  Pulp-nodules  in  the  Canal  Por- 

tion of  the    Pulp 

460. 1  .\brasion  of  a  Cuspid  Tooth  and 
4()1.J       Microscopical  Section     .    .    . 

462.  Narrowing  of  the  Pulp-chamber 

in  a  Molai' 

463.  Deposit   of    Secondary    Dentine 

e.xcited  by  Abrasion 

464.  Deposit  of  Secondary  Dentine, 

resulting  from  caries  of  an  in- 
cisor          

465.  Secondary      Dentine,     resulting 

from  irritation  of  the  dentinal 
fibrils  by  caries 

466.  Secondary     Dentine     in     Pulp- 

chamber  

(  Carious  Cavity  in  Molar  Tooth, 
r     and  microscopical  appearances 

Dentinal     Tumor     within     the 
Pulp-chamber 

471.  Proximal  Decay  in  Incisor,  and 

microscopical  appearances   .    . 

472.  Calcification  of  the  Dental  Pulp 

473.  Calcific  Deposit  in  Incisor  .    .    . 

474.  Lower  Molar,  with  a  large  cari- 

ous    cavity,    with    cylindrical 
calcifications 

475.  Cylindrical  Calcification  of  the 

Pulp 

476.  Cylindrical    Calcification,    more 

advanced  stage 

477. 1  Representations    of   Osteo-den- 

478.  /      tine 

479  ) 

AQQ   >  Atrophy  of  the  Odontoblasts  . 


846 

846 
847 
850 


4^../  I  Effect  of  Caries  in  Producing 
r      Secondary  Dentine     .... 


482. 
483 


850 


467 
468. 
469. 
470. 


851 

854 
855 
856 
858 
860 

861 
863 
863 

864 

866 

867 

868 

869 

870 
871 

872 

873 

875 
876 
877 

878 
879 
879 

881 

884 


484. 
485. 


486. 


487. 


489. 


491. 


492. 
493. 


494. 


914 

Root  and  Membrane  of  Tooth  .    919 

Acute  Alveolar  Abscess  of  Supe- 
rior Incisor  pointing  on  the 
Gum 930 

Acute  Alveolar  Abscess  of  the 
Lower  Incisor  pointing  on  the 
Gum 931 

Acute  Alveolar  Abscess,  with 
Pocket  of  Pus  between  the 
Periosteum  and   the  Bone  .    .   932 

Necrosis  of  the  Buccal  Plate  .    .   932 

Acute    Alveolar    Abscess    of    a 

Lower  Incisor 932 

490.  Upper  Molar  with  Acute  Abscess 
at  theBuccal  Roots  and  Chronic 
Abscess  at  the  Palatine  Root   .   933 

Ui)per  Incisor  with  Acute  Alveo- 
lar Abscess  the  Pus  from  which 
has  raised  the  Periosteum  from 
the  Hard  Palate 933 

Blind  Abscess  at  the  Root  of  an 
Upper  Incisor 936 

Chronic  Alveolar  Abscess  at  the 
Root  of  a  Lower  Incisor  .    .    .   938 

Chronic  Alveolar  Abscess  at  the 
Root  of  an  Upper  Incisor,  with 
Fistula     discharging     on    the 

Gum 938 

495.  Alveolar  Abscess  at  the  Buccal 
Roots  of  an  Upper  Molar  dis- 
charging on  the  Face  ....   939 

Scar  caused  by  Alveolar  Abscess 
discharging  on  the  Face   .    .    .   939 

497.  Alveolar  Abscess  at  the  Root  of 

a  Superior  Incisor  discharging 
into  the  Nose 940 

498.  Relations   of  the   Roots  of  the 

Teeth  to  the  Antriun  ....    941 

499.  Alveolar  Abscess  at  the  Root  of 

an  Upper  Molar  discharging 
into  the  Antrum  of  Highmore.   941 

500.  Abscess  of  Lower  Incisor  with 

Fistula  discharging  under  the 
Chin .   942 

Abscess  of  Lower  Incisor  with 
Cavity  passing  through  the 
Body  of  the  Bone  and  dis- 
charging  beneath    the   Chin  .   942 

Fistula  through  the  Lower  Max- 
illa     942 

503.  Loss  of  Bone   and   Teeth   fi'oin 

vSubperiosteal  Inflammation     .    944 

504.  Operation   for   the    Remedy   of 

Scar  caused  by  Alveolar  Ab- 
scess   952 

The  Gingival  Border 955 

Deposit  of  Serumal  Calculus  un- 
der the  Gingival  Borders      .    .   958 
Deposit    of    Serumal     Calculus 
within    the    Free    Margin    of 
the  Gum 958 


496. 


501. 


502. 


505. 
506. 

507. 


16 


//./.  USTBA  TIO^'S. 


FIGURE  PAGE 

508.  Calculus  and  Destruction  of  the 

Lower  Border  of  tlie  Alveolar 
Wall  and  Peridental  Mem- 
brane     959 

509.  Absorption   of    the    Septum    of 

Bone  and  Kecession    of    Gum  959 

510.  Inflannnation  of  the  Gum  from 

Deposit  of  Salivary  Calculus   .  960 

511.  Inflannnation  and  Absorption  of 

the  Ciuni  and  Lower  Border  of 
the  Peridental  Membrane  and 
Alveolar  Wall  from  Calculus  . 


512. 
513. 
514. 
515. 


960 

Destruction    of  Tissues  from 
Salivary  Calculus 961 


Dr.  George  H.  Cushing's  Scalers  964 

516.  Farrar's  Syringe 967 

517.  Alveoli  irreparably  Destroyed  by 

Calcic  Inflammation 968 

970 


518. 
519. 
520. 
521. 
522. 
523. 
524. 


Destruction  of  Membrane  and 
Alveolus  from  Phagedenic 
Pericementitis  ...... 


970 
970 
971 
971 
971 
972 


527. 
528. 
529. 

530. 

531. 


533. 

534. 

535. 
536. 


537, 


973 


975 
981 


FIGURE 

525.  Acute  Pericementitis  with  Ever- 

sion  of  the  Alveolar  Wall    .    . 

526.  Phagedenic  Pericementitis  com- 

plicated w'ith   Serumal   Calcu- 
lus   

Incisions    for    Exposing    the   f 
Roots  of  the  Teeth  .    .    .    .    (,  981 

Chronic  Case  of  Phagedenic  Peri- 
cementitis    ...•••...   990 

Amputation  of  the  Aflfected  Boot 
and  Filling  of  tlie  Pulp-cavity.  991 

Amputation  of  the  Posterior  Root 
of  the  First  Lower  Molar     .    .  991 
532.  Erosion  of  the  Lower  Anterior 

Teeth 999 

Erosion  of  both  LTpper  and  Lower 
Dentures 1000 

Peculiar  Case  of  Erosion  of  the 
Superior  Anterior  Teeth  .   .    .   1001 

Artificial  Erosion 1004 

Section  of  the  Crown  of  an 
Incisor,  showing  effects  of  ero- 
sion      1007 

Group  of  Odontoblasts  with  their 
Processes 1009 


LIST   OF  PLATES. 


Platk  I 505 

Plate  II 507 

Plate  III 509 

Plate  IV 511 

Plate  V 513 

Plate  VI 515 


PART  I. 


REGIONAL  ANATOMT 


T 


REGIONAL    ANATOMY. 

By  M.  H.  CRYER,  M.  D.,  D.  D.  S. 


BONES. 

Bones  belong  to  one  of  the  three  groups  of  connective  tissue,  fibro- 
conneetive,  cartilage,  and  bone  connective  tissue.  Each  of  these  divis- 
ions may  be  again  subdivided  into  several  minor  divisions;  but  under 
all  circumstances  the  ground  substance,  or  matrix,  or  intercellular  sub- 
stance of  each  is  distinguished  by  the  cells  peculiar  to  it.  The  matrix 
of  fibro-connective  tissue  yields  gluten  or  gelatin,  that  of  cartilage 
connective  tissue  yields  chondrin,  and  that  of  bone  connective  tissue 
yields  the  salts  of  calcium.  With  the  single  exception  of  the  teeth, 
bone  is  the  hardest,  heaviest,  and  most  solid  structure  of  the  body: 
it  forms  the  framework  of  the  body,  keeps  the  parts  in  position,  and 
acts  as  lever  and  fulcrum;  its  grooves  act  as  pulleys  through  which 
glide  the  tendons  of  certain  muscles ;  it  protects  vital  parts,  such  as 
the  brain  and  spinal  cord,  from  injury;  it  also,  in  great  measure, 
gives  character  and  individuality  of  expression  to  the  head  and  body 
generally. 

Bones  are  derived  from  the  two  great  kingdoms  of  nature — the 
organic  and  inorganic. 

The  principal  portions  of  the  several  bones,  such  as  the  shafts  of 
long  bones,  are  called  the  diaphyses ;  and  the  smaller  parts,  such  as  the 
ends  of  long  bones,  their  epiphyses,  the  term  apophyses  being  a])])lied 
to  those  nodules  on  bones  which  are  not  formed  from  separate  points  of 
ossification. 

If  a  long  bone  be  cut  longitudinally  (Fig.  1),  it  is  seen  to  be  made 
up  of  an  outer  and  an  inner  layer ;  the  outer  being  called  the  compact, 
the  inner  the  spongy  or  cancellated,  portion. 

Note. — The  writer  claims  no  originality  for  the  purely  descriptive  matter  herein 
contained.  In  its  preparation  notes  of  the  lectures  of  Professors  Allen,  Garretson, 
Stelhvagen,  and  Leidy  have  been  of  great  value,  and  the  following  works  have  been 
consulted  and  freely  drawn  from :  Gray's,  Allen's,  Quain's,  and  Leidy's  works  on 
Human  Anaioimi ;  Treves's  Applied  Anatomy  ;  Bell's  Anatomi/ of  Exprrmon  ;  Allen's 
Facial  Region ;  Tomes's  Dental  Anatomy  ;  Garretson's  Si/stem.  of  Oral  Surf/eri/ ;  Parker 
and  Bessang's  Morphology  of  the  Skull ;  Klein's  Elements  of  Histology  ;  p'lint's  Pliyxiologg 
and  Diseases  of  the  Xerrous  System;  Cole's  Studies  in  Microscopical  Science;  Prudden's 
Practical  Histology  ;  and  Duhring  on  Diseases  of  the  Skin. 

35 


36 


ANATOMY 


The  outer  or  compact  portion  is  hard  and  ivory-hke  in  texture,  giving 
rigidity  and  firmness  to  the  shaft.  In  long  bones  the  compact  substance 
is  thickest  in  the  centre  of  the  diaphysis,  gradually  growing  thinner 
toward  the  ends,  the  fibres  running  longitudinally. 

The  inner,  spongy,  or  cancellated  portion  is  softer  than  the  outer 
covering,  and  is  made  up  of  slender  bars  and  thin  lamellae,  which  cross 
each  other  in  various  directions  (see  a  a,  b  b,  e  c,  Fig.  2),  and  produce 


Fig.  1. 


Fig.  2. 


Section  of  a  Sound  Adult  Femur. 


Diagram  showing  the  Structure  of  tlie  Neck 
of  the  lemur. 


an  open  structure  having  a  reticular  appearance,  so  arranged  as  to  form 
an  internal  support  to  the  outer  portion  of  the  bone.  This  formation 
is  specially  marked  in  the  upper  end  of  the  femur. 

The  cancellated  portion  is  found  in  greatest  quantity  at  the  ends  of 
long  l)oncs,  at  ^vhicli  position  the  surfaces  are  enlarged  for  purposes  of 
articulation.  It  is  the  more  vascular  portion  of  bone;  adds  bulk  with- 
out greatly  increasing  weight;  acts  as  a  cushion  to  articulating  surfaces; 
and  by  its  elastic  projierties  modifies  the  force  of  concussion. 

The  flat  bones,  such  as  those  found  in  the  skull,  furnish  surfaces  for 
the  more  convenient  attachment  of  ligaments,  nuiscles,  and  tendons. 
They  are  comjioscd  of  two  tables,  an  outer  and  an  inner,  with  the 
cancellated  j^ortion  (diploe)  between. 

The  cancellar  substance  of  bones  generally,  but  especially  in  those 
of  the  cranium,  is  pervaded  liy  irregular  canals  for  the  accommodation 
of  })lood-vosscls.  The  two  ])Iates  or  tables  of  flat  bones  are  bound 
together  by  the  cancellated  tissue,  wliich  not  only  helps  to  resist  fracture, 
but  acts  as  a  cushion,  deadening  the  force  of  shock  by  distributing  it 
over  larger  surfaces,  thus  in  great  measure  preventing  injury  to  the 
brain  :  it  also  combines  great  strength  M-ith  lightness  of  weight. 

If  a  close  examination  is  made  of  a  specimen,  as  shown  in  Fig.  1,  by 
the  aid  of  a  magnifving-glass,  it  will  be  found  that  the  compact  tissue 
is  porous  in  a  greater  or  less  degree,  its  density  depending  u])on  the 


BONES.  37 

amount  of  solid  matter  deposited  in  it.  In  other  words,  where  the 
spaces  are  small  and  contracted  the  solid  matter  is  abundant ;  in  the 
spongy  portions,  the  spaces  being  large,  the  solid  matter  is  proportion- 
ately less.  It  will  also  be  observed  that  there  is  no  line  of  demarcation 
between  the  outer  and  inner  structure,  the  compact  gradually  expanding 
into  the  cancellated  portion. 

The  color  of  bone  depends  upon  the  condition  in  which  it  is  when 
examined ;  if  fresh,  it  will  be  of  a  yellowish  hue,  due  to  the  contained 
lymph  and  the  fatty  medulla.  The  blue  shade  so  frequently  seen  is  due 
in  a  great  measure  to  the  mode  of  death.  If  the  subject  from  which 
the  bone  is  taken  died  from  drowning,  suifocation,  or  any  kindred  cause, 
a  bluish  tinge  would  be  imparted  to  the  bone.  The  redness  of  fresh 
bone  is  dependent  upon  its  vascularity ;  therefore  some  bones  will  be 
redder  than  others,  and  the  bones  of  young  healthy  jjersons  more  so  than 
those  of  the  aged,  whose  osseous  tissues  contain  a  relatively  greater 
amount  of  inorganic  matter. 

Bones  which  have  been  cleaned,  first  by  maceration  in  water,  then  in 
ether,  become  white,  the  cartilaginous  material,  the  blood,  fat,  and  mem- 
branes having  been  removed.  By  this  process  bones  become  extremely 
porous  by  reason  of  the  removal  of  the  contents  of  the  innumerable 
small  openings  for  blood-vessels  which  are  found  scattered  over  their 
surface. 

After  exposure  for  a  long  time  to  the  atmosphere,  bones  undergo 
exfoliation  and  split  into  laminae,  thus  demonstrating  that  osseous  tissue 
is  heterogeneous  and  not  homogeneous  in  its  formation. 

The  weight  of  bones  varies  in  direct  proportion  to  their  compactness 
of  structure.     Their  chemical  analysis  yields,  on  an  average — 

Calcium  carbonate 7.05 

Magnesium  phosphate 2.08 

Calcium  phosphate 58.39 

Calcium  fluoride  , 2.25 

Organic  matter 30.23 

100.00 

It  is  seldom  that  the  analytical  chemists  will  produce  exactly  the 
same  results  in  their  respective  analyses  of  different  bones,  as  it  would 
be  difficult  to  find  two  bones  identical  in  structure  and  composition. 
There  are  many  reasons  for  this,  among  which  age  may  be  mentioned 
as  a  prominent  factor.  During  youth  bone  is  principally  made  up  of 
organic  matter,  but  as  life  advances  there  is  assimilated  continually  more 
inorganic  material,  part  of  the  organic  matter  being  lost.  Disease  may 
also  influence  the  proportional  quantity  of  the  inorganic  constituents, 
and,  as  might  be  expected,  bones  taken  from  different  parts  of  the  body 
will  be  dissimilar  in  composition,  as  they  are  designed  for  different 
functions. 

If  bone  be  placed  in  a  solution  consisting  of  one  part  of  hydrochloric 
acid  to  sixteen  parts  of  water,  the  fluid  being  changed  each  day,  the 
inorganic  matter  will  be  dissolved  out,  leaving  the  organic  material, 
which  is  held  together  by  its  connective  tissue,  in  its  original  shape, 
these  remaining  parts  being  quite  soft  and  flexible.     Thus  treated,  a 


38 


AXATOMY. 


Fig.  3.  vertebra  will  become  like  a  sponge,  and  the  long  bones 
may  be  tied  into  knots  (see  Fig.  3).  In  this  ^\•ay  the 
internal  parts  of  bone  may  be  prepared  for  study  by 
cutting  away  portions  with  a  sharp  knife  or  pair  of 
scissors. 

A  preferable  manner  of  preparing  bone  for  microscopi- 
cal examination  is  to  take  a  small  piece,  about  half  a 
cubic  inch  in  size,  of  the  compact  portion  of  a  long  bone, 
either  of  man,  dog,  cat,  or  rabbit,  and  immerse  it  in  an 
aqueous  solution  of  chromic  or  picric  acid,  either  of 
which  hardens  the  organic  tissue  as  well  as  dissolves 
the  inorganic  matter,  and  renders  the  tissue  capable  of 
being  cut  into  thin  sections,  Avhich  are  to  be  stained  or 
not  according  to  methods  in  vogue  by  practical  histol- 
ogists.  Hard  sections  can  also  be  made  by  sawing  a 
small  piece  from  a  long  bone  and  grinding  it  upon  a 
whetstone  or  plate  of  glass  with  emery-powder  until 
sufficiently  thin. 

When  a  bone  is  placed  in  a  slow  fire  or  a  sufficiently 
^  heated  furnace,  the  organic  material  will  be  consumed, 
ration  in  j  Bihife  leaving  oulv  inorgauic  substance  and.  the  ash  from  the 
men  preserved  in  Organic  matter.  The  shape  is  still  preserved,  but  the  speci- 
spiiitA  j^gj^  jg  ^,gj,^,  brittle  and  will  crumble  almost  at  the  touch. 


Fibula    tied 
Knot  after  JIace 


Minute  Structure  of  Bone. 
A  transverse  and  longitudinal  section  of  the  compact  structure  of 

Fig.  4. 


Fransverse  Section  of  rompact  Tissue  "f  Humerus  (mapnitied  about  InO  diameters).  Tbree  of  the 
Haversian  canals  are  seen,  with  their  concentric  rings;  also  the  lacunie,  with  the  canaliculi 
extendinc  from  them  across  the  direction  of  the  lamellie.  The  Haversian  apertures  had  become 
tilled  with  ;iir  and  d'bris  in  grindinc  down  the  section,  and  therefore  appear  black  in  the  figure, 
wh.ch  represents  the  object  as  viewed  with  transmitted  light. 


BOXES. 


59 


s — viz.  («) 


Fig 


bone  examined  under  a  mieroscope  will  demonstrate  the  appearance,  as 
.shown  in  Figs.  4  and  5. 

The  minute  structure  of  bone  is  examined  in  five  divisions 
the  Haversian  canals ;  (6)  the  bony 
lamellae ;  (c)  the  Sharpey  or  perforat- 
ing fibres ;  (r/)  bone  lacunae ;  (c)  can- 
aliculi ;  and  (/)  bone-cells. 

(a)  The  Haversiax  Canals 
(Figs.  4  and  5)  are  named  after  their 
discoverer,  Clopton  Havers.  They 
are  from  yglg-Q-th  to  2-oir^h  of  an  inch 
in  diameter,  occasionally  being  found 
as  small  as  ytfVo^^^  of  an  inch.  The 
smallest  canals  are  found  near  the 
surface  or  outside  of  the  boiie,  the 
larger  ones  near  the  medullary  canal. 
Their  general  direction  is  longitudi- 
nal  with  the  axis  of  a  long  bone, 
althougli  they  anastomose  with  .each 
other  by  short  or  oblique  branches 
at  varying  angles,.while  others  pass 
into  the  periosteum  and  the  medul- 
lary cavity,  thus  forming  a  reticu- 
lated intercommunication  by  which 
capillary  blood-  and  lymph-vessels 
pass,  not  only  longitudinally,  but  from 
the  outer  to  the  inner  portion  of  the 
bone.  When  the  canals  are  not  filled 
by  the  above  vessels  the  remaining 
space  is  occupied  by  delicate  loose 
connective  tissue  enclosing  cellular 
elements  identical  with  the  bone  marrow,  hereafter  to  be  described. 

(h)  The  Boxy  La:mella  is  divided  into  three  systems — viz.  (1)  the 
Haversian,  (2)  interstitial,  and  general  or  (3)  circumferential  systems. 

(1)  The  Haversian  or  Concenfrie  System  is  a  series  of  concentric  ring.^ 
immediately  surrounding  each  Haversian  canal,  varying  in  number  from 
four  to  twenty  according  to  the  age  of  the  formation.  All  the  laminoe 
do  not  form  complete  circles,  some  terminating  •  between  two  others. 
Frequently  the  rings  are  oval  in  shape,  this  form  depending  to  some 
extent  on  the  cutting  of  the  section.  If  cut  obliquely  to  the  canal,  both 
the  rings  and  canal  have  an  oval  appearance,  though  the  canal  is  not 
always  in  the  centre  of  its  system. 

(2)  The  Interstitial  Si/stcni: — The  lamellae  of  this  system  are  com- 
posed of  bands  of  osseous  tissue  of  varying  thickness,  running  in  dif- 
ferent directi(ms  between  the  Haversian  and  the  circumferential  systems. 

(3)  The  Circumferential  or  Parietal  System. — The  lamellae  here  are 
principally  found  upon  the  surface  of  bone,  although  they  are  also  seen 
passing  through  the  interstitial  system,  and  even  next  to  the  medullary 
cavity.  They  have  a  general  direction  parallel  to  the  surface  of  the 
bone. 


Section  Panllel  to  the  suilice  from  the  "^haft  of 
the  I  emur  (niaenitied  100  tirae^)  a  Ha\ersnn 
camlb  li  HciincL  (roni  the  side  r  others  seen 
fiom  the  surface  in  1  unellce  which  me  tut  hor 
izontali\ 


40 


AX  ATOMY, 


(c)  Sharpey's  or  Perforating  Fibres. — Besides  the  three  systems 
of  lamellte  which  form  for  the  most  part  all  the  intercellular  substance . 
of  bone,  there  is  found  in  many  instances  a  well-defined  system  of  fibres 
known  as  Sharpey's  fibres  (see  Fig.  6).  These  pass  through  or  pene- 
trate the  lamellffi  in  a  perpendicular  or  oblique  direction,  appearing  to 
dowel  or  bind  the  parts  together.  Many  pass  from  the  periosteum — 
especially  is  this  marked  in  the  external  table  of  the  cranial  bones — 
while  others  seem  to  have  their  origin  from  some  of  the  intermediate 

Fig.  6. 


LamellK  torn  off  from  a  Decalcified  Human  Parietal  Bone  at  some  depth  from  the  surface:  n.  Ions; 
lamellse ;  b,  h,  thiclver  part,  where  several  lanielUe  are  siiperpos'  d  ;  c,  r,  perforating  fibres :  the  tilirils 
wliich  compose  them  are  not  sliown  in  the  figure.  j\perfures  through  which  perforating  fibres  liad 
passed  are  seen,  especially  in  the  lower  part,  a,  a,  of  I  he  figure  (magnitude  as  seen  under  a  power  of 
200,  but  not  drawn  to  a  scale). 

lamellse  of  the  interstitial  or  circumferential  systems,  though  it  is  more 
probable  they  had  their  origin  from  the  periosteum  when  that  mem- 
brane Avas  in  close  contact  with  the  lamella  from  which  their  fibres  start. 
These  fibres  are  not  found  in  the  Haversian  lamellae.  If  a  lamella  is 
torn  away  from  a  decalcified  bone,  these  fibres  can  be  seen  attached  to 
the  under  surface  of  the  removed  portion,  the  apertures  being  visible  in 
the  remaining  l^one  from  which  the  fibres  have  been  drawn.  They 
are  suppo.'^ed  to  be  o.'*sified  bundles  of  white  fibrous  tissue  originally 
belonging  to  the  inner  layer  of  the  periosteum.^ 

Occasionally  the.se  fibres  do  not  ossify,  and  as  they  shrink  or  are 
drawn  out  in  removing  the  periosteum,  perforations  will  be  found  lead- 
ing into  the  bone.  It  is  by  means  of  these  perforating  fibres  that  tendons 
and  ligaments  obtain  such  firm  hold  upon  bones,  their  number  being 
increased  at  the  points  of  such  attachments.^ 

'  Perfriratinir  fibres  (r,  e,  Fig.  Pi)  exist  almndantly  in  the  crnsta  petrosa  or  cementum 
of  the  teeth  iSiiarpey).  H.  Miiller  has  shown  that  some  are  of  the  nature  of  elastic 
tissue  (Qnain's  Amilomii). 

'  The  filtre-liiindles  of  the  tendon  are  continued  into  the  bone  as  perforating  fil)res. 
Some  of  the  l)uiidles  of  white  fdires  of  the  periosteum  may  also  |)ass  into  the  bone  as 
perforating  tibres,  and  the  same  is  the  case  with  elastic  fibres  (Qnain's  Anatomy). 


41 


Fig.  8. 


Transverse  Section  of  Decalcified  Human  Tibia,  from  near  the  surface  of  the  shaft :  H,  II,  Haversian 
canals,  with  their  systems  of  concentric  lamellae ;  in  all  the  rest  of  the  figure  the  lamellte  are  cir- 
cuniferrntial ;  S,  ordinary  perforating  fibres  of  Sharpey  ;  e,  c,  elastic  perforating  fibres  (drawn 
under  a  power  of  about  15U  diameters). 

(d)  The  Lacunae  or  Lymph-spaces  (osseous  corpuscles)  are  best 
demonstrated  in  thin  sections,  prepared  by  grinding  instead  of  softening 
by  acids  and  cutting  with  a  knife  or 
microtome.  When  examined  by  trans- 
mitted light  the  lacunse  have  a  dark 
appearance,  but  when  seen  with  a  dark 
background,  the  light  being  thrown 
u]3on  them,  they  will  appear  quite 
white.  They  are  very  small  cavities 
situated  between  the  lamellae  of  the 
bone,  flattened  ellipsoidal  in  shajje, 
and  with  many  radiating  elongations. 

(e)  The  Canaliculi  are  very  fine 
canals  opening  into  the  radiating  elongations  of  the  lacunse.  They  ex- 
tend between  and  through  the  different  lamellae,  giving  free  communica- 
tion to  the  lacunae  situated  between  the  various  lamellae ;  they  also  pass 
from  the  lacunae  to  the  Haversian  canals,  the  surface  of  the  bone,  and 
the  medullary  canals,  and  are  intimately  connected  with  the  lymphatic 
vessels  situated  in  and  around  the  bones,  showing  that  the  lacunae  and 
canaliculi  form  the  lymphatic  system  of  the  osseous  structure, 

(/)  The  Bone-cells  are  flattened  and  nucleated,  and  are  situated 
within  each  lacuna,  with  prolongations  extending  into  the  canaliculi. 
In  structure  they  are  analogous  to  the  connective-tissue  corpuscle. 
"  Rouget  and  Neumann  have  been  able  to  detach  tlie  proper  wall  of  the 


Lacunae  of  Osseous  Substance  (niacnified  oOO 
diameters) :  a,  lacuna ;  b,  canaliculi. 


42 


ANATOMY. 


lacuna  and  its  appertaining  canaliculi  after  decalcification,  and  to  obtain 
it  separate  with  its  included  corpuscle."  ''  It  can  scarcely  be  doubted 
that  the  protoplasm  of  the  nucleated  corpuscle  takes  an  important  share 
in  the  nutritive  process  in  bone,  and  very  probably  serves  both  to  mod- 
ify the  nutritive  fluid  supplied  from  the  blood  and  to  further  its  distri- 
bution through  the  lacunar  and  canalicular  system  of  the  bony  tissue."^ 
In  flat,  thin,  or  irregular-shaped  bones  the  Haversian  canals^'  the 
lamellpe,  etc.  are  similar  to  those  in  the  diaphyses  of  long  bones,  just 
described,  though  the  Haversian  system  is  not  so  regular  in  formation. 


The  Periosteum. 

The  periosteum  is  that  membrane  which  covers  the  greater  portion 
Fig  9  '^^  ^^^  surfaces  of  bone,  and  is  composed  in  a  great  meas- 

ure of  fibrillated  connective  tissue.  Between  the  inter- 
lacing of  the  fibrous  bundles  lymph-spaces  are  formed 
which  contain  elementary  cellular  matter.  Although  it 
is  made  up  of  several  closely-attached  lamella?,  for  con- 
venience of  description  this  structure  is  divided  into  two 
principal  layers,  an  outer  and  an  inner. 

The  outer  layer  is  the  firmer  of  the  two,  being  com- 
posed mainly  of  one  or  more  strata  of  dense  white  con- 
nective tissue,  with  a  few  fine  yellow  elastic  fibres  inter- 
spersed with  several  lat-cells.  Blood-  and  lymjih-channels 
are  found  in  abundance ;  the  latter  anastomose  quite  free- 
ly with  those  of  the  inner  layer. 

The  inner  or  osteogenic  layer  has  its  fibrous  bundles 
more  loosely  arranged  than  the  outer,  and  is  composed 
chiefly  of  elastic  fibres  of  connective  tissue,  generally  ar- 
ranged in  several  distinct  strata.     It  is  much  more  vas- 
The  External  Peri-  cular  than  the  outcr  layer,  the  blood-vessels  forming  a 
an(r"uiraeV'''off  "etworlv  of  ca]-)illaries  Avhich  anastomose  with  those  of 
lium  r'*    ^'°""s  the    outer  layer   and  send  numerous  oifshoots    into  the 
substance  of  the  bone.    In  the  lower  strata  of  this  layer, 
or  that  one  next  to  the  bone,  especially  during  the  period  of  formation, 
there  is  a  large  number  of  spheroidal  or  oblong  granular  cells  or  cor- 
puscles, with  oval  nuclei,  which  are  usually  situated  on  the  side  of  the 
cell.     These  cells  were  named  osteoblasts  by  Gegenbauer.     The  bone- 
producing  ]iroperty  of  the  inner  layer  of  the  periosteum  is  especially 
well  marked  in  the  fully-developed  inferior  maxilla,  clavicle,  and  bones 
of  the  arm  and  forearm.     If  the  surgeon  when  operating  is  careful  to 
first  strip  this  membrane  aside,  he  can  excise  or  resect  a  large  portion 
of  bone,  the  lost  tissue  being  subsequently  renewed  to  a  great  extent 
througli  tlie  agency  of  the  osteoblasts. 

If  by  disease  or  otherwise  the  periosteum  be  removed  from  any  living 
bone,  the  portion  thus  denuded  generally  suffers  atrophy,  and  finally 
necrosis.  This  is  not  usually  the  case,  however,  with  the  bones  of  the 
cranial  vault,  as  will  be  hereafter  explained. 

The  periosteum  serves  as  a  support  to  the  vessels  which  supply  the 

'  Qnain's  Avatomy. 


BONES.  43 

bones  Avith  blood,  these  capillaries  being  assisted  bv  the  niedullaiy 
(nutritive)  arteries,  which  pass  directly  into  the  bone  and  are  distributed 
throughout  its  system  of  Haversian  canals,  until  they  anastomose  with 
the  branches  coming  from  the  periosteum.  Thus  the  bones  are  per- 
meated by  the  blood  and  absorbent  vessels,  a  few  nerves  also  entering 
their  structure.  In  the  bones  containing  marrow  there  is  an  endosteum, 
composed  of  a  fine  layer  of  areolar  tissue,  which  lines  the  medullary 
canals  and  other  spaces.  This  lining  membrane  is  very  vascular,  and 
contains  myeloplaxes  or  osteoclasts.  Osteoclasts  are  also  found  at  the 
roots  of  deciduous  teeth  when  their  roots  are  being  absorbed,  and  in  the 
lining  membranes  of  bony  sinuses.  When  the  periosteum  is  stripped 
from  living  bone,  numerous  bleeding  spots  appear,  which  indicate  the 
points  where  the  vessels  pass  from  the  membrane  into  the  bone.  The 
muscles,  aponeuroses,  tendons,  and  ligaments  are  attached  to  the  bone 
through  the  intervention  of  the  periosteum,  which  is  attached  to  the 
bone  by  its  perforating  fibres.  Tendons  and  ligaments  obtain  firm  ad- 
herence to  bones  by  sending  prolongations  of  their  fibre-bundles  through 
the  periosteum. 

In  inflammation  of  the  bone  the  periosteum  often  becomes  thickened, 
and  may  be  easily  removed.  At  the  point  of  attachment  of  a  muscle 
to  a  bone  there  is  seen  a  roughening,  a  depression,  or  a  protuberance 
corresponding  in  size  to  the  strength  of  the  attached  muscle. 


The  Marrow  of  Bone. 

The  marrow  is  a  highly  vascular,  soft  tissue  situated  within  all  bones. 
It  fills  the  medullary  canals  of  long  bones,  the  spaces  within  spongy 
bones,  and  to  a  greater  or  lesser  extent  the  Haversian  canals  of  compact 
bone  tissue.  As  a  matrix  it  has  a  small  amount  of  fine  delicate  con- 
nective tissue  woven  or  interlacing  in  such  a  way  as  to  form  very  thin 
septa  between  the  vesicles.  Its  color  and  composition  vary  according 
to  age  and  the  position  it  occupies  within  the  bone ;  and  this  difference 
has  led  to  its  generally  being  divided  into  two  kinds — yelloip  and  red. 
The  yellow  receives  its  color  from  the  large  number  of  fat-vesicles  it 
contains,  and  is  principally  found  in  the  medullary  canals  of  long  bones 
and  in  small  (quantity  in  some  of  the  cavities  of  spongy  bone.  Yellow 
marrow  is  not  found  in  young  bones. 

The  red  marrow  is  dependent  for  its  color  on  its  greater  vascularity  and 
upon  its  containing  red  cell-elements  independent  of  the  blood  ;  it  lacks 
adipose  tissue  in  its  substance,  and  is  more  fluid  than  the  yellow.  Red 
marrow  is  situated  in  the  spaces  of  spongy  bones,  especially  the  bodies 
of  the  vertebra,  sternum,  the  ribs,  and  diploe  of  the  cranial  Ijones. 
The  vessels  of  the  marrow,  which  are  numerous,  are  imbedded  within 
its  substance.  Their  walls  are  very  thin,  and  they  su])ply  in  part  the 
adjacent  bone  as  well  as  tlie  surrounding  marrow;  They  anastomose 
through  the  bone  with  those  of  the  periosteum.  Within  the  marrow 
are  found  a  variety  of  cell-elements  (Fig.  10)  which  vary  according  to 
position  and  age,  and  are  described  as — the  mediTllary  or  true  mar- 
row-cells; fat-vesicles  or  adipose-tissue  cells;  multinuclear  giant-cells; 


44 


ANATOMY 


nucleated  red  blood-cells ;  osteoblasts ;  colored  cells  similar  to  the  red 
blood-corpuscles. 

The  Medullary  or  True  Marrow-cells  are  round  and  nucleated.    They 
have  amoeboid  movements,  and  in  general  appearance  may  be  coni- 

FiG.  10. 

,r\  „  -Ik 


Fig. 11. 


Cells  from  the  ^Marrow  of  Fone  during  their  Period  of  Pevelopment :  a,  h,  miiltinuelear  "giant-cells;" 
''i/i  fli  lymph-cells  from  the  marrow  of  the  tibia  of  the  guinea-pig,  examined  in  the  serum  of  the 
blood  ;  c,  (I,  //,  after  the  action  of  alcohol  and  water  :W  per  cent. ;  i, ./,  so  caded  osteoblasts  from 
the  femur  of  a  new-born  dog,  after  the  action  of  alcohol  33  per  cent,  (high  power). 

pared  to  lymph-cells  or  the  white  corpuscles  of  the  blood,  though  some- 
what larger  and  possessing  a  clearer  protoplasm.  This  class  is  more 
abundant  in  red  than  yellow  marrow. 

The  Fat-vc>:>ielcs  are  similar  to  those  found  in  adipose  tissue.  As 
previously  stated,  the  color  of  yellow  marrow  is  due  to  these  vesicles, 
of  which  it  is  in  greater  part  made  up.  Fat-vesicles  are  found  in  very 
small  numbers  in  the  red  marrow. 

The  Midtinuclear  Giant-cells  are  large,  soft,  protoplasmic  masses, 
granular   in    appearance.      They   generally   contain   a   large    number 

of  nuclei ;  these  are  sometimes 
grouped  on  one  side,  and  have 
a  fine  fibrillated  network  run- 
ning through  them.  Some- 
times they  contain  only  one 
nucleus,  which  is  large  and 
shows  indications  of  segmenta- 
tion. These  cells  have  been 
called  by  Kobin  myelo})laxes, 
and  by  Kolliker  osteoclasts. 
The  latter  authoritv  considers 

Three  Multinuclear  Giant-cells  fOsteoclastsV  from  ah-    +1,„™    tior.occ-ii-ir  f<^  iVnnn  nli^ni-i-, 
sorptioii-surfaces  of  growing  bone  H(m)  diameters—     mciU    IlCCefehdiy    lU    UUllt-aUbUip- 
Kolliker).  ^J^^j^^ 

The  Nucleated  Red  Blood-cells  resemble  the  red  corjiuscles  of  the 
blood,  but  are  somewhat  larger;  they  have  a  smooth,  homogeneous 
cell-body  with  a  distinct  nucleus.  These  cells  are  supposed  by  some  to 
lose  their  nuclei,  become  biconcave,  and  assume  the  character  -of  the 


BONES.  45 

ordinary  red  blood-corpuscles.  Those  holding  this  view  claim  that 
the  marrow  of  the  bones  is  one  of  the  blood-producing  tissues  of  the 
body. 

Osteoblasts  (described  p.  42)  are  found  princi])ally  and  in  large 
numbers  in  red  marrow  along  the  osseous  trabeculi,  especially  during 
the  development  of  bone. 

Red  cells,  having  every  appearance  of  red  blood-corpuscles,  are 
numerous.  Their  presence  has  been  explained  by  the  fact  that  the 
walls  of  the  capillary  blood-vessels  are  very  thin  and  delicate,  permit- 
ting the  escape  of  the  corpuscles  into  the  surrounding  tissue. 

Development  of  Bone. 

The  central  column  of  the  body,  consisting  of  the  vertebrae  and  the 
base  of  the  skull,  is  seen  in  rudimentary  outline  at  a  very  early  period  of 
embryonal  life.  This  outline,  formed  from  the  mesoblastic  layer  of  the 
blastoderm,  and  composed  of  tissue  not  unlike  the  primordial  structure 
by  which  it  is  surrounded,  soon  becomes  cartilage ;  and  in  man,  about 
the  fortieth  day  of  embryonal  life,  bone-development  commences  in  the 
clavicle  and  inferior  maxilla.  This  early  ossification  of  the  lower  jaw, 
before  the  up])er,  may  be  explained  as  due  to  the  same  law  of  develop- 
ment that  brings  about  the  eruption  of  the  inferior  teeth  before  the 
superior.  Some  of  the  lower  animals,  however,  have  more  teeth  in  the 
lower  .than  the  upper  maxilla,  the  former  being  more  important,  as  in 
mastication  it  has  active  movement,  while  the  upper  jaw  is  passive. 
Nearly  all  the  bones  of  the  body  have  their  commencement  in  hyaline 
cartilage.  Those  of  the  face,  with  the  two  exceptions  of  a  portion  of 
the  inferior  maxilla  and  the  inferior  turbinated,  and  those  covering  the 
brain,  excepting  a  part  of  the  occipital,  are  developed  within  memliranes. 
In  addition  to  these  two  modes  of  formation,  the  cartilaginous  and  mem- 
branous, bone  seems  to  be  principally  developed  from  the  osteogenetic 
layer  of  the  periosteum.  From  this  it  will  be  seen  that  it  is  best  to  con- 
sider the  development  in  three  divisions — viz. :  I.  Intracartilaginous ; 
II.  Subperiosteal ;    III.  Intramembranous. 

I.  The  Intracartilaginous  (endochondral)  Bones  are  those  hav- 
ing their  origin  or  first  formation  in  hyaline  cartilage,  whicli  usually 
presents,  in  minature,  a  general  outline  of  the  future  bone.  The  trans- 
formation from  cartilage  to  bone  is  gradual,  and  commences  at  one  or 
more  points,  called  centres  of  ossification.  In  the  bones  of  the  higher 
animals,  including  man,  the  number  of  ossific  centres  varies,  being 
dependent  on  the  degree  of  complexity  in  the  formation  of  the  bones 
and  the  number  of  vessels  and  nerves  which  pass  through  them.  If 
there  is  but  one  point,  it  is  usually  situated  near  the  middle  and  upon 
the  surface,  else  next  to  the  perichondrium  or  future  periosteum.  For 
convenience  of  description  and  facility  of  study  the  development  of 
endochondral  bone  may  be  divided  into  four  stages  : 

1st.  The  first  observable  change  is  at  one  or  more  of  the  ossific  points, 
at  which  the  cartilage-cells  (for  description  see  p.  138)  immediately  under 
the  perichondrium  enlarge  and  multiply  within  their  capsules,  the  matrix- 
substance  becoming  partly  absorbed. 


46 


AXAT03IY 


Fig.  12. 


2d.  Into  this  area  blood-vessels  enter  from  the  under  layer  of  the 
perichondriiun  (chondrogenetio  layer),  accompanied  by  osteoblasts  (bone- 
germs)  and  marrow-tissue. 
As  the  vessels  and  osteo- 
blasts advance  into  the 
partly-absorbed  cartilage,  the 
change  of  the  cartilage  is  car- 
ried on  in  front  of  them ;  thus 
the  cartilage  becomes  chan- 
nelled, forming  cavities  ir- 
regular in  shape  named  me- 
dullary spaces.  These  are 
lined  by  osteoblasts  and  in- 
vaded or  permeated  l)y  blood- 
vessels and  marrow-tissue. 

3d.  That  poi-tion  of  the 
cartilage  basement-substance 
which  is  not  absorbed  forms 
irregular  septa  or  trabeculse, 
and  is  infiltrated  with  fine 
particles  of  calcic  salts,  caus- 
ing opacity  and  a  granular 
ajjpearance,  M'hich,  when  cut, 
has  a  gritty  feel :  this  process 
is  called  calcification,  and  is 
an  intermediate  stage  between 
the  absorption  of  the  carti- 
lage-matrix into  medullary 
spaces,  and  the  ossification  of 
the  bone  by  the  infiuence  of 
the  osteoblasts. 

4th.  The  last  stage,  fol- 
lowing closely  that  of  calci- 
fication, is  called  ossification 
through  the  influence  of  the 
osteoblasts.     Portions  of  the 

Section  of  Part  of  one  of  the  Limb  Bones  of  a  Fa?tal  Cat.    -walls  of  the  nicdullary  SUaCCS 
Tlie  c:ilcitication  of  the  cartilage-niatri.\  has  advanced     ,  i  i      i  •         j. 

from  the  centre,  and  is  extending  between  the  groups  of      OCCOme  abSOrbeCl,  CaUSUlg  tWO 
caitilage-cells,  whieli  are  arranged  in  characterisiic  rows.  ,-,,    ,.^   ^C  +K^    ,^,.;,itti.iV  .no 

The  subperiosteal  bony  deposit  {im)  has  extended  pari  Ol  molC  01  lUe  piUUai}  lUL- 
;i«.s-.vi/ with  tlie  Ciih'itica'tion  of  the  cartilage-nuitrix.  Tlie 
cartiUitie-CfUs  in  tlie  primary  areol-.e  are  mostly  shrunken 
and  steMatc;  in  some  cases  tlicy  have  iimppcd  nut  of  the 
.space.  .\t  /)■  and  in  two  other  places  an  irrujition  of 
the  sul)periostc:il  tissue,  cuniiiosed  of  ramified  ci'lls  with 

osteoblast.s  and  growing  blood-vessels,  has  penetrated  the       '     j.      i?  j.i  •  ,  -  U -.nTi  //->.. 

subperiosteal  bony  crust,  and  has  begun  to  excavate  the     pari  01    Uie  pnmai}     OOUC  ^^OI 
secondary  areola;  or  medullary  spaces;  i<,  fihrous  layer  of     nn^r^^f^aA     r»ivtilnrrt>  ni«itriv^    ic: 
the  periosteum  ;  o,  layer  of  osteoblasts  -.some  of  them  are     CaicmCCl    Cdl  lliage-nUUl  1\)    Jb 
imbedded  in   the    osseous    layer  as  bone-corpuscles   in     jj^    OIK'C    rcmOVcd. 
lacnnie ;  W,  blood-vessels  occupied  by  blood-corpuscles.  ,,  rr\         •  j^      j_*        j. 

''  Turnuig  our  attention  to 
the  exact  wav  in  which  bone  is  formed  under  the  influence  of  the  osteo- 
bla.sts,  we  find  tliat  just  beneath  these  cells,  lying  along  the  walls  of  the 
new-formed  medidlary  spaces,  the  ba.sement-substance  of  true  bone  begins 
to  be  deposited,  at  fir.'^t  in  the  fi)rm  of  a  narrow  shell  beneath  each  osteo- 


dullaiy  spaces  to  become 
united  and  form  secondary 
spaces.     In  this  way  a  great 


BONES.  47 

blast.  These  deposits,  which  on  cross-section  have  a  crescentic  shape, 
become  thicker  and  thicker,  rising-  up  around  the  cell,  which  they  iinally 
enclose — the  enclosed  osteoblast  becoming,  as  it  would  seem,  a  bone-cell. 
This  process  occurring  around  each  osteoblast,  the  walls  of  the  medullary 
cavities  soon  become  covered  with  a  layer  of  bone  containing  bone-cells. 
New  osteoblasts  appear  on  the  walls,  and  in  turn  become  enclosed  in  a 
layer  of  bone,  and  thus  the  lamellar  arrangement  of  bone-tissue  is  pro- 
duced. The  remains  of  cartilage  basement-substance  between  the 
medullary  space  thus  covered  by  bone  finally  disappear  in  a  manner 
unknown  to  us."  ^ 

II.  The  Subperiosteal  Bone  is  the  portion  formed  on  the  outer 
surface  of  that  which  is  developed  within  the  cartilage,  and  by  the 
formation  of  which  bones  increase  in  thickness.  It  is  deposited  in  a 
manner  similar  to  endochondral  bone,  through  the  influence  of  osteo- 
blasts found  on  the  inner  portion  of  the  osteogenetic  layer  of  the  peri- 
chondrium, which  has  now  become  periosteum.  The  osteoblasts  are 
arranged  along  the  line  of  blood-vessels  and  connective-tissue  bundles 
of  the  osteogenetic  layer  of  the  periosteum,  and  as  these  structures  are 
not  parallel  to  each  other  or  to  the  surface  of  the  bone,  but  cross  at 
various  angles,  forming  an  uneven  network,  they  cause  newly-formed 
bone  to  have  an  uneven  surface,  with  branching  grooves  and  canals 
passing  in  diiferent  directions.  Upon  the  walls  or  sides  of  these  grooves 
and  canals  the  osteoblasts,  by  means  of  which  bone-tissue  is  deposited, 
are  distributed,  spaces  being  left  for  blood-vessels  and  marrow-tissue: 
these  spaces  subsequently  become  the  Haversian  canals.  During 
the  time  these  canals  and  spaces  are  being  encroached  upon  by  ossific 
deposit  newer  layers  are  commenced  on  the  outer  surface  of  the  bone, 
the  fully-formed  or  ossified  layer  being  continually  overlaid  by  fresh 
coatings  in  a  manner  similar  to  the  lamellne  of  the  Haversian  system : 
by  this  process  the  bone  grows  in  thickness.  These  lamellne  are  held 
or  bound  together  by  perforating  fibres  (Sharpey's  fibres),  which  pass 
through  several  layers  at  nearly  right  angles  ^^'ith  the  surface.  These 
fibres  originate  from  the  bundles  of  connective  tissue  of  the  subperios- 
teal membrane,  but  do  not  all  have  connection  with  the  periosteum 
itself,  though  doubtless  they  had  their  origin  from  that  membrane,  the 
same  as  the  bone  in  which  they  are  found.  Perforating  fibres  are 
usually  ossified,  but  in  some  instances  they  are  not,  and  in  the  drying 
of  the  bone  they  become  shrunken,  leaving  perforations. 

In  the  long  bones  the  caitilage  grows  and  extends  toward  the 
epiphyses,  where,  by  gradually  incr&asing  in  diameter,  it  causes  the  can- 
cellated portion  of  the  bone  to  ])resent  a  somewhat  similar  shape  to  that 
of  an  elongated  hour-glass.  Where  deposition  of  bone  first  commenced 
the  cancellated  part  is  the  narrowest,  and  the  cortical  portion,  which  grows 
from  the  periosteum,  is  the  thickest.  Toward  the  ends  of  the  bones 
the  cortical  substance  gradually  diminishes  to  a  thin  layer,  thus  main- 
taining a  nearly  equal  diameter  for  the  bone  from  end  to  end,  A  little 
before  or  about  the  time  of  the  development  of  the  periosteal  bone  the 
central  portion  of  the  embryonal  spongy  or  endochondral  bone  under- 
goes a  process  of  softening  or  absorption  (osteoporosis,  Schwalbe).     In 

^  Pruden's  Practical  Histoiogy,  2d  ed.,  p.  73. 


48  ANAT03IY. 

this  way  the  central  or  marrow  cavity  is  formed,  and  the  partitions  or 
septa  of  the  medullary  spaces  become  absorbed,  especially  art)iind  the 
medullary  canal,  thereby  enlarging  it.  This  absorption  may  be  carried 
on  until  the  entire  embryonal  spongy  bone  is  remov^ed. 

III.  The  Intramembraxous  Ossification  takes  place  within 
membranes  of  fibrillar  connective  tissue,  independent  of  any  carti- 
laginous formation.  It  is  found  within  the  roof  of  the  brain-case,  as 
in  the  i^arietal  and  frontal  bones  and  portions  of  the  occipital  and  tem- 
poral, and  within  all  the  facial  bones,  except  the  inferior  turbinated  and 
part  of  the  inferior  maxilla.  (The  base  of  the  skull,  the  two  inferior 
turbinated,  and  part  of  the  inferior  maxillary  bones  are  developed 
within  cartilage.)  This  development  of  bone  is  analogous  to  that  of 
periosteal  formation,  which  takes  place  on  or  around  endochondral 
bones. 

The  parietal  bone  presents  a  good  example  of  this  development.  At 
first  it  is  composed  of  a  single  fibrous  membrane ;  next  it  divides  near 
its  centre  into  two  layers,  these  eventually  becoming  the  external  and 
internal  periosteums.  Between  these  two  layers  are  numerous  inter- 
lacing bundles  of  connective-tissue  fibres,  making  an  intervening  network 
between  the  two  membranes  and  forming  irregular  medullary  spaces 
similar  to  the  partially-absorbed  cartilage  in  endochondral  bone-forma- 
tion. The  bundles  of  connective-tissue  fibres  forming  the  walls  of  the 
medullary  spaces  become  infiltrated  with  calcic  salts ;  the  spaces  them- 
selves are  occupied  by  blood-vessels  and  marrow-tissue,  and  their  walls 
lined  by  osteoblasts,  M'hich  develop  bone,  as  described  p.  42. 

As  the  centre  thickens  the  cleavage  of  tlie  membrane  extends  toward 
the  circumference,  and  bony  spicula  grow  outward  in  radiating  lines  until 
they  meet  neighboring  bones,  with  which  they  miite  l)y  sutures. 

While  this  process  is  going  on,  the  two  osteogenetic  membranes  deposit 
successive  layers  of  bone,  causing  an  increase  in  thickness,  each  layer 
becoming  more  dense,  thus  forming  Avhat  are  known  as  the  external 
and  internal  plates.  Between  the  two  tables  of  a  fully-formed  bone  is 
the  cancellated  structure  or  dij)loe.  These  irregularly-formed  spaces 
are  made  through  absorption  of  portions  of  the  bony  tissue  by  osteo- 
])orosis.  The  di])loe  is  a  highly  vascular  tissue,  in  which  the  arteries 
of  the  external  and  internal  periosteum  anastomose. 

Bones  arc  divided  into  four  classes — viz.  long  bones,  such  as  those  of 
the  arm  and  leg;  tahidar  or  JJ((f  bones,  as  those  forming  the  vault  of  the 
cranium  ;  irref/uldr  bones,  such  as  the  vertebrae ;  and  short  bones,  as 
those  of  the  car])us  and  tarsus. 

Many  of  the  bones  are  arranged  in  synnnctrical  pairs,  one  on  each 
side,  as  illustrated  in  the  ribs,  arms,  legs,  parietal  and  temporal  bones ; 
while  the  vertebra?,  conunencing  with  the  coccyx,  and  continuing  upward 
through  the  skull  with  the  occipital,  sphenoid,  ethmoid,  frontal,  and 
vomer,  arc  single  l)()ncs,  develojK'd  from  two  symmetrical  halves.  The 
inferior  maxilla  is  usually  described  as  a  single  bone,  but  in  embryonal 
life  and  in  some  of  the  lower  animals  there  are  two.  In  man  the 
bones  on  either  side  of  the  body  are  seldom  of  equal  size,  those  of  the 
right  side  usually  being  slightly  larger;  their  markings,  such  as  processes 
and  foramina,  are  also  dissimilar  in  size  and  shape. 


BONES. 


49 


Inijierfectly  and  Ill-developect  Upper  Jaw. 


Disease  of  the  soft  parts  often  changes  the  shape  of  bones,  particu- 
larly in  the  young.  Aggravated  tonsillitis  in  childhood  will,  if  chronic 
and  accompanied  by  hyper- 
trophy, cause  the  roof  of  the  Fig  13. 
moutii  to  take  an  inverted 
V-form  (Fig.  13).  If  the 
patient  has  suffered  from  the 
disease  on  one  side  only,  that 
side  will  be  pulled  down. 
This  is  due  to  the  extra  ten- 
sion of  the  palato-glossus  and 
palato-pharyngeus  muscles. 
Tims  the  palatal  processes  of 
the  superior  maxillae  and  pal- 
ate bones  are  prevented  from 
forming  the  normal  dome- 
shape  roof  of  the  mouth,  and 
the  vomer  is  directed  or 
pushed  from  its  proper  posi- 
tion ;  becoming  crooked  or 
lacking  space  to  occupy  its 
normal  position,  it  is  de- 
flected or  pushed  forward,  thus  forming  an  unduly  large  nose.  By 
proper  treatment  at  an  early  period,  many  such  deformities  can  be 
avoided.  Tumors  of  the  maxillary  sinus  may  change  the  shape  of  one 
or  more  of  the  surfaces  of  the  superior  maxilla,  and  an  aneurism  or 
other  soft  tumor  constantly  pressing  against  a  bone  will  cause  its 
absorption. 

In  describing  bones, the  following  terms  will  be  used  : 

Proximal,  the  end  or  surface  of  a  bone  next  to  the  centre  of  the  body. 

Didal,  the  end  or  surface  that  is  farthest  away  from  the  centre. 

Head.  If  the  extremity  forms  a  single  rounded  prominence,  it  is 
called  the  head. 

Condyles.  If  there  are  a  pair  of  prominences,  they  are  called  con- 
dyles, though  this  name  is  applied  to  the  single  articular  eminence  of 
the  occipital  bone  and  of  the  lower  jaw. 

Neck  is  that  portion  which  is  constricted  just  below  a  head,  condyle, 
or  other  articular  eminence. 

Process  is  an  elevation,  projection,  or  prominence  on  a  bone. 

Spinous  Process,  a  narrow  and  tapering  prominence  or  elevation  on 
a  bone. 

Tubercle  or  a  Tuberosity,  an  obtuse  prominence. 

Line,  Ridge,  or  Crest,  an  elevation  extending  some  distance  along  the 
surface  of  a  bone,  a  prominent  border. 

Foramen  (plural  Foramina),  an  aperture  in  a  bone  or  between  several 
bones. 

Canal  or  Meatus,  a  prolongation  of  a  foramen  for  some  distance  in 
the  bone. 

Fossa  (plural  Fossce),  a  broad,  shallow  depression. 

Sinus,  a  cavity  with  a  small  external  communication. 
4 


50 


AN  ATOM  r. 


A  line  in  measurement  is  one-twelfth  part  of  an  inch.  In  describing 
the  development  of  bones,  weeks  and  months  refer  to  embryonic  and 
foetal  life.  • 

An  articulating  surface  is  that  portion  of  a  bone  where  it  joins 
another. 

A  facet  is  a  portion  of  an  articular  surface  which  is  distinguished 
from  adjacent  portions  of  the  same  surface  by  difference  of  its  curva- 
ture. 

The  Skull. 

The  skull  is  composed  of  twenty-two  bones,  exclusive  of  the  six 
otic  (ear  bones),  the  AV^ormian  bones,  and  the  teeth.  These  are  united 
by  sutures  and  synchondroidal  articulations,  with  the  exception  of  the 

Fig  14. 


i.'O  ^.^    Lie.    %« 


y^^ 


Occipitivl   lione,  outer  surface. 


inferior  maxilla,  which  is  a  diarthroidal  joint.  The  skull  approaches 
the  spheroidal  shape,  flattened  at  the  sides,  broader  posteriorly  than 
anteriorlv,  and  is  supported  upon  the  atlas,  the  first  bone  of  the  verte- 
bral column.  Anatomists  divide  the  bones  of  the  skull  into  two 
groups — the  cranial  and  the  flicial.     The  cranial  bones,  M'hich  encase 


BONES.  51 

the  brain,  are  eight  in  number — one  occipital,  two  temporal,  one  sphe- 
noid,  two  parietal,  one  frontal,  and  one  ethmoid.  The  remaining  four- 
teen bones  form  the  oral  cavity,  nasal  chamber,  and  portions  of  the 
orbits.  They  are  called  the  facial  bones,  and  consist  of  the  two  superior 
maxillary,  two  palatal,  one  vomer,  two  inferior  turbinated,  two  lachry- 
mal, two  nasal,  two  malar,  and  the  inferior  maxilla,  six  being  in  pairs, 
and  two  being  single  bones.  The  hvoid  bone,  though  generally  classed 
as  a  bone  of  the  neck,  will  be  described  with  the  bones  of  the  head. 

Occipital  Bone. — Tlie  occipital  bone  (Fig.  14)  is  situated  at  the  base 
of  the  cranium,  at  the  top  of  the  spinal  column,  and  articulates  with  the 
atlas.  It  is  oval  in  form,  resembling  somewhat  a  saucer,  and  presents 
for  examination  four  angles,  four  borders,  two  condyles,  two  surfaces — 
one  concave  or  inner  toward  the  brain,  the  other  or  outer  convex.  It  is 
also  perforated  on  its  under  surface  by  a  large  oval  foramen. 

Tke  Bcmkw  Process  forms  the  anterior  (inferior)  angle  of  the  bone. 
If  a  section  of  this  process  were  made  through  the  mesial  line,  the  sur- 
face would  assume  the  appearance  of  a  wedge  about  an  inch  in  length, 
widening  from  the  anterior  border  of  the  foramen  magnum,  the  base 
of  the  wedge,  about  half  an  inch  in  thickness,  being  that  portion  of 
the  process  which  articulates  with  the  sphenoid  bone.  In  early  life 
a  layer  of  cartilage  intervenes  between  the  basilar  process  of  the 
occipital  and  the  sphenoid  bones.  This  cartilage  becomes  ossified  at 
the  age  of  puberty.  The  upper  surface  of  the  basilar  process  is  grooved 
for  the  accommodation  of  the  medulla  oblongata  and  basilar  artery ;  the 
under  surface  (laterally)  is  convex  and  forms  the  roof  of  the  pharynx. 
Near  its  centre  is  a  rounded  prominence  called  the  pharyngeal  spine,  for 
the  attachment  of  tlie  raphe  and  the  superior  constrictor  of  the  pharvnx. 
On  each  side  of  this  prominence  is  a  rough  depression  for  the  attachment 
of  the  rectus  capitis  anticus  major  and  minor  muscles.  Laterallv,  the 
superior  border  of  this  process  is  roughened  for  articulation  with  the 
petrous  portion  of  the  temporal  bone,  forming  the  petro-basilar  suture. 
During  life,  the  under  portion  of  this  process  is  filled  with  a  mass  of 
fibrous  tissue. 

The  Siqjerior  Angle  of  the  occi])\ta\  bone  articulates  with  tlie  posterior 
superior  angles  of  the  parietal  bones  at  the  position  occupied  in  foetal 
life  by  the  posterior  fontanelle.  The  lateral  angles  articulate  at  the 
posterior  juncture  of  the  parietals  with  the  mastoid  portions  of  the 
temporal  bones.  The  superior  borders  extend  from  the  superior  to  the 
lateral  angles  of  the  bone ;  they  are  deeply  serrated  for  articulation  with 
the  posterior  borders  of  the  parietal  bones,  and  form  the  occipito-parietal 
(lambdoid)  suture.  In  this  suture  AVormian  bones  of  diiferent  sizes  are 
most  frequently  met,  the  denticulations  being  distinctly  marked.  The 
inferior  borders  extend  from  the  lateral  angles  to  the  sphenoid  bone. 
Each  border  is  divided  into  two  portions  by  the  jugular  process.  The 
upper  part  is  serrated  for  articulation  with  the  mastoid  portion  of  the 
temporal  bone,  forming  the  occipito-mastoid  suture ;  the  lower  portion 
is  simply  roughened. 

The  Jugular  Processes,  two  in  number,  are  sharp  points  of  bone 
extending  laterally,  and  are  analogous  to  the  transverse  processes  of  a 
vertebra ;  they  form  the  posterior  boundary  of  the  jugular  notch. 


52 


ANATOMY 


TIic  Jugular  Notch  is  a  smooth  semicircular  concavity,  extending 
half  an  inch  outwardly  and  three-fourths  of  an  inch  anteriorly,  forming  by 
its  articulation  with  the  temporal  bone  the  jugular  or  posterior  lacerated 
foramen.  This  foramen  is  frequently  divided  by  one  or  more  septa,  and 
through  it  the  ninth,  tenth,  and  eleventh  pairs  of  nerves  pass  out  of  the 
brain-case.  It  is  at  this  point  also  that  the  lateral  sinuses  terminate  and 
the  internal  jugular  vein  commences. 

Fig.  15. 
Su/ievLo,-  Antflf: 


^'i^^ Lateral 


,,■      y^Angl, 


Jaifcriop  Analp  \^ 

Occipital  Hone,  inner  surface. 

The  External  Surface. — On  each  side  of  the  lateral  borders  of  the 
foramen  magnum  are  the  two  condyloid  processes  (exoccipitales)  which 
articidate  with  the  atlas  (the  Hrst  cervical  vertebra). 

The  ComJi/les  are  elliptical  in  form  and  converge  somewhat  in  front. 
Their  surfaces  are  convex,  both  transversely  and  longitudinally,  being 
divided  into  two  articulating  ihcets,  which  are  occasionally  sc])arated  by 
a  transverse  groove.     The  inner  side  of  each  condyle  is  roughened  for 


BONES.  53 

the  attachment  of  the  odontoid  ligament  of  the  axis  (the  second  cervical 
vertebra).  Immediately  above  the  anterior  facet  on  either  side  are  tlie 
anterior  condyloid  foramina,  situated  at  the  side  and  above  the  foramen 
mau-num  ;  they  transmit  the  hypoglossal  nerves.  Occasionally  these 
foramina  are  found  doubled,  which  allows  the  superior  and  inferior  bun- 
dles of  the  hvpoglossal  nerve  to  pass  through  separate  foramina  in  their 
exit.  Behind  the  posterior  facet  is  the  condyloid  fossa,  which  usually 
contains  the  posterior  condyloid  foramen,  for  the  transmission  of  the 
occipital  emissary  vein  to  the  lateral  sinus.  Two  foramina  are  also 
occasionally  found  in  this  situation.  The  outer  surface  of  the  tabular 
portion  of  the  occipital  bone  (supraoccipital)  is  divided  transversely  into 
three  sections  by  the  superior  and  inferior  curved  lines.  The  superior 
curved  line  runs  inwardly  from  the  lateral  angles  of  the  bone,  at  the 
temporo-parietal  suture,  to  the  external  occipital  protuberance ;  it  forms 
the  major  portion  of  that  line,  which  extends  in  the  articulated  skull 
from  the  apex  of  the  mastoid  portion  of*  the  temporal  bone  on  the  one 
side  of  the  cranium  to  the  same  point  on  the  opposite  side.  The  inferior 
curved  line  runs  almost  parallel  with  the  superior.  Its  extremities  are 
situated  at  each  jugular  process,  from  which  point  it  ascends  to  the 
occipital  crest.  The  lower  two-thirds  of  the  external  surface  is  divided 
longitudinally  by  the  occipital  crest.  This  crest  is  a  slight  ridge  run- 
ning from  the  external  occipital  protuberance  to  the  foramen  magnum. 
The  upper  third,  or  that  portion  above  the  superior  curved  lines,  is 
comparatively  smooth.  The  external  occipital  protuberance,  A^hich 
gives  attachment  to  the  liy-amentum  nuchne,  is  situated  in  the  centre  of 
the  superior  curved  line,  and  is  analogous  to  the  spinous  process  of  a 
vertebra.  Its  size  varies  in  diiferent  individuals,  being  much  larger  in 
some  persons  than  in  others.  The  upper  margin  of  the  superior  curved 
line  gives  attachment  to  the  occi])ito-frontalis  muscle,  its  inner  extremity 
to  the  trapezius,  and  just  beneath  the  outer  extremity  are  the  points  of 
attachment  of  the  splenius  capitis  nniscle.  On  either  side  of  the  crest, 
between  tlie  curved  lines,  are  marked  depressions  for  the  attachment  of 
the  complexus  muscles,  and  just  below  and  to  the  outer  side  of  these  is 
a  smooth  surface  for  the  insertion  of  the  superior  oblique  muscles.  The 
space  below  the  inferior  curved  line  gives  attachment  to  the  rectus  capitis 
posticus  major  and  minor  muscles. 

The  Internal  Surface  of  the  bone  is  divided  into  four  fossae  In'  two 
distinct  ridges,  transverse  and  longitudinal :  the  former  runs  from  the 
lateral  angles  to  the  internal  occipital  protuberance,  the  longitudinal 
ridge  extending  from  the  superior  angle  of  the  bone  to  the  foramen 
magnum.  The  point  where  these  ridges  intersect  is  called  the  internal 
occipital  protuberance.  The  superior  fossfe  afford  lodgment  to  tlie  lobes 
of  the  cerebrum,  while  the  inferior  accommodate  those  of  the  cei-ebel- 
lum.  The  superior  part  of  the  longitudinal  and  the  transverse  ridges 
are  generally  grooved,  to  accommodate  the  longitudinal  and  the  lateral 
venous  sinuses.  Frequently  the  longitudinal  sinus  is  found  to  the  right 
side  of  the  superior  longitudinal  ridge,  particularly  Avhere  it  approaches 
the  intersection  of  the  ridges. 

The  inferior  portion  of  the  longitudinal  ridge  is  rounded,  and  is  gen- 
erally called  the  internal  occipital  crest. 


54 


ANATOiMY. 


The  Foramen  Magnum  is  the  largest  foramen  of  the  brain-case. 
It  is  situated  on  the  inferior  surface,  between  the  jugular  and  l)asilar 
processes  and  the  tabular  portion  of  the  bone.  It  is  oval  in  shape, 
its  long  diameter  being  antero-posterior.  It  transmits  the  spinal  cord 
and  its  membranes,  the  spinal  accessory  nerves,  and  the  vertebral 
arteries. 

Structure. — About  one-third  of  the  basilar  process,  commencing  at 
the  foramen  magnum,  is  made  up  of  two  plates  of  compact  tissue. 
These  plates  then  divide  and  enclose  between  them  cancellated  tissue. 
The  jugular  processes  are  principally  made  up  of  spongy  substance, 
the  fosste  being  composed  of  compact  tissue.  The  fossae  for  the  lodg- 
ment of  the  two  lobes  of  the  cerebellum  are  formed  of  compact  bone, 
the  remainder  of  the  tabular  portion  of  the  bone  being  made  up  in 
a  great  part  of  two  plates,  with  abundant  diploe  between  them. 
Especially  is  this  the  case  near  the  occipital  protuberance. 

Development. — The  occipital  bone  is  developed  from  osseous  carti- 
lage and  osseous  membrane.  The  condyloid  (ex-occipital)  and  the  basilar 
(basi-occipital)  portions  commence  to  ossify  in  cartilage  about  the  sev- 
enth or  eighth  week  of  embryonic  life,  each  having  a  separate  nucleus 

Fig.  16. 

J3t/  ^  centres 


/    for  ocoijinlai 

pOTtWIl 


^^'f£\  —  /for  each  conJiilovd 
3\  jjortion 

^  J  or   oasbLar  poi-tioii 


Development  of  Occipital  Bone. 

or  centre.  The  osseous  union  of  the  basilar  and  condyloid  portions 
begins  at  the  third  or  fourth  year,  and  is  completed  by  the  end  of  the 
fifth  or  sixth  year.  The  basi-occipital  and  the  basi-sphenoidal  ])orti(nis 
of  the  respective  bones  are  united  by  intervening  cartilage  until  about 
the  fifteenth  year,  at  which  tnne  ossification  commences,  and  it  is  gen- 
erally com]ileted  by  the  twentieth  year. 

The  tabulated  portion  (supraoccipital)  commences  its  process  of  ossi- 
fication in  membranous  tissue  a  short  time  before  the  remainder  of  the 
bone,  from  l()ur  centres,  which  at  birth  have  been  united  and  form  one 
bone.  At  this  time  three  deep  fissures  are  noticeable  at  the  superior 
and  lateral  angles.  Occasionally  the  lateral  fissures  run  into  each  other, 
and  the  up})er  portion  fi)rms  the  inter]iarietal  bone  of  many  animals. 

The  osseous  union  of  the  supra  and  the  condyloid  jwrtions  begins  during 
the  second  or  third  year,  and  is  completed  by  the  third  or  fourth  year. 


BONES. 


55 


Remarks. — The  basilar  and  condyloid  portions  of  this  bone,  being 
so  nearly  connected  with  the  mouth  and  associate  pai-ts,  claim  special 
attention. 

The  basilar  process  forms  the  roof  of  the  pharynx,  and  is  situated  on 
a  level  with  the  posterior  nares,  and  in  surgical  operations  may  be 
reached  through  the  nose  or  through  the  oral  cavity. 

Hydatid  or  exostosed  cysts  and  other  enlargements  within  the  ante- 
rior condyloid  foramen,  producing  pressure  upon  the  hyjjoglossal  nerve, 
would  cause  paralysis,  atrophy,  or  deflection  of  the  tongue. 

The  Temporal  Bone  (Fig.  17)  is  situated  at  the  side  and  base  of  the 
brain-case.  It  articulates  in  front  with  the  great  wing  of  the  sphe- 
noid bone,  above  with  the  parietal  bone,  behind  with  the  lateral  portion 
of  the  occipital  bone,  and  at  the  base  of  its  petrous  portion  is  wedged 

Fig.  17. 


Left  Temporal  Rone,  outer  surface. 

in  between  the  basilar  process  of  the  occipital  and  the  great  wing  of  the 
sphenoid  bone.  By  its  outer  surface  it  assists  in  the  formation  of  the 
temporal  and  the  zygomatic  fossae  and  the  zygomatic  arch ;  by  its  under 
surface  it  forms  part  of  the  roof  of  the  parotid  region  ;  and  by  its  inner 
surface  it  forms  part  of  the  middle  fossae  of  the  brain-case.  For  con- 
venience of  description  this  bone  is  generally  divided  into  three  portions 
— viz.  the  squamous  (scale),  the  mastoid  (nipple),  and  the  petrous  (rock). 


56  ANATOMY. 

The  styloid  process  may  also  be  added  to  this  division,  and  studied  sepa- 
rately, as  it  has  its  own  centre  of  ossification. 

The  Squwnous  Portion  is  divided  into  three  parts — the  ascending,  the 
horizontal,  and  the  part  forming  the  wall  of  the  glenoid  cavity.  The 
ascending  portion  is  concavo-convex,  the  convexity,  which  is  almost  per- 
pendicular, being  smooth  and  giving  origin  to  the  temporal  muscle.  It 
is  marked  by  two  grooves  running  upward,  one  near  its  anterior  border, 
the  other  at  the  posterior  termination  of  the  zygomatic  arch.  They  in- 
dicate the  position  of  the  deep  temporal  arteries  at  the  upper  border  of 
the  squamous  portion,  where  it  articulates  with  the  parietal  bone,  form- 
ing the  temporo-parietal  suture  (squamous) ;  the  outer  table  is  extended 
considerably  beyond  the  inner,  thus  forming  a  scale  or  bevel  at  the 
expense  of  the  inner  border.  This  scale  overlaps  the  corresponding 
surface  of  the  parietal  bone.  That  portion  which  forms  the  suture  is 
bevelled  inwardly,  the  middle  portion  is  serrated,  and  the  lower  portion 
anteriorly  is  bevelled  outwardly. 

The  zygomatic  process  (horizontal  portion)  has  a  triangidar  origin 
from  the  squamous  portion  of  the  bone,  where  it  bends  abruptly  inward 
toward  the  base  of  the  skull,  and  has  three  roots.  Its  large  posterior 
root  passes  backward,  above  the  external  auditory  meatus,  behind  which 
it  forms  the  boundary  betAveen  the  squamous  and  the  mastoid  portions 
of  the  bone,  and  is  called  the  supramastoid  ridge ;  this  then  curves 
upward,  and,  uniting  with  the  temporal  ridge  of  the  parietal  bone, 
forms  the  posterior  boundary  of  the  temporal  fossa.  The  middle  root 
forms  the  outer  boundary  of  the  glenoid  fossa;  then  bends  inwardly 
and  terminates  in  the  posterior  glenoid  process  at  the  outer  extremity 
of  the  t»:lenoid  fissure.  The  anterior  root  runs  directlv  inward  in  front 
of  the  glenoid  fossa,  forming  its  anterior  border,  which  is  also  known 
as  the  eminentia  articularis.  At  the  juncture  of  this  root  with  the 
zygomatic  process  is  a  rounded  eminence,  called  the  tubercle,  for  the 
attachment  of  the  external  lateral  ligament  of  the  inferior  maxilla. 
The  zygomatic  process  projects  outwardly  from  the  skull  about  one- 
fourth  of  an  inch,  and  has  an  upper  and  a  lower  surface ;  it  then  turns 
upon  itself,  and  its  posterior  edge,  which  is  thin,  forms  the  superior 
border.  The  inferior  border  is  about  half  an  inch  in  length,  its 
extremity  being  serrated  and  bevelled  at  the  expense  of  the  inferior 
border,  where  it  articulates  with  the  zygomatic  process  of  the  malar 
bone.  The  masseter  muscle  arises  in  part  from  the  lower  border  of  this 
process,  and  each  side  of  the  upper  border  gives  attachment  to  the  two 
layers  of  the  tem])oral  fascia. 

The  Glenoid  Fo^m  is  situated  at  the  base  of  the  squamous  portion 
of  the  bone.  It  is  bounded  in  front  by  the  anterior  root  of  the  zygoma, 
behind  by  the  tympanic  plate  of  the  petrous  portion,  externally  by  the 
auditory  process  and  middle  root  of  the  zygoma.  It  is  divided  into  an 
anterior  and  posterior  ])ortion  by  the  glenoid  fissure  (fissure  Glaserius, 
the  squamoso-tympanic  suture).  The  anterior  Jialf  is  the  articulating 
portion  of  the  fossa,  and  is  occupied  by  the  condyle  of  the  inferior 
maxilla.  In  man  this  is  a  complicated  articulation,  which  will  be 
described  subsequently.  The  posterior  half  accommodates  the  upper 
portion  of  the  parotid  gland. 


BONES. 


57 


The  glenoid  fissure  communicates  with  the  tympanum  (middle  ear), 
and  lodges  the  processus  gracilis  of  the  malleus.  It  is  at  this  point 
that  Meckel's  cartilage  is  united  to  the  bones  of  the  ear  in  the  early- 
stage  of  development.  It  also  transmits  the  levator  tympani  muscles 
and  the  tympanic  branch  of  the  internal  maxillary  artery.  The  cliorda 
tympani  nerve  passes  through  a  separate  canal  parallel  to  the  glenoid 
fissure  (canal  of  Hugier)  on  the  outer  side  of  the  Eustachian  tube  and 
between  it  and  the  carotid  canal. 

The  Internal  Surface  of  the  temporal  bone  (Fig.  18)  is  concave 
and  marked  by  depressions  for  the  middle  lobe  of  the  cerebrum.     It  is 


Fig.  18. 


fietal 


I  Ca.7iaL 


Agueductus  Vestibuli 
Depression  for  Dura-mater 
Meatus  Audiloruis  internus 


Linituiucjor  Superior  i^eimeircttlar 
Hiatus   I'tvlLopiL 

O^onuufjor  S,„a,Ucr  Fttrosal  Nel-ve 
Bcpresuon  for  Casscri.an  ffanffho^n 
■Snstle  vaascd  throuijh  Carotid  Ctuial 


Left  Temporal  Boae,  inuer  surface. 


grooved  for  the  meningeal  arteries,  Avhich  run  almost  parallel  with  the 
deep  temporal  arteries  on  its  outer  surface.  At  the  lower  portion  there 
is  an  eminence  corresponding  partially  to  the  glenoid  fossa  on  the  outer 
surface.     At  this  point  the  bone  is  so  thin  as  to  be  almost  transparent. 

The  Petrous  Portion  (Fig.  19),  so  named  from  its  hardness,  con- 
tains the  internal  and  middle  ear.  The  facial  nerve  passes  outward 
through  this  part  of  the  bone,  and  the  internal  cartoid  artery  inward ; 
it  supports,  in  part,  the  cartilaginous  portion  of  the  Eustachian  tube. 
It  forms  a  three-sided  pyramid,  with  its  base  directed  outward,  its  apex 
forward,  inward,  and  slightly  down^vard,  Avhere  it  is  Avedged  between 
the  basilar  process  of  the  occipital   bone  and  the  great  wing  of  the 


58 


ANA  TOM  Y. 


sphenoid,  leaving  a  portion  unoccupied  by  bone.  This  unoccupied 
portion  is  called  the  middle  lacerated  foramen,  and  is  filled  up  ^vith 
cartilage  in  the  recent  state.  It  has  three  surfaces :  two  (the  anterior 
and  posterior)  are  situated  within  the  brain-case;  the  other,  the  inferior, 
on  the  outside. 

The  Anterior  Surface  looks  forward  and  upward,  marking  in  the  base 

Fig.  19. 


C'tvahfirlu.^tachan  tube 


LEVATOR     PAL 


Rough  Quadrilateral SnrJ'a^e 

^r^-^iny  of  carotid  en.,nd 

Ca7ialfor  Iacol.,on\  nerve 

^\ijur^i,ctus  Ciir/ilecc 

Canal  for  Avnold:,  mrve  ■ 

Ji'ffiilar  /hs-sa 

^'■tt/Lnal  jyrijceas 

jSffyloid  process- 

Stylo-  mastoid  foramen 

Jii^xUor  Surface 

Auricular  fissure 


STVLO-PHARyNGEus 


Petrous  Portiou  of  Temporal  Bone,  inferior  surface. 

of  the  brain-ca.se  the  posterior  border  of  its  middle  fossa,  being  divided 
into  a  superior  and  an  inferior  })ortion. 

The  Sxpcrior  Portion  of  the  ])ctrous  portion  of  the  temporal  bone 
is  of  hard  consistency;  near  the  centre  is  a  rounded  eminence  mark- 
ing the  situation  of  the  snj)erior  semicircular  canal.  A  depression 
near  the  apex  defines  the  position  of  the  Gasserian  ganglion  (semilunar 
ganglion  of  the  fifth  ])air  of  nerves;  see  p.  284).  Below  this  depression 
is  the  termination  of  the  internal  carotid  canal.  A  narrow  groove, 
sometimes  doul)lc,  divides  the  superior  from  the  inferior  portions  of  the 
surface.  Along  this  groove  arc  one  or  more  minute  openings,  the  prin- 
cipal one  being  the  hiatus  Fallopii,  for  the  transmission  of  the  greater 
superficial  petrosal  nerve ;  a  smaller  opening  below  is  occupied  by  the 
lesser  petrosal  nerve.      Tlie   inferior   portion,  known  as  the  tegmen 


BONES.  59 

tyrapani,  is  a  thin  layer  of  bone  which  forms  the  roof  of  the  tympanum 
and  the  bony  portion  of  the  Eustachian  tube.  It  is  bounded  anteriorly 
by  the  petro-squamous  fissure,  which  commences  internally  at  the  angle 
between  the  squamous  and  petrous  portions  of  the  bone,  and  extends 
outwardly  to  the  masto-parietal  suture:  internally  it  extends  downward 
and  backward,  forming  the  glenoid  fissure  (fissure  of  Glasserius). 

The  Posterior  Surface  looks  backward  and  inward  ;  it  is  less  oblique 
than  the  anterior,  and  forms,  in  great  part,  the  anterior  border  of  the 
posterior  fossa  of  the  brain-case.  Near  its  centre  is  a  large  orifice 
leading  into  a  short  canal.  The  canal  is  directed  outward,  and  is  called 
the  internal  auditory  meatus.  It  transmits  the  seventh  (facial)  and 
eighth  (auditory)  nerves  and  the  auditory  artery. 

The  meatus  is  about  four  lines  in  depth,  and  terminates  in  a  thin 
plate  of  bone,  the  lamina  cribrosa,  in  the  lower  portion  of  which  are 
several  small  openings  for  the  transmission  of  the  divisions  of  the  audi- 
tory nerve ;  in  the  upper  portion  is  tlie  aqueduct  of  Fallopius,  for  the 
passage  of  the  facial  nerve.  This  canal  has  a  tortuous  course  through 
the  petrous  portion  of  the  temporal  bone,  passing  at  first  outward  for 
a  short  distance  between  the  cochlea  and  vestibule  to  the  inner  wall  of 
the  tympanum  ;  then  backward  over  the  fenestra  ovalis,  the  ear,  and  then 
downward,  terminating  at  the  stylo-mastoid  foramen.  External  to  the 
internal  auditory  meatus,  and  between  it  and  the  posterior  fossa,  is  a 
slit-like  opening,  quite  indistinct  in  some  cases,  which  leads  to  a  canal, 
tlie  aqueductus  vestibuli.  This  canal  transmits  venous  blood  from  the 
internal  ear.  The  superior  border,  which  divides  the  anterior  from  the 
posterior  surface,  is  grooved  for  the  superior  petrosal  sinus,  but  it  never 
extends  to  the  apex  of  the  bone.  That  portion  of  the  border  internal 
to  the  meatus  is  depressed  for  the  reception  of  a  thick  fold  of  dura  mater, 
under  which  the  third,  fourth,  fifth,  and  sixth  nerves  pass. 

The  Inferior  Surface  of  the  petrous  portion  is  rough  and  uneven. 
From  within  outwardly,  or  from  the  apex  to  a  large  foramen  situ- 
ated about  midway  of  this  surface,  is  a  rough  triangular  space  which 
gives  attachment  to  the  levator  palati  and  tensor  tympani  muscles.  The 
large  round  foramen  is  the  external  o])ening  to  the  canal  for  the  internal 
carotid  artery.  It  first  passes  upward,  then  horizontally  forward  and 
inward  to  the  apex  of  the  bone,  from  which  point  the  vessel  enters  the 
brain-case. 

A  plexus  of  the  sympathetic  nerve  accompanies  the  artery  in  its 
course  through  the  canal.  External  to  and  a  little  above  this  foramen 
is  a  smooth,  deep  depression,  the  jugular  fossa,  which  varies  in  size  in 
different  skulls,  and  when  articulated  with  the  jugular  notch  in  tlie 
occipital  bone  the  two  form  the  jugular  foramen.  Just  back  of  the 
jugular  fossa,  at  the  commencement  of  the  border  of  the  mastoid  por- 
tion of  the  bone,  is  an  irregular,  rough  surface,  the  jugular  facet,  which 
articulates  by  synchondrosis  with  the  transverse  process  of  the  occipital 
bone. 

Several  small  foramina  are  situated  in  this  portion  of  the  bone.  In 
the  ascending  portion  of  the  carotid  canal  is  a  small  foramen  f  )r  the 
tympanic  branch  of  the  internal  carotid  artery,  and  between  the  jugular 
fossa  and  the  opening  for  the  carotid  canal  will  be  found  a  foramen  for 


60  AXATOMY. 

the  tympanic  branch  of  the  glosso-pharvngeal  (Jacobson's)  nerve.  Ou 
the  border  between  the  posterior  and  the  inferior  surfaces,  internal  to 
the  jugular  fossa,  is  the  aqueductus  cochlea,  which  transmits  a  vein  from 
the  cochlea  to  join  the  internal  jugular  vein.  In  the  internal  portion 
of  the  jugular  fossa  is  a  foramen  for  the  auricular  branch  of  the  pneumo- 
gastric  nerve  (Arnold's  nerve). 

The  Tt/mpanic  Portion  forms  part  of  the  roof  of  the  external  audi- 
tory meatus,  and  is  that  ]>art  of  the  glenoid  fossa  which  lies  beloAV 
and  posterior  to  the  glenoid  fissure.  It  is  irregular  in  outline,  and  is 
wholly  made  up  of  compact  tissue.  When  examined  externally,  it  pre- 
sents a  U-shaped  portion  which  bounds  three-fourths  of  the  external 
auditory  meatus ;  which  opening  leads  direct  to  the  tympanic  mem- 
brane. The  remaining  or  up])er  boundary  of  the  meatus  is  formed  by 
the  squamous  portion  of  the  l)one.  The  curve  of  the  U  is  roughened 
for  the  attachment  of  the  cartilage  of  the  ear.  The  tympanic  division 
extends  inward  and  downward,  encasing  the  base  of  the  styloid  process. 
This  division  terminates  anteriorly  in  the  vaginal  process  and  poste- 
riorly in  the  glenoid  fossa.  It  is  concave  in  form,  and  receives  the 
upper  portion  of  the  jiarotid  gland.  It  terminates  in  the  point  opposite 
the  spinous  process  of  the  sphenoid  bone,  at  the  commencement  of  the 
opening  for  the  cartilaginous  portion  of  the  Eustachian  tube. 

The  Styloid  Portion  is  of  hard  consistency,  long  and  tapering,  point- 
ing downiward,  inward,  and  forward  in  the  direction  of  the  great  cor- 
nu  of  the  hyoid  bone ;  its  average  length  is  about  one  inch,  though 
sometimes  it  is  greater,  com])I;cating  surgical  operations  in  the  region 
through  which  it  passes.  It  is  situattd  directly  in  front  of  the  digastric 
fossa  and  behind  the  vaginal  ])roccss,  which  in  great  part  surrounds  it. 
It  gives  origin  to  the  stylo-jiharyngeus,  the  stylo-glossus,  and  the  stylo- 
hyoideus  muscles ;  also  to  it  the  etylo-hyoid  and  the  stylo-maxillary 
ligaments  are  attached.  The  mastoid  portion  is  the  enlarged  roughened 
portion  situated  at  the  posterior  inferior  extremity  of  the  bone.  It 
assists  in  forming  the  masto-occi])ital  and  the  masto-parietal  sutures, 
the  mastoid  ridge  separating  it  from  the  squamous  })t>rtion  of  the  bone. 
It  is  divided  into  two  ])ortions,  tlie  mastoid  and  the  posterior  mastoid, 
by  tlie  extension  over  it  of  the  superior  semicircular  line  from  the  occip- 
ital bone,  which  line  continues  its  curve,  terminating  at  the  extremity 
of  the  mastoid  process.  The  last  is  large,  extending  downward  and 
forward  behind  the  external  auditory  meatus  and  the  tympanic  jxirtion 
of  the  glenoid  fossa.  It  is  small  (hiring  infancy,  l)ut  increases  and 
becomes  of  large  size  in  the  adult,  especially  in  individuals  with  large 
and  powerful  muscles.  It  serves  for  the  attachment  of  the  sterno-cleido- 
mastoideus,  tlie  splenius  cajiitis,  and  the  trachelo-mastoid  nnisdes,  the 
two  former  extending  tlieir  attachment  along  tlie  su]>erior  semicircular 
line  f»f  the  occipital  bone.  The  internal  ])ortion  of  the  mastoid  process 
is  full  of  cells,  which  comnuuiicate  with  the  middle  car.  On  the  inner 
portion  and  at  the  base  of  the  process  is  a  deep  groove,  the  digastric 
fossa,  for  the  attachment  of  the  digastric  nuiscle ;  and  on  the  inner  side 
of  the  groove  and  parallel  with  it  is  the  occipital  groove  for  the  occipital 
artery. 

Between  the  mastoid  and  the  styloid  processes,  and  immediately  in 


BONES. 


61 


Fig.  20. 


1  for  S^uamoUyS 

fOTlwn  inclttcliimi 

Zijqoma, 


front  of  the  diga-stric  fossa,  is  the  stvlo-mastoid  foramen,  which  is  the 
termination  of  the  aqueductus  Fallopii,  and  transmits  the  facial  nerve 
and  the  stylo-mastoid  artery.  Beneath  tlie  semicircular  curved  line  are 
one  or  more  foramina  of  variable  size  which  admit  veins  to  the  lateral 
sinus.  When  these  foramina  are  large,  wounds  in  this  region  are  dan- 
gerous, as  the  blood  would  flow  freely  from  the  sinus.  Sometimes  these 
veins  enter  the  sinus  through  the  suture. 

The  internal  surface  is  marked  by  a  deep  groove,  the  sigmoid  groove, 
for  the  accommodation  of  the  lateral  sinus.  Frequently  these  sinuses 
vary  greatly  in  depth  in  the  same  skull. 

Development. — The  temporal  bone  is  developed  from  four  centres 
of  ossification.  Tlie  squamous,  the  zygomatic,  and  the  tympanic  por- 
tions are  developed  from 
membrane,  tlie  petrous  por- 
tion and  the  styloid  pro- 
cess from  cartilage.  The 
squamo-zygomatic  portion 
commences  to  ossify  in  the 
lower  part  of  the  squamous 
portion  at  the  latter  part  of 
tlie  second  or  the  beginning 
of  the  third  month  of  em- 
bryonic life.  Ossification 
extends  upward  into  the 
squamous  and  outward  into 
the  zygomatic  portions. 
Shortly  afterward  an  os- 
sific  centre  appears  in  the 
lower  part  of  the  membran- 
ous tympanum,  ossification 
spreading  upward  and  in- 
ward until  it  joins  the  petro- 
mastoid  portion  behind  and 
the  squamo-zygomatic  in 
front,  forming  the  incom- 
plete tympanic  ring.  Ossification  of  the  petro-mastoid  portion  com- 
mences much  later,  usually  about  the  end  of  the  fifth  or  the  beginning 
of  the  sixth  month  of  foetal  life.  The  osseous  deposits  are  made  at 
many  points  in  the  cartilage,  being  all  united,  however,  at  birth.  The 
styloid  portion  is  the  last  to  ossify,  remaining  cartilaginous  until  after  birth. 

The  temporal  bone  is  composed  of  four  separate  pieces  at  birth.  The 
mastoid  process  has  not  appeared,  and  does  not  commence  to  develop 
until  the  second  year ;  from  this  period  it  increases  in  size  until  adult 
life,  the  air-cells  appearing  about  the  age  of  puberty.  The  external 
auditory  meatus  at  first  is  shallow,  but  increases  in  depth  by  the  out- 
growth of  the  united  squamous  and  petro-mastoid  portions  above  and 
behind,  and  the  tympanic  portion  in  front  and  below. 

The  glenoid  fossa  is  superficial,  the  articulating  eminence  being  slight. 
By  the  growth  of  the  tympanic  portion  downward  the  depth  of  the 
fossa  is  increased. 


2'^?  mo. 


I  for  Auditor)! 
jtrnetss 


foT  Petrous 
h  Mcustuid 
portions 


If  on'  StyloiH  proo. 

Development  of  the  Temporal  Bone  by  Four  Centres. 


62  ANATOMY. 

The  Sphenoid  Bone. 

The  sphenoid  bone  is  situated  across  the  base  of  the  skull,  extending 
upward  and  anteriorly  until  it  joins  the  frontal  and  parietal  bones.  It 
is  placed  mostly  in  front  of,  but  partially  internal  to,  the  temporal  bones. 
The  posterior  face  of  the  body  of  the  sphenoid  bone  articulates  Avith  the 
basilar  process  of  the  occipital  bone ;  anteriorly  the  articulation  is  with 
the  malar  and  palate  bones,  the  ethmoid,  and  the  vomer,  and  occasion- 
ally, through  the  inferior  angle  of  its  anterior  border,  with  the  superior 
maxilla.  Acting  as  a  key  or  wedge,  the  central  location  of  this  bone 
causes  it  to  enter  into  the  formation  of  the  anterior  and  middle  Ibssa  of 
the  brain-case  by  the  inner,  and  of  the  temporal,  zygomatic,  and  spheno- 
maxillary fossa  by  the  external,  surface ;  also  the  orbital  and  nasal  cav- 
ities internally.  It  forms  part  of  the  roof  of  the  pharynx,  and  the 
hamular  process  of  its  internal  pterygoid  plate  can  be  reached  through 
the  mouth  just  posterior  to  the  tuberosity  of  the  superior  maxillary 
bone.  It  gives  support  to  the  superior  dental  arch  and  origin  to  three 
of  the  four  muscles  of  mastication.  The  great  sensory  nerve  of  the 
teeth  and  lace  and  the  branch  of  this  nerve  governing  the  muscles  of 
mastication  pass  from  the  brain-case  through  three  of  the  foramina  of 
this  bone.  It  also  gives  passage  to  the  optic,  motor  oculi,  pathetic,  and 
abducens  nerves,  the  ophthalmic  artery  and  veins,  and  to  two  of  the 
meningeal  arteries. 

For  convenience  of  study  the  sphenoid  bone  is  divided  into  a  body 
and  six  processes,  three  on  each  side,  a  greater  and  lesser  wing,  and  a 
pterygoid  process  composed  of  two  plates.  The  body  of  the  bone  is 
cuboidal  in  shape,  having  six  surfaces — a  superior,  inferior,  anterior, 
posterior,  and  two  lateral. 

The  /Superior  Surface  (Fig.  21),  the  most  irregular  of  the  six,  is 
situated  within  the  brain-case.  Its  anterior  border,  known  as  the  eth- 
moidal spine,  is  thin,  projects  forward  and  slightly  upward,  and  by  its 
centre  articulates  with  the  crista  galli  of  the  ethmoid  bone.  Just  poste- 
rior to  this  spine  is  a  smooth,  slightly  concave  surface  extending  back- 
ward to  the  optic  groove  and  laterally  into  the  lesser  wings.  This 
surface  forms  i)art  of  the  floor  of  the  anterior  fossa  of  the  brain-case. 
The  optic  groove,  slightly  curved,  passes  nearly  transversely  across  the 
body  of  the  bone,  and  terminates  on  either  side  in  the  optic  foramina. 
These  foramina  transmit  the  o])tic  nerves  and  the  ophthalmic  arteries, 
wliile  the  groo\e  lodges  tlie  optic  commissure.  Just  behind  the  optic 
groove,  and  between  it  and  the  pituitary  fossa  (sella  turcica),  is  a  small 
surface  of  bone,  the  olivary  process,  \Ahich  assists  in  supporting  the 
optic  commissure.  Posterior  to  this  process  is  a  deep  concavity,  the 
pituitary  fossa  (sella  turcica)  for  the  reception  of  the  pituitary  body. 
All  that  portion  of  the  bone  situated  behind  this  fossa,  and  between  it 
and  the  spheno-oceipital  articulation,  is  termed  the  dorsum  sellse.  At 
the  superior  lateral  angles  of  this  ])ortion  of  the  bone  are  the  })osterior 
clinoid  jn'ocesses.  The  posterior  border  of  the  lesser  wings  terminates 
in  rounded  points,  the  anterior  clinoid  processes.  At  the  superior 
lateral  angle  of  the  anterior  border  of  the  pituitary  fossa,  on  the  poste- 
rior margin  of  the  olivary  process,  is  sometimes  seen  a  small  tubercle 


BONES. 


63 


of  bone,  the  middle  clinoid  process.  Occasionally  this  process  is  con- 
nected by  a  spiculura  of  bone  with  the  anterior  clinoid  process,  forming  a 
foramen  ;  more  rarely  to  both  the  anterior  and  posterior  processes,  form- 
ing two  foramina  and  a  continuous  and  uninterrupted  border  from  the 
superior  anterior  angle  of  the  lesser  wing  to  the  superior  angle  of  the 
dorsum  sellte. 

The  lateral  surfaces  of  the  body  of  the  sphenoid  bone  are  almost 
entirely  within  the  brain-case.  A  small  portion,  however,  of  this 
surface  runs  forward  and  forms  the  proximal  border  of  the  foramen 
rotundum,  the  base  and  proximal  boundary  of  the  sphenoidal  fissure, 
and  continues  forward  until  it  meets  the  sphenoidal  turbinated  bones. 

Fig.  21. 

Jf^dJl.   Cli^md  procc^^       J,7.„,^rf^Z  Smvc 
_Fustcrior  CUncid jproccss  \     f^^^^^^p,.  i 

Wiut/rnf  tu:  PTC  I 


Sphenoid  Bone,  superior  surface. 

On  that  portion  of  the  lateral  surface  within  the  brain-case  is  a  marked 
depression,  the  sigmoid  groove,  for  the  accommodation  of  the  internal 
carotid  artery  and  the  cavernous  sinus. 

The  posterior  surface  is  quadrilateral  in  shape.  Until  about  the 
fifteenth  year  this  surface  is  separated  from  the  occipital  bone,  \\\i\\ 
which  it  articulates,  by  a  layer  of  cartilage.  At  this  time  ossification 
commences  between  the  two  bones,  and  is  completed  about  the  twentieth 
year. 

In  the  middle  of  the  anterior  (nasal)  surface  is  a  thin  vertical  lamina 
of  bone  which  forms  part  of  the  septum  of  the  nose  and  articulates  with 
the  perpendicular  plate  of  the  ethmoid  bone.  On  each  side  of  this  lam- 
ina are  irregular  openings,  varying  in  size  in  different  bones,  and  often 
in  the  same  bone ;  they  lead  into  the  sphenoidal  sinuses  situated  in  the 
body  of  the  bone.  The  body  of  the  bone  is  completely  hollowed  by 
these  sinuses,  which  accounts  for  the  complete  thinness  of  its  walls. 
The  septum  of  bone  between  these  cavities  is  generally  deflected  to 


64 


ANAT03IY. 


the  one  side  or  the  other,  making  tlie  sinuses  of  unequal  size.  Other 
incomplete  septa  may  be  seen  at  the  posterior  portion  of  these  cavities, 
which  divide  them  into  several  compartments.  Sometimes  they  extend 
back  and  penetrate  the  basilar  process  of  the  occipital  bone.  They  are 
lined  by  mucous  membrane,  which  is  continuous  with  that  of  the  nasal 
cavity.  The  larger  part  of  the  anterior  surface  of  the  body  is  formed 
by  the  sphenoidal  turbinated  or  spongy  bones;  they  are  triangular  in 
shape,  their  apices  pointing  downward  and  backward,  their  upper  mar- 
gins being  some^yhat  deflected,  which  opens  a  passage  or  communication 
between  the  sinuses  and  the  nose.  They  are  formed  from  separate 
points  of  ossification,  but  soon  unite  with  the  sphenoid  behind  and  the 
ethmoid  in  front. 

The  Inferior  Surface  (Fig.  22)  is  apparently  a  continuation  of  the 
anterior.     It  presents  in  the  middle  line  a  triangular  spine,  the  ros- 


LAXATOD    TYMPANI 


JUdtnulua'   /iTOCest  - 

Sphenoid  Bone,  anterior  surface.  (In  this  figure  both  the  anterior  and  inferior  surfaces  of  the 
body  of  tlie  sphenoid  bone  are  shown,  the  bone  being  held  with  the  pterygoid  jirocesses  almost 
horizontal.) 

trum,  which  is  a  continuation  of  the  vertical  lamina  of  the  bone  of  the 
anterior  surface,  and  articulates  with  the  fissure  formed  by  the  alse  of 
the  vomer.  These  alse,  together  Avith  the  vaginal  process  of  the  sjihe- 
noid,  \vhich  are  prolongations  of  the  internal  pterygoid  plates,  cover 
the  greater  part  of  the  inferior  surface  of  the  body  of  the  bone,  and 
lock  the  parts  together. 

The  Greater  Wings  are  two  irregular  strong  processes  of  bone 
arising  from  the  lateral  surflices  of  the  body.  Thev  extend  outMard, 
forward,  upward,  and  backward,  and  jM'esent  for  examination  three  sur- 
faces, the  internal,  external,  and  orbital;  and  five  borders,  the  superior, 
inferior,  anterior,  lateral,  and  posterior. 

The  Internal  or  Cerebral  Surface  is  situated  entirely  within  the 
brain-case,  and  forms  part  of  the  middle  fossa  of  the  cranium.  This 
surface  is  deeply  concave,  and  marked  by  eminences  and  depressions 


BONES.  65 

for  the  convolutions  of  the  brain.  At  the  point  where  the  win^ 
joins  the  body  of  the  bone  anteriorly  is  a  round  opening,  the  foramen 
rotundum,  which  transmits  the  second  division  of  the  fifth  nerve. 
About  half  an  inch  posterior  to  this  may  be  seen  an  oval  aperture 
larger  than  the  preceding.  This  is  called  the  foramen  ovale,  and 
transmits  the  third  division  of  the  lifitli  and  the  small  petrosal  nerves 
from  within  outwardly,  and  the  lesser  meningeal  artery  from  without 
inwardly.  Behind  and  a  little  external  to  the  former,  in  the  spinous 
process  of  the  bone,  is  a  small  aperture,  the  foramen  spinosum,  for  the 
transmission  of  the  middle  meningeal  artery. 

The  External  iyTemporo-zygomatic)  /Surface  is  convex  from  above 
downward,  and  is  divided  into  two  portions,  a  superior  and  an 
inferior,  by  a  ridge  of  bone,  the  infratemporal  crest.  The  superior 
portion  is  the  larger  of  the  two,  averaging  about  half  an  inch  in 
width  and  an  inch  and  a  half  in  height.  This  is  concave,  forms  part 
of  the  temporal  fossa,  and  gives  attachment  to  part  of  the  temporal 
muscle.  The  inferior  portion  is  also  concave,  enters  into  the  formation 
of  the  zygomatic  fossa,  and  gives  attachment  to  the  outer  part  of  the 
external  pterygoid  muscle.  The  posterior  border  of  this  portion  of  the 
bone  extends  downward  and  outward,  and  terminates  externally  in  a 
point  of  bone  called  the  spinous  process,  wJiich  gives  attachment  to 
the  internal  lateral  ligament  of  the  lower  jaw  and  the  laxator  tympani 
muscle. 

The  Orbital  Surface,  or  that  portion  of  the  greater  wing  which 
assists  in  forming  the  outer  wall  of  the  orbit,  is  smooth,  and  may  be 
divided  for  purposes  of  description  into  two  portions,  an  outer  and  an 
imier,  by  an  imaginary  line  drawn  from  the  notch  found  in  its  superior 
border,  for  the  accommodation  of  a  branch  of  the  lachrymal  artery  to 
a  point  just  external  to  the  foramen  rotundum.  The  outer  portion  is 
quadrilateral  in  form,  while  the  inner,  or  that  immediately  above  the 
pterygoid  process,  is  triangular. 

The  Quadrilateral  or  Outer  Portion  is  composed  principally  of 
spongy  tissue,  though  that  which  joins  the  malar  bone  is  compact 
and  helps  to  form  the  orbito-temporal  partition.  This  surface  articu- 
lates above  with  the  frontal  bone,  externally  with  the  malar  bone,  and 
inforiorly  it  forms  the  posterior  boundary  of  the  spheno-maxillary  fis- 
sure. The  inner  portion  is  thin,  being  made  up  of  compact  tissue.  The 
superior  border  forms  the  posterior  boundary  of  the  sphenoidal  fissure. 
Just  below  this  border,  on  the  inner  surface,  near  the  imaginary  line 
dividing  the  orbital  surface,  there  is  generally  found  a  small  spine  of 
bone,  for  the  origin  of  part  of  the  lower  head  of  the  external  rectus 
muscle. 

Borders. — The  Superior  Border  is  divided  into  two  jiortions,  an 
outer  and  an  inner ;  the  outer  is  broad,  triangular,  and  roughened,  the 
greater  part  being  for  articulation  with  the  frontal,  the  remainder  with 
the  parietal  bone.  The  inner  portion  is  thin,  and  forms  the  outer 
boundary  and  anterior  superior  angle  of  the  sphenoidal  fissure  or 
anterior  lacerated  foramen. 

The  Inferior  Border  is  smooth,  rounded,  and  forms  the  posterior 
l)oundary  of  the  spheno-maxillary  fissure. 

Vol.  I.— 5 


66 


ANAT03IY. 


The  Anterior  or  Malar  Border  is  serrated  for  articulation  with  the 
malar  bone. 

The  Lateral  Border  is  serrated,  and  bevelled  above  and  below  by  the 
projections  of  the  outer  plate  and  by  the  extension  of  the  inner  plate. 
This  border  articulates  with  the  squamous  portion  of  the  temporal 
bone. 

The  Posterior  Border  (Fig.  23),  somewhat  concave  in  form,  commences 
at  the  body  of  the  bone  and  terminates  in  the  spinous  process,  the  outer 

Fig.  23. 


Sphenoid  Bone,  posterior  isurface. 

portion  beino;  rough  for  articulation  with  the  apex  of  the  petrous  portion 
of  the  temporal  bone.  The  internal  portion  of  this  border  is  smooth, 
and  forms  the  anterior  boundary  of"  the  middle  lacerated  foramen,  and 
is  perforated  by  the  posterior  opening  of  the  Vidian  canal. 

The  Lesser  Winr/s  are  two  thin  triangidar  plates  of  compact  bone  ris- 
ing by  two  pedicles  from  the  anterior  superior  portion  of  the  body.  They 
extend  outwardly  in  the  direction  of  the  superior  border  of  the  greater 
wings,  and  terminate  in  short  points.  The  superior  surface  of  the 
lesser  wing  is  smooth,  being  a  continuation  of  the  body  of  the  bone,  and 
helps  to  form  the  base  of  the  anterior  fossa  of  the  brain-case.  The  infe- 
rior surface  is  part  of  the  roof  of  the  orbit,  and  forms  the  superior  and 
part  of  the  internal  boundary  of  the  s])henoidal  fissure  (lacerated 
foramen). 

The  ,Sj)liciioid((l  Fissure  is  an  opening  approaching  an  isosceles  triangle 
in  shape,  the  l)ase  of  the  triangle  being  the  body  of  the  bone,  the  apex 
extending  outward  to  the  notch  in  the  superior  border  of  the  greater 
wing.  When  the  sphenoid  bone  is  articulated  with  the  frontal,  this 
fissure  becomes  the  ant(>rior  lacerated  foramen,  which  transmits  from 
within  outwardly  the  third,  fourth,  ophthalmic  division  of  the  fifth, 
which  breaks  into  three  brauciies  in  this  foramen,  and  the  sixth  nerve, 
and  from  witliout  iuwardly  the  o])htlialmic  vein  and  a  branch  of  the 
lachrymal  artery.  The  anterior  border  of  the  lesser  wing  is  serrated  for 
articulation  with  the  orbital  plate  of  the  frontal  bone. 

The  Posterior  Border  of  the  lesser  wing  is  short,  and  by  its  junction 


BONES.  67 

with  the  lateral  border  forms  the  anterior  clinoid  process.  The  inter- 
nal aspect  of  this  border  at  the  point  where  it  joins  the  body  of  the  bone 
is  pierced  by  the  optic  foramen,  which  follows  the  line  of  junction  of  the 
lesser  wing  with  the  body. 

The  Lateral  Border  is  free,  smooth,  and  rounded,  and  is  received  into 
the  fissure  of  Sylvius  of  the  brain. 

The  Superior  Pedicle  is  broad,  thin,  and  forms  the  roof  of  the  optic 
foramen. 

The  Inferior  Pedicle  forms  the  base  and  external  boundary  of  the 
ojjtie  foramen.     It  is  in  shaj^e  a  three-sided  prism. 

The  Optic  Foramen  transmits  the  optic  nerve  and  the  ophthalmic 
artery. 

The  Pterygoid  Processes  project  downward  from  the  junction  of  the 
great  wings  with  the  body  of  the  bone.  Each  process  is  composed  of 
two  plates,  which  separate  at  their  lower  third,  forming  a  triangular 
notch  for  the  reception  of  the  pyramidal  process  of  the  palate  bone,  with 
which  it  articulates  by  a  serrated  surface.  Above  the  pterygoid  notch, 
anteriorly,  is  a  smooth,  triangular  surface  of  bone  which  forms  the  pos- 
terior wall  of  the  spheno-maxillary  fossa.  At  the  upper  border  of  this 
triangular  surface  is  seen  the  foramen  rotund um,  while  at  its  superior 
inner  angle,  or  apex,  will  be  found  the  anterior  opening  of  the  Vidian 
canal.  It  is  just  at  this  point  that  the  spheno- palatine  or  Meckel's  gan- 
glion is  situated. 

The  external  plate  is  broader  than  the  internal.  It  is  a  continuation 
of  the  great  wing,  passing  downward  and  outward,  forming  a  concavity 
externally.  Its  anterior  border  articulates  with  the  palate  bone  near  to 
the  tuberosity  of  the  superior  maxilla.  Its  external  surface  gives  origin 
to  the  lower  head  of  the  external  pterygoid  muscle.  The  upper  two- 
thirds  of  these  two  plates  of  bone  are  joined  anteriorly.  Posteriorly 
they  diverge,  forming  the  pterygoid  fossa. 

The  Pterygoid  Fossa. — The  internal  pterygoid  muscle  in  this  fossa 
arises  from  the  outer  plate  only. 

The  inner  plate  is  vertical,  longer,  and  thinner  than  the  outer  plate. 
Its  anterior  border  articulates  M'ith  the  palate  bone.  The  posterior  bor- 
der is  free,  and  forms  the  distal  and  lateral  boundary  of  the  posterior 
naris. 

The  Scaphoid  Fossa. — Above  the  pterygoid  fossa,  and  between  it  and 
the  posterior  opening  of  the  Vidian  canal,  is  situated  the  scaphoid  fossa. 
It  gives  origin  to  the  tensor  palati  muscle,  the  tendon  of  which  descends 
the  outer  siu'face  of  the  internal  pterygoid  plate  to  its  inferior  extremity, 
winds  around  the  hook-like  projection,  the  hamular  process,  and  is 
inserted  into  the  soft  palate. 

The  hamular  process  can  be  felt  at  the  posterior  lateral  portion  of 
the  mouth,  behind  the  tuberosity  of  the  superior  maxilla. 

Vaginal  Process. — The  internal  pterygoid  plate  at  its  upper  internal 
surface  curves  inwardly  until  it  meets  and  partially  leaves  the  body  of 
the  bone.  The  extremity  of  this  curve  is  called  the  vaginal  process. 
The  internal  surface  of  the  external  pterygoid  plate  forms  part  of  the 
external  wall  of  the  nasal  chamber. 

Development. — The  sphenoid  bone  is  developed  from  fourteen  cen- 


68 


ANATOMY. 


tres  of  ossification.     There  is  a  natural  division  of  these  o.ssific  points 
into  a  posterior  (postsphenoid)  and  an  anterior  (presphenoid)  portion. 

TJte  Hc!/a  Turcka  and  the  great  wings  belong  to  the  former  of  these 
divisions,  while  that  portion  of  the  body  in  front  of  the  olivary  process 
and  the  lesser  wings  belong  to  the  latter.  This  division  is  found  com- 
plete and  persistent  throughout  life  in  many  of  the  lower  animals.  At 
about  the  eighth  week  of  embryonal  life  ossification  commences  in  the 
postsphenoid  division.  There  is  one  nucleus  for  each  great  wing  (ali- 
sphenoid),  including  the  external  })terygoid  plates.  About  the  same 
time  two  nuclei  appear  for  the  posterior  part  of  the  body  of  the  bone 
(basLsphenoid).     These  unite  about  the  fourth  month.     After  this  union 

Fig.  24. 


a 


A,  the  sphenoid  bone  of  ii  fu'tus,  aged  about  three  months,  is  seen  from  above.  The  great  wings  are 
ossified  ;  the  body  has  two  round  granules  of  bone  beneath  the  sella  turcica,  and  the  rest  of  it  is 
cartilaginous.  In  the  small  wings,  which  are  formed  from  a  single  centre,  the  ossification  has 
encircled  the  optic  foramen,  and  a  small  suture  is  distinguishable  at  its  posterior  and  inner  side. 
The  internal  pterygoid  processes  are  still  separate  (C<)  in  the  preparation  from  which  the  draw- 
ing was  made. — I-!.  This  figure  is  copied  from  Meckel  (Arvhiv,  lid.i.  Taf.  vi.  F.  23).  It  is  stated  to 
be  from  a  fcutus  at  the  middle  of  the  sixth  month.  The  two  granules  for  the  body  are  united,  and 
a  trace  of  their  union  is  observable  in  the  notch  in  front.  The  lateral  projections  of  the  body  (■'') 
aie  separate  pieces.— ('  is  a  sketch  of  the  back  part  of  the  preparation  shown  in  A.  The  internal 
pterygoid  process,  which  was  united  only  by  cartilage  to  the  rest  of  the  bone,  has  been  drawn 
aside. — D.  This  figure  represents  the  sphenoid  at  the  usual  period  of  birth.  The  great  wings  are 
separate.     The  anterior  sphenoid  is  joined  to  the  body. 

1.  The  great  wings;  2.  The  small  wings;  2*.  x\dditional  nuclei  for  the  small  wing;  3.  The  body :  4. 
The  internal  pterygoid  process;  n.  The  lateral  processes  of  the  body. 

two  other  centres  appear,  from  whicii  are  formed  the  tongue  of  the  bone 
(basitemporal). 

The  Interudl  Pfcri/f/olfl  Plate  arises  from  two  separate  points  of 
ossification,  which  a])pear  about  the  fourth  month.  The  internal  plates 
unite  with  the  external  pterygoid  plates  about  the  fifth  or  sixth  month, 
and  are  analogous  to  the  ])tervgoid  bones  of  some  animals,  in  which 
thev  remain  .separate  throughout  life.  In  the  anterior  (presphenoid) 
division  ossification  commences  about  the  eighth  or  ninth  week  by  two 
luiclei,  which  are  <le])osited  ju.st  outside  the  optic  foramina.  These  form 
the  le.sser  wings  (orl)ito-s])henoid).  Two  more  centres  appear  on  the 
inside  of  the  optic  fiu'amina,  and  form  the  ])resphenoidal  portion  of 
the  body  of  the  bone.  Some  authors  describe  this  portion  of  the  bone 
as  developed  from  one  centre  of  ossification,  while  others  say  that  it  is 
formed  from  the  same  centres  of  <lc])osit  which  build  the  lesser  wings. 
The  sphenoidal  turbinated  bones  arise  from  two  centres  of  ossification, 
generally  after  birth. 


BONES. 


69 


At  birth  the  sphenoid  bone  is  in  three  separate  parts,  exehKling  the 
sphenoidal  tin-binatetl  Ijones.  The  great  wings  and  external  })tervgoid 
plates  have  joined  the  internal  pterygoid  plates  on  either  side,  and  the 
posterior  portion  of"  the  body  has  joined  the  anterior  portion,  including 
the  lesser  wings.  The  great  wings  join  the  body  about  the  end  of  the 
first  year.  The  spheno-turbinated  bones  unite  with  the  body,  and  the 
posterior  surface  of  the  l)ody  with  the  basilar  process  of  the  occipital 
bone,  about  the  age  of  puberty. 


The  Paeietal  Bone. 

The  parietal  bones  form  a  large  portion  of  the  walls  and  the  greater 
part  of  the  roof  of  the  brain-case.  They  are  two  in  nunilier,  <juadri- 
lateral  in  shape,  and  have  two  surfaces,  an  external  and  an  internal ;  four 
borders  anterior,  posterior,  superior,  and  inferior ;  and  four  angles,  ante- 
rior superior,  posterior  superior,  anterior  inferior,  and  posterior  inferior. 

The  External  Surface  (Fig.  25)  is  convex  in  form,  the  greatest  con- 

FiG.  25. 


W'/?/, 


rO^ 


Left  Parietal  Bone,  external  surface. 

vexity  being  in  the  centre  of  the  bone,  forming  the  parietal  eminence 
and   indicating  the  point  where   ossification  commences.     Below  this 


70 


ANATOMY. 


eminence  is  ahvays  one,  and  generally  two,  curved  lines  :  the  lower  one 
marks  the  superior  boundary  of  the  temporal  fossa,  and  divides  the 
bone  into  two  portions ;  the  upper  one  limits  the  attachment  of  the  tem- 
poral aponeurosis.  The  superior  portion  of  the  external  surface  is  rough, 
porous,  and  covered  by  the  aponeurosis  of  the  occipito-frontalis  muscle. 
Close  to  the  upper  border,  near  the  posterior  sujDerior  angle,  in  one  bone 
or  the  other,  is  a  small  foramen,  the  parietal  foramen,  M^hich  transmits  a 
vein  to  the  superior  longitudinal  sinus.  This  foramen  is  not  constant ; 
it  varies  in  size  in  different  bones :  sometimes  it  is  situated  between  the 
two  bones.  The  inferior  portion  is  flatter  and  smoother  than  the  supe- 
rior, and  forms  part  of  the  temporal  fossa. 

The  Infernal  Surface  (Fig.  26)  is  deeply  concave,  and  forms  the  pari- 
etal fossa.     It  presents  eminences  and  depressions  corresponding  to  the 

Fig.  26. 


Post  Slip 
A  iigle 


Ant.  Sup 
r*  Angle 


Left  Parietal  Bone,  internal  surface. 

convolutions  of  the  cerebrum.  Near  the  anterior  inferior  angle,  at 
a  point  posterior  to  the  middle  of  the  inferior  border,  will  be  seen 
the  connncncement  of  grooves  which  extend  upwardly  and  divide 
into  numerous  branches.  These  grooves  are  for  the  accommodation 
of  the  anterior  and  posterior  branches  of  the  middle  meningeal  arteries. 
Sometimes  the  groove  commencing  at  the  anterior  inferior  angle  has  its 
origin  in  a  long  canal.  Along  the  inner  aspect  of  the  su])erior  border 
of  this  bone  is  a  slight  depression,  which,  together  with  itri  fellow  on 


BONES.  71 

the  opposite  side,  forms  the  groove  for  the  longitudinal  sinus.  The 
elevated  edges  of  this  groove  give  attachment  to  the  falx  cerebri.  Below 
this  groove,  especially  in  bones  of  old  subjects,  are  seen  several  depres- 
sions, which  lodge  the  Pacchionian  bodies.  Extending  across  the  poste- 
rior inferior  angle  of  the  bone  is  a  depression  which  forms  part  of  the 
groove  for  the  lateral  sinus. 

Borders. —  The  Anterior  Border  is  deeply  serrated,  and  above  is 
slightly  bevelled  by  the  prolongation  of  the  inner  table,  but  toward  the 
lower  angle  it  is  bevelled  bv  the  extensions  of  the  external  table.  This 
anterior  border  articulates  with  the  frontal  bone,  forming  the  parieto- 
frontal part  of  the  coronal  suture. 

The  Posterior  Border  is  irregular  in  outline,  deeply  serrated,  and 
articulates  with  the  occipital  bone,  forming  the  parieto-occipital  part  of 
the  lambdoid  suture.  Xumbers  of  what  are  known  as  Wormian  bones 
are  often  found  attached  to  this  border. 

The  Superior  Border  is  the  longest  and  thickest  of  the  four.  It  is 
deeply  serrated,  and  articulates  with  its  fellow  on  the  opposite  side, 
forming  the  interparietal  or  posterior  portion  of  the  sagittal  suture, 
being  all  that  remains  after  the  ossiiic  union  of  the  two  halves  of  the 
frontal  bone.     Wormian  bones  are  less  frequently  found  in  this  border. 

The  Inferior  Border  is  divided  into  three  portions.  The  anterior 
portion,  about  half  an  incli  in  extent,  is  thin  and  fluted,  bevelled  on  its 
outer  surface  for  articulation  with  the  great  wing  of  the  sphenoid  bone, 
which  overlaps  it  and  forms  the  spheno-parietal  suture.  The  posterior 
portion  is  thick,  serrated,  and  articulates  with  the  mastoid  portion  of 
the  temporal  bone,  forming  the  masto-parietal  suture. 

Angles. — The  anterior  superior  angle  is  nearly  a  right  angle.  It 
is  completely  ossified  in  adult  life,  but  in  infancy  it  is  membranous, 
and  in  conjunction  with  the  membranous  portions  of  the  bone  of  the 
opposite  side  and  the  adjoining  jjortion  of  the  frontal  bone  forms  the 
anterior  or  great  fontanelle. 

The  posterior  superior  angle  is  an  obtuse  angle.  In  the  articulated 
skull  it  is  situated  at  the  junction  of  the  interparietal  (sagittal)  and 
parieto-occipital  (lamljdoid)  sutures.  In  infancy  this  space  is  occupied 
by  the  posterior  superior  fontanelle. 

The  Anterior  Inferior  Angle  is  the  most  prominent  of  the  four. 
It  is  thin  and  elongated,  filling  up  the  space  between  the  frf)ntal 
bone  and  the  squamous  portion  of  the  temporal  bone.  It  articulates 
with  the  great  wing  of  the  sphenoid  bone.  In  infancy  this  space  is 
occupied  by  the  anterior  inferior  fontanelle. 

The  Posterior  Inferior  Angle  is  thick,  broader,  and  more  rounded 
than  the  others,  and  articulates  with  the  mastoid  portion  of  the  tem- 
poral and  the  lateral  angle  of  the  occipital  bone ;  this  is  the  location 
of  the  posterior  inferior  fontanelle  in  infancy. 

Structure. — The  parietal  bone  is  made  up  of  an  outer  plate  of 
compact  tissue  and  an  inner  vitreous  table,  enclosing  between  them  a 
mass  of  cancellated  fibrous  bone. 

Development. — The  parietal  bone  is  developed  within  a  membran- 
ous matrix  from  one  point  of  ossification,  which  appears  about  the 
sixth  week  of  embryonal  life. 


72 


ANATOMY. 


Frontal  Bone. 

The  Frontal  Bone  (Fig.  27)  is  symmetrical  in  form — /.  e.  equal 
on  both  sides  of  the  median  line  of  the  head.  It  is  situated  in  front 
of  the  two  parietal  and  a  portion  of  the  sphenoid  bones,  and  above  the 
malar,  lachrymal,  nasal,  part  of  the  sphenoid,  and  ethmoid  bones. 
Though  it  is  a  true  cranial  bone,  it  forms  that  portion  of  the  face  called 
the  forehead,  and  is  included  in  the  "  facial  region."  Its  ascending 
portion  forms  the  anterior  boundary  and  part  of  the  roof  of  the  brain- 

FiG.  27. 


Wm  Internal  Ejoier^iaf 

ml  Angular  jiroc.  Angular  hroe 


A^asal   I  S/i/n 


Frontal  Bone,  outer  surface. 


case.  Its  horizontal  portion  forms  nearly  the  entire  floor  of  the  anterior 
fossa  of  the  skull  and  the  roof^  of  the  orbits.  Laterally,  the  bone  also 
enters  into  the  formation  of  the  tcm])oral  fossa.  It  is  composed  prin- 
ci])ally  of  coin])act  tissue,  and  is  divided  into  an  ascending  and  a  hori- 
zontal portion. 

The  ascending  portion  commences  at  the  supraorbital  arch,  and 
extends  upward  and  backward  until  it  articulates  with  the  parietal 
bones.  It  has  two  surfaces,  an  external  and  an  internal,  and  is  divided 
in  the  median  line  by  a  slight  ridge.  In  young  subjects  before  this 
ridge  is  developed  a  suture  occupies  this  line. 


BONES.  73 

The  Supraorbital  Arches  are  prominent  curved  borders  of  bone, 
forming  the  superior  boundaries  of  the  orbits.  They  are  most  promi- 
nent toward  their  outer  extremities,  and  form  the  dividing-line  between 
the  horizontal  and  ascending  portions  of  the  bone. 

The  Supraorbital  Notch  or  Foramen. — At  the  inner  third  of  the 
supraorbital  arch  is  a  well-defined  notch,  the  supraorbital  notch ; 
sometimes  this  is  converted  into  a  foramen  bv  a  spiculum  of  bone 
thrown  out  from  its  lower  margin.  When  this  spiculum  is  not  present 
the  foramen  is  formed  by  fibrous  tissue.  It  transmits  the  frontal 
branches  of  the  ophthalmic  nerve,  artery,  and  vein.  There  is  generally 
a  small  opening  in  the  base  of  the  notch  for  the  passage  of  an  emissary 
vein  from  the  diploe  to  join  the  ophthalmic  vein. 

The  Frontal  Notch  is  not  constant :  when  it  is,  it  is  situated  to  the 
median  side  of  the  supraorbital  notch.  * 

The  External  Angular  Process. — The  outer  extremity  of  the  supra- 
orbital arch  termin£ites  in  the  external  angular  process.  This  is 
strong,  and  projects  to  articulate  with  the  frontal  process  of  the  malar 
bone ;  the  outer  margin  forms  a  sharp  curved  crest,  which  is  the  com- 
mencement of  the  temporal  ridge  and  aifords  attachment  to  the  tem- 
poral fascia.  Just  posterior  to  this  crest  is  a  slight  concavity  which 
forms  the  anterior  boundary  of  the  temporal  fossa. 

The  Internal  Angular  Process. — The  inner  extremity  of  the  supra- 
orbital arch  terminates  in  the  internal  angular  process,  which  is  less 
marked  than  the  external,  and  articulates  with  the  lachrymal  bone.  It 
also  gives  origin  to  part  of  the  orbicularis  palpebrarum  muscle. 

The  Nasal  Eminence  is  between  and  slightly  above  the  two  internal 
angular  processes ;  it  is  a  rounded  elevation  which  forms  a  portion  of 
the  anterior  wall  of  the  frontal  sinuses. 

The  Frontal  Sinuses  are  two  irregular  chambers  situated  above  and 
between  the  orbital  plates,  and  separated  by  a  thin  lamina  of  bone. 
They  appear  about  the  second  year,  and  are  formed  by  the  dissolution 
of  tissue  through  the  agency  of  osteoclasts.  They  continue  to  increase 
in  size  until  advanced  age,  at  which  time  they  often  extend  over  the 
orbits  and  occupy  a  larger  or  smaller  portion  of  the  bone  above  the 
superciliary  ridge  :  in  the  hollow-horned  animals  these  cavities  extend 
into  the  bony  base  or  cores  of  the  horns.  They  are  lined  by  mucous 
membrane,  and  communicate  with  the  nasal  chambers  through  the 
infundibidum  of  the  ethmoid  bone. 

The  Nasal  Notch  is  situated  below  the  na'^al  eminence :  it  is  a 
semilunar  serrated  border  of  bone  for  articulation  with  the  ascending- 
process  of  the  superior  maxillae,  the  vertical  plate  of  the  ethmoid,  and 
the  nasal  bones. 

The  Nasal  Spine  is  a  prominent  process  of  bone  in  the  centre  of  tlie 
nasal  notch  :  it  is  firmly  wedged  between  the  nasal  bones  when  they  are 
in  position. 

The  Superciliary  Ridges  are  above  the  supraorbital  arches  :  they  are 
broad  externally,  where  they  are  continuous  with  the  nasal  eminence. 
They  curve  outwardly,  becoming  less  prominent  as  they  approach  the 
lateral  surface  of  the  bone.  The  internal  portions  of  these  ridges  give 
origin  to  the  corrugator  supercilii  muscles. 


74 


ANATOMY. 


The  Frontal  Eminences  are  about  an  inch  above  the  superciliary 
ridges,  near  the  centre  of"  each  lateral  halt"  (jf  the  bone :  the}'  are  two 
rounded  prominences,  varying  in  size  in  different  individuals,  and  are 
seldom  of  equal  size  in  the  same  bone. 

The  External  or  Upper  Surface  is  smooth  and  rounded,  and  passing 
over  it  is  the  aponeurosis  of  the  occipito-frontalis  muscles. 

The  Inner  or  Eicranial  Surface  (Fig.  28)  is  marked  by  depressions 
for  the  convolutions  of  the  brain ;  by  grooves  running  inwardly  from 

Fig.  28. 


UiSh  PerpeniUulur  2'l^.te  of  EtKwoUl       U        -f^r-vumj  part  </  Rorf  ^f   IV^se 
Frontal  Bone,  inner  .surface. 

the  lateral  border  for  the  accommodation  of  the  anterior  meningeal 
arteries  and  their  branches ;  and  by  several  irregular  hollows  on  either 
side  of  the  median  line  for  the  lodgment  of  the  Pacchionian  bodies. 

The  Internal  Frontal  Crext  is  the  anterior  termination  of  a  groove 
which  occu])ics  the  median  line  of  the  internal  surface  of  the  bone. 

The  Foramen  (hcum,  anterior  to  tlic  frontal  cre.^t,  is  a  groove  which, 
when  the  frontal  bone  is  articuhited,  with  the  ethmoid,  forms  a  blind 
foramen.  This  foramen  is  continuous  in  childhood  with  the  nasal 
chambers,  and  transmits  a  small  vein  to  the  longitudinal  sinus.  In 
adult  life  this  so-culled  foramen  is  closed  at  its  base. 


BONES.  75 

The  Longitudinal  Sinus  commences  at  the  foramen  csecum,  passes 
upward  along  the  frontal  crest  to  the  groove,  and  thence  backward  over 
the  internal  surface  of  the  dome  of  the  brain-case  to  the  internal  occip- 
ital protuberance. 

7  he  Horizontal  Surface  is  divided  by  the  ethmoidal  not(;h  into  two 
portions,  the  orbital  plates.  The  orbital  plates  are  two  concavo- 
convex,  triangular  surfaces  of  bone  separated  by  the  ethmoidal  notch. 
They  are  each  composed  of  two  thin  plates  of  compact  tissue,  the  space 
between  them  being  largely  occupied  by  the  frontal  sinuses. 

The  Inferior  Surfaces  of  the  orbital  plates  are  concave  and  form  the 
roofs  of  the  orbits. 

The  Lachrymal  Fossce  are  slight  depressions  just  internal  to  the 
external  angular  process  within  the  orbits;  they  lodge  the  lachrymal 
glands. 

TJie  Trochlear  Fossce  are  small  concavities,  sometimes  tubercles,  situ- 
ated immediately  behind  the  internal  angular  processes,  within  the 
orbits ;  they  afford  attachments  to  the  pulleys  of  the  superior  oblique 
muscles. 

The  Superior  or  Encranial  Surfaces  of  the  orbital  plates  are  convex 
in  form,  deeply  marked  by  eminences  .and  depressions  for  the  convolu- 
tions of  the  brain  :  they  form  the  greater  portion  of  the  floors  of  the 
anterior  fossae  of  the  brain-case.  The  "  digital  depressions "  are  so 
called  because  of  a  fancied  resemblance  to  markings  made  by  pressing 
the  ends  of  the  fingers  upon  some  soft  substance. 

The  Ethmoidal  Notch,  between  the  two  orbital  plates,  is  a  quadri- 
lateral opening.  In  the  articulated  skull  this  notch  is  filled  by  the 
cribriform  plate  of  the  ethmoid  bone.  On  each  side  of  the  nasal  spine, 
running  its  entire  length,  is  a  grooved  surface  which  enters  into  the 
formation  of  the  roofs  of  the  nasal  chambers. 

The  Fronto-ethvioidcd  Celh. — The  borders  of  the  ethmoidal  notch 
are  marked  by  numerous  depressions,  which  form  half  cells  of  irregular 
shape.  The  ethmoid  bone  contains  depressions  of  similar  form  in  the 
superior  surface  of  its  lateral  masses,  and  when  articulated  with  the 
frontal  bone  forms  the  frontf)-ethmoidal  cells. 

The  Anterior  and  the  Posterior  Ethmoidcd  Foramina. — The  borders 
of  the  ethmoidal  notch  are  each  traversed  at  various  angles  by  two 
grooves.  In  the  articulated  skull  these  grooves,  in  connection  with 
similar  ones  in  the  ethmoid  bone,  form  the  anterior  and  posterior 
ethmoidal  foramina.  The  anterior  foramina  transmit  the  nasal  nerves 
and  the  anterior  ethmt)idal  blood-vessels,  while  the  posterior  foramina 
transmit  the  posterior  ethmoidal  blood-vessels. 

The  Borders  of  the  Frontal  Bone. — The  npper  half  of  the  ascending 
border  is  thick,  serrated,  and  slightly  bevelled  by  the  prolongation  of 
the  upper  table.  The  lower  half  oiP  this  border  is  thinner  than  the 
upper;  it  is  serrated  and  bevelled  by  extension  of  the  inner  plate.  The 
upper  seven-eighths  of  the  border  of  the  bone  on  either  side  articulate 
with  the  parietal  bones,  forining^the  fronto-parietal  (coronal)  suture. 
The  lo^ver  eighth  is  rough  and  triangular,  and  articulates  with  the  great 
wing  of  the  Sphenoid  bone,  forming  the  spheno-frontal  suture. 

The  inner  border  of  the  horizontal  portion  of  the  bone,  just  external 


76 


ANATOMY. 


to  the  posterior  margin  of  tlio  otlimoidal  notch,  is  thin  and  serrated, 
j.j^,  ,,(,  iuid    articulates    with    the    lesser 

wing  of  the  sphenoid  bone. 

Development. — The  frontal 
bone  is  an  intra-menibranous 
bone,  developing  from  two  cen- 
tres of  ossification,  which  are 
ileposited,  one  on  each  side  above 
the  orbital  arches,  about  the 
seventh  week  of  embryonal  life. 
At  birth  the  bone  is  in  tAvo  por- 
tions, w'hich  about  the  first  year 
unite  by  a  vertical  suture  (saggi- 
tal)  in  the  median  line.  The 
union  commences  from  below 
completed  about  the  third  year, 

though  occasionally  the  two  halves  remain  sej^arate  nuich  later  in  life. 


Frontal  Bone  at  Birth,  developed,  by  two  lateral  halve; 

and  extends  upward ;  it  is  generally 


Ethmoid  Bone. 

The  ethmoid  bone  (Fig.  30),  like  the  occipital,  sphenoid,  frontal, 
vomer,  inferior  maxillary,  and  all  bones  in  the  median  line  of  the 
skeleton,  is  symmetrical.     It   is  cuboid   in  form,  and  though  a  true 

Fig.  30. 


viiA   inf.'iarbinateJ  b. 

Ethmoid  Bone,  outer  surface  of  right  lateral  mass  (enlarged). 

cranial  bone  it  extends  largely  into  the  region  of  the  face.  It  is 
situated  at^  the  anterior  part  of  the  brain-case,  between  the  orbits,  and 
fi)rms  ])art  of  the  floor  of  the  anterior  cerebral  fos.'^a.  "When  articulated 
it  clo.-;cs  the  ethmoidal  notch  in  the  frontal  bone  and  fi)rms  the  greater 
part  of  the  internal  walls  of  the  orbital  cavities.  It  also  forms  the 
roof  and  part  of  the  septum  and  external  walls  of  the  nasal  chambers. 
It  is  divided  into  a  vertical  plate  and  lateral  masses,  with  a  horizontal 


BONES. 


77 


(cribritorm)  plate  unitin<r  the  masses.    The  vertical  plate  (meso-ethmoid) 
is  ao-ain  divided  into  the  perpendicular  plate  and  the  crista  galli. 

The  Perpendicufar  Plate  (Fig.  31)  is  a  thin  lamina  of  compact  bone 
situated  in  the  median  line  between  the  two  lateral  masses.     It  extends 


Fig.  31. 


.f/ffiZ  TZthmoidac^J^ 


Perpendicular  Plate  of  Ethmoid  (enlarged),  shown  by  removing  the  right  lateral  mass. 

downward  and  forward  in  the  direction  of  the  intermaxillary  suture, 
though  it  is  frequently  deflected  to  the  one  .side  or  the  other.  It  forms 
the  upper  third  of  the  septum  of  the  nose,  and  articulates  posteriorly 
with  the  cre.st  of  the  sphenoid  bone. 

Borders. — The  superior  border  of  the  perpendicular  plate  conjoins 
the  cribriform  plate. 

The  Infei-ior  Border  is  divided  nearly  in  the  centre  into  two  portions. 
The  po.sterior  inferior  portion  articulates  with  the  vomer,  while  the 
anterior  inferior  is  roughened  for  the  attachment  of  the  nasal  cartilage. 
This  cartilage  is  triangular  in  shape,  and  in  the  recent  .state  forms  part 
of  the  septum  of  the  nose. 

The  Anterior  Border  articulates  with  the  under  surface  of  the  na.sal 
bones  and  also  with  the  nasal  spine  of  the  frontal  bone. 

Grooves  for  Olfactory  Nerves. — Immediately  below  the  cribriform 
plate,  on  the  sides  of  the  perpendicular  plate,  are  fine  grooves,  running 
downward,  forward,  and  backward,  in  which  are  lodged  the  olfactory 
nerves. 

The  Crista  GaUi  (named  from  its  resemblance  to  a  cock's  comb  in 
shape)  is  an  extension  of  the  perpendicular  plate  above  the  horizontal 
portion  of  the  bone  between  the  anterior  fossae  of  the  brain-case.  It  is 
ivory-like  in  appearance. 

The  anterior  border  of  the  crista  galli  is  vertical  in  direction  and 
grooved  at  its  base.  In  the  articulated  skull  this  groove,  joining  a 
similar  one  in  the  frontal  bone  just  anterior  to  the  internal  frontal 
crest,  forms  the  so-called  foramen  cfficum. 

The  Ethmoidal  Wings. — Extending  outwardly  from  the  base  of  the 


78 


ANATOMY. 


Ethmoid  Bone,  inner  surface  of  right  lateral  mass  (enlarged). 


crista  galli  are  two  wing-like  processes  of  bone,  the  ethmoidal  wings  or 
alae. 

The  posterior  border  of  the  crista  galli  is  long,  thin,  and  slightly 
curved. 

The  longitudinal  fold  of  the  dura  mater  and  the  commencement  of  the 
falx  cerebri  are  both  attached  to  the  crista  galli. 

Lateral  Classes  (Fig.  32). — The  lateral  masses  (ethmo-turbinated)  are 

cuboidal  in  form  and  present  six  surfaces — the  superior  and  inferior, 

,.      „.,  external  and  internal,  anterior 

hio.  32.  ,        ^    .  ' 

and  posterior. 

The  Superior  Surface. — 
The  anterior  portion  is  com- 
posed of  irregular  cell-like 
openings,  which  are  covered 
in  and  completed  by  articu- 
lation with  the  frontal  bone. 
The  Ethmoidal  Foramina 
(Tnternal  Orbital  Canals). — 
Crossing  this  border,  about 
half  an  inch  apart,  are  two 
slight  grooves,  which,  when 
conjoined  to  similar  grooves 
on  the  external  border  of  the  ethmoidal  notch  of  the  frontal  bone,  form 
the  anterior  and  posterior  ethmoidal  foramina :  the  first  transmits  the 
internal  nasal  nerve,  a  branch  of  the  ophthalmic  and  anterior  ethmoidal 
vessels,  the  posterior  transmitting  the  posterior  ethmoidal  vessels  and 
spheno-ethmoidal  nerve,  a  branch  of  tlie  nasal. 

The  Inferior  Surface  extends  from  the  inferior  external  border  of  the 
lateral  mass  to  the  free  margin  of  the  middle  turbinated  bone  in  the 
articulated  skull,  and  from  the  anterior  to  the  posterior  surface  of  the 
lateral  mass.     It  is  divided  into  three  portions : 

(a)  The  external  portion  lies  b(4^veen  the  inferior  external  border  of 
the  lateral  mass  and  the  uncinate  process  anteriorly,  the  middle  and  pos- 
terior lino  being  formed  by  a  curved  plate  of  bone  in  the  median  line  of 
the  inferior  surface  of  the  external  mass.  This  portion  articulates  with 
the  superior  border  of  the  nasal  surface  of  the  superior  maxilla,  closing 
in  the  cell-like  cavities  found  on  that  border. 

(6)  Anteriorly,  the  middle  jiortion  is  formed  by  the  uncinate  process 
and  posteriorly  by  the  curved  plate  of  bone  forming  the  internal  wall  of 
the  anterior  ethmoidal  cells.  The  uncinate  process  arises  from  the  mid- 
dle of  the  anterior  surface  of  the  ethmoid  bone,  and  extends  downward, 
outward,  and  backward,  being  somewhat  hook-shaped  in  outline.  It 
articulates  with  tlie  inner  surface  of  the  nasal  process  of  the  superior 
maxilla,  the  ethmoidal  process  of  the  inner  surface  of  the  lachrymal 
bone,  and  the  infeiior  tuil>iiiated  bone;  it  also  assists  in  closing  the 
orifice   leading  to  the   ma.xillarv  sinus. 

(c)  The  internal  j)ortioii  is  free,  and  is  formed  by  the  curved  border 
of  the  middle  turbinated  bone  in  the  articulated  skull. 

The  Internal  or  Nasal  Surface  is  the  mo.'^t  complex  portion  of  the 
bone.     It  forms  part  of  the  external  wall  of  the  nasal  chamber,  or  all 


BONES.  79 

that  portion  of  the  wall  which  is  devoted  to  olfaction.  It  commences  at 
the  cribriform  plate  and  descends  downward  and  slightly  forward.  Its 
posterior  two-thirds  is  divided  by  a  sulcus,  which  is  directed  backward 
and  inward.  This  groove  forms  the  superior  meatus  of  the  nose.  It 
extends  backward  to  the  posterior  margin  of  the  bone  and  terminates  in 
a  deep  notch.  The  anterior  third  of  the  internal  surface  is  uninterrupted 
from  the  cribriform  plate  to  its  lower  border. 

The  Superior  Meatus  divides  the  internal  surface  of  the  lateral  mass 
into  two  portions — the  superior  and  middle  turbinated  bones  ;  it  extends 
antero-posteriorly  upward,  outward,  and  forward  from  the  median  line, 
and  communicates  with  the  ethmoidal  cells. 

The  Superior  Turbinated  Bone  is  all  that  portion  between  the  sulcus 
and  the  cribriform  plate. 

The  Middle  Turhinated,  Bone  is  that  portion  of  the  internal  surface 
lying  below  the  sulcus  and  between  it  and  the  lower  free  border.  The 
middle  turbinated  bone  is  free,  and  extends  downward  into  the  nasal 
chamber.  Its  lower  border  curves  outward  and  upward  toward  the 
superior  maxilla,  the  outer  surface  of  the  curve  appearing  like  a  scroll. 
This  bone  overhangs  the  middle  meatus  of  the  nose. 

The  Infundibuluni. — At  the  anterior  portion  of  the  middle  meatus 
may  be  seen  a  passage  known  as  the  infundibuluni,  leading  up  through 
the  anterior  ethmoidal  cells  into  the  frontal  sinus. 

The  External  or  Orbited  Surface  of  each  lateral  mass  is  a  thin,  smooth 
lamina  of  bone,  quadrilateral  in  form.  Its  length  from  the  front  to  the 
back  is  about  double  its  width.  This  surface  has  also  received  the  name 
"  OS  planum,"  on  account  of  its  smoothness ;  it  forms  part  of  the  inner 
wall  of  the  orbit.  The  two  grooves  which  in  the  articulated  bone  assist 
in  forming  the  anterior  and  posterior  ethmoidal  foramina  indent  the 
superior  edge  of  this  surface,  M-hich  articulates  with  the  frontal  bone. 
The  inferior  edge  articulates  with  the  superior  maxilla. 

The  Anterior  Surface  extends  inwardly  from  the  os  planum  until  it 
reaches  the  nasal  surface  of  the  bone.  It  presents  numerous  cell-like 
depressions.  The  inner  portion  of  the  anterior  surface  articulates  with 
the  nasal  process  of  the  superior  maxilla,  the  internal  portion  being 
covered  by  the  lachrymal  bone ;  this,  with  the  aid  of  the  frontal  bone, 
already  referred  to,  completes  the  anterior  ethmoidal  cells. 

The  Posterior  Surface  of  the  lateral  masses  is  thin  and  penetrated  by 
numerous  openings.  It  is  divided  into  two  portions,  a  superior  and  an 
inferior.  The  superior  portion  articulates  with  the  turbinated  plates  of 
the  sphenoid  bone,  and  the  inferior  portion  with  the  orbital  process  of 
the  palate  bone.  These  bones  conjointly  complete  the  posterior  ethmoid 
cells. 

The  Cribriform  Plate  is  symmetrical  in  outline,  being  divided  into  two 
lateral  halves  by  the  crista  galli.  It  forms  part  of  the  base  of  the  ante- 
rior fossa  of  the  brain-case,  and  fits  the  ethmoidal  notch  of  the  frontal 
bone.  It  unites  the  two  lateral  masses  and  vertical  plate  of  the  bone.  The 
olfactory  sulcus,  for  the  lodgment  of  the  olfactory  bulbs  of  the  brain, 
are  depressions  of  the  cribriform  plate  situated  on  each  side  of  the  crista 
galli.  This  plate  is  pierced  by  numerous  foramina  for  the  transmission 
of  the  filaments  of  the  olfactory  nei'ves :  those  next  the  crista  galli  pass 


80 


ANATOMY. 


into  the  delicate  perpendicular  grooves  and  canals  of  the  perpendicular 
plate  of  the  bone ;  next  and  external  are  those  for  the  tilanients  distrib- 
uted to  the  roof  of  the  nasal  chambers  ;  and  the  outer  ones  pass  into 
fine  canals  which  subdivide  as  they  penetrate  the  lateral  masses  of  the 
bone.  Some  anatomists  speak  of  these  holes  as  forming  three  rows  or 
lines,  but  the  irregular  arrangement  of  them  makes  it  an  ideal  rather 
than  a  definite  or  distinct  description. 

The  Cerebro-naml  8Ut  is  innnediately  posterior  to  the  ethmoidal 
wings  at  the  base  of  the  crista  galli.  It  is  a  narrow  or  strait  opening 
uniting  the  cranial  cavity  with  the  nasal  chamber.  External  to  this 
above  may  be  seen  a  groove  extending  posteriorly  to  the  anterior  eth- 
moidal foramen.  The  passage,  groove,  and  foramen  are  for  the  accom- 
modation of  the  nasal  nerve,  a  branch  of  the  ophthalmic,  and  also  a 
branch  of  the  ophthalmic  artery. 

Development. — The  ethmoid  bone  arises  from  three  points  of  ossi- 
fication— one  for  each  lateral  mass,  the  other  for  the  perpendicular  and 
cribriform  plates.  They  are  deposited  in  the  orbital  plates  of  the  late- 
ral masses  about  the  fourth  or  fifth  month,  and  gradually  extend  into 
the  turbinated  bones.  During  the  first  year  it  commences  to  ossify  in 
the  perpendicular  and  cribriform  lamellae,  the  three  parts  uniting  early 
in  the  second  year,  ossification  being  completed  during  the  fourth  or 
fifth  year,  at  which  time  the  ethmoidal  cells  commence  formation. 

Vomer. 

The  Vomer  (Fig.  33)  is  a  single  bone,  situated  in  the  median  line 
of  the  nasal  chamber,  forming  the  principal  portion  of  the  bony  sep- 

Fio.  33. 


"i'^h    Sup  -MaX' 


tum.  It  usually  is  more  or  less  deflected  to  one  or  the  other  side,  and 
is  placed  in  front  of  and  below  the  sphenoid  bone,  with  the  rostrum  of 
which  it  articulates,  and  below  th(!  ethmoid  bone,  articulating  with  the 
perpendicular  ])late  of  the  latter.  It  is  a  thin  plate  of  bone,  rhomboidal 
in  form,  having  four  borders,  superior,  inferior,  anterior,  and  posterior; 
and  two  surfaces,  a  right  and  a  left. 


BONES.  81 

The  Superior  Border  is  the  thickest  of  the  four,  iind  is  shaped  like 
the  letter  V.  The  upper  portion  of  this  V  is  described  as  two  alse  or 
wings,  which  extend  on  both  sides  of  the  rostrum  of  the  sphenoid  bone. 
The  latei'al  edge  of  each  wing  articulates  Avith  the  superior  margin  of 
the  internal  plate  of  the  pterygoid  process  (vaginal  process)  of  the  sphe- 
noid bone  and  the  sphenoidal  process  of  the  palate  bone. 

The  Inferior  Border  is  long,  thick,  and  uneven,  for  articulation  with 
the  nasal  crest  of  the  superior  maxillary  and  palate  bones.  It  is  thin- 
ner posteriorly  where  it  articulates  with  the  latter  bones. 

The  Anterior  Border  slopes  downward  and  forward  at  an  angle  of 
about  forty-five  degrees.  The  upper  half  of  this  border  generally  con- 
sists of  two  thin  laminse  of  bone,  between  which  articulates  the  perpen- 
dicular plate  of  the  ethmoid.  The  inferior  half  is  rough  and  uneven, 
to  give  attachment  in  the  recent  state  to  the  nasal  cartilage. 

The  Posterior  Border  is  free,  and  forms  the  septum  of  the  posterior 
nares.  It  is  the  shortest  of  the  four  borders — thin,  smooth,  and  slightly 
concave. 

Tlie  Surfaces. — The  right  and  left  surfaces  are  smooth,  but  marked 
by  narrow  grooves  for  the  accommodation  of  blood-vessels.  A  larger 
groove,  sometimes  formed  into  a  canal  (naso-palatine),  traverses  each 
surface  of  this  bone,  running  downward  and  forward,  terminating  in 
the  anterior  palatine  canal  in  the  intermaxillary  suture.  These  grooves 
transmit  the  naso-palatine  vessels  and  nerves. 

Development. — The  vomer  is  an  intracartilaginous  bone  formed 
from  one  centre  of  ossification,  which  makes  its  appearance  in  the  poste- 
rior part  of  the  bone  at  about  the  eiglith  week  of  embryonic  life.  From 
this  centre  two  laminae  arise,  and  pass  upward  and  forward  on  each  side 
of  the  median  line  until  they  meet  the  nasal  cartilage.  These  two  plates 
of  bone  gradually  unite  from  behind  forward  until  about  the  age  of 
puberty,  at  which  period  they  form  a  single  plate  of  bone,  marked  on 
its  anterior  and  superior  borders  by  a  slight  groove,  indicating  the 
position  where  the  two  parts  unite. 

Superior  Maxillary  Bones. 

The  superior  maxillary  bones  are  of  the  utmost  importance  to  the 
dentist  and  to  the  surgeon.  They  give  support  to  the  upper  teeth  and 
are  subject  to  defects  of  development  and  to  various  pathological  changes. 
Chief  among  these  may  be  mentioned  cleft  palate,  congenital  or  acquired, 
necrosis,  caries,  and  odontocele.  Either  of  these  bones  may  be  affected 
by  alveolar  abscess,  diseases  of  the  antrum,  which  may  give  rise  to  such 
symptoms  as  impaired  respiration  and  discharge  of  offensive  matter 
through  the  nasal  chamber.  Tumors  or  abscesses  of  the  antrum  often 
grow  to  such  a  size  as  to  elevate  the  floor  of  the  orbit,  depress  the  roof 
of  the  mouth,  and  bulge  out  the  wall  of  the  cavity,  distorting  the  face 
in  the  region  of  the  canine  fossa.  Neuralgic  trouble  in  the  teeth  may 
be  only  symptomatic  of  disease  of  this  bone,  as  neuralgia  in  the  head 
often  may  be  traceable  to  the  teeth.  It  is  therefore  highly  necessary 
that  the  bone  should  be  carefully  studied. 

Together,  the  superior  maxillae  are,  of  the  bones  of  the  face,  second  in 

Vol.  1.-6 


82 


ANAT031Y. 


importance  and  size  only  to  the  lower  maxilla.  When  articulated  they 
form  the  bony  base  of  the  entire  central  portion  of  the  face.  Each  one 
assists  in  forming  three  cavities — first,  part  of  the  floor  and  the  infra 
and  internal  borders  of  the  orbit ;  second,  part  of  the  sides  and  floor  of 
the  nasal  chamber  ;  third,  it  contributes  largely  to  form  the  roof  or  hard 
palate  of  the  mouth.  It  also  assists  in  the  formation  of  the  zygomatic 
and  spheno-maxillary  fossae  and  the  spheno-maxillary  and  pterygo- 
maxillary  fissures. 

Its  body  forms  the  walls  of  the  maxillary  sinus  (antrum  Highmori- 
anum).  It  presents  for  examination  a  body,  four  surfaces,  the  orbital,  the 
proximal  or  nasal,  the  lateral  or  facial,  and  posterior  or  zygomatic ;  and 
four  processes,  the  nasal,  the  malar,  the  palatal,  and  the  alveolar. 

The  Body  (Fig.  34)  may  be  compared  to  a  ve;y  irregular  triangular 

Fig.  34. 
Outer        Surface. 


TCNDO    OeUL 


Incisive  fossa 


Posterior Dentat  Cunaia 


xil'uru  Tuleros'itu, 


■Bicusjiids.  -Z^"' 

Left  Superior  Maxillary  I?one,  outer  surface. 

pyramid,  the  base  being  the  proximal  surface  and  the  apex  under  the 
malar  process. 

The  Orbital  Surface  is  a  triangular  plate,  smooth  and  slightly  concave, 
constituting  the  greater  part  of  the  floor  of  the  orbit. 

The  LifWiorbital  Canal  runs  forward  from  the  posterior  border  as  a 
groove,  which  at  the  centre  dips  or  is  covered  by  the  orbital  floor,  and 
makes  its  exit  just  above  the  centre  of  the  facial  surface,  at  the  infra- 
orbital foramen.  It  transmits  the  infraorbital  vessels  and  nerve.  A 
branch  of  the  infraorbital  canal  passes  down  the  anterior  wall  of  the 
maxillary  sinus  and  transmits  the  anterior  dental  nerve  and  vessels. 


BONES. 


83 


Just  external  to  the  junction  of  this  plate  with  the  nasal  process  is  a 
small  depression  which  gives  origin  to  the  inferior  oblique  muscle  of 
the  eye. 

The  Mesial  Border  of  the  orbital  surface  at  its  anterior  portion  is 
smooth,  and  in  it  is  the  commencement  of  the  lachrymal  groove,  which 
in  the  articulated  skull  becomes  a  canal  and  runs  downward  and  slightly 
backward  to  communicate  witli  the.  inferior  meatus  of  the  nose.  The 
remainder  of  this  border  is  roughened  for  articulation  with  the  lachry- 
mal bone  anteriorly  and  the  os  planum  of  the  ethmoid  bone  posteriorly. 

The  Anterior  Border  of  the  orbital  plate  and  the  orbital  process  of 
the  malar  bone  from  the  infraorbital  ridge  is  sharp  at  its  inner  third, 
but  the  remainder  is  rounded. 

The  Posterior  Border  of  the  above  plate  is  frequently  referred  to  as 
the  outer  border :  it  extends  from  the  centre  of  the  malar  process  back- 
ward and  inward  to  the  orbital  process  of  the  palate  bone.  The  inar- 
ticulated  portion  of  this  border,  together  with  part  of  the  orbital  process 
of  the  palate  bone,  forms  the  anterior  boundary  of  the  spheno-max- 
illary  fissure. 

The  Proximal  or  Nasal  Surface  (Fig.  35)  presents  a  large  irregular 
opening  into  the  maxillary  sinus.     This  orifice  is  jDartially  closed  by 

Fig.  35. 


:,ti^'^ 


Bon..  p<t,toc;lly  clo^l.,,^  Or/fice  ofAn^trum 
niurkfd    in    ourJtut 


JEtli.rri/jid 
Inferior  Turlinaied 
jPnlocte 


Ant.  J\rasa,2S: 


yni 


£ristie 
/Jaiscd  rhroucfJi, 
Ant.palat.  Ca?ia7. 

Left  Superior  Maxillary  Boue,  inner  surface. 

articulation  with  the  lachrymal,  the  uncinate  process  of  the  ethmoid, 
the  vertical  plate  of  the  palate,  and  the  ethmoidal  process  of  the  inferior 
turbinated  bones  of  the  same  side.  In  the  articulated  skull  one  or  two 
small  openings  communicate  from  the  antrum  with  the  middle  meatus 


84  ANATOMY. 

of  the  nose.  Usually  there  is  left  but  one  small  0}3ening.  Along  the 
superior  border  of  this  surface  are  a  number  of  cellular  openings,  which 
are  closed  in  by  articulation  with  the  lachrymal  and  ethmoid  bones. 
The  anterior  two-thirds  of  the  thin  plate  of  bone  below  the  aperture  is 
smooth  and  concave,  forming  most  of  the  external  wall  of  the  inferior 
meatus  of  the  nose.  The  posterior  third  is  slightly  roughened  for  artic- 
ulation with  the  vertical  plate  of  the  palate  bone. 

The  Lachnpnal  Groove  is  at  the  anterior  superior  angle  of  the  nasal 
surface,  behind  the  nasal  process :  it  is  converted  into  a  canal  by  articu- 
lation with  the  lachrymal  bone,  the  uncinate  process  of  the  ethmoid, 
and  the  lachrymal  process  of  the  inferior  turbinated  bone.  The  canal 
extends  downward  and  backward,  terminating  in  the  inferior  meatus 
of  the  nose.  In  the  recent  state  it  is  lined  by  a  mucous  membrane, 
the  lachrymal  duet. 

The  Lachri/mal  Tubercle  is  a  small  prominence  of  bone  at  the  junc- 
tion of  the  infraorbital  ridge  with  the  external  border  of  the  nasal 
process.  This  tubercle  serves  as  a  guide  to  the  lachrymal  sac,  which  is 
the  expanded  portion  of  the  lachrymal  duct,  situated  posterior  to  the 
tubercle. 

The  Posterior  Palatine  {Palato-maxiUary)  Canal,  for  the  passage  of 
the  posterior  palatine  vessels  and  anterior  palatine  nerves,  commences 
about  the  middle  of  the  posterior  border  of  the  bone  and  runs  downward 
and  forward  as  a  groove,  which  in  the  articulated  bone  is  closed  by  the 
vertical  plate  of  the  palate  bone  to  form  a  canal. 

The  Anterior  Border  of  the  nasal  surface  is  thin  and  deeply  indented 
in  its  central  portion,  forming  the  lateral  boundary  of  the  anterior  naris. 
The  portion  of  this  border  above  the  indentation  is  roughened  and 
articulates  with  the  nasal  bone ;  that  below  articulates  with  its  fellow 
of  the  opposite  side,  and  forms  half  of  the  nasal  spine. 

The  Lateral  or  Facial  Surface  is  concave,  and  extends  from  the  anterior 
border  to  the  root  of  the  malar  process.  The  outer  portion  of  its  supe- 
rior bord(!r  is  roughened  for  articulation  with  the  lower  border  of  the 
orbital  process  of  the  malar  bone.  Internally,  this  border  is  smooth, 
and  curves  upward  from  the  imier  portion  of  the  infraorbital  ridge. 

The  Infraorbital  Foramen. — Just  below  this  ridge,  about  midway  of 
the  border,  is  an  oval  aperture  for  the  passage  of  the  infraorbital  nerve 
and  vessels.  Between  this  foramen  and  the  infraorbital  ridge  arises  the 
proper  elevator  nuiscle  of  the  upper  lip  (levator  labii  superioris  proprius). 

71ie  Canine  Fminence  is  a  vertical  ridge  that  divides  the  lower  portion 
of  this  surface,  and  corresponds  in  position  to  the  root  of  the  canine  tooth. 
It  gives  origin  to  the  depressor  muscle  of  the  wing  of  the  nose  and  also  to 
the  depressor  of  the  upper  lip.  Tlie  Incisive  or  3Iyrtiform  Fossa  is  a  slight 
depression  between  the  canine  eminence  and  the  median  border  of  the 
bone.  It  gives  origin  to  the  depressor  muscle  of  the  wing  of  the  nose 
and  to  the  dej>ressor  of  the  upper  lip.  Above,  and  a  little  external  to 
the  incisive  fos>^a,  arises  the  compressor  of  the  nose  (compressor  nasi). 

The  Canine  Fosm  is  a  larger  depression  on  the  outer  side  of  the 
canine  eminence.  The  floor  is  very  thin,  and  an  opening  into  the 
antrum  may  be  readily  made  through  it.  This  fossa  gives  origin  to 
the  elevator  muscle  of  the  angle  of  the  mouth  (levator  anguli  oris). 


BONES.  85 

The  Posterior  or  Zygomatic  Surface  is  convex,  and  extends  from  the 
root  of  the  malar  process  inward  and  backward  to  its  articulation  with 
the  vertical  plate  of  the  palate  bone. 

The  Superior  Border  is  Mell  defined,  and  is  the  dividing-line  between 
this  and  the  orbital  surfaces.  The  central  portion  of  the  border  is 
marked  bv  the  infraorbital  groove. 

The  Posterior  Superior  Angle  is  bevelled  for  articulation  with  the 
orbital  process  of  the  palate  bone. 

The  Tuberosity  is  a  rounded  eminence  of  bone  just  behind  the  posterior 
inferior  angle,  back  and  above  the  wisdom  tooth ;  it  is  often  so  fragile 
as  to  be  broken  away  in  extracting  this  tooth,  the  roots  of  which  curve 
upward,  outward,  and  backward  in  it.  The  inner  surface  of  the  tuber- 
osity is  frequently  roughened  for  articulation  with  the  pyramidal  pro- 
cess of  the  palate  bone.  The  tuberosity  in  the  living  bone  is  jjenetrated 
by  numbers  of  nutrient  vessels.  Midway  between  it  and  the  zygomatic 
surface  are  several  larger  apertures  which  lead  into  canals  in  the  sub- 
stance of  the  bone  ;  they  are  the  posterior  dental  canals.  One  of  them 
passes  into  the  substance  of  the  bone,  traverses  the  outer  wall  of  the 
maxillary  sinus,  and  joins  the  anterior  dental  canal,  which  branches 
from  the  infraorbital  posterior  to  the  infraorbital  foramen.  These 
canals  transmit  the  posterior  dental  vessels  and  nerves. 

The  Nasal  Process  is  a  thick  irregular  process  of  bone.  Commencing 
at  the  anterior  superior  angle  of  the  facial  surface  of  the  bone,  it  extends 
upward,  inward,  and  backward,  and  forms  part  of  the  inner  boundary 
of  the  orbit  and  external  surface  of  the  nasal  chambers.  Its  upper 
extremity  is  serrated  for  articulation  with  the  frontal  bone  in  front 
and  the  ethmoid  bone  behind,  thus  completing  the  anterior  ethmoidal 
cells.  The  anterior  border  is  serrated  for  articulation  with  the  nasal 
bones. 

The  External  Surface  or  Anterior  Surface  is  marked  by  shallow 
grooves,  which  are  traces  of  the  development  and  growth  of  the  bone 
downward.  It  is  perforated  by  several  foramina  for  the  passage  of 
nutrient  vessels  to  the  substance  of  the  bone.  This  surface  gives  origin 
to  the  elevator  muscle  of  the  upper  lip  and  of  the  wing  of  the  nose 
(levator  labii  superioris  alseque  nasi),  the  sphincter  muscle  of  the  orbit 
(orbicularis  palpebrarum),  and  the  tendon  of  the  eye  (tendo  oculi). 

The  Internal  Surface  of  the  Xasal  Process  is,  for  convenience  of 
description,  all  that  portion  of  bone  included  between  the  superior 
border  and  the  floor  of  the  anterior  nares.  This  surface  is  marked  by 
two  slightly  concave  portions  of  bone  and  two  ridges.  The  lower  ridge 
articulates  with  the  inferior  turbinated  bone,  while  the  upper  one  articu- 
lates with  the  middle  turbinated  bone. 

The  Inferior  Meatus  of  the  nose  is  bounded  on  the  outside  anteriorly 
by  the  concave  portion  of  bone  below  the  inferior  ridge.  The  Middle 
Meatus  is  partly  bounded  externally  by  that  concave  portion  betAveen 
these  ridges.  The  Superior  Meatus  at  its  commencement  is  similarly 
bounded  by  that  portion  of  this  surface  above  the  superior  ridge. 

The  Malar  Process  is  rough  and  triangular,  and  projects  outward  and 
upward  from  the  external  surface  of  the  body  of  the  bone.  It  forms  a 
strong  abutment  immediately  above  the  first  molar  tooth,  and  articulates 


86  ANATOMY. 

with  the  malar  bone.  It  gives  origin  to  a  portion  of  the  masseter 
muscle. 

The  Palate  Process,  with  its  fellow  of  the  opposite  side,  forms  about 
three-fourths  of  the  hard  palate,  the  same  process  of  the  palate  bones 
making  up  the  remaining  fourth.  This  process  has  two  surfaces.  The 
nasal  or  superior  surface  is  smooth  and  concave  from  side  to  side ;  the 
oral  or  inferior  surface  is  vaulted  and  roughened  to  give  attachment  to 
the  muco-periosteum.'  It  is  also  marked  by  numerous  small  depressions 
for  the  lodgment  of  the  mucous  glands.  Its  anterior  half  is  pierced  by 
minute  foramina  for  the  passage  of  nutrient  vessels,  and  the  antero-pos- 
terior  grooves  on  the  posterior  half  are  for  the  accommodation  of  the 
posterior  palatine  nerves  and  vessels. 

The  Anterior  Border  of  this  process,  where  it  fuses  with  the  premax- 
illa  (see  paragraph  on  development  of  superior  maxilla,  p.  88),  is  thick 
and  roughened,  while  its  posterior  border  is  thin,  serrated,  and  articu- 
lates with  the  palate  bone. 

The  Mesial  Border  of  this  process  and  that  of  the  premaxilla:  is 
thicker  before  than  behind,  and  is  serrated  for  articulation  with  its  fel- 
low of  the  opposite  side. 

The  Nasal  Spine. — The  anterior  border  of  the  palate  process  is  smooth 
and  concave;  it  terminates  superiorly  in  a  well-defined  spine,  which 
gives  attachment  to  the  cartilage  which  forms  the  anterior  portion  of 
the  septum  of  the  nose. 

The  Incisor  Crest  is  a  sharp  projection  just  posterior  and  continuous 
with  the  nasal  spine,  and  between  it  and  the  incisor  foramen. 

The  Nasal  Crest  is  an  elevation  of  the  median  border  of  this  bone, 
including  the  same  border  of  the  jxdate  bone.  These  when  joined  form 
the   nasal  crest  for  articulation  witli  the  vomer. 

The  Incisor  Foramen  (or  foramen  of  Stenson)  is  situated  immediately 
behind  the  incisor  crest,  and  leads  downward  and  forward  from  the  nasal 
Y^Q  og  chamber  toward  the  oral  cavity,  terminating  just 

back  of  the  incisor  teeth.  As  this  foramen  ex- 
tends downward,  it  is  soon  converted  into  a 
groove  by  the  deficiency  of  its  inner  wall.  In 
the  articulated  bones  this  groove  forms  the  ante- 
rior ])a]atinc  meatus  or  canal,  and  opens  on  the 
nasal  surface  of  the  palatal  process  through  four 
The  Anterior  Palatine  Fossa,  It  fbramiua — the  incisivc  foramina  iust  described, 

will  be  found  to  contain  four  i       '  /•  •  n    ci  i  i 

openings-two  i.iaceri  latir-  and   tuc  loramiua  oi   ocariw  or  the  naso-iiala- 

ailv,  1  ,•_',  and  two  in  thy  niitl-    ,•  t>  •  rp,  ^  '^      .  i       , 

die,  one  (4)  before  the  other  tiue  toranumi.      1  lie  meatus  IS  seen  as  a  single 
*■"•  orifice  back  of  the  incisor  teeth  at  the  point  of 

union  of  the  prcmaxillary  l)oiics  witli  the  ])a]atal  processes. 

The  Foramina  of  Scarpa,  or  Naso-p(dati)ie  Foramina,  are  situated  in 
the  ])lates  of  bone  that  separate  the  upper  part  of  the  incisor  foramina, 
and  are  anterior  and  posterior  or  directly  in  the  mesial  line,  the  posterior 
opening  transmitting  the  right  and  tiie  anterior  the  left  naso-palatine 
nerves. 

The  Alveolar  ]*rocess  extends  fi)rwar(l  from  the  tuberosity,  along  the 
'inferior  margins  of  the  zygomatic  and  ficial  surfaces,  to  the  median  line 
^  Harrison  Allen,  Human  Anulomu. 


BONES. 


87 


of  the  bone,  where  it  articulates  with  its  fellow  of  the  opposite  side.  It 
is  broader  behind  than  in  front,  and  composed  principally  of  cancellous 
or  spongy  tissue.  It  is  curved  in  outline,  corresponding  to  some  extent 
to  the  body  of  the  bone  above.  This  curve  varies  in  different  bones, 
the  extent  of  variation  depending  in  great  measure  on  the  race  and  tem- 
perament of  the  individual  from  which  the  bone  is  taken.  With  its 
fellow  in  well-formed  mouths  its  axis  is  parabolic.  It  is  composed  of 
two  plates  of  bone — an  inner  and  an  outer — with  numerous  septa  of  can- 
cellous tissue  uniting  them  and  forming  the  alveoli  for  the  accommoda- 
tion or  reception  of  the  roots  of  the  teeth. 

The  Older  Plate  of  the  alveolar  process  is  continuous  with  the  facial 
and  zygomatic  surfaces  of  the  bone.  It  is  the  thinner  and  weaker  of 
the  two,  whicli  accounts  for  the  fact  that  a  healthy  tooth  is  more  easily 
pressed  outward  than  inward.  After  a  tooth  has  been  extracted  the 
outer  plate  absorbs  much  more  quickly  and  to  a  greater  extent  than  the 
inner. 

The  Inner  Plate  is  well  defined  superiorly,  where  it  forms  an  angle 
wath  the  palate  process.    It  is  thicker  and  stronger  than  the  outer  plate. 

The  Outer  Surface  is  marked  by  eminences  corresponding  to  the  roots 
of  the  teeth,  and  depressions  marking  the  position  of  the  interspaces. 
The  eminence  over  the  canine  tooth  is  more  prominent  than  the  others. 
This  surface  at  or  near  its  superior  margin,  over  the  second  bicuspid  and 
three  molar  teeth,  gives  origin  to  the  buccinator  muscle. 

Fig.  37. 


Alveoli  of  Permanent  Teeth. 


The  Alveoli  (Fig.  37)  in  the  normal  adult  bone  are  eight  in  number, 
and  correspond  in  shape  and  size  with  the  roots  of  the  teeth  which  they 


88  ANATOMY. 

accommodate.  The  socket  for  the  central  incisor  tooth  is  nearly  conical 
in  shape.  That  for  the  lateral  incisor  is  conical,  but  smaller  and  more 
compressed  meso-distally  than  the  central  socket,  and  often  presents  a 
slight  distal  curve  at  its  upper  extremity.  The  socket  for  the  cuspid 
(canine)  tooth  is  conical  in  form,  deeper  and  larger  than  those  for  the 
incisors,  and  somewhat  compressed,  especially  at  its  inner  aspect,  form- 
ing an  oval  in  transverse  section.  The  sockets  for  the  bicuspidati 
resemble  flattened  cones,  that  for  the  first  bicuspid  generally  bifurcating 
at  the  upper  portion,  as  this  tooth  frequently  has  two  roots.  The  same 
reason  occasionally  causes  a  bifurcation  of  the  socket  for  the  second 
bicuspid.  The  sockets  for  the  molar  teeth  are  broad,  and  divided  at 
their  upper  three-fourths  into  three  compartments.  The  socket  for  the 
wisdom  tooth  is  an  exception  to  this  formation,  frequently  not  dividing 
at  all,  and  sometimes  having  more  than  three  compartments. 

The  septa  between  the  alveoli  extend  downward  to  a  lower  levei 
than  the  plates  composing  the  alveolar  processes,  so  that  their  free 
margins  are  convex — a  point  to  be  remembered  in  practical  dentistry 
in  fitting  permanent  bands  and  metal  crowns  on  roots  that  are  embraced 
in  the  alveolar  walls. 

Each  alveolar  wall  consists  of  a  shell  of  thin,  compact  bony  structure 
surrounded  by  spongy  tissue.  This  shell  comes  into  contact  with  the 
dense  cortical  plates  composing  the  surfaces  of  the  bone,  mainly  at  the 
margin  near  the  neck  of  the  tooth.  At  the  apical  portion  of  the  sockets 
are  small  openings  for  the  entrance  of  vessels  and  nerves  supplying  the 
teeth. 

The  teeth  are  held  in  their  sockets  by  alveolo-dental  connective  tissue. 
It  is  elastic,  and  allows  a  considerable  motion  of  the  teeth.  In  the 
dried  bone  the  loss  of  this  tissue  loosens  the  teeth  and  permits  their 
detachment  from  the  sockets. 

Development. — The  development  of  the  superior  maxillary  bone 
(Fig.  38)  commences  so  early  and  increases  with  such  rapidity  that  it  is 
difficult  to  mark  out  its  line  of  growth.  It  arises  in  membrane  from 
many  points  of  ossification,  at  least  one  each  for  the  orbital  plate,  the 
nasal  process,  and  tiie  alveolar  border.  These  appear  about  the  sixth 
or  seventh  week  of  embryonal  life,  and  soon  coalesce.  Hence  these 
parts  are  claimed  by  some  to  arise  from  one  centre.  They  form  the 
lateral  portion  of  the  bone,  which  contains  all  the  teeth  except  the  two 
incisors,  and  is  called  by  comparative  anatomists  the  true  maxilla. 
That  portion  of  the  bone  which  contains  the  central  and  lateral  incisor 
teeth  arises  from  a  separate  point  of  ossification,  and  is  known  as  the 
premaxilla.  In  many  of  the  lower  animals  it  remains  distinct  from  the 
true  maxilla  throughout  life. 

When  there  is  union  between  the  two  premaxillary  bones  in  the 
median  line,  but  no  lateial  union  between  them  and  the  true  maxillae, 
thev  form  the  intermaxillary  bone  of  the  lower  animals.  In  man  the 
premaxilla  soon  unites  with  the  maxilla  ]M'()per  by  a  suture,  which  on  the 
facial  surface  may  be  seen  until  the  sixth  year,  and  on  the  hard  palate 
it  generally  remains  until  adult  life.  The  suture  on  the  hard  palate 
extends  as  fiu-  back  as  the  posterior  portion  of  the  anterior  palatal  canal. 
In  single  or  unilateral  complete  cleft  palate — i.  e.  the  clefib  extending 


BONES. 


89 


from  the  facial  surface  to  the  posterior  portion  of  the  palate  process — 
the  premaxilla  does  not  unite  with  the  parts  containing  the  other  teeth, 
neither  do  the  true  maxillre  and  palatal  processes  of  the  palate  bones 
unite.  In  double  cleft  palate  the  incisorial  divisions  may  have  united 
in  the  median  line  (forming  an  intermaxillary  bone),  but  not  laterally 


Fig.  38. 


J  Jot  Nascbl    ^ 
Taeial  ^ort.V? 


1  for  Orbital  lip 
Malar  j'ort^^ 


1    fur Incistvt  Jtort ' 


I    for  Palatal jiorr^ 


Anterior  Surface. 


at 
Birth 


Development  of  the  Superior  Maxillary  Bone,  by  four  centres. 

with  the  true  maxillae.  In  some  of  these  cases  the  vomer  can  be  seen 
protruding  in  the  median  line  between  the  two  halves  of  the  hard  palate. 

The  alveolar  process  is  developed  as  a  special  support  for  the  teeth. 
At  birth  it  is  represented  by  the  walls  of  a  deep  groove,  in  which 
the  deciduous  and  the  germs  of  the  permanent  teeth  are  situated. 
As  the  teeth  grow  the  alveolar  process  advances,  until  it  encases  them. 
Just  prior  to  the  shedding  of  the  deciduous  teeth  their  roots  and  tlieir 
bony  processes  are  absorbed,  and  the  latter  are  re-formed  on  the  ai)pear- 
ance  of  the  permanent  teeth.  This  process  again  commences  to  disap- 
pear on  the  loss  of  the  second  set  of  teeth,  and  in  time  may  be  wholly 
removed.  In  certain  diseased  conditions  of  the  bones  this  process  dis- 
appears to  some  extent  before  the  permanent  teeth  are  lost ;  and  this 
bone-absorption  may  go  on  until  teeth  otherwise  healthy  become  loose 
and  drop  out. 

The  Maxillary  ShxuH  (antrum  of  Highmore)  is  the  large  air-cavity 
situated  in  the  body  of  the  bone.  It  is  irregularly  pyramidal  in  shape, 
the  apex  bearing  toward  the  malar  bone,  into  which  it  may  extend,  and 
its  base  toward  the  nasal  cavity.  Its  development  is  similar  to  the 
sinuses  in  the  frontal  bone,  and  like  them  is  not  completed  until  after 
the  age  of  puberty,  although  it  makes  its  apj^earance  as  early  as  the 
fifth  or  sixth  month  of  foetal  life.     Hence  in  early  life  the  surrounding 


90  ANATOMY. 

walls  are  much  thicker  than  in  the  adult.  Its  capacity  varies  in  dif- 
ferent subjects  and  in  the  opposite  bones  of  the  same  subject,  ranging 
from  one  drachm  to  one  ounce  fluid  measure,  the  average  being  about 
three  drachms.     It  is  somewhat  larger  in  the  male  than  in  the  female. 

The  floor  of  the  sinus  is  marked  by  irregular  eminences  correspond- 
ing to  the  roots  of  the  molar  teeth.  Somedmes  it  is  punctured  by  the 
roots  of  these  teeth,  which  may  extend  into  the  sinus.  The  walls  of 
the  sinus  often  support  thin  plates  of  bone  which  subdivide  it  into 
small  compartments.  A  knowledge  of  this  fact  is  of  importance  in 
operating  on  tumors  and  abscesses  in  this  location,  as  the  drill  may 
simply  penetrate  one  of  these  distinct  compartments,  misleading  the 
operator  as  to  the  extent  of  the  sinus  or  of  the  disease. 

The  sinus  opens  into  the  middle  meatus  of  the  nose  by  an  orifice 
of  variable  size  situated  at  the  base  of  the  pyramid.  This  orifice 
is  partly  closed  by  the  uncinate  process  of  the  ethmoid,  the  vertical 
plate  of  the  palate,  the  inferior  turbinated,  and  the  lachrymal  bones, 
also  by  soft  tissue,  so  that  in  the  recent  state  it  is  about  the  size  of  an 
ordinary  lead-pencil.  This  small  opening  is  situated  near  the  upper 
part  of  the  sinus,  and  does  not,  when  the  head  is  perpendicular,  afford 
a  ready  outlet  to  fluids  collected  within  the  chamber. 

The  mucous  membrane  lining  the  sinus  is  ciliated,  and  is  continuous 
through  this  quill-like  opening  with  the  membrane  lining  the  nasal 
cavity.     It  is,  however,  less  vascular  than  the  nasal  mucous  membrane. 

The  sinus  may  be  encroached  upon  by  any  of  the  teeth  situated  in 
the  superior  maxilla,  but  those  that  most  frequently  protrude  into  it  are 
the  roots  of  the  first  and  second  molars. 

With  the  exception  of  the  alveolar  border  the  walls  of  the  sinus  are 
quite  thin.  These  walls  are  four  in  number — one  extending  toward  the 
orbit ;  another  toward  the  nose  and  roof  of  the  mouth,  including  a 
portion  of  the  palatal  process ;  a  third  toward  the  facial  and  zygomatic 
surfaces  of  the  bone;  and  a  fourth  is  formed  by  the  alveolar  border. 
Morbid  growths  within  the  sinus  will  more  readily  cause  either  of  the 
first  three  walls  to  project  or  bulge  than  the  alveolar  process. 

The  ])osterior  wall,  or  that  toward  the  zygomatic  surface  of  the  bone, 
is  marked  by  the  j)osterior  dental  canals,  through  which  the  posterior 
dental  vessels  and  nerves  are  conducted  to  the  teeth.  The  anterior  M^all 
is  in  like  manner  grooved  by  the  anterior  dental  or  incisor  vessels 
arid  nerves. 

Palate  Bone. 

The  palate  bones,  two  in  number,  arc  Mcdged  between  the  superior 
maxillary  bones  and  the  pterygoid  ])lates  of  the  sphenoid  bone  at  the 
back  part  of  the  nasal  chambers.  Tluy  assist  in  forming  the  bound- 
aries of  the  (H'bital,  nasal,  and  oral  cavities,  the  spheno-maxillary,  the 
spheno-palatine,  and  the  ])terygoid  fossa,  the  s})heno-maxillary  fissure, 
the  ])()st('rior  etlimoidal  cells,  and  the  maxillary  sinus. 

The  jialate  bone  is  com])(>sed  of  thin,-  delicate,  and  compact  tissue. 
Its  general  iorm  is  that  of  tlie  letter  L.  It  is  composed  of  two  plates, 
a  horizontal  and  v'ertical ;  and  three  processes,  a  pyramidal,  orbital,  and 
sphenoid. 


BONES. 


91 


The  Horizontal  or  Palate  Process. — This  corresponds  to  the  palate 
process  of  the  superior  maxilla.  It  is  thin,  quadrilateral  in  form,  and 
•jDresents  for  examination  two  surfaces  and  four  borders. 

The  Superior  Surface  is  smooth,  concave  from  side  to  side,  and  forms 
the  posterior  portion  of  the  floor  of  the  nasal  chamber. 

The  Inferior  Surface  is  smooth,  excepting  at  its  posterior  portion, 
where  it  is  marked  by  a  transverse  ridge  for  the  attachment  of  the 
tensor  palati  muscle.  This  surface  forms  the  posterior  portion  of  the 
hard  palate. 

The  Posterior  Palatine  (or  Palato-maxillari/)  Canal  is  a  groove, 
sometimes  a  canal,  situated  at  the  outer  portion  of  the  ridge,  for  the 
attachment  of  the  tensor  palati  muscle.  It  is  converted  into  a  canal 
bv  articulation  with  the  superior  maxilla.  It  transmits  the  posterior 
palatine  vessel  and  anterior  palatine  nerves. 

The  Accessory  Posterior  Palatine  Canal,  or  Canals,  are  between  this 
ridge  and  the  pyramidal  process. 

The  Anterior  Border  is  serrated  for  articulation  with  the  palatal  pro- 
cess of  the  superior  maxilla. 

The  Posterior  Border  is  free,  smooth  and  concave,  forming  the  pos- 
terior boundary  of  the  hard  palate  and  floor  of  the  nasal  chamber. 

Fig.  39. 


liol  Pi 


Suptriar  Mcatu.^ 

J-idathi 

e.Tor<^„u,^ 

-   ^51-^ 

< 
PI 

9 

H 

"**     ^'  ^"-^^ 

^     -*  (^jrrfC 

o 

K'''^ 

> 

"''^'ij^ 

MaxiHicry 
~  J^roccss 


HORIZONTAL      FLATC 


Left  Palate  Bone,  iutemal  view  (enlarged). 

This  border  gives  origin  to  the  soft  palate,  and  terminates  in  the  median 
line  in  a  sharp  point.  This  point,  when  articulated  with  its  fellow  of 
the  opposite  side,  forms  the  posterior  nasal  or  palatine  spine  and  gives 
origin  to  the  azygos  uvula  luuscle. 

The  Exto^nal  Border  is  situated  just  below  the  junction  of  the  hori- 
zontal and  vertical  plates.  In  it  is  the  groove  which  assists  in  forming 
a  portion  of  the  posterior  palatine  canal. 


92 


ANAT03IY. 


The  Internal  Border  is  much  thicker  than  any  of  the  others.  It  is 
serrated  and  elevated  into  a  ridge,  which,  when  articulated  with  the 
corresponding  one  of  the  opposite  bone,  forms  a  continuation  of  the 
nasal  crest  of  the  superior  maxilla,  with  which  the  vomer  articulates. 
The  Vertical  Plate  is  thin,  and  extends  from  the  floor  of  the  nasal 
chamber  to  the  upper  extremity  of  the  spheno-palatine  notch.  It  has 
two  surfaces,  an  external  and  an  internal ;  and  four  borders,  an  anterior, 
jDOsterior,  superior,  and  inferior. 

The  Ldernal  Surface  is  similar  in  structure  to  the  same  surface  of 
the  superior  maxilla.  It  is  divided  into  three  portions  by  two  antero- 
posterior ridges,  the  superior  and  inferior  turbinated  crests.  The  inferior 
crest  articulates  with  the  inferior  turbinated  bone,  and  thus  forms  the 
division  between  the  inferior  and  middle  meati  of  the  nose.  The 
superior  crest  articulates  with  the  middle  turbinated  bone  (part  of  the 
ethmoid),  and  forms  the  division  between  the  middle  and  superior 
meati  of  the  nose.  Between  the  superior  turbinated  crest  and  the 
superior  border  of  the  bone  is  a  groove  which  forms  part  of  the  superior 
meatus. 

The  External  Surface  is  generally  rough  and  uneven.  Its  posterior 
boundary  is  marked  by  a  groove  (occasionally  a  canal)  M'hich,  in  the 
articulated  skull,  forms  the  posterior  palatine  canal,  already  described. 
The  Anterior  Border  is  thin,  its  inferior  turbinated  crest  projecting 
anteriorly  to  form  the  maxillary  process.  This  process  assists  in  closing 
the  maxillary  sinus. 

The  Posterior  Border  (Fig.  40)  is  irregular  and  serrated.  Its  lower 
third  is  marked  internally  by  a  deep  groove,  the  edges  of  which  articu- 
late with  the  internal  plate  of  the 
pterygoid  process  of  the  s])henoid 
bone,  a  portion  of  which  fits  into 
the  groove.  Above  the  groove 
this  border  articulates  with  tlie 
outer  edge  of  the  internal  ptery- 
goid plate,  the  thin  projecting 
border  overlapping  its  internal 
surface. 

The  Superior  Border  is  divi- 
ded by  a  deep  notch,  sometimes 
a  foramen,  the  spheno-palatine 
notch  or  foramen,  which  divides 
the  orbital  from  the  sphenoidal 
process. 

The  Spheno-palatine  Notch  or 
Foramen  is  converted  into  a  fora- 
men by  articulation  with  the  sphe- 
noid bone.  It  transmits  the  sphe- 
no-palatine vessels  and  nerves 
from  the  spheno-palatine  fossa 
into  the  nasal  chambers. 
The  Inferior  Border  joins  the  external  border  of  the  horizontal  plate. 
The  Pyramidal  Process  extends  downward  and  backward  from  the 


Fig.  40. 


t*' 


ShhcnoiJ-al  /i  roress. 

-Articu lur  hort. 

iS  on.  uritcuui'r  Aort  ^ 


Left  Palate  Boue,  posterior  view  (enlarged). 


BONES.  93 

inferior  and  posterior  borders,  and  fits  into  the  pterygoid  notch  between 
the  two  pterygoid  plates  of  the  sphenoid.  Posteriorly,  this  process  has 
a  triangular  surface  which  rounds  out  the  lower  portion  of  the  ptery- 
goid fossa.  The  borders  of  this  process  are  serrated  for  articulation 
with  both  pterygoid  plates  of  the  sphenoid  bone. 

The  Orbital  Process  extends  outwardly  from  the  superior  border  of 
the  vertical  plate,  overhanging  its  outer  surface.  This  process  has  five 
surfaces,  enclosing  a  cellular  cavity,  generally  opening  through  its  inter- 
nal or  ethmoidal  surface.  When  it  so  opens  it  communicates  with  the 
posterior  ethmoidal  cells.  Sometimes,  however,  this  cell-like  cavity 
opens  through  the  posterior  or  sphenoidal  surface  and  communicates 
with  the  sphenoidal  sinus,  or  it  may  open  both  ways.  Three  of  these 
surfaces — the  anterior  or  maxillary,  the  posterior  or  sphenoidal,  and  the 
internal  or  ethmoidal — are  articulating  surfaces,  while  the  remaining  two, 
the  superior  or  orbital  and  the  external  or  zygomatic,  are  free. 

The  Anterior  or  llaxillary  Surface  is  directed  forward,  outward,  and 
downward.  It  is  oblong  in  form  and  articulates  with  the  posterior 
superior  angle  of  the  inner  surface  of  the  superior  maxilla. 

The  Posterior  or  Sphenoidal  Surface  is  directed  backward,  upward, 
and  inward,  and  articulates  with  the  vertical  portion  of  the  sphenoidal 
turbinated  bone. 

The  Internal  or  Ethmoidal  Surface  is  directed  inward,  upward, 
and  forward,  and  articulates  with  the  vertical  plate  of  the  ethmoid 
bone. 

The  Superior  or  Orbital  Surface  is  triangular  in  form,  extends  up- 
ward and  outward,  and  forms  the  posterior  angle  of  the  floor  of  the 
orbit. 

The  External  or  Zygomatic  Surface  is  smooth  and  oblong  in  form,  is 
directed  outward,  backward,  and  downward,  and  forms  a  portion  of  the 
spheno-maxillary  fossa. 

The  Sphenoidal  Process  curves  upward,  backward,  and  inward  from 
the  posterior  third  of  the  superior  border,  and  presents  three  surfaces, 
the  superior,  external,  and  internal ;  and  two  borders,  the  anterior  and 
posterior. 

The  Superior  Surface  is  the  smallest  of  the  three,  and  articulates  with 
the  horizontal  portion  of  the  sphenoidal  turbinated  bone.  It  is  marked 
by  a  groove  which  assists  in  forming  the  ptery go-palatine  canal. 

The  External  Surface  is  divided  into  two  portions,  anterior  and  pos- 
terior. The  anterior  portion  is  smooth,  and  helps  to  form  the  spheno- 
maxillary fossa,  while  the  posterior  portion  is  rough,  for  articulation 
with  the  inner  surface  of  the  pterygoid  plate  of  the  sphenoid  bone. 

The  Internal  Surface  is  smooth  and  concave,  and  forms  part  of  the 
outer  wall  of  the  posterior  nares. 

The  Anterior  Border  forms  the  posterior  margin  of  the  spheno-pala- 
tine  notch. 

The  Posterior  Border  is  serrated,  and  articulates  with  the  inner  sur- 
face of  the  pterygoid  process. 

Development. — The  palate  bone  is  developed  from  a  single  centre 
of  ossification,  which  is  deposited  in  membrane,  and  appears  at  the 
junction  of  the  vertical  with  the  horizontal  plate  about  the  seventh  or 


94 


ANATOMY. 


eighth  week  of  embryonal  life, 
than  the  vertical  plate. 


Before  birth  the  horizontal  is  longer 


Right  Inferior  Turbinated  Bone,  internal  surface. 


The  Inferior  Turbinated  Bone. 

The  inferior  turbinated  bones  (maxillo-turbinal),  two  in  number,  are 
situated  at  the  lower  third  of  each  lateral  wall  of  the  nasal  chamber. 
Each  bone  forms  the  upper  boundary  of  the  inferior  meatus  of  the 
nose  and  the  lower  boundary  of  the  middle  meatus.     It  is  thin  and 

frail,  full  of  small  foramina 
Fig.  41.  and    minute    canals.      It    is 

scroll-like  in  form,  curving 
outward  and  downward.  It 
presents  a  body  with  two 
surfaces,  an  internal  and  an 
external ;  two  borders,  supe- 
rior and  inferior ;  and  two 
extremities,  anterior  and  pos- 
terior. 

TJie  Interned  Surface  (Fig. 
41)  is  convex  from  above 
downward,  and  is  marked  by  numerous  foramina  and  longitudinal  canals 
for  the  passage  of  blood-vessels  and  nerves. 

The  External  Surface  (Fig.  42)  is  concave,  smoother  than  the  inter- 
nal, excepting  at  its  lower  margin. 
Fig-  42.  where  it  is  somewhat  cellular  in 

structure  and  marked  by  numer- 
ous foramina.  It  forms  the  roof 
of  the  middle  meatus  of  the  nose. 
TJte  Superior  Border  is  thin  and 
irregular,  and  is  divided  into  three 
portions,  anterior,  middle,  and  pos- 
terior. 

The  Anterior  Portion  articulates 
with  the  inferior  turbinated  crest 
on  the  internal  surface  of  the  nasal  process  of  the  superior  maxilla. 

The  Middle  Portion  has  arising  from  it  three  processes — the  lachry- 
mal, the  ethmoidal,  and  the  maxillary. 

The  Lachrymal  Process  runs  ujiward  and  forward,  and  articulates 
with  tlie  anterior  inferior  angle  of  the  lachrymal  bone.  The  outer  por- 
tion of  this  process  is  grooved  and  assists  in  forming  the  lachrymal  canal. 
The  Ethmoidal  Process  arises  just  anterior  to  "the  posterior  third  of 
the  superior  border.  It  is  broad,  and  extends  upward  to  articulate  with 
the  uncinate  process  of  the  ethmoid  bone. 

The  Maxillary  Process  arises  from  the  base  of  the  ethmoidal  process 
externally,  and  curves  outward  and  downward,  forming  a  hook-like  pro- 
jection semicircular  in  shape.  This  process  articulates  with  the  inferior 
border  of  the  opening  to  the  maxillary  sinus. 

The  Posterior  Portion  of  the  sujierior  border  articulates  with  the 
inferior  turbinated  crest  of  the  palate  bone. 


Eiglit  Inferior  Turbinated  Hone,  outer  surface. 


BONES.  95 

The  Inferior  Border  is  thickened,  and  marked  by  several  indentations 
of  a  cell-like  character. 

The  Extremities  are  narrowed  and  somewhat  pointed,  especially  the 
posterior. 

Development. — The  inferior  turbinated  l)one  is  developed  from 
cartilage  from  one  point  of  ossification,  which  appears  about  the  fifth 
month  of  foetal  life. 

The  Lachrymal  Bones. 

The  lachrymal  bones,  or  os  unguis,  two  in  number,  are  situated  at  the 
inner  and  anterior  portion  of  the  orbit,  just  posterior  to  the  nasal  pro- 
cess of  the  superior  maxilla.  They  pass  downward  into  the  nasal 
chamber. 

The  lachrymal  bone  (Fig.  43)  is  the  smallest  and  most  delicate  bone 
of  the  face.     It  is  quadrilateral  in  shape,  and  pre- 
sents two  surfaces,  the  external  or  orbital  and  the  • 
internal  or  nasal ;  and  four  borders,  anterior,  pos-          ^^^^-^^ 
terior,  superior,  and  inferior. 

The  Orbital  or  External  Surface  is  divided  into 
two  portions,  an  anterior  and  posterior,  by  a  verti- 
cal ridge  of  bone,  the  lachrymal  crest. 

The  Anterior  Portion  of  the  orbital  surface  pre- 
sents a  smooth  perpendicular  groove,  the  lachrymal 
groove,  the  upper  part  of  which  lodges  the  lachry- 
mal sac.  In  the  articulated  skull  this  groove  as- 
sists in  forming  the  lachrymal  canal. 

The  Posterior  Portion  of  the  orbital  surface  is     «/"-C'^ 
smooth  and  concave,  and  forms  part  of  the  inner  ('^  ^^     .y    *"      J     > 
wall  of  the  orbit.     The  tensor  tarsus  muscle  arises    Left  Lachrymal  Pone,  ex- 

„  ,111  1  i  1  ^1  !•!  terual  surlace. 

irom  the  lachrymal  crest  and  part  ot  tiie  orbital 

surface  just  posterior  to  the  crest.  The  hook-like  process  seen  at  the 
lower  portion  of  the  lachrymal  crest  articulates  with  the  lachrymal 
tubercle  of  the  superior  maxilla,  and  completes  the  orbital  orifice  of 
the  lachrymal  canal.  Occasionally  this  hook-like  process  exists  as  a 
separate  bone  known  as  the  lesser  lachrymal  bone. 

The  Internal  Surface  forms  part  of  the  outer  wall  of  the  nasal  cham- 
ber. It  is  marked  opposite  the  lachrymal  crest  on  the  external  surface 
by  a  longitudinal  depression.  That  portion  of  the  bone  in  front  of  this 
depression  enters  into  the  formation  of  the  outer  surface  of  the  middle 
meatus  of  the  nose ;  that  behind  it  articulates  with  the  ethmoid  bone, 
and  in  conjunction  with  the  superior  maxilla  closes  the  anterior  ethmoi- 
dal cells. 

The  Anterior  Border  is  the  longest  of  the  four,  and  articulates  at  the 
inner  margin  of  the  lachrymal  groove  with  the  nasal  process  of  the 
superior  maxilla. 

The  Posterior  Border  is  thin  and  uneven  ;  it  articulates  with  the 
anterior  border  of  the  os  planum  of  the  ethmoid  bone. 

The  Superior  Border  is  the  thickest  and  shortest  of  the  four.  It 
articulates  with  the  internal  angular  process  of  the  frontal  bone. 


96 


ANATOMY. 


The  Inferior  Border  is  more  complicated  than  any  of  the  others.  It 
is  thicker  at  the  termination  of  the  lachrymal  ci'cst  than  elsewhere, 
which  gives  strength  to  the  posterior  wall  of  the  lachrymal  canal.  It 
is  divided  by  the  lower  extremity  of  the  lachrymal  crest  into  two  por- 
tions, an  anterior  and  a  posterior. 

The  Anterior  Portion,  or  that  portion  in  front  of  the  extremity  of  the 
crest,  extends  downward,  backward,  and  inward,  and  terminates  in  a 
pointed  process  which  articulates  with  the  lachrymal  process  of  the  eth- 
moid bone.  As  it  extends  downward  it  passes  on  the  outer  side  of  the 
uncinate  process  of  the  ethmoid  bone,  and  to  the  inner  side  of  the  orifice 
to  the  maxillary  sinus,  and  thus  assists  in  closing  the  anterior  portion 
of  the  opening  leading  to  the  sinus.  This  portion  also  partly  bounds 
the  lachrymal  canal,  and  is  supported  by  the  uncinate  process  of  the 
ethmoid. 

The  Posterior  Portion,  or  that  situated  behind  the  extremity  of  the 
crest  and  below  the  orbital  surface,  articulates  with  the  orbital  plate 
of  the  superior  maxilla. 

Development. — The  lachrymal  bone  arises  from  one  point  of  ossi- 
fication, which  is  deposited  about  the  eighth  week  of  fcetal  life. 


The  Nasal  Bones. 

The  nasal  bones,  two  in  number,  are  situated  at  the  upper  portion  of 
the  external  nose,  and  form  what  is  often  termed  the  "  bridge  "  of  the 
nose ;  also  the  anterior  boundary  of  the  nasal  chambers. 

The  nasal  bone  is  oblong  in  shape,  has  the  lower  extremity  wider 
than  the  upper,  and  presents  two  surfaces,  anterior  and  posterior ;  Mith 
four  borders,  superior,  inferior,  lateral,  and  median. 

The  Anterior  or  Outer  iSurface  (Fig.  44)  varies  in  shape,  but  may  be 
said  to  be  generally  convex  from  side  to  side  and  concave  from  above 


Fig.  U. 
vitA    Frontnl  B» 


■until 
— Opposite  boiiA, 


Fm.  45. 

^l^^th 
Fro  ntaZ  ^jniie- 

'Orest 

with 
W\\    \Rrpcmlic-iuur 

*  '*     ^lafcrfEtJimoid. 


groove  for  luteal  nerve 


Outer   Surface.. 

Kigbt  Kasal  Boiiu. 


In«'»r  Surface 

Left  Xasal  Bone. 


downward.  The  upper  portion  is  punctured  by  numerous  nutrient 
foramina ;  the  lower  portion  is  smooth  and  rounded.  Near  the  centre 
of  tliis  surface  will  be  seen  a  foramen  which  passes  through  to  the 
internal  aspect  of  the  bone,  and  transmits  a  small  vein.     This  foramen 


BONES.  97 

is  not  constant,  and  sometimes  two  foramina  are  found  in  this  location. 
Occasionally  the  foramen  caecum,  the  commencement  of  the  longitudinal 
sinus  of  the  brain,  opens  on  this  surflice. 

The  Posterior  or  Internal  Surface  (Fig.  45)  is  concave  from  side  to  side 
and  convex  from  above  downward.  Upon  this  surface  is  a  longitudinal 
groove  (sometimes  a  canal)  for  the  transmission  of  the  internal  branch 
of  the  nasal  nerve,  which  passes  out  between  the  bone  and  the  lateral 
cartilage  of  the  nose. 

The  Superior  Border  is  triangular  in  form,  and  serrated  for  articula- 
tion in  the  nasal  notch  of  the  frontal  bone. 

The  Inferior  Border  is  the  broadest  part  of  the  bone.  It  is  thin  and 
notched  in  the  centre  for  the  transmission  of  the  anterior  branch  of  the 
nasal  nerve ;  this  border  extends  downward,  outward,  and  backward, 
terminating  in  a  sharp  point ;  it  gives  support  to  the  lateral  cartilage  of 
the  nose.  In  the  articulated  skull  the  inferior  borders  of  the  two  nasal 
bones  form  a  triangular  notch  called  the  nasal  angle,  serving  for  partial 
attachment  of  the  lateral  nasal  cartilage. 

The  Latercd  or  External  Border  is  the  longest  of  the  four ;  it  is  ser- 
rated and  bevelled  at  the  expense  of  the  anterior  surface,  and  articulates 
with  the  nasal  process  of  the  superior  maxilla. 

The  Median  or  Internal  Border  at  its  upper  portion  is  thick,  gradu- 
ally becoming  thinner  and  tapering  as  it  descends.  When  the  bone 
is  articulated  with  its  fellow  of  the  opposite  side  the  border  produces 
internally  a  vertical  crest  which  forms  part  of  the  se})tum  of  the  nose, 
and  articulates  with  the  nasal  spine  of  the  frontal,  the  perpendicular 
plate  of  the  ethmoid  bone,  and  atfords  attachment  to  the  nasal  carti- 
laginous septum. 

Developmext. — The  nasal  bone  is  developed  in  membrane  from 
one  point  of  ossification,  which  appears  about  the  eighth  week  of 
embryonal  life. 

The  Malar  Bones. 

The  malar  (or  cheek)  bones  are  two  in  number,  situated  at  the  lateral 
angles  of  the  face,  and  support  the  most  prominent  portion  of  the 
cheeks ;  they  assist  in  forming  the  outer  wall,  lower  border,  and  floor 
of  the  orbit,  the  anterior  portions  of  the  temporal  and  zygomatic  fossae, 
and  the  zygomatic  arch.  The  bone  is  quadrangular  in  shape,  and  pre- 
sents for  examination  a  body  with  two  surfaces,  external  and  internal ; 
four  proccs-es,  frontal,  orbital,  maxillary,  and  zygomatic ;  and  five  bor- 
ders, superior,  inferior,  anterior,  posterior,  and  sphenoidal. 

Tlie  External  or  Facial  Surface  (Fig.  4(3)  is  convex  in  form ;  the 
upper  portion  is  smooth,  and  supports  the  sphincter  muscle  of  the  eye, 
the  orbicularis  palpebrarum  ;  the  lower  portion  is  roughened,  and  gives 
origin  to  the  major  and  minor  zygomatic  muscles.  The  upper  portion 
of  this  surface  is  pierced  by  one  or  two  foramina,  which  pass  into  the 
orbit  and  transmit  the  terminal  ends  of  the  lachrymal  blood-vessels 
and  nerves.  The  foramina  or  canals  in  the  malar  bone  vary  with 
different  subjects  :  sometimes  they  are  double,  and  occasionally  they  are 
wanting. 

Vol.  I.— r 


ANATOMY. 


The  Internal  or  Zi/r/omatic  /Surface  (Fig.  47)  is  directed  backward 
and  outward  toward  the  temporal  fossa  above  and  the  zygomatic  fossa 
below;  it  is  concave  in  form,  and  near  the  outer  portion  it  is  punctured 
by  one  or  two  small  foramina  for  the  passage  of  blood-vessels  and 


Fig.  46. 


Bnstlfs  pa^'sctl  through 
Tem^in'o- Miliar  Citruds 


Left  Malar  Bone,  outer  surface. 

nerves!  At  the  anterior  inferior  angle  of  this  surface  is  a  rough  tri- 
angular plate  of  bone  for  articulation  with  the  malar  process  of  the 
superior  maxilla.  The  remainder  of  the  internal  surface  is  smooth, 
and  enters  into  the  formation  of  the  temporal  and  zygomatic  fossae;  the 

Fig.  47. 


^V(W*?^ 


Left  Malar  Bone,  inner  surface. 


lower  third  of  this  surface,  extending  as  far  as  the  lower  border  of  the 
bone,  gives  origin  to  the  greater  part  of  the  masseter  muscle. 

The  Frontal  Process  is  the  most  prominent  of  the  four :  its  upper 
portion  is  thick  and  serrated,  and  arti(;ulates  with  the  external  angular 
process  of  the  frontal  bone. 


BONES.  99 

The  Orbital  Process  is  situated  at  the  outer  wall  and  floor  of  the 
orbit :  it  is  divided  into  two  surfaces,  the  orbital  and  the  temporal ;  and 
two  borders,  the  external  and  the  internal. 

The  Orbital  or  Anterior  Surface  is  smooth  and  concave,  generally 
presenting  two  grooves,  which  extend  to  near  its  anterior  border,  and 
terminate .  in  two  foramina  or  canals  for  the  passage  of  vessels  and 
nerves — one  to  the  facial  surface  of  the  bone,  and  the  other  into  the 
temporal  fossa.  This  surface,  together  with  the  great  wing  of  the 
sphenoid  bone,  forms  the  external  wall  and  part  of  the  floor  of  the 
orbit. 

The  Temporal  or  Posterior  Surface,  in  connection  with  the  external 
angular  process  of  the  frontal  bone,  forms  the  anterior  boundary  of  the 
temporal  fossa.  This  surface  is  smooth  and  convex :  it  is  pierced  by  a 
foramen  leading  to  the  orbit. 

The  Maxillary  Process  is  the  strongest  and  thickest  of  the  four :  it 
extends  alono;  the  entire  anterior  border  of  the  bone,  formino;  the  articu- 
lating  portion  of  the  zygomatic  surface,  and  joining  the  malar  process 
of  the  superior  maxilla. 

The  Zygomatic  Process  is  situated  at  the  posterior  inferior  portion  of 
the  bone.  It  is  broad  and  extends  backward,  its  extremity  being 
bevelled  at  the  extension  of  its  lower  part.  It  is  rough  and  serrated, 
and  articulates  Math  the  zygomatic  process  of  the  temporal  bone,  com- 
pleting the  zygomatic  arch. 

The  Superior  or  Orbital  Border  is  smooth  and  rounded,  and  presents 
in  outline  an  inverted  arch.  It  forms  a  large  portion  of  the  outer 
boundary  of  the  orbit. 

The  Inferior  or  Zygomatic  Border  extends  horizontally  backward  to 
the  zygomatic  process,  which,  together  with  the  lower  border  of  the 
zygomatic  process  of  the  temporal  bone,  forms  the  inferior  border  of 
the  zygomatic  arch.  This  border  is  roughened  for  the  origin  of  the 
masseter  muscle. 

The  Anterior  Border  is  continuous  with  the  articulating  surface  of 
the  maxillary  process.  The  elevator  muscle  of  the  upper  lip  (levator 
labii  superioris  proprius)  arises  just  above  the  suture  marking  this 
articulation,  its  point  of  origin  extending  slightly  on  to  the  external 
surface  of  the  bone. 

The  Posterior  or  Temporal  Border  is  thin  and  curved  somewhat  like 
an  italic  /.  It  faces  backward,  and  is  continuous  above  with  the  tem- 
poral ridge,  and  below  with  the  superior  border  of  the  zygomatic  arch. 
This  border  completes  the  circle  enclosing  the  temporal  region  which 
gives  attachment  to  the  temporal  muscle. 

The  Sphenoidcd  Border  extends  downward  and  inward  from  the 
frontal  process  to  the  non-articulating  notch,  when  it  exists,  at  the  l)ase 
of  the  great  wing  of  the  sphenoid  bone.  This  notch  forms  the  anterior 
boundary  of  the  spheno-maxillary  fissure.  Occasionally  the  malar 
bone  does  not  enter  into  the  formation  of  this  fissure.  When  this 
happens  it  is  prevented  from  so  doing  by  the  articulation  of  the  great 
wing  of  the  sphenoid  with  the  superior  maxilla,  or  by  a  small  Wor- 
mian bone.  This  border  is  serrated,  and  articulates  with  the  great 
wing  of  the  sphenoid. 


100 


ANATOMY 


Development. — The  malar  bone  is  developed  in  membrane  from 
two  points  of  ossification,  which  appear  abont  the  eighth  week  of 
embryonal  life,  uniting  about  the  fourth  month.  Occasionally  the  two 
portions  of  the  bone  remain  seimrate  throughout  life.  When  this  is 
the  case  the  bone  is  divided  into  an  upper  and  a  lower  portion  by  a 
horizontal  interspace,  the  upper  portion  being  the  larger. 

The  Inferior  Maxillary  Bone. 

The  importance  of  the  inferior  maxillary  bone,  mandible,  or  lower 
jaw  to  the  dentist  and  the  surgeon  cannot  be  over-estimated.  Its  posi- 
tion, composition,  and  development,  its  nerve-  and  blood-supply,  com- 
bine to  render  it  liable  to  various  and  grave  diseases.  In  order  that 
these  shall  be  thoroughly  understood  and  properly  treated,  a  detailed 
knowledge  of  its  anatomy  is  absolutely  necessary. 

The  inferior  maxilla  is  symmetrical  in  form,  and  is  situated  below 
the  alveolar  border  of  the  superior  maxilla,  beneath  the  zygomatic  and 
glenoid  fossre,  articulating  in  the  latter  cavity.  The  lower  border, 
extending  from  side  to  side,  forms  the  anterior  inferior  boundary  of 
the  face.  It  assists  in  forming  the  lateral  portions  of  the  outer  bound- 
aries of  the  zygomatic  fossae.  It  also  forms  the  greater  portion  of  the 
superior  boundary  of  the  surgical  squares  of  the  neck  and  the  digastric 
triangles. 

The  inferior  maxilla  is  the  largest,  heaviest,  and  strongest  bone  of  the 
head,  and  contains  one-half  the  teeth.     It  presents  for  examination  a 

Fig.  48. 


.V«-«/«Z       ,,^^_  ..^_        _„ 

/troc/xj    uf   ^4cp:■Lflal|■^•NV6.?"^:■:•;;.lUis'.•■*■■*  S 
»   &    DEp-'-ANculi....?.?.'---'   ^^f 

G foove  J'o>-  farinf  arty 
Inferior  Maxillary  Boue,  outer  surface,  side  view. 

body,  which  is  horizontal  in  direction,  and  two  rami,  which  extend 
almost  perpendicularly  upward  to  the  articulation  with  the  temporal 
bones. 


BONES.  101 

The  Body  or  Horizontal  Portion  of  the  bone  is  parabolic  in  form, 
the  anterior  portion  presenting  a  slight  vertical  ridge,  the  symphysis. 
This  symphysis  indicates  the  point  of  union  between  the  primitive 
halves  of  the  bone,  which  unite  shortly  after  birth.  The  body  is 
divided  into  two  surfaces,  external  and  internal ;  and  two  borders, 
superior  and  inferior. 

The  External  or  Facial  Surface  (Fig.  48).  The  vertical  ridge  in  the 
median  line  of  the  external  surface  extends  outward  and  forward  about 
halfway  between  the  upper  and  lower  borders  of  the  bone.  It  divides 
to  the  right  and  left  and  forms  a  triangular  process,  the  mental  process 
or  chin,  a  feature  exclusively  human. 

The  Incisor  Fossa. — Above  the  mental  process  and  below  the  incisor 
teetli  is  a  shallow  depression,  the  incisor  fossa.  This  fossa  gives  origin 
to  the  elevator  muscle  of  the  lower  lip  (levator  labii  inferioris).  At  the 
side,  a  little  below  the  incisor  fossa,  beneath  the  cuspid  (canine)  tooth,  is 
a  depression  for  the  origin  of  the  depressor  muscle  of  the  lower  lip 
(depressor  labii  inferioris). 

The  Mental  or  Anterior  Dental  Foramen  is  not  constant  in  its  position. 
When  the  teeth  are  imbedded  in  the  bone  it  is  generally  placed  midway 
between  the  superior  and  lower  borders  of  the  bone,  below  the  root  of 
the  second  bicuspid  tooth,  though  it  may  appear  as  far  back  as  the  first 
molar  or  as  far  forwaitl  as  the  first  bicuspid.  This  foramen  transmits 
the  mental  branches  of  the  inferior  dental  nerve  and  vessels. 

The  Exicrnal  Oblique  Line  commences  at  the  lateral  portion  of  the  men- 
tal process,  passes  backward  beneath  the  mental  foramen,  and  extends 
slightly  upward  and  backward  to  the  anterior  margin  of  the  ramus  of 
the  jaw.  That  portion  of  this  line  below  the  mental  foramen  gives  origin 
to  the  depressor  muscle  of  the  angle  of  the  mouth  (depressor  anguli  oris). 
Between  the  line  of  origin  of  this  muscle  and  the  inferior  border  of 
the  bone  is  a  roughened  surface  for  the  attachment  of  the  platysma 
myoides  muscle.  This  roughened  surface  divides  the  body  of  the  bone 
into  two  portions,  a  superior  alveolar  or  mucous  portion,  and  an  inferior 
basilar  or  non-mucous  portion. 

The  Superior  Alveolar  or  Mucous  Portion  is  situated  within  the  ves- 
tibule of  the  mouth,  and  is  covered  by  mucous  membrane  and  muco- 
periosteum.  It  gives  origin  to  the  buccinator  muscle  just  below  the 
three  molar  teeth. 

The  Inferior  Basilar  or  Non-Mucous  Portion  is  outside  and  below 
the  vestibule  of  the  mouth,  and  is  covered  with  periosteum  similar  to 
other  bones. 

The  Internal  Surface  (Fig,  49)  in  the  median  line  is  marked  by  a 
slight  vertical  depression  corresponding  to  the  symphysis  externally. 

The  Mi/lo-ht/oid  or  Internal  Oblique  Ridge  commences  at  the  base  of 
the  coronoid  process  and  extends  downward  and  forward  to  a  point 
just  below  the  genial  tubercles,  where  it  joins  the  ridge  of  the  ojipo- 
site  side.  This  ridge  is  but  faintly  marked  as  it  reaches  the  median 
line  of  the  bone ;  it  divides  the  internal  surf  ice  into  t^vo  portions,  a 
superior  and  inferior,  and  gives  origin  throughout  its  whole  extent  to 
the  raylo-hyoideus  muscle.  This  muscle  forms  the  floor  of  the  mouth. 
Between  the  posterior  portion  of  this  ridge  and  the  wisdom  tooth  the 


102 


ANATOMY 


buccinator  muscle  of  the  cheek  and  the  superior  constrictor  muscle  of 
the  pharynx  have  slight  attachments. 

The  Siq^erior  Portion  is  situated  within  the  mouth,  and  Ls  covered  by 
mucous  membrane  and  muco-periosteum. 

The  Inferior  Portion  is  all  that  surface  of  bone  below  the  mylo-hyoid 
ridge.  It  is  situated  below  the  floor  of  the  mouth,  and  is  covered  by 
periosteum. 

The  Genial  Tubercles  are  situated  at  the  lower  portion  of  the  median 
line  of  the  bone.  They  are  four  in  number,  two  on  each  side.  Occa- 
sionally, these  tubercles  are  indistinct,  and  sometimes  they  unite  and  form 

one  tubercle.    The  superior  pair  aflbrd 
Fig.  49.  origin  to  the  genio-hyo-glossi    mus- 

cles,  the    lower    pair   to    the   genio- 
hyoidei   muscles. 

The  Sublingual  Fossa  is  an  oval 
depression,  posterior  to  the  genial 
tubercle,  below  the  cuspid  teeth  and 
above  the  mylo-hyoid    ridge.     This 


.tV^.., 


CENtO-HYO-GLOSSUS 


CENIO-HYOIDEUS 


Mula-hyoid  Ridge 


B  o  dy 


Inferior  Slaxillary  Eone,  inner  surface,  side  view. 

fossa  supports  the  anterior  border  of  the  sublingual  gland.  It  is  wider 
behind  than  in  front. 

The  T)ir/astrio  Fossa  is  a  depression  for  the  insertion  of  the  digastric 
muscle.  It  is  situated  at  the  anterior  portion  of  the  internal  surface  of 
the  bone,  near  the  symphysis  and  tlie  lower  border  of  the  inferior  maxilla. 

The  Subinaxillart/  Fossa  is  an  oblong  depression,  wider  behind  than  in 
front,  situated  near  the  centre  of  the  internal  surface  and  between  the 
mvlo-hvoid  ridge  and  the  lower  border  of  the  bone.  In  it  rests  the 
external  surface  of  the  submaxillary  muco-salivary  gland. 

The  3Ij/lo-Jii/oi(J  (rroore  is  situated  beneath  the  mylo-hyoid  ridge,  com- 
mencing at  the  posterior  (inferior)  dental  canal.  This  groove  accommo- 
dates the  mylo-hyoid  nerve,  artery,  and  vein  as  they  pass  to  the  floor  of 
the  mouth. 

The  Superior  Border  of  the  bone  extends  from  the  ramus  of  one 
side  to  the  same  point  on  the  otlier.  It  is  situated  on  that  portion 
of  the  bone  analogous  to  the  alveolar  process  of  the  superior  maxilla. 


BONES.  103 

It  is  broader  behind  than  in  front,  and  is  marked  by  sixteen  pits  of 
various  shapes  for  the  accommodation  of  the  teeth.  The  pits  for  the 
central  incisors  are  the  smallest,  conical  in  shape,  and  compressed  later- 
ally. Those  for  the  lateral  incisors  are  somewhat  larger  and  not  (piite 
so  compressed.  The  cavities  for  the  cuspids  (canine  or  stomach)  teeth 
are  situated  at  the  angles  of  this  border,  are  larger  and  deeper  than 
those  for  the  incisors,  but  less  compressed  in  proportion  to  their  size. 
The  six  anterior  sockets  just  described  are  arranged  in  the  form  of  an  arc, 
while  those  for  the  remainder  of  the  teeth  extend  in  almost  a  straight 
line  posteriorly,  the  straightness  of  the  line  varying  with  the  tempera- 
ment of  the  individual.  The  sockets  for  the  bicuspid  teeth  are  variably 
compressed  and  occasionally  bifurcated,  though  it  is  exceptional  to  find 
a  double-rooted  inferior  Jbicuspid.  The  sockets  for  the  molar  teeth  are 
round  superiorly,  but  as  they  descend  soon  bifurcate  into  two  flattened 
cone-shaped  depressions.  Those  for  the  third  molar  or  wisdom  tooth, 
however,  vary  from  this  rule  just  as  their  roots  vary. 

The  Alveolar  Proces.^  is  very  similar  to  that  of  the  superior  maxilla 
before  described,  the  principal  point  of  difi'erence  being  in  the  external 
plate.  The  external  plate  of  the  superior  maxilla  is  thin  throughout 
the  entire  surface — so  much  so  that  the  roots  of  the  teeth  are  often  bared 
in  macerating  the  bone.  In  the  inferior  maxilla  the  external  plate  is 
thick  and  compact,  thus  rendering  the  lower  teeth  more  difficult  of 
extraction  than  those  in  the  upper  jaw.  After  extraction  the  external  plate 
of  the  superior  maxilla  is  absorbed  much  more  rapidly  and  to  a  greater 
extent  than  the  internal  plate,  while  with  the  external  and  internal  plates 
of  the  inferior  maxilla  the  rate  of  absorption  is  more  uniform. 

The  Inferior  Border  of  the  bone  extends  from  a  depression  at  the 
union  of  the  ramus  with  the  body  of  the  bone  to  the  same  point  ujjon 
the  opposite  side.  It  is  thick,  strong,  rounding,  and  composed  of  com- 
pact tissue.  The  depression  or  groove  at  the  union  of  the  ramus  at  the' 
base  of  the  bone  is  sometimes  called  "  the  facial  notch."  It  is  at  this 
point  that  the  facial  artery  passes  from  the  neck  to  the  face — an  import- 
ant fact  to  remember  when  the  parts  are  wounded  or  in  surgical  opera- 
tions on  the  face,  for  hemorrhage  can  generally  be  controlled  by  pressure 
at  this  point. 

The  Rami  or  Ascending  Portions  of  the  inferior  maxilla  arc  quad- 
rilateral in  shape  and  divided  into  two  surfaces,  external  and  internal ; 
f  jur  borders,  superior,  inferior,  anterior,  and  posterior ;  and  two  pro- 
cesses, the  condyloid  and  coronoid. 

The  External  Surface  is  nearly  flat.  It  is  slightly  roughened  near 
its  posterior  inferior  angle  for  the  insertion  of  the  masseter  muscle. 

The  Internal  Surface. — The  central  portion  is  marked  by  an  oblique 
opening,  the  posterior  or  inferior  dental  foramen.  Running  downward 
and  forward  from  the  lower  border  of  this  foramen  is  a  groove,  the 
mylo-hyoid,  already  described.  Posterior  to  this  groove,  extending  to 
the  angle  of  the  bone,  is  a  roughened  surface  for  the  insertion  of  the 
internal  pterygoid  muscle. 

The  Posterior  or  Inferior  Dental  Foramen  is  oval  in  shape;  a  sharp 
border  of  bone  extends  along  its  anterior  margin,  and  terminates  above  in 
a  spine  for  the  insertion  of  the  internal  lateral  ligament  of  the  lower  jaw. 


104  ANATOMY. 

The  Dented  Caned  extends  through  the  body  of  the  bone  from  the 
posterior  (inferior)  dental  foramen  to  the  anterior  (mental)  foramen. 
Its  course  is  at  first  downward  and  forward,  until  it  reaches  the  body 
of  the  bone,  through  which  it  runs  in  a  horizontal  direction,  finally 
passing  forward  and  opening  through  the  mental  foramen  on  the  outer 
surface  of  the  bone.  It  lies  beneath  the  alveolar  process,  and  communi- 
cates with  the  teeth  and  bony  tissue  through  small  canals.  Opposite 
the  mental  foramen  in  the  substance  of  the  bone  there  are  small  canals 
passing  forward  to  the  cuspid  and  incisor  teeth  and  the  symphysis  of  the 
chin.  The  posterior  (inferior)  dental  canal  and  its  branches  transmit 
the  inferior  dental  nerve,  artery,  and  vein. 

The  Superior  Border  of  the  Reimus. — Arising  from  this  anteriorly  is 
an  elevated  process  of  bone,  the  coronoid  process.  From  its  posterior 
portion  there  arises  a  rounded  eminence  of  bone,  the  condyloid  process, 
which  is  continuous  with  the  posterior  border  of  the  ramus. 

Tlie  Coronoid  Process  is  flat  and  pointed,  being  thinner  at  the  apex 
than  at  the  base.  The  anterior  border  is  a  continuation  of  the  external 
oblique  line.  This  border  bends  slightly  outward  as  it  ascends,  and 
terminates  in  the  apex  of  the  process.  Extending  downward  and  for- 
ward from  the  apex  of  this  process  on  its  internal  surface  is  a  curved 
ridge  of  bone  Mhich  joins  the  internal  oblique  line  just  posterior  to  the 
wisdom  tooth.  Between  the  anterior  border  and  this  rounded  ridge  of 
bone,  posterior  to  the  third  molar  tooth,  is  a  wide  groove  for  the  inser- 
tion of  a  part  of  the  temporal  muscle  above  and  the  buccinator  muscle 
below.  The  posterior  border  of  this  process  is  thin,  and  forms  the 
anterior  margin  of  the  sigmoid  notch.  The  outer  surface  of  this  process 
is  smooth,  and  affords  attachment  to  a  portion  of  the  temporal  and 
masseter  muscles.  The  inner  surface  is  rough,  and  gives  attachment  to 
the  temporal  muscle  sujieriorly. 

The  Condyloid  Process  is  shorter,  thicker,  and  more  massive  than 
the  coronoid.  It  is  continuous  with  the  posterior  or  free  border  of  the 
ramus.  As  this  border  extends  upward  it  widens,  until  it  forms  an 
articulating  surface  convex  in  outline.  Tlie  superior  surface  of  the 
condvloid  process  articulates  with  the  anterior  portion  of  the  glenoid 
fossa  of  the  temporal  bone.  This  surface  is  separated  from  the  glenoid 
fossa  by  interarticular  fibro-cartilage. 

The  Neck  is  that  constricted  portion  of  bone  immediately  below  the 
articulating  surface.  Just  internal  to  the  posterior  portion  of  the  supe- 
rior border  of  the  ramus  it  presents  a  depression,  the  pterygoid  fossa,  for 
the  insertion  of  the  greater  part  of  the  external  pterygoid  muscle.  At 
the  junction  of  the  nec^k  with  tlie  articulating  surface  of  the  bone 
externally  is  a  tubercle  for  the  insertion  of  the  external  lateral  ligament. 
Between  the  coronoid  and  condyloid  processes  is  situated  the  sigmoid 
notch.  The  border  of  this  notch  is  thin  and  crossed  by  tlie  masseteric 
artery  and  nerve  on  their  way  to  the  masseter  muscle. 

The  Inferior  Border  of  the  ramus  is  continuous  with  that  of  the  body 
of  the  l)one.  The  point  of  junction  l)etwecn  the  inferior  and  posterior 
borders  is  the  angle.  This  angle  extends  outwaixlly,  and  is  grooved 
and  roughened  for  the  insertion  of  part  of  the  superficial  portion  of  the 
masseter  muscle. 


BONES. 


105 


be 
It 


Fig.  50. 


The  Anterior  Border. — (For  description  see  Coronoid  Process.) 

The  Posterior  Border  at  its  upper  portion  is  smooth  and  rounding. 
As  it  approaches  the  angle  of  the  bone  it  is  roughened  for  the  insertion 
of  the  stylo-maxillary  ligament. 

Development. — The  inferior  maxilla  is  the  second  bone  developed, 
the  clavicle  being  the  first ;  it  is  developed  from  the  first  pair  of  what 
are  known  as  the  visceral  or  branchial  folds  or  arches  of  the  embryo, 
called  the  uTandibular  plates.  These  plates  from  the  twenty-fifth  to  the 
twenty-eighth  day  of  embryonal  life  advance  from  the  sides  of  the  base 
of  the  cranium  and  meet  in  the  median  line.  Soon  after  this  union 
the  cartilage  of  Meckel  appears  in  the  deeper  portion  of  the  mandibular 
plate.  In  mammals  the  proximal  end  of  this  cartilage  forms  the  mal- 
leus (one  of  the  small  bones  of  the  middle  ear),  and  its  distal  portion 
advances  along  the  mandibular  plate  until  it  meets  its  fellow  of  the 
opposite  side  at  the  symphysis  menti. 

INIeckel's  cartilage  (Fig,  50)  forms  in  great  measure  what  may 
termed  a  temporary  framework  for  the  support  of  the  lower  jaw. 
disappears  at  the  latter  part  of  the 
fifth  or  beginning  of  the  sixth  month 
of  foetal  life,  and  ossification  proceeds. 
About  the  fortieth  day  of  embry- 
onic life  ossification  commences  from 
several  centres  deposited  on  the  out- 
side, about  midway  between  the  prox- 
imal and  the  distal  extremities,  in  the 
membrane  which  partially  surround 
the  cartila";e  of  Meckel.  These  cen 
tres  speedily  unite.  Ossification  then 
proceeds  in  both  directions  along  the 
outer,  under,  and  inner  surface  of  the  cartilage,  but  doss  not  unite  with 
it.  About  the  sixtieth  day  a  miniature  jaw  is  formed,  a  siuall  portion 
of  the  body  at  the  symphysis  resulting  from  direct  ossification  of 
Meckel's  cartilage.  The  condyles  and  a  portion  of  the  rami  are  also 
ossified  from  other  cartilage.  From  the  centre  of  the  rami  internally 
Meckel's  cartilage  is  prolonged  backward  to  the  glenoid  fissure,  and 
thence  to  the  middle  ear.  That  portion  which  passes  between  the 
temporal  bone  and  the  inferior  maxilla 
becomes  surrounded  by  fibrous  tissue  and 
forms  the  internal  lateral  ligament  of  the 
jaw. 

At  birth  osseous  union  between  the  lat- 
eral halves  of  the  bone  has  not  taken  place, 
they  being  connected  by  fibro-cartilaginous 
tissue.  They  unite,  however,  during  the 
first  year,  ossification  commencing  below 
and  extending  upward,  a  trace  only  remain- 
ing at  the  upper  portion  at  the  beginning 
of  the  second  year.  The  body  of  the  bone 
is  shell-like,  open  at  the  top,  and  contains  the  germs  of  the  teeth.  The 
coronoid  processes  are  large  proportionately  to  the  remainder  of  the 


Internal  Face  of  the  Right  Maxilla  of  a 
Human  Embryo  of  about  Three  Months, 
showing  the  naturnl  size  atid  the  relative 
position  of  Meckel's  cartilage. 


Thp  Inferior  Maxilla  of  a  Foetus  at 
about  the  Full  Teriofl  of  Intra-uter- 
ine  Life.  The  two  sides  (o,  /))  are 
separate. 


Fig  52. 


Fig.  52.  Appearnnce  of  Lower  Jaw  with  Deciduous  Teeth. 
"     53.  Lower, law  willi  Peruianent  Teeth  in  position. 
"     54.  Partial  Absorption  of  Alveolar  Process. 
"     55.  Complete  Absorption  of  Process. 


lOt? 


BONES. 


107 


bone,  the  condyloid  processes  being  short  and  inclined  slightly  back- 
Avard.  The  rami  are  short,  and  but  slightly  deflected  upward  from  the 
axis  of  the  body  of  the  bone. 

After  birth  the  body  of  the  bone  becomes  elongated  (Fig.  52),  increas- 
ing backward  behind  the  anterior  (mental)  foramen  to  a  greater  extent 
than  it  does  in  front  of  it.  This  dilierence  is  to  giye  greater  space  for 
the  accommodation  of  the  permanent  molar  teeth. 

The  growth  of  the  body  of  the  bone  aboye  the  oblique  line  is  made 
up  principally  of  its  alyeolar  process,  which  sustains  the  teeth.  The 
growth  below  the  oblique  line,  both  in  extent  and  thickness,  .giyes 
strength  to  the  bone  and  space  for  the  attachment  of  muscles,  lodg- 
ment of  glands,  etc.  The  rami  and  condyles  of  the  bone  increase  in 
length,  and  the  angles  between  the  rami  and  the  body  of  the  bone 
become  less  obtuse ;  finally,  they  are  almost  at  right  angles  with  the 
body  (Fig.  53),  the  diiference  in  direction  being  due  to  the  gradual  sep- 
aration of  the  jaws  by  the  growth  of  the  teeth.  As  the  teeth  wear 
away,  the  jaws  approach  each  other  more  closely  again,  and  the  angles 
between  the  rami  and  the  body  of  the  bone  begin  to  reassume  their 

Fig.  56. 


Engraving  showing  Absorption  of  Alveolar  Process  in  upper  and  lower  jaw  after  loss  of  all  the 

tseth. 

former  shape  (Fig.  54).  AVhen  the  teeth  are  lost  by  decay  or  otherwise, 
the  alyeolar  process  is  absorbed  (Fig.  55),  the  depth  of  the  bone  thereby 
diminishes,  the  mental  foramen  being  nearly  on  a  level  with  the  supe- 
rior border  of  the  bone,  the  dental  canal  becoming  superficial.  The 
buccinator,  levator  labii  inferioris,  and  the  genio-glossus  muscles  ara 


108 


ANAT03IY. 


attached  just  below  the  superior  border  of  the  bone,  sometimes  extend- 
ing well  up  on  this  border — a  fact  which,  in  such  jaws,  interferes^  in 
a  measure  with  the  wearing  of  artificial  teeth.  The  endeavor  to  bring 
the  jaws  together  after  the  "teeth  and  alveolar  process  are  lost  causes  the 
angle  between  the  ramus  and  body  of  the  bone  to  assume  almost  the 
same  obtuse  form  as  at  birth  (Fig.  56).  The  employment  of  artificial 
teeth  immediately  after  the  loss  of  the  natural  ones  delays  to  a  certain 
extent  this  change  of  form. 


The  Hyoid  Bone. 
The  hyoid  bone  (Fig.  57),  or  os  linguae,  is  symmetrical  in  outline.    It 

Fig.  57. 
Greater  Cornu. 

Middle  Constrictor  of  Pharynx., 


Thyrohyoid, 
tylo-hyoid. 


Onio-hyoid. 
^Mylo-hyoid. 
Gcnio-hyoid.  Sterno-hyoid. 

Hyoid  Bone,  anterior  surface  (enlarged). 

is  situated  in  the  median  line  of  the  upper  part  of  the  neck,  at  the 
base  of  the  tongue,  and  above  the  larynx.  It  is  so  superficially 
placed  that  ordinarily  the  outlines  of  the  bone  can  be  traced  beneath 
the  skin  below  the  chin.  It  is  a  floating  bone,  having  no  osseous 
articulation.  In  form  it  is  U-shaped,  the  convexity  of  the  U  being 
directed  forward  and  its  concavity  backward.  It  is  divided  into  a 
body  and  four  processes  called  horns  or  cornua,  two  on  each  side. 

The  Body  or  Central  Port  ion  (basihyal)  of  the  bone  is  quadrilateral 
in  form.  It  is  compres.sed  from  before  backward,  the  anterior  surface 
being  convex  and  marked  in  the  median  line  by  a  vertical  ridge.  On 
each  side  of  this  ridge  are  eminences  and  depressions  for  tlie  attachment 
of  the  genio-hyoid  nuisclcs.  Below  these  the  two  mylo-hyoid,  the  two 
stylo-hyoid,  and  the  aponeuroses  of  the  digastric  muscles  are  inserted. 
Between  the  surfaces  for  the  attachment  of  these  muscles  are  inserted 
portions  of  the  two  hyo-glossus  muscles. 

The  Poslenor  Surface  is  smooth  and  deeply  concave.  It  is  directed 
backward  and  downward  toward  tlie  epiglottis.  The  space  between 
this  surface  and  the  epiglottis  is  filled  by  loose  areolar  tissue. 

The  Superior  Border  is  thin,  rounding,  and  continuous  with  the 
inner  margin  of  the  great  cornua.  It  gives  attachment  to  the  thyro- 
hyoid membrane. 


BONES.  109 

The  Inferior  Border  is  thicker  than  the  superior,  and  gives  attach- 
ment to  the  sterno-hyoid  muscles  anteriorly  and  the  thyro-hyoid  muscles 
posteriorly.  The  omo-hyoid  muscles  are  attached  at  the  junction  of 
the  body  with  the  great  cornua. 

The  Great  Coniua  (thyrohyals)  project  backward  from  the  body  of 
the  bone  on  each  side.  They  are  compressed  from  above  downward, 
the  ends  being  rounded  for  the  attachment  of  the  thyro-hyoid  ligaments. 
Their  outer  surfaces  give  attachment  to  the  hyo-glossus  muscles.  The 
superior  borders  of  these  horns  give  attachment  to  the  superior  con- 
strictor of  the  pharynx,  while  on  their  inferior  borders  are  inserted  the 
thyro-hyoid  muscles. 

The  Lesser  Cornua  (ceratohyals)  are  short  and  conical ;  they  accom- 
pany the  great  cornua,  and  project  upward  and  backward  from  the 
body  of  the  bone.  Their  extremities  give  attachment  to  the  stylo- 
hyoid ligaments. 

Development. — The  hyoid  bone  is  developed  from  the  second  pair 
of  visceral  arches,  and  ossified  from  five  centres  of  deposit — one  for  the 
body  and  one  for  each  of  the  cornua.  The  first  centres  for  the  body  and 
the  great  cornua  are  deposited  during  the  last  period  of  foetal  life,  those 
for  the  lesser  cornua  not  appearing  until  the  first  year.  Ossific  unions 
between  the  greater  cornua  and  the  body  of  the  bone  take  place  during 
middle  life,  while  unions  between  the  lesser  cornua  and  the  body  do  not 
take  place  until  advanced  age.  Occasionally  the  stylo-hyoid  ligaments 
are  partially  ossified. 

The  Skull  as  a  Whole. 

The  study  of  the  skull  as  a  whole  includes  a  consideration  of  all  the 
bones  of  the  head  and  face  articulated,  described  under  three  heads : 
I.  General  Development ;  II.  Articulation ;  III.  Regional  Anatomy. 

GENERAL   DEVELOPMENT. 

The  entire  bony  structure  of  the  head  is  developed  from  the  meso- 
blastic  layer  of  the  embryo.  The  axis  around  which  the  first  parts  of 
the  foetus  are  formed  is  called  the  notochord  or  chorda  clorsalis.  The 
anterior  or  superior  portion  of  this  chord  extends  forward  into  the 
mass  of  tissue  which  forms  the  principal  matrix  of  the  future  bony 
walls  of  the  base  of  the  brain-case,  and  terminates  at  the  posterior 
border  of  the  pituitary  fossa,  its  extreme  anterior  portion  forming  the 
dorsum  sellse  of  the  sphenoid  bone. 

From  the  anterior  portion  of  the  dorslim  sellse,  in  close  proximity 
to  the  posterior  clinoid  ])rocesses,  two  cartilaginous  rudiments  (known 
as  the  trabeculse  cranii  of  Rt)thke)  are  thrown  out  and  pass  forward, 
uniting  in  front  of  the  olfactory  depressions.  As  these  rudiments  pass 
forward  they  unite  and  separate  from  each  other  at  intervals,  enclosing 
small  interspaces  between  them.  The  nasal  cartilage  is  developed 
directly  from  these  trabecule  at  or  near  their  union  in  front  of  the  ollhc- 
tory  fossse. 

This  axis,  or  line  of  origin,  at  the  base  of  the  brain-case  is  divided 
into  two  portions,  anterior  and  posterior. 


110  ANATOMY. 

The  Anterior  Portion,  or  splieno-ethmoid  portion,  forms  in  front  of 
the  notoehord,  along  the  trabeculee  cranii,  and  includes  the  matrix  of 
the  presphenoid  and  the  septal-ethmoid  cartilage.  It  extends  forward 
to  the  anterior  portion  of  the  nasal  cartilage  and  the  aperture  for  the 
external  nose. 

Behind  the  nasal  cartilage  the  trabeculse  cranii  unite  to  form  the 
etlimo- vomerine  cartilage,  which  forms  part  of  the  nasal  septum.  Later- 
ally, the  presphenoid  cartilage,  the  matrix  of  the  orbito-sphenoid,  the 
lesser  wings  of  the  sphenoid  bone,  and  the  optic  foramen  are  developed. 

The  Posterior  Portion,  or  occipito-sphenoid  portion,  is  formed  from 
that  part  of  the  notoehord  situated  behind  the  pituitary  fossa,  and,  in 
conjunction  with  the  surrounding  tissue,  contains  the  matrix  of  the  basi- 
sphenoidal  cartilages.  This  portion  also  extends  laterally,  and  forms 
the  matrix  of  the  exoccipital  and  periotic  mass  of  cartilage  which  sur- 
rounds the  primary  auditory  vesicles. 

The  greater  part  of  the  occipito-sphenoid  portion  prolongs  forward, 
and  extends  below  the  posterior  and  middle  primary  encephalic  vesicles, 
and  the  matrix  for  the  great  wing  of  the  sphenoid  process  derived  from 
the  basisphenoid. 

It  will  thus  be  seen  that  the  base  of  the  brain-case,  extending  to  the 
most  anterior  portion  of  the  cartilage  of  the  nose,  is  a  foundation  of 
cartilaginous  tissue,  and  all  the  bones — speaking  of  them  as  they  are 
divided  by  the  comparative  anatomist — arising  immediately  from  this 
foundation  to  form  the  base  of  the  brain-case  are  cartilaginous  bones. 
The  remainder  of  the  bones  of  the  brain-case,  or  those  formed  on  each 
side  of  the  chorda  dorsalis  and  trabeculae  cranii,  such  as  the  interpari- 
etals and  squamo-zygomatics,  are  developed  in  membrane.  These  mem- 
branous bones  are  claimed  by  Kolliker  to  be  of  dermal  origin  ijnd  to 
belong  to  the  group  of  investing  bones. 

The  facial  bones,  except  the  inferior  turbinated,  are  developed  in 
membrane,  similarly  to  the  tabular  bones  of  the  head ;  and  as  the  mem- 
branous bones  of  the  cranial  vault  articulate  with  the  cartilaginous 
bones  which  form  the  base  of  the  brain-ease,  so  all  the  membranous 
bones  of  the  face  articulate  from  below  with  this  same  cartilaginous 
foundation.  The  inferior  maxilla  would  seem  to  be  an  exception  to 
this  membro-cartilaginous  articulation  ;  but  in  the  early  stages  of  its 
development  it  is  connected,  through  the  cartilage  of  Meckel,  with  the 
periotic  bones. 

The  Face. — The  bones  of  the  brain-case,  formed  from  the  notoehord 
and  trabeculte,  are  in  an  advanced  state  of  development  before  the 
facial  bones  commence  to  be  built.  To  such  an  extent  is  this  the  fact 
that  the  dermoid  structure  (the  skin)  lies  almost  in  contact  with  all 
that  portion  of  the  head  below  and  anterior  to  the  notoehord,  and 
there  is  at  this  time  no  opening  to  the  upper  portion  of  the  aliment- 
ary canal. 

The  facial  bones  arise  from  the  under  surface  of  the  base  of  the 
brain-case  from  certain  ]n'ocesses,  and  push  outward  and  downward, 
leaving  a  layer  of  dermoid  tissue  on  their  inner  as  well  as  their  outer 
surfaces.  This  dermoid  tissue  becomes  the  mucous  or  epidermoid 
(epiblastic)  lining  of  the  mouth,  nasal  cavities,  and  all  the  internal  sur- 


BO^^ES.  111 

faces  of  the  face,  excepting  the  tympanum  and  Eustachian  tubes.  These 
tubes  are  Hned  with  hypoblastic  tissue  similar  to  that  which  lines  the 
alimentary  canal. ^ 

The  processes  in  front  which  push  downward  and  forward  are  called 
the  fronto-nasal ;  those  on  the  side,  the  maxillary  and  mandibular. 
Those  which  are  situated  deeply  within  the  face  are  known  as  the 
spheno-ethmo  prolongations  of  the  trabeculse  cranii. 

The  changes  that  occur  during  the  formative  process  are  complex  : 
they  produce  the  external  nose,  the  lips,  and  the  cheeks ;  the  mouth, 
including  the  upper  and  lower  jaws,  the  hard  and  soft  palate ;  the  nasal 
chambers  ;  the  orbits  ;  the  labyrinths  ;  the  external  auditory  meatus  and 
tympano-Eustachian  tubes ;  the  different  air-sinuses,  such  as  the  eth- 
moidal, spheno-maxillary,  and  frontal  cells.  This  explains  how  it  is 
that  all  the  facial  bones  proper,  excepting  the  malar,  are  lined  by 
mucous  membrane.  (The  special  development  of  each  bone  is  described 
under  the  head  General  Anatomy.) 

ARTICULATIONS. 

When  two  or  more  bones  are  united  together,  this  union  is  called  a 
joint  or  articulation.  There  are  three  varieties  of  articulation  in  the 
head — viz.  sutura,  synchondroses,  and  diarthroses. 

The  Sutura  are  those  articulations  which  exist  between  the  inter- 
membranous  bones  and  also  between  the  intermembranous  and  inter- 
cartilaginous  bones  of  the  head.  This  articulation  jiermits  of  but  slight 
or  no  appreciable  movement.  The  bones  forming  this  variety  of  articu- 
lation are  separated  from  each  other  by  a  thin  layer  of  membrane,  that 
on  the  outer  surface  of  the  joint  being  derived  from  the  pericranium, 
and  that  on  the  inside  from  the  dura  mater. 

There  are  four  kinds  of  sutures — viz.  harmonic,  squamosa,  dentata, 
and  serrata. 

The  Harmonic  sutures  are  those  that  have  comparatively  smooth 
articulating  surfaces  or  borders.  Examj^les,  the  articulation  between 
the  palate  process  of  the  superior  maxilla  and  the  palate  bones,  also 
the  internal  surfaces  of  the  articulations  of  the  cranial  vault. 

The  Squamosa  (squama,  a  scale)  are  those  in  which  the  opposing 
surfaces  of  bone  are  bevelled,  overlapping  each  other  like  the  scales  of 
a  fish.  Examples,  the  temporo-parietal  and  the  temporo-sphenoidal 
articulations. 

The  Dentata  {dens,  a  tooth)  are  those  in  which  the  articulating  bor- 
ders of  the  bones  are  severally  armed  with  numerous  tooth-like  pro- 
jections fitting  into  corresponding  indentations.  Example,  the  suture 
between  the  two  parietal  bones. 

The  Serrata  (serra,  a  sa^v)  are  those  in  which  the  articulating  borders 
of  the  bones  are  marked  like  the  teeth  of  a  saw.  Example,  the  suture 
between  the  two  halves  of  the  frontal  bone. 

The  dentation  and  serration  of  the  borders  of  the  bones  of  the  brain- 
case  are  not  marked  internally,  the  under  surface  of  the  dome  of  the 
skull  being  smooth.     On  the "  internal  surface,  therefore,  these  sutures 

^  Quain's  Anatomy. 


112  ANATOMY. 

would  be  called  harmonic,  no  matter  under  what  head  they  might  be 
classed  externally. 

The  Syxchondeoses  are  almost  immovable  articulations.  A  thin 
layer  of  cartilage  intervenes  between  the  intercartilaginous  bones  which 
go  to  form  this  articulation,  uniting  them  together.  It  is  found  between 
the  epiphyses  and  shafts  of  long  bones.  Examples,  the  occipito-sphe- 
noidal  articulation  and  the  articulations  of  the  liyoid  bone  at  the  cornua. 

The  Diarthroses. — The  greater  number  of  the  joints  of  the  body 
are  of  this  variety.  These  articulations  have  extensive  movement,  such 
as  is  seen  in  the  elbow,  knee,  shoulder,  hip,  and  temporo-maxillary 
joints.  The  articulating  surfaces  of  these  bones  are  either  convex  or 
concave,  and  covered  by  a  thin  layer  of  cartilage,  forming  a  smooth 
articulating  extremity.  Synovial  cavities  also  exist  between  the  ex- 
tremities of  the  bones  forming  these  joints,  which  are  further  lubricated 
by  a  synovial  fluid  secreted  by  a  delicate  membrane  lining  all  the  inter- 
nal portions  of  the  joints  excepting  the  cartilaginous,  though  it  invests 
the  borders  of  the  cartilages  interp(jsed  between  the  joints  and  assists  in 
holding  the  bones  in  apposition.  In  some  joints  interarticular  discs  of 
iibro-cartilage  are  placed  between  the  articulating  surfaces  of  bones 
composing  them,  these  discs  dividing  the  space  into  two  compartments 
of  dissimilar  size.  An  example  of  this  is  seen  in  the  temporo-maxil- 
lary articulation. 

Articulating  surfaces  are  also  often  marked  by  irregular  facets,  so  that 
when  the  bones  are  at  diiferent  degrees  of  flexion  and  extension  in  the 
joint-cavity  there  is  a  special  articulating  point  for  that  particular  posi- 
tion. The  opposing  surfaces  of  bones  forming  these  joints  are  held  in 
apposition  by  fibrous  tissue  of  various  shapes  as  well  as  by  synovial 
membrane.  This  fibrous  tissue  receives  its  name  according  to  its 
relation  with  the  joint.  For  example,  the  crucial  ligaments  of  the 
knee  receive  their  name  because  they  cross  each  other  (obliquely),  while 
the  capsular  ligaments  of  joints  are  so  named  because  they  surround  the 
joints. 

Tlie  diartlirodial  articulation  is  variously  subdivided.  Gray  speaks 
of  f  )ur  divisions — viz.  Arthr(xlia,  Enarthrodia,  Ginglymus,  and  Diar- 
thnxlia  Rotatoria ;  while  Allen  recognizes  five  divisions — the  Arthro- 
dial,  Spherical,  Cylindrical,  Conical,  and  Composite.  Here  it  will  be 
necessary  only  to  describe  the  combination  of  these  subdivisions  which 
covers  the  movements  of  the  temporo-maxillary  joint. 

The  T('iiijjoro-in(fxi//fin/  Articulation.'^  are  formed  by  the  union  of  the 
condyloid  processes  of  the  inferior  maxilla  with  the  anterior  porticms  of 
the  glenoid  fossfe  of  the  temporal  bones,  the  glenoid  fissures  being  imme- 
diately behind  the  condyles,  while  the  eminentise  articularise  are  in 
front. 

Gray  descrilx>s  the  arthrodial  as  "that  form  of  joint  which  admits  of 
a  gliding  movement,  ....  the  amount  of  nioticm  between  them  being 
limited  by  the  ligaDicnts  or  osseous  processes  surrounding  the  articula- 
tion, as  in  the  articular  processes  of  the  vertebrae,  the  temporo-maxillary, 
sterno-clavicular,  and  acromio-clavicular,"  etc.  etc. 

Allen  describes  the  ginglymus  or  hinge-joint,  which  is  a  subdivision 
of  the  cylindrical  division  of  diarthrotic  joints,  as  the  ''  best  expression 


BONES. 


113 


of  a  cylindroid  joint.  The  axis  of  rotation  is  perpendicular  to  the  axis 
of  the  moving  bone,  or,  as  in  the  case  of  the  elbow,  the  axis  of  two 
bones,  the  radius  and  ulna,  since  both  of  these  describe  curvations 
around  the  axis  of  rotation.  The  paths  of  movement  of  the  hinge- 
joint  are  free  within  certain  limits.  These  degrees  of  freedom  are  of 
necessity  fixed  by  the  direction  of  the  greatest  convexity.  The  co-opera- 
tion of  the  surfaces  is  exact." 

In  man  the  temporo-maxillary  articulation  presents  a  combination 
of  these  movements.  In  the  Carnivora,  however,  this  joint  has  no 
gliding  movement,  as  the  condyle  is  a  half  cylinder  working  in  a  deep 
glenoid  fossa  of  corresponding  form,  which  only  allows  an  up-and-down 
or  hinge  movement.  In  ruminants  the  condyles  of  the  inferior  maxillse 
are  only  slightly  convex,  and  the  glenoid  fossae  of  the  temporal  bones 
but  slightly  concave.  This  arrangement  allows  great  latitude  of  motion, 
and  the  joint  is  a  combination  of  the  arthrodial  and  of  the  hinge,  as  it 
likewise  is  in  man. 

The  gliding  movement  of  this  joint  in  man,  characteristic  of  the 
arthrodial  articulation,  has  an  important  bearing  in  the  adjustment  of 
artificial  teeth.  If  the  condyles  of  the  inferior  maxilla  are  carried 
well  up  into  the  glenoid  fossae  when  the  mouth  is  closed,  the  jaws  or 
their  teeth  will  be  in  proper  apposition  to  each  other. 

The  structures  connected  with  the  temporo-maxillary  articulation  are 
generally  described  as  five  ligaments  and  two  synovial  sacs.     The  liga- 

FxG.  58. 


Temporo-maxillary  Articulation,  internal  view. 


ments  are  the  capsular,  external  and  internal  lateral,  stylo-maxillary, 
and  an  interarticular  fibro-cartilage.  The  capsular  and  external  lateral 
will  be  described  as  one  ligament,  while  the  internal  lateral  and  stylo- 


VoL.  I.— 8 


114 


ANA  TOMY 


maxillary,  not  being  in  direct  connection  with  the  joint,  will  be 
described  as  accessory  ligaments  to  the  articulation  (Fig.  58). 

The  Capsular  Ligaments  of  the  temporo-maxillary  articulation  is  an 
exceedingly  loose  fibrous  bag.  It  is  thin  in  front  and  on  the  inner  side, 
being  thick  and  strong  behind  and  on  the  outer  side.  It  is  attached 
above  to  the  articulating  circumference  of  the  glenoid  fossa,  and  below 
it  encircles  the  neck  of  the  condyle  of  the  inferior  maxilla.  The  most 
superficial  fibres  of  this  ligament  extend  downward  and  backward  from 
the  outer  surface  and  tubenslc  at  the  anterior  root  of  the  zygoma  to  the 
outer  surface  and  posterior  border  of  the  neck  of  the  inferior  maxilla. 
This  portion  is  generally  spoken  of  as  the  external  lateral  ligament  of 
the  articulation. 

The  structures  found  within  this  joint  (Fig.  59)  are  the  interarticular 
disc  of  cartilage  and  the  synovial  sacs. 

Ym.  59. 


Vertical  Sectiou  of  Temporo-maxillary  Articulation. 

The  Interarticular  Dhic  of  Fibro-cartilage  is  a  thin  jilate  of  cartilag- 
inous tissue  situated  between  the  articulating  bones.  It  is  elliptical  in 
form,  its  broadest  diameter  being  transverse.  Its  lower  surface  is  con- 
cave for  the  accommodation  of  the  condyle  of  the  jaw,  its  upper  surface 
being  concave  in  front,  where  it  passes  under  the  articular  eminence, 
and  thick  and  convex  behind,  where  it  adapts  itself  to  the  deeper  por- 
tion of  the  glenoid  fossa.  Its  circumference  affords  attachment  to  the 
common  capsular  ligament,  while  its  anterior  portion  gives  insertion  to 
part  of  the  tendon  of  the  external  pterygoid  muscle.  Its  surfaces  are 
smooth  and  divide  the  articulating  cavity  into  two  unequal  pockets. 
Sometimes  an  opening  will  be  fi)und  in  the  centre  of  this  cartilage  which 
allows  communication  between  the  chambers.  When  this  is  the  case 
the  synovial  sacs  are  continuous  with  each  other. 

The  Synovial  Sacs  are  two  pouches  which  secrete  the  fluid  for 
lubricating  the  joint.  They  are  situated  one  above  the  other  below  the 
interarticular  disc  of  cartilage. 

The  Superior  Synovial  S((e  is  the  larger  and  freer  of  the  two.  It 
begins  at  the  margin  of  the  disc,  and  passes  over  the  eminentia 
articularis,  the  roof  of  the  glenoid  fossa,  and  the  upper  surface  of  the 
cartilage. 


BONES.  115 

The  Inferior  Synovial  Sac  is  situated  betM'een  the  cartilage  and  the 
condyle..  It  extends  on  the  condyle  posteriorly  to  a  greater  extent  than 
it  does  anteriorly. 

The  Internal  Lateral  Ligament  is  not  directly  connected  with  the 
temporo-maxillary  articulation,  but  acts  as  an  accessory  ligament  to  the 
joint.  It  is  a  fascia-like  band  extending  from  the  spinous  process  of 
the  sphenoid  bone;  becoming  broader  as  it  descends,  it  is  inserted  into  a 
triangular  process  of  bone  on  the  anterior  border  of  the  posterior  dental 
foramen.  The  external  pterygoid  muscle  crosses  the  superior  portion 
of  this  ligament  externally,  the  internal  maxillary  artery  and  the  infe- 
rior dental  vessels  and  nerve  passing  lower  down  between  the  ligament 
and  the  bone. 

The  Stylo-maxillary  Ligament  is  the  other  accessory  ligament  of  the 
temporo-maxillary  articulation.  It  is  a  strong  fibrous  band  connected 
with  the  deep  cervical  fascia,  extending  from  a  point  in  close  proximity 
to  the  apex  of  the  styloid  process  of  the  temporal  bone  to  the  inferior 
portion  of  the  posterior  border  of  the  ramus  of  the  jaw,  where  it  is 
inserted  between  the  masseter  muscle  externally  and  the  internal  ptery- 
goid muscle  internally.  The  stylo-maxillary  ligament  divides  the 
parotid  from  the  submaxillary  region,  and  is  connected  by  fasciculi 
with  the  stylo-glossus  muscle. 

The  movements  permitted  by  the  temporo-maxillaiy  articulation  are 
more  varied  and  of  greater  number  than  those  of  any  joint  in  the  body. 
The  jaw  has  the  power  of  extension  and  retraction ;  it  can  be  depressed 
and  elevated,  moved  from  side  to  side,  and  combines  all  the  movements 
intermediate  between  these,  thus  allowing  the  gliding  motion  necessary 
to  mastication.  The  interarticular  hbro-cartilage  assists  in  these  varied 
movements  and  acts  as  a  multiplier  of  them.  The  superior  surface. of 
this  cartilage  glides  forward  on  to  the  articidar  eminence  of  the  anterior 
root  of  the  zygoma,  while  the  condyle  of  the  inferior  maxilla  rotates 
on  a  transverse  axis  in  the  concavity  of  the  inferior  surface  of  this 
cartilage.  When  the  mouth  is  widely  opened  the  cartilages  of  each 
articulation  move  forward  on  to  the  articular  eminence,  the  condyles 
being  carried  upward  on  the  lower  surfaces  of  these  cartilages.  If  the 
inferior  maxilla  is  drawn  forward,  so  that  the  lower  incisor  teeth  are  in 
advance  of  the  upper  ones,  the  action  of  this  articulation  is  restricted 
to  a  gliding  of  the  superior  surface  of  the  interarticular  cartilage  over 
the  anterior  root  of  the  zygoma. 

If  the  lower  jaw  is  too  much  depressed,  as  is  sometimes  the  case  in 
"yawning,  vomiting,  the  extraction  of  the  teeth,  or  as  the  result  of  blows, 
dislocation  will  follow.  This  luxation  is  caused  by  the  interarticular 
cartilage  being  carried  forward  to  the  eminence  on  one  or  both  sides, 
or  by  one  of  the  condyles  of  the  inferior  maxilla  breaking  through  the 
anterior  portions  of  the  capsular  ligament,  its  weakest  point,  and  lodg- 
ing in  the  zygomatic  fossa. 

Sutures. 

The  bones  of  the  skull,  ^vith  the  exception  of  the  inferior  maxilla  and 
temporal  bones  and  the  cartilaginous  bones  at  the  base  of  the  skull,  are 


116 


ANATOMY. 


closely  united  through  borders  more  or  less  uneven.  This  variety  of 
union  is  called  a  suture,  and  those  occurring  in  the  head  may  be  sepa- 
rated into  four  divisions — viz.  those  of  the  cranial  vault,  those  of  the 


Fig.  60. 


FtouIo I 


Side  View  of  Skull. 

lateral  portions  of  the  cranium,  those  of  the  face,  and  those  of  the  occi- 
put (Fig.  00). 

In  des('ril)ing  sutures  the  names  of  the  bones  forming  them  should 
always  be  used. 

SiTTUiiES  OF  THE  Craxial  Vai'I^t. — Tliosc  between  the  bones 
forming  the  cranial  vault  are  three  in  number. 

I.  The  I))fevparietaJ  or  Snrjiffal  Suture  is  between  the  two  parietal  bones, 
extending  from  the  frontal  bone  to  the  .><U])erior  angle  of  the  occipital 
bone.  In  childhood,  and  occasionally  in  adult  life,  ossification  between 
the  two  halves  of  the  frontal  bone  is  not  ('onii)leted  in  the  median  line. 
This  causes  the  formation  of  a  frontal  sutiu'c,  and  a  continuation  of  the 
sagittal  suture  from  the  sujierior  angle  of  the  occipital  bone  posteriorly 
to  the  nasal  bones  anteriorly.     On  either  side  of  the  suture  posteriorly 


BOXES.  117 

the  parietal  foramen  or  foramina  are  located,  and  Wormian  bones  of 
large  size  are  often  found  within  the  suture. 

II.  The  Fronto-parietal  or  Coronal  t'^uture  is  between  the  frontal  and 
parietal  bones,  extending  across  the  anterior  portion  of  the  cranial  vault 
from  the  superior  extremity  of  the  great  wing  of  the  sphenoid  bone  on 
one  side  to  the  same  point  on  the  other. 

III.  The  Occipito-parietal  or  Lmnbdoid  Suture  is  between  the  occipital 
and  parietal  bones,  extending  from  the  mastoid  portion  of  the  temporal 
bone  on  one  side  upward  to  the  interparietal  suture,  and  thence  down- 
ward to  the  mastt)id  portion  of  the  temporal  bone  of  the  other.  Wor- 
mian bones  are  more  numerous  within  this  than  the  other  sutures. 

The  Sutures  of  the  Lateral  Portions  of  the  Cranial 
Vault  are  six  in  number,  without  referring  to  the  parieto-li'ontal 
and  the  parieto-occipital  articulation  where  they  come  within  these 
regions. 

The  Fronto-malar  tSuture,  describing  this  region  from  its  anterior  to 
its  posterior  boundary,  is  lietween  the  external  angular  process  of  the 
frontal  bone  and  the  frontal  j^rocess  of  the  malar  bone. 

The  Fronto-splienoklcd  Suture  is  within  the  temporal  fossa,  where  the 
frontal  bone  articulates  with  the  great  wing  of  the  sphenoid  bone.  This 
articulation  forms  the  second  suture. 

The  Spheno-maJar  Suture  is  the  third  ;  it  also  is  within  the  temporal 
fossa,  and  is  formed  by  articulation  of  the  malar  bone  with  the  anterior 
border  of  the  great  wing  of  the  sphenoid  bone. 

The  Farieto-sphenoid  is  the  fourth,  and  is  found  between  the  parietal 
bone  and  the  tip  of  the  great  wing  of  the  sphenoid  bone.  In  some  rare 
cases  the  parietal  bone  does  not  articulate  with  the  sphenoid  at  this 
point ;  the  frontal  bone  then  articulates  directly  with  the  squamous  por- 
tion of  the  temporal  bone. 

The  Farieto-squamous  Suture,  the  fifth,  is  formed  by  the  articula- 
tion of  the  parietal  bone  with  the  squamous  portion  of  the  temporal 
bone. 

The  Farieto-mastoid  Sidure  is  the  sixth,  and  is  formed  by  the  artic- 
ulation of  the  parietal  bone  with  the  mastoid  portion  of  the  temporal 
bone. 

The  Sutures  of  the  Face. — In  the  face  the  frontal  bone  assists 
in  forming  several  sutures.  These  likewise  receive  their  names  from 
the  bones  that  form  them,  as  the  fronto-sphenoid,  fronto-ethmoid,  fronto- 
lachrymal,  fronto-maxillary,  and  fronto-nasal.  This  rule  for  naming 
sutures  is  carried  out  in  describing  the  articulations  betw^een  the  other 
bones  of  the  face. 

The  Articulations  of  the  Occiput  are  those  between  the  occipital 
bone  and  the  posterior  inferior  angle  of  the  parietal  bone,  and  of  the 
occipital  bone  and  mastoid  portion  of  the  temporal  bone. 

The  articulations  between  the  bones  at  the  base  of  the  brain-case  are 
the  occipito-sphenoid,  occipito-temporal,  and  the  temporo-sphenoid.  In 
early  life  a  thin  layer  of  cartilage  is  inter})osed  between  these  bones, 
which  at  adult  age  becomes  ossified.  These  articulations,  therefore,  are 
of  the  synchondroidal  variety. 


118  Ay  ATOMY. 

The  Skull  and  its  Articulations  at  Different  Periods  op 

Life. 

About  the  second  month  of  embryonal  life  the  brain-case  is  divided 
into  two  almost  equal  compartments  by  the  tentorium  cerebelli,  which 
at  this  period  extends  almost  perpendicularly  from  its  anterior  attach- 
ment within  the  skull.  This  division  shows  the  posterior  or  cerebellar 
portion  of  the  encephalon  at  this  period  to  be  larger  in  proportion  to 
the  anterior  or  cerebral  than  in  the  adult.  Shortly  after  the  second 
month  the  rapid  growth  of  the  parietal  bones  causes  the  occipital  por- 
tion of  the  cranium  to  be  pushed  backward.  By  the  final  enlargement 
of  the  frontal  bones  the  anterior  or  cerebral  fossae  are  completed. 

At  birth  the  parietal  bones  are  large  in  proportion  to  the  other  bones 
of  the  head,  and  their  centres  of  ossification  are  extremely  prominent. 
The  frontal  eminences  and  the  occipital  protuberance  are  also  noticeably 
convex. 

During  the  first  year,  to  accommodate  the  enlarging  brain,  the  dome 
of  the  case  grows  with  greater  rapidity  than  the  base,  the  upper  portion 
of  the  frontal  bone  developing  to  a  greater  extent  than  the  orbital  ])or- 
tion,  which  causes  the  prominence  of  the  forehead  peculiar  to  children 
at  this  age.  At  this  period  the  facial  bones  occupy  but  about  one-eighth 
of  the  entire  skull,  while  at  adult  life  they  form  almost  one-half  The 
external  auditory  meatus  and  the  alveolar  processes  are  but  partially 
developed,  and  only  the  anterior  deciduous  teeth  are  erupted.  The 
sutures  are  more  or  less  open,  while  the  dilferent  parts  of  the  bones 
formed  by  separate  centres  of  ossification  in  many  instances  are  not 
united. 

During  the  first  year  the  sutures  of  the  cranial  vault  are  generally  so 
widely  open  that  the  border  of  one  bone  can  be  made  to  overlap  that 
adjoining  without  damage  to  either  or  to  the  brain  of  the  child.  Such 
overlapping  takes  place  during  the  birth  of  a  child,  and  the  head  may 
be  sul)jected  to  considerable  compression  of  various  kinds  during  early 
life  with  comparatively  little  or  no  injury. 

The  sutures  according  to  their  location,  disappear  at  diiFerent  periods  ; 
the  general  ossific  development  of  tlie  individual  likewise  seems  to  influ- 
ence their  disappearance.  Traces  <jf  them  can  be  found  in  the  skull  as 
late  as  the  fiftieth  or  sixtieth  year.  When  a  suture  is  obliterated  by 
ossification  such  complete  union  is  called  synostosis. 

Occasionally  some  pathological  condition  will  cause  a  suture  to  close 
prematurely.  When  tliis  occurs  the  cranium  will  bulge  on  the  opposite 
side,  in  order  to  accommodate  the  brain  as  it  develops. 

Wormian  Jionc.s  (ossa  tri<pietra). — Wormian  bones  of  various  shapes 
and  sizes  are  found  within  tlie  sutures  uniting  the  membranous  bones  of 
the  cranial  vault.  They  are  rarely  found  in  the  face.  Their  form  is 
irregular,  and  their  borders  are  adapted  to  the  suture  within  which  they 
are  situated.  Generally  they  are  small,  l)ut  occasionally  they  exceed  an 
inch  in  diameter.  They  are  most  frccjuently  found  in  the  occipito- 
parietal suture,  where  tliey  are  occasionally  met  with  in  considerable 
numbers.  Their  function  between  membranous  bones  is  similar  to 
that  of  cartilage  between  cartilaginous  bones.     They  have  their  own 


BONES. 


119 


centres  of  ossification,  and  act  independently  until  synostosis  takes 
place. 

FoNTAXELLES. — The  fontanelles  of  the  head  are  six  in  number — two 
situated  in  the  median  line,  anterior  and  posterior,  and  four  laterally. 
They  are  membranous  interspaces  formed  by  the  incomplete  ossification 
at  the  four  angles  of  the  parietal  bones  (Figs.  61  and  62). 

The  Anterior  Median  Fontanelle  is  situated  at  the  anterior  superior 
angle  of  the  parietal  bones,  and  is  formed  by  the  incomplete  ossific  con- 


P^IG.  Gl. 


Fig.  fi2. 


Skull  at  Birth,  showing  the  Anterior  and 
Posterior  Fontanelles. 


The  Lateral  Fontanelles. 


dition  of  these  angles  as  well  as  the  superior  angles  of  the  two  halves  of 
the  frontal  bone.  It  is  quadrilateral  in  form,  its  angles  extending  into 
the  four  sutures  belonging  to  the  frontal  and  parietal  bones.  It  is  the 
largest  of  the  six  fontanelles,  and  usually  remains  partially  open  until 
the  tenth  or  fifteenth  month  after  birth,  holding  in  this  respect  a  dose 
relation  with  the  rapidity  of  the  developmod  of  the  entire  osseous  system. 
In  quickly-closing  fontanelles  the  teeth  appear  soon  and  the  child  walks 
early}  Sometimes  this  fontanelle  remains  open  through  years  of  early 
life,  and  it  has  been  known  to  exist  in  the  adult. 

The  Posterior  Median  Fontanelle  is  situated  at  the  posterior  su])erior 
angles  of  the  parietal  bones  and  the  superior  angle  of  the  occipital  bone. 
It  is  triangular  in  outline,  the  angles  extending  into  tlie  sutures  formed 
by  the  parietal  and  occipital  bones.  This  fontanelle  is  closed  at  birth 
or  shortly  thereafter,  the  bones  being  united  by  membrane  which  per- 
mits them  to  move  freely  upon  each  other. 

The  Lateral  Fontanelles,  four  in  number,  are  situated  at  the  inferior 
angles  of  the  parietal  bones  and  the  bones  in  immediate  juxtaposition 
therewith.  They  are  small  in  size  and  irregular  in  form,  those  situated 
posteriorly  being  the  larger.     They  are  closed  at  birth  or  soon  thereafter. 

The  fontanelles  are  gradually  closed  by  the  extension  of  the  bones  into 
the  membranes  which  fill  the  spaces:  It  is  in  this  way  that  the  angles 
of  the  bones  are  completed  and  the  sutures  formed. 

The  posterior  lateral  and  occasionally  the  anterior  fontanelles  are  filled 

^Allen's  Human  Anatomy. 


120  ANATOMY. 

in  by  Wormian  bones ;  usually  all  traces  of  the  fontanelles  disappear 
about  the  fourth  year. 

The  Walls  of  the  Brain- case.^ 

The  bones  forming  the  walls  of  the  brain-case  are  composed  of  two 
plates  of  compact  tissue,  an  outer  and  an  inner,  with  intervening  can- 
cellated tissue,  called  diploe,  between  them. 

The  Older  or  Fibrous  Plate  or  Table  is  thick  and  tough,  and  rough- 
ened in  different  places  for  the  origin  and  insertion  of  muscles.  It  is 
also  covered  by  minute  orifices  for  the  attachment  of  the  pericranium 
(periosteum)  and  entrance  of  the  nutrient  vessels. 

The  Inner  Plate  or  Vitreom  Table  is  thinner,  smoother,  closer-grained, 
and  more  brittle  than  the  outer,  and  has  a  glossy  appearance.  The 
minute  orifices  are  not  so  numerous  as  they  are  externally,  and  they 
give  attachment  to  the  dura  mater,  which  acts  as  the  internal  peri- 
osteum. 

The  Diploe  (see  Fio-.  115,  veins)   is  the  cancellated  tissue  situated 

T»  11  I'l 

between  the  external  and  the  internal  plates.  It  gives  the  bone  light- 
ness, and  at  the  same  time  acts  as  a  cushion  to  diffuse,  and  thus  mod- 
erate, shocks.  It  is  extremely  vascular,  and  gives  passage  to  numerous 
blood-vessels,  which  communicate  with  both  the  pericranium  and  the 
dura  mater  in  such  manner  that  death  of  the  pericranium  is  not  always 
followed  by  death  of  the  bone.  It  is  unevenly  distributed  throughout 
the  different  parts  of  the  skull,  being  thick  in  some  places,  as  in  the 
region  of  the  greater  portion  of  the  occipital  bone  and  the  mastoid  por- 
tion of  the  temjioral  bone,  while  it  is  entirely  absent  in  others,  as  in 
portions  of  the  orbital  plates  of  the  frontal  bone  and  the  glenoid  fossae 
of  the  temporal  bones. 

The  Internal  Surface  of  the  Brain-cam  is  smooth,  glossy,  and  marked 
by  digitate  depressions  corresponding  to  the  convolutions  of  the  brain. 
The  interior  of  the  skull  is  separated  into  two  principal  divisions — first, 
the  roof  or  dome  ;  and  second,  the  floor  or  base. 

The  Dome  or  Vertex  of  the  brain-case  is  oval-shaped  and  vaulted, 
generally  wider  behind  than  in  front,  and  made  up  of  the  frontal,  two 
parietal,  and  a  jiortion  of  tlie  occipital  bones.  The  sutures  between 
these  internally  belong  to  the  variety  known  as  harmonia.  It  is 
marked  by  the  superior  longitudinal  groove,  which  extends  from  its 
anterior  to  its  posterior  portion.  This  groove  is  deeper  in  front  and 
behind  than  in  its  central  ]iortion.  The  surfaces  of  the  bones  are  fur- 
rowed for  the  accommodation  of  the  meningeal  vessels,  and  marked  by 
depressions  of  different  depths  for  the  lodgment  of  the  Pacchionian 
bodies. 

The  Floor  or  Base  of  the  internal  portion  of  the  brain-case  is  divided 
into  three  pairs  of  fossa;,  tlie  anterior,  middle,  and  ])osterior  (Fig.  63). 

The  Anterior  Fossa',  arc  formed  by  the  cribriform  plate  of  the  ethmoid, 
the  orbital  plates  of  the  frontal,  the  lesser  wings,  and  a  portion  of  the 

*  For  detailed  particulars  of  the  processes,  surfaces,  and  foramina  of  the  bones  form- 
ing the  brain-case  see  description  of  individual  hones.  Foramina  formed  by  the  union 
of  two  or  more  bones  will  be  described  under  this  heading. 


Fig.  63. 


drooi.'e  for  Slider,  lungiti/d. Sinus 

Grooves  for  Ajitfr.  Mentnyeal  A''- 

Foyamtii.  ('tcfum 

Crintct  GfiUi 

Slit  for  Kii.mJ,  fi^rtf^. 

C^-oavb  Jni-WMxalj  Ttr-nti. 

A.ntcrior  J!&hm.oiclnl  Siyr. 

Orifices  fop  Olfactwyi  vcn-c 
Posterior  EtliDioidul  Fon 

EtJimoidai  SjpittA 


Olfacivry  Ch-onvs^ 

P^ttio    Yoravieir 

Ojitie  Orootfe- 

OLwary  pToe^ 
Anterwr  Clinvid  pratt- 

Middle  CLinoid  proc' 

Posterior  Ch'nm'J,  ^proo. 

Cromt  for  (??*  nerve 

For-'i  laaerum  medium- 

Orifoc£  of  Carotid  Canal 

epvessCoTi  for  Casscrian  Ga-ngUcn 


Meat  a  s  Auditin-.  iKfernus 

Slit  for  Dura-Mat^ir 

Sup.  Petrosal  cj/roaj'^ 

FnT,  lacerunt  poitcriiia 

Anterior  Condyloid  For. 

Aqueduct.  Vestibuli 

Postorior  Condyloid  For. 


Mastoid  TnR. 
fast,  3l6nlnqea,l  (iroovex. 


Base  of  the  Skull,  inner  or  cerebral  surface. 


121 


122  '  ANATOMY. 

body  of  the  sphenoid  bone.  They  are  convex  and  digitated  over  the 
orbits,  concave  over  the  ethmoid  bone,  the  crista  galli  projecting  upward 
from  the  centre  of  its  cribriform  plate.  Just  anterior  to  the  crista  galli 
is  situated  the  foramen  csecum,  the  openings,  including  the  cerebro-nasal 
slit,  for  the  olftictory  and  nasal  nerves  and  vessels  being  fnmd  on  either 
side  of  the  projection.  At  the  union  of  the  lesser  wings  with  the  body 
of  the  sphenoid  bone  the  optic  foramina  are  found.  These  foramina 
transmit  the  optic  nerves  and  ophthalmic  arteries.  The  lesser  wings  and 
a  portion  of  the  body  of  the  sphenoid  Ijone  form  the  posterior  boundary 
of  these  fossae,  the  wings  extending  outwardly  into  the  fissure  of 
Sylvius  of  the  brain.  The  anterior  fossa?  support  the  frontal  lobes 
of  the  brain. 

The  Middle  Fossce  of  the  brain-case  are  formed  by  the  great  wings 
and  part  of  the  body  of  the  sphenoid  bone,  the  squamous  portion  of 
the  temporal  bone,  and  the  anterior  inferior  portion  of  the  parietal 
bones.  They  are  cup-shaped  in  form,  and  situated  on  a  lower  plane 
than  the  anterior  fossse.  They  are  bounded  in  front  by  the  lesser  and 
a  portion  of  the  greater  wings  of  the  sphenoid  bone,  behind  l)y  the 
anterior  surface  of  the  petrous  portion  of  the  temporal  bone,  externally 
by  the  squamous  portion  of  the  temporal  bone  and  the  anterior  inferior 
angle  of  the  parietal  bones,  and  internally  by  the  body  of  the  sphenoid 
bone. 

The  Pituitary  Fossa  separates  these  fossse  in  the  median  line. 

The  middle  fossse  are  digitated  and  their  floors  are  pierced  by  numer- 
ous openings.  The  anterior  lacerated  foramina,  which  are  formed  by  the 
approximation  of  the  frontal  bone  and  the  body  and  two  wings  of  the 
sphenoid  bone,  open  into  these  fossae  anteriorly.  Each  of  these  foramina 
transmits  from  within  outwardly  the  third,  fourth,  and  sixth,  and  the 
ophthalmic  division  of  the  fifth  cranial  nerves.  The  ophthalmic  vein  and 
a  branch  of  the  lachrymal  artery  pass  through  this  foramen  from  with- 
out inwardly.  Just  posterior  to  the  anterior  lacerated  foramen,  close  to 
the  body  of  the  bone,  is  the  foramen  rotundum.  This  transmits  the 
superior  maxillary,  the  second  division  of  the  fifth  nerve.  Behind  the 
foramen  rotundum,  in  the  deepest  portion  of  the  fossa,  is  situated  a 
large  oval  foramen,  the  foramen  ovale..  It  gives  passage  from  within 
outwardly  to  the  inferior  maxillary  or  the  third  division  of  the  fifth 
cranial  nerves,  and  from  without  inwardly  to  the  lesser  meningeal 
artery. 

External  to  the  foramen  ovale,  and  a  little  posterior  to  it,  in  the 
spine  of  the  great  wing  of  the  sphenoid  bone,  is  situated  the  foramen 
■^jiinosuni.  This  foramen  gives  passage  from  without  inwardly  to  the 
middle  meningeal  artery. 

Between  the  round  and  the  oval  foramina  is  sometimes  located  a 
small  foramen,  the  foramen  A'^esali,  for  the  transmission  of  a  small  vein 
to  the  cavernous  sinus. 

Between  the  apex  of  the  ])etrous  portion  of  the  temporal  bone  and 
the  bodv  and  posterior  border  of  the  great  wing  of  the  sphenoid  bone 
will  be  found  the  middle  lacerated  foramen  (foramen  lacerum  medius). 
In  the  recent  state  this  foramen  is  filled  up  from  below  with  fibrous 
tissue.     The  carotid  canal  terminates  at  the  apex  of  the  petrous  portion 


BONES.  123 

of  the  temporal  bone  at  the  external  boundary  of  this  foramen,  while 
the   Vidian  canal  commences  below  at  its  anterior  margin. 

Tlie  hiatus  Fallopii  is  a  small  canal,  the  opening  of  which  is  situated 
on  the  anterior  surface  of  the  petrous  portion  of  the  temporal  bone 
just  external  to  the  termination  of  the  carotid  canal.  This  canal  trans- 
mits the  Vidian  nerve,  Mhicli  is  a  branch  of  the  seventh  or  facial  nerve, 
and  goes  to  the  spheno-palatine  ganglion.  On  the  apex  of  the  petrous 
portion  of  the  temporal  bone  is  an  irregular  depression  for  the  lodg- 
ment of  the  ganglion  of  Gasser  (semilunar  ganglion).  This  is  the 
laro-e  o-ano-lion  of  the  fifth  nerve. 

Three  divisions  are  thrown  off  from  this  ganglion  within  the  middle 
fossa,  and  pass  outwardly  through  its  walls  or  floor. 

The  middle  cerebral  lobes  of  the  brain  rest  upon  the  floor  of  the 
middle  fossae  of  the  skull. 

The  Posterior  Foshcb  of  the  brain-case  are  in  great  part  formed  l)y 
the  occipital  bone.  This  bone,  in  conjunction  with  a  portion  of  the 
body  of  the  sphenoid  bone,  forms  the  floors;  their  anterior  boundary 
is  formed  by  the  posterior  surface  of  the  petrous  portion  of  the  tem- 
poral bone,  while  the  mastoid  portion  of  the  temporal  bone  and  a  small 
portion  of  the  parietal  bones  complete  the  sides. 

These  fossse  are  deeper  and  larger  than  the  others.  Their  central 
portions  anteriorly  are  marked  by  the  posterior  clinoid  processes. 

The  elongated  concave  surface  (^f  bone  between  the  posterior  clinoid 
processes  and  the  foramen  magnum  is  composed  of  the  dorsum  sellse  of 
the  sphenoid  bone  anteriorly  and  the  basilar  process  of  the  occipital 
bone  posteriorly.  This  surface  lodges  the  medulla  oblongata  and  the 
basilar  artery. 

The  posterior  surface  of  the  petrous  portion  of  the  temporal  bone  is 
marked  by  a  large  opening,  the  internal  auditory  meatus.  The  seventh 
and  eighth  nerves  pass  into  this  opening,  the  seventh  going  to  the  face, 
while  the  eighth  passes  to  the  internal  ear. 

The  posterior  lacerated  foramen  (foramen  lacerum  posterius)  is  below 
the  internal  auditory  meatus,  between  the  petrous  portion  of  the  tem- 
poral bone  and  the  basilar  process  of  the  occipital  bone.  It  is  a  large, 
irregular,  twisted,  wedge-  or  pear-shaped  aperture,  the  base  rounded  and 
directed  to  the  posterior  and  distal  portion  of  the  base  of  the  skull,  the 
axis  of  its  external  opening  being  toward  the  mastoid  process  of  the 
temporal  bone.  This  base  is  rounded,  being  formed  by  the  jugular 
fossa  of  the  occipital  and  temporal  bones.  It  is  Iiere,  within  this  fora- 
men, that  the  internal  jugular  vein  is  formed  by  the  termination  of  the 
lateral  sinuses.^  The  apex  of  the  posterior  lacerated  foramen  is  gener- 
ally separated  into  two  divisions  by  the  intrajugular  processes  of  bone. 
The  posterior  division  transmits  from  the  brain-case  the  ninth  (glosso- 
pharyngeal), the  tenth  (pneumogastric),  and  the  eleventh  (spinal  acces- 
sory) nerves,  wdiile  the  anterior  division  gives  passage  to  the  inferior 
petrosal  sinus. 

The  deep  groove  for  the  accommodation  of  the  lateral  sinus  termi- 

*  The  sinuses  of  the  brain-case  are  membranous  for  the  passage  of  venous  blood. 
They  resemble  veins,  diflering  from  them  in  that  they  lack  the  fibrous  and  muscuLar 
coats  of  these  vessels. 


124  A^UTOMY. 

nates  at  the  posterior  boundary  of  this  foramen.  From  this  point  it 
extends  outwardly  over  the  junction  of  the  petrous  M^th  the  mastoid 
portion  of  the  temporal  bone,  curves  backward  over  the  posterior  infe- 
rior angle  of  the  parietal  bone,  and  thence  inward  over  the  occipital 
bone  to  the  torcular  Herophili,  which  is  situated  at  the  internal  occipital 
protuberance,  and  formed  by  the  confluence  of  all  the  sinuses  of  the  brain 
excepting  those  transmitted  through  the  petrosal  sinuses.  The  posterior 
condyloid  and  mastoid  foramina  open  into  this  groove.  In  the  region 
of  these  sinuses  the  bones  are  generally  extremely  thick. 

The  central  portion  of  the  floor  of  the  posterior  fossse  of  the  cranium 
is  pierced  by  the  foramen  magnum.  This  foramen  transmits  the  spinal 
cord  and  ith  n  embranes,  the  vertebral  arteries,  and  the  roots  of  the 
spinal  accessory  nerves.  The  anterior  condyloid  foramen  opens  into 
the  anterior  border  of  the  foramen  magnum.  It  transmits  the  twelfth 
cranial  nerve  (hypoglossal). 

The  CerebeUar  Fossce  form  that  portion  of  the  posterior  fossse  situated 
between  the  lateral  sinuses  and  the  foramen  magnum  ;  they  lodge  the 
lobes  of  the  cerebellum. 

The  External  Surface  of  the  Brain-case. 

The  external  surface  of  the  brain-case  (Fig.  64)  is  divided  into 
five  regions — a  superior,  inferior,  anterior  or  facial,  and  two  lateral 
regions. 

The  Superior  Bee/ion  extends  longitudinally  from  the  supraorbital 
arches  anteriorly  to  the  superior  curved  line  on  the  occipital  bone  pos- 
teriorly, and  from  the  right  to  the  left  temporal  ridges.  It  is  in  shape 
an  elongated  dome,  its  length  extending  antero-posteriorly.  It  is  flat- 
tened in  front  to  form  the  forehead,  and  projects  behind.  It  is  marked 
by  four  eminences,  two  frontal  and  two  parietal. 

The  greatest  width  of  the  superior  region  is  generally  from  one  pari- 
etal eminence  to  that  of  another.  No  muscles  arise  or  are  attached  in 
this  region,  but  it  is  well  marked  by  fine  pits  for  the  attachment  of  the 
pericranium,  over  whicli  })lay  the  fibres  and  aponeuroses  of  the  occipito- 
frontalis  muscle. 

Base  of  the  Brain-case. — When  the  fiicial  bones  are  removed 
from  the  anterior  portion  of  the  skull,  the  under  surface  of  the  brain- 
case  corresponds  in  great  measure  with  the  floor  of  its  internal  surface, 
like  which  it  is  separated  into  three  divisions — anterior  or  facial,  middle 
or  cervical,  and  posterior  or  occipital ;  and  these  divisions  are  situated 
directly  under  corres])onding  ones  internally.  This  surfiice,  however, 
is  rougher  and  the  jjrojcctions  of  bones  are  nnich  more  prominent  than 
on  the  internal  surfiu-e. 

The  Anterior  Portion  is  bounded  anteriorly  by  the  supraorbital  arches, 
with  their  notches  or  foramina,  and  the  rough  articulating  surface  for 
the  nasal  bones  and  the  nasal  ))r()cesses  of  the  sujx'rior  maxillary  bones; 
laterally  by  the  external  angular  processes  of  the  frontal  bone  and  the 
anterior  border  of  the  great  wing  of  the  s])licnoid  ;  and  posteriorly  by 
the  inferior  border  of  the  great  wing  of  tlie  sphenoid  bone,  and  a  line 
drawn  from  the  base  of  the  anterior  surface  of  the  pterygoid  process  on 


A/it.  palcrttTU fossa 

Transmits  Ant .  palat  xfcss. 
Iransinita  right Nasopalat.n. 


Aeees  soTTf  palatine 

rtZYQOS     UVUliC 

Hamiilar  ^roc 


SpJiejtoCd.proc,  of  Po/lo/te. 
erytj/n-pail/ititie  C, 


TENSOR    TYMPAMI. 

PJiari/n(f£til Spiivcfm  sup.'cONSTHIflE 

Vi/"  ofSitsUw/aan  ttt.ili&LCa.mtlfor7ins:tyrTtiiap 
LAXATOR     TVMPAWr. 

Ajjucduct.  CocliUa. 
For.  laec  ru.  mposte  rut  s. 
CuiUjclfoTArnoliis  2fr- 
uxCcldar  fissure- 


Base  of  the  Skull,  external  surface. 


125 


126  ANAT03IY. 

one  side,  across  the  body  of  the  sphenoid  ])one,  to  the  same  process  on 
the  other  side. 

This  region  is  symmetrically  divided  by  the  descending  plate  of  the 
ethmoid  and  the  rostrum  of  the  sphenoid  bone. 

Tlie  structures  forming  the  anterior  division  on  each  side  of  this  cen- 
tral division,  from  within  outwardly,  arc,  tirst,  the  cribriform  plate  of 
the  ethmoid  bone,  which  forms  the  roof  to  the  nasal  chamber ;  second, 
the  lateral  masses  of  the  ethmoid,  which,  through  its  os  planum,  forms 
a  portion  of  the  inner  >vall  of  the  orbital  cavity ;  third,  the  orbital 
plate  of  the  frontal  bone  and  a  portion  of  the  lesser  wing  of  the  sphe- 
noid ;  and  fourch,  the  great  wing  of  the  sphenoid,  together  with  the 
rough  articulating  surface  of  the  external  angular  process  of  the  frontal 
bone. 

Immediately  in  front  of  the  ethmoid  bone,  and  between  the  internal 
angular  processes  of  the  frontal  bone,  will  be  found  the  articulating  sur- 
faces for  the  lachrymal,  maxillary,  and  nasal  bones. 

The  foramina  of  this  region  have  already  been  described.  They  are 
as  follows  :  The  perforations  of  the  cribriform  plate  of  the  ethmoid 
bone,  the  anterior  and  posterior  ethmoidal  Ibramina,  the  supraorbital, 
anterior  lacerated,  and  optic  foramina  within  the  orbital  cavity,  and  the 
foramen  rotundum  and  Vidian  canal. 

The  Median  or  Cervical  Region  is  bounded  anteriorly  by  the  inferior 
border  of  the  great  wing  of  the  sphenoid  bone,  and  by  a  line  drawn  from 
the  base  of  the  anterior  surface  of  the  pterygoid  process  on  one  side, 
across  the  body  of  the  sphenoid  bone,  to  the  same  point  on  the  other. 
The  lateral  boundary  is  formed  by  a  line  drawn  along  the  pterygoid 
ridge  of  the  sphenoid  bone,  extending  to  the  extreme  outer  point  of  the 
glenoid  fossa,  and  thence  to  the  apex  of  the  mastoid  portion  of  the  tem- 
poral bone.  The  posterior  boundary  is  formed  by  a  line  drawn  from 
the  apex  of  the  mastoid  portion  of  the  temporal  bone  on  one  side  to  the 
same  point  on  the  other,  crossing  the  centre  of  the  condyloid  processes 
of  the  occi])ital  bone  and  the  foramen  magnum. 

A  line  drawn  froiu  the  anterior  portion  of  the  rostrum  of  the  sphenoid 
bone  to  the  centre  of  the  anterior  portion  of  the  foramen  magnum  Avill 
divide  the  middle  region  into  two  symmetrical  halves. 

The  structures  forming  this  division  on  each  side  of  the  central 
line  from  its  anterior  to  its  })osterior  portion  are  as  folloM's  : 

First :  the  P(eri/e/oid  Process^  which  extends  downwardly. 

Second  :  the  Pterygoid  Fossa,  which  is  situated  posteriorly  between  the 
plates  composing  the  jiterygoid  jirocess.  The  outer  plate  of  this  process 
gives  origin  witliin  the  fossa  to  the  internal  pterygoid  muscle. 

Tiiird  :  the  XcapJioid  Fossa,  at  the  base  of  the  roots  of  the  pterygoid 
fossa  posteriorly.     This  fossa  gives  origin  to  the  tensor  palati  muscle. 

Fourth  :  the  Vaginal  Process,  situated  at  the  base  of  the  internal 
pterygoid  plate,  at  its  junction  with  the  body  of  the  bone. 

Fifth:  the  Inferior  Surface  of  the  Great  Wing  of  the  Sphenoid  Bone. 
— This  surface  is  smooth,  concave,  and  quadrilateral ;  it  is  situated  just 
external  to  i\\v  jitcrygoid  jiroccss.  It  gives  origin  to  the  external  liead 
of  the  external  ])terygoid  nuiscle. 

Sixth  :  the  Foramen  Ovale,  situated  in  the  posterior  portion  of  the 


BONES.  127 

inferior  surface  of  the  great  wing  of  the  sphenoid,  back  of,  and  a  little 
external  to,  the  pterygoid  process.  This  foramen  transmits  the  inferior 
maxillary  nerve  and  the  lesser  meningeal  artery. 

Seyenth  :  the  Foramen  Sjnnosum,  situated  behind  and  externally  to 
the  foramen  oyale  in  the  inferior  surface  of  the  great  wing  of  the  sphe- 
,noid  bone.     It  transmits  the  middle  meningeal  artery. 

Eighth  :  the  tSpinout^  Froce^n  of  the  SpJienoid  Bone,  which  is  the  ])os- 
terior  external  angle  of  the  inferior  surface.  This  process  gives  origin 
to  the  laxator  tympani  muscle. 

Ninth  :  the  Glenoid  i'o.y.s-a,  situated  external  to  the  spinous  process  of 
the  sphenoid  bone.  This  fossa  is  a  large  oval  depression  which  receives 
the  condyle  of  the  inferior  maxillary  bone  in  the  articulated  skull,  and 
also  the  superior  portion  of  the  parotid  gland. 

Tenth  :  the  Extenml  Auditori/  Ilecdiii^,  situated  behind  the  })osterior 
external  boundary  of  the  glenoid  fossa. 

Eleventh  :  the  Glenoid  Fi.ssure,  which  passes  inward  and  forward 
through  the  centre  of  the  glenoid  fossa. 

Twelfth  :  the  Eustachian  Sidcus,  which  is  between  the  inner  extremity 
of  the  glenoid  fissure  and  the  body  of  the  sphenoid  bone.  The  sides  of 
this  sulcus  are  formed  by  part  of  the  petrous  portion  of  the  temporal 
and  the  great  wing  of  the  sphenoid  bone,  its  internal  portion  being 
frequently  incomplete. 

Thirteenth  :  the  Middle  Laeereded  Foramen,  A\hich  is  situated  between 
the  apex  of  the  petrous  portion  of  the  temporal  and  the  body  of  the 
sphenoid  bone.  In  the  recent  state  it  is  filled  up  by  fibro-cartilage. 
Its  size  varies  in  different  skulls,  and  occasionally  it  is  found  filled  with 
bone. 

Fourteenth  :  the  Petro-basilar  Groove,  between  the  petrous  portion 
of  the  temporal  and  the  basilar  process  of  the  occipital  bones.  This 
groove  in  the  recent  state  is  filled  with  fibrous  tissue. 

Fifteenth  :  the  Posterior  Lacerated  Foramen,  which  extends  back- 
ward and  outward  from  the  petro-basilar  groove.  This  foramen  is 
formed  by  the  union  of  the  jugular  fossie  of  the  temporal  and  occip- 
ital bones.  It  transmits  the  jugular  vein  and  the  ninth,  tenth,  and 
eleventh  nerves,  a  septum  of  bone  often  separating  the  vein  from 
the  nerves. 

Sixteenth  :  the  Opening  for  the  Cewotid  Canal  is  situated  on  the  under 
surface  of  the  petrous  portion  of  the  temporal  bone,  just  anterior  to  the 
posterior  lacerated  foramen. 

Seventeenth  :  the  Digastric  Groove,  situated  on  the  internal  surface 
of  the  mastoid  portion  of  the  temporal  bone.  It  is  long,  deep,  and 
narrow,  for  the  origin  of  the  digastric  muscle. 

Eighteenth:  the" Stylo-mastoid  Foramen,  situated  at  the  anterior 
extremity  of  the  digastric  groove  at  the  base  of  the  styloid  process  of 
the  temporal  bone.  This  foramen  gives  exit  to  the  seventh  or  facial 
nerve. 

Nineteenth  :  the  Styloid  Process  of  the  Temporal  Bone  extends  do^n- 
ward  from  a  point  just  anterior  to  the  stylo-mastoid  foramen.  The  base 
of  this  process  is  surrounded  by  what  is  termed  the  vaginal  process. 

Twentieth  :  the  Pharyngeal ' Spine  is  a  small  tubercle  situated  about 


128  ANAT03IY. 

the  centre  of  the  basilar  process  of  the  occipital  bone.  This  spine  gives 
attachment  to  what  is  known  as  the  raphe  of  the  pharynx. 

Twenty-first:  the  Anterior  Concti/loid  Foramen  is  just  in  front  of  the 
condyles  of  the  occipital  bone,  on  the  lateral  surface  of  the  basilar  pro- 
cess.    This  foramen  is  the  external  orifice  of  the  hypoglossal  canal. 

Twenty-second  :  the  Condyloid  Processes  of  the  Occipital  Bone  are 
situated  on  each  side  of  the  foramen  magnum  anteriorly.  They  are 
double-convex  articulating  facets,  upon  which  the  head  rocks  within  the 
corresponding  concavities  of  the  atlas  or  first  cervical  vertebra. 

Posterior  Region. 

The  Posterior  Division  of  the  base^  of  the  brain-case  is  semicircular 
in  outline.  Its  anterior  boundary  extends  from  the  apex  of  the  mastoid 
portion  of  the  temporal  bone  on  one  side,  across  the  articnlating  condyles 
of  the  occipital  bone,  to  the  same  point  on  the  other  side.  Its  posterior 
or  semicircular  boundary  extends  from  the  apex  of  the  mastoid  portion 
of  the  temporal  bone  on  one  side,  upward  and  backward,  joining  the 
superior  curved  line  of  the  occipital  bone,  and  passing  along  this  ridge 
to  the  occipital  protuberance,  from  which  point  it  runs  forward  and 
downward  on  the  ridge  of  the  other  side  to  the  apex  of  the  mastoid 
portion  of  the  temporal  bone.  The  surface  of  bone  included  within  this 
semicircular  outline,  excluding  the  condyles,  the  posterior  condyloid 
foramina,  and  the  foramen  magnum,  affords  attachment  to  muscles. 

The  line  forming  the  anterior  boundary  of  the  posterior  region  not 
only  separates  it  from  the  middle  region,  but  is  the  axis  between  the 
anterior  muscles,  which  act  as  the  motor  power  in  bowing  the  head, 
from  those  which  antagonize  these  and  raise  and  draw  the  head  back- 
ward :  this,  therefore,  is  tlie  axis  upon  which  the  head  oscillates  ;  its 
centre  is  the  point  around  which  the  head  rotates. 

On  either  side,  immediately  behind  the  condyles,  are  depressions 
pierced  by  foramina  leading  to  the  lateral  sinuses.  These  are  known 
respectively  as  the  posterior  condyloid  fossae  and  foramina. 

Lateral  Regions  op  the  Skull. 

The  points  of  interest  on  the  lateral  region  (see  Fig.  60)  from  the 
posterior  to  the  anterior  Ijoundary  are  the  mastoid  process,  the  external 
auditory  meatus,  the  auditory  process,  the  glenoid  fossa,  all  of  which 
are  parts  of  tlic  tcmpoi-al  bone  ;  the  zygomatic  arch,  formed  by  union 
of  the  zygomatic;  ])rocesses  of  the  temporal  and  the  malar  bones ;  the 
condyloid  and  coronoid  processes  of  the  inferior  maxilla. 

Two  deep  fosste  mark  the  lateral  region  of  the  skull — one  above  the 
zygomatic  arch,  known  as  tlic  tcmj)oral  fossa,  and  the  other  below  the 
arch,  known  as  the  zygomatic  fi)ssa. 

The  Temporal  Fossa  occupies  the  greater  portion  of  the  lateral  region 

^  In  comparative  anatomy  this  is  the  posterior  half  of  the  roof  of  the  brain-case  in 
animals,  it  being  above  the  spinal  cord  or  neural  cavity,  and  the  only  portion  of  the 
roof  formed  from  cartilage. 


BONES.  129 

of  the  skull.  It  is  made  up  of  parts  of  five  bones — the  temporal,  the 
sphenoid,  and  the  malar  below,  the  parietal  and  the  frontal  above — and 
is  crossed  by  seven  sutures  uniting  these  bones.  It  is  also  traversed  by 
grooves  for  the  accommodation  of  the  deep  temporal  arteries,  and 
marked  by  fim-like  grooves  for  the  origin  of  the  deep  fibres  of  the 
temporal   muscle. 

The  temporal  fossa  is  bounded  in  front  by  the  posterior  surface  of  the 
frontal  process  of  the  malar,  the  external  angular  process  of  the  frontal, 
and  part  of  the  great  wing  of  the  sphenoid  bones.  It  is  bounded  above 
and  behind  by  the  supratemporal  ridge.  This  is  formed  by  two  slightly- 
elevated  borders  that  originate  near  the  fronto-malar  articulation  from  a 
single  point,  from  which  it  diverges  into  two  nearly  semicircular  lines 
that  curve  upward,  backward,  and  downward  across  the  fronto-parietal 
suture  at  a  distange  of  about  a  half  inch  or  more  from  each  other. 

The  Inferior  Line  extends  backward  and  curves  downward  to  join  the 
posterior  root  of  the  zygomatic  process  of  the  temporal  bone.  This 
line  is  the  uppermost  limit  of  the  deep  attachment  of  the  temporal 
muscle. 

The  Superior  Line,  which  is  separated  from  the  inferior,  gradually 
increasing  the  distance  as  it  proceeds  backward  and  downward,  termi- 
nates near  the  parieto-occipito-mastoid  articulation.  This  upper  line 
and  space  between  it  and  the  lower  afford  attachment  to  the  temporal 
fascia.  The  inferior  boundary  of  the  temporal  fossa  internally  is  foi-med 
by  the  infratemporal  ridge.  This  ridge  extends  from  the  parieto-occip- 
ito-mastoid articulation  forward  along  the  posterior  root  of  the  zygo- 
matic process  of  the  temporal  bone,  across  the  pterygoid  ridge,  Aviiich 
separates  the  lateral  from  the  inferior  surface  of  the  great  wing  of  the 
sphenoid  bone,  to  the  roughened  prominence  on  the  posterior  border  of 
the  malar  bone.  The  external  boundary  of  the  temporal  fossa  is  formed 
by  the  zygomatic  arch,  and  in  the  recent  state  by  the  temporal  fascia. 
This  fossa  accommodates  the  tendon  and  muscular  fibres  of  the  temporal 
muscle. 

The  Zygomatic  Fossa  is  below  the  zygomatic  arch.  It  is  an  irregularly- 
shaped  cavity,  bounded  anteriorly  by  the  posterior  or  zygomatic  sur- 
face of  the  superior  maxilla ;  internally,  by  the  external  pterygoid 
plate ;  superiorly,  by  the  inferior  surface  of  the  great  wing  of  the 
sphenoid  bone  and  a  part  of  the  squamous  portion  of  the  temporal 
bone,  the  infratemporal  ridge  dividing  the  zygomatic  from  the  tem- 
poral fossa  in  this  region ;  and  laterally  by  the  ramus  of  the  inferior 
maxilla. 

The  following  openings  will  be  found  within  the  fossa  :  The  orifices 
of  the  Posterior  Dental  Canals,  situated  in  the  superior  maxillary  bone 
for  the  transmission  of  the  posterior  dental  vessels  and  nerves ;  the 
Spheno-maxillary  Fissure,  between  the  sjihenoid  and  the  superior  max- 
illary bones,  leading  into  the  orbit ;  the  Pteri/f/o-maxiUary  Fissure, 
between  the  pterygoid  process  of  the  sphenoid  bone  and  the  superior 
maxilla,  leading  into  the  spheno-maxillary  space  or  fossa ;  the  Foramen 
Ovale  and  Foramen  Spinosum,  situated  in  the  great  wing  of  the  sphe- 
noid bone  in  close  proximity  to  each  other.  The  foramen  ovale  trans- 
mits the  third  division  of  the  fifth  nerve  and  a  small  meningeal  artery, 
Vol.  I.— 9 


130  A^\iTOMY. 

while  the  spinous  foramen  transmits  the  middle  meningeal  artery.  The 
Inferior  Dental  Foramen  is  situated  in  the  inferior  maxillary  bone,  and 
transmits  the  inferior  dental  vessels  and  nerve,  while  between  the  zygo- 
matic arch  and  the  infratemporal  ridge  is  the  temporo-zygomatic  strait, 
joining  it  with  the  temporal  fossa. 

The  zygomatic  fossa  accommodates  the  tendon  and  lower  portion  of 
the  temporal  muscle,  the  external  and  internal  pterygoid  muscles,  the 
inferior  maxillary  nerve  and  its  bi'anches,  and,  linally,  the  internal  max- 
illary artery,  passing  through  and  giving  off  branches  as  it  extends 
inward  and  forward  into  the  pterygo-maxillary  fissure. 

The  Spheno-maxillari/  Foma  is  a  triangular  space  bounded  behind  by 
the  upper  portion  of  the  anterior  surface  of  the  pterygoid  process ;  in 
front  by  the  internal  portion  of  the  zygomatic  surface  of  the  superior 
maxilla  and  a  portion  of  the  palate  bone ;  above  by  the  under  surface 
of  the  body  of  the  sphenoid  bone  and  the  orbital  process  of  the  palate 
bone;  and  internally  by  the  perpendicular  plate  of  the  palate  bone, 
which  separates  this  fossa  from  tire  nasal  chambers. 

This  fossa  lodges  the  spheno-palatine  (INIeckel's)  ganglion  and  the 
terminal  end  of  the  inferior  maxillary  artery.  Opening  into  it  are  the 
pterygo-maxillary  and  spheno-maxillarv  fissures  and  five  foramina — the 
anterior  lacerated,  the  rotund,  the  Vidian,  the  pterygo-palatine,  and  the 
spheno-palatine. 

The  Pterygo-maxillary  Fissure  extends  vertically  between  the  superior 
maxilla  and  the  pterygoid  ]3rocess  of  the  sphenoid  bone.  It  is  wider 
above  than  below,  and  comnnniicates  with  the  zygomatic  fossa,  trans- 
mitting the  internal  maxillary  artery  and  vein. 

The  Sphe)io-maxill((ry  Fissure  extends  nearly  horizontally  outward 
and  forward  from  the  body  of  the  sphenoid  bone  at  an  angle  of  about 
forty-five  degrees.  Its  posterior  boundary  is  formed  by  the  inferior 
border  of  the  orbital  surface  of  the  great  wing  of  the  sphenoid  bone ; 
its  anterior  boundary  is  formed  by  the  angle  between  the  orbital  and 
zygomatic  surfaces  of  the  superior  maxilla  and  a  portion  of  the  orbital 
process  of  the  palate  bone.  Externally  it  is  bounded  by  a  smooth  notch 
in  tlie  orbital  process  of  the  malar  bone,  and  internally  by  the  body  of 
the  sphenoid  bone. 

This  fissure  extends  between  the  orbit  and  the  spheno-maxillary  and 
pterygo-maxillary  fossa,  and  transmits  the  superior  maxillary  division 
of  the  fifth  nerve,  the  infraorbital  artery  and  vein,  and  the  ascending 
branches  of  the  spheno-palatine  (Meckel's)  ganglion. 

J'/ie  Pterygo-palatine  Foramen  is  situated  between  the  pterygoid 
process  of  the  s|)hen<>id  bone  and  the  jiosterior  border  of  the  horizontal 
plate  of  the  palate  bono.  This  foramen  opens  into  a  canal,  the  posterior 
palatine,  which  passes  directly  downward,  opening  into  the  roof  of  the 
mouth  at  the  ])osterior  lateral  angle  of  the  hard  ]>alate. 

Occasi(jnally  there  will  be  fi)und  in  this  locality  two  or  more  acces- 
sory palatine  canals,  which  give  passage  to  branches  of  nerves  from  the 
spheno-palatine  ganglion  to  the  hard  and  soft  palate.  These  canals  also 
transnnt  vessels  to  the  roof  of  the  mouth. 

The  Spheno-palatine  Foramen  is  situated  between  the  sujierior  bor- 
der of  the  perpendicular  plate  of  the  palate  bone  and  the  under  surface 


BONES. 


131 


of  the  body  of  the  sphenoid  bone.  This  foramen  opens  into  the  pos- 
terior portion  of  the  superior  meatus  of  the  nose,  and  transmits  the 
naso-palatine  nerve  and  vessels. 


Facial  or  Anterior  Region  of  the  Skull. 

The  facial  region  of  the  brain-case  is  bounded  above  by  a  curved 
line  extending  from  the  extremity  of  the  angular  process  of  the 
frontal  bone  on  one  side,  upward  across  the  frontal  eminences,  to  the 

Fig.  65. 


TENOO     OCULI 


A/it.  N^asal  Sjjirie 
Jncisluc  fossa 


Anterior  Region  of  Skull. 


angular  process  of  the  frontal  bone  on  the  other  side ;  laterally  by  a 
line  drawn  from  the  commencement  of  the  superior  boundary,  down- 
ward and  slightly  backward,  across  the  malar  bone  to  the  angle  of  the 
lower  jaw,  and  below  by  the  lower  border  of  the  inferior  maxilla.     It 


132  ANAT03IY. 

is  nearly  oval  in  shape,  being  slightly  broader  above  than  below  (see 
Fig.  65). 

The  surface  of  the  facial  region  is  extremely  irregular,  presenting  as 
it  does  the  orifices  to  several  large  cavities  which  protect  three  of  the 
organs  of  special  sense — viz.  that  of  sight,  of  smell,  and  of  taste.  This 
region  is  divided  into  three  portions — one  central  and  two  lateral. 

The  Central  Portion  commences  a  little  above  the  nasal  eminence, 
situated  between  the  internal  angular  processes  of  the  frontal  bone. 
This  eminence  marks  the  position  of  the  frontal  sinuses. 

Below  the  nasal  eminence  is  a  semicircular  suture  uniting  the  superior 
maxilla  and  nasal  bones  with  the  frontal  bone. 

Directly  under  this  suture  is  the  bridge-roof  or  arch  of  the  nose.  It 
is  formed  by  the  nasal  bones  and  the  nasal  processes  of  the  superior 
maxillte.  It  is  convex  from  side  to  side,  and  concave  from  above  down- 
ward. The  median  line  of  this  arch  presents  the  internasal  suture, 
while  its  lateral  surfaces  are  marked  by  the  naso-maxillary  sutures. 

The  nasal  arch  is  generally  pierced  by  a  foramen  on  either  side  for 
the  passage  of  a  vein. 

Below  the  arch  of  the  nose  are  situated  the  anterior  openings  to  the 
nasal  chambers.  Conjointly,  they  are  pyriform  in  shape,  bounded 
above  by  the  inferior  border  of  the  nasal  bones,  the  lateral  and  inferior 
boundaries  being  formed  by  the  superior  maxillse. .  The  borders  of  this 
opening  are  sharp  and  give  attachment  to  the  lateral  cartilage  of  the 
nose. 

Beneath  the  anterior  opening  to  the  nasal  chambers  are  situated  the 
two  incisive  fossae,  between  which  will  be  found  the  intermaxillary 
suture. 

Continuing  downward,  are  next  found  the  four  incisor  teeth,  situated 
in  the  alveolar  border  of  the  intermaxillary  bone. 

Below  this,  in  the  median  line  of  the  inferior  maxilla,  will  be  found 
the  four  inferior  incisor  teeth  and  the  symphysis  menti,  a  slight  vertical 
ridge  at  its  commencement,  but  as  it  passes  outward  and  downward 
diverging  to  form  the  mental  process  or  chin,  a  feature  characteristic  of 
man  alone.  On  each  side  of  the  upper  portion  of  the  ridge  are  the 
inferior  incisive  fossae. 

The  Lateral  Portions  of  the  face  commence  above  in  the  frontal 
eminences.  These  eminences  are  rarely  of  the  same  size  on  both  sides 
of  the  forehead.  Below  the  frontal  eminence  is  a  depression  situated 
just  above  the  superciliary  ridge.  Beneath  this  depression  is  the  large 
circular  opening  to  the  orbital  cavity.  This  cavity  is  bounded  above 
by  the  Supraorbital  Arch,  which  extends  superiorly  from  the  internal 
to  the  external  angular  jiroccsscs  of  the  frontal  bone. 

The  inner  tiiird  of  this  l)()uudary  is  marked  by  a  notch  or  foramen, 
the  Supraorbital  Notch  or  Foramen,  for  the  passage  of  the  frontal  nerve 
and  vessels.  The  inferior  boundary  of  the  orbital  cavity  is  formed 
externally  by  the  malar  bone,  below  by  the  superior  maxilla,  and 
internally  by  the  nasal  process  of  the  superior  maxilla  and  the  lachrymal 
bone. 

The  Infraorbital  Foramen  is  below  the  infraorbital  border,  and  aifords 
exit  to  the  nerve  and  artery  of  the  same  name.     It  is  internal  to  the 


BONES.  133 

maxillo-malar  articulation,  and  below  the  foramen  is  situated  the  canine 
fossa. 

The  Canine  Fossa  is  above  the  alveolar  process  of  the  superior  max- 
illa, whicli  supports  the  teeth. 

Anterior  Dental  or  Ilental  Foramen  is  usually  situated  below  a  line 
between  the  bicuspid  teeth  and  above  the  external  oblique  line  of  the 
inferior  maxilla.     This  tbramen  transmits  the  mental  nerve  and  vessels. 

The  Supi^aorbital  Notch  or  Foramen,  the  Infraorbital  Foramen,  and 
the  Anterior  Dental  Foramen  are  situated  in  a  vertical  line,  one  beneath 
the  other.  They  give  exit  to  the  terminal  branches  forming  the  three 
divisions  of  the  fifth  or  trifacial  nerve,  which  transmits  sensation  from 
the  face. 

The  Orbital  Cavities  are  two  in  number.  They  are  situated 
between  the  anterior  portion  of  the  brain-case  and  the  superior  portion 
of  the  facial  bones.  They  are  irregular  quadrilateral  pyramids  in  shape, 
their  bases  being  directed  forward  and  a  little  outward,  and  their  apices 
backward  and  a  little  inward.  Their  outer  walls  diverge  from  the  median 
line  of  the  face  at  about  an  angle  of  forty-five  degrees,  while  their  inner 
walls  are  nearly  parallel  with  each  other. 

The  roof  of  the  orbit  is  concave,  and  formed  by  the  horizontal  or 
orbital  plate  of  the  frontal  bone  and  a  portion  of  the  lesser  wing  of  the 
sphenoid  bone.  The  outer  portion  of  the  roof  anteriorly  is  marked  by 
the  laclirvmal  fossa  for  the  lodgment  of  the  lachrymal  gland.  There 
is  also  a  depression  at  the  inner  portion  of  the  roof  anteriorly  for  the 
attachment  of  the  pulley  of  the  superior  oblique  muscle. 

The  floor  of  the  orbit  is  formed  by  the  orbital  surface  of  the  superior 
maxilla  and  the  orbital  processes  of  the  malar  and  palate  bones,  the  lat- 
ter being  situated  at  the  posterior  median  angle. 

At  the  inner  third  of  this  surface  anteriorly  will  be  found  the  open- 
ing to  the  Lachrymal  Canal.  The  depression  just  external  to  the  lach- 
rymal canal  is  for  the  origin  of  the  inferior  oblique  muscle  of  the  eye. 

The  outer  wall  of  the  orbit  is  formed  by  the  anterior  or  orbital  surface' 
of  the  great  wing  of  the  sphenoid  and  part  of  the  malar  bone,  its  inter- 
nal wall  being  formed  by  the  nasal  process  of  the  superior  maxilla,  the 
OS  planum  or  orbital  plate  of  the  ethmoid  bone,  and  the  lachrymal  bone, 
making,  in  all,  seven  bones  involved  in  the  formation  of  the  orbital 
cavity.  Three  of  these  bones,  however,  the  frontal,  ethmoid,  and  sphe- 
noid, enter  into  the  formation  of  each  orbit,  so  that  it  takes  but  eleven 
bones  to  form  the  tw-o  cavities. 

The  circumference  of  the  orbit  was  described  with  the  structures  of 
the  face. 

The  apex  of  the  orbit  corresponds  to  the  optic  foramen. 

There  are  ten  openings  into  the  orbit — viz.  the  optic,  anterior  lacerated,, 
supraorbital,  malar,  and  the  anterior  and  posterior  ethmoidal  foramina, 
the  lachrymal  and  infraorbital  canals,  the  spheno-maxillary  fissure,  and 
the  facial  opening. 

The  Optic  Foramen  opens  into  the  apex  of  the  orbital  cavity, 
between  the  body  and  lesser  M'ing  of  the  sphenoid  bone.  It  trans- 
mits the  optic  nerve  and  the  ophthalmic  artery  from  the  brain  into 
the  orbit. 


134  ANATOMY. 

The  Anterior  Lacerated  Foramen  is  situated  near  the  apex  of  tlie 
orbital  cavity,  just  external  to  the  optic  foramen,  and  extends  upward 
and  outward  between  the  greater  and  lesser  wings  of  the  sphenoid  bone. 
It  transmits  from  the  brain  into  the  orbit  the  third,  fourth,  first  division 
(ophthalmic)  of  the  fifth  and  sixth  nerves,  and  through  the  orbit  into 
the  brain  the  ophthalmic  vein  and  a  small  artery,  a  branch  of  the 
lachrymal. 

The  Anterior  and  Posterior  Ethmoidal  Foramina  are  situated  on  the 
inner  wall  of  the  orbital  cavity  in  the  ethmo-frontal  suture,  between  the 
ethmoid  and  frontal  bones.  The  anterior  foramen  transmits  from  the 
orbit  into  the  brain-case  the  nasal  branch  of  the  ophthalmic  nerve  and 
an  artery  and  vein,  branches  of  the  ophthalmic,  which  accompany  this 
nerve. 

The  Posterior  Foramen  transmits  from  the  orbit  the  posterior  eth- 
moidal artery  and  vein. 

The  Lachrymal  Caned  is  situated  at  the  anterior  inferior  angle  of  the 
orbital  cavity.  Its  superior  orifice  is  between  the  nasal  process  of  the 
frontal  bone  and  the  lachrymal  bone.  From  this  point  the  canal  extends 
downward,  inward,  and  backward,  terminating  in  the  inferior  meatus 
of  the  nose.     It  accommodates  the  lachrymal  duct. 

The  LnfraorbiUd  Canal  commences  by  a  groove  situated  about  the 
centre  of  the  posterior  border  of  the  floor  of  the  orbital  cavity.  This 
groove  passes  forward  and  downward  into  the  body  of  the  superior 
maxilla,  and  makes  its  exit  on  the  face  in  the  infraorbital  foramen 
below  the  middle  of  the  infraorbital  ridge.  It  transmits  the  infra- 
orbital nerve,  which  is  a  continuation  of  the  second  division  of  the 
fifth  or  superior  maxillary  nerve,  and  infraorbital  vessels. 

The  Spheno-maxillari/  Fissure  is  situated  in  the  posterior  portion  of 
the  orbital  cavity,  extending  from  the  body  of  the  sphenoid  bone  for- 
Avard  and  outw^ard  to  the  sphenoidal  border  of  the  malar  bone.  It  is 
bounded  in  front  by  the  posterior  superior  border  of  the  superior  max- 
illa and  orbital  process  of  the  palate  bone,  and  behind  by  the  inferior 
border  of  the  great  wing  of  the  sphenoid  bone.  It  transmits  from  the 
brain  to  the  orbit  the  infraorbital  nerve  and  vessels  and  branches  of 
nerves  from  the  spheno-maxillary  ganglion. 

The  Malar  Foramina  are  situated  within  the  orbital  cavity  on  the 
orbital  surface  of  the  malar  bone.  They  transmit  from  the  orbital 
cavity  to  the  cheek  and  temporal  fossa  terminal  branches  of  nerves  and 
vessels.  The  facial  opening  is  that  opening  formed  by  the  anterior 
borders  of  the  orbit. 

The  Nasal  Fossje. 

The  Nasal  Fossa,  two  in  number,  forming  the  internal  nose,  are  situ- 
ated on  either  side  of  the  niedian  line  of  the  face,  and  extend  from  the 
under  surface  of  the  anterior  portion  of  the  brain-case  superiorly  to  the 
upper  surface  of  the  bones  fi)rming  the  hard  palate  inferiorly,  and  from 
the  facial  border  of  the  external  aperture  of  the  nose  anteriorly  to  the 
free  border  of  the  internal  ]itervgoid  plate  posteriorly.  They  are  sepa- 
rated by  a  thin  partition  of  bone,  the  nasal  septum,  open  on  the  face  by 


BONES.  135 

the  anterior  apertures,  and  posteriorly  into  the  pharyngeal  space  by  the 
posterior  nares.  Tliere  are  also  several  smaller  openings  leading  from 
the  nasal  fossae  in  other  directions. 

For  convenience  of  description  the  nasal  fossee  are  divided  into  a  roof, 
a  floor,  outer  walls,  and  inner  walls  formed  by  the  septum. 

The  Inner  Walls  or  JVctsal  Septum. — These  are  composed  of  six  bony 
structures,  named  in  the  order  of  their  importance  viz, — the  perpendicular 
plate  of  the  ethmoid,  the  vomer,  the  crest  of  the  superior  maxillary  and 
palate  bones,  the  rostrum  of  the  sphenoid  bone,  and  the  nasal  spine  of 
the  frontal  bone.  These  bones  do  not  complete  the  septum,  but  have 
a  triangular  notch  in  the  anterior  portion.  In  the  recent  state  this  is 
filled  by  the  nasal  cartilage. 

The  nasal  septum  is  rarely  perpendicular,  but  is  deflected  either  to 
the  one  side  or  the  other.  In  skulls  with  the  flat  or  normal  palate  the 
nasal  septum  is  most  apt  to  be  jjerpendicular,  but  in  those  having  the 
inverted  V-shai^ed  (A)  palate  either  the  septum  must  be  greatly  deflected, 
or  pressure  upward  upon  the  vomer  will  push  the  perpendicular  plate 
of  the  ethmoid  bone  forward,  thus  causing  that  external  protrusion 
characteristic  of  the  Roman  nose. 

The  cause  of  this  abnormal  formation  of  one  of  these  structures  pari 
passu  with  that  of  the  other  has  been  ascribed  by  Prof.  Harrison  Allen 
to  an  inflammatory  condition  of  the  walls  of  the  oro-naso-pharyngeal 
space,  frequent  in  some  children,  this  producing  tension  of  the  muscles, 
thus  pressing  the  lateral  portions  inward,  contracting  this  space,  thereby 
deforming  the  roof  of  the  mouth,^  and  changing  the  natural  dome  shape 
to  the  gable  or  A  shape. 

The  septum  of  the  nose  is  also  occasionally  incomplete,  and  this 
imperfection  is  generally  situated  at  the  junction  of  the  perpendicular 
plate  of  the  ethmoid  bone  with  the  vomer.  It  is  also  occasionally 
marked  by  a  groove  or  canal  on  each  side  for  the  passage  of  the  naso- 
palatine nerve. 

The  Roof  of  the  nasal  fossa  is  long,  narrow,  and  irregular  in  outline. 
It  is  divided  into  three  portions — anterior,  middle,  and  posterior. 

Tlie  Anterior  Portion  is  formed  by  the  under  surface  of  the  nasal 
bones  and  the  nasal  spine  of  the  frontal  bone.  It  is  concave  from  side 
to  side,  and  extends  inward  and  upward  at  an  angle  of  about  forty- 
five  degrees. 

The  Middle  Portion  is  narrow,  nearly  horizontal  in  direction,  and  is 
composed  of  the  cribriform  plate  of  the  ethmoid  bone. 

The  Posterior  Portion  is  the  longest  of  the  three,  and  extends  from 
the  posterior  extremity  of  the  cribriform  plate,  obliquely  downward  and 
backward,  to  the  free  margin  of  the  internal  pterygoid  plate.  It  is 
composed  of  the  body  of  the  sphenoid  bone  and  the  alse  of  the  vomer. 

The  Floor  of  the  nasal  fossa  extends  from  the  face  anteriorly  to  the 
pharyngeal  space  posteriorly.  It  is  smooth,  inclining  slightly  down- 
ward and  backward,  being  concave  from  side  to  side.     It  is  composed 

^  It  is  of  great  importance  to  recognize,  and  early  in  life  gnard  against,  the  evil 
results  of  the  inflammation  of  the  throat  in  children  of  a  strumons  diathesis,  since  it 
is.  liable  to  produce  deformity  of  these  parts  and  irregularity  of  arrangement  of  the 
teeth. 


136  ANAT03IY. 

of  that  portion  of  the  bony  strncture  of  this  region  which  forms  the 
premaxillse  and  the  palatal  processes  of  the  superior  maxillae  and  hori- 
zontal plates  of  the  palate  bones. 

The  External  or  Lateral  Wall  is  the  most  extended,  uneven,  and  com- 
plicated portion  of  the  nasal  fossa.  Seven  bones  enter  into  the  forma- 
tion on  each  side — viz.  the  nasal,  superior  maxilla,  lachrymal,  ethmoid, 
inferior  turbinated,  and  palate  bones,  and  the  pterygoid  process  of  the 
sphenoid  bone.  To  form  the  outer  walls  of  both  sides  twelve  bones  are 
required — two  of  the  brain-case,  the  ethmoid  and  the  sphenoid,  and  all 
the  bones  of  the  face  excepting  four,  the  malar,  the  vomer,  and  the 
inferior  maxilla.  These  walls  are  divided  by  the  projections  of  the  tur- 
binated processes  of  the  ethmoid  bone  and  the  inferior  turbinated  bone 
into  three  horizontal  compartments,  the  superior,  middle,  and  inferior. 

The  Superior  Jleatus  is  the  shortest  and  shalloM'est  of  the  three.  It 
is  situated  between  the  superior  and  inferior  turbinated  masses  of  the 
ethmoid  bone,  and  in  the  articulated  skull  between  the  superior  and 
inferior  turbinated  bones.  • 

The  Middle  3Ieatus  is  situated  between  the  middle  and  inferior  tur- 
binated bones,  and  forms  two-thirds  of  the  posterior  portion  of  the  outer 
wall  of  the  nasal  fossa. 

The  Inferior  Meatus  is  situated  between  the  inferior  turbinated  bone 
and  the  floor  of  the  nose.     It  is  the  longest  of  the  three  meati. 

The  openings  into  the  nasal  fossa  are  numerous,  and  may  be  classified 
as  follows : 

The  Anterior  Aperture  is  that  pyriform  opening  leading  from  the 
face  into  the  fossa,  and  has  been  previously  described. 

The  Posterior  Aperture  opens  into  the  pharyngeal  space.  It  is 
bounded  above  by  the  vaginal  process  of  the  sphenoid  bone  and  the 
alse  of  the  vomer;  below  by  the  palatal  process  of  the  palate  bone; 
internally  by  the  vomer;  and  externally  by  the  free  border  of  the  inter- 
nal plate  of  the  pterygoid  process  of  the  sphenoid  bone. 

The  Lachrymal  Canal  ojjens  into  the  superior  portion  of  the  inferior 
meatus,  behind  the  nasal  process  of  the  superior  maxilla  and  external 
to  the  inferior  turbinated  bone.  This  canal  is  occupied  by  the  nasal  or 
lachrymal  duct,  which  conveys  the  lachrymal  fluid  froni  the  eye  into 
the  nose. 

The  Spheno-palatine  Foramen  is  situated  in  a  line  just  back  of  the 
superior  meatus.  It  is  bounded  below  by  the  palate  bone,  above  by 
the  sphenoid  bone,  and  opens  into  the  spheno-palatine  space.  It  trans- 
mits into  the  nasal  fossa  the  naso-palatine  nerves  and  vessels. 

The  Incisor  Foramen,  or  Foramen  of  Stenson,  is  situated  in  the 
anterior  portion  of  the  nasal  fossa,  near  the  septum  and  back  of  the 
premaxilla.  It  opens  into  the  anterior  palatine  canal  on  the  oral  aspect 
of  the  hard  palate,  and  transmits  the  anterior  palatine  vessels. 

The  Foramen  of  Scarpa  is  situated  within  the  intermaxillary  suture, 
and  opens  into  the  anterior  jxilatine  canal  on  the  oral  aspect  of  the  hard 
palate.     It  transmits  the  naso-palatine  nerve. 

The  Olfactory  Apertures  are  those  numerous  small  openings  found  in 
the  cribriform  plate  of  the  ethmoid  bone.  They  communicate  with  the 
brain-case,  and  transmit  the  filaments  of  the  olfactory  nerves. 


BONES. 


137 


The  slit-like  openings  in  the  anterior  portion  of  the  cribriform  plate 
communicate  with  the  brain-case,  and  transmit  the  nasal  nerve  and  the 
vessels  which  accompany  it. 

The  Openings  into  Air-cells. — In  the  dried  skull  there  are  generally 
two  openings  into  the  maxillary  sinus,  but  in  the  recent  state  there  is 
not  often  more  than  one.  It  is  situated  about  the  centre  of  the  middle 
meatus,  and  permits  the  passage  of  fluid  from  the  antrum  into  the  nasal 
chambers. 

The  Infundihulum  extends  from  the  superior  portion  of  the  middle 
meatus  anteriorly  to  the  outer  side  of  the  middle  turbinated  bone,  unit- 
ing this  meatus  with  the  frontal  sinuses  and  the  anterior  ethmoidal 
cells ;  it  allows  the  fluid  from  these  openings  to  descend  into  the  nasal 
chambers. 

The  other  openings  into  the  remaining  air-cells  have  already  been 
fully  described  under  the  headings  of  the  bones. 


Fig.  66. 


The  Cavity  of  the  Mouth. 

The  Cavity  of  the  Mouth  is  situated  between  the  two  superior  maxil- 
lary bones  above  and  the  inferior  maxillary  bone  and  their  attached 
muscles.  When  the  jaws  are  closed  this  cavity  is  paraboloid  in  shape, 
opening  behind  and  below.  In  the  recent  state  the  inferior  opening  is 
closed  by  the  tongue  and  mylo-hyoid  muscle. 

The  Roof  of  the  Mouth  (Fig.  QQ),  which  is  formed  by  the  hard  palate, 
is  generally  arched  in  front  and  flattened  behind.  It  is  composed  of 
the  palatal  processes  of  the 
two  superior  maxillary  and 
palate  bones. 

The  Posterior  Border  is 
free,  thin,  and  divided  into 
two  portions  by  the  posterior 
nasal  spine.  On  each  side 
of  this  spine  the  border  is 
concave,  and  terminates  later- 
ally in  the  pyramidal  process 
of  the  palate  bone  and  the 
hamular  process  of  the  sphe- 
noid bone. 

Situated  within  the  palato- 
maxillary suture,  just  inter- 
nal to  the  tuberosity  of  the 
superior  maxilla,  are  the  pos- 
terior and  accessory  palatine 
canals  for  the  transmission  of  the  posterior  palatine  nerves  and  vessels. 

The  surface  of  the  roof  of  the  mouth  is  perforated  by  numerous 
small  foramina  for  the  transmission  of  nutrient  vessels  to  the  body  of 
the  bone,  pitted  for  the  lodgment  of  the  mucous  glands,  and  grooved 
longitudinally  for  the  accommodation  of  vessels. 

The  Floor  of  the  3Iouth. — The  circumference  of  the  floor  of  the 
mouth  is  formed  by  the  mylo-hyoid  ridge.     This  ridge  gives  attach- 


Roof  of  the  Mouth. 


138  ANATOMY. 

ment  throughout  its  entire  extent  to  the  mvlo-hyoid  muscle,  which, 
together  with  the  base  of  the  tongue,  forms  the  true  floor. 

The  anterior  and  two  Uiteral  walls  of  the  mouth  are  formed  by  the 
alveolar  processes  and  the  teeth  of  both  jaws. 

Posteriorly  the  oral  cavity  opens  into  the  pharyngeal  space. 


CARTILAGE. 


Cartilage  is  one  of  the  three  groups  of  connective  tissues  of  the 
body.  It  is  made  up  of  cells  imbedded  in  a  matrix,  which  yields,  on 
boiling,  chondrin,  the  basement-substance.  That  this  differs  from  other 
connective  tissue  has  of  late  been  questioned,  and  the  view  that  it  is  a 
distinct  chemical  substance  now  appears  to  be  undergoing  a  change. 
By  some  it  is  believed  to  be  a  mixture  of  gelatin,  mucin,  and  salts. 
(See  Prudden's  Normal  Histology,  p.  53.)  Cartilage  forms  the  entire 
skeleton  of  many  of  the  cold-blooded  (or  lower  order  of)  animals,  and 
of  others  it  constitutes  a  varying  proportion.  In  the  highest  verte- 
brates only  a  small  portion  of  cartilage  exists  at  puberty,  though  it  is 
found  after  this  period  in  the  covering  of  the  articulating  surfaces  of 
bones  and  connecting  the  ribs  with  the  sternum  ;  in  the  rings  of  the 
trachea,  walls  of  the  bronchi,  larynx,  and  other  parts  of  the  air- 
passages  ;  in  the  grooves  through  which  muscular  tendons  glide ;  and 
in  interarticular  discs  situated  between  the  articulating  surfaces  of  bones, 
where  a  decidedly  firm  though  more  yielding  structure  than  bone  is 
required.  The  early  embryonic  life  of  the  entire  skeleton,  with  but 
minor  exceptions,  is  composed  of  cartilage,  in  which  is  gradually  depos- 
ited calciferous  matter;  it  is  then  apparently  absorbed  and  replaced  by 
bone-cells  or  osteoblasts,  which  first  appear  at  the  different  points  of 
ossification  and  develop  the  entire  bony  structure.  Temporary  cartilage 
is  that  which  gradually  develops  into  bone.  Permanent  cartilage  is  that 
which  remains  cartilage  throughout  life,  as  the  interarticular  discs  that 
cover  the  articular  extremities  of  bones,  etc. 

The  principal  function  of  cartilage  in  the  higher  vertebrates  is  its 
physical  property  of  elasticity.  It  yields  to  pressure  or  to  muscular 
force,  but  immediately  resimies  its  normal  position  or  shape  when  such 
pressure  or  force  is  removed. 

When  placed  between  articulating  extremities,  as  the  proximate  sur- 
faces of  tlie  vertebne,  the  temporo-maxillary  articulation,  etc.  etc.,  it 
acts  as  a  cushion,  diminishing  the  force  of  concussion.  In  positions 
where  shock  would  be  particularly  harmful  there  is  interposed  within 
the  joint,  in  addition  to  the  cartilage  covering  the  articular  surfaces  of 
bones,  a  cartilaginous  disc  or  extra  cushion.  Were  it  not  for  the  car- 
tilage placed  within  the  joints  situated  between  the  feet  and  the  head, 
the  shock  communicated  to  the  brain  in  the  simple  act  of  walking 
would  probably  be  so  great  as  to  absolutely  prevent  its  practice  in  man. 

The   cartilages   connecting   the   ribs  with  the   sternum   permit  the 


CARTILAGE. 


139 


expansion  and  contraction  of  the  chest  necessary  to  breathing,  and 
those  within  the  walls  of  the  air-passages  prevent  closnre  of  the  tubes 
when  they  are  flexed. 

Histologists  divide  cartilage  into  two  parts — the  cartilage-cell  and 
the  hyaline  or  intercellular  substance  or  matrix. 

Cartilage  is  also  divided  into  three  kinds,  according  to  the  chai'acter 
of  the  matrix — hyaline  cartilage,  fibro-cartilage,  and  iibro-elastic  carti- 
lage. 

HyaUne  Cartilage  is  so  named  from  its  resemblance  to  glass.  It 
is  firm,  homogeneous,  and  more  or  less  transparent  according  to  thick- 

Fifj.  fi7. 


o 

■r^ 

' 

- 

-:- 

m 

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'^ 

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S:1 


Vertical  Section  of  Articular  Cartilage  covering  the  lower  eml  of  the  Tibia,  human  (magnified  about 
."0  dianietersi :  n.  cells  and  cell-groups  flattened  conlormably  with  the  surface;  h,  cell-groups 
irreguhirly  arranged;  c,  cell-groups  disposed  perpendicularly  to  the  surface;  d,  layer  of  calcified 
cartilage  ;V,  bone. 

ness.  It  is  found  at  the  articulating  surfaces  of  all  except  intermem- 
branous  bones  (articulating  cartilage);  at  the  anterior  extremities  of 
the  ribs  (costo-cartilage) ;  in  the  wings  of  the  trachea,  walls  of  the 

Fig.  68. 


White  Fibro-cartilage  from  an  Intervertebral  Disc,  human  (highly  magnified).  The  concentric  Hues 
around  the  cells  indicate  the  limits  of  deposit  of  successive'  capsules.  One  of  the  cells  has  a 
forked  process  which  extends  beyond  the  hyaline  area  surrounding  the  cell,  amongst  the  fibres 
of  the  general  matrix. 

bronchi,  and  in  the  septum  and  lateral  cartilages  of  the  nose,  etc.  etc. 
The  articulating  cartilage  has  cells  and  cell-groups,  which  near  the  sur- 
face are  flattened  (Fig.  67).  Late  in  life  the  costal  cartilages  become 
finely  fibrillated  and  occasionally  completely  ossified. 


140  ANATOMY. 

Fibro- Cartilage  (white)  (Fig.  68)  receives  its  name  because  its  matrix 
is  composed  of  bundles  of  fibrous  connective  tissue,  the  bundles  being 
arranged  in  layers.     Between  the  lamellae  of  these  fibrous  bundles  are 
rows  of  flattened,  oval,  nucleated  cells,  each  cell  being  surrounded  by  a 
delicate  capsule.     These  cells  are  similar  to  those  found  in  tendons,  though 
they  are  not  so  flat,  and  are  distinguished  by  their  surrounding  capsule. 
Where  fibro-cartilage  unites  with  tendinous  tissue,  as  does  the  inter- 
articulating  fibro-cartilage  of  the  temporo-maxillary  articulation  with 
the  tendon  of  the  external  pterygoid  muscle,  the  two  kinds  of  cells 
merge  imperceptibly  into  one  another.     The  sesamoid  cartilage,  inter- 
vertebral discs,  interarticular  cartilage,  the  interarticular  fibro-cartilage 
of  the  temporo-maxillary  articulation,  all  are  of  the  fibrous  variety. 
The  Fibi'o-elastiG    Cartilage  (yellow  elastic)   is  spoken  of  by  some 
p,  as  reticular  cartilage,  by  reason  of  the 

arrangement    of    its    fibres.      In    early 
I    ^  '  ;  1     life  this  varietv  of  cartilage  is  hyaline, 

*  -A:         ;  '.  ev(^i^l;ii.'   v3         but  in  adult  life  it  becomes  permeated 
' '^  J     with  elastic  fibres  which  proceed  from 

.,  ('0  the   perichondrium   inward.      It   is  the 

•^^  --   '>^W^''^^  most  elastic  of  all  cartilage.     Its  fibres 

are  fine,  and  so  branch  and  anastomose 

i    with  each  other  as  to  form  a  dense  net- 

Avork,  with   spherical  or  oblong  spaces 

'^    I    or  meshes,  in  which  lie  nucleated  cells 

,      ,    ,  '   ''.    of  varying  sizes  surrounded  by  a  zone 

;    of  hyaline  cartilage.      This  cartilage  is 

'     found  in  the  epiglottis,  in  the  auditory 

Fibrocartilage^_of^an^Jntervertebral       oauals,    the     Cartilage    of    Wrisbcrg    and 

Santorini,  of  the  larynx,  etc,  etc. 

Cartilage-cells  have  one  characteristic  which  distinguishes  them  from 
all  others — viz.  the  power  of  casting  around  themselves  a  halo  composed 
of  a  substance  similar  to  the  matrix  of  hyaline  cartilage ;  this  halo  or 
capsule,  however,  possesses  the  property  of  absorbing  certain  stains 
which  do  not  affect  true  hyaline  cartilage.  It  is  therefore  an  independ- 
ent structure,  and  forms  M'hat  is  known  as  the  cartilage  lacunar,  ^vhich 
are  in  reality  lymph-spaces. 

These  lacunae  are  not  isolated  cavities,  but  have  minute  capillary 
tubes  communicating  with  each  other,  and  finally  open  into  larger  tubes 
Avhich  extend  to  the  surface  of  the  cartilage. 

Cartilage-cells  are  spherical  or  oval-shaped  bodies,  usually  containing 
one  nucleus.  Under  certain  circumstances,  however,  the  shape  of  the 
cell  may  be  modified,  as  will  be  shown  hereafter.  They  increase  by 
division  (Fig.  70).  At  first  the  tAvo  new  cells  formed  from  the  original 
old  one  are  arranged  side  by  side,  in  close  proximity  to  each  other,  and 
are  half-moon  shape  in  outline.  These  cells  gradually  separate  from 
each  other  through  the  increase  of  the  capsular  substance  between  them. 
Finally,  a  division  takes  place  in  the  capsules  or  lacunae  and  the  new 
cells  are  completed.  But  one  cell  usually  occupies  a  lacuna,  and  during 
the  increase  of  cells  by  division  each  lacuna  may  contain  two,  four,  six, 
or  eight  cells,  according  to  the  rapidity  of  the  proliferation. 


THE  SKIN. 


141 


Cells  are  often  differently  arranged  in  the  same  kind  of  cartilage,  this 
depending  npon  the  depth  of  the  cartilage  and  the  connection  it  has 
with  other  tissues.  Where  cartilage  is  joined  to  a  synovial  membrane 
and  an  articulating  capsule,  the  cartilage-cells  are  more  or  less  branched, 
and  pass  insensibly  into  the  branched  connective-tissue  cells  of  the  mem- 
brane.    In  the  hyaline  cartilage  of  the   foetus  are  many  spindle  or 

Fig.  70. 


1  «!i!'  MWm  iii::uii;iiiiiiiii;i!  i!i.;iiiii: :  J!':!ii'i;i::  Ti':3;ii  iii:ii;!i  'im  'M  :iKi!  saiie:  liiil  m  w  i; «': 

Plan  of  the  Multiplication  of  Cells  of  Cartilage  :  A,  cell  in  its  capsule :  B,  divided  into  two,  each  with 
a  capsule;  C,  primary  capsule  disajipeared,  secondary  capules  coherent  with  matrix;  i>,  tertiary 
division  ;  E,  secondary  capsules  disappeared,  tertiary  coherent  with  matrix. 

branched  cells.  The  cells  in  the  cartilage  which  separates  an  apophysis 
from  a  diaphysis  of  long  bones  are  arranged  uniformly  in  vertical  rows. 

The  Penchondrium  covers  cartilage  as  periosteum  covers  bone  :  it  is 
a  vascular,  fibro-connective  tissue  envelope  containing  a  few  elastic 
fibres.  It  is  furnished  with  blood-vessels,  lymphatics,  and  nerves,  and 
is  important,  as  it  furnishes  protection  to  the  blood-vessels  that  supply 
the  cartilage.  It  covers  all  cartilage  excepting  that  on  the  articulating 
surfaces  of  bone  and  in  the  lines  of  ossification.  Through  the  blood- 
vessels of  the  perichondrium  the  adjacent  cartilage  receives  nourishment 
— not  by  the  passage  of  the  blood  itself  into  the  cartilage,  but  from  the 
plasma  of  the  blood  in  the  perichondrium,  which  permeates  the  cartilage 
through  numberless  minute  tubes  that  open  into  the  lacunse  or  capsules 
of  the  cartilage  by  one  end,  while  by  the  other  they  open  into  larger 
tubes,  freely  communicating  with  the  perichondrium. 

The  distance  between  the  substance  of  the  cartilage  and  its  source 
of  pabulum  or  nourishment  accounts  for  its  slow  repair  after  injury. 
When  cartilage  has  been  injured  the  wound  at  first  fills  up  with  connec- 
tive tissue.  This  connective  tissue  at  times  remains  permanent,  but  is 
occasionally  transformed  into  hyaline  cartilage.  When  the  lesions  are 
deep  the  margins  of  the  wound,  being  situated  nearer  to  the  perichon- 
drium, are  more  likely  to  heal  than  the  deeper  portions. 


THE  SKIN. 

The  skin  is  the  superficial  covering  of  the  body,  extending  over  its 
entire  surface  and  into  the  openings  of  its  mucous  canals  to  varying 
depths  until  it  joins  their  mucous  membrane.  It  is  flexible,  elastic, 
and  extensible.     It  is  loosely  attached  to  the  parts  directly  beneath, 


142  ANATOMY. 

excepting  at  such  places  as  the  palmar  surface  of  the  hand,  soles  of  the 
feet,  face,  and  the  calvarium,  Avhere  it  is  attached  to  the  fascia  beneath 
by  numerous  stout  fibrous  trabeculse,  the  spaces  between  these  bands 
being  filled  with  cushions  of  fat. 

In  the  region  of  the  face  and  neck,  as  is  shown  by  the  action  of  the 
muscles  of  expression,  -the  skin  is  movable  and  is  under  the  control  of 
the  striated  or  voluntary  muscular  structui'e. 

The  thickness  of  the  skin  varies  in  different  regions  of  the  body.  On 
the  back,  the  palmar  and  plantar  regions  it  is  very  thick,  while  in  the 
inguinal  and  axillary  regions  and  on  the  eyelids  it  is  extremely  thin. 
Hairs,  either  long  or  short,  coarse  or  fine,  are  found  protruding  from 
the  skin  throughout  almost  its  entire  extent,  but  they  are  much  more 
plentiful  in  some  places  than  in  others. 

The  Tactile  Corpuscles  are  in  the  papillse  of  the  skin  ;  they  are  the 
principal  organs  of  touch,  and  are  capable  of  a  high  degree  of  cultiva- 
tion, as  is  aptly  illustrated  in  the  marvellous  sensitiveness  of  many  blind 
persons.  By  this  sense  can  be  detected  degrees  of  heat  and  cold,  hard- 
ness and  softness,  and  the  direction  of  the  air-current  when  but  gentle. 
The  sensitiveness  of  the  skin  varies  in  different  parts  of  the  body,  it 
being  most  acute  at  the  tips  of  the  fingers  and  lips. 

The  skin  is  also  an  important  excretory  organ,  and,  under  certain 
circumstances,  is  capable  of  effecting  absorption,  its  functions  in  this 
respect  varying  in  different  parts  of  the  body. 

In  some  of  the  lowest  orders  of  animals  there  is  no  integumentary 
covering,  while  in  others  of  a  somewhat  higher  scale  there  is  a  distinct 
outer  layerof  cells  performing  the  functions  of  the  integument.  Others 
are  provided  with  special  organs  of  secretion,  as  is  illustrated  in  the  shell 
membrane  of  the  mollusca,  etc. 

In  the  higher  forms  of  animal  life  (the  vertebrates)  the  integument 
can  be  separated  into  two  great  divisions — the  epidcrm,  or  cuticle,  or 
scarf  skin,  and  the  derm,  or  corium,  or  cutis  vera — synonymous  names 
for  the  skin  layers  that  have  much  complicated  its  study. 

The  Blastoderm  at  a  very  early  stage  of  its  existence  divides  into  two 
layers,  the  epiblastio  and  the  hypoblastic  ;  a  third,  or  mesoblastic  layer, 
derived  from  the  contiguous  portion  of  the  epiblast  and  hypoblast,  forms, 
and  is  situated  between  them.  From  the  epiblastic  or  upper  layer 
are  formed  the  epiderm,  or  cuticle  of  the  skin,  and  all  its  appendages, 
such  as  the  hair,  the  nails,  the  enamel  of  the  teeth,  the  brain,  and  the 
nerves.  From  the  mesoblastic  or  middle  layer  are  formed  the  true 
skin,  the  cartilage,  the  bones,  muscles,  the  dentine  and  cementum  of  the 
teeth,  etc.  From  the  hypoblastic  or  lower  layer  are  formed  the  epithe- 
lium of  the  mucous  membrane  and  the  various  glands  of  the  alimentary 
canal  situated  posterior  to  or  below  the  ])alato-glossal  fold  of  the  mouth, 
and  in  front  or  above  the  lower  third  of  the  rectum. 

Fig.  71  is  a  diagram  of  the  skin  divided  into  different  strata  or  layers. 
The  first  natural  or  embryonic  division  is  formed  through  its  separation 
into  two  layers,  the  upper  one,  the  epiderm,  being  derived  from  the 
epiblastic,  and  the  lower  one,  the  true  skin,  from  the  mesoblastic  layer, 
an  apparent  basement-membrane  (hereafter  explained)  being  situated 
between  them. 


THE  SKIN. 


143 


The  Epidermis  is  that  portion  of  the  skin  which  is  separated  from  the 
deeper  structure  in  the  formation  of  a  blister.  It  is  clearly  demonstrated, 
as  it  constitutes  the  thin  wall  or  covering  of  the  blister.     It  comprises 


Fig.  71. 


Vertical  Section  of  the  Skin  of  the  Thumb,  partly  diagrammatic  :  a,  stratum  corneum,  or  epiblastic 
portion,  traversed  bv  ducts  of  two  glnnds;  b,  rcte  mucosum.  with  prolongations  extending 
between  papilla  beneath:  between  "  and  h  is  seen  the  stratum  luciduni,  also  tlie  basement-mem- 
brane ;  c,  mesoblastic  portion  or  papillarv  layer  of  corium.  Near  the  centre  of  the  figure  is  seen 
a  nervous  papilla  ;  d.  reticular  laver  of  corium  with  vascular  plexus,  nucleated  connective  tissue, 
and  interspaces;  e,  coils  of  four  sweat-glands;  /,  fat-giobules  in  the  meshes  of  connective  tissue. 
(From  Hyde's  Diseases  of  the  Skin.) 

all  that  portion  of  the  first  division  above  the  basement-membrane.  Its 
under  surface  is  uneven,  being  marked  by  depressions  and  elevations 
corresponding  to  and  fitting  over  the  papillse  of  the  true  derm.     Com- 


144  ANATOMY. 

mencing  at  its  foundation  or  lower  portion,  it  is  subdivided  as  follows  : 
stratum  Malpighii  or  rete  mucosum,  stratum  granulosum,  stratum 
lucidum,  and  stratum  corneum.  The  continued  growth  of  the  epidermis 
as  a  whole,  with  its  appendages,  the  hair,  nails,  and  the  enamel  of 
the  teeth,  depends  upon  this  function  of  development  of  the  stratum 
Malpighii. 

Slratum  31alpighii. — Just  above  the  papillary  layer  of  the  corium  is 
a  layer  of  oval  cells,  each  containing  nuclei.  These  cells  are  constantly 
undergoing  proliferation,  and  are  connected  by  numerous  fine  filaments 
(imbricated  cells).  As  the  cells  multiply,  those  which  have  been  pre- 
viously formed  are  pushed  upward  toward  the  surface,  die,  and  are 
cast  off. 

Stratum  Granulosum. — Above  the  stratum  Malpighii  the  cells  change 
their  form — become  more  flattened  and  possess  large  and  distinct  nuclei. 
The  prot(^3lasmic  contents  of  the  cells  also  exhibit  numerous  granular 
masses,  and  from  this  appearance  the  layer  thus  formed  receives  its 
name. 

Stratum  Lucidum. — Above  the  stratum  granulosum  the  cells  flatten 
out  still  more,  become  narrower  and  homogeneous,  and  sections  of  them 
freely  transmit  light;  hence  the  name. 

Stratum  Corneum. — Above  the  stratum  lucidum  another  change  in 
the  cells  takes  place.  At  first  they  appear  to  swell  up,  but  soon  assume 
a  more  flattened  appearance,  tlie  most  superficial  of  them  becoming 
structurally  horny  scales  are  constantly  undergoing  desquamation. 

The  True  Skin,  Derm,  Corium,  or  Cutis  Vera  is  a  tough,  flexible, 
elastic,  highly  vascular,  and  nervous  tissue,  containing  lymphatic  ves- 
sels. It  is  developed  from  the  mesoblastic  or  middle  layer  of  the 
blastoderm. 

Structure. — The  true  derm  is  principally  composed  of  a  reticulum 
of  white  fibrous  connective  tissue  largely  interwoven  with  elastic  fibres. 
There  are  also  found  in  it  many  independent  lymphoid  cells  and  a 
complicated  network  formed  by  an  intimate  association  of  the  processes 
of  the  connective-tissue  corpuscles.  Unstriated  or  involuntary  muscular 
fibres  are  found  in  the  vicinity  of  the  nipples  and  their  alveoli,  etc.,  and 
striated  or  voluntary  muscular  fibres  are  to  be  met  with  in  the  region  of 
the  face,  head,  neck,  and  portions  of  the  hand. 

The  Papilla. 

The  true  skin  is  divided  into  two  portions,  upper  and  lower,  known 
as  the  jxipillary  and  reticular  (or  vascular)  layers.  These  receive  their 
name  from  their  anatomical  formations.  The  papillse  of  these  layers 
arc  considered  to  be  the  organs  of  touch,  as  they  are  found  more  highly 
developed  at  those  ]X)ints  wliere  the  sense  of  touch  is  most  delicate. 
They  act  by  extending  the  surface  for  the  production  of  cuticular 
tissue,  and  hence  are  fi)und  large  and  numerous  under  the  nails.  The 
pulps  of  the  teeth  and  the  papillie  of  the  hairs  are  developed  from 
them.  They  are  conical  or  finger-like  in  shape,  and  are  either 
simple  or  compound,  sometimes  dividing  near  their  apices  into  two 
or  more  projections.     They  vary  both  in  shape  and  size  in  diflerent 


THE  SKIN.  145 

parts  of  the  body,  beino;  largest  on  the  pahuar  surfaces  of  the  hands  and 
the  soles  of  the  leet.  These  papillae  of  the  true  derm  fit  into  correspond- 
ing depressions  of  the  epiderm.  As  the  superior  surface  of  the  papillary 
layer  is  approached  the  fibrous  network  of  the  connective  and  the  elastic 
tissue  becomes  finer  and  finer,  the  fibres  approximating  more  closely  until 
they  appear  to  form  a  homogeneous  layer  known  as  the  basement  mem- 
brane of  Todd  and  Bowman. 

The  fibres  toward  the  inferior  surface  of  the  papillary  layer  are 
coarser  and  more  loosely  interwoven  than  they  are  at  the  superior  sur- 
face, and  finally  pass  into  the  subareolar  tissue. 

l^he  Reticidar  Layer. — The  line  of  demarcation  between  the  upper 
and  the  lower  layers  of  the  true  skin  is  not  clear  and  distinct,  but  one 
part  gradually  merges  into  the  other,  the  principal  point  of  difference 
being  in  the  arrangement  of  the  fibrous  network.  Descending  from 
above,  the  fibres  become  fewer  and  are  situated  farther  apart,  until  a 
coarse  network  is  formed,  which  is  finally  lost  in  the  subcutaneous  con- 
nective tissue.  At  this  point  these  bands  form  a  loose  reticulum,  the 
meshes  of  which  are  generally  filled  Mith  an  abundance  of  fat. 

The  quantity  of  fat  within  the  reticulum  varies  considerably  in  dif- 
ferent regions  of  the  body,  being  large  about  the  mammary  glands  and 
in  the  palms  of  the  hands  and  the  soles  of  the  feet,  while  in  the  eye- 
lids and  about  the  ears  but  little  if  any  is  found. 

The  Blood-vessels  of  the  Skin  ascend  through  the  subcutaneous  con- 
nective tissue,  and  divide  as  they  pass  through  the  true  derm  toward 
the  surface.  They  give  off  branches  which  pass  to  the  fat-clusters, 
sweat-glands,  hair-follicles,  and  the  corium.  As  they  approach  the 
papillary  layer  they  form  a  fine  capillary  network  of  anastomosing 
vessels,  the  papillae  being  supplied  with  capillary  vessels  Avhich  pass 
through  their  central  portion,  furnishing  an  abundant  supply  of  blood. 
Veins  accompany  the  arteries  in  their  ramifications,  but  no  blood-ves- 
sels pass  into  the  epiderm. 

The  Lymphatics  are  distributed  throughout  the  entire  surface  of  the 
skin,  except  the  epidermal  layer,  though  not  equally  in  all  parts,  being 
larger  and  more  abundant  around  the  nipples  and  on  the  scrotum. 
They  are  arranged  in  two  strata,  with  anastomosing  vessels  between 
them.  The  superior  stratum  is  situated  just  below  the  network  of 
capillary  blood-vessels,  passing  up  into  some  of  the  papilla3  in  the 
palms  of  the  hands  and  soles  of  the  feet.  Valves  are  found  in  the 
larger  vessels  of  the  corium,  but  not  in  the  smaller  ones  or  in  those 
of  the  superior  layer.  The  hair-follicles  and  the  glands  of  the  skin  have 
special  plexuses  of  lymphatics  as  well  as  of  blood-vessels. 

The  lymphatics  of  the  skin  orginate  in  the  spaces  between  the  cells, 
as  they  do  in  other  kinds  of  connective  tissue,  and  have  a  linear  arrange- 
ment between  the  bundles  of  fibres. 

The  Nerves. — As  the  skin  is  the  organ  of  the  body  possessing  the 
special  function  of  touch-perception,  it  is  but  natural  to  expect  many 
nerves  to  be  distributed  over  its  surface ;  and  as  the  degree  of  sensi- 
bility varies,  it  is  also  to  be  supposed  that  the  nerves  are  not  equally 
distributed.  The  principal  branches  pass  through  the  subcutaneous 
connective  tissue,  divide  at  the  corium,  and  run  in  various  directions, 
Vol.  I.— 10 


146 


ANATOMY. 


forming  plexuses  of  fine  nerve-fibres  near  the  surface.  From  the 
most  superficial  of  these  plexuses,  or  those  situated  immediately  below 
tlie  epidermis/  fine  non-medullated  nerve-fibres  pass  upward  between 
the  cylindrical  cells  of  the  stratum  Malpighii  of  the  cuticle,  where  they 
terminate.  The  nerves  are  abundantly  distributed  to  parts  that  are 
covered  with  hair,  especially  where  such  hair  is  used  as  a  sentient  organ, 
as  is  the  case  with  the  whiskers  of  the  cat.  The  termination  of  many 
of  the  nerves  will  be  found  in  the  tactile  and  Pacinian  corpuscles. 
The  Tactile  or  Touch  Corpuscles  (Figs.  72,  73)  are  usually  oval  in 

Fig  72 


Fig.  73. 


Fp 


Section  of  .Skin,  sliowing  two  PajjilUe  and  deei)er  layers  of 
Epidermis:  o,  vascular  papilla  with  capillary  loop  passing 
from  subjacent  vessel,  c ;  b,  nerve-papilla  with  tactile  cor- 
puscle, t  (the  latter  exhibits  transverse  fibrous  markings) ; 
d,  nerve  passing  up  to  it;  /, /,  sections  of  spirally  winding 
nerve-fibres. 


Tactile  Corpuscle  within  a  papil- 
la of  the  skm  of  the  hand, 
stained  with  chloride  of  gold. 
The  convolutions  of  the  nerve- 
fibres  within  the  corpuscle  are 
seen.    is);,  epidermis. 


shape — they  may  be  straight  or  slightly  folded — and  are  situated  within 
certain  of  the  papillae  of  the  corium  ;  they  are  attached  to  medullary 
nerve-fibres.  These  papillfe  contain  no  blood-vessels,  and  are  called 
tactile  or  sensory,  in  contradistinction  to  the  vascular  papillae  which 
contain  the  blood-vessels.  Their  number  varies  according  to  location, 
they  being  most  numerous  where  the  touch  is  mofst  acute,  as  on  the 
inner  or  palmar  side  of  the  last  phalanges  of  the  fingers. 

The  Pacinian  Corpuscles  are  oval  or  olive-shaped  bodies,  receiving 
the  terminal  ends  of  cutaneous  nerves.  In  the  skin  they  are  situated 
in  the  subcutaneous  connective  tissue,  and  like  the  touch-corpuscles  are 
most  abundant  on  the  palms  of  the  hands,  soles  of  the  feet,  the  fingers 
and  toes,  and  more  especially  on  their  distal  phalanges. 

Pigment. — The  color  of  the  skin  depends  upon  the  deposit  of  pig- 
ment-granules.    This  is  generally  found  in  the  lowest  .stratum  of  the 

'  The  lymphatics  do  not  pass  into  the  epidenn,  and  that  is  the  reason  normal  skin  is 
not  an  al)sorbin<r  orMn. 


THE  SKIN. 


147 


Malpighian  layer,  and  appears  to  fade  away  gradually  as  it  approaches 
the  surface.  In  the  normal  condition  it  is  never  found  in  the  corium. 
The  color  of  the  skin  will  depend  upon  the  quantity  of  this  pigmentary 
deposit, A'arying  from  white  to  black  according  to  race,  and  differing  in 
shade  in  the  same  race,  as  is  illustrated  in  the  blonde  and  brunette. 


Fig. 74. 


Appendages  of  the  Skin. 

In  man  these  are  the  hair,  teeth,  nails,  and  sebaceous  glands.  The 
teeth  will  be  described  elsewhere  in  this  work. 

The  Hair,  like  the  nails  and  the  enamel  of  the  teeth,  is  a  peculiar 
modification  of  the  epidermis.  It  is  developed  from  the  epiblastic  or 
ujjper  layer  of  the  blastoderm,  and  consists  necessarily  of  the  same  struc- 
ture, and  is  governed  by  the  same  general  laws  of  development,  growth, 
and  sustenance,  as  the  epidermis.  It  is  found  on  nearly  every  part  of 
the  surface  of  the  body,  the  exceptional  parts  being  the  soles  of  the  feet, 
the  palms  of  the  hands,  the  eyelids,  the  inner  surface  of  the  prepuce, 
glans  penis,  and  the  last  phalanges  of  the  fingers  and  toes. 

Its  color,  length,  and  thickness  vary  according  to  the  part  of  the 
body  on  which  it  is  found,  and  are  influenced  by  race  and  tempera- 
ment. The  color,  like  that  of  the  skin,  depends  upon  the  quantity  of 
pigment  deposited  within  its  structure,  absolutely  white  hair  having 
none.  Oftentimes  the  color  varies,  not  alone  in  different  individuals, 
but  in  the  same  person,  as  the  hair  of  the  face 
is  seldom  of  the  same  shade  as  that  on  the 
head. 

The  length  of  the  hair  varies  from  that 
which  does  not  extend  beyond  the  opening  of 
the  follicle  to  the  longest  grown  upon  the  head. 
Its  thickness  also  varies  considerably,  that  cov- 
ering the  head  being  finer  than  that  found  on 
the  face  and  on  the  borders  of  the  eyelids,  etc. 
etc.  Straight  hair  is  coarser,  and  its  trans- 
verse sections  are  more  circular,  than  curly 
hair,  which  is  generally  fine  and  oval  in  trans- 
verse section. 

Anatomically,  the  hair  is  divided  into  a 
root,  shaft,  and  point. 

The  Follicle  is  formed  by  the  dipping  down 
of  the  epiderm  into  the  tissue  below  (Fig.  72). 

The  Root  of  the  hair  is  that  portion  which 
is  in  the  hair-follicle  of  the  skin. 

The  Bulb  is  the  expansion  of  the  extremity 
of  the  root. 

The  Shaft  is  that  portion  of  the  hair  above 
the  mouth  of  the  follicle.    In  straight  hair  its 
transverse    section  is  almost   cylindrical ;    in 
curly  hair  it  is  compressed  or  oval.     It  is  composed  of  compact  tissue, 
which  gradually  tapers  as  it  approaches  the  end. 

Histologically,  the  hair  is  also  divided  into  three  portions — the  cuti- 


Section  of  Hair-follicle:  1,  dermic 
coat  of  follic'e;  2,  epidermic  coat 
or  root-sheath ;  n,  outer  layer  of 
dermic  coat,  with  blood-vessels,  ft, 
h,  cut  across ;  c,  middle  layer ;  d, 
inner  or  hyaline  layer;  e,  outer 
root -sheath;  /,  .7,  "inner  root- 
sheath  ;  h,  cuticle  of  root-sheath  ; 
/,  hair. 


148 


ANAT03IY. 


cle,  fibrous  (cortical),  and  medullary  portions,  though  the  latter  is  not 
always  present. 

The  Cuticle  is  the  outer  or  investing  membrane  of  the  hair,  firmly- 
binding  its  bundles  of  fibres  together.  Under  the  microscope  this  mem- 
brane is  seen  to  be  composed  of  fine  imbricated  scales.  The  upper  edges 
of  these  project  and  form  fine  transverse  wave-like  lines.  They  are 
without  nuclei,  and  are  analogous  to  the  upper  cells  of  the  corneous 
layer  of  the  epidermis,  and  perform  a  like  function  for  the  hair. 

The  Fibrous  or  Cortical  Portion. — The  bulk  of  the  hair  is  made  up 
of  this  substance ;  it  is  translucent,  and  is  arranged  in  longitudinal 

Fig.  75. 


Lowov  portion  of  Hair  pouch  from  the  lip  of  a  kitten  r,  follicle  ,  T,  tnns\  er^e  sections  of  connectivo- 
tissue  bundles  of  derma;  M,  arrector  pili  muscle;  Is,  inner  root-sheath;  OS',  outer  root-sheath; 
I',  papilla  ;  C,  cuticle ;  11,  root  of  hair  ;  II,  hyaline  or  so-called  structureless  membrane  (magnitied 
500  diameters). 

bundles  containing  oblong  patches  of  pigment-granules  and  other  color- 
ing matter  of  less  intensity. 

The  fibres  which  make  up  the  bundles  composing  this  portion  are 
subdivided  into  flattened  fusiform  cells  with  slender  elongated  nuclei, 
which  are  distinctly  visible  when  certain  reagents  are  used.     There  are 


THE  SKIN.  149 

also  spaces  between  these  cells  containing  air  -svhich  are  called  hair- 
lacunae  ;  these  are  more  abundant  in  white  hair  than  in  colored.  Ex- 
amined by  transmitted  light,  these  spaces  are  dark,  but  with  reflected 
light  they  are  a  brilliant  white. 

The  Medulla  or  Pith  is  usually  absent  in  the  fine  hairs  coverino-  the 
surface  of  the  body,  and  is  not  commonly  met  with  in  those  coverino-  the 
scalp.  It  is  also  lacking  in  the  hair  of  children  under  five  years  of  aoe. 
It  is  met  M'ith,  however,  in  the  short  thick  hairs.  When  present,  it  is 
found  in  the  centre  of  the  shaft  and  is  lost  before  reaching  the  point. 
It  is  composed  of  soft  cells,  oblong  or  rectangular  in  shape,  containing 
minute  particles,  some  of  which  appear  like  fat-granules.  There  are 
also  air-spaces  between  the  cells. 

Under  the  microscope,  with  transmitted  light,  the  medulla  appears  to 
be  darker  than  the  fibrous  substance  of  the  hair.  When  reflected  light 
is  used,  however,  it  ajjpears  white.  This  change  in  appearance  is  due  to 
the  lacunae  found  within  its  substance. 

The  Hair-follides  contain  the  hair,  and  are  generally  found  in  groups 
of  three  or  four,  more  rarely  two ;  very  rarely  are  they  single.  With 
few  excepted  places  they  are  found  all  over  the  entire  integument.  This 
follicle  is  an  elongated  pear-shaped  sac  passing  obliquely  down  through 
the  dilFerent  strata  of  the  skin  into  the  subcutaneous  tissue,  in  which  tat 
is  found.  The  follicles  of  small  hairs  do  not  pass  so  deeply  as  those 
of  larger  ones,  and  those  which  accommodate  Moolly  hairs  are  curved 
at  the  bottom,  the  ends  often  curving  so  far  as  to  extend  upward. 

The  mouth  of  the  follicle  is  slightly  funnel-shaped,  the  lower 
portion  being  enlarged  to  accommodate  the  bulb  or  root  of  the  hair. 
The  follicle  is  also  invaginated  over  a  pear-shaped  papilla.  It  is 
formed  by  the  skin  dipping  down  into  the  tissue  below. 

The  coats  of  the  follicle  are  separated  into  two  divisions,  dermic  and 
epidermic.  These  are  again  subdivided,  the  dermic  into  three  layers — 
external,  middle,  and  internal ;  and  the  epidermic  into  an  outer  and  an 
inner  root-sheath. 

The  External  Layer  is  formed  in  a  manner  precisely  similar  to  the 
lower  layer  of  the  corium,  with  which  it  is  continuous  above.  It,  in  a 
measure,  determines  the  form  of  the  follicle,  and  in  composition  is  highly 
vascular  and  supplied  with  nerve-filaments.  No  elastic  tissue  enters 
into  its  structure.  The  bundles  composing  this  layer  are  laid  longitu- 
dinally with  the  axis  of  the  follicle. 

The  3Iiddle  Layer  is  very  similar  in  its  structure  and  arrangement 
of  blood-vessels  to  the  external  layer  of  the  corium.  It  is  thinner,  and 
composed  of  transverse  connective-tissue  fibres  with  elongated  nuclei. 
Nerves  have  not  been  found  in  this  layer. 

The  Internal  Layer,  or  "  glass  membrane,"  corresponds  in  structure  to 
the  basement-membrane  of  Todd  and  Bowman.  It  is  a  transparent, 
homogeneous  stratum,  the  inner  surface  of  which  is  raised,  the  outer 
surface  being  smooth. 

The  Epidermic  or  Cuticidar  Coat  is  that  portion  of  the  follicle  derived 
exclusively  from  the  epidermis,  and  is  continuous  with  it.  It  adheres 
closely  to  the  root  of  the  hair,  and  is  generally  removed  with  the  root 
in  extractina;  the  hair.     For  this  reason  it  is  called  the  root-sheath, 


150  ANATOMY. 

and  is  composed  of  two  layers,  called  the  external  and  the  internal  root- 
sheaths. 

The  External  Root-sheath  is  that  portion  of  the  hair-follicle  which  is 
derived  from  the  lowest  or  Malpighian  stratum  of  the  cuticle.  It  is 
composed  of  several  layers  of  polygonal  cells  with  nuclei,  as  far  as  the 
hair-bulb,  where  it  is  composed  of  but  one  row  of  cells,  which  become 
continuous  with  the  hair-bulb  at  its  lowest  portion. 

The  external  root-sheath  contains  pigment-granules  in  the  dark  races, 
and  Langerhaus  claims  to  have  found  in  it  nerve-filaments  similar  to 
those  found  in  the  Malpighian  layer  of  the  skin. 

The  Internal  Root-sheath  is  derived  from  the  corneous  layer  of  the 
epidermis,  but  is  not  connected  ^vith  it.  It  commences  just  below  the 
orifices  of  the  sebaceous  glands,  passing  downward  to  the  bottom  of 
the  follicle,  where  it  joins  the  layer  of  columnar  cells  covering  the  hair- 
bulb. 

This  sheath  is  composed  of  two  layers — an  outermost,  or  layer  of 
Henle,  and  an  innermost,  or  layer  of  Huxley.  These  two  layers  com- 
mence as  one  just  below  the  orifices  of  the  sebaceous  glands.  As  they 
pass  downward  they  again  unite  and  form  one  layer  of  large  polygonal 
nucleated  cells  having  no  spaces  between  them,  and  finally  become  con- 
tinuous with  the  hair-bulb. 

The  Outermost,  or  Layer  of  Henle,  is  composed  of  elongated,  flat- 
tened, non-nucleated  cells,  generally  having  spaces  between  them. 

The  Innermost,  or  Layer  of  Huxley,  is  composed  of  flattened,  nucle- 
ated scales  two  or  three  deep.  The  layer  thus  made  forms  the  internal 
lining  of  the  follicle  below  the  orifices  of  the  sebaceous  glands.  The 
innermost  scales  are  imbricated,  lapping  over  the  superimposed  layer  of 
cuticular  imbricated  scales  of  the  hair,  and  thus  serve  to  hold  the  hair 
in  position. 

The  Papilla  of  the  Hair  is  a  conical-shaped  eminence  in  every  respect 
similar  to  the  papilla  of  the  skin — in  fact,  is  a  papilla  of  the  skin  car- 
ried to  a  lower  level  than  those  entering  into  this  structure,  and  being 
continuous  with  the  dermic  layer  of  the  follicle.  It  is  highly  vascular, 
and  is  supplied  with  nerve-filaments.  Its  blood-vessels  supply  the 
nourishment  for  its  development  and  growth. 

The  bulbous  expansion  at  the  root  of  the  hair  is  soft,  and  consists  of 
polyhedral  epidermic  cells  united  together  by  a  cement-like  substance. 
These  cells  are  continuous  at  the  circumference  of  the  bulb  with  the 
outer  root-sheath,  from  which  they  were  originally  derived.  The  base 
of  the  bulb  is  attached  to  the  bottom  of  the  follicle,  where  the  latter  is 
invaginated  over  the  papilla,  there  being  a  depression  in  the  base  for 
this  purpose.  The  circumference  of  the  base  is  attached  to  and  contin- 
uous with  the  lining  membrane  of  the  hair-follicle. 

Extending  over  the  surface  of  the  papilla  (above  the  basement-mem- 
brane) is  a  special  layer  of  short  oval  cells  (hair-builders)  which  are 
analogous  to  all  similar  V)uilding  cells,  such  as  those  of  the  epidermis, 
the  nails,  and  the  enamel  of  the  teeth.  The  formation  of  these  structures 
is  governed  by  one  general  law  :  that  is,  the  special  layer  of  cells  at  the 
base  and  on  the  circumference  of  the  papilla  are  constantly  in  an  active 
state  of  proliferation.     New  cells  are  thus  formed  which  push  the  older 


THE  SKIN. 


151 


ones  upward  into  the  bulb,  where  a  special  action  takes  place,  some 
going  to  form  hair,  others  nails,  etc.  etc.  They  form  the  hair  :  the 
great  bulk  of  the  cells  become  elongated  and  spindle-shaped,  and 
form  what  has  been  described  as  the  fibrous  substance  of  the  shaft. 

The  Sudoriferous  or  Szceat  Glanch  (Fig.  76)  are  distributed  over 
nearly  the  entire  surface  of  the  body.  They  are  most  numerous  in  parts 
not  supplied  by  hair,  though  they  are  plentiful  in  parts  where  the 
growth  of  hair  is  abundant,  their  ducts  occasionally  emptying  into  the 
hair-follicle.  Krause  has  estimated  the  entire  number  distributed  over 
the  body  to  be  2,381,248,  or  from  400  to  600  to  the  square  inch  on  the 
lower  limbs,  back  of  the  neck,  and  trunk,  where  they  are  fewest,  while 
in  the  palms  of  the  hands  and  on  the  soles  of  the  feet  they  are  found 
in  their  greatest  number,  and  reach  2800  to  the  square  inch. 

The  length  of  the  sudoriferous  gland,  together  with  its  tube,  has  been 
estimated  to  be  about  a  quarter  of  an  inch.  This  gives  the  human  body, 
containing  as  it  does  2,381,248  such  glands,  about  fifty  thousand  feet,  or 
over  nine  miles,  of  perspiratory  tubing. 

The  size  of  the  sudoriferous  glands  varies  in  different  parts  of  the 
body,  those  in  the  axilla  being  the  largest.  Here  they  have  been 
found  about  a  sixth  of  an  inch  in  diameter,  though  their  averag-e  diam- 
eter  ni  this  region  is  from  one-thirty-sixth  to  one-twelfth  of  an  inch,  tlie 
average  over  the  entire  body  being  one-seventieth  of  an  inch. 


e  Sweat-sland  within  the  epithelial  layers  of  the  skin:  BP.  papilla  with  injected  bloo<l-ves- 
',  valley  between  two  papilUe;  />,  duct  in  the  rete  nuicosum ;  K  ^,  epidermal  layer;  /  A, 
y  granulated  epithelia.  deeply  stained  with  carmine;  /',  diiqt  with  corkscrew  windings  in 


Duct  of  the 
sels ;   r 
coarsely  ^ 
the  epidermal  layer  (liiagnitied  20u  diameters) 


These  glands  eliminate  a  large  proportion  of  the  aqueous  and  gaseous 
matter  from  the  body.  Under  ordinary  temperatures,  in  the  absence  of 
too  severe  physical  exercise,  perspiration  goes  on  imperce])tibly,  but  in 
warmth  and  the  stimulus  of  vigorous  bodily  exercise  there  is  a  percepti- 
ble and  more  or  less  profuse  flow. 

These  glands  are  situated  in  the  lowest  stratum  of  the  corium,  and 


152 


ANATOMY 


are  found  at  various  depths  in  the  subcutaneous  connective  tissue,  sur- 
rounded by  adipose  tissue. 

They  are  tubular,  with  a  coiled,  rounded,  or  flattened  extremity,  the 
duct  through  the  epiderm  resembling  a  spiral  screw.  This  duct  ascends 
vertically  through  the  true  skin  and  cuticle,  terminating  in  an  enlarged 
pore  or  aperture  (Fig.  76).  Occasionally  these  glands  are  formed  of  two 
tubes  coiled  around  each  other.  When  so  formed  the  tubes  unite  at  the 
superior  extremity  of  the  gland  and  form  one  duct. 

Both  the  duct  and  the  gland  proper  are  invested  with  connective 
tissue  similar  to  and  continuous  with  the  corium.     Situated  within  this 

tissue,  which  forms  the  outer 


Fig.  7 


Section  of  Coil  of  a  Sweat-^land :  S\  tuhule  lined  by 
cuboidal  epithelia;  T,  central  calibre  of  the  tuhule;  D, 
the  beginning  of  the  duct;  C,  connective  tissue  wiih 
Injected  blood-vessels  (magnifieid  500  diameters). 


portion  of  the  tube,  is  a 
thin  membrane  which  tra- 
verses the  gland  and  the 
duct  as  far  as  the  epidermis, 
and  is  analogous  to,  and 
continuous  with,  the  base- 
ment-membrane of  the  skin. 
That  portion  of  the  tube 
above  this  basement-mem- 
brane is  epidermic  in  struc- 
ture, while  the  coiled  por- 
tion, or  the  true  secreting 
gland,  is  lined  by  a  single 
layer  of  cuboidal  and  poly- 
hedral epithelium  (Fig.  77), 
with  nuclei,  and  often  con- 
taining pigment  -  granules. 
Between  these  cells  of  the 
basement  -  membrane  is  a 
layer  of  non-striated  mus- 
cular fibres  arrano-ed  lone-i- 
tudinally.  These  fibres  are 
coils  several  times  before  leavino^  the 


not   found  in  the  duct,  which 
gland. 

The  duct  proper  is  lined  by  an  extremely  fine  cuticular  membrane. 
Between  this  lining  and  the  basement-membrane  are  situated  two  or 
three  layers  of  epithelial  cells.  The  epithelium  within  the  tube  forming 
both  the  gland  and  the  duct  is  continuous  with  the  epidermis. 

The  Cerumlnous  Glands  found  within  the  external  auditory  meatus 
are  so  similar  to  the  sudoriferous  glands  in  structure  and  mode  of 
development  that  they  have  been  classed  as  of  that  varietv. 

Sweat-glands  are  tJurrounded  by  numerous  blood-vessels. 

The  Sebaceous  Glands  belong  to  the  racemose  variety.  They  are  dis- 
tributed over  almost  the  entire  surfiice  of  the  body,  with  the  exception 
of  the  palms  of  the  hands,  soles  of  the  feet,  and  the  backs  of  the  last 
])halanges  of  the  fingers  and  toes.  They  are  situated  within  the  corium 
of  the  skin,  and  are  usually  connected  with  the  hair-follicle  by  two 
ducts  which  empty  into  it  a  little  below  its  mouth.  These  glands  do 
not  pass  into  the  subcutaneous  tissue. 


THE  SKIN. 


153 


The  number  and  size  of  these  glands  connected  with  each  follicle  do 
not  depend  upon  the  calibre  of  the  hair,  for  some  of  the  finest  hairs 
found  upon  the  surface  of  the  body  have  as  many  as  six  sebaceous 
glands  emptying  into  their  follicles.  Occasionally  the  gland  has  its 
outlet  upon  the  surface  of  the  skin. 

The  largest  of  this  variety  of  glands  are  found  in  connection  with 
the  eyelashes,  within  the  eyelid,  and  have  received  the  name  of  Mei- 
bomian glands.  Sebaceous  or  cystic  tumors,  which  sometimes  appear  on 
the  external  surface  of  the  head  and  in  the  eyelids,  are  caused  by  the 
clogging  of  the  orifices  of  these  glands  while  active  secretion  goes  on 
within.  The  secretion  of  these  glands  on  the  face  often  becomes  inspis- 
sated, especially  in  the  region  of  the  alse  nasi. 

Sebaceous  glands  diifer  in  shape,  though  their  general  outline  is  pyri- 
form,  the  duct  of  the  gland  corresponding  to  the  stem  of  the  pear. 

In  structure  they  are  lobular  (Fig.  78),  each  lobule  consisting  of  a 

Fig.  78. 


Sebaceous  Gland  of  the  btcoud  Class,  from  the  ate  nasi. 


cluster  of  spherical  secreting  saccules.  The  secretion  of  each  saccule  is 
collected  into  the  principal  duct  of  the  lobule,  and  passes  into  the  main 
duct  of  the  gland,  which  usually  has  its  outlet  a  little  below  the  mouth 
of  the  hair-follicle. 


154  ANAT03IY. 

The  outer  surface  of  the  saccules  is  formed  by  a  basement-membrane 
which  is  continuous  with  the  basement-membrane  of  the  skin.  Next  to 
this  membrane,  within  the  gland,  is  situated  a  layer  of  polyhedral  gran- 
ular epithelial  cells,  each  containing  a  spherical  or  an  oval  nucleus. 
Resting  upon  this  layer  and  filling  the  saccule  is  a  layer  of  large  poly- 
hedral cells  with  spherical  nuclei.  The  cells  are  largest  near  the  centre 
of  the  saccule,  while  toward  its  outlet  they  become  atrophied. 

The  duct  of  the  gland  is  a  continuation  of  the  outer  root-sheath.  The 
cuboidal  cells  of  the  gland  undergo  active  proliferation ;  as  this  process 
continues  the  older  cells  are  pushed  toward  the  duct  until  they  reach  the 
surface  of  the  skin,  where  they  form  sebaceous  matter. 


AREOLAR  TISSUE,  TENDONS,  AND  MUSCLES. 

The  Areolar  Tissue  is  the  third  variety  of  connective  tissue,  bone 
and  cartilage  representing  the  other  two.  It  is  a  soft  filamentous  sub- 
stance, with  considerable  tenacity  and  elasticity.  It  is  found  immedi- 
ately below  the  skin,  extending  between  and  forming  the  sheaths  of  the 
muscles.  It  comprises  the  subcutaneous  or  superficial  fascia  and  the 
reflections  into  deeper  planes  known  as  deep  fascia,  and  connects 
mucous  and  serous  membranes  with  the  parts  which  they  line  or 
invest,  in  which  position  it  is  known  as  submucous  or  subserous  areolar 
tissue.  It  likewise  both  separates  and  encloses  all  muscles,  forming 
envelopes  for  them.  It  forms  the  sheaths  around  the  blood-vessels  and 
deep-seated  parts  or  organs,  in  which  position  it  is  designated  interme- 
diate  areolar  tissue,  and  if  it  comes  in  immediate  contact  with  the  part  it 
is  called  lavedhig  areolar  tissue.  In  a  word,  it  is  found  throughout  the 
various  organs  of  the  body,  penetrating  between  the  muscular  bundles, 
the  lobes  and  lobules  of  the  compound  glands,  following  the  vessels 
and  nerves  to  their  finest  divisions.  It  is  continuous  with  itself,  and 
can  be  traced  from  one  part  of  the  body  to  another  without  interruption. 
Hypodermic  injections  intended  to  enter  the  general  circulation  are 
thrown  within  this  tissue.  It  serves  as  the  storehouse  of  fat.  Drop- 
sical fluids,  by  reason  of  the  sieve-like  arrangement  of  its  meshes,  may 
be  diffused  through  it  from  one  part  of  the  body  to  another.  It  allows 
the  skin  to  move  freely  over  adjoining  parts,  and  assists  it  in  reassuming 
the  normal  position  after  having  been  drawn  in  any  one  direction. 

Fascia. 

Fascia,  one  of  the  divisions  of  areolar  tissue,  is  composed  of  a  multi- 
tude of  soft,  fine,  and  somewhat  elastic  fibres,  transparent  in  appearance, 
but  intermixed  with  numerous  delicate  colorless  membranous  laminae. 
These  fibres  and  laminse  are  interwoven  in  every  imaginable  direction, 
forming  net-like  meshes  of  different  sizes.  These  interspaces  communi- 
cate freely  with  each  other,  many  of  them  being  filled  witli  fat,  which 


AREOLAR  TISSUE,   TENDONS,  AND  MUSCLES.  155 

is  enclosed  in  its  own  vesicle.  In  health  this  tissue  is  moistened  and 
lubricated  by  a  transparent  fluid  of  the  nature  of  lymph. 

Fascia  is  divided  into  two  varieties,  superficial  and  deep. 

Superficial  or  Subcutaneous  Fascia  connects  the  skin  with  the  deeper 
and  firmer  parts  beneath  by  numerous  delicate  bands  or  trabeculae ;  its 
structure  is  more  open  than  that  of  the  deep  fascia,  and  its  bands  run 
more  irregularly.  It  varies  in  thickness  and  density  in  different  parts, 
and  is  found  distributed  throughout  nearly  the  entire  surface  of  the 
body.  Within  the  meshes  of  this  tissue  is  found  the  subcutaneous  fat, 
which  forms  a  blanket  of  adipose  tissue  and  serves  to  keep  the  body 
warm,  fat  being  a  poor  conductor  of  heat.  No  adipose  tissue  is  found 
upon  the  eyelids,  the  penis,  and  the  scrotum.  In  animals,  such  as  the 
cow,  the  horse,  and  the  dog,  the  superficial  fascia  contains  within  its 
structure  a  muscle  known  as  the  panniculus  carnosus,  which  extends 
over  almost  the  entire  body.  In  man  a  muscle  corresponding  to  this, 
known  as  the  platysma  myoides,  is  found  in  the  region  of  the  head  and 
neck. 

In  some  portions  of  the  body  the  superficial  fascia  is  separable  into 
several  layers ;  this  is  especially  true  in  the  region  of  the  groin.  In 
health  the  superficial  fascia  often  becomes  loaded  with  fat,  this  tissue  in 
corpulent  people  being  much  thicker.  The  opposite  is  the  case  with 
emaciated  people,  the  superficial  fascia  becoming  extremely  thin  ;  its 
fibrous  bands  are  closely  approximated,  and  the  skin  appears  wrinkled 
or  in  folds.  Also  on  the  soles  of  the  feet  and  in  the  palms  of  the  hands 
it  is  very  thin  and  closely  attached  to  the  skin.  It  is  generally  divided 
into  two  or  more  layers,  between  which  are  the  glands,  and  through 
Mdiich  pass  the  superficial  blood-vessels,  nerves,  and  lymphatics,  these 
structures  having  free  communication  with  each  other. 

The  Deep  or  Aponeurotic  Fascia  is  immediately  beneath  the  super- 
ficial fascia.  The  course  of  its  fibres  is  not  so  irregular  as  that  of  the 
superficial  fascia,  inclining  more  to  an  arrangement  in  layers  or  bands, 
with  much  less  adipose  tissue  confined  within  its  meshes;  this  forma- 
tion makes  it  denser  and  stronger  than  the  superficial  fascia. 

Like  the  superficial,  the  deep  fascia  extends  over  nearly  the  entire 
surface  of  the  body,  forming  an  envelope  which  holds  the  muscles  to 
their  shape  and  in  their  proper  position.  Numerous  septa  are  given  off 
from  it  which  dip  down  between  the  muscles,  dividing  and  enclosing 
their  bands,  subdividing  and  enclosing  their  fibres,  and  forming  a  sheath 
which  enwraps  the  vessels  and  nerves  wherever  met.  It  encloses  the 
tendinous  structures  in  the  same  manner  as  the  muscular.  That  portion 
of  the  fascia  which  invests  a  tendon  is  called  its  theca  or  vagina. 

This  fascia  also  assists  in  forming  intermuscular  connections  and 
septa,  as  those  between  the  two  bellies  of  the  digastric  and  the  occipito- 
frontalis  muscle.  When  the  fascia  is  broad  and  well  defined  it  is 
called  an  aponeurosis.  The  deep  fascia,  in  different  forms,  serves  to 
attach  muscles  and  tendons  to  osseous  and  other  structures,  and  throws 
off  stout  fibrous  bands  wdiich  form  various  ligaments,  such  as  those  sur- 
rounding the  joints,  the  annular  and  the  bicipital,  the  palmar  and  the 
plantar  fascia,  etc. 

The  deep  fascia  likewise  forms  pulley-like  apertures  through  which 


156  ANATOMY. 

pass  the  tendons  of  muscles,  good  illustrations  of  these  being  found  in 
the  trochlear  of  the  superior  oblique  muscle  of  the  eye  and  the  pulley 
for  the  passage  of  the  intermuscular  tendon  of  the  digastric  muscle. 

A  thorough  knowledge  of  this  fascia  will  materially  assist  in  the  diag- 
nosis of  deep  tumors  and  in  prognosticating  the  direction,  course,  or  route 
likely  to  be  taken  by  morbid  fluids  and  growths  from  one  point  to  another. 

Fascia  of  the  Neck,  Face,  and  Head. — The  superficial  fascia  of  the 
face  and  anterior  portion  of  the  neck  is  so  slightly  developed,  and  so 
intimately  blended  with  the  adjoining  parts,  that  it  is  not  recognized  as 
a  separate  tissue.  Its  thickness  varies  inversely  to  the  development 
of  the  platysma  myoides  and  facial  muscles,  the  one  seeming  to  take 
the  place  of  the  other.  That  portion  of  the  fascia  of  the  head  situated 
between  the  aponeurosis  of  the  occipito-frontalis  muscle  and  the  integu- 
ment is  dense  and  firm,  and  by  its  fibres  unites  the  skin,  the  fascia,  and 
the  aponeurosis  closely  together.  This  union  is  so  intimate  that  the 
structures  are  difficult  to  separate  in  dissection.  Between  the  layers  of 
the  fascia  as  it  extends  over  the  temporal  aponeurosis  are  situated  the 
muscles  which  move  the  external  ear,  as  well  as  the  superficial  temporal 
vessels  and  nerves.  It  is  continuous  behind  with  the  superficial  fascia 
of  the  back  part  of  the  neck. 

The  Deep  Cervical  Fascia  anteriorly  is  a  dense  structure,  having  a 
somewhat  complex  arrangement,  and  is  of  great  importance  from  a 
surgical  point  of  view :  it  limits  to  a  certain  degree  the  growth  of  cervical 
tumors  and  abscesses  and  modifies  their  direction  and  their  extent. 
Deep-seated  abscesses  often  follow  the  course  of  the  fiiscia,  though  occa- 
sionally these  as  well  as  tumors  penetrate  or  stretch  this  membrane  in 
their  growth  and  adopt  a  course  of  their  own.  The  deep  cervical  fascia 
is  divided  into  two  portions,  superficial  and  deep,  the  superficial  form- 
ing a  complete  covering  for  the  neck,  enclosing  every  structure  belonging 
to  it  except  the  skin,  the  superficial  fascia,  the  platysma  myoides  muscle, 
and  some  superficial  veins  and  nerves.  In  the  anterior  portion  of  the 
neck  it  passes  forward  from  the  upper  surface  of  the  trapezius  muscle 
as  it  passes  under  the  platysma,  to  the  posterior  border  of  the  sterno- 
cleido-mastoid  muscle,  where  it  divides  into  two  lamellae — one,  the  super- 
ficial, passing  over,  and  the  other,  the  deep,  passing  under,  the  muscle. 
At  the  internal  ])()rder  of  the  sterno-cleido-mastoideus  it  again  reunites, 
thus  fi>rniiug  a  sheath  for  the  entire  muscle:  from  this  point  it  passes 
forward  to  the  median  line  and  joins  its  fellow  of  the  opposite  side. 
Its  attachment  above  anteriorly  commences  at  the  symphysis  of  the 
lower  jaw,  passing  backward  along  the  base  of  the  bone  to  the  parotid 
region,  where  it  divides  into  two  laminae,  the  deep  layer  jiassing  beneath 
the  parotid  ghind  to  be  inserted  into  the  base  of  the  skull.  The  stylo- 
maxillary  ligament  is  developed  from  this  leaflet  of  fiiscia.  The  upper 
layer  passes  over  the  parotid  gland  and  masseter  muscle,  forming  their 
upper  covering.  Laterally,  above,  the  fascia  is  attached  to  the  zygo- 
matic arch,  from  which  it  extends  backward  along  the  zygoma  to  the 
posterior  root,  thence  to  the  mastoid  process  of  the  temporal  bone  and 
the  superior  curved  line  of  the  occipital  bone,  to  which  it  is  also 
attached.  The  inferior  attachment  of  this  fascia  is  to  the  clavicle,  near 
which  it  is  pierced  for  the  passage  of  the  external  jugular  vein  on  its 


AREOLAR  TISSUE,   TEyBONS,   AND  MUSCLES.  157 

way  from  the  neck  to  its  deeper  relations.  In  the  median  line  in  front 
the  fascia  is  also  attached  to  the  hyoid  bone. 

Below  the  thyroid  body  the  deep  fascia  divides  into  two  layers,  the 
upper  and  thinner  going  to  the  outer  and  upper  portion  of  the  sternum, 
to  which  and  the  interclavicular  ligament  it  is  attached,  while  the  lower 
layer  is  attached  to  the  inner  and  upper  portion  of  the  sternum.  Both 
layers  are  superficial  to  the  sterno-hyoid  muscles.  The  space  betNveen  the 
layers  of  fascia  extends  laterally  until  it  encloses  the  sternal  heads  of  the 
sterno-cleido-mastoid  muscles.  The  anterior  jugular  vein  passes  through 
this  interfascial  space,  which  contains  loose  connective  tissue  and  fat, 
also  sometimes  a  small  lymphatic  gland.  Thus  the  upper  portion  of 
the  deep  fascia  of  the  anterior  part  of  the  neck  covers  in  all  that  por- 
tion known  as  the  surgical  square  of  the  neck,  and  externally  offers  a 
barrier  to  the  extension  of  abscesses  and  growths  from  the  deeper 
parts  toward  the  surface,  which  causes  them  to  burrow  more  deeply. 
Abscesses  forming  exterior  to  this  fascia  rarely  if  ever  burroAV. 

(«)  The  Deep  Portion  of  the  Cervical  Fascia. — Near  the  anterior  mar- 
gin of  the  sterno-cleido-mastoid  muscle  a  process  is  given  off  from  the 
superficial  layer  of  the  deep  fascia  which  descends  behind  that  muscle 
and  is  associated  with  the  depressors  of  the  hyoid  muscular  system.  It 
invests  the  thyroid  body  and  the  front  of  the  trachea,  spreads  out  in 
front  of  the  large  vessels  of  the  neck,  and  passes  into  the  thorax  as  far 
as  the  pericardium.     It  is  supposed  to  assist  in  suspending  the  heart. 

(6)  The  Prevertebral  Fascia  is  a  layer  of  the  deep  fascia  which, 
being  attached  to  the  base  of  the  skull,  descends  on  the  prevertebral 
muscles  into  the  thorax,  separating  them  from  the  pharynx  and 
oesophagus.  Laterally,  it  becomes  continuous  with,  and  forms  the  back 
portion  of,  the  carotid  sheath,  from  which  it  extends  outward  and  down- 
ward over  the  scaleni  muscles,  the  brachial  plexus  of  nerves  and  sub- 
clavian vessels,  which  it  accompanies  beneath  the  clavicle  into  the  axilla, 
where  it  forms  the  axillary  sheath,  and  becomes  connected  with -the 
Under  surface  of  the  costo-coracoid  membrane. 

(e)  The  Carotid  Sheath. — The  upper  portion  of  this  sheath  is  formed 
from  the  fascia  described  as  a,  while  the  under  portion  is  derived  from 
that  described  as  b.  This  sheath  forms  a  complete  covering  to  the  caro- 
tid artery,  the  internal  jugular  vein,  and  the  pneumogastric  nerve.  A 
thin  fibrous  septum  is  interposed  between  the  artery  and  vein,  thus  form- 
ing a  separate  sheath  for  each. 

(d)  The  Omo-hyoid  Fascia,  which  encloses  the  lower  belly  of  the  mus- 
cle of  the  same  name,  is  a  strong  fascia  which  passes  over  the  muscle 
extending  down  to  the  first  rib.  It  is  from  this  layer  of  fascia  that  the 
band  binding  down  the  intermediate  tendon  of  the  omo-hyoid  muscle  is 
obtained. 

(c)  The  Submaxillary  Fascia  consists  of  two  triangular  layers  of  the 
deep  fascia  which  enclose  a  space  containing  the  submaxillary  salivary 
and  lymphatic  glands ;  the  fascia  is  attached  below  to  the  intermediate 
tendon  of  the  digastric  nmscles ;  the  outer  layer  passes  upward  to  be 
attached  to  the  body  of  the  lower  jaw ;  the  other  layer  passes  inward 
to  be  connected  with  the  fascia  covering  the  raylo-hyoid,  the  hyo-glossus, 
and  the  stylo-glossus  muscles ;  surgically  speaking,  it  is  attached  to  the 


158  ANATOMY. 

mylo-hyoid  ridge  of  the  lower  jaw,  the  outer  sheaths  of  these  muscles 
being  a  continuation  of  this  fascia. 

A  study  of  the  arrangement  and  attachments  of  the  fascia  described 
above  will  show  that  abscesses  forming  in  certain  regions  or  between 
certain  fascia  can  burrow  into  other  regions.  For  instance,  an  abscess 
forming  between  a  and  6  would  be  likely  to  burrow  toward  the  media- 
stinum, or  an  abscess  immediately  in  front  of  the  spine  and  beneath  the 
fascia  b  would  probably  pass  downward  to  the  posterior  mediastinum, 
or  laterally  toward  the  posterior  triangle,  or  even  into  the  axilla,  etc. 

The  Beep  Fascia  of  the  head  is  divided  into  three  well-defined  por- 
tions :  («)  the  occipito-frontalis  aponeurosis,  (6)  the  right,  and  (c)  the 
left  temporal  fascia.  The  first  extends  between  the  occipital  and  fron- 
talis muscles,  and  is  attached  laterally  to  the  temporal  ridge.  The  tem- 
poral fasciae  extend  over  the  temporal  muscles,  being  attached  above  to 
the  temporal  ridges  and  below  to  the  zygomas. 

Abscesses  forming  under  the  occipito-frontalis  aponeurosis  generally 
burrow  backward  to  a  V-shaped  interspace  near  the  external  occipital 
protuberance,  while  those  beneath  the  temporal  fascia  will  burrow  down- 
ward under  the  zygomas  into  the  zygomatic  fossae. 

57?e  Beejj  Fascia  of  the  Face,  like  the  superficial,  is  indistinctly 
developed.  Its  place,  however,  is  supplied  by  an  abundant  quantity 
of  areolar  connective  tissue  distributed  through,  and  intricately  asso- 
ciated with,  the  muscular  tissue,  though  it  does  not  form  a  distinct 
covering  or  fascia  for  the  face,  nor  is  it  developed  sufficiently  to  com- 
pose sheaths  to  the  muscles.  It  is  lax,  and  readily  allows  the  diifasion 
of  infiltrations,  thus  accounting  for  the  sudden  and  marked  swelling  of 
the  face  during  certain  inflammatory  affections. 

This  areolar  tissue  holds  within  itself  a  quantity  of  cushion-like 
masses  of  connective  tissue  which  are  prominent  in  the  following 
localities :  the  hollow  of  the  cheek ;  between  the  zygomatic  and  bucci- 
nator muscles ;  at  the  lower  margin  of  the  orbit,  particularly  where  the 
orbicularis  palpebrarum  overlaps  the  elevators  of  the  upper  lip ; 
beneath  the  muscles  elevating  the  upper  lip  above  the  oral  angle ;  at 
the  groove  where  the  facial  artery  passes  over  the  inferior  maxillary 
bone ;  and  beneath  the  depressors  of  the  lower  lip. 

As  the  skin  of  the  face  is  thin  and  vascular,  scars  from  plastic  opera- 
tions and  other  causes  are  comparatively  inconspicuous.  Prof.  Allen  in 
his  work  on  Hitman  Anatomy  observes  that  a  very  different  result  fol- 
lows extensive  cicatrization  of  the  deeper  parts :  here  the  connective 
tissue  is  abundantly  present,  and,  as  seen  after  ulceration  from  mercurial 
sore  mouth  or  after  destructive  stomatitis  from  any  cause,  serves  to  con- 
vert the  cheeks  into  false  ligaments  holding  the  jaws  close  together. 
A  very  marked  case  of  this  kind  presented  itself  at  the  Hospital  of 
Oral  Surgery,  Philadelphia,  in  1883.^ 

Tendons. 

The  tendons,  with  but  few  exceptions,  are  made  up  of  bundles  of 
white  fibrous  connective  tissue  bound  together  by  fasciculi  from  the 

'  See  Garretson's  Oral  Suryery. 


AREOLAE   TISSUE,   TENDONS,  AND  MUSCLES.  159 

deep  fascia,  which  form  tlieir  sheaths.  The  sheaths  not  only  enclose 
the  individual  fibres  composing  the  bundles,  but  the  entire  tendon. 
This  latter  covering  is  called  the  theca. 

The  fibres  which  make  up  a  tendon  are  arranged  parallel  with  each 
other,  and  have  an  undulating  course.  Occasionally  the  fibrous  bun- 
dles send  oft'  fasciculi,  some  running  forward  and  others  backward, 
interlacing  with  each  other.  The  bundles  proper,  however,  do  not 
subdivide,  but  keep  intact  from  one  extremity  to  the  other. 

The  connective-tissue  cells  of  tendons,  called  tendon-cells,  are  arranged 
in  parallel  rows  (Fig.  79),  and  follow  the  line  of  the  fibrous  bundles 
composing  the  tendon.  They  are  so  closely  approximated  that  in  a 
longitudinal  section  they  have  a  stellate  appearance,  due  to  compression 
of  the  cells  and  the  elongated  processes  characteristic  of  all  connective- 

FiG.  79. 


Tendon  of  Mouse's  Tail,  stained  with  logwood,  showing  chains  of  cells  between  ilie  tendon-bui  dies 

(175  diameters). 

tissue  cells,  which  protrude  from  them,  uniting  one  cell  to  another.  These 
cells  are  minute  protoplasmic  bodies,  thicker  in  the  centre  than  at  the  cir- 
cumference, and  contain  a  round  or  oval  nucleus  with  several  nucleoli. 

Tendons  are  found  connected  with  muscles  at  either  terminal  extrem- 
ity or  between  the  two  bellies  of  the  same  muscle.  Their  fibres  usually 
run  continuously  with  those  of  the  muscle,  but  they  may  join  the  mus- 
cle at  an  angle.  When  the  tendinous  fibres  unite  with  the  muscular 
fibres  end  to  end,  the  tendon  is  subdivided  into  as  many  fibres  as  there 
are  fibres  in  the  muscle  to  which  it  is  united.  Adherence  to  this  law  is 
so  uniform  that  the  fibres  of  the  tendon  seem  to  be  but  a  continuation 
of  those  of  the  muscle.  A  close  examination,  however,  of  the  muscular 
extremity  of  the  fibres  of  the  tendon  will  show  that  they  suddenly  end 
on  coming  in  contact  with  the  truncated  extremity  of  the  muscle-fibre. 

The  sheaths,  formed  by  fasciculi  from  the  deep  fascia,  which  enclose 
the  bundles  of  fibres  forming  the  tendon,  pass  from  the  tendon-bundles 
to  the  muscular  fasciculi,  and  are  lost  by  overlapping  the  similar  sheaths 
which  enclose  the  muscular  fibres,  they  all  being  continuous. 

Where  the  fibres  of  the  tendon  are  obliquely  united  to  those  of  the 
muscle  the  small  tendinous  bundles  are  given  off  laterally  just  at  their 
point  of  union,  and  extend  between  or  over  the  muscular  fibres,  but 
their  sheaths  are  lost  in  the  muscle  in  a  manner  precisely  similar  to  the 
union  of  the  parallel  fibres. 

Muscular  Tissue. 
Muscular  tissue  is  made  up  of  fibres  collected  into  distinct  and  sepa- 
rate masses.     By  means  of  this  tissue  all  the  active  movements  of  the 


160  ANATOMY. 

body  are  produced.  It  is  familiarly  known  as  "flesh,"  and  it  is  dis- 
tributed over  the  entire  framework  of  the  body  and  in  the  coats  of 
blood-vessels  and  the  viscera. 

In  the  higher  vertebrates  the  color  of  the  muscular  tissue  is  generally 
red,  varying  in  shade,  however,  according  to  the  locality  in  which  it  is 
found  and  to  other  circumstances.  The  voluntary  muscles,  called  into 
most  constant  action,  are  deeper  in  color  than  others  of  their  class.  A 
marked  illustration  of  this  is  shown  in  the  pectoral  muscles  of  the  bird 
and  the  common  fowl.  The  former,  being  called  into  almost  constant 
use  in  the  act  of  flying,  are  dark  in  color,  while  the  latter,  being  almost 
wholly  inactive,  are  extremely  light  in  shade. 

Muscular  tissue  also  constitutes  a  large  proportion  of  the  weight  of 
the  human  body.  It  has  been  estimated  by  Liebig  that  a  man  weighing 
150  pounds  is  27  pounds  skeleton,  60  pounds  viscera  (with  skin,  lat, 
blood,   etc.),  63  pounds  muscle. 

Each  muscle  constitutes  a  separate  organ,  and  either  acts  independ- 
ently or  in  conjunction  with  other  muscles  as  accessories.  The  great 
vital  property  of  muscular  tissue  is  contractility,  which  power  is 
excited  to  activity  by  the  influence  of  various  stimuli. 

The  greater  number  of  the  muscles  of  the  body,  such  as  those  of 
locomotion,  respiration,  mastication,  the  first  part  of  deglutition,  expres- 
sion, etc.,  are  compelled  by  the  will  acting  through  the  nerves  with 
which  the  parts  are  supplied.  These  are  known  as  voluntary  muscles. 
Others,  again,  as  those  of  the  intestinal  canal  and  the  vascular  system, 
cannot  be  brought  into  action  by  the  force  of  the  will.  These  are  called 
involuntary  muscles,  and  are  controlled  by  the  sympathetic  nervous  system. 
These  two  classes  of  muscles  differ  also  in  their  histological  construc- 
tion, and  will  therefore  be  considered  separately. 

The  Voluntary  Muscles  are  fibres  appearing  under  the  microscope  trans- 
versely striated,  and  generally  oblong  in  shape.  Usually,  tendons  are  at- 
tached to  their  extremities,  by  means  of  which  they  are  united  to  bones,  and 
sometimes  to  other  tissues ;  for  instance,  the  sphincter  muscle  of  the  mouth. 
The  fleshy  part  of  a  muscle  is  called  its  belly,  and  its  terminal  pro- 
lono-ations  are  its  tendons  of  origin  and  insertion.  The  term  origin 
of  a  muscle  or  tendon  generally  applies  to  that  extremity  which  is 
stationary,  and  the  term  insertion  is  applied  to  the  more  movable 
point.  Example :  the  origin  of  the  temporal  muscle  is  that  portion 
arising  in  the  temporal  fossa  on  the  side  of  the  head,  while  its  insertion 
is  at  the  coronoid  process  of  the  inferior  maxilla.  The  skull  is  the  fixed 
point  of  the  muscle,  while  the  loM'er  jaw  is  the  movable  one.  This 
rule  is  not  without  exceptions,  as  in  certain  localities  the  fixed  point  of 
a  muscle  may  become  the  movable  point.  The  origin  of  a  muscle  may 
be  large  and  its  insertion  small,  and  vice  versa;  or  the  origin  and  inser- 
tion may  be  of  equal  size. 

A  thorough  knowledge  of  the  origin  and  insertion  of  muscles  is 
absolutely  necessary  to  a  full  understanding  of  the  mechanical  action 
of  the  parts  to  which  they  are  attached.  It  is  essential  in  diagnostica- 
tino-  fractures  and  dislocations.  A  knowledge,  also,  of  the  direction  of 
the  fibres  composing  muscles,  and  of  the  relation  of  muscles  to  adjoining 
parts,  enables  the  surgeon  to  locate  disease,  and  serves  as  a  guide  to  the 


AREOLAR   TISSUE,    TENDONS,   AND  MUSCLES. 


161 


position  of  blood-vessels  and  nerves.     The  power  of  a  muscle  depends 

upon  the  number  of  its  contractile  fibres.     When  contracted,  it  increases 

in  thickness ;   its  action,  unless  otherwise  intluenced  by  associate  parts 

or  by  its  tendon  passing  through  loops  of  fascia  or  over  a  pnlley,  is  in 

a  direct  line  with  the  course  of  its  fibres. 

Faaclcull  are  the  bundles   of  the  fibres  composing  muscles.      The 

fibres  which  make  up  the  fasciculi  vary  greatly  in  length  in  different 

muscles.     Tlie  fasciculi  Avhich  form  the  bundles  com})osing  a  muscle 

run  parallel  with  each  other,  never  inter- 
lacing, but  extending  from  one  terminal  to 
the  other,  except  when  interrupted  by  the 
interposition  of  tendinous  tissue,  as  in  the 
case  of  the  digastric  muscle. 

The  Perimysium  (Fig.  SO)  is  the  sheath 
of  areolar  tissue  that  invests  the  nniscles 
and  sends  partitions  inward  between  the 
fasciculi,  providing  each  with  a  special 
sheath. 

The  Endomysium  is  the  portion  of  the 
above  membrane  partially  surrounding  the 
fibres  composing  the  fasciculi ;  the  latter 
are  not  continuously  invested  with  it.  The 
chief  uses  of  the  perimysium  and  its  parti- 
tions are  to  connect  the  fibres  and  fasciculi 
together,    and    to    furnish    spaces    for   the 

accommodation  of  blood-vessels  and  nerves  that  supply  the  parts. 

The  fasciculi  (Figs.  81  and  82)  are  prismatic  in  form,  and  the  number 

of  fibres  of  which  they  are  composed  in  different  parts  of  the  body 

causes  the  variations  in  their  thickness. 

The  texture  of  a  muscle,  whether  coarse  or  fine,  dc])ends  upon  this 

circumstance.     The  length  of  a  fasciculus 

depends  upon  the  length  of  the  muscle,  as 

well  as  upon  the  arrangement  of  the  tendons 

to  which  the  extremities  of  the  muscle  are 

attached.     When  the  tendons  are  limited  to 

Fia.  81. 


Transverse  Section  from  the  Steriio- 
mastoid  in  man  (50  times  magni- 
fied) :  o,  perimysium  ;  6,  endomys- 
ium ;  f,  fasciculi. 


YiG.  82. 


A,  a  small  portion  of  Muscle,  natural  size ; 
B,  same  magnified  .5  diameters,  of  larger 
and  smaller  fasciculi,  seen  in  a  trans- 
verse section. 


A  few  Muscular  Fibres,  being  part  of 
a  small  fasciculus  (highly  magni- 
fied). 


the  ends  or  extremities  of  long -muscles,  the  fasciculi  are  of  great  length. 


Vol.  I.— 1 1 


162 


ANATOMY. 


Fig.  83. 


having  to  pass  from  one  extremity  of  the  muscle  to  the  other.  But  a 
long  muscle  may  be  composed  of  a  number  of  short  fasciculi  attached 
obliquely  to  the  sides  of  its  tendon,  which  may  advance  upon  its  surface 
or  into  its  fleshy  parts.  Many  short  tiisciculi,  thus  connected,  produce 
by  their  combined  operation  a  more  powerful  effect  than  a  few  fasciculi 
extending  the  entire  length  of  a  muscle.  The  latter  arrangement,  how- 
ever, gives  greater  extent  of  motion. 

The  Fibres  composing  the  Fasciculi  are  cylindrical  or  prismatic  in 
form.  Their  size  is  generally  uniform,  being  in  the  muscles  of  the 
trunk  and  limbs  from  yjo^th  to  ^^th  of  an  inch  in  diameter.  It  is 
less  in  those  of  the  head,  especially  in  the  face,  where  they  range  from 
2  4^)  0  th  to  yyo-th  of  an  inch. 

The  general  length  of  the  fibres  does  riot  exceed  an  inch  and  a  half. 
In  long  fasciculi,  therefore,  they  do  not  extend  from  the  tendon  of  one 
extremity  to  that  of  the  other,  but  end  in  a  rounded  p(jint  invested  by 
sarcolemma  adhering  to  approximate  fibres. 

Muscle-fibres  generally  neither  divide  nor  anastomose.  In  the 
tongue  of  the  frog  (Fig.  83),  however,  the  muscular  fibres  as  they 
approach  the  surface  divide  into  numerous  branches,  which  are 
attached  to  the  under  surface  of  the  mucous 
membrane.  This  is  also  true  of  man  and  vari- 
ous animals. 

The  fibres  of  the  fticial  muscles  of  mammals 
and  those  of  the  panniculus  carnosus  follow  the 
same  rule.  The  numerous  attachments  of  the 
latter  muscle  to  the  under  surface  of  the  skin 
causes  the  peculiar  external  twitching  movement 
seen  in  these  animals. 

Muscular  filjre  is  soft  and  contractile,  and  is 
enclosed  in  a  tubular  envelope  known  as  the  sar- 
colemma or  myolemma.  This  envelope  consists 
of  a  transparent,  apparently  homogeneous  mem- 
brane, similar  to 
elastic  tissue.    It  is  ^^''-  ^'^■ 

tough,  and  will  oc- 
casionally remain 
entire  when  the 
fibres  which  it  en- 
closes are  ruptured 
(Fig.  84).  Nuclei 
are  found  on  the 
inner  surface  of  the 
sarcolennna,  but 
they  belong  to  the  ccmtractile  substance  of  the  fibre,  and  not  to  the 
sarcolemma. 

The  (bnfracti/e  Suhsf(nicc  of  voluntary  muscular  fi1)re,  when  examined 
under  a  microscope  of  high  ])ower  and  A\ith  transmitted  light,  appears 
marked  with  parallel  bands  (Fig  8.)),  alternating  dark  and  light ;  the 
former  are  named  the  contractile  discs,  the  latter  the  interstitial  discs. 
These  bands  pass  across  the  fibx'e  with  great  regularity.     They  are  of 


A  Branched  Muscular  Fibre 
from  the  frog's  tongue 
(magnified  :!•">((  diameters). 


Fragments  of  an  Elementary  Fibre  of 
the  Skate,  held  together  by  the  un- 
torii  but  twisted  sarcolemma. 


AREOLAR  TISSUE,   TENDONS,  AND  3IUSCLES.  1H3 

equal  breadth,  but  when  the  fil)re  is  considerably  extended  a  dotted  line 
becomes  visible  in  the  centre  of  the  light  band.  This  characteristic 
cross-striped  appearance  is  found  in  all  voluntary  muscles,  but  is  not 
absolutely  confined  to  them,  as  it  is  seen  in  the  fibres  of  the  heart,  which 

Fig.  85. 


A,  portion  of  a  medium-sized  Human  Muscular  Fibre  (magnified  nearlj-  800  diameters) :  B,  separated 
bundles  of  fibrils,  equally  magnified;  f,  a,  large,  and  l>,  h,  smaller  collections;  c,  still  smaller;  rf,  </, 
the  smallest  whicli  could  be  detached. 

is  considered  an  involuntary  organ,  though  it  is  claimed  that  some  per- 
sons have  partial  control  over  it. 

There  is  also  a  longitudinal  striation  seen  in  voluntary  muscular 
fibre,  better  marked  where  the  transverse  striation  is  somewhat  indis- 
tinct. After  hardening  in  alcohol,  voluntary  muscular  fibre  may  be 
broken  up  longitudinally  into  so-called  fil)rils.  The  fibre  is  not,  how- 
ever, composed  entirely  of  fibrils,  but  contains  a  considerable  quantity 
of  an  intermediate  substance.  After  the  action  of  dilute  acids  or  of 
gastric  juice  on  muscle,  the  fibres  display  a  disposition  to  break  up  trans- 
versely" in  a  direction  parallel  to  the  bands,  and  even  into  transverse 
plates  or  discs  formed  by  the  lateral  adhesion  of  the  particles  of  approx- 
imated fibrils.  This  separation  of  muscular  fibre  into  discs  is  only  pos- 
sible after  the  coagulation  of  muscle-plasma  or  the  action  of  reagents 
upon  it. 

Muscular  fibres  also  exhibit  a  number  of  clear  oval  nuclei  (Fig.  86). 
In  the  muscles  of  mammals  these  nuclei  are  situated  upon  the  under 
surface  of  the  sarcolemma.  Surrounding  these  nuclei  there  is  sometimes 
a  certain  amount  of  granular  matter  which  is  derived  from  the  original 
primitive  embryonic  protoplasm. 

The  nuclei  of  muscular  fibre  are  not  readily  seen  without  the  addi- 
tion of  acetic  acid.  One  or  two  nucleoli  may  also  be  found  within  each 
nucleus. 


164 


ANATOMY. 


Blood-vessels  in  muscular  tissue  are  extremely  numerous.  These  earrv 
the  material  for  the  nourishment  of  the  tissues  and  for  the  chemico-vilal 
changes  which  take  place  within  them.  When  these  vessels  are  filled 
with  coloring  matter,  the  fleshy  part  of  the  muscles 
supplied  by  them  is  in  strong  contrast  with  the  tendons. 
Arteries,  accompanied  by  veins,  enter  the  muscle  at 
various  points,  divide  into  branches,  pass  among  the 
fasciculi,  and  break  up  more  and  more  as  they  extend 
into  the  finer  divisions  of  the  muscle.  Finally,  they 
penetrate  the  smallest  fasciculi  and  terminate  in  capil- 
lary vessels  which  run  between  the  fibres.  They  are 
supported  by  the  subdivisions  of  the  perimysium,  and 
supply  it  with  capillaries.  The  diameter  of  these  is 
extremely  small,  and  they  form  a  fine  network  among 
the  fibres. 

Lymphatics. — It  is  not  known  that  there  are  any 
lymphatic  vessels  in  the  voluntary  muscular  tissue,  but 
they  are  found  in  great  abundance  in  the  connective 
tissue  of  its  sheaths  and  tendons.  They  have  their 
commencement  in  connective  tissue,  and  their  office  is 
to  collect  and  convey  the  lymph  from  the  muscular 
substance  and  tendons. 

The.  Nerves  of  the  voluntary  muscles  are  of  large 
size,  and  their  branches  pass  between  the  fasciculi,  often 
uniting  to  form  plexuses,  from  which  smaller  nerve- 
fibre,  and  in  profile    filauieuts  are  givcu  oiF  and  form  finer  plexuses,  each 
containing  not  more  than  two  or  three  dark-bordered 
nerve-fibres.     Single  nerve-fibres  pass  from  these  between  the  fibres  of 
the  muscles,  divide  into  branches,  and  finally  terminate  in  motor  end- 
plates,  which  are  situated  upon  the  sarcolemna  of  the  muscular  fibres. 
Small  nerves  also  accompany  the  branches  of 
blood-vessels  within  the  muscle. 

Involuntary  Smooth  or  Unstriped  Muscle. — 
Excepting  in  the  heart  and  a  few  other  organs 
of  the  body,  involuntary  muscular  tissue  is  un- 
^  striated,  and  its  ap]:>arent  fibres  are  made  uj)  of 
elongated  contractile  cells  bound  together  by  a 
homogeneous  intercellular  substance. 

Unstriated  muscular  tissue  is  composed  of  con- 
tractile fibre-cells  (Fig.  87).  These  cells  may 
form  fibrous  bundles  or  they  may  be  less  regu- 
larly arranged.  They  are  elongated,  and  usual- 
ly pointed  at  the  ends.  They  vary  greatly  in 
length  in  the  dififerent  organs  of  the  body,  and 
may  bifurcate  at  one  or  both  extremities.  Each 
cell  has  a  nucleus,  which  is  either  oval  or  rod- 
shaped,  and  situated,  as  a  rule,  centrally. 

Involuntary  nuiscle  fibre-cells  are  spindle  or 
fusifi)rm  in  shape.     Tlie  wall  or  envelope,  whicli 
may  wrinkle  on  the  contraction  of  the  fibre  and  produce  an  indistinct 


Fig.  Sfi 


Muscular  Fibre  of  a 
IManiinal,  exaiiiiiied 
fresh  in  serum,  high- 
ly magnified,  the  sur- 
face of  the  fibre  be- 
ing accurately  focus- 
ed. The  nuclei  are 
seen  on  the  flat  at 
the    surface    of    the 


Fio.  87. 


Involuntary    Muscular    Fibre- 
cells  from  Human  Arteries. 


AREOLAR   TISSUE,   TENDONS,  AND  3IUSCLES.  165 

appearance  of  striation,  is  very  delicate  and  homogeneous.  The  cells 
are  united  by  an  intercellular  cementing  substance.  They  are  closely 
packed  into  fasciculi,  which  in  most  cases  cross  and  interlace  one  with 
the  other,  the  spindle-end  of  the  cell  fitting  in  between  the  bodies  of 
the  other  cells.  The  fasciculi  are  united  at  their  ends  by  connective 
tissue  to  the  membranous  parts,  where  such  })arts  occur. 

Unstriated  muscular  tissue  is  largely  distributed  in  the  coats  of  the 
arteries,  veins,  and  viscera.  It  is  also  found  in  the  ducts  of  the  sweat- 
glands  of  the  skin  in  the  form  of  minute  muscles  attached  to  the  hair- 
follicles,  and  in  the  subcutaneous  tissue  of  the  scrotum.  This  tissue  is 
supplied  by  numerous  nerves  from  the  sympathetic  system  and  abundant 
blood-vessels,  though  these  are  fewer  in  proportion  than  in  voluntary 
muscular  tissue.  In  the  walls  of  the  stomach  and  intestines  numerous 
h^iiphatic  vessels  are  found. 

The  fibres  of  the  muscular  tissue  of  the  heart,  however,  differ  from 
those  of  involuntary  muscular  organs  generally,  presenting  as  they  do 
transverse  striae.  These  strise  are,  however,  less  distinct,  and  the  mus- 
cle-fibres are  smaller  in  diameter,  than  those  of  voluntary  nuiscles.  The 
fibres  are  also  made  uj)  of  quadrangular  cells  joined  end  to  end,  each  cell 
having  a  single  oval  nucleus  situated  near  its  centre ;  occasionally  two 
nuclei  are  found.  The  fibres  composing  this  variety  of  muscle  divide 
and  interlace,  though  they  are  not  invested  by  sarcolenuua. 

Varieties  of  Muscees. — General  names  have  been  given  to  mus- 
cles significant  of  the  arrangement  of  their  fasciculi.  Thus,  when  the 
fasciculi  of  a  muscle  are  attached  to  a  central  tendon  obliquely,  like  the 
feathers  of  a  quill  pen,  the  muscle  is  called  pen )u  form.  If  the  fasciculi 
of  a  muscle  converge  from  a  broad  surface  and  are  attached  to  a  narroAV 
tendon,  the  muscle  is  called  radiated.  When  the  fasciculi  of  a  muscle 
are  turned  or  twisted  upon  themselves  the  muscle  is  called  a  torsion 
muscle.  If  the  tendon  of  a  muscle  passes  through  a  loop  or  around  a 
bony  process,  and  its  action  is  thereby  diverted  from  a  straight  line  with 
the  longitudinal  axis  of  its  body,  it  is  called  a  pidley  or  trochlear  muscle. 
Those  situated  at  the  opening  of  tubes  ^hich  separate  one  compartment 
from  another,  and  the  fasciculi  of  which  form  circular  bands,  are  called 
spkincter  muscles  ;  they  generally  have  no  osseous  attachment,  and  their 
action  is  frequently  antagonized  by  others. 

Muscles  also  receive  special  names  according  to  the  regions  which  they 
occupy,  their  situation  in  the  region,  and  their  origin  and  insertion. 
Thus,  the  superficial  muscles  include  the  subcutaneous  muscles,  the 
panniculus  carnosus ;  in  man  the  rudiments  of  this  muscle  are  the 
muscles  of  expression,  those  moving  the  ears,  and  the  platysma  myoides. 
These  muscles  contain  a  greater  amount  of  contractile  tissue  than  those 
composing  the  deeper  layers. 

Muscles  yield  to  pressure  produced  by  tumors,  aneurism  or  abscess, 
and  the  products  of  inflammation  pass  with  facility  throughout  their 
tissue,  generally  taking  the  course  of  the  areolar  partitions. 

These  organs  can  be  increased  in  size  and  firmness,  by  the  enlarge- 
ment of  the  individual  fibres,  through  judicious  exercise  or  training,  but 
they  become  smaller  by  an  excess  of  physical  activity  or  deteriorated  by 
inaction.     The  complete  rest  of  the  parts  following  fractures  and  other 


166  ANATOMY. 

local  injuries  reduces  the  size  and  tonicity  of  muscles,  and  this  atrophied 
condition  often  remains  persistent.  Modern  surgery,  to  avoid  this  and 
other  pathological  sequences,  attempts  the  adjustment  and  fixation  of 
the  ends  of  fractured  bones  with  as  little  loss  of  muscular  exercise  as 
possible. 

The  Number  of  Muscles. — The  whole  number  of  muscles  belong- 
ing to  the  voluntary  system  is  about  229  :  those  of  the  head,  52  ; 
of  the  neck,  24,  exclusive  of  those  belonging  to  the  vertebral  column. 

The  muscles  of  the  head  are  divided  into  four  groups — those  of  the 
face,  auricle,  orbit,  and  of  mastication. 

The  facial  muscles  (Fig.  88)  are  subdivided  into  three  sets,  named, 
according  to  their  location,  the  fronto-palpebi'al,  the  nasal,  and  the  oral. 

The  fronto-palpebral  muscles  are  the  occipito-frontalis,  the  pyra- 
raidalis  nasi,  the  orbicularis  palpebrarum,  and  the  corrugator  supercilii. 

The  nasal  muscles  are  the  compressor  nasi,  the  depressor  ake  nasi,  the 
dilator  naris  anterior,  and  the  compressor  narium  minor. 

The  oral  muscles  are  the  orbicularis  oris,  the  levator  labii  superioris 
aheque  nasi,  the  levator  labii  superioris  proprius,  the  depressor  labii 
superioris,  the  zygomaticus  minor,  the  zygomaticus  major,  the  levator 
anguli  oris,  the  risorius,  the  de])ressor  anguli  oris,  tlie  depressor  labii 
inferioris,  the  levator  labii  inferioris,  and  the  buccinator. 

The  muscles  of  the  auricle  consist  of  the  attolens  aurem,  the  attrahens 
aurem,  and  the  retrahens  aurem. 

The  muscles  of  the  orbit  are  the  levator  palpebrse,  the  rectus  supe- 
rioris, the  rectus  inferioris,  the  rectus  internus,  the  rectus  externus,  the 
obliquus  superioris,  and  the  obliquus  inferioris. 

The  muscles  of  mastication  are  the  masseter,  the  temporalis,  the 
pterygoideus  externus,  and  the  pterygoideus  internus. 

The  muscles  of  the  neck  are  the  platysma  myoides,  sterno-cleido- 
mastoideus,  the  depressors  of  the  hyoid  bone,  the  muscles  of  the  supra- 
hyoid space,  those  of  the  ])harynx  and  soft  palate,  the  deep  lateral,  and 
the  prevertebrals. 

The  Facial  Muscles. 

The  facial  differ  markedly  from  all  other  voluntary  muscles  of  the 
body.  In  the  first  place,  some  of  them  have  no  bony  origin  ;  none 
have  bony  insertions.  That  is  to  say,  some  of  the  facial  muscles  have 
but  one  extremity  attached  tc;  bone,  the  other  being  inserted  into  mus- 
cles; while,  again,  several  liave  no  osseous  attachment  whatever.  Their 
fibres  are  more  delicate,  and,  having  no  investing  sheath  of  perimysium, 
merge  one  into  the  other. 

The  voluntary  muscles  of  the  face  are  not  as  wholly  under  the  power 
of  the  will  as  are  the  voluntary  muscles  of  the  limbs,  and  are  often 
aifected  by  mental  impressions. 

The  Occipito-frontalis  is  in  reality  two  muscles  divided  by  an 
aponeurosis.      These  are  called  the   Occipitalis  and  the  Frontalis. 

The  Occipitalis  Muscle  is  thin  and  flat,  arises  from  the  outer  two- 
thirds  of  the  superior  semicircular  line  of  the  occipital  bone  and  the 
mastoid   portion  of  the  temporal   bone  above  the  attachment  of  the 


AREOLAR   TISSUE,   TENDONS,  AND  MUSCLES. 


1G7 


sterno-cleido-mastoid,  passes  upward  and  foi'Mard,  and  terminates  in 
distinct  tendinous  fibres,  which  are  continuous  with  the  epicranial  or 
occipito-frontal  aponeurosis. 

The  Frontalis  Muscle  is  tliinner  and  paler  than  the  occipitalis,  and  is 
more  intimately  connected  with  the  skin.  It  arises  from  the  aponeu- 
rosis, on  a  transverse  line,  between  the  fronto-parietal  suture  and  the 

Fig.  88. 


LE\  ATOR 

ANGL  LI 

SUPERIORIb 


The  Muscles  of  Expression. 

frontal  eminences.  It  is  larger  than  the  occipitalis,  and  arises  by  two 
heads  slightly  separated  from  the  fibrous  epicranial  or  occipito-frontal 
aponeurosis,  and  passes  downward  over  the  forehead.  The  fibres  con- 
verge as  they  descend,  the  two  portions  of  the  muscle  uniting  just  above 
the  nasal  eminence  to  be  inserted  into  the  eyebrows.  The  central  por- 
tion of  the  muscle  is  continuous  with  the  pyramidalis  nasi,  while  a 
large  number  of  its  fibres  are  interlaced  with  the  corrugator  supercilii 
and  orbicularis  palpebrarum,  and  extend  outward  over  the  external 
angular  process  of  the  frontal  bone. 

The  Epicranial  or  Occipito-frontal  Aponeurosis  is  a  fibrous  connec- 
tive extension  of  the  above  muscles,  covering  the  upper  portion  or 
vertex  of  the  skull  from  side  to  side,  without  division.  Superiorly,  it 
is  intimately  connected  with  the  scalp,  though  interspaces  will  be  found 
filled  with  granules  of  fat.  So  close  is  this  connection  that  it  is 
difficult  to  separate  the  tw^o  by  dissection:      Between  the  epicranial 


168  ANATOMY. 

aponeurosis  and  the  pericranium  there  is  a  small  amount  of  loose 
connective  tissue,  which  permits  easy  movement  and  readily  admits  of 
dissection 

Posteriorly,  this  aponeurosis  is  attached  to  the  occipitalis  muscle,  a 
portion  of  the  superior  semicircular  line,  and  the  occipital  protuberance. 
Anteriorly,  it  terminates  in  the  frontalis  muscle.  Laterally,  it  presents 
no  distinct  marginal  termination,  but  is  gradually  blended  into  the 
superficial  temporal  fascia,  and  affords  attachment  to  the  superior  and 
anterior  aural  muscles.  Its  outer  surface  is  closely  attached  to  the 
skin  by  numerous  bands  of  connective  tissue. 

Aotio7i. — By  the  contraction  of  the  frontalis  muscle  the  eyebrows  are 
elevated  or  arched,  as  in  expressing  surprise,  delight,  or  doubt.  This 
elevation  of  the  eyebrows  causes  the  skin  to  wrinkle  over  the  surface 
of  the  forehead. 

By  the  contraction  of  the  occipitalis  muscle  the  scalp  is  drawn  back- 
ward, and  by  an  alternating  action  of  the  two  muscles  the  scalp  may 
be  moved  forward  and  backward.  Most  people  have  not  the  power  of 
moving  the  scalp  in  both  directions,  the  motion  being  limited  to  an 
anterior  direction  only. 

The  Pt/ramidales  Nasi  are  two  in  number.  Their  form,  as  their 
name  indicates,  is  pyramidal,  and  they  are  formed  by  the  continuation 
of  the  fasciculi  from  the  frontalis  muscle.  They  extend  downward  on 
either  side  of  the  nose,  widening  as  they  descend,  and,  becoming  ten- 
dinous, join  the  tendinous  insertion  of  the  compressor  nasi. 

Relations. — By  its  upper  surface  with  the  skin,  and  below  with  the 
nasal  bones. 

The  Orbicularis  Palpebrarum  is  a  thin  sphincteric  or  elliptical  muscle 
having  a  bony  attachment.  It  is  closely  adherent  to  the  integument 
covering  the  eyelids  and  surrounding  the  orbits.  It  is  divided  into 
three  portions — orbital,  jxilpebral,  and  concentric. 

The  Orbital  or  Peripheral  Portion  arises  fi'om  the  internal  angular 
process  of  the  frontal  bone,  the  nasal  ])rocess  of  the  superior  maxilla,  and 
the  lachrymal  groove.  Its  fasciculi  diverge  as  they  extend,  the  superior 
passing  ujnvai'd  and  outward  over  the  superior  orbital  arch  toward  the 
temple,  while  the  inferior  pass  downward  and  outward,  inosculating  with 
the  superior  fibres  at  the  outer  portion  of  the  orbit.  The  orbital  por- 
tion of  tlie  orbicularis  palpebrarum  is  the  strongest,  while  its  fibres  are 
of  deeper  color  than  the  other  two  portions.  Internally,  its  fibres  are 
attached  to  the  tarsal  ligament,  while  next  to  the  nose  it  has  a  bony 
attachment  such  as  described  above.  Its  superior  border  is  partially 
held  in  position  by  descending  fibres  from  the  frontalis  and  by  the 
corrugator  supercilii  muscles.     Its  lower  and  outer  margins  are  free. 

The  Palpebral  Portion  arises  from  the  superior  and  inferior  margins 
of  the  tarsal  ligament,  passes  outward  over  the  eyelids,  and  is  inserted 
into  the  outer  and  lesser  tarsal  ligaments.  This  portion  is  much  thinner 
and  its  fibres  are  paler  than  the  preceding. 

The  Concentric  Ciliary  or  Inner  Portion  is  somewhat  stronger  than 
that  covering  the  eyelids,  and  is  confined  to  the  margins  of  the  vela. 
The  inner  edges  are  free. 

Relations. — By  its  upper  surface  with  the  integnment ;  by  its  under 


AREOLAR   TISSUE,   TENDONS,  AND  MVSCLES.  169 

surface  the  orbital  portion  is  in  relation  with  the  frontalis  and  corrugator 
supercilii  muscles,  their  fibres  interlacing,  and  with  the  supraorbital 
vessels  and  nerves,  the  lachrvnial  sac,  the  origin  of  the  levator  labii 
superioris,  alseque  nasi,  and  the  levator  labii  superioris  muscles  ;  inter- 
nally with  the  pyramidalis  nasi,  and  externally  with  the  temporal  fascia. 
The  under  surface  of  the  palpebral  portion  of  this  nuiscle  is  connected 
to  the  cartilage  of  the  eyelid  by  fibrous  connective  tissue. 

The  Internal  lendo-jxi/pebrariim  (tendo-occuli)  is  a  small  white 
fibrous  band  about  two  lines  in  length  and  one  line  in  breadth.  It  is 
attached  to  the  nasal  ])rocess  of  the  superior  maxilla  in  front  of  the 
lachrymal  groove,  and  runs  outwardly  across  the  lachrymal  sac  to  the 
inner  commissure  of  the  eyelids,  where  it  divides  into  two  portions,  one 
going  to  each  lid.  As  the  tendon  crossess  the  lachrymal  sac  it  gives 
off  from  its  under  surface  a  strong  aponeurotic  lamina  which  covers  the 
sac  and  is  attached  to  the  lachrymal  bone. 

The  External  Tendo-palpebrarum  is  much  weaker  than  the  internal, 
and  is  attached  to  the  malar  bone. 

The  Tensor  Tarsi  (Horner's  nuiscle)  is  a  thin  layer  of  fibres  arising 
from  the  lachrymal  crest  behind  the  lachrymal  sac.  It  jiasses  forward 
and  outward,  and  divides  into  two  fasciculi,  which  are  lost  in  the  con- 
centric portion  of  the  orbicularis  palpebrarum. 

The  Corrugator  Supercilii  is  a  small,  deeply-colored  muscle  arising 
from  the  inner  extremity  of  the  superciliary  ridge,  passing  outward  and 
upward,  its  fibres  diverging,  some  extending  into  the  orbicularis  and 
frontalis  nniscles,  terminating  about  the  middle  of  the  eyebrow.  This 
muscle  is  intimately  adherent  to  the  integument. 

Relations. — By  the  inner  portion  of  its  upper  surface  with  the  orbic- 
ularis and  frontalis  muscles,  the  outer  extremities  of  its  fibres  being 
inserted  into  these  muscles ;  by  its  under  surface  with  the  frontal  bone, 
the  supratrochlear  branches  of  the  o])hthalmic  nerve  and  accompanying 
vessels. 

(The  levatores  palpebrse  will  be  described  with  the  motor  muscles  of 
the  eye.) 

Actions. — The  orbicular  portion  of  the  orbicularis  palpebrarum  is 
wholly  under  the  control  of  the  will.  Its  upper  fibres  act  by  depressing 
the  eyebrow  and  drawing  down  the  integument  of  the  forehead,  antag- 
onizing the  frontalis  muscle.  The  lower  portion  elevates  the  integu- 
ment of  the  cheek,  and  both  combined  wrinkle  the  skin  at  the  outer  and 
inner  angles  of  the  orbital  cavities.  The  office  of  this  muscle  is  fully 
exerted  when  the  eye  is  closed  with  force. 

The  Palpebral  Portion  gives  the  peculiar  movement  to  the  eyelids 
seen  in  winking  or  in  sleep.  It  also  draws  forward  the  internal  tarsal 
ligament  and  the  anterior  wall  of  the  lachrymal  sac,  causing  it  to  open 
for  the  reception  of  lachrymal  fluid. 

The  ConcentriG  or  Ciliary  Portion  closes  in  the  edges  of  the  vela  of 
the  eyes,  and  draws  the  cilia  or  lashes  of  the  respective  lids  against  each 
other. 

The  Corrugator  Supercilii  muscle  draws  the  skin  over  the  forehead 
downward  and  inward  toward  the  upper  part  of  the  nose,  causing  the 
vertical  grooves  made  in  frowning. 


170 


ANATOMY 


The  Nasal  Set  of  muscles  comprises  the  compressor  nares,  depres- 
sor alse  nasi,  and  the  dihitores  nares.  These  are  unimportant  muscles, 
composed  of  few  fasciculi,  and  their  actions  are  implied  in  their  names. 


Fig.  89. 


COBRUGATOR   SUPERCIL 


DILATOR  NARIS  POSTE 
:C">RC5S0Bu*Hliir«l 
orPRCsSOB  AL/e 


Muscles  of  the  Head,  Face,  and  Neck. 


The  Compressor  Ncire><  is  a  small  trian<rular  muscle  arising  by  its  apex 
from  the  inner  portion  of  tlie  canine  fossa  of  the  superior'maxilla,  its 
fibres  pa-ssing  inward  aud  upward,  gradually  expanding  into  a  thin 


AREOLAE  TISSUE,   TENDONS,  AND  MUSCLES.  171 

aponeurosis,  uniting-  with  the  corresponding  muscle  of  the  op})osite  side 
and  with  the  pyramidaHs  nasi. 

The  Depressor  Alee  Nasi  are  short  radiated  muscles  arising  from  the 
incisive  fossse  of  the  superior  maxillte,  the  fibres  passing  upward  to  be 
inserted  into  the  integument  of  the  nasal  septum  and  to  the  alee  of  the 
nose. 

Besides  those  just  described,  there  are  several  other  muscles,  with 
irregular  and  indistinct  fasciculi,  which  assist  in  enlarging  the  opening 
of  the  nose.  Among  these  are  the  compressor  narium  minor  and  the 
dilatores  naris  anterior  and  posterior. 

The  Oral  Group  (Fig.  89)  consists  of  the  orbicularis  and  those 
muscles  having  their  insertion  into  it. 

The  Orbicularis  Oris  is  a  thin  layer  of  muscular  fibres,  forming  the 
sphincter  of  the  mouth.  It  is  elliptical  in  form,  its  fibres  being  con- 
tinued from  one  lip  to  the  other  around  the  angles  of  the  oral  opening. 
It  is  divided  into  two  portions,  labial  and  facial,  the  labial  or  marginal 
circle  or  rim  forming  the  red  portion  of  the  lij).  Tlie  iacial  or  external 
portion  blends  with  the  muscles  which  converge  toward  the  mouth, 
its  fibres  being  inserted  into  them,  and  acting  antagonistically  to  them. 
The  portion  of  this  muscle  corresponding  to  the  upper  lip  is  composed 
of  four  slips  of  muscular  fibres,  two  situated  on  each  side  of  the  cen- 
tral portion.  The  outer  slips  are  thin  and  weak,  ])ass  downward,  and 
are  attached  to  the  superior  maxilla  in  the  incisor  fossa  below  the  ori- 
gin of  the  depressor  alse  nasi.  The  inner  two  slips,  thicker  and  stronger, 
pass  upward,  and  are  inserted  into  the  septum  of  the  nose.  At  the 
median  line  the  space  between  these  slips  corresponds  to  the  perpendic- 
ular groove  on  the  lip  immediately  below  the  nose.  The  two  fasciculi 
of  the  loAAcr  lip  arise  in  the  incisor  fossa  of  the  inferior  maxilla  exter- 
nal to  the  levator  labii  inferioris.  They  pass  upward  and  outAvard 
toward  the  angles  of  the  mouth,  their  fibres  interlacing  with  the  other 
muscles  of  the  lip. 

Relations. — By  the  inner  margin  of  the  superficial  surface  it  is  closely 
connected  with  the  integument,  whilst  superimposed  between  the  outer 
portion  and  the  integument  is  a  layer  of  fatty  tissue  ;  by  its  deep  surface 
with  the  mucous  membrane,  labial  glands,  and  coronary  arch  of  vessels 
of  each  lip.  Its  internal  circumference  is  immediately  beneath  the  integu- 
ment, and  forms  the  free  margins  of  the  lips,  whilst  the  outer  circum- 
ference is  blended  with  the  several  muscles  that  converge  from  various 
portions  of  the  face  to  this  point  or  muscle. 

The  Levator  Labii  Superioris  Alceque  Nasi  is  a  thin  triangular  muscle 
situated  along  the  side  of  the  nose,  extending  from  the  inner  angle  of 
the  orbital  cavity  to  the  ujjper  lip.  It  arises  by  a  pointed  extension 
from  the  upper  and  outer  part  of  the  nasal  ])rocess  of  the  superior 
maxilla,  passes  downward  and  outward,  and  divides  into  two  portions. 
The  smaller  of  these  is  inserted  into  the  ala  of  the  nose,  the  other  being 
prolonged  downward  and  blending  with  the  orbicularis  oris  and  the 
special  elevator  muscle  of  the  upper  lip. 

Belations. — By  its  superficial  surface  superiorly  with  the  oi'bicularis 
palpebrarum,  and  below  with  the  integument. 

The  Levator  Labii  Superioris  Propi'ius  is  the  special  elevator  muscle 


172  ANATOMY. 

of  the  upper  lip.  It  is  thin  and  quadrilateral  in  outline,  arising  imme- 
diately below  the  orbital  cavity  above  the  intraorbital  foramen.  Its 
origin  is  chiefly  confined  to  the  superior  maxilla,  but  a  few  of  its  fibres 
extend  from  the  malar  bone.  It  passes  downward  and  inward  to  be 
inserted  into  the  orbicularis  oris  and  the  integument  of  the  superior  lip. 
It  is  situated  on  the  same  general  plane  as  tlie  levator  labii  snperioris 
alteque  nasi,  and  is  connected  with  it  throughout  its  lower  third. 

Relation)^. — By  its  superficial  surface  with  the  orbicularis  palpebrarum 
and  the  integument ;  by  its  inner  surface  with  the  infraorbital  nerve 
and  its  accompanying  vessels  as  they  emerge  from  the  infraorbital  fora- 
men, a  portion  of  the  levator  anguli  oris,  and  the  origin  of  the  com- 
pressor nasi  muscle. 

The  Depressor  Labii  Siq^erioris  is  a  small  muscle  arising  from  the 
lower  portion  of  the  incisive  fossa  of  the  superior  maxilla  and  ihe 
alveolar  process  immediately  below  the  fossa.  Its  fibres  pass  upward 
to  the  lower  border  of  the  nostrils  and  the  partition  of  the  nose.  A 
portion  of  the  fibres  of  this  muscle  are  attached  to  the  integument  cov- 
ering the  wing  of  the  nose ;  the  balance  pass  downward  and  are  inoscu- 
lated with  the  fibres  of  the  muscles  of  the  upper  lip.  It,  with  its  fellow 
and  the  mucous  membrane,  forms  the  frifiuuni  of  the  upper  lip,  and  when 
the  alveolar  process  is  absorbed  after  the  loss  of  the  teeth,  it  is  often  found 
attached  on  the  lower  margin  of  the  gum. 

Re/ations. — Within  the  vestibule  of  the  mouth  it  is  covered  by  mucous 
membrane ;  above  that  portion  it  is  covered  with  the  muscles  of  the 
upper  lip ;  its  deep  surface  rests  upon  the  bone,  and  the  median  border 
joins  with  its  fellow  of  the  opposite  side. 

The  Zyc/omaticus  Minor  is  an  extremely  slender  muscle  arising  from 
the  anterior  inferior  jx»rtion  of  the  malar  bone,  just  behind  the  malo- 
maxillary  suture.  It  passes  downward  and  forward,  its  fibres  becom- 
ing lost  in  those  of  the  special  elevator  muscle  of  the  upper  lip  near  the 
angle  of  the  mouth. 

Rekdions. — By  its  superficial  surface  with  the  orbicularis  palpebrarum 
and  the  integument ;  by  its  deep  surface  with  the  levator  anguli  oris. 

The  Zygomaticm  Major  is  situated  just  external  to  the  smaller  muscle 
of  the  same  name.  It  arises  from  the  malar  bone  in  close  proximity  to 
the  zygomatic  suture,  and  passes  obliquely  downward  to  the  angle  of  the 
mouth,  where  it  is  attached  to  the  integument  and  becomes  blended  with 
the  fibres  of  the  orbicularis  oris  and  depressor  anguli  oris  muscles. 

Relations. — By  its  superficial  surface  with  the  subcutaneous  adipose 
tissue ;  by  its  deep  surface  with  the  malar  bone  and  the  masseter  and 
buccinator  muscles. 

Variations. — The  zygoraaticus  minor  is  oflen  absent,  and  occasionally 
its  fibres  are  lost  in  the  integument  before  reaching  the  muscle  of  the  lip. 
At  times  also  it  arises  in  part  or  entirely  from  the  orl)icularis  palpebra- 
rum muscle,  and  is  blended  with  the  zygomaticus  major  and  the  levator 
labii  su]>erioris.  Occasionally  it  is  separated  into  two  muscles.  The 
zygomaticus  major  is  also  occasionally  wanting,  or  it  may  be  double, 
and  arises  at  times  from  the  masseteric  fascia. 

The  Levator  Anr/ii/i  Oris  (canine  muscle)  arises  from  the  canine  fossa 
immediately  below  the  infraorbital  foramen.     It  passes  downward  and 


AREOLAR   TISSUE,    TENDONS,   AND  MUSCLES.  173 

slightly  outward  to  its  insertion  at  the  angle  of  the  mouth.  In  this 
position  its  fibres  become  blended  with  those  of  the  orbicularis  oris, 
zygomaticus  major  and  minor,  and  depressor  anguli  oris  muscles. 

Belations. — Its  upper  surface  is  in  relation  Avith  the  special  elevator 
muscle  of  the  upper  lip,  the  infraorbital  nerve,  and  vessels  passing 
between  these  two  muscles.  At  the  point  of  its  insertion  it  is  inti- 
mately adherent  to  the  integument ;  by  its  deep  surface  ^^ith  the 
superior  maxillary  bone,  the  buccinator  muscle,  and  the  mucous  mem- 
brane of  the  mouth. 

The  Riso7'ius  (smiling  muscle),  when  present,  consists  of  a  few  thin 
fasciculi  which  arise  from  the  deep  fascia  covering  the  masseter  muscle 
or  the  parotid  gland,  and  occasionally  as  far  back  as  the  mastoid  pro- 
cess of  the  temporal  bone.  From  this  point  it  passes  transversely  for- 
ward and  inward,  its  fibres  becoming  blended  with  those  of  tlie  depressor 
anguli  oris  and  the  orbicularis  oris  at  the  angle  of  the  mouth. 

The  Depressor  Amjull  Oris  (triangularis  menti)  is  a  triangular  mus- 
cle arising  by  its  base  from  the  external  oblique  line  of  the  inferior 
maxilla,  becoming  narrow  as  it  ascends  to  the  angle  of  the  mouth, 
where  its  fibres  become  blended  with  the  orbicularis  oris  and  the 
other  muscles  of  this  region. 

Belations. — By  its  superficial  surface  with  the  integument ;  by  its 
deep  surface  with  the  Iniccinator  and  depressor  muscles  of  the  lip. 

The  Depressor  Labii  Inferioris  (quadratus  menti)  is  quadrilateral  in 
shape,  and  arises  from  the  inferior  maxilla  by  a  line  of  attachment  extend- 
ing from  near  the  symphysis  to  a  point  a  little  posterior  to  the  mental 
foramen.  Its  fibres  pass  upward  and  inward,  uniting  with  its  fellow  of 
the  opposite  side  and  blending  with  the  fibres  of  the  orbicularis  oris.  It 
is  continuous  below  with  the  platysma  myoides,  and  above  it  is  inserted 
into  the  integument.  Between  the  fibres  of  this  muscle  will  be  found  a 
considerable  quantity  of  adipose  tissue. 

Relations. — By  its  superficial  surface  with  a  portion  of  the  depressor 
anguli  oris  and  the  integument,  with  which  it  is  intimately  connected ; 
by  its  deep  surface  with  the  mental  nerve  and  vessels,  the  mucous  mem- 
brane lining  the  lower  lip,  the  labial  glands,  and  the  elevator  muscle  of 
the  lower  lip. 

The  Levator  Labii  Inferioris  (levator  menti)  can  be  best  exposed  by 
everting  the  lower  lip  and  removing  the  mucous  membrane.  It  is  a 
small  conical  fasciculus  arising  from  the  upper  portion  of  the  incisor 
fossa  of  the  inferior  maxilla,  its  fibres  radiating  as  they  pass  downward 
between  the  depressors  of  the  lower  lip  to  be  inserted  into  the  integu- 
ment covering  the  chin. 

Belations. — By  its  superficial  surface  with  the  mucous  membrane  of 
the  vestibule  of  the  mouth,  with  the  lower  margin  of  the  orbicularis 
oris  and  the  integument  covering  the  chin  ;  by  its  deep  surface  with  the 
bone  and  the  depressor  muscle  of  the  lower  lip,  and  on  its  median  bor- 
der with  its  fellow  of  the  opposite  side. 

The  Buccinator  is  a  thin  and  flat  though  powerful  muscle  situated 
between  the  upper  and  lower  jaws,  and  forming  a  considerable  portion 
of  the  wall  of  the  vestibule  of  the  mouth.  Correctly  speaking,  it  is  not 
a  true  facial  muscle,  belonging  more  properly  to  the  pharyngeal  con- 


174  ANATOMY. 

strictor  muscles,  being  advaneed  forward  into  the  face.  It  also  differs 
from  the  facial  muscles  hy  being-  enclosed  in  a  sheath  of  thin  fascia,  and 
is  suj)plied  by  a  different  motor  nerve.  It  arises  from  the  lower  margin 
of  the  outer  surface  of  the  alveolar  })rocesses  of  the  superior  and  inferior 
maxillary  bones  oj)posite  the  molar  teeth,  from  the  anterior  surface  of 
the  ptervgo-maxillaiy  ligament,  which  is  a  narrow  band  of  tendinous 
fibres  extending  from  the  upper  extremity  of  the  hanudar  process 
of  the  internal  ])terygoitl  plate  of  the  s})henoid  bone  to  the  mylo-hyoid 
ridge  of  the  inferior  maxillary  bone,  close  to  the  position  of  the  wisdom 
tooth.  From  this  extensive  origin  its  fibres  ])ass  forward,  converge, 
and  become  thickened  as  they  ivacii  the  lateral  margin  of  the  orbicularis 
oris.  At  this  point  its  central  fibres  decussate,  those  from  the  U})[)er 
]>ortion  becoming  blended  with  the  nuiscles  of  the  lower  lip,  and  those 
from  the  lower  portion  blending  with  the  muscles  of  the  upper  lip.  The 
superior  and  inferior  fibres  of  the  nuiscle  continue  forward  without 
decussation,  inosculating  with  the  superficial  fibres  of  tiie  orbicidaiis 
oris,  becoming  lost  on  the  opj)osite  side  of  the  mouth. 

Rel((tions. — J^y  its  superficial  surface  with  a  considerable  quantity 
of  soft  adipose  tissue,  which  separates  it  from  behind  forward  from  the 
ramus  of  the  jaw,  a  small  part  of  the  temporal  niuscle,  the  masseter 
nuiscle,  the  muscles  of  ex])ression  connected  with  the  angle  of  the 
mouth,  the  parotid  duct,  which  ])icrces  the  muscle  opposite  the  second 
molar  tooth  of  the  up])er  jaw,  and  the  fiicial  artery  and  vein  ;  branches 
of  the  fiicial  and  buccal  nerves  pass  over  it.  By  its  deep  surfiice  it  is  in 
relation  with  the  buccal  glands  and  mucous  membrane  of  the  vestibule 
of  the  mouth. 

Actions  of  thk  Okal  Miscles. — When  the  whole  of  the  orbicu- 
laris oris  muscle  is  brought  into  independent  action,  it  closes  the  lips 
l)oth  vertically  and  transversely,  and  when  a  forced  action  is  brought 
about,  it  projects  the  lips  and  wrinkles  the  integuments;  when  acting 
jointly  with  the  buccinator,  the  lips  are  closecl  and  elongated  trans- 
versely. A\'hen  the  associatt'd  muscles  wiiich  converge  from  nearlv  all 
points  act  singly,  they  draw  the  orbicularis  oris  in  the  longitudinal  direc- 
tion of  their  fibres.  WJien  two  or  more  nmscles  act  together,  the  line  of 
traction  will  be  between  these  muscles,  the  direction  depending  upon  the 
relative  power  of  each  muscle. 

The  common  elevators  of  the  lip  and  nose  and  the  depressors  of  the 
wing  of  the  nose  act  ujion  these  ])arts  in  oi>p()sition  to  each  other,  the 
former  elevating,  the  latter  depressing.  Tiic  muscles  which  are  inserted 
at  the  angles  of  tiie  mouth  not  only  elevate  and  draw  the  angle  back- 
ward, but  in  (h)ing  so  they  push  the  cheeks  u|)ward  and  thus  elevate  the 
margin  of  the  lower  eyelid,  as  is  shown  by  the  ex])ression  of  the  mouth 
and  cheeks  in  merriment ;  while  those  which  depress  the  angles  also 
depress  the  cheeks,  as  illustrated  by  the  face  in  grief. 

The  Muscles  of  the  Ear. 

The  auricular  nuiscles  are  those  that  belong  to  the  pinna  of  the  ear. 
There  are  several  minute  bundles  of  muscular  fibres  which  extend  from 
one  point  to  another  in  the  pinna  ;  also  three  larger  muscles,  two  aris- 


AREOLAR  TISSUE,   TENDONS,  AND  MUSCLES. 


175 


ing  from  the  temporal  aponeurosis,  the  other  from  the  mastoid  process 

of  the  temporal  bone  and  inserted  in  the  pinna  :  they  are  named  the 
attolens  aurem,  the  attrahens  aureni,  and  the  retrahens  aurem.  They 
are  only  slijjrhtly  developed  in  man. 

The  AftolciiH  Aurem,  or  Auricidaris  Superior,  is  the  largest  of  the  three. 
It  is  fan-shaped,  arising  by  a  bnjad  head  from  the  superfieial  faseia  over 
the  temporal  muscle,  and  is  inserted  into  the  anterior  part  of  the  helix 
and  the  eminence  upon  the  inner  surface  of  the  pinna.  Its  fibres  are 
extremely  delicate ;  it  is  furnished  with  branches  from  the  occipital 
nerve. 

The  AttrdhriiH  Avrcni,  or  Aiiricnkirin  Anterior,  is  the  smallest  of  the 
three  ;  it  is  thin,  fan-shaped,  and  its  fibres  are  pale  and  indistinct,  aris- 
ing from  the  superficial  faseia  over  the  temporal  muscle,  and  are  inserted 
into  the  tragus.  ,  The  nerve  supplying  it  is  derived  from  the  facial  and 
the  auriculo-temporal  branch  of  the  inferior  maxillary. 

The  liefraheiis  Aurem,  or  Avrieidaria  Posterior,  is  stouter  than  the 
other  two,  and  is  composed  of  two  or  three  fasciculi.  The  •fil)res  are 
deeper  in  color  and  distinctly  marked.  It  arises  from  the  mastoid  por- 
tion of  the  temjioral  bone ;  passing  forward,  it  narrows  slightly  and  is 
inserted  into  the  posterior  aspect  of  the  concha.  The  nerve-supply  is 
derived  from  the  posterior  auricidar  branch  of  the  facial. 

Muscular  Action. — ^\  ith  few  exce])tions  man  has  ntj  power  to  move 
the  ears ;  therefore  the  muscular  action  is  of  little  or  no  consequence. 

MUSCLES    OF    THE    ORBIT. 

The  muscles  of  the  orbit  (Figs  90  and  91)  are  seven  in  number — six 
belonging  to  the  movement  of  tlie  eyeball :  one  is  the  elexator  of  the 

P^iG.  90. 


Muscles  of  the  Right  Orbit. 

upper  lid.     With  one  exception,  the  seven  muscles  ari.«e  from  the  back 
part  of  the  orbit,  pa.ssing  forward  to  their  insertions.     The  other,  the 


176 


ANATOMY. 


Straight  muscles  of  the  eye. 


P^IG.  91. 


OKitfiuis  Suvcrinr 


Reetus  Infc 


Jiowtr  Mead 


The  Relative  Pus 
^Muscles 


inferior  oblique,  arises  from  the  floor  of  the  anterior  portion  of  the 
orbit.     They  are  named  as  follows : 
The  Levator  Palpebrse, 
The  Superior  Rectus, 
The  Inferior  Rectus, 
The  External  Rectus, 
The  Internal  Rectus, 
The  Superior  Oblique, 
The  Inferior  Oblique. 
The  Levator  Palpebne  is  thin,  flat,  and  triangular  in  shape.    It  arises 
by  a  narrow  ribbon-like  band  from  the  under  surface  of  the  lesser  wing 

of  the  sphenoid  bone  above  and  in 
front  (jf  the  optic  foramen.  It  passes 
forward  over  the  eyeball,  expanding 
as  it  does  so,  and  is  inserted  in  the 
fibrous  tissue  on  the  anterior  surface 
of  the  superior  tarsal  cartilage. 

Relatione. — Bet  ween  the  muscle  and 
the  roof  of  the  orbit  are  situated  the 
frontal  nerve  (branch  of  the  ophthal- 
mic or  first  division  of  the  fifth),  the 
fourth  nerve,  and  the  supraorbital  ves- 
sels. Below  it  is  the  superior  rectus 
ition  and  Attachiuent  of  the  and  the  globc  of  the  cve  wlicrc  it  joins 

of  the  Left  Eveball.  ,i       t  i       ■,    •        •,        ,     i"  i     i  •      1,1  ^ 

the  lid  ;  it  is  situated  behind  the  pal- 
pebral ligament,  and  its  deep  surface  rests  on  the  conjunctiva.  A  small 
branch  of  the  third  nerve  controls  its  action  and  enters  its  under  sur- 
face. 

The  Four  Recti  or  Straight  3Iusdes  of  the  eye  are  straight,  flattened 
bands  which  arise  from  the  borders  of  the  optic  foramen  ;  they  then 
pass  forward,  as  their  names  indicate,  to  be  inserted  into  the  sclerotic 
coat  three  or  four  lines  from  the  cornea.  With  the  exception  of  the 
su])erior  rectus  they  may  be  said  to  have  one  common  origin,  which  is 
in  the  form  of  an  oval  ring,  the  ligament  of  Zinn,  which  commences 
above,  passing  downward  on  the  inner  side  to  the  lower  margin  of  the 
ojitic  foramen,  thence  transversely  across  the  anterior  lacerated  foramen, 
where  it  is  attached  to  the  great  wing  of  the  sphenoid  bone  ;  from  this 
it  ])asses  again  to  the  lesser  wing  on  the  outer  side  of  the  optic  foramen. 

The  Superior  Rectus  is  the  weakest  of  the  four  straight  muscles.  It 
has  its  origin  between  the  levator  palpebrpe  and  the  ring  or  ligament 
of  Zinn,  some  of  its  fibres  having  their  origin  in  the  ring. 

The  Inferior  Rectus  principally  arises  from  the  ligament  of  Zinn  on 
the  inner  margin  of  the  anterior  lacerated  foramen. 

The  Infernal  Rectus  arises  from  the  ligament  of  Zinn  on  the  inner 
and  lower  margin  of  the  optic  foramen. 

The  External  Rectus  is  the  strongest  muscle  of  its  group.  It  usually 
arises  by  two  heads.  The  louier  head  is  the  stronger,  and  arises  from  the 
ligament  of  Zinn  and  a  spine  on  the  lower  margin  of  the  anterior  lace- 
rated foramen,  and  also  joins  the  inferior  rectus  muscle  at  its  origin.  The 
upper  head  is  the  weaker,  and  arises  between  the  anterior  lacerated  and 


AREOLAR   TISSUE,   TENDONS,  AND  MUSCLES.  177 

optic  foramina.  Fibres  are  giv^en  off  from  the  two  heads  of  the  muscle, 
forming  a  tendinous  arch  over  the  foramen,  through  which  pass  the 
third,  the  nasal  branch  of  the  fifth,  and  the  sixth  nerves,  also  the 
ophthalmic  vein. 

The  Superior  Oblique,  or  Troehlearis,  is  a  narrow  elongated  muscle 
situated  at  the  upper  and  inner  part  of  the  orbit,  internal  to  the  levator 
palpebrse.  It  arises  close  to  and  in  front  of  the  inner  margin  of  the 
optic  foramen.  It  extends  forward  to  the  upper  and  inner  angle  of  the 
orbit,  where  it  becomes  tendinous  as  it  passes  through  a  tibro-cartilagi- 
nous  ring  or  pulley  (trochlea)  attached  to  the  trochlear  fossa  or  process, 
near  the  internal  angular  process  of  the  frontal  bone.  The  contiguous 
surface  of  the  tendon  and  ring  is  lined  by  a  delicate  synovial  mem})rane 
enclosed  in  a  thin  fibrous  sheath.  After  the  tendon  passes  through  the 
ring  it  resumes  its  fleshy  appearance;  it  is  deflected  backward,  outward, 
and  downward,  and  passes  between  the  eye  and  the  superior  rectus,  to 
be  inserted  into  the  sclerotic  coat,  a  little  beyond  the  outer  margin  of 
that  muscle  and  midway  between  the  cornea  and  the  entrance  of  the 
optic  nerve. 

The  Inferior  Oblique  is  a  thin,  narrow  muscle  situated  near  the  ante- 
rior margin  of  the  orbit  and  close  to  the  outside  of  the  orifice  of  the 
lachrymal  duct.  It  arises  from  a  slight  depression  in  the  orbital  plate 
of  the  superior  maxillary  bone  near  the  lachrymal  canal,  from  which  it 
passes  outward,  backward,  and  upward  between  the  inferior  rectus  and 
the  floor  of  the  orbit,  and  betMcen  the  external  rectus  and  the  eyeball, 
terminating  in  a  tendinous  expansion  which  is  inserted  into  the  sclerotic 
coat  between  the  external  and  superior  recti  muscles  near  to  the  insertion 
of  the  superior  oblique. 

Actions  of  the  Orbital  Muscles. — The  Levator  Palpebrce  Supe- 
rioris  is  the  elevator  of  the  upper  eyelid,  being  antagonized  by  the  upper 
palpebral  part  of  the  orbicularis  muscle,  which  is  the  closer  of  the  eye. 

The  eyeball  is  so  suspended  within  the  orbit  that  it  is  easily  moved 
upon  a  fixed  axis,  but  does  not  apparently  change  its  position  as  a  whole, 
nor  do  the  actions  of  the  muscles  make  any  distinct  alteration  in  its 
form.  The  fixed  axis  upon  which  the  eye  moves  is  nearly  in  the  centre 
of  the  curvature  of  the  posterior  wall,  and  a  little  back  of  the  middle 
of  the  antero-posterior  axis  of  the  eyeball. 

The  movement  of  the  eye  is  best  classified  in  four  actions:  (a)  lateral 
movement  (in  and  out) :  the  inward  motion  is  caused  by  the  action  of 
the  internal  rectus,  the  outward  by  the  action  of  the  external  rectus; 
(6)  perpendicular  movement  (up  and  down),  the  upward  motion  being 
caused  by  the  superior  rectus,  and  the  downward  by  the  inferior  rectus 
muscles;  (c)  rotary  movement,  caused  by  the  oblique  muscles:  the 
superior  oblique  rotates  the  eye  inward,  and  at  the  same  time  turns  it 
downward ;  the  inferior  oblique  turns  it  outward  and  upward.  The 
rotary  movement  of  the  eyeball  is  required  when  looking  at  an  object 
with  the  head  inclined  to  either  side,  in  order  that  the  vision  may 
fall  equally  upon  the  retina  of  each  eye.  (d)  Is  a  movement  in  which 
two  or  more  muscles  act  together ;  for  example,  if  the  external  and 
superior  rectus  muscles  are  acting  with  equal  power,  the  eyeball  will  be 
directed  in  a  line  between  the  insertions  of  these  muscles.     It  is  by  this 

Vol.  I.— 12 


178  ANATOMY. 

co-ordination  of  movement  that  the  muscles  of  the  orbit  cause  the  eye- 
ball to  move  in  the  desired  direction. 

Fascia  of  the  Orbit. — The  orbital  space  that  is  not  occupied  by  the 
eyeball,  muscles,  vessels,  nerves,  ganglia,  and  glands  is  tilled  up  with 
a  soft  cushion  of  fat  and  delicate  yielding  connective  tissue.  The 
Capsule  or  Fascia  of  Tenon  is  formed  from  this  connective  tissue.  It 
is  a  thin  membrane  surrounding  the  greater  part  of  the  eyeball,  and 
forms  a  socket  for  the  globe  to  turn  in.  It  arises  from  the  boi'ders  of 
the  orbit,  passing  behind  the  conjunctiva  and  giving  it  support,  thence 
backward  over  the  eyeball  to  the  entrance  of  the  optic  nerve.  The 
capsule  is  pierced  behind  by  the  optic  nerve  and  the  ciliary  vessels  and 
nerves.  The  tendons  of  the  muscles  of  the  eyeball  also  perforate  it 
near  their  insertions,  and  it  sends  tubular  prolongations  over  each 
muscle,  these  extensions  gradually  taking  the  appearance  of  simple 
areolar  investment,  except  in  the  case  of  the  superior  oblique,  to  M-hich 
it  forms  a  sheath  as  far  as  the  pulley  of  that  muscle. 

The  sheaths  of  the  recti  muscles  send  prolongations  from  their  outer 
surfaces  to  be  attached  to  the  outer  margins  of  the  orbits,  which  pre- 
vent too  great  contractions  of  the  muscles.  The  prolongations  from 
the  inner  and  outer  recti  are  stronger  than  those  from  the  others,  this 
being  especially  so  with  the  external  recti,  which  are  attached  to  the 
malar  bone  and  external  tarsal  ligament ;  the  inner  expansion  is  fixed 
to  the  crest  of  the  lachrymal  bone,  and  the  npper  one  connected  with 
the  tendon  of  the  levator  palpebrie,  thus  enabling  the  superior  rectus  to 
have,  an  influence  in  the  movement  of  the  eyelid. 

The  inner  surface  of  the  capsule  is  connected  with  the  eye  by  delicate 
bundles  of  yielding  connective  tissue,  allowing  a  large  lymph-space  to 
exist  between  the  capside  and  the  eye,  which  appears  to  act  as  a  synovial 
membrane 'in  the  movements  of  the  globe. 

The  movements  of  the  eye  and  its  lids  are  to  a  certain  extent  governed 
by  the  sympathetic  nerves  supplying  the  involuntary  (non-striated) 
muscular  fibres  Avhich  are  found  interspersed  among  the  voluntary 
muscles  of  this  region. 

Nerves. — The  levator  palpebrfe,  inferior  oblique,  and  all  the  recti 
muscles  are  supplied  by  the  third  nerve  (motor  oculi),  the  superior 
oblique  by  the  fourth,  and  the  external  rectus  by  the  sixth  nerve. 

MUSCLES    OF   MASTICATION. 

The  Masseter,  the  Temporal,  the  Internal  Pterygoid,  and  the  External 
Pterygoid  are  generally  classed  as  the  muscles  of  mastication,  leading 
tlie  student  to  infer  that  they  are  the  only  ones  brought  into  action  in 
the  ]ir()ccss.  This  is  not  correct ;  the  first  three  act  in  closing  the  jaws 
together,  while  the  fi)urth  protrudes  the  lower  jaw  l)eyond  the  ujiper, 
none  of  them  having  jiower  to  oj^en  the  mouth,  although  with  the  head 
erect  the  relaxation  of  the  masseter,  temporal,  and  internal  ptervgoid  per- 
mits the  lower  jaw  to  drop  by  gravitation.  The  muscles  of  the  neck 
open  the  mouth  Avhen  the  head  is  thrown  backward.  The  mouth  is 
rigidly  closed  during  the  tonic  spasm  of  the  first-named  muscles,  as  in 
locked  jaw  or  trismus. 


AREOLAR  TISSUE,   TENDONS,  AND  MUSCLES.  179 

The  Masseter  is  a  stout,  thick,  short,  quadrilateral  muscle  extendiug 
from  the  zygomatic  arch  to  the  inferior  maxillary  bone.  It  is  composed 
of  two  portions,  superficial  and  deep,  which  differ  in  size  and  direction. 

The  /Superficial  Portion  is  the  largest  and  strongest,  and  arises  by  a 
thick  tenclinons  aponeurosis  (which  passes  downward  into  the  muscular 
fasciculi)  from  the  lower  border  of  the  anterior  two-thirds  of  the  zygo- 
matic arch  and  the  lower  margin  of  the  malar  bone  :  extending  down- 
ward and  backward,  it  is  inserted  into  the  lower  and  outer  half  of  the 
angle  of  the  jaw. 

The  Deep  Portion  is  of  triangular  form  ;  it  is  smaller  and  its  muscu- 
lar fibres  are  shorter  than  those  of  the  superficial  jiortion.  It  arises 
from  the  posterior  third  of  the  lower  border  and  from  all  the  internal 
surface  of  the  zygomatic  arch  ;  passing  downward  and  slightly  forward, 
it  joins  some  of  the  superficial  portion,  and  is  inserted  by  a  tendinous 
aponeurosis  into  the  upper  half  of  the  ramus  and  outer  surface  of  the 
coronoid  process  of  the  lower  jaw  ;  only  the  upper  and  back  part  of  the 
nniscle  is  lefb  uncovered  by  the  superficial  portion. 

Relations. — It  is  princijially  covered  by  the  skin  and  the  fascia  or 
platysma  myoides  and  its  own  fascia,  which  latter  adheres  intimately  to 
the  tendon  at  its  origin  ;  at  the  back  portion  the  parotid  gland,  the  duct, 
which  lies  across  the  muscle,  and  at  the  anterior  border  turns  inward, 
pierces  the  buccinator  muscle  and  opens  into  the  mouth  through  a  little 
teat-like  projection  of  the  mucous  membrane :  the  upper  portion  of  the 
masseter  muscle  is  overlaid  by  the  orbicularis  palpebrarum  and  zygo- 
matic. A  few  branches  of  the  facial  nerve  (seventh)  and  the  transverse 
facial  vessels  pass  over  it. 

The  muscle  lies  in  contact  below  with  the  ramus  of  the  jaw  and  the 
buccinator  muscle.  Between  the  two  muscles  there  is  a  large  quantity  of 
delicate  fat  covering  a  nerve  and  vessels  which  enter  the  muscle  through 
the  sigmoid  notch. 

Artery. — The  Masseteric  Artery,  a  branch  from  the  second  division  of 
the  internal  maxillary,  conveys  the  blood-supply. 

Nerve. — The  masseteric  branch  of  the  inferior  maxillary  (third  divis- 
ion of  the  fifth). 

The  ^Temporal  Fascia  is  a  dense  glistening  layer  of  fibres  firming 
an  aponeurosis  covering  the  temporal  muscle  above  the  zygoma,  and 
giving  origin  to  its  superficial  portion.  The  fascia  is  attached  supe- 
riorly to  the  temporal  crest  of  the  frontal  bone  and  to  the  upper  of  the 
two  curved  lines  on  the  parietal  bone,  extending  as  far  back  as  the 
parieto-occipito-temporal  junction.  It  is  thin  and  weak  at  its  origin, 
becoming  thicker  and  stronger  as  it  approaches  the  zygomatic  arch, 
near  which  it  divides  into  two  layers,  these  being  separated  by  a  quan- 
tity of  compact  adipose  tissue ;  these  layers  are  attached  respectively  to 
the  inner  and  outer  margins  of  the  sujierior  border  of  the  zygomatic 
arch.  The  fascia  is  separated  from  the  skin  by  a  thin  membrane  which 
descends  from  the  epicranial  aponeurosis,  and  by  the  auricular  muscles ; 
also  by  some  adipose  tissue  at  the  lower  portion.  If  an  abscess  should 
form  beneath  this  fascia  or  within  the  nmscle,  the  pus  would  be  directed 
to  the  coronoid  process  of  the  inferior  maxilla,  and  thence  into  the  mouth 
along  the  adipose  tissue  of  this  region. 


180 


ANATOMY 


The  Temporal  Muscle  (Fig.  92)  is  a  radiating  or  fan-shaped  muscle 
situated  in  the  temporal  fossa  and  descending  to  the  coronoid  process  of 
the  inferior  maxillary  bone.  It  is  composed  of  a  superficial  and  a  deep 
portion. 

The  Superficial  Portion  is  thin  and  delicate,  arising  from  the  temporal 
fossa  or  aponeurosis ;  its  fibres  are  continuous  above  with  those  of  the 

Fig.  92. 


The  Temporal  Muscle,  the  zygoma  and  masseter  having  been  removed. 

deep  portion,  but  are  gradually  lost  below  in  the  deep  layer  of  the  mas- 
seter muscle. 

The  Deep  Portion  is  thick  and  powerful ;  its  anterior  fibres  are 
almost  vertical,  while  those  behind  pass  obliquely  forward.  The  mus- 
cle arises  by  fleshy  fibres  from  all  the  surface  of  the  temporal  fossa 
except  the  anterior  or  that  portion  known  as  the  orbital  septum.  The 
fibres  gradnally  converge  as  they  descend  to  form  a  central  tendon, 
which  is  inserted  chiefly  into  the  inner  surfiice  of  the  coronoid  process 
of  the  lower  ja^v. 

Relations. — Its  superficial  surface  is  covered  by  the  temporal  fascia  ; 
the  lower  and  anterior  part  is  imbedded  in  fat  which  is  a  continuation 
of  that  which  lies  between  the  mnsseter  and  buccinator  muscles.  The 
upper  part  of  its  deep  surface  rests  upon  the  bone ;  the  deej)  temporal 
arteries  and  nerves  which  supply  tlie  muscle  pass  between  the  nuiscle 
and  the  bone  ;  in  its  lower  })ortion  it  is  in  relation  with  the  external 
pterygoid  and  })art  of  the  buccinator,  the  internal  maxillary  artery,  and 
temporal  nerves. 

Arteries. — It  is  sn])])li('d  by  the  superficial  temporal  branches  of  the 
external  carotid  and  the  deci)  temporal  arteries,  branches  of  the  internal 
maxiliarv. 


AREOLAR   TISSUE,    TENDONS,   AND  MUSCLES. 


181 


Nerves. — Its  supply  is  from  branches  of  the  inferior  maxiHarv  nerve. 

The  Internal  Pterygoid  (Fig.  93)  is  a  thick  quadrilateral  muscle  of 
coarse  structure,  interspersed  with  stout  bands  of  fibrous  tissue,  extend- 
ing- from  the  pterygoid  fossa  to  the  inner  angle  of  the  jaw.  It  arises 
principally  in  the  pterygoid  fossa  from  the  inner  surface  of  the  external 
])terygoid  plate  and  from  part  of  the  tuberosity  of  the  palate  bone  within 
the  fossa  ;  it  also  has  a  smaller  muscular  strip  from  the  external  portion 
of  the  tuberosity  of  the  palate  bone  and  the  tuberosity  of  the  superior 
maxillary  bone.  It  passes  backward,  downward,  and  outward,  and  is 
inserted  into  the  roughened  portion  on  the  inner  side  of  the  ramus  of 
the  jaws  between  the  angle  and  the  posterior  dental  foramen. 

"  The  internal  pterygoid  muscle  is  an  important  factor  in  maintain- 
ing false  ankylosis  of  the  temporo-maxillary  joint.     After  the  division 

Fig.  93. 


The  Pterygoid  Muscle :  the  zygomatic  arch  and  a  portion  of  the  ramus  of  the  jaw  have  heen  removed. 

of  the  anterior  border  of  the  masseter  muscle  this  condition  may  persist, 
but  the  ankvlosis  readily  yields  to  the  division  of  the  internal  pterygoid  " 
(Allen). 

Belations. — The  muscle  is  situated  on  the  inside  of  the  ramus  of  the 
jaw,  somewhat  in  the  same  manner  as  the  masseter  is  on  the  outside. 
Between  its  outer  or  lateral  surface  and  the  ramus  of  the  jaws  are  the 
accessory  lateral  ligament  of  the  temporo-maxillary  articulation,  the 
internal  maxillary  vessels,  and  the  inferior  dental  artery  and  nerve ;  at 
its  upper  part  it  is  crossed  by  the  external  pterygoid  muscle.  Its  inner 
or  median  surface  is  related  to  the  tensor  palati  and  superior  constrictor 
of  the  pharynx,  though  there  is  a  quantity  of  areolar  tissue  between  the 
constrictor  and  the  internal  pterygoid  muscles. 

Arteries. — The  internal  pterygoid  is  supplied  by  branches  'from  the 
second  division  of  the  internal  maxillary  artery. 


182  ANATOMY. 

Nerves. — Branches  from  the  inferior  maxillary  division  of  the  fifth. 

The  External  Pterygoid  is  a  short,  thick,  conical  muscle,  extending 
almost  horizontally  from  the  under  surface  of  the  great  wing  and  the 
pterygoid  process  of  the  sphenoid  bone  to  the  condyle  of  the  inferior 
maxilla  and  the  interfibro-articulating  cartilage  of  the  temporo-maxil- 
lary  articulation.  It  arises  by  t^vo  fleshy  heads  placed  close  together, 
an  inferior  and  a  superior. 

The  Superior  Head  arises  from  the  zygomatic  surface  of  the  great 
wing  of  the  sphenoid  bone  and  the  infratemporal  ridge  (pterygoid  ridge) 
which  separates  the  temporal  and  zygomatic  fossse. 

The  Inferior  Head  is  the  larger  of  the  two,  and  arises  from  the  outer 
surface  of  the  external  plate  of  the  pterygoid  process  and  the  tuberosity 
of  the  palate  and  the  superior  maxillary  bones. 

The  two  heads  soon  unite,  forming  a  short,  stout  muscle  passing  back- 
ward and  outward  almost  horizontally  to  be  inserted  by  two  portions, 
superior  and  inferior. 

The  Superior  Portion  is  inserted  into  the  anterior  portion  of  the  inter- 
articular  tibro-cartilage  of  the  temporo-maxillary  articulation. 

The  Lower  or  Inferior  Portion  is  attached  to  the  depression  on  the 
anterior  surface  of  the  neck  of  the  lower  jaw. 

Relations. — On  its  outer  surface  the  internal  maxillary  artery  is 
usually  situated,  passing  between  its  two  heads  of  origin  :  the  buccal 
nerves  also  come  out  between  them.  The  ramus  of  the  jaws  and  the 
tendon  of  the  temporal  muscle  are  in  relation  with  the  outer  surface. 
The  deep  surface  rests  upon  the  upper  part  of  the  internal  pterygoid 
and  the  internal  lateral  ligament,  the  inferior  maxillary  nerve  and  mid- 
dle meningeal  artery.  The  superior  border  is  crossed  by  the  temporal 
and  masseteric  branches  of  the  inferior  maxillary  nerve. 

Arteries. — The  muscle  is  supplied  by  a  branch  from  the  middle  or 
second  division  of  the  internal  maxillary. 

Nerve. — Branch  of  the  inferior  maxillary  (third  division  of  the  fifth). 

Variations. — The  external  pterygoid  sometimes  receives  a  slip  from 
the  temporal  muscle. 

The  Pteri/r/oideus  Proprius  (Henle),  not  constant,  is  a  longitudinal 
cleavage  of  the  upper  portion  of  the  external  pterygoid,  forming  a  band 
of  muscular  and  tendinous  fibres,  sometimes  entirely  tendinous,  extend- 
ing from  the  infratemporal  crest  over  the  external  pterygoid  muscle  to 
the  lower  and  outer  portion  of  the  external  pterygoid  plate,  or  to  the 
tuberosities  of  the  palate  and  superior  maxillary  bones.  Occasionally 
it  sends  a  slip  to  the  pterygo-maxillary  ligament  or  to  the  lower  jaw. 

The  Pterj/f/o-spinosus  is  a  muscular  strip  occasionally  found  extend- 
ing from  the  spine  of  the  sphenoid  bone  to  the  jiosterior  margin  of  the 
external  plate  of  the  ptierygoid  jjrocess,  betMcen  the  two  pterygoid  mus- 
cles. Sometimes  this  is  replaced  by  a  ligament,  or  even  bone,  leaving  a 
large  foramen  between  the  pterygoid  and  zygomatic  fossse. 

Action  of  the  Mt'.scles  of  Masticatiox. — AVith  the  exception 
of  the  external  pterygoid^  these  muscles  act  as  elevators  of  the  inferior 
maxillary  bono,  and  bring  the  teeth  of  the  lower  jaw  forcibly  into  con- 
tact with"  the  upper ;  the  muscles  which  antagonize  them  (those  which 
open  the  mouth)  are  of  much  less  strength. 


AREOLAR   TISSUE,   TESDOXS,  AXB  MUSCLES.  183 

The  external  pterygoid,  having  its  fibres  directed  backward,  and 
nearly  all  of  them  horizontally,  di-aws  the  condyle  forward  and  brings 
the  interarticular  fibro-cartilage  upon  the  eniinentia  artieularis ;  when 
the  muscles  of  both  sides  act  in  unison,  they  cause  the  lower  jaw  to  pro- 
ject. Their  action  is  usually  alternate,  causing  a  sort  of  oscillating  or 
grinding  motion  of  the  riiolar  teeth.  The  superficial  portion  of  the  mas- 
seter  acts  in  conjunction  with  the  external  pterygoid  muscle  in  drawing 
the  jaw  forward,  while  the  posterior  fibres  of  the  temporal  antagonize  it, 
drawing  the  jaw  backward,  thus  acting  for  the  trituration  of  the  food. 

THE  MUSCLES   OP  THE  NECK. 

The  Platysma  Myoides  lies  immediately  below  the  skin  on  the  side 
of  the  neck.  It  is  a  broad^  thin^  quadrangular,  pale-colorecl  sheet 
of  muscular  fibres,  superficial  to  the  deep  cervical  fascia,  extending 
over  the  front  and  sides  of  the  neck  and  the  loMcr  portion  of  the 
face.  It  arises  by  thin  bands  from  the  subcutaneous  connective  tissue 
over  the  deltoid,  pectoral,  and  trapezius  muscles :  the  fibres  are  directed 
obliquely  upward  and  forward  over  the  clavicle  and  acromion  process 
to  the  side  of  the  neck,  gradually  converging  and  approaching  its  fellow 
of  the  opposite  side,  the  most  anterior  fibres  crossing  over  and  inter- 
lacing witli  each  other  in  front  of  and  below  the  chin.  The  greater 
number  of  fibres  are  inserted  in  the  outer  surface  of  the  lower  jaw, 
below  the  external  oblique  line  anterior  to  the  masseter  muscle ;  others 
pass  upward  to  the  lower  lip  and  angle  of  the  mouth ;  while  others  are 
lost  in  the  muscles  of  expression  and  the  areolar  connective  tissue  of 
the  face. 

Variations. — The  platysma  myoides  of  man  is  the  rudiment  of  the 
panniclilus  carnosus,  or  great  subcutaneous  muscle,  of  quadrupeds;  this 
may  explain  its  many  variations  in  the  human  subject.  Sometimes  the 
fibres  extend  upon  the  face  and  downward  on  the  neck,  shoulder,  and 
l)reast  farther  than  usual,  occasionally  having  attachment  to  the  clavicle, 
and  also  give  off  slips  which  pass  from  one  muscle  of  expression  to 
another.  The  upper  part  of  the  muscle  is  occasionally  joined  by  a  slip 
from  the  occipital  bone  or  the  mastoid  process  of  the  temporal ;  more 
rarely  it  is  absent  on  one  or  both  sides. 

Vessels. — The  numerous  superficial  branchings  of  the  region. 

Xerves, — The  platysma  myoides  receives  its  principal  nerves  of  motion 
from  the  descending  branches  of  the  facial ;  it  is  also  influenced  by 
some  of  the  spinal  nerves. 

Relations. — Above  with  the  skin,  to  which  it  is  closely  united,  espe- 
cially in  its  lower  portion ;  by  its  internal  surface  with  the  pectoralis 
major,  deltoid,  trapezius,  and  the  clavicle ;  in  the  neck  with  the  deep 
cervical  fascia,  between  which  and  the  muscle  passes  the  superficial 
cervical  "plexus  of  nerves,  the  external  jugular  vein  and  its  tributaries, 
and  the  anterior  jugular  vein.  In  the  supra-hyoid  region  the  facial 
artery  lies  underneath  it,  separated  by  the  deep  cervical  fascia;  all 
the  superficial  cervical  lymphatics,  sterno-cleido-raastoideus,  omo-hyoid, 
sterno-hyoid,  and  diagastric  muscles  are  under  it. 

Actions. — The  platysma  elevates  the  skin  of  the  breast  and  shoulder, 


184 


ANAT03IY. 


and  when  these  parts  are  fixed  it  dra^s  the  angle  of  the  mouth  down- 
ward and  outward.  The  muscle  is  brought  into  use  in  the  act  of 
deglutition,  and  also  acts  during  sudden  fright. 

The  Stcnio-cleido-mastoideus  (Fig.  94)  is  a  long,  strong  muscle,  extend- 
ing obliquely  across  the  neck,  from  the  mastoid  process  of  the  temporal 
bone  to  the  sternum  and  clavicle.  It  divides  the  surgical  square  of  the 
neck  into  two  great  triangles,  anterior  and  posterior,  and  is  ensheathed 

Fig.  94. 


Muscles  of  the  Neck,  anterior  view. 

by  two  layers  of  the  deep  cervical  fascia.  It  arises  by  two  heads,  the 
sternal  and  the  clavicular. 

The  Sternal  Head  is  thick  and  rounded,  tendinous  in  front,  fleshy 
behind,  arising  from  the  superior  and  outer  part  of  the  manubrium  of 
the  sternum. 

The  Clavicular  Head  is  flat,  and  is  composed  of  fleshy  and  tendinous 
fibres;  arising  from  the  inner  third  of  tlie  superior  border  of  the  clavicle, 
it  passes  ahnost  directly  upward.  The  triangular  space  between  the 
two  heads  is  filled  up  by  areolar  tissue.  The  two  divisions  gradually 
unite  midway  in  the  neck,  forming  a  thick  round  prominent  muscle, 
which  extends  u])\vard  and  backward,  and  is  in.serted  by  short  and 
strong  tendinous  fibres  into  the  external  surface  of  the  mastoid  process, 
commencing  at  its  apex  and  extending  upward  and  backward  along  the 
superior  curved  line  of  the  occipital  bone,  or  semicircular  line  of  the 


AREOLAR   TISSUE,    TENDONS,   ASD  3IUSCLES.  185 

base  of  the  skull,  terminating  in  a  thin  aponeurosis  ^vllere  it  is  attached 
to  the  outer  two-thirds  of"  the  line. 

delations. — Its  middle  three-fifths  are  covered  superficially  by  the 
platysma  myoides,  the  remainder  by  the  integument,  and  it  is  crossed 
by  the  external  jugular  vein  and  the  superficial  branches  of  the  cervical 
plexus.  Its  deep  surface  passes  over  the  sterno-hyoid,  sterno-thvroid, 
omo-hyoid,  the  posterior  belly  of  the  digastric,  levator  anguli  scapulae, 
the  splenius,  and  the  scaleni  muscles ;  also  the  cervical  plexus,  the 
occipital  arteiy,  and  a  part  of  the  parotid  gland. 

The  common  carotid  artery,  the  internal  jugular  vein,  and  the  pneu- 
mogastric  nerve  enclosed  in  their  sheath,  clescendens  noni,  and  com- 
municaris  noni  nerves,  pass  under  its  anterior  border,  and  the  spinal 
accessory  nerve  pierces  its  upper  third. 

Nerves. — The  muscle  is  supplied  by  the  deep  cervical  plexus  and  the 
spinal  accessory  nerves. 

Variations. — The  muscle  is  sometimes  divided  longitudinally  into 
two  portions,  called  the  sterno-mastoid  and  cleido-mastoid ;  they  are 
not  infrequently  described  as  separate  muscles.  Part  of  the  muscle  is 
sometimes  attached  to  the  lower  jaw ;  this  condition  is  normal  in  the 
bone.     Besides  this,  it  has  many  other  varieties  (see  Quain  and  Allen). 

Action. — AVhen  both  muscles  are  acting  together,  the  head  is  brought 
forward,  as  in  nodding ;  when  extreme  action  is  brought  about,  the 
head  is  drawn  upon  the  neck  and  the  neck  upon  the  chest.  When 
either  muscle  acts  singly,  especially  when  combined  with  the  splenius, 
the  head  is  drawn  toward  the  shoulder  of  the  same  side,  the  face  being 
rotated  to^^■ard  the  opposite  side.  In  the  condition  known  as  Avry  neck 
or  torticollis,  the  muscle  on  one  side  is  rigidly  contracted,  or  the  opposite 
muscle  is  paralyzed.  When  the  head  is  fixed,  these  muscles  become 
accessory  muscles  of  respiration  by  assisting  in  the  elevation  of  the 
thorax;  it  also  serves  to  fix  the  clavicle,  and  in  animals  where  the 
clavicle  is  lacking  the  muscles  assist  in  the  elevation  of  the  arms,  as 
their  fibres  are  continued  into  the  clavicular  portion  of  the  pectoralis 
major  and  the  deltoid. 

The  Infra-hyoid  31uscles. — The  depressors  of  the  hyoid  bone  and  the 
larynx  are  the  sterno-hyoid,  the  sterno-thyroid,  the  thyro-hyoid,  and 
the  omo-hyoid. 

The  Sterno-hyoid  is  a  thin,  flat  band  of  longitudinal  fibres,  arising 
inconstantly  from  the  upper  and  posterior  portion  of  the  sternum  and 
the  posterior  sterno-clavicular  ligament ;  from  that  ligament  and  the 
clavicle,  or  from  the  clavicle  alone ;  and  occasionally  it  partially  arises 
from  the  cartilage  of  the  first  rib.  The  fibres  pass  upward,  and  are 
inserted  into  the  body  of  the  hyoid  bone  near  the  inner  side  of  the  omo- 
hyoid muscle. 

Relations. — Its  superficial  surface  below  is  covered  by  the  sternum 
and  sternal  end  of  the  clavicle,  and  by  the  sterno-cleido-mastoid  and 
the  platysma  myoides  muscles  above.  Its  deep  surface  passes  over  the 
sterno-thyroid,  crico-thyroid,  and  thyro-hyoid  muscles,  and  in  part  the 
thyroid  gland,  the  superior  thyroid  vessel,  and  the  crico-thyroid  and 
thyro-hyoid  membranes.  The  mesial  borders  of  the  two  muscles  vary  in 
their  proximity :  at  the  upper  third  there  is  a  slight  interval ;  in  the  middle 


186  ANATOMY. 

third  they  approach  eacli  other,  and  are  again  separated  as  they  near  the 
clavicle.  Close  to  the  hyoid  bone  the  outer  margin  is  in  contact  with 
the  orao-hyoid  muscle. 

Action. — To  depress  the  hyoid  bone. 

The  Sterno-thyroid  muscle  is  shorter  and  broader  than  the  sterno- 
hyoid, and  is  under  that  muscle.  It  arises  near  its  fellow  of  the  oppo- 
site side  from  the  posterior  surface  of  the  manubrium  (first  bone  of  the 
sternum),  below  and  nearer  the  median  line  than  the  origin  of  the 
sterno-hyoid  nniscle,  and  inconstantly  from  the  first  and. second  costal 
cartilages.  It  ascends,  and,  diverging  from  its  fellow  of  the  opposite 
side,  is  inserted  into  the  oblicpie  line  on  the  ala  of  the  thyroid  cartilage. 

Relations. — Its  superficial  surface  is  in  contact  with  the  sternum, 
sterno-cleido-mastoid,  and  the  sterno-hyoid  muscles.  The  deep  surface 
rests  upon  the  innominate  vein,  the  lower  part  of  the  common  carotid 
artery,  the  trachea,  and  the  thyroid  gland. 

Action. — It  depresses  the  thyroid  cartilage  and  indirectly  the  floor  of 
the  mouth. 

The  Thi/ro-h}/oid  is  a  small  quadrilateral  muscle,  its  fibres  interlacing 
with  the  sterno-thyroid,  of  which  it  is,  to  all  appearance,  a  continuation. 
It  arises  on  the  oblicpie  line  on  the  ala  of  the  thyroid  cartilage  ;  it  passes 
upward  and  is  inserted  into  the  lower  border  of  the  body  and  great 
cornu  of  the  hyoid  bone. 

Relations. — Its  superficial  surface  is  in  contact  with  the  sterno-hyoid 
and  omo-hyoid  muscles.  Its  under  surface  rests  upon  the  thyroid  car- 
tilage and  thyro-hyoid  membrane.  The  superior  laryngeal  nerve  and 
artery  pass  between  the  membrane  and  muscle  before  entering  the 
larynx. 

Actions. — The  thyro-hyoid  muscle  raises  the  thyroid  cartilage,  or, 
when  that  body  is  fixed,  it  lowers  the  hyoid  bone. 

Nerve. — The  muscle  is  supplied  by  a  branch  of  the  hypoglossal  nerve. 

The  Omo-hi/oid  is  a  long,  ribbon-shaped  muscle.  Math  two  bellies 
united  by  an  intervening  tendon  ;  it  extends  from  the  shoulder  to  the 
hyoid  bone,  crossing  the  neck  diagonally  and  dividing  the  anterior  and 
posterior  surgical  triangles  into  four.  The  muscle  arises  from  the  upper 
Ijorder  of  the  scapula,  near  the  suprascapular  notch ;  it  passes  forward 
and  slightly  upward,  in  a  flattened  narrow  fasciculus,  across  the  lower 
portion  of  the  neck  to  the  point  at  which  it  lies  beneath  the  sterno- 
cleido-mastoid  muscle,  when  it  becomes  tendinous,  the  tendon  being  held 
down  by  a  loop  formed  from  the  deep  fascia,  which  has  an  attachment 
to  the  (!artilage  of  the  first  rib  ;  it  then  passes  nearly  vertically  close  to 
the  outer  border  of  the  sterno-hyoid  muscle,  to  be  inserted  into  the 
lower  border  of  the  body  of  the  hyoid  bone,  in  close  proximity  to,  and 
outside  of,  the  sterno-hyoid  muscle. 

Relations. — The  superficial  surface  with  the  trapezius  and  sterno- 
cleido-mastoid  muscles,  the  deep  cervical  fascia,  the  platysma  myoides, 
and  the  integument.  Its  under  surface  passes  over  the  scaleni,  the 
brachial  plexus,  the  sheath  containing  the  common  carotid  artery,  the 
internal  jugular  vein  and  pneumogastric  nerve,  the  noni  nerve,  and 
the  sterno-hyoid  and  sterno-thyroid  muscles. 

Variations. — The  muscle  is  sometimes  divided  throughout  or  in  part ; 


AREOLAR   TISSUE,   TENDONS,  AND  MUSCLES. 


187 


occasionally  only  one  belly  is  present,  or  the  anterior  belly  is  sometimes 
fused  with  the  sterno-hyoid  muscle. 

Action. — It  depresses  and  carries  the  hyoid  bone  backward  ;  it  is  also 
a  tensor  of  the  cervical  iascia. 


THE  MUSCLES   OF  THE   SUPRA-HYOID   SPACE. 

The  muscles  of  the  supra-hyoid  space  (Fig.  95)  are  the  digastric, 
stylo-hyoid,  mylo-hyoid,  genio-hyoid,  genio-glossus,  lingualis,  hyo- 
glossus,  and  stylo-glossus. 

The  Digastric,  as  its  name  implies,  is  a  double-bellied  muscle,  one 
posterior  and  one  anterior,  extending  from  the  mastoid  portion  of  the 
temporal  bone  to  the  anterior  part  of  the  lower  jaw.      The  posterior  belly 

Fig.  95. 


Muscles  of  the  Tongue,  left  side. 


is  the  longer  and  narrOM^er  of  the  two,  and  arises  from  the  digastric 
groove  of  the  temporal  bone,  close  to  the  stylo-mastoid  foramen ;  pass- 
ing downward,  forward,  and  inward,  it  gradually  diminishes  as  it 
approaches  the  hyoid  bone,  and  is  lost  in  a  tendon  which  usually 
passes  through  the  stylo-hyoid  muscle  near  its  insertion,  and .  also 
through  its  aponeurotic  loop,  which  is  lined  by  a  synovial  membrane, 


188  ANATOMY. 

and  liolds  it  in  connection  with  the  body  and  the  great  cornu  of  the 
hyoid  bone.  The  anterior  belli/  is  shorter  and  broader  than  the  pos- 
terior. It  commences  at  the  intermuscular  tendon,  passes  upward  and 
forward,  and  is  inserted  into  the  rough  depression  on  the  internal  lower 
border  of  the  inferior  maxillary  bone  near  the  symphysis :  its  fibres 
sometimes  decussate  with  those  of  its  fellow-muscle  on  the  opposite  side. 

Stretching  between  the  intermediate  tendons  and  sheaths  of  the  ante- 
rior portions  of  these  muscles  of  each  side  is  a  broad  layer  of  fascia  known 
as  the  supra-hijokl  aponeurosis,  which  is  also  attached  to  the  great  cornu 
of  the  hyoid  bone  and  the  anterior  bellies  of  each  muscle ;  this  gives  a 
firm  support  for  the  other  muscles  in  the  supra-hyoid  space.  This 
aponeurosis  corresponds  to  a  layer  of  muscular  fibres  belonging  to 
the  digastric  muscle  of  some  of  the  lower  animals. 

The  digastric  mu;?cle  subdivides  the  anterior  superior  surgical  triangle 
of  the  neck  into  the  submaxillary  and  superior  carotid  triangles. 

The  Subma.villari/  Triangle  is  inverted,  the  base  being  above,  and  is 
bounded  by  the  lower  border  of  the  inferior  maxillary  bone  and  a  line 
to  the  mastoid  process ;  the  other  or  lower  sides  are  formed  by  the  two 
bellies  of  the  digastric  muscle,  its  tendon  being  held  down  by  a  loop  of 
fibrous  tissue  which  forms  the  inferior  angle.  The  outer  or  superficial 
surface  of  this  triangle  is  covered  by  a  firm  layer  of  the  deep  fascia 
attached  below  to  the  tendon  and  to  the  bellies  of  the  muscle,  above  to 
the  body  of  the  inferior  maxilla  and  to  the  fascia  which  extends  over 
the  parotid  gland.  The  inner  surface  is  bounded  by  a  deep  layer  of  the 
same  fliscia  attaclied  below  to  the  tendon  and  muscle,  while  above  it  is 
lost  in  the  sheaths  of  the  muscles  of  the  floor  of  the  mouth.  Surgically 
considered,  it  is  continuous  over  those  muscles,  and  is  attached  to  the 
lower  border  of  the  mylo-hyoid  ridge  of  the  lower  jaw.  In  the  tume- 
faction of  the  submaxillary  gland  the  enlargement  exhibits  a  triangular 
form  on  account  of  the  shape  of  this  envelope. 

The  fiuperior  Carotid  Triangle  is  bounded  above  by  the  posterior 
belly  of  the  digastric,  below  by  the  omo-hyoid,  and  behind  l)y  the 
sterno-cleido-mastoid  muscle,  its  apex  presenting  anteriorly  at  the  loop 
of  the  digastric  and  insertion  of  the  stylo-hyoid  muscle.  The  import- 
ance of  this  triangle  to  the  surgeon  is  due  to  the  fact  that  in  it  are 
found  the  points  for  ligation  of  many  arteries. 

fielatio}ts. — The  anterior  belly  of  the  digastric  muscle  is  more  super- 
ficial than  the  jiosterior  ;  its  outer  surface  being  covered  by  the  platysma 
myoides  and  tlie  deep  cervical  fliscia,  its  deep  surface  rests  uj)on  the 
mylo-hyoid  muscle.  Its  posterior  belly  is  deeply  covered  by  the  mas- 
toid process  of  the  temporal  bone,  the  sterno-cleiclo-mastoid,  and  part  of 
the  stylo-hyoid  muscles,  a  lobule  of  the  parotid  gland,  and  part  of  the 
submaxillary  gland.  Its  deep  surface  is  in  relation  with  the  transverse 
process  of  the  atlas,  the  internal  jugular  vein,  the  internal  carotid  artery, 
and  the  origins  of  the  facial  and  lingual  arteries.  The  hypoglossal 
nerve  lies  a  little  below  the  tendon. 

Variations. — This  muscle  has  many  variations,  and,  like  the  omo- 
hyoid, the  entire  muscle  may  be  divided  through  one  or  both  bellies. 
The.  posterior  belly  may  receive  an  accessory  slip  from  the  styloid 
process,  the  angle  of  the  jaw  bone,  or  the  splenius  muscle ;  it  has  been 


AREOLAR   TISSUE,   TENDONS,   AND  MUSCLES.  189 

known  to  arise  entirely  from  the  styloid  process.  In  rare  instances  the 
muscle  has  been  monogastric,  in  which  case  it  is  inserted  into  the  mid- 
dle of  the  lower  jaw.  Slips  may  pass  from  the  anterior  belly  to  the 
hyoid  bone.  The  tendon  does  not  always  pass  through  the  stylo- 
hyoid muscle. 

The  Ilento-hyoid  (Macalister)  is  an  occasional  slip  found  passing  from 
the  body  of  the  hyoid  bone  to  the  chin.  It  is  sometimes  composed  of 
parallel  bands,  and  Macalister  suggests  that  it  may  be  a  differentiated 
portion  of  the  platysma  myoides. 

Nerves. — The  posterior  belly  of  the  muscle  is  supplied  by  the  facial 
(seventh),  and  the  anterior  by  the  mylo-hyoid  branch  of  the  inferior 
dental  nerve. 

Actions. — The  digastric  muscles  act  in  antagonism  to  the  muscles  of 
mastication  by  assisting  in  depressing  the  inferior  maxilla.  AVhen  the 
lower  jaw  is  firmly  fixed  by  the  masticatory  muscles,  the  digastric 
assists  in  elevating  the  hyoid  bone. 

The  Stylo-hyokl  is  a  small  slender  muscle  situated  along  the  upper 
border  of  the  posterior  belly  of  the  digastric.  It  arises  by  a  narrow 
tendon  from  the  upper  half  of  the  outer  surtace  of  the  styloid  process  of 
the  temporal  bone.  It  passes  downward,  forward,  and  inward,  to  be 
inserted  into  the  hyoid  bone  at  the  junction  of  the  great  cornu  with  the 
body.  It  is  usually  divided  into  two  portions  near  its  insertion  for  the 
transmission  of  the  digastric  muscle. 

Relations. — These  are  almost  identical  with  those  of  the  posterior  belly 
of  the  digastric  muscle. 

Variations. — The  variations  of  the  muscle  are  numerous  :  amongst 
them  mav  be  noted  cleavage  throughout  its  whole  course,  forming  two 
muscles,  in  some  instances  three.  It  is  occasionally  placed  on  the 
inner  side  of  the  external  carotid  artery ;  the  insertion  is  sometimes 
partiallv  or  wholly  in  the  tendon  of  the  digastric  muscle.  It  may  be 
fused  with  the  omo-hyoid,  thyro-hyoid,  or  mylo-hyoid  muscles  at  the 
hyoid  bone.  It  may  send  slips  to  the  lower  jaw.  Its  place  of  origin 
varies ;  sometimes  there  is  an  extra  slip  given  off'  from  the  styloid  pro- 
cess and  inserted  into  the  small  cornu,  and  accompanying  or  taking  the 
place  of  the  stylo-hyoid  ligament. 

Nerves. — The  muscle  is  supplied  by  the  facial  nerve. 

Action. — To  elevate  and  draw  backward  the  hyoid  bone. 

The  Stylo-hyoid  Liejament. — This  being  so  intimately  associated  with 
this  group  of  muscles,  it  ^yill  receive  next  consideration.  The  ligament 
is  a  thin  fibrous  cord  developed  from  the  deep  fascia  attached  to  the 
lower  portion  of  the  styloid  process,  passing  downward,  forward,  and 
inward,  to  be  inserted  into  the  lesser  cornu  of  the  hyoid  bone.  Some- 
times this  ligament  is  of  a  cartilaginous  nature,  and  even  ossifies.  In 
many  animals  it  is  naturally  osseous,  and  is  named  the  epihyal  bone. 

The  Myh-hyoid  is  a  triangular  flat  muscle  placed  between  the  inferior 
maxillary  and  hyoid  bones,  and  with  its  fellow  of  the  opposite  side 
forms  the  muscular  floor  of  the  mouth  (diaphragma  oris,  Meyer).  _  It 
arises  from  the  mylo-hyoid  (internal  oblique)  ridge  of  the  lower  jaw, 
extending  from  about  the  third  molar  tooth  to  the  sym]ihysis.  At  its 
insertion" it  is  divided  into  twa- portions,  a  posterior  and  an  anterior. 


190  ANATOMY. 

The  Posterior  Portion  consists  of  those  fibres  wliich  give  the  muscle 
its  name.  They  pass  downward,  inward,  and  backward,  to  be  inserted 
into  the  body  of  tlie  hyoid  bone. 

The  Anterior  Portion  passes  in  a  more  oblique  direction,  and  is  not 
inserted  into  the  hyoid  bone,  but  into  an  indistinct  intermuscular  raphe 
which  extends  from  the  symphysis  of  the  jaw  to  the  centre  of  the  hyoid 
bone ;  the  muscular  fibres  are  the  longest  near  the  hyoid  bone,  and 
gradually  grow  shorter  as  the  symphysis  of  the  jaw"  is  approached. 

Relations. — The  mylo-hyoid  muscle  forms  the  floor  of  the  mouth, 
and  at  the  same  time  part  of  the  roof  of  the  neck,  thus  giving  it  an 
oral  or  superior  and  a  cervical  or  inferior  surface.  The  cervical  surface 
is  in  relation  with  the  submaxillary  muco-salivary  gland,  the  anterior 
belly  of  the  digastric  muscle,  the  facial  artery  and  its  submental  branches, 
and  the  mylo-hyoid  vessels  and  nerves.  The  oral  surface  is  in  relation 
with  the  genio-hyoid,  genio-glossus,  parts  of  the  hyo-glossus  and  stylo- 
glossus muscles;  also  the  lingual  branch  of  the  fifth  and  twelfth  nerves, 
the  sublingual  gland,  and  the  mucous  membrane  of  the  alveolo-lingual 
groove.  Its  posterior  border  is  free,  a  part  of  the  submaxillary  muco- 
salivary  gland  curving  around  it  to  the  upper  surface,  the  duct  of  the 
gland  (duct  of  Wharton)  passing  along  the  upper  surface  of  the  muscle. 

Variations. — Sometimes  the  raphe  is  absent ;  in  such  cases  the  fibres 
of  each  muscle  interlace.  It  may  be  fused  with  the  anterior  belly  of 
the  digastric  muscle,  or  it  may  be  entirely  lacking  and  be  substituted 
by  the  digastric.  Slips  are  sometimes  received  from  some  of  the  other 
hyoid  muscles.  Occasionally  the  anterior  portion  of  the  muscle  is  defi- 
cient, its  origin  extending  no  farther  than  the  cuspid  teetli :  this  muscle 
is  sometimes  perfi)rated  and  dissected  by  the  lobules  and  duct  of  the 
submaxillary  muco-salivary  gland. 

Nerves. — The  mylo-hyoid  nerve,  a  branch  of  the  inferior  maxillary. 

Action. — The  mylo-hyoid  muscle  draws  the  hyoid  bone  forward  and 
upward,  and  slightly  assists  in  opening  the  mouth. 

The  Genio-hyoid  is  a  narrow  muscle  extending  from  the  symphysis 
of  the  chin  to  the  hyoid  bone.  It  arises  from  the  inferior  genial 
tubercle  (mental  spine)  on  the  inner  side  of  the  inferior  maxillary  bone, 
and  passes  downward  and  backward  to  be  inserted  into  the  anterior 
portion  of  the  hyoid  bone. 

Relations. — Below  with  the  mylo-hyoid  muscle,  above  ^vitli  the  genio- 
glossus  and  with  its  fellow  on  the  proximal  border. 

Variations. — The  genio-hyoid  may  separate  into  two  muscles,  or  it 
may  be  united  with  the  muscle  of  the  opposite  side.  Slight  variations 
may  be  found  between  its  origin  and  insertion. 

Nerve. — The  genio-hyoid  is  supplied  by  a  branch  of  the  hypoglossal 
nerve. 

Action. — Same  as  the  mylo-hyoid — to  elevate  and  draw  forward  the 
hyoid  bone  and  to  depress  the  lower  jaw. 

The  Genio-f/lossus  (often  called  genio-hyo-glossus,  from  its  sup- 
posed insertion  on  the  body  of  the  hyoid  bone)  is  a  thin,  flat,  radiat- 
ing muscle,  placed  vertically  on  each  side  of  the  median  line  in  front 
of  the  tongue.  It  arises  by  a  short  tendon  from  the  superior  genial 
tubercle  (mental  spine)  on  the  inner  -aspect  of  the  inferior  maxillary 


AREOLAR   TISSUE,    TENDONS,   AND  MUSCLES.  191 

bone ;  from  the  tendon  its  fibres  diverge  from  before  backward,  and  are 
inserted  mainly  into  the  nnder  surface  and  body  of  the  tongue,  consti- 
tuting the  bulk  of  the  structure  of  that  organ.  Some  of  its  fibres  pass 
backward  to  the  hyoid  bone  and  to  the  side  of  the  pharynx. 

Relations. — On  its  median  surface  with  its  fellow  of  the  opposite  side, 
from  which  it  is  separated  within  the  tongue  by  the  median  raphe.  Its 
lateral  surfaces  are  in  contact  with  the  lingualis,  hyo-glossus,  and  stylo- 
glossus muscles,  the  sublingual,  the  ranine  vessel,  the  gustatory  nerve, 
and  sublingual  glands.  The  terminal  portion  of  the  hypoglossal  nerve 
penetrates  its  posterior  part.  The  frsenum  linguae  is  formed  by  the 
union  of  the  anterior  ui)per  borders  of  the  two  genio-glossus  muscles, 
which  are  covered  by  mucous  membrane. 

Variations. — This  muscle  is  sometimes  united  with  the  genio-hyoid 
muscle,  or  it  may  give  a  few  fine  bundles  to  the  epiglottis,  to  the  stylo- 
hyoid, or  to  the  smaller  cornu  of  the  hyoid  bone. 

Nerve. — This  muscle  is  supplied  by  the  hypoglossal  nerve. 

Action. — To  draw  forward  and  protrude  the  tongue. 

The  Lingualis  muscle  is  a  longitudinal  fasciculus  placed  in  the  sub- 
stance of  the  tongue,  arising  at  the  base  and  extending  between  the  hyo- 
glossus  and  genio-glossus  muscles  to  the  apex  of  the  organ.  Some  of 
•its  fibres  intermingle  with  the  stylo-glossus  and  hyo-glossus.  The 
ranine  artery  (the  terminal  portion  of  the  lingual  artery)  passes  along 
its  under  surface. 

The  Hyo-glossus  is  a  thin  quadrate  muscle,  arising  from  the  upper 
border  and  the  lateral  portion  of  the  great  cornu  of  the  hyoid  Ijone, 
also  from  the  lesser  cornu.  Its  fibres  pass  upward  and  slightly  forward 
to  the  posterior  half  and  lateral  portions  of  the  tongue ;  they  then 
spread  inward  and  forward  over  the  dorsum,  joining  those  of  the  stylo- 
glossus toward  the  apex. 

Relations. — The  hyo-glossus  is  related  by  its  external  surface  with  the 
digastric,  stylo-hyoid,  stylo-glossus,  and  mylo-hyoid  muscles,  also  the 
deep  part  of  the  submaxillary  muco-salivary  gland,  and  is  crossed  from 
below  upward  by  the  duct  of  Wharton  and  by  the  hypoglossal  and 
lingual  nerves.  Its  internal  surface  rests  upon  the  posterior  portion  of 
the  genio-glossus  and  the  origin  of  the  middle  constrictor  of  tlie  pharynx ; 
it  is  crossed  by  the  lingual  artery  and  the  glosso-pharyngeal  nerve. 

Variations. — The  lingual  artery  occasionally  passes  through  the  mus- 
cle near  the  hyoid  bone ;  it  is  at  times  composed  of  a  number  of  sepa- 
rate bundles.  The  muscles  sometimes  receive  a  slip,  triticeo-glossus 
(Bochdalek),  from  the  thyro-hyoid  ligament,  which  passes  upward  and 
forward,  lying  on  the  inner  side  of  the  lingual  artery  and  joining  the 
hyo-glossus. 

Nerves. — The  muscle  receives  branches  of  the  hypoglossal  nerve. 

Action. — To  aid  in  depressing  the  tongue. 

The  Stylo-glossus  is  the  shortest  and  smallest  of  the  styloid  muscles, 
and  passes  from  the  styloid  process  to  the  tongue.  It  arises  from  the 
outer  and  anterior  portion  of  the  apex  of  the  process,  and  passes  for- 
ward and  slightly  downward  and  inward  to  the  posterior  part  of  the 
tongue,  where  it  divides  into  two  portions,  the  longitudinal  and  the  oblique. 

The  Longitudinal  Portion  passes  forward,  and  is  inserted  along  the 


192 


ANATOMY. 


side  of  the  tongue  as  far  as  the  tip,  blending  with  the  fibres  of  tlie  lin- 
gualis  in  front  of  the  hyo-glossus. 

TJie  Oblique  Portion  passes  slightly  downward  over  the  hyo-glossus,  its 
fibres  interlacing  with  those  of  that  muscle  and  those  of  the  palato-glossus. 

Relations. — On  its  lateral  surface  the  stylo-glossus  is  associated  with 
the  parotid  gland,  the  internal  pterygoid  muscle,  sublingual  gland,  gus- 
tatory nerve,  and  mucous  membrane  of  the  mouth ;  the  internal  sur- 
face with  the  tonsils,  the  superior  constrictor  of  the  pharynx,  and  the 
hyo-glossus  muscle. 

Variations. — The  muscle  has  many  variations,  sometimes  being  absent ; 
at  others  it  has  been  found  to  be  double.  It  may  receive  slips  or  may 
arise  entirely  from  the  angle  of  the  jaw,  the  stylo-maxillary  ligament, 
the  internal  pterygoid  muscle,  or  the  tympanic  portion  of  the  temporal 
bone.     Slips  may  pass  to  the  pharynx. 

Nerves. — Its  nerve-supply  is  derived  from  the  hypoglossal. 

Action. — To  assist  in  retracting;  and  elevatinsr  the  tono-ue. 


Fig.  96. 


THE   MUSCLES   OF   THE   PHARYNX  AND   THE   SOFT  PALATE. 

This  group  (Fig.  96)  includes  the  superior  constrictor,  middle  con- 
strictor, inferior  constrictor,  stylo-pharyngeus,  palato-pharyngeus,  palato-  ■ 

glossus,  palato-Eustachian  or 
tensor  palati,  levator  palati, 
and  azygos  uvulae. 

The  Hiuperior  Constrictor 
muscle  of  the  pharynx  is  a 
thin  quadrilateral  muscle,  sit- 
uated, as  its  name  implies,  at 
the  upper  portion  of  this  mus- 
cular pouch :  its  fibres  are  paler 
than  those  of  the  middle  and 
inferior  muscles.  It  arises, 
commencing  from  above  down- 
ward, from  the  lower  third  of 
the  free  margin  of  the  internal 
pterygoid  plate  and  its  hamu- 
lar  process,  the  tuberosity  of 
the  palate  bone,  the  reflected 
tendon  of  the  palato-Eusta- 
chian or  tensor  palati  muscle, 
and  the  ptervgo-maxillary  liga- 
ment— at  which  point  some 
of  its  fibres  are  continuous 
from  the  buccinator ;  it  also 
arises  from  the  posterior  ex- 
tremity of  the  mylo-hyoid 
ridge,  the  mucous  membrane 
of  the  mouth,  and  the  sides  of 
the  tongue  continuous  -with  the 

Muscles  of  the  Pharynx  external  view.  gCuio-gloSSUS       mUScls.  The 


AREOLAR   TISSUE,    TENDONS,   AND  MUSCLES.  193 

fibres  from  these  various  points  of  origin  pass  baclvMard  and  curve  inward 
until  they  meet  those  of  the  opposite  side,  where  many  of  the  fibres  inter- 
lace. The  remainder  are  inserted  into  the  median  line  of  the  pharyngeal 
raph6,  in  front  of  the  cervical  vertebrse,  and  a  few  of  the  fibres  are  inserted 
in  the  pharyngeal  spine  and  the  aponeurosis  attached  t(j  tlie  basilar  process 
of  the  occipital  bone. 

The  upper  margin  of  the  muscle  is  concave,  being  suspended  at  its 
corners  by  the  pterygoid  process  in  front  and  the  pharyngeal  aponeurosis 
behind.  The  surface  between  the  border  of  the  muscle  and  the  base  of 
the  brain-case  is  occupied  by  the  pharyngeal  aponeurosis,  the  lower 
border  of  which  becomes  part  of  the  wall  of  the  pharynx,  and  is  covered 
by  the  middle  constrictor  muscle. 

YariaUons. — The  different  heads  of  origin  may  be  from  various  mus- 
cles. The  azygos  pharvngis  (Meckel)  is  a  slip  arising  from  the  pharyn- 
geal spine  and  inserted  into  the  posterior  pharyngeal  wall. 

Relations. — To  the  outer  surface  of  the  muscle  are  the  cervical  verte- 
brae, the  internal  curotid  artery,  the  pneumogastric,  the  glosso-pharyn- 
geal,  and  spinal  accessory  nerves,  the  middle  constrictor  and  the  stylo- 
pharyngeus  muscles ;  related  to  its  inner  surface  are  the  palato-pharyn- 
geus  muscle  and  the  tonsils.  The  origin  of  the  levator  palati  muscle 
and  the  Eustachian  fossa  are  also  near  to  this  surface. 

Nerves — The  nerve-supply  is  derival  from  the  pharyngeal  plexus. 

Actions. — When  it  contracts,  the  pterygoid  portion,  l)eing  fixed  at 
both  its  origin  and  insertion,  straightens  the  curvature  of  the  superior 
border  and,  at  the  same  time,  narrows  the  diameter  of  the  naso- 
pharynx. The  pterygo-maxillarv  and  inferior  maxillary  portions  assist 
in  drawing  the  posterior  wall  of  the  pharynx  forward, 

Tlte  Middle  Constrictor  of  the  Pltarynx  is  a  flattened  radiating  muscle 
situated  on  a  plane  below  the  superior  constrictor.  It  arises  from  the 
greater  and  lesser  cornua  of  the  hyoid  bone  and  the  stylo-hyoid  ligament. 
The  fibres  radiate  as  they  pass  backward,  and,  curving  inward,  are 
inserted  in  the  posterior  median  raphe,  some  of  them  interlacing  with 
those  of  the  opposite  muscle.  The  extent  of  their  insertion  is  from 
below  the  level  of  the  hyoid  bone  to  a  position  near  the  occipital  bone. 
The  lower  portions  descend  beneath  the  inferior  constrictor  as  it  passes 
backward,  while  the  upjier  fibres  ascend  and  overlap  those  of  the  supe- 
rior constrictor,  the  middle  portion  passing  directly  backward. 

Variations. — As  in  the  previous  muscle,  the  slips  arising  from  differ- 
ent points  of  origin,  as  those  from  the  greater  and  lesser  cornua,  may 
serve  as  separate  and  distinct  muscles.  Fibres  may  be  received  from  the 
body  of  the  hyoid  bone,  and  a  slip  (cyndesmo-pharyngeus,  Douglas) 
from  the  thyro-hyoid  ligament  is  frequently  present.  Fibres  may  also 
arise  from  the  tongue  and  posterior  ])art  of  the  mylo-hyoid  ridge  of  the 
inferior  maxilla,  and  interlace  with  the  genio-glossus,  as  does  the  superior 
constrictor.     The  upper  fibres  may  reach  the  occipital  bone. 

Belations. — The  external  and  posterior  surface  with  the  longus  colli 
and  rectus  anticus  major ;  laterally,  the  carotid  vessels,  the  pharyngeal 
plexus,  and  some  lymphatic  glands.  The  inferior  constrictor  overlaps 
its  lower  portion.  The  stylo-pharyngeus  muscle  passes  between  the 
superior  and  middle  constrictors,  and  the  superior  laryngeal  nerve  lies 

Vol.  1.-13 


194  ANAT03IY. 

between  the  middle  and  inferior  constrictors  on  its  way  to  the  thyro- 
hyoid membrane.  The  internal  surface  where  it  does  not  overlap  the 
superior  muscle  is  covered  by  mucous  membrane  and  the  stylo-pharyn- 
geus  and  the  palato-pharyngeus  muscles. 

Nerves. — The  nerve-supply  is  from  the  pharyngeal  plexus. 

Actions. — The  upper  fibres  assist  in  elevating  the  hyoid  bone  and  all 
the  structures  connected  with  it ;  it  also  draws  forward  the  posterior 
pharyngeal  wall. 

The  Inferior  Constrictor  muscle  of  the  pharynx  is  the  broadest,  thick- 
est, and  shortest  of  the  three,  and  lies  the  most  superficially.  As  its 
name  implies,  it  is  at  the  lower  or  inferior  portion  of  the  pharynx.  It 
arises  from  various  points,  commencing  below  at  the  lower  and  posterior 
part  of  the  ci  icoid  cartilage,  and  from  a  tendinous  arch  between  the  cri- 
coid and  thyroid  cartilages,  from  the  inferior  cornu  and  the  oblique  line 
and  upper  border  of  the  thyroid  cartilage.  From  these  points  of  origin  the 
fibres  pass  backward  and  upward,  and,  curving  inward,  join  the  raphe 
and  the  fibres  of  its  fellow  from,  the  opposite  side.  The  fibres  of  the 
lower  portion  are  the  shortest ;  their  direction  is  horizontal,  and  they 
combine  with  those  of  the  oesophagus  without  a  line  of  demarcation. 
The  balance  of  the  fibres  are  about  one-eighth  of  an  inch  below  the 
basilar  process,  and  pass  upward  and  backward,  with  an  increase  of 
obliquity,  to  the  posterior  median  line  of  the  pharynx,  covering  more 
than  half  its  length. 

Variations. — The  muscle  sometimes  receives  a  fasciculus  from  the 
thyro-hyoid,  crico-thyroid,  and  sterno-thyroid  muscles,  or  even  from 
the  trachea. 

Relations. — The  external  surface  posteriorly  is  in  apposition  with  the 
cervical  vertebrae  and  the  muscles  of  this  region ;  laterally  with  the 
thyroid  gland,  the  carotid  arteries,  and  the  sterno-hyoid  muscles,  the 
internal  surface  of  the  middle  constrictor,  the  stylo-pharyngeus,  and  the 
palato-pharyngeus  muscles,  also  the  mucous  membrane  of  the  pharynx. 
The  superior  laryngeal  nerve  and  vessels  pass  over  the  upper  border  to 
the  larynx,  and  the  inferior  ascend  beneath  its  lower  border. 

Nerves. — The  muscle  is  supplied  by  the  pharyngeal  plexus  and  the 
external  laryngeal  nerve. 

Actions. — It  assists  in  propelling  the  bolus  of  food  into  the  oesophagus, 
reduces  the  size  of  the  lower  part  of  the  pharynx,  and  can  act  independ- 
ently of  the  other  muscles  of  the  set. 

The  Stijlo-pharyngeus  muscle  is  slender,  though  the  largest  and  longest 
of  the  styloid  set :  above  it  is  round  ;  below  it  is  broad  and  thin.  It 
arises  from  the  inner  side  and  near  the  base  of  the  styloid  process,  passes 
downward  and  inward  Ijotween  the  superior  and  middle  constrictors  of 
the  pharynx,  and  gradually  expands  under  tlie  mucous  membrane,  some 
of  its  fibres  being  inserted  into  the  lateral  walls  of  the  pharynx  and 
united  with  the  palato-pharyngeus  :  these  are  inserted  into  the  posterior 
border  of  the  thyroid  cartilage. 

The  glosso-pharyngeal  nerve  accompanies  this  muscle,  commencing 
on  the  outer  side,  and  crosses  over  on  its  way  to  the  tongue. 

Variations. — Cleavage  or  doubling  of  the  stylo-pharyngeus  muscle 
is  frequent ;  occasionally  it  has  been  found  divided  into  three.     Super- 


AREOLAR  TISSUE,   TENDONS,  AND  MVSCLES. 


195 


numerary  elevators  of  the  pharynx  are  frequently  present ;  they  arise 
from  the  base  of  the  skull  in  juxtaposition  to  the  styloid  process,  or 
from  the  petrous  process  of  the  temporal  bone  (anterior  to  the  carotid 
foramen)  or  the  vaginal  process  of  the  same  bone.  These  muscles  are 
named  the  petro-pharyngeus,  which  arises  from  the  petrous  portion ; 
spheno-pharyngeus,  from  the  spine  of  the  sphenoid  ;  pterygo-pharyngeus 
externus,  from  the  hamular  process ;  occipito-pharyngeus,  from  the  bas- 
ilar process ;  pharyngo-mastoideus,  from  the  mastoid  process :  the  last 
named  is  very  rare.      The  azygos  pharyngis  is  frequently  classed  in 

Fig.  97. 


o  fi  h  a  3 

Muscles  of  the  Soft  Palate,  the  Pharynx  being  laid  open  from  behind. 

this  group  :  a  description  of  it  is  given  with  that  of  the  superior  con- 
strictor of  the  pharynx. 

Nerves. — This  muscle  receives  branches  from  the  glosso-pharyngeal 
nerve. 

Action. — To  assist  in  elevating  the  pharynx. 

The  Palato-phai-yngeus  muscle  (Fig.  97)  is  long  and  narrow,  wider 
at  the  extremities  than  in  the  middle,  and  extends  from  the  soft  pal- 
ate to  the  pharynx ;  it  arises  in  the  soft  palate  by  an  anterior  and  a  pos- 


196  ANATOMY. 

terior  portion^  which  embrace  the  levator  palati  and  the  azygos  uvulae 
muscles. 

The  Anterior  Head  or  Portion  is  the  thickest ;  the  fibres  at  the  com- 
mencement near  the  median  line  of  tlie  palate  are  associated  with  those 
of  the  opposite  side ;  they  pass  outward  between  the  levator  and  tensor 
palati  nuiscles  ;  fibres  are  also  received  from  the  free  edge  of  the  hard 
palate  and  the  aponeurosis  of  the  velum. 

The  Posterior  Head  or  Portion  consists  of  scattered  fibres,  commen- 
cing in  the  median  line  and  associating  with  those  of  the  opposite  side. 

At  the  edge  of  tlie  soft  palate  the  two  portions  unite,  and  receive  two 
slender  bundles  which  arise  from  tlie  inferior  and  anterior  part  of  the 
Eustachian  tube  (salpingo-pharyngeus,  Santorini) ;  from  this  it  passes 
outward,  downward,  and  backward  posteriorly  to  the  tonsils ;  it  spreads 
out,  joining  the  fibres  of  the  stylo-pharyngeus  muscle,  and  is  inserted 
mainly  into  the  superior  and  posterior  border  of  the  thyroid  cartilage. 
The  remainder  of  its  fibres  are  received  into  the  fibrous  layer  of  the 
inferior  part  of  the  pharynx,  passing  as  far  as,  or  crossing,  the  median 
line,  and  interlacing  with  those  of  the  opposite  side. 

This  muscle  and  the  mucous  membrane  covering  it  form  the  palato- 
pharyngeal fold,  or  "  posterior  half  arch." 

Relations. — At  its  origin  the  soft  palate.  Its  anterior  and  posterior 
surfaces  are  covered  by  mucous  membrane,  a  layer  of  palatine  glands 
resting  between  the  membrane  and  the  muscle.  Its  superior  surtace  is 
related  with  the  levator  palati  muscle.  In  the  pharynx  it  passes  between 
the  mucous  membrane  and  the  constrictor  muscles. 

Nerves. — Branches  of  nerves  from  Meckel's  ganglion  (spheno-pala- 
tine). 

Action. — To  elevate  the  pharynx  in  deglutition,  the  palate  having 
first  been  elevated  by  the  levator  palati.  In  its  action  it  assumes  a 
nearly  vertical  position  in  the  posterior  part  of  the  pharynx.  Allen  ^  and 
Yule^  conclude  from  observation  that  the  palato-pharvngeus  is  the  chief 
factor  in  opening  the  Eustachian  tube ;  it  also  keeps  the  soft  palate  in 
position  during  respiration. 

The  Palato-glossus  is  a  small  muscle  extending  from  the  soft  palate 
to  the  posterior  part  of  the  tongue ;  it  is  narrower  in  the  middle  than 
at  its  origin  or  insertion,  and  arises  from  the  under  surface  of  the  soft 
palate  neal'  the  base  of  the  uvula,  the  fibres  of  each  side  interlacing 
at  their  origins.  It  passes  downward,  forward,  and  outward  along 
the  lateral  wall  of  the  pharynx,  anterior  to  the  tonsils,  and  is  inserted, 
with  the  stylo-glossus,  into  the  side  and  base  of  the  tongue.  This 
muscle  and  the  mucous  membrane  covering  it  form  the  palato-glossus 
fold,  or  "  anterior  half  ai'ch." 

Relcdions. — It  passes  downward  along  the  outer  wall  of  the  pharynx, 
between  the  constrictors  and  the  mucous  membrane. 

Nerves. — Branches  of  the  facial. 

Action. — To  depress  and  draw  slightly  forward  the  palate  and  assist 
in  elevating  and  drawing  back  the  tongue.  Allen ^  observes  :  "Both 
muscles,  acting  together,  depress  the  soft  palate  and  dra^v'  it  forward, 

^  Allen's  "Memoir  on  Soft  Palate,"  Tmn^.  Amer.  ^fe(l.  AKsnr.,  1872,  p.  537. 

2  Joicrnal  of  Anut.  and  P/iys..  viii.,  1873.  •*  Allen's  Human  Anatomu,  p.  259. 


AREOLAR   TISSUE,    TENDONS,   AND  MUSCLES.  197 

and  in  the  act  of  sncking  constrict  the  nipple.  Each  muscle  may  be 
looked  upon  as  a  sphincter  on  a  deeper  plane  than  the  lips,  but  like  it 
in  nature,  and  it  is  supplied  by  the  same  motor  nerve — viz.  the  facial. 
It  is  also  a  noteworthy  fact  that  the  plane  of  the  two  muscles  limits 
the  region  of  involution  of  the  epiblast,  so  that  the  palato-glossal  mus- 
cles are  less  splanchnic  than  the  pharyngeal  muscles  proper." 

Tlie  Palato-Eudachian,  or  Totsor  Falati,  is  a  broad  thin  muscle 
extending  from  the  orifice  of  the  Eustachian  tube  to  the  palate,  and 
having  a  vertical  and  a  horizontal  portion. 

TJic  Vertical  Portion  arises  from  the  scaphoid  fossa  at  the  root  of  the 
pterygoid  plates,  the  spinous  process  of  the  sphenoid  bone,  and  the 
lower  and  outer  side  of  the  Eustachian  tube.  Its  flattened  belly  descends 
perpendicularly  between  the  inner  side  of  the  internal  ])terygoid  muscle 
and  the  outer  side  of  the  inner  pterygoid  plate,  at  the  lower  portion  of 
Avhich  it  becomes  a  tendon  and  passes  around  the  hanuilar  process,  and 
continues  thence  to  its  insertion,  forming  the  horizontal  portion  of  the 
muscle.  There  is  a  synovial  bursa  in  connection  with  the  tendon  and  the 
process  which  allows  the  tendon  to  work  backward  and  forward. 

The  Horizontal  Portion  passes  inward,  and  is  inserted  into  the  apo- 
neurosis of  the  soft  palate  and  transverse  ridge  on  the  under  surface 
of  the  palate  bone. 

Relations. — Vertical  portion,  on  its  external  surface,  with  the  internal 
pterygoid  muscle ;  internal  surface  with  the  levator  palati  muscle. 
Horizontal  portion,  at  the  point  of  its  insertion  into  the  soft  palate ; 
the  aponeurotic  expansion  is  anterior  to  the  levator  palati  muscle ;  the 
under  surface  is  covered  by  mucous  membrane. 

Neri^es. — The  muscle  is  supplied  by  branches  from  the  otic  ganglion. 

Action. — The  palato-Eustachian,  or  tensor  palati,  has  generally  been 
supposed  to  make  the  palate  tense,  and  for  this  reason  severance  of  the 
tendon  at  the  hamular  process  previous  to  performing  the  operation  of 
staphylorrhaphy  Avas  frequently  favored.  The  principal  function  of  the 
muscle  is  now  considered  to  be  to  open  the  orifice  of  the  Eustachian 
tube. 

The  Levator  Palati  is  a  long,  thin,  round  muscle,  extending  from  the 
temporal  bone  to  the  palate  at  the  lateral  borders  of  the  posterior  nares. 
It  arises  by  a  narrow  tendon  from  the  under  surface  of  the  petrous  por- 
tion of  the  temporal  bone,  anterior  to  the  carotid  canal,  and  from  the 
hnver  margin  of  the  cartilage  of  the  Eustachian  tube,  thence  passing- 
downward,  inward,  and  forward  into  the  pharynx  over  the  concave 
margin  of  the  superior  constrictor,  spreading  out  as  it  approaches  the 
soft  ])alate,  where  the  anterior  and  lesser  part  is  inserted  into  the 
aponeurosis  of  the  palate ;  the  posterior  or  larger  part  meets  the  fibres 
from  the  opposite  side  underneath  the  azygos  uvulse  muscle. 

Relations. — Its  lateral  surface  with  the  tensor  palati  and  superior 
constrictor  muscles ;  the  internal  surface  is  covered  with  mucous  mem- 
brane. 

Actions. — "■  With  reference  to  the  soft  palate  :  the  muscle  elevates  the 
soft  palate  and  makes  it  tense,  since  the  right  and  left  muscles  act  syn- 
chronously. With  reference  to  the  Eustachian  tube  :  the  shortening  of 
the  body  of  the  muscle,  too-ether  with  the  increase  of  its  diameter,  has  a 


198  ANAT03IY. 

tendency  to  close  the  orifice  of  the  tube  by  elevating  the  lower  border. 
The  action  of  the  levator  palati  can  readily  be  studied  in  the  living  sub- 
ject by  the  rhinal  mirror.  By  such  aid  the  course  of  the  muscle,  even 
when  at  rest,  can  be  seen  corresponding  to  an  oblique  fold  of  mucous 
membrane,  which  may  receive  the  name  of  the  salpingo-palatal  fold. 
The  levator  palati  receives  much  attention  in  the  improved  operation 
of  staphylorrhaphy.  Fergusson,  having  noticed  the  influence  of  this 
muscle  in  widening  the  cleft  in  the  soft  palate,  essays  its  division  before 
uniting  the  freshened  edges.  This  procedure  is  now  an  established 
antecedent  to  the  operation. 

"  The  actions  of  the  levator  palati  and  tensor  palati  muscles  have  been 
the  subject  of  controversy.  Valsalva  as  long  ago  as  1742  described 
both  the  above  muscles  as  dilators  of  the  tube.  Toynbee^  in  1853 
revived  Valsalva's  account,  and  later  Riidinger  and  other  German 
writers  have  accepted  this  as  the  true  action.  Respecting  the  tensor 
palati,  Henle  ^  is  inclined  to  adopt  the  view  that  the  muscle  closes  the 
orifice.;  while,  as  seen  in  another  part  of  the  same  volume  (p.  117),  he 
doubts  the  ability  of  the  muscle  to  close  the  tube.  His  views  upon  the 
function  of  the  levator  palati  agree  with  those  expressed  in  the  text. 

"  The  author  has  long  taught  that  the  contraction  of  the  levator  palati 
narrows  the  plraryngoal  orifice  of  the  tube.  This  action  can  be  readily 
seen  in  the  living  subject  by  the  aid  of  reflected  light.  Cleland^  studied 
the  action  of  the  same  muscles  in  a  man  who  had  lost  the  soft  palate  by 
ulceration.  He  doubts  the  efficacy  of  the  tensor  palati  in  dilating  the 
tube,  while  he  assigns  to  the  levator  palati  its  proper  function,  in  assist- 
ing to  narrow  the  orifice.  That  the  Eustachian  tube  (q.  v.)  is  always 
patulous  in  health,  and  that  while  certain  muscles  tend  to  narrow  its 
lumen  none  can  obliterate  it,  seem  to  be  fair  deductions  from  its  nature."* 

The  Azi/gos  Uvuke  is  not  a  single  muscle,  as  its  name  implies,  but 
consists  of  a  pair  of  narrow  fasciculi,  arising,  one  on  each  side,  from  the 
posterior  palatine  spine  of  the  palate  bone  and  the  aponeurosis  of  the 
soft  palate,  the  fibres  passing  backward  to  be  inserted  into  the  uvula. 

Kerves. — The  muscle  is  controlled  by  the  facial  nerve. 

Action. — To  contract  the  uvula. 


Mucous  Membrane  and  its  Glands. 

Mucous  membrane  forms  the  lining  of  all  cavities  and  canals  having 
an  external  opening,  such  as  the  respiratory  tracts,  the  passages  trans- 
mitting f  jod  in  its  various  forms,  and  all  outlets  for  excretive  and  secre- 
tive fluids.  The  surface  of  the  membrane  is  soft  and  yielding,  and  is 
covered  by  a  thick  glistening,  tenacious,  transparent  fluid  called  mucus, 
which  is  secreted  by  numerous  small  glands  hereafter  to  be  described. 
The  mucus  protects  the  membrane  beneath  from  any  deleterious  matter 
contained  in  foods,  either  in  a  solid  state  or  in  the  form  of  solution. 

The  nnicous  membrane  of  tlie  body  can  l)e  divided  int(j  two  great 
systems — the  genito-urinary  and  the  gastro-pneumonic — each  being 
complete  and  continuous  in  itself. 

^  Trans.  Phil.  Soc.  LonrK,  1853.  *  Avn/nmie,  i.  755. 

3  JouvjKil  of  Anal,  and  Plii/s.,  iii.,  ]8G9,  97.         *  Allen's  Iluman  Anatomy,  pp.  259.  260. 


AREOLAR  TISSUE,   TESBOyS,  ASD  MUSCLES.  199 

The  Genito-urinary  System  is  that  which,  commencing  at  the  kidney.-, 
lines  the  urinary  passages  of  both  sexes,  passing  through  the  ureters, 
bladder,  and  uretlu-a,  also  the  sexual  organs,  as  the  seminal  ducts  and 
vesicles  of  the  male,  the  vagina,  uterus,  and  Fallopian  tubes  of  the 
female. 

The  Gadro-pneumonic  System  lines  the  alimentary  canal  and  all  ducts 
and  glands  which  o|>en  into  it ;  this  system  invests  the  air-jjassages 
from  the  opening  of  the  nostrils  to  the  air-vesicles  of  the  Imigs.  It 
also  lines  the  frontal  sinuses  and  air-cells  which  communicate  with  them 
(jr  the  air-passages.  The  membrane  passes  from  the  nasal  chamber 
through  the  Eustachian  tube  to  the  ear,  also  through  the  lachrymal 
ducts  to  the  eyes  and  lachrymal  glands.  The  latter  gland  is  developed 
from  a  solid  ingro^\th  of  the  conjtmctiva. 

The  construction  of  the  mucous  membrane  is  very  similar  to  that  of 
the  skin,  being  develojjed  from  two  layers  of  the  blastoderm — the  skin 
from  the  epiblast  and  mesoblast,  the  mucous  membrane  (with  certain 
exceptions)  from  the  hypo-  and  mesoblast :  it  is  divided  into  two  layers, 
epithelium  and  corium,  separated  by  an  intermediate  or  basement-mem- 
brane. 

Epithelium  of  Mucous  Membeaxe. — The  epithelial  layer  is 
the  most  constant  part  of  mucous  membrane — /.  e.  it  passes  over  and 
into  parts  where  the  corium  cannot  be  traced,  as  in  the  alveoli  of  the 
luug-s  and  upon  the  cornea  of  the  eye  ;  it  is  develojjed,  with  the  excep- 
tion hereafter  given,  from  the  lower  layer  (h^-]Xlblastic)  of  the  blasto- 
derm. This  laver  is  variotisly  classified,  either  according  to  its  function 
or  to  the  shape  and  arrangement  of  the  cells  entering  into  its  formation, 
as  simple,  stratified,  and  transitional,  the  simple  variety  being  again 
subdivided  into  pavement,  columnar,  spheroidal  or  glandular,  and  cili- 
ated. 

"When  classified  according  to  function,  it  is  arranged  as  protective  and 
secretory,  the  first  division  being  made  up  of  stratified,  transitional,  cili- 
atetl,  and  pavement  varieties  ;  the  latter  is  divided  into  columnar  and 
spheroidal  (glandular). 

The  Epitheliu:m  of  the  Oral  Cavity. — The  epithelium  within 
the  oral  cavity  is  reg-ardcd  as  squamous  stratified  epithelium  ;  the  same 
variety  is  also  found  in  the  lower  part  of  the  larynx,  upon  the  edges  of 
the  epiglottis,  the  true  vocal  cords,  and  in  the  cesophagus ;  also  in  the 
anterior  two-thirds  of  the  nasal  chamber. 

The  general  arrangement  of  cells  in  the  epithelium  is  very  similar  to 
that  of  the  epiderm ;  its  deep  or  Malpighian  layer  contains  very  little 
pigment,  and  is  columnar  in  form,  though  this  is  not  the  case  in  embiy- 
onal  life — the  stratum  granulosum  and  stratum  lucidum  of  the  epiderm 
are  not  present ;  but  with  this  exception  the  development.  gro\nh.  main- 
tenance, and  desquamation  are  the  same.  It  is  analogous  with  the  skin, 
and  is  develo]^  from  the  same  layer  of  the  blastoderm,  which  extends 
internally  as  far  as  the  palato-glossal  fold,  and  sometimes  farther. 

Should  any  portion  of  the  mucous  membrane  of  the  mouth  become 
constantly  exjiosed  to  the  action  of  the  atmosphere  as  the  result  of  surgi- 
cal operations  or  other  cause,  it  will  assume  the  horny  character  of  the 
skin.     In  like  manner,  should  any  part  of  the  skin  become  part  of  the 


200  ANATOMY. 

oral  cavity,  or  be  continuously  subjected  to  the  action  of  the  fluids  of  the 
mouth,  it  will  take  upon  itself  the  functions  and  cliaracteristies  of  mucous 
membrane,  assuming-  greater  translucency,  its  cells  becoming  compara- 
tively thin,  some  of  them  having  small  nuclei. 

In  the  olfactory  portion  of  the  nasal  chamber,  the  upper  part  of  the 
pharynx,  also  in  the  larynx,  trachea,  and  bronchi,  the  cellular  invest- 
ment is  made  up  of  stratified  cylindrical  ciliated  epithelium. 

The  epithelial  cells  of  the  nuicous  membrane  are  slightly  separated, 
but,  like  those  of  the  skin,  are  held  together  by  an  intercellular  cement 
substance,  and  it  is  through  this  cement  substance  that  absorption 
(very  slight)  takes  place  when  medicaments  are  placed  either  on  the 
skin  or  nuicous  membrane  ;  as  they  pass  through  they  enter  the  lymph- 
spaces  in  the  areolar  connective  tissue,  and  in  this  way  get  into  the  cir- 
culation through  the  larger  lymphatics. 

The  Cor'nim  of  the  mucous  membrane  lies  immediately  beneath  the 
basement-membrane,  but  is  not  always  demonstrable.  It  is  made  up 
very  similarly  to  the  corresponding  layer  of  the  skin — /.  e.  of  areolar 
connective  tissue,  sometimes  containing  a  large  intermixture  of  lymphoid 
tissue.  It  also  contains  white  and  yellow  fibrous  connective  tissue, 
muscular  tissue,  vessels,  lymphatics,  and  nerves.  The  corium  varies  in 
thickness  according  to  its  locality.  In  the  oesophagus,  bladder,  and 
vagina  the  fibrous  tissue  is  abundant,  forming  almost  a  compact  web 
and  making  the  mucous  membrane  of  these  parts  somewhat  stout  and 
tough.  In  other  parts,  as  in  the  stomach  and  intestines,  the  tissue  is 
retiform  or  lymplioid,  lacking  the  white  elastic  tissue.  Along  the  side 
and  beneath  the  tongue  in  the  alveolo-lingual  groove,  also  at  the  base 
of  the  tongue  and  the  epiglottis,  and  from  that  to  the  side  of  the  pharynx, 
the  corium  is  exceedingly  loose  and  pliable. 

On  the  alveolar  processes  of  the  inferior  and  superior  maxillary  bones 
this  layer  is  made  up  of  dense  connective  tissue,  and  is  firmly  attached 
to  the  membrane  immediately  upon  the  bone  which  forms  the  gum  tis- 
sue or  mueo-})eriosteum  (Allen).  This  muco-periosteum  has  both  the 
function  of  nuicous  membrane  and  periosteum,  and  it  is  througli  it 
tliat  the  bone  receives  nourishment.  AVhen  the  membrane  is  lost  or 
destroyed,  necrosis  takes  place  the  same  as  in  bones  which  are  supplied 
with  a  true  periosteum.  Where  cartilage  is  covered  by  mucous  mem- 
brane, as  in  the  septum  of  the  nose.  Eustachian  tubes,  the  larynx,  etc., 
it  is  called  nuico-perichondrium  (Allen),  and  acts  as  a  nourisher  and  pro- 
tector to  the  cartilage  similarly  to  the  ])erich()ndrium  of  cartilage. 

Upon  the  hard  palate  the  muco-periosteum  is  united  by  a  fine 
trabecula  to  the  ridges  of  the  bony  surface.  In  the  interspaces  and 
within  the  muco-periosteum  there  are  small  racemose  glands.  Upon 
the  soft  palate  it  is  more  firmly  adherent  at  the  anterit)r  surface  than 
tiie  posterior,  where  it  comes  in  contact  with  the  gland  tissue.  It  is 
found  on  the  roof  of  the  pharynx  attached  to  the  aponeurotic  membrane 
of  the  base  of  the  skull,  and  upon  the  tongue  it  is  firndy  attached  and 
forms  the  cortex. 

Blood-vessels  of  the  mucous  membrane  are  generallv  very  abundant. 
The  brandies  of  the  arteries  and  veins  divide  and  subdivide  in  the  sub- 
mucous tissue  as  in  the  skin,  and  pass  into  the  corium,  where  they  again 


AREOLAR  TISSUE,   TENDONS,  AND  MUSCLES.  201 

divide  and  form  a  complete  network  of  capillaries.  This  network, 
when  present,  lies  below  the  basement-membrane,  projecting  into  the 
papillae  of  the  papillary  layer.  The  tubular  and  other  glandular 
apparatus  are  abundantly  supplied  with  nourishment  by  this  vascular 
rete,  which  surrounds  them  for  that  purpose. 

Lymphatics  are  found  in  the  form  of  a  network  in  the  mucous  mem- 
brane, communicating  with  larger  vessels  in  the  submucous  layer. 

Nerves. — When  muscular  fibres  exist  in  mucous  membrane,  the  nerves 
are  chiefly  distributed  to  them,  also  to  the  glandular  aj)paratus ;  there 
are  also  ganglionic  plexuses  in  the  submucous  tissue.  Some  terminal 
nerves  have  been  found  to  pass  through  into  the  ejjithelium  and  ter- 
minate between  the  epithelial  cells  :  this  appears  to  have  been  demon- 
strated in  the  epithelium  of  the  mucous  membrane  of  the  palate  of  a 
rabbit.^ 

Pupiike  and  Villi  are  found  upon  some  parts  of  the  nuicous  mem- 
brane :  the  former  are  conspicuous  upon  the  tongue,  as  hereafter  described, 
and  the  latter  are  abundant  and  fully  developed  on  the  mucous  membrane 
of  the  small  intestines. 

The  Secretoky  Glands  of  the  Mucous  Me^mbeane. — The 
secretory  glands  are  organs  which  vary  in  structure  and  in  their  secre- 
tion ;  part  of  them  are  situated  within  the  mucous  membrane,  \\hile 
others  are  at  various  distances  from  it,  though  in  all  instances  their 
ducts  open  upon  its  surfiice.  Although  they  differ  considerably  in  their 
function  and  locality,  they  have  an  embryonal  derivation  similar  to  that 
of  the  epithelial  tissue  upon  which  their  ducts  empty  their  fluid  ;  their 
development  usually  begins  during  intra-uterine  life.  These  glands  are 
essentially  made  up  of  one  or  more  layers  of  secreting  cells,  usually 
resting  upon  a  basement-membrane.  Immediately  below  the  basement- 
membrane  there  is  an  abundant  supply  of  fine  blood-vessels ;  when  the 
membrane  is  absent,  the  vessels  are  in  close  contact  A\'ith  the  attached 
ends  of  the  cells. 

Enlargement  of  secreting  surfaces  of  any  part  is  generally  by  reces- 
sion or  inversion  (there  are  examples  in  nature  Avhere  the  increase  of  sur- 
face is  produced  by  protrusion  or  an  elevation),  which  is  carried  from 
very  simple  forms  to  various  degrees  of  complexity.  The  first  or  most 
rudimentary  of  these  varieties  is  a  recess,  the  result  of  the  dipping  down 
of  the  jNIalpighian  layer  into  the  subepithelial  tissue,  and  forming  what 
is  sometimes  called  an  epithelial  sac,  the  shape  of  which  is  tubular  or 
saccular.  This  simple  tube  sometimes  lengthens  considerably  and  coils 
upon  itself,  forming  a  ball,  which  is  known  as  a  coiled  tube.  The  sweat- 
glands  of  the  skin  are  of  this  kind,  and  are  formed  by  the  dipj)ing  down 
of  the  lower  strata  of  the  cells  or  the  embryonal  Malpighian  strata. 
These  embryonal  cells  are  not  columnar  in  shape,  as  found  in  adult 
tissue,  and  have  been  described  by  Zeigler^  thus:  "The  cell  by  itself 
appears  originally  as  a  microscopic  mass  of  pale,  finely-granular  matter, 
the  so-called  protoplasm.  It  usually  contains  within  it  a  nucleus — that 
is  to  say,  a  structure  like  a  tiny  vesicle — whose  form  may  be  round, 

^  Quain's  Avnfnmy. 

2  From  a  paper  read  by  Dr.  W.  X.  Suddutli  before  the  Odontographic  Societv, 
Oct.,  18S4. 


202 


ANATOMY. 


Fig.  98. 


rod-like,  or  irregular,  and  in  whose  interior  Ave  can  make  out,  by  proper 
handling,  (1)  small  definite  bodies,  the  nucleus  corpuscles;  (2)  a  net-like 
framework  of  nucleus  substances ;  and  (3)  a  clear  fluid,  the  nucleus 
juice.  The  young  cell  is  at  first  naked ;  only  in  its  matured  stages  does 
it  develop  on  its  surface  an  optically  distinct  membrane  or  other  struc- 
ture according  to  the  .special  tissue  of  which  it  forms  a  part." 

The  cells  of  the  embryonal  jNIalpighian  layer  dip  down  into  the 
subepithelial  connective  ti.ssue  (the  coriura)  and  form  epithelial  biids, 
which  are  the  commencement  of  the  mucous  glands,  although  varying 
in  shape  according  to  their  locality  and  function.  The  glands,  judging 
from  the  nature  of  their  epithelial  lining,  can  be  described  under 
three  general  modifications :  I.  Simple  tubular  mucous  glands ;  II. 
Compound  tubular  mucous  glands;  III.  Compound  tubular  salivary 
glands. 

I.  Simple  Tubular  Mucous  Glands  (Fig.  98). — The  crypts  or 
follicles  of  Lieberkiihn  that  are  found  in  the  intestinal  canal  may  be 

taken  as  typical  glands  of  this  class.  They 
usually  present  the  shape  of  a  te.st-tube,  form- 
ed of  the  epithelium,  the  csecal  end  pushing 
the  basement-membrane  into  the  corium  or 
substance  of  the  mucous  membrane,  the  tube 
opening  on  the  surface.  The  cells  lining  the 
tubes  are  of  a  single  layer,  and  apparently  of 
the  same  character  and  continuous  with  the 
columnar  epithelial  cells  of  the  surface.  They 
are  well  distributed  within  the  mucous  mem- 
brane, varying  in  number  and  kind  accord- 
ing to  locality.  They  are  generally  placed 
perpendicularly  to  the  surface,  and  often  close 
together,  in  which  position  they  constitute  the 
bulk  of  the  mucous  membrane,  the  thickness 
of  the  membrane  often  depending  ujion  the 
length  of  the  tubes,  which  differs  in  different 
localities.  The  cells  are  short,  cubical,  or 
columnar,  pos.sessing  a  spherical  or  oval  nu- 
---^  --  -  -  -  ''  cleus.  Although  the  gland-tubes  are  usually 
From  a  vertical  section  throuKh  single,  somc  are  bifurcatcd  at  the  deep  ex- 
jIlVe^'Mt"esti,'esT.V'aD^^^  trcmity,  aud  thcjowcr  end  may  be  somewhat 

enlarged  in  its  diameter. 

The.se  glands  are  found  in  large  numbers  in 
the  stomach,  large  and  small  intestines,  and 
the  uterus. 

Simple  tubular  glands  occasionally  have  their  secreting  surfaces 
increased  by  becoming  pouched  or  loculated. 

II.  Co:^rpoT^ND  Tubular  Mucous  Glands.— The  mucous  glands 
found  in  the  mouth  and  the  glands  of  Brunner  in  the  intestines  are 
typical  of  this  class,  being  small  racemo.se  glands.  Tlie.se  glands  open 
upon  the  surface  of  the  mucous  membrane  with  a  funnel-shaped  mouth, 
from  which  a  duct  passes  in  an  oblique  direction  (the  angle  of  obliquity 
not  always  being  the  same)  through  the  corium  into  the  submucous 


r 


IJn^ 


iiig,  (»,  the  crypts  i)f  Lielierkiihn 
closely  placed  side  by  side,  each 
crypt  lined  with  a  layer  of 
coluninar  epithelium;'  jnm, 
muscularis  inticosse  ;  .v,  sub- 
miicosK. 


AREOLAE   TISSUE,   TEXDO^S,  AXD  MUSCLES.  203 

tissue,  at  which  point  the  duct  divides  into  several  smaller  ones,  each 
of  which  enlarges  innuediately  after  bifurcation  and  forms  a  separate 
infundibulum  ;  the  tubes  again  narrow  and  make  several  irregular  turns 
or  convolutions,  and  have  acsecal  termination.  It  is  these  small  twisted 
tubes  that  form  the  secreting  part  of  the  gland.  The  epithelium  lining 
the  glands  varies  in  their  different  portions  :  the  funnel-shaped  moutii 
has   in  man   a  stratified  or  pavement  epithelium. 

The  duct  proper  is  lined  by  a  single  layer  of  long,  narrow,  columnar 
cells  with  intracellular  and  intranuclear  network,  giving  a  distinct  long- 
itudinal striation  and  slightly  granular  appearance  to  the  cell.  The 
calibre  of  the  duct  is  of  considerable  width. 

The  infundibular  portion  is  lined  with  more  or  less  flattened  epithelial 
cells,  which  gives  comparatively  a  wide  lumen  to  this  portion  of  the 
gland.  The  epithelial  cells  lining  the  convoluted  portion  of  the  small 
tubes  are  columnar  and  very  slightly  granular,  with  a  round  or  oval 
nucleus  situated  near  the  outer  end  of  the  cell.  The  cell  and  nucleus 
are  made  up  of  a  network  of  fibrils,  forming  rather  large  meshes  when 
the  gland  is  fully  developed. 

When  the  gland  is  active  the  cell  contains  drops  of  mucin  ;  but  when 
it  is  inactive  the  cells  are  shorter,  and  become  very  granular  and  some- 
what opaque ;  the  lumen  of  this  part  of  the  gland  is  large. 

The  epithelium  of  these  glands  rests  upon  the  basement-membrane, 
and  is  made  up  of  connective-tissue  cells  which  are  more  branched,  some 
of  the  branches  penetrating  the  septa  between  the  intercellular  cement 
which  holds  them  together. 

Sometimes  in  the  convoluted  portion  of  the  glands  several  embryonal 
cells  are  found ;  these  are  located  between  the  columnar  epithelium  and 
the  cells  forming  the  basement-membrane  or  connective  tissue  of  the 
tubes. 

These  compound  tubular  glands  sometimes  assume  a  saccular  form, 
thus  giving  us  the  names  of  tubular,  saccular,  or  racemose  glands. 

Sacculo-tubular  glands  are  those  which  are  intermediate  in  form 
between  saccular  and  tubular.  The  saccules  or  acini  have  a  tubular 
form. 

The  racemose  glands,  so  called  from  their  resemblance  to  bunches  of 
grapes,  are  modifications  of  the  compound  tubular  glands,  containing  a 
multitude  of  saccules  having  a  rounded,  pyriform,  or  thimljle  shape  ; 
they  are  arranged  in  clusters,  forming  lobules  and  open  into  the  extremi- 
ties of  the  branched  tubes;  these  tubes  form  ducts  which  join  other  sac- 
cular ducts,  forming  larger  branches  of  the  clusters  or  lobules ;  the 
lobular  branches  join  together  and  form  the  main  duct  or  ducts  of  the 
whole  gland,  which  empties  its  fluid  upon  the  mucous  membrane.  The 
size  of  the  gland  usually  depends  upon  the  number  of  lobules  or  clusters 
and  the  number  of  saccules  in  a  lobule ;  thus  there  are  the  small  race- 
mose glands,  as  those  of  the  roof  of  the  mouth,  and  others  of  large  size, 
like  the  parotid. 

Mucus. — The  fluid  that  is  secreted  by  these  glands  is  viscid,  lubrie, 
and  transparent.  Examined  under  the  microscope,  it  is  found  to  con- 
tain epithelial  cells,  also  round  cells  or  mucous  corpuscles.  They  so 
closely  resemble  the  white  or  pale  blood-corpuscles  that  they  are  con- 


204 


ANATOMY. 


Fig.  99. 


sidered  identical  with  them,  having  either  migrated  directly  from  the 
blood-capillaries  or  from  the  lymphoid  tissue  surrounding  the  glands. 
The  ninnber  of  mucous  corpuscles  depends  on  the  glands  which  produce 
the  mucus  ;  they  vary  according  to  locality. 

III.  Compound  Tubular  Salivary  Glands. — These,  generally 
speaking,  are  six  in  number,  three  on  each  side,  named  sublingual,  sub- 
maxillary, and  parotid. 

Tlie  minute  anatomy  and  the  physiological  action  of  the  salivary 

glands   prompted   Lavdowsky  to  classify  them  into  three  groups:   1. 

Mucous  glands ;    2.  True   salivary  glands ;   3.  Muco-salivary  glands. 

3Iucous  Glands, — Examples :  submaxillary  and  orbital  glands  of  the 

dog  (Fig.  99)  and  cat  and  the  sublingual  glands  of  man.     They  are 

similar  to,  though  larger  tlian, 
the  compound  tubular  glands  of 
the  mucous  membrane  of  the 
mouth ;  their  general  construc- 
tion is  the  same,  with  the  excep- 
tion of  the  epithelial  lining  of 
the  convoluted  portion  of  the 
j^^  ^  ^  tube,  which  is  composed  of  mu- 
cous cells — the  same  kind  of  epi- 
thelial cells  as  described  in  the 
mucous  membrane — and  the  pari- 
:  etal  cells,  or  crescents  of  Gianuzzi. 
These  cells  are  somewhat  similar 
to  the  embryonal  cell  already  de- 
scribed ;  they  stain  deeper  than 
the  surroundiny;  tissue  with  hoem- 
otoxylin  and  eosin,  thus  showing 
their  protoplastic  condition  ;  they 
are  granular  in  ajipearance,  and 

Submaxillary  Gland  of  the  Dog:  rt,  mucous  cells;  ft,  form     somihinnr    mnsSPS    Avithoilt 

protoplasm     cells;    c,  demilune    of    (iiaiuizzi;    ,/,  ^^^^^^    ^LUlllUliai      llUlbstiJi     WlUKHlL 

transverse  section  of  an  excretory  duct,  with  its  definite  membrane,  but  witll  pi'O- 

peculiur  columnar  epithelial  cells.  .      ^ .           ,-,      ,    n ,   •     ,      ,■>      •              i 

jections  that  fit  into  the  uTegular- 
sliaped  spaces  between  the  epithelial  mucous  cells  and  the  basement- 
membrane  with  which  they  are  in  contact.  The  lumen  of  the  convo- 
luted portion  is  o])en  and  of  considerable  size. 

When  tliese  glands  are  stimulated  to  secretion,  either  through  the 
natural  source  or  by  artificial  means,  the  mucous  cells  at  first  increase 
in  size,  and  a  viscous  fluid  is  secreted  which  passes  out  by  the  ducts ; 
after  the  action  has  been  continued  a  short  time,  the  cell-nucleus  changes 
its  shape  and  position,  becoming  smaller  and  granular,  more  rounded 
and  central,  and  the  cell  takes  a  deeper  stain  with  carmine.  If  this 
stimulation  be  ])rolonged  until  the  glands  become  exhausted,  the  mucous 
cells  lo.'^e  their  identity,  and  are  either  lost  by  being  carried  oif  in  the 
mucus,  or  they  become  granular  and  look  like  the  parietal  cells  found 
next  to  the  basement-membrane. 

"  Heidenhain  and  Lavdowsky  have  asserted  that  they  are  destroyed, 
and  that  their  ])laces  are  taken  by  a  process  of  new  cell-formation  from 
the  parietal  areas  ;  but  Ewald  regards  these  smaller  granular  cells  as  the 


AREOLAR   TISSUE,   TENDOJVS,  AND  MUSCLES. 


205 


Fig.  100. 


shrunken  remains  of  the  mucous  cells,  consequent  on  exhaustion  ;  and 
Klein  is  of  the  opinion  that  such  is  in  reality  the  case ;  for,  arguing  by 
analogy,  he  finds  that  excessive  stimulation  results  in  structural  changes 
Avhich  have  already  been  noted,  and  accompanied  by  watery  secretion — 
/.  e.  the  cells  have  evidently  discharged  all  their  nuicin,  and  have  col- 
lapsed and  become  both  morphologically  and  physiologically  like  those 
of  the  true  salivary  glands.  He  also  states  that  in  the  submaxillary 
gland  of  young  animals  all  gradations  are  met  with  from  small  alveoli 
with  small  lumen  lined  only  with  small  granular  cells,  and  alveoli  some- 
what larger  and  lined  either  partly  with  mucous  cells,  partly  with  gran- 
ular cells,  or  altogether  with  muccnis  cells,  to  which  are  applied  from 
place  to  place  groups  of  granular  cells." ' 

The  True  Salkanj  Glandn. — Examples:  the  parotid  gland  of  mam- 
mals, parts  of  the  submaxillary  gland  of  man  and  the  guinea-pig,  the 
orbital  and  submaxillary 
glands  of  the  rabbit.  These 
are  also  compound  tubnlar 
glands,  and  the  general  ana- 
tomical form  is  the  same. 
The  epithelial  cells  lining 
the  convoluted  secreting 
tubes  or  alveoli  are  different, 
consecpiently  their  function 
is  not  the  same  (Fig.  100). 
Its  epithelial  cells  are  cubi- 
cal, though  the  angles  are 
somewhat  rounded  ;  they  are 
placed  in  a  simple  layer,  con- 
tain a  spherical  nucleus  placed 
near  the  basement-membrane, 
and  are  united  with  those  of 
the  cell  proper,  forming  to- 
gether irregular  and  small 
meshes.  When  the  gland  is 
inactive  these  meshes  contain  a  small  quantity  of  fluid  substance.  In 
osmic  preparations  the  cell  appears  to  be  packed  full  of  distinct  granules 
of  an  albuminous  nature  which  obscure  the  nuclei. 

Between  the  cells  and  basement-membrane  there  are  quantities  of 
embryonal  cells  (crescents  of  Gianuzzi),  though  not  so  abundant  as  in 
the  glands  last  described. 

The  lumen  in  the  convoluted  portion  of  these  glands  is  quite  different 
from  that  of  the  mucous  glands  ;  it  is  doubted  by  some  whether  it  is 
open  at  all.  In  the  embryonal  cell  the  protoplasm  or  intercellular 
cement  so  completely  fills  the  tube  that  it  is  not  discernible. 

"After  a  short  period  of  activity  the  granules  are  found  to  have  dis- 
appeared in  the  outer  part  of  the  cell,  the  inner  part  being  still  distinctly 
granular,  and  some  granules,  being  apparently  free  within  the  lumen 
of  the  alveolus  [tube],  now  becoming  distinct  (Fig.  101).  With  more 
prolonged  activity  the  clear   outer  part  increases  in  extent,  and  ihe 

'  Coles's  Microscopical  Science. 


Section  of  part  of  tlie  Uunian  Submaxillary  filaiul.  To  the 
right  ol  the  tigiiie  is  a  group  of  luucous  alveoli,  to  the 
left  a  group  of  serous  alveoli. 


206 


ANATOMY. 


granules  are  found  only  in  the  part  of  the  cells  which  is  close  to  the 
lumen,  and  in  those  parts  which  are  contiguous  to  the  adjacent  cells 
(corresponding,  perhaps,  to  fine  capillary  clefts  which  pass  from  the 
cavity  of  the  alveolus  between  the  cells).     The  nuclei  have  now  become 


Fig.  101. 


Alveoli  of  a  Serous  Gland  :  A,  at  rest ;  B,  after  a  short  period  of  activity  ;  C,  after  a  prolon;,'ed  period 
of  activity.     In  A  and  B  the  nuclei  are  obscured  by  the  granules  of  zymogen. 

distinct  and  the  cells  are  smaller ;  we  may  suppose,  therefore,  that  the 
granules,  which  no  doubt  contain  the  specific  elements  of  secretion,  are 
formed  by  or  from  the  protoplasm  of  the  cells  during  rest,  and  are  dis- 
charged into  the  lumen  and  dissolved  during  activity.  Probably,  how- 
ever, during  activity,  new  granules  are  constantly  being  formed  and 
passed  outward  toward  the  lumen.  According  to  Langley,  the  three 
processes — of  growth  of  the  clear  protoplasm,  conversion  of  this  into 
granules,  and  discharge  of  these  into  the  lumen — are  all  proceeding 
simultaneously  in  different  parts  of  the  cell  during  activity."  ^ 

TJie  Muco-saUvary  Glands. — Examples:  the  submaxillary  glands  of 
man  and  of  the  guinea-pig.  They  are  all  compound  glands  with  a 
double  function,  which  makes  their  anatomy  complicated.  Some  of 
the  lobules  composing  the  gland  are  constructed  and  their  functions 
are  the  same  as  tho.se  of  the  pure  mucous  glands  (sublingual  gland  of 
man),  while  other  lobules  are  constructed  and  their  functions  are  the 
same  as  the  pure  salivary  glands  (the  parotid  of  man) ;  even  some  of 
the  convoluted  tubes  in  the  same  lobule  differ,  some  having  the  func- 
tion of  secreting  mucus,  while  others  secrete  saliva. 

"  Besides  these  three  forms,  Bermann  has  observed  that  in  connection 
with  a  large  gland  of  Wharton's  duct  in  many  mammals  he  has  discov- 
ered a  compound  tubular  mucous  gland  of  unique  structure."  ^ 

The  special  mucous  and  salivary  glands  associated  with  the  mouth, 
nose,  ancl  pharynx  are  labial,  buccal,  molar,  palatine,  lingual,  parotid, 
submaxillary,  sublingual,  and  lachrymal. 

The  Labial  Glands  are  of  two  kinds — the  mucous  and  sebaceous. 
The  mucous  glands  are  small  round  racemose  or  compound  tubular 
glands  about  the  size  of  small  peas,  situated  between  the  mucous  mem- 
brane and  the  orbicularis  oris  muscle  ;  their  ducts  open  upon  the  mucous 
membrane.  The  sebaceous  glands  are  small,  and  situated  on  the  outer 
part  of  the  red  margin  of  the  lip. 

The  Buccal  Glands  are  smidl  i^ound  racemose  or  compound  tubular 
glands  (smaller  than  the  labial),  situated  between  the  mucous  membrane 
and  buccinator  muscle ;  the  ducts  open  upon  the  mucous  membrane. 

The  3Iolar  Glands  are  small  round  racemose  or  compound  tubular 

^  Quaiii's  Anatomy,  9th  ctl.  ^  Coles's  i\ncroscnpical  Science. 


AREOLAR  TISSUE,   TENDONS,  AND  MUSCLES. 


207 


glands  (larger  tlian  the  buccal  glands),  situated  between  the  buccinator 
and  masseter  muscles,  and  having  separate  ducts,  which  have  their 
orifices  near  the  third  molar  tooth. 

The  Palatine  Glands  are  situated  in  the  deep  portion  of  the  muco- 
periosteum  of  the  hard  palate  and  under  the  mucous  membrane  of  the 
oral  and  nasal  surfaces  of  the  soft  palate  and  uvula ;  they  are  small, 
round,  racemose,  or  compound  tubular  glands,  and  form  a  continuous 
layer  upon  each  side  of  the  roof  of  the  mouth,  but  are  absent  in  the 
median  line. 

The  Lingual  Glands  are  of  two  kinds — the  small  racemose  or  com- 
pound tubular  and  the  simple  tubular  variety — situated  under  the 
mucous  membrane,  principally  on  the  posterior  portion  of  the  upper 
surface  of  the  tongue  near  the  circumvallate  papilhe  and  foramen 
caecum,  several  of  the  ducts  of  the  glands  opening  into  the  foramen. 
Those  which  open  near  the  circumvallate  papillse,  and  Avhere  the  taste- 
buds  are  situated,  secrete  a  watery  fluid  instead  of  mucus,  as  was  for- 
merly supposed.     These  glands  are  also  found  under  the  mucous  mem- 

FiG.  102. 


The  Salivary  Glands. 

brane  on  the  borders  of  the  tongue.  On  the  under  surface  of  the  tongue, 
near  its  apex,  a  number  of  these  glands  are  grouped  together,  forming  a 
small  oblong  mass  having  several  ducts  in  a  line,  which  open  upon  the 
mucous  membrane. 

The  Parotid  Gland  (Fig.  102),  so  named  from  being  situated  near 


208  ANATOMY.    ■ 

the  ear,  is  the  largest  of  the  salivary  glands.  Its  size  varies  consider- 
ably in  difterent  people,  the  average  ^veight  being  one  ounce.  It  is  a 
compound  tubular  racemose  salivary  gland. 

Situation. — The  Parotid  Space  is  bounded  in  great  part  by  a  bony 
framework,  although  the  gland  is  not  confined  by  the  lines  of  the  bony 
structures.  Anteriorly,  it  is  bounded  by  the  ramus  of  the  inferior  max- 
illary bone ;  posteriorly,  by  the  mastoid  and  styloid  processes  and  the 
tympanic  portion  of  the  temporal  bone ;  its  superior  boundary  is 
formed  by  the  convergence  of  the  above  structures ;  belo\v,  the  boundary 
is  formed  by  an  imaginary  line  drawn  from  the  angle  of  the  jaw  to  the 
sterno-cleido-mastoid  muscle.  Between  the  mastoid  and  styloid  pro- 
cesses the  gland  comes  in  juxtaposition  with  the  transverse  processes 
of  the  ujiper  cervical  vertebra,  especially  the  atlas.  Upon  examination 
of  an  articulated  skeleton  it  will  be  observed  that  by  depressing  the  head 
upon  the  chest  this  bony  space  will  be  decreased  by  the  jaw  coming 
closer  to  the  vertebrae,  while  in  the  movement  of  raising  or  extending 
the  head  it  is  enlarged.  By  protruding  the  lower  jaw  until  the  inferior 
teeth  articulate  outside  the  superior,  the  space  also  is  enlarged.  If  the 
jaw  is  depressed  the  space  becomes  compressed  below,  while  above  it  is 
increased  by  the  slipping  forward  of  the  condyle. 

The  parotid  gland  has  a  very  irregular  shape ;  its  superficial  surface 
is  convex  and  lobulated  and  in  close  relation  with  its  external  fascia. 
The  anterior  surface  is  divided  by  a  perpendicular  groove  into  an  exter- 
nal and  an  internal  portion,  the  external  of  which  extends  forward  to  a 
varied  extent  over  the  masseter  muscle.  It  is  from  this  anterior  portion 
that  the  parotid  duct  (duct  of  Steno)  is  given  off;  the  internal  portion 
passes  forward  on  the  inside  of  the  ramus  between  the  pterygoid  muscles. 

The  deep  portion  of  the  gland  passes  far  inward  toward  the  base  of 
the  skull,  vertebrae,  and  pharynx ;  the  upper  portion  passes  into  and 
occupies  the  posterior  part  of  the  glenoid  fossa ;  the  posterior  and  lower 
portion  rests  upon  the  styloid  process  and  its  muscles,  the  sterno-cleido- 
mastoid  and  digastric. 

The  Glandula  Soda  Parotidis,  or  Accessory  Parotid,  is  a  small  sepa- 
rate lobe,  not  always  present,  situated  at  the  anterior  external  border, 
below  the  zygomatic  arch  and  upon  the  masseter  muscle.  The  duct  of 
this  lobe  enters  the  parotid  duct,  where  it  crosses  the  masseter  nuiscle. 

The  Parotid  Duct,  or  Duct  of  Steno  (or  Steno's  canal),  is  about  tw^o 
and  a  half  inches  in  length,  its  diameter  varying  at  dilferent  portions, 
its  orifice  being  the  narrowest  part,  only  permitting  the  entrance  of  a 
small  probe.  Where  it  pierces  the  buccinator  muscle  it  is  as  large  as 
a  crowquill,  and  at  the  position  where  it  passes  over  the  masseter  mus- 
cle it  is  from  one-twelfth  to  one-eighth  of  an  inch  in  diameter.  The 
duct  commences  at  the  anterior  portion  of  the  gland,  leads  over  the 
masseter  muscle  about  one  finger's  breadth  below  the  zygomatic  arch,  and 
passes  forward  beneath  an  imaginary  line  drawn  from  the  lower  mar- 
gin of  the  concha  of  the  ear  to  a  point  midway  between  the  ala  of  the 
nose  and  the  red  margin  of  the  upper  lip,  the  transverse  facial  artery 
lying  above  it.  At  the  anterior  border  of  the  masseter  muscle  the  duct 
makes  a  short  curve,  almost  at  a  right  angle,  inward  ;  thence  it  passes 
through    the    cushion   of  fat   and  the   buccinator  muscle ;    continuino- 


.    AREOLAR  TISSUE,   TE^^DONS,  AND  MUSCLES.  209 

obliquely  forward  a  short  distance  beneath  the  mucous  membrane,  it  has 
its  outlet  through  a  small  papilla  opposite  the  crown  of  the  second  supe- 
rior molar  tooth. 

The  Parotid  Fascia. — The  gland  is  closely  encased  in  a  covering  derived 
from  the  deep  cervical  fascia.  The  superficial  layer  of  the  parotid  fascia 
is  dense  and  strong,  arising  posteriorly  from  the  sheath  covering  the 
sterno-cleido-mastoid  muscle ;  after  jjassing  over  the  gland  it  is  con- 
tinuous anteriorly  with  the  sheath  of  the  masseter  muscle.  Above, 
it  is  attached  to  the  zygomatic  arch ;   below,  to  its  own  deep  leaflet. 

The  Deep  Layer  of  the  parotid  fascia  is  neither  so  strong  nor  so  dense 
as  its  superficial ;  below,  it  is  formed  from  a  division  of  the  deep  cervi- 
cal fascia  where  it  passes  beneath  the  gland  to  be  inserted  into  the  base 
of  the  skull ;  it  forms  the  stylo-maxillary  ligament,  and  is  connected 
with  the  sheaths  of  the  pterygoid  muscles,  leaving  a  space  or  gap 
between  the  anterior  edge  of  the  styloid  process  and  the  posterior 
border  of  the  external  pterygoid  muscle.  Thus  it  will  be  seen  that  the 
gland  is  tightly  bound  down  upon  the  outside  by  a  close  covering,  while 
within  it  is  not  so.  The  opening  in  the  deep  fascia  spoken  of  above 
gives  communication  between  the  parotid  space  and  the  connective  tissue 
above  the  pharynx. 

The  arteries  of  the  gland  are  very  numerous,  consisting  of  a  branch 
direct  from  the  external  carotid,  and  branchlets  from  the  divisions  of 
that  trunk  in  its  immediate  vicinity,  as  the  internal  maxillary,  tem- 
])oral,  transversalis,  facial,  posterior  auricular.  The  veins  follow  a  sim- 
ilar course.  The  external  carotid  in  passing  behind  the  ramus  of  the 
jaw  enters  the  gland,  not  at  the  lowest  portion,  but  at  its  inner  and 
anterior  surface,  and  passes  slightly  backMard  and  outward,  becoming 
more  superficial  as  it  ascends. 

The  Ii/mj)hatic  glands  join  those  of  the  deep  and  superficial  parts  of 
the  neck,  one  or  more  being  found  in  the  substance  of  the  parotid,  and 
others  upon  its  surface.  These  glands  are  liable  to  become  enlarged  and 
form  a  species  of  parotid  tumor. 

The  nerves  are  derived  from  the  facial,  the  auriculo-temporal,  great 
auricular,  and  the  sympathetic  plexus  of  the  external  carotid  artery. 
Experiments  upon  the  dog  and  cat  have  shown  that  the  cerebro-spinal 
nerve-supply  to  this  gland  is  from  the  glosso-pharyngeal.  In  addition 
to  the  above  are  the  lesser  superficial  petrosal  nerve  and  the  otic  gan- 
glion, the  fibres  finally  l)eing  distributed  to  the  gland  through  a  branch 
of  the  auriculo-temporal.  The  facial  nerve  passes  through  the  gland, 
though  not  so  intimately  bound  up  in  its  substance  as  is  the  carotid  artery. 

The  ^Submaxillary  Gland — so  named  from  its  position  beneath  the 
maxillary  bone — is  smaller  than  the  parotid,  and  weighs  about  two  or 
two  and  a  half  drachms.  It  is  a  muco-salivary  gland,  derived  from 
epiblastic  structure.  The  lobules  comprising  the  gland  are  not  held  so 
tightly  together  as  are  those  of  the  parotid,  though  they  are  more  defined. 
The  gland  is  situated  below  the  mylo-hyoid  ridge  of  the  inferior  maxil- 
lary i)one  in  the  submaxillary  depression  and  in  the  submaxillary  triangle 
of  the  neck,  which  is  bounded  by  the  mylo-hyoid  ridge  of  the  bone  and 
a  line  drawn  backward  to  the  digastric  groove  of  the  temporal  bone 
above.  The  lower  boundaries  are  composed  of  the  posterior  and  ante- 
VOL.  I.— u 


210 


ANATOMY. 


rior  bellies  of  the  digastric  muscle.  It  is  covered  externally  by  the 
superficial  layer  of  the  submaxillary  fascia,  the  platysma  myoides  mus- 
cle, and  the  skin ;  internally  by  its  deep  fascia,  which  separates  it  from 
the  mylo-hyoid,  hyo-glossus,  and  stylo-glossus  muscles.  The  gland 
extends  backward  to  the  posterior  border  of  the  mylo-hyoid  muscle, 
where  it  sometimes  passes  around  its  border  to  the  upper  surface,  and 
is  separated,  at  the  posterior  part,  from  the  parotid  gland  by  the  stylo- 
hyoid ligament. 

The  Hubmaxillari/  Dad  (Wharton's),  through  which  the  secretion  of 
the  above  gland  passes  to  the  mouth,  is  about  two  inches  in  length, 
and  its  coats  are  not  so  thick  as  those  of  the  parotid  duct.  It  com- 
mences by  the  union  of  the  ducts  originating  in  the  different  lobules  near 
the  posterior  surface  of  the  gland,  and  with  some  of  the  tissue  of  the 
gland  winds  around  the  posterior  border  of  the  mylo-hyoid  muscle.  It 
then  passes  forward  and  inward  over  the  muscle  and  beneath  the  hyo- 
glossus  and  the  sublingual  gland,  terminating  in  a  narrow  opening 
through  a  soft  papilla  at  the  side  of  the  fraiuum  linguae,  near  the  duct 
on  the  opposite  side.  Occasionally  isolated  lobules  of  gland  tissue  are 
found  along  the  duct. 

The  arteries  which  supply  the  gland  are  branches  of  the  facial  and 
lingual.     The  veins  belong  to  the  facial  and  lingual. 

Its  nerve-supply  is  derived  from  the  submaxillary  ganglion,  which 
obtains  its  motor  filaments  from  the  chorda  tympani,  and  its  sensory  from 

the  lingual  branch  of  the  inferior 
maxillary — sometimes,  though  sel- 
dom, from  the  mylo-hyoid,  a  branch 
of  the  inferior  dental ;  the  sympa- 
thetic nerve  branches  from  those 
accompanying  the  arteries  in  this 
vicinity. 

The  Sublingual  or  Gland  of  Bar- 
f  hoi  in  (Fig.  103)  is  so  named  from 
its  position  under  the  tongue.  It  is 
smaller  than  the  submaxillary  gland, 
and  secretes  mucus  only.  The  lobules 
of  jthis  gland  are  not,  as  in  the  parotid 
and  submaxillary,  united  into  one 
with  a  single  duct  leading  from  it, 
but  are  divided  into  several  smaller 
glands,  each  having  an  independent 
duct.  They  are  arranged  in  a  nar- 
row, oblong  form  situated  beneath 
the  mucous  membrane  of  the  mouth, 
forming  a  ridge  in  the  alveolo-lingual 
groove.  The  ridge  commences  in 
front  of  the  tongue  near  the  franum, 
and  in  close  proximity  to  the  gland 
of  the  opposite  side ;  it  extends 
backward  and  outward  about  one 
and  a  half  inches  to  near  the  iirst  molar  tooth.     The  inner  surface  of 


Fig.  103. 


View  of  the  Right  Submaxillary  and  Sublingual 
Cjlands,  from  the  inside,  i'art  of  the  ritrlit 
side  of  the  jaw,  divided  from  the  left  at  the 
symphysis,  remilins;  the  tongue  and  its  nius- 
cle.s  have  been  removed,  and  the  mucous 
membrane  of  the  rifjht  side  has  been  dis- 
sected off  aTid  liHoked  upward,  so  as  to  expose' 
the  sublingual  glands;  .v/»,  the  larger  super- 
ficial part  of  the  submaxillary  gland;.;",  the 
facial  artery  passing  through  it;  .vj?*',' deep 
portion  prolonged  on  the  inner  side  of  the 
mylo-hyoid  niuse'e,  m/i ;  xl  is  pbiced  below 
the  antnrior  large  part  of  the  sublingual 
gland,  wiih  the  duct  of  f^artbolin  partly 
shown  ;  x/\  placed  above  the  hinder  small 
end  of  the  gland,  ii  dic;ites  <ine  or  two  of 
the  ducts  perforating  the  mucous  membrane  ; 
(/,  the  papilla,  at  which  the  duct  of  Wharton 
opens  in  front  behind  tlie  incisor  teeth;  </', 
the  commencement  of  the  duct  ;  A,  the  hyoid 
bone ;  n,  the  gustatory  nerve ;  close  to  it  is 
the  submaxillary  ganglion. 


AREOLAE   TISSUE,    TENDONS,  AND  MUSCLES. 


211 


the  gland  is  in  relation  with  the  genio-glossus  muscle,  its  lower  surface 
with  the  mylo-hyoid,  and  closely  relates  with  the  submaxillary  duct 
and  the  lingual  branch  of  the  fifth  nerve. 

The  sublingual  or  ducts  of  Rivinus  vary  in  number  from  eight  to 
twenty,  corresponding  generally  to  the  lobules  contained  in  the  gland  ; 
they  open  separately  upon  the  surface  of  the  nuicous  membrane  over 
the  ridge  formed  by  the  gland,  and  a  few  may  open  into  the  submax- 
illary duct. 

The  Duct  of  Bartholin  is  a  single  duct  of  the  sublingual  gland  formed 
by  the  confluence  of  small  ducts  arising  from  the  posterior  lobules, 
which,  at  times,  receive  small  branches  from  the  submaxillary  gland. 
It  passes  in  close  proximity  to  the  submaxillary  duct,  and  either  opens 
into  it  or  upon  the  nuicous  membrane  near  the  orifice  of  the  latter 
duct. 

The  blood-vessels  of  the  sublingual  gland  are  from  the  submaxillary 
and  sublingual  arteries  and  the  veins. 

The  neyve-svpply  is  derived  from  the  submaxillary  ganglion. 

The  Lachrymal  Gland  and  its  Ducts  (Figs.  104,  10-5)  leading  to  the 
Nascd  Chamber. — The  lachrymal  gland  is  situated  principally  within 

Fig.  104. 


Xaclivtivial in.  'I'       "^ 


The  Meibomian  Glands,  etc  ,  seeii  from  the  inner  surface  of  tVie  eyelids. 

the  lachrymal  fossa  of  the  frontal  bone,  at  the  superior  lateral  angle  of 
the  orbit,  behind  the  external  angular  process  of  the  frontal  bone,  Avhich 
aifords  it  protection.  It  is  about  half  an  inch  wide  by  thi'ce-fourths  of 
an  inch  long.  Its  shape  is  somewhat  that  of  a  flattened  almond.  It  is 
concavo-convex,  and  has  two  surfaces,  inferior  and  superior. 

The  Inferior  or  Concave  Surface  is  in  relation  with  the  capsule  of  Tenon 
or  the  fascia  of  the  ball  of  the  eye,  and  the  superior  and  external  recti 
muscles. 

The  Superior  or  Convex  Surface  is  closely  applied  to  the  periosteum 
of  the  frontal  bone,  to  which  it  is  connected  by  a  few  tendinous  fibres. 

The  lachrymal  gland  is  racemose  in  structure,  and  is  identical  with 
the  true  salivary  glands,  such  as  the  parotid  in  man.     It  is  enclosed  in 


212 


ANATOMY. 


a  capsule  and  divided  into  two  unequal  portions,  a  superior  or  larger  and 
an  inferior  or  smaller,  with  a  thin  layer  of  fascia  between  them. 

The  Siqjerior  Portion,  which  comprises  the  greater  part  of  the  gland, 
is  firmer  in  structure  than  the  inferior — made  so  by  the  larger  size  of 

its  lobules  and  their  greater 
^'  compactness   of  arrangement. 

It  is  placed  within  the  lach- 
rymal fossa. 

The  Inferior  Portion  (glan- 
dula  lachrymalis  inferior,  Ro- 
senmiiller)  is  smaller  than  the 
superior.  Its  lobules  are  mi- 
nute in  size  and  loosely  col- 
lected together,  which  gives  it 
a  softer  appearance  than  the 
superior  portion.  It  is  situ- 
ated in  the  subconjunctival 
connective  tissue,  just  back 
of  the  lateral  portion  of  the 
upper  eyelid. 

Harder's  Gland,  found  in 
most  mammals,  is  situated  at 
the  inner   angle  of  the   eye. 

The  Lachrymal  Apparatus,  right  side.  j^^     ^j^^     ^^^     skeop,    and    pig, 

according  to  Wendt,  it  is  similar  in  structure  and  function  to  the  lach- 
rymal gland,  while  in  the  musk-rat  and  guinea-pig  it  is  like  the  seba- 
ceous glands  of  the  body.  This  gland  is  found  in  man  and  in  the  ape 
in  a  rudimentary  state  (Gracomini). 

The  Canmcula  Lachrymalis  is  a  small  pinkish-red  body  situated  at 
the  inner  angle  of  the  eye — the  rudiment  of  the  nictitating  membrane 
of  birds,  which  forms  a  kind  of  third  eyelid  for  protection,  without 
obstructing  the  functions  of  the  organ. 

The  Buds  of  the  Lachrymal  Gland  leading  to  the  surface  of  the  eye 
are  from  ten  to  fourteen  in  number.  They  pass  obliquely  downward 
beneath  the  mucous  membrane,  diverging  slightly  as  they  do  so,  and 
finally  open  into  the  outer  third  of  the  superior  palpebral  sinus  on  a 
line  with  each  other.  A  few  of  the  lobules  composing  the  inferior 
portion  of  the  gland  have  independent  ducts  which  open  separately, 
while  others  join  the  ducts  coming  from  the  superior  or  main  portion 
of  the  gland. 

Arteries. — The  lachrymal  gland  is  supplied  with  blood  through  the 
medium  of  the  lachrymal  artery,  which  is  a  branch  of  the  ophthalmic. 

Nerves. — The  lachrymal  gland  receives  its  nerve-supply  from  the 
lachrymal  nerve,  which  is  a  branch  of  the  ophthalmic  or  first  division 
of  the  fifth  cranial  nerve. 

Tlie  Lachrymal  Canals,  or  Canaliculi,  are  four  in  number,  a  supe- 
rior and  an  inferior  for  each  eye.  They  have  their  origin  in  small 
openings,  the  puncta  lachrymalia,  situated  in  the  centre  of  a  teat-like 
elevation  at  the  inner  edge  of  each  eyelid  near  the  inner  angle  of  the 
eye  the  lachrymal  papilla.     These  canals  terminate  separately  by  open- 


AREOLAE  TISSUE,    TENDONS,  AND  MUSCLES.  213 

ing  into  the  lachrymal  sac,  though  they  may  open  by  one  common  duct. 
They  are  lined  by  pavement  epitheHum.  They  pass  to  their  termina- 
tion imbedded  in  connective  tissue  and  surrounded  by  longitudinal 
fibres  of  the  concentric  or  ciliary  portion  of  the  orbicularis  palpebrarum 
muscle,  and  empty  by  independent  openings  into  the  lachrymal  sac. 
Occasionally  these  canals  merge  into  one  another  and  terminate  in  one 
common  duct.     They  are  lined  by  pavement  epithelium. 

The  Superior  Lachrymal  Canal  is  smaller  in  calibre  than  the  inferior, 

though  it. is  slightly  longer,  being  nearly  five  lines  in  length  and  two 

lines  in  width.     It  commences  on  the  inner  margin  of  the  upper  eyelid, 

curves  slightly  upward,  inward,  and  downward,  and  enters  the  orbital 

•aspect  of  the  sac  a  little  below  its  summit. 

The  Inferior  Lachrymal  Canal  is  somewhat  thicker  and  shorter  than 
the  superior.  It  commences  at  the  inner  margin  of  the  lower  eyelid, 
passes  slightly  downward,  inward,  and  upward,  and  enters  the  lachrymal 
sac  just  below  the  superior  canal. 

The  Lachrymo-naaal  Passage  is  divided  into  two  portions,  the  sac 
and  the  duct,  the  latter  being  lined  by  a  ciliated  epithelium  similar  to 
that  of  the  nose. 

The  Lachrymal  Sac  is  the  upper  enlarged  portion  of  the  lachrymo- 
nasal  jmssage,  and  is  situated  in  the  sulcus  formed  by  the  upper  portion 
of  the  lachrymal  grooves  in  the  lachrymal  and  superior  maxillary  bones. 
It  is  retained  in  position  by  connective-tissue  fibres  which  unite  with  the 
periosteum  of  the  bone,  and  by  fibres  with  the  internal  tendo-palpe- 
brarum  and  tensor  tarsi.  The  sac  is  about  half  an  inch  long,  being 
a  little  M'ider  than  long  at  its  broadest  portion.  It  is  flat  on  its  inner 
surface,  which  is  that  portion  next  the  bone,  but  its  external  surface, 
or  that  next  the  orbit,  where  the  canaliculi  find  entrance,  is  rounded 
and  projects  toward  the  eye.  The  superior  portion  of  the  sac  is  dome- 
shaped,  while  the  inferior  portion  is  smaller  and  passes  into  the  nasal 
duct  without  any  line  of  demarcation  between  them. 

The  Lachrymo-naml  Buct  is  formed  by  the  lower  portion  of  the 
lachrymo-nasal  passage.  It  is  slightly  over  half  an  inch  in  length,  and 
extends  from  the  lachrymal  sac  into  the  inferior  meatus  of  the  nose  by 
passing  through  the  lachrymal  canal.  The  duct  is  larger  at  its  extrem- 
ities than  in  "the  middle,  and  is  adherent  to  the  bony  walls,  through 
which  it  passes,  by  connective-tissue  fibres  uniting  it  with  the  periosteum. 

Valve-like  folds  of  the  lachrymo-nasal  ]iassage  have  been  described 
as  existing  at  the  openings,  Avithin  the  canaliculi  of  the  sac,  in  the  duct, 
and  at  its  termination  in  the  nasal  chamber. 

The  Tonsils. 

The  Tonsils  (tonsillffi  amygdala?)  are  two  glandular  bodies  situated  on 
each»side  of  the  oro-])haryngeal  space,  which  is  in  relation  in  front  with 
the  palato-glossal  fold  (anterior  palatine  arch) ;  behind,  with  the  palato- 
pharyngealfold  (posterior  palatine  arch) ;  laterally,  with  the  constrictor 
muscles  of  the  pharynx  ;  and  proximally  or  internally  it  is  open,  this 
surface  being  covered  by  the  mucous  membrane  of  the  oro-pharyngeal 
space  above  referred  to.'     The  fact  that  the  palato-glossal  and  palato- 


214  ANATOMY. 

pharyngeal  muscles  arise  from  closely-related  portions  of  the  palate, 
and  diverge  as  they  descend  to  their  insertions,  causes  the  tonsillar  space 
to  be  narrow  at  the  top  and  wider  at  the  bottom ;  and  the  further  fact 
that  the  gland  is  about  of  eipial  width  and  thickness  causes  it  to  be 
compressed  above,  while  below  it  is  comparatively  free  from  pressure. 

The  tonsils  are  about  three-fourths  of  an  inch  long,  half  an  inch 
wide,  and  about  the  same  in  thickness,  their  extremities  being  rounded. 
They  vary  considerably  in  size  in  different  individuals,  the  two  often 
being  dissimilar  in  the  same  person.  They  are  comjjosed  of  masses  of 
connective-tissue  fibres  and  diffused  adenoid  tissue  embracing  lymph- 
follicles.  On  their  free  or  proximal  surface  they  are  pitted  with  from 
twelve  to  twenty  indentations  or  f)ldings,  in  such  a  way  that  they  pro-' 
duce  small  recesses  or  crypts  situated  within  the  substance  of  the  gland. 
These  give  the  free  surface  of  the  gland  a  perforated  appearance.  The 
crypts  are  lined  by  a  continuation  of  the  stratified  epithelium  covering 
the  mucous  membrane  of  the  mouth.  The  lymph-follicles  above 
referred  to  are  arranged  around  the  walls  of  the  crypts,  and  outside 
of  the  follicles  are  a  number  of  small  mucus-secreting  glands.  The 
secretion  from  these  mucous  glands  is  thick  and  grayish  in  appearance ; 
it  is  discharged  into  the  crypts.  The  retention  of  this  fluid  causes  the 
breath  to  become  fetid.  Sometimes  this  secretion  becomes  inspissated, 
and  is  discharged  in  the  shape  of  small  balls  of  yellowish-gray  matter 
having  a  very  offensive  odor.  The  retention  of  this  matter  may  cause 
the  tonsils  to  become  highly  infiamed. 

AVhen  the  tonsils  are  in  normal  condition,  lymph-corpuscles  migrate 
from  the  body  of  the  gland,  through  the  mucous  membrane  on  its  free 
surface,  and  enter  the  muco-salivarv  fluid  of  the  mouth.  These  corpus- 
cles, when  detected  in  the  saliva,  are  called  In-  some  writers  mucous  or 
salivary  corpuscles.  These  corpuscles  absorb  water,  become  splierical 
in  form,  and  finally  disintegrate. 

The  InfratonxiUar  or  Pharymjeal  Tonnih  are  situated  below  the  ton- 
sils proper,  in  the  upper  part  of  the  pharynx.  As  the  raucous  mem- 
brane in  parts  of  this  region  is  covered  by  ciliated  columnar  ejjithelium, 
it  follows  that  some  of  the  crypts  of  these  glands  are  lined  Avith  the 
same  structure. 

Arfrries. — The  tonsils  are  extremely  vascular  bodies,  being  supplied 
with  blood  through  tlie  medium  of  the  tonsillar  and  palatine  branches 
of  the  facial  artery,  the  descending  palatine  branch  of  the  internal  max- 
illary, and  the  ascending  ])hnryngeal.  From  these  arteries  a  fine  ]>lexus 
of  capillaries  is  fi)rmed.  These  ca]Mllaries  are  distributed  to  the  differ- 
ent tissues  within  the  gland.  The  extreme  vascularity  of  the  gland 
causes  its  excision  in  wliolc  or  in  part  to  be  followed  by  considerable 
hemorrhage.  Although  tlie  internal  carotid  artery  passes  to  the  outside 
of  the  superior  constrictor'of  the  pharynx,  and  is  usually  about  three- 
fourths  of  an  inch  back  of  the  gland,  it  has  been  cut  in  performing 
tonsillotomy,  with  verv  serious  results.  In  operations  upon  the  gland 
the  sursjeon  should  direct  liis  knife  awav  from  the  arterv. 


BLOOD-VESSEL  SYSTEM   OF  THE  HEAD,   ETC. 


215 


BLOOD-VESSEL    SYSTEM    OF    THE    HEAD    AND 
ANTERIOR  CERVICAL  REGION. 

The  head  is  supplied  Avith  blood  by  the  two  vertebral  and  the  two 
common  carotid  arteries,  besides  numerous  anastomotic  branches  from 
other  trunks. 

THE  ARTERIES. 

The  Common  Carotids  (Right  and  Left). 

The  Common  Carotids  (Fig.  106)  are  very  similar  in  position  and  in 
their  course  through  the  neck  on  either  side.     They  give  off  the  same 

Fig.  106. 


Th/nliOali^    , 


Zfft  Vagus 


Recurrent  Zari/iigeai 


\i*  ^ Flun  jf  tJuBra/iiJitg 


Lift  Co 


The  Arch  of  the  Aorta,  and  its  Branches. 


216  ANATOMY. 

number  of  branches,  though  these  may  vary  in  size.  They  are  about 
8  mm.  (^  inch)  in  calibre.  Tliey  diiier  both  in  their  length  and  origin, 
the  left  being  the  longer :  it  arises  directly  from  the  arch  of  the  aorta, 
and  is  more  deeply  situated  than  the  right. 

The  Right  Common  Carotid  Artery  is  the  shorter  of  the  two,  and  at 
its  origin  is  more  superficially  situated  than  the  left.  It  is  one  of  the 
terminal  branches  of  the  brachio-cephalic  (innominate)  artery,  the  other 
branch  being  the  subclavian.  The  bifurcation  of  the  brachio-cephalic 
into  the  right  common  carotid  and  subclavian  arteries  takes  place  within 
the  thorax  behind  the  sterno-clavicular  articulation  and  above  the  level 
of  the  second  dorsal  vertebra.  In  front  it  is  in  relation  with  the  right 
brachio-cephalic  (innominate)  vein,  and  externally  with  the  subclavian 
vein  and  the  pneumogastric  and  phrenic  nerves. 

The  Left  Common  Carotid  Artery  arises  from  the  left  of  the  arch  of 
the  aorta,  and,  with  the  exeption  of  the  coronary  arteries,  which  supply 
the  heart,  is  the  second  branch  given  off  from  that  vessel.  At  its  origin 
it  is  situated  within  the  thorax.  It  then  passes  upward  and  a  little  out- 
ward to  the  left  of  the  sterno-clavicular  articulation,  from  which  point 
its  course  is  similar  to  the  artery  of  the  right  side.  It  is  situated  just 
b?hind  the  upper  jiortion  of  the  sternum,  and  is  covered  by  the  sterno- 
hyoid and  sterno-thyroid  muscles,  and  in  early  childhood  by  a  portion 
of  the  thymus  gland.  The  left  brachio-cephalic  vein  crosses  it  in  front, 
and  behind  it  is  in  relation  with  the  trachea,  oesophagus,  and  thoracic 
duct.  Externally  will  be  found  the  pleura,  pneumogastric  (tenth 
cranial),  and  phrenic  nerves. 

In  the  neck  the  common  carotids  are  generally  similar  in  course  and 
situation,  though  they  may  differ  slightly  in  size,  and  their  termination 
may  be  at  a  point  slightly  higher  or  lower  on  one  side  than  the  other. 
They  extend  from  the  sterno-clavicular  articulation  on  either  side  to 
their  termination  opposite  the  upper  border  of  the  thyroid  cartilage, 
without  giving  off  any  branches.  At  the  upper  border  of  the  thyroid 
cartilage  they  divide  into  two  large  branches,  the  external  and  internal 
carotids. 

The  Line  of  the  Common  Carotid  Artery  extends  from  the  sterno- 
clavicular articulation  to  a  point  midway  between  the  angle  of  the  jaw 
and  the  mastoid  process  of  the  temporal  bone.  At  the  point  where  the 
carotid  arteries  emerge  from  the  thorax  and  enter  the  neck  thev  are 
closely  approximated,  being  separated  only  by  the  anterior  semicircum- 
ference  of  the  trachea.  As  they  ascend  the  neck  they  diverge,  and  at 
their  termination  are  separated  by  the  larynx  and  the  pharvnx,  -which 
structures  are  pushed  forward  between  them.  They  are  deeply  seated 
at  their  origin,  but  become  quite  superficial  in  the  region  of  the  larvnx. 

T lie  Sheath  of  the  Common  Carotid  Artery  \ii  derived  from  the  deep 
cervical  fascia,  and  encloses,  together  with  the  artery,  the  pneumogastric 
nerve  and  internal  jugular  vein.  The  artery  is  situated  to  the  median 
side  of  the  nerve,  Avhile  the  vein  is  external  to  both  artery  and  nerve. 
Each  of  these  structures  is  separated  from  the  others  by  a  distinct 
investment  of  connective  tissue.  The  descendens  noni  nerve  is  occa- 
sionally within  the  sheath  of  the  common  carotid,  but  more  frequently 
it  passes  down  the  neck  upon  the  sheath. 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,  ETC. 


217 


Superficial  Relations.— At  the  base  of  the  neck  the  common  carotid 
artery  is  covered  by  tlie  skin,  platysma  myoides,  and  deep  fascia,  and 
by  the  sterno-cleido-mastoid,  sterno-hvoid,  and  sterno-thyroid  muscles. 


Fig.  107. 


Surgical  Aiiatoiii)  ol  t lie  Aiteiies  of  the  Neck,  right  side. 


It  is  cro.ssed  by  the  omo-liyoid  muscle  opposite  the  cricoid  cartilao-e,  and 
below  this  by  the  anterior  jugular  vein.  The  upper  portion  of  th^  com- 
mon carotid,  or  that  portion  Mhich  extends  from  the  omo-hyoid  muscle 
to  its  termination,  is  covered  by  the  skin,  platysma  myoides,  and  deep 


218  ANATOMV. 

fascia,  and  by  the  anterior  border  of  the  sterno-cleido-mastoid  muscle. 
On  dissection,  however,  because  of  the  slirinkage  which  takes  place  in 
the  muscle  after  death,  it  is  usually  found  that  the  anterior  border 
of  the  sterno-cleido-mastoid  does  not  cover  tlie  artery  in  this  position, 
but  it  is  found  in  the  carotid  triangle,  which  is  bounded  above  by 
the  posterior  belly  of  the  digastric  muscle,  in  front  by  the  anterior 
belly  of  the  omo-hyoid  muscle,  and  behind  by  tlie  sterno-cleido-mas- 
toid muscle,  the  sterno-mastoid  branches  of  the  superior  thyroid  artery, 
and  by  the  facial,  lingual,  and  superior  thyroid  veins,  crossing  it  in  this 
triangle.     Occasionally  it  is  partially  covered  by  the  thyroid  gland. 

Deep  Relcdions. — The  common  carotid  artery  lies  directly  in  front  of 
the  cervical  vertebme,  separated  from  them  by  the  longus  colli  and  the 
rectus  capitis  anticus  major  muscles.  The  interval  between  the  artery 
and  the  transverse  processes  of  the  vertebrae  being  small,  compression 
backward  in  this  situation  to  a  great  extent  controls  the  flow  of  blood 
through  the  vessels.  In  the  median  line  the  vessel  is  related,  as  it 
passes  from  below  upward,  with  the  trachea,  thyroid  gland  (the  gland 
at  times  overlapping  the  artery),  larynx,  oesophagus,  and  pharynx. 

Variations. — Normally,  the  common  carotid  artery  gives  off  no 
branches,  and  it  is  of  the  same  calibre  from  its  commencement  to  its 
bifurcation.  At  other  times  either  the  superior  or  inferior  thyroid 
artery  may  arise  from  it,  the  artery  being  reduced  in  size  above  the 
branches.  The  division  of  the  common  carotid  into  the  external  and 
internal  carotids  may  take  place  as  high  or  higher  than  the  hyoid  bone, 
or  it  may  bifurcate  lower  down  than  its  normal  position  ;  the  common 
carotid  may  be  entirely  absent,  when  the  external  and  internal  caro- 
tids will  generally  arise  directly  from  the  aorta.  At  times,  however, 
the  right  common  carotid  may  arise  directly  from  the  aorta  alone  or 
in  conjunction  with  the  left — a  condition  common  in  some  of  the  lower 
animals. 

The  origin  of  the  left  common  carotid  is  more  varied  than  that  of  the 
right.  It  may  arise  in  either  of  the  following  ways  :  from  or  in  con- 
junction with  the  brachio-cephalic  or  subclavian,  or  by  a  common  trunk 
with  the  right  common  carotid,  when  the  subclavian  will  arise  directly 
from  the  aorta. 

Collateral  Circulation. — If  the  common  carotid  artery  be  ligated,  the 
blood  for  the  parts  usually  supplied  by  the  internal  carotid  will  be  car- 
ried by  the  vertebral  arteries  and  the  internal  carotid  of  the  opposite  side. 
These  arteries,  together  with  the  other  internal  carotid,  freely  communi- 
cate with  each  other  through  the  circle  of  Willis  at  the  base  of  the 
brain.  The  blood  for  the  parts  supplied  by  the  external  carotid  is  car- 
ried by  the  superior  and  inferior  thyroids,  which  freely  anastomose  ;  by 
the  occipital  and  deep  cervical,-  which  also  anastomose ;  and  by  the 
external  carotid  of  the  opposite  side  through  its  communication  with 
the  two  superior  thyroids,  the  lingual,  facial,  temporal,  internal  maxil- 
lary, and  occipital  arteries. 

The  External  Carotid  Artery  is  so  called  because  it  supplies  the 
external  portion  of  the  head  with  blood.  It  is  about  6  mm.  {\  inch) 
in  calibre,  and  arises  from  and  is  one  of  the  terminal  branches  of  the 
common  carotid.     This  origin  is  within  the  carotid  triangle  opposite 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,  ETC.  219 

the  upper  border  of  the  thyroid  cartilage.  From  this  point  it  passes  up 
the  neck  between  the  pharynx  and  the  muscles  resting  upon  tlie  vertebra 
in  this  region,  to  a  point  opposite  the  surgical  neck  of  the  lower  jaw, 
where  it  divides  into  two  terminal  branches,  the  internal  maxillary  and 
the  superficial  temporal.  As  it  ascends  the  neck  it  decreases  in  size,  the 
reduction  in  calibre  being  due  to  the  number  of  large  branches  it  gives 
off.  In  early  life  it  is  smaller  than  the  internal  carotid,  but  it  gradually 
increases  until  adult  life,  M'hen  both  arteries  are  of  the  same  size. 

Relations. — At  its  origin  the  external  carotid  artery  is  situated  at  the 
median  side  of  the  internal  carotid,  but  soon  becomes  superficial  to  that 
artery.  It  is  covered  by  the  skin,  the  platysma  myoides  and  stcrno- 
cleido-mastoid  muscles,  and  the  deep  fascia.  The  superior  laryngeal 
nerve  passes  behind  the  artery  in  this  situation.  Its  deep  relation  at 
its  commencement  is  with  the  pharynx  and  hyoid  bone.  From  this 
position  it  passes  up  internally  to  the  stylo-hyoicl  and  posterior  belly  of 
the  digastric  muscle  and  part  of  the  parotid  gland,  "which  separates  it 
from  the  back  part  of  the  ramus  of  the  jaw.  The  posterior  belly  of 
the  digastric  muscle  is  a  good  guide  in  the  ligation  of  the  artery. 
Throughout  its  upper  portion  it  is  separated  from  the  internal  carotid 
by  the  stylo-glossus  and  stylo-pharyngeus  muscles,  the  glosso-pharyn- 
geal  nerve,  and  part  of  the  parotid  gland. 

The  external  carotid  artery  is  usually  unaccompanied  by  a  vein, 
although  the  temporo-maxillary  vein  crosses  it  within  the  parotid  gland, 
the  anterior  division  of  the  temporo-maxillary  vein  passing  downward 
to  the  facial.  The  facial  and  lingual  veins  cross  the  artery  below  the 
digastric  muscle  on  their  way  to  join  the  internal  jugular.  Higher  up, 
in  the  substance  of  the  parotid  gland,  the  artery  is  crossed  by  the  facial 
nerve,  the  hypoglossal  nerve  crossing  it  just  below  the  posterior  belly 
of  the  digastric  muscle. 

Branches  of  the  External  Carotid  Artery. — The  external  carotid  artery 
in  its  ascent  through  the  neck  gives  off  eight  branches.  Their  names, 
in  great  measure,  indicate  their  distribution.  Three  of  the  branches — 
viz.  the  superior  thyroid,  lingual,  and  facial — pass  anteriorly;  two — viz. 
the  occipital  and  posterior  auricular — pass  posteriorly ;  one,  the  ascend- 
ing pharyngeal,  passes  internally  :  it  terminates  in  two  branches,  the 
superficial  temporal  and  the  internal  maxillary. 

Variations. — The  general  variations  in  the  origin  of  the  external 
carotid  artery  have  been  mentioned  under  the  head  of  the  common 
carotid.  Other  variations  are  caused  by  the  manner  in  w^hich  its 
branches  are  given  off.  The  external  carotid  may  at  times  be  entirely 
M-anting.  When  this  is  the  case  the  different  branches  which  are  usually 
given  off  by  it  arise  from  a  common  trunk  which  represents  the  inter- 
nal and  external  carotids.  The  superior  thyroid  and  the  lingual  arteries 
may  arise  from  a  single  branch,  instead  of  two  separate  branches,  or 
the"  lingual  and  facial  or  the  superior  thyroid,  lingual,  and  facial  may 
originate  in  a  similar  manner.  The  superior  thyroid  may  also  arise 
from  the  common  carotid.  The  external  carotid  artery  occasionally 
divides  at  the  angle  of  the  jaw,  reuniting  again  near  the  neck  of  the 
inferior  maxilla  to  form  the  temporal  artery. 

The  Superior   Thyroid  Artery  is  the  first  anterior  branch   of  the 


220  ANATOMY. 

external  carotid.  It  is  about  3^  mm.  (|  inch)  in  calibre,  and  arises 
close  to  tlie  bifurcation  of  the  common  carotid,  on  a  level  with  or 
slightly  below  the  great  cornu  of  the  hyoid  bone.  It  is  very  super- 
ficially located  within  the  carotid  triangle.  It  passes  slightly  upward 
and  forward  at  first,  after  which  it  passes  forward  and  downward,  to 
the  upper  margin  of  the  thyroid  cartilage,  forming  an  arch.  Here  it 
passes  beneath  the  omo-hyoid,  sterno-hyoid,  and  sterno-thyroid  muscles, 
supplying  them  witli  branches,  and  is  finally  distributed  to  the  thyroid 
gland,  breaking  up  into  numerous  terminal  branches,  which  anastomose 
quite  freely  with  the  terminal  branches  of  the  inferior  thyroid. 

The  Transverse  Artery,  which  is  not  universal  in  its  existence,  is  one 
of  the  terminal  branches  that  pass  along  the  upper  border  of  the  isth- 
mus of  the  thyroid  body  within  its  capsule.  The  transverse  artery  may 
be  of  large  size,  and  give  olf  branches  that  overlie  the  isthmus. 

The  Superior  Thyroid  Artery  gives  off  tlie  following  branches :  the 
hyoid,  superficial  descending  or  sterno-mastoid,  superior  laryngeal,  and 
crico-thyroid. 

The  Hyoid  or  Inferior  Hyoid  Artery  is  a  small  vessel  that  passes 
inward  from  the  superior  thyroid  along  the  under  surface  of  the  hyoid 
bone  beneath  the  thyro-hyoid  muscle.  It  gives  off  branches  that  sup- 
ply the  muscles  attached  to  the  under  surface  of  the  hyoid  bone,  and 
anastomoses  with  similar  branches  of  the  opposite  side. 

The  Superficial  Descending  or  Sterno-mastoid  Artery  passes  downward 
across  the  sheath  of  the  common  carotid  artery.  It  is  of  importance  to 
remember  this  fact  in  operations  for  the  ligation  of  the  common  carotid 
in  this  region.  This  artery  is  distributed  to  the  following  muscles  :  the 
omo-hyoid,  sterno-hyoid,  sterno-thyroid,  sterno-cleido-mastoid,  and  infe- 
rior constrictor  of  the  pharynx. 

The  Superior  Laryngeal  Artery  is  the  largest  of  the  several  branches 
of  the  superior  thyroid,  being  about  2  mm.  (yL.  inch)  in  calibre.  It 
extends  inward,  accompanied  by  the  superior  laryngeal  nerve  ;  jiasses 
under  the  thyro-hyoid  muscle  to  the  thyro-hyoid  membrane ;  pierces 
this  membrane  and  enters  the  larynx,  where  it  separates  into  two  divis- 
ions, superior  and  inferior. 

The  Superior  Dirision  supplies  the  posterior  surface  of  the  epiglottis 
and  its  mucous  membrane. 

The  Inferior  Division  supplies  the  intrinsic  muscles  of  the  larynx  and 
its  mucous  membrane. 

The  Crico-thyroid  Branch  is  a  small  artery  about  -^  to  1  mm.  (J^-  to 
^L-  inch)  in  calibre.  It  passes  across  the  crico-thyroid  membrane,  and 
anastomoses  with  the  corresponding  artery  of  the  other  side.  The 
position  of  this  artery  gives  it  importance,  on  account  of  the  fact  that 
hemorrhage  often  occurs  from  its  division  in  the  operation  of  laryn- 
gotomy. 

Variations. — The  superior  thyroid  artery  may  be  larger  or  smaller 
than  usual.  AVhen  this  difference  exists  either  way,  one  or  more  of  the 
other  three  thyroid  arteries  will  be  found  to  be  increased  or  diminished 
in  size.  Occasionally  it  is  found  to  arise  in  common  with  the  lingual 
or  facial,  or  both.  It  may  also  be  a  division  of  the  common  carotid. 
The  branch  of  this  artery  which  supplies  the  sterno-cleido-mastoid  mus- 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,  ETC.  221 

cle  is  sometimes  a  separate  and  distinct  branch  of  the  common  carotid. 
It  occasionally  gives  origin  to  the  ascending  pharyngeal  artery,  and  its 
hyoid  branch  is  often  very  small  or  entirely  absent.  The  snperior 
laryngeal  branch  also  often  arises  from  the  external  carotid,  and  occa- 
sionally from  the  common  carotid,  and  may  pierce  the  crico-thyroid 
space  or  pass.throngh  a  foramen  in  the  thyroid  cartilage.  The  crico- 
thyroid branch  is  sometimes  of  considerable  size,  and  may  interchange 
with  a  branch  to  the  thyroid  body  or  a  division  of  the  inferior  thyroid 
artery. 

The  Lingual  Artery. 

The  lingual  artery  is  about  3|^  mm.  (^  inch)  in  calibre,  and  is  the 
second  anterior  branch  of  the  external  carotid.  It  arises  Mithin  the 
carotid  triangle  between  the  snperior  thyroid  and  facial  arteries,  and 
nearly  opposite  the  great  cornu  of  the  hyoid  bone.  It  passes  upward  a 
short  distance,  then  turns  downward,  forming  a  concavity  which  is  crossed 
by  the  hypoglossal  nerve.  Thence  it  extends  beneath  the  digastric  and 
stylo-hyoid  muscles  to  reach  the  great  cornu  of  the  hyoid  bone,  running 
parallel  with  it,  under  cover  of  the  hyo-glossus  muscle,  to  a  point  near 
its  anterior  border,  where  it  turns  upward  and  passes  to  the  under  sur- 
face of  the  tongue,  through  which  it  extends  to  the  tip,  where  it  termi- 
nates in  the  ranine  artery. 

Relations. — This  artery  is  divided  into  four  portions,  according  to 
the  regions  through  which  it  passes.  The  first  or  superficial  portion 
is  wholly  within  the  carotid  triangle,  and  is  covered  by  the  skin, 
platysma  myoides,  and  fascia  of  the  neck,  and  rests  upon  the  connective 
tissue  and  middle  constrictor  muscle  of  the  pharynx.  The  second  or 
horizontal  portion  is  covered  externally  by  the  sterno-hyoid,  digastric, 
and  the  greater  part  of  the  hyo-glossus  muscle,  the  hypoglossal  nerve 
passing  to  the  outer  side  of  the  muscles  :  this  portion  of  the  artery 
rests  uj)on  the  middle  constrictor  muscle  of  the  pharynx.  The  third  or 
ascending  portion  is  that  part  which  extends  upward  to  the  under  sur- 
face of  the  tongue  :  it  passes  between  the  hyo-glossus  and  genio-glossus 
muscles.  The  fourth  or  ranine  portion  is  generally  in  relation  whh  the 
intrinsic  muscles  of  the  anterior  part  of  the  tongue.  Near  its  termina- 
tion it  becomes  quite  superficial  and  communicates  with  its  fellow  of  the 
opposite  side. 

The  branches  of  the  lingual  artery  are  the  hyoid,  dorsalis  lingual, 
sublingual,  and  ranine  arteries. 

The  Hyoid  or  Superior  Hyoid  Artery  is  the  first  branch  of  the  lin- 
gual, and  arises  within  the  carotid  triangle.  It  passes  to  the  upper 
border  of  the  hyoid  bone,  supplying  the  bone,  the  muscles  attached 
to  its  upper  portion,  and  the  fiJDro-adipose  tissue  between  the  bone 
and  the  base  of  the  epiglottis. 

The  Dorsalis  Lingual  Artery,  which  is  occasionally  replaced  by  sev- 
eral smaller  ones,  arises  from  the  second  ]5art  of  the  lingual  artery  as  it 
passes  beneath  the  hyo-glossus  muscle.  It  extends  to  the  upper  surfiice 
of  the  tongue,  sup])lies  the  mucous  membrane  of  this  surface,  as  Avell  as 
the  substance  of  the  organ,  and  communicates  with  its  fellow  of  the 


222  ANATOMY. 

other  side.  Occasionally  the  artery  will  be  found  to  be  exceedingly 
large.  When  this  is  the  case,  in  addition  to  the  structures  already 
mentioned  it  usually  supplies  the  stylo-glossus  muscle,  the  tonsils, 
epiglottis,  and  soft  palate. 

The  Subl'mgiud  Artery  is,  in  reality,  one  of  the  terminal  branches  of 
the  lingual,  the  ranine  artery  being  the  other.  It  arises  from  the 
lingual  at  a  point  opposite  the  anterior  margin  of  the  hyo-glossus 
muscle.  From  this  margin  it  passes  forward  between  the  genio-glossus 
muscle  and  the  sublingual  gland,  supplying  the  gland,  the  mucous 
membrane  of  the  floor  of  the  mouth,  the  alveolo-lingual  groove,  and 
gums ;  also  extending  to  the  myhj-hyoid  and  other  muscles  of  this 
reo-ion. 

The  Ranine  Artery  is  one  of  the  terminal  branches  of  the  lingual.  It 
arises  opposite  the  anterior  margin  of  the  hyo-glossus  muscle,  and  passes 
in  a  tortuous  course  within  the  structure  of  the  muscle  to  a  point  near 
the  tip  of  the  tongue,  where  it  is  quite  superficial.  In  its  course  it  gives 
off  numerous  branches  and  communicates  with  the  corresponding  artery 
of  the  opposite  side.  This  anastomosis  is  the  most  important  between 
the  branches  of  the  lingual  artery,  the  others  being  capillary  in  cha- 
racter. 

The  nutrition  of  the  two  halves  of  the  tongue  supplied  by  each  lin- 
gual artery  and  its  branches  is  comparatively  independent.  The  ranine 
artery  being  so  superficially  situated,  and  so  close  to  tlie  fraenum  linguse, 
there  is  some  danger  of  cutting  it  in  the  operation  for  so-called  tongue- 
tie. 

Variations. — The  lingual  artery  may  arise  in  conjunction  with  the  facial 
or  superior  thyroid,  or  the  tliree  arteries  may  arise  as  a  common  trunk 
from  the  external  carotid.  Occasionally  it  arises  from  the  internal  max- 
illary artery.  Sometimes  it  accompanies  the  hypoglossal  nerve  along 
the  outer  margin  of  the  hyo-glossus  muscle.  The  artery  may  be 
entirely  absent,  and  its  place  supplied  by  branches  from  the  internal  max- 
illary, submental  branches  of  the  facial,  or  by  the  corresponding  artery 
of  the  other  side.  It  occasionally  gives  origin  to  the  ascending  pha- 
ryngeal artery,  and  the  superior  laryngeal,  the  submental,  and  the  ascend- 
ing palatine  have  been  known  to  spring  from  it.  Sometimes  the  supe- 
rior hvoid  branch  of  the  lingual  is  entirely  absent.  When  this  is  the 
case  its  place  is  supplied  by  the  inferior  hyoid.  The  sublingual  branch 
of  the  lingual  artery  arises  at  times  from  the  facial,  and  reaches  its  des- 
tination by  piercing  the  mylo-hyoid  muscle. 

The  Facial  or  External  Maxillary  Artery. 

The  Facial  or  External  Maxillary  Artery  (Fig.  108)  is  about  3-^  mm. 
(^  inch)  in  calibre,  and  arises  from  the  external  carotid  within  the 
carotid  triangle  a  little  above  the  lingual  artery.  It  extends  upward, 
forward,  and  inward,  passes  beneath  the  posterior  belly  of  the  digas- 
tric and  the  stylo-hyoid  muscles,  and  enters  the  posterior  part  of 
the  submaxillary  triangle.  It  then  passes  forward  within  the  sub- 
stance of  the  submaxillary  muco-salivary  gland,  extending  parallel 
with  the  base  of  the  lower  jaw,  close  to  the  mylo-hyoid  muscle.     Leav- 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,   ETC. 


223 


ing  the  gland,  it  makes  a  sharp  turn  upward  over  the  body  of  the 
inferior  maxillary  bone,  curving  through  a  notch  just  in  front  of  the 
insertion  of  the  masseter  muscle.  From  its  origin  to  this  point,  where 
it  curves  over  the  body  of  the  inferior  maxilla,  it  constitutes  the  first 
or  cervical  division  of  the  artery.  As  it  passes  over  the  body  of  the 
jaw  the  artery  is  quite  superficial,  being  covered  only  by  the  skin  and 
platysma  myoides  muscle.     In  this  situation  the  pulsation  of  the  artery 

Fig.  lOS. 


The  Arteries  of  the  Face  and  Scalp. 

can  be  distinctly  felt,  and  the  flow  of  blood  to  parts  above  can  be  con- 
trolled by  direct  pressure  of  the  artery  against  the  bone.  This  is  like- 
wise a  favorable  location  for  the  ligation  of  the  artery.  From  the  base 
of  the  jaw  it  passes  obliquely  upward  and  forward  toward  tlie  inner 
canthus  of  the  eye,  w^here  it  terminates  in  the  angular  artery  and  com- 
municates with  branches  of  the  ophthalmic  artery.  From  the  body  of 
the  jaw  it  passes  between  the  masseter  and  depressor  anguli  oris  muscles 
to  near  the  angle  of  the  mouth.    It  then  extends  beneath  the  two  zygc- 


224  ANATOMY. 

matici  muscles  and  the  levator  labii  superioris,  passing  over  the  buccina- 
tor, the  levator  anguli  oris,  and  occasionally  over  the  levator  labii  supe- 
rioris proprius.  It  terminates  either  upon  the  levator  labii  superioris, 
alffique  nasi,  or  within  the  substance  of"  the  muscle. 

The  facial  artery  is  very  tortuous  both  in  the  neck  and  in  the  face ; 
for  if  the  course  was  a  straight  line  from  its  origin  to  its  termination 
the  artery  by  its  inelasticity  would  bind  the  different  structures  through 
or  over  which  it  passes,  interfering  with  the  free  action  of  the  jaws  and 
the  mobility  of  the  lips  and  muscles  of  expression.  The  same  winding 
of  this  vessel  in  the  neck  permits  free  movement  of  the  larynx  and  its 
associate  parts,  and  prevents  interference  with  deglutition. 

The  Facial  Vein  is  superficial  to  and  accompanies  the  facial  artery 
throughout  its  course ;  part  of  the  submaxillary  gland  is  interposed 
between  them  in  the  neck.  As  they  cross  the  jaw  the  artery  and  vein 
are  in  close  proximity,  but  in  the  face  they  are  separated  by  the  zvgo- 
maticus  minor  and  the  levator  labii  superioris.  Branches  of  the  fiujial 
nerve  pass  over  the  artery  as  it  crosses  the  infraorbital  nerve ;  these 
latter  are  usually  separated  by  the  elevator  muscle  of  the  uj^per  lip. 

Branches  of  the  Facial  Artery. — The  branches  of  the  facial  artery 
are  divided  into  two  sets,  cervical  and  facial,  according  to  the  locality 
through  which  they  extend.     They  are  as  follows : 

Cervical  Branches.  Facial  Branches. 

Inferior  or  ascending  palatine,  Inferior  labial, 

Tonsillar,  Inferior  coronary, 

Glandular,  Superior  coronary, 

Submental,  Lateralis  nasi. 

Angular. 
The  Inferior  or  Ascending  Palatine  Artery  is  the  first  branch  of  the 
facial,  though  in  some  instances  it  arises  from  the  external  carotid.  It 
extends  upward,  and  passes  beneath  the  stylo-glossus  and  stylo-pharyn- 
geus  muscles,  above  which  it  will  be  found  running  between  the  internal 
pterygoid  and  the  walls  of  the  pharynx  to  a  level  with  the  soft  palate. 
In  its  course  it  distributes  branches  to  the  surrounding  muscles,  the 
tonsils,  and  the  Eustachian  tube.  Near  the  levator  palati  muscle  it 
divides  into  two  branches,  superior  aiid  inferior.  The  superior  sup]ilies 
the  levator  palati  muscle,  the  soft  palate,  and  the  palatine  glands.  The 
inferior  supplies  the  tonsils  and  anastomoses  with  the  tonsillar  artery. 
These  two  vessels  also  communicate  with  the  posterior  palatine  branches 
of  the  inferior  maxillary  arterv. 

The  Tonsillar  Artery,  a  branch  of  the  facial,  extends  upward  super- 
ficially to  the  stylo-glossus  muscles,  passes  through  a  perforation  in  the 
superior  constrictor  of  the  pharynx,  and  gives  off  small  branches  to  the 
tonsils,  side  of  the  tongue,  and  mucous  membrane  of  the  surrounding 
parts.  When  the  tonsillar  branch  of  the  facial  artery  is  absent,  the 
])arts  to  which  it  is  generally  distributed  are  sujiplied  by  the  descending 
palathie  or  ascending  pharyngeal  branches,  or  both. 

The  Ghinchilar  Arteries  (submaxillary)  are  several  short  branches 
from  the  facial  wliich  are  distributed  to  the  muco-salivary  submaxillary 
gland.     Some  of  these  branches  extend  through  the  substance  of  the 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,  ETC.  225 

gland,  and  are  distributed  to  the  stylo-hyoid,  internal  pterygoid,  and 
masseter  muscles. 

llie  Submental  Artery  is  the  largest  and  most  important  of  the  cervi- 
cal branches  of  the  facial  artery.  It  arises  at  a  point  between  the 
submaxillary  gland  and  the  position  of  the  facial  artery  as  it  turns 
upward  across  the  body  of  the  jaw  to  reach  the  face.  Occasionally  it 
arises  from  the  sublingual  artery ;  it  extends  in  a  continuous  line  from 
the  facial  artery  below  the  base  of  the  jaw  to  its  symphysis,  where  the 
artery  turns  upward  to  the  chin,  supplying  the  muscles  of  this  region 
and  anastomosing  with  the  inferior  labial  and  mental  arteries  and  its 
fellow  of  the  opposite  side.  The  mylo-hyoid  muscle  is  situated  on  its 
inner  side,  branches  of  the  artery  perforating  the  muscle  and  anastomos- 
ing with  the  sublingual  artery.  In  its  course  it  distributes  branches  to 
the  neighboring  tissues. 

The  Inferior  Labial  Artery  is  the  first  of  the  facial  branches  of  the 
facial  artery.  It  arises  soon  after  the  artery  reaches  the  face,  and  passes 
forward  beneath  the  depressor  anguli  oris  muscle.  Its  branches  are 
distributed  to  the  integument  and  muscles  of  the  lower  lip,  and 
anastomose  with  the  inferior  coronary,  submental,  and  mental  arteries. 

The  Inferior  Coronary  Artery  supplies  the  lower  lip.  It  arises  at 
the  outer  margin  of  the  depressor  anguli  oris  muscle,  a  little  below  the 
level  of  the  angle  of  the  mouth,  passes  a  short  distance  upward  and 
inward  beneath  the  depressor  anguli  oris,  depressor  menti,  and  the 
orbicularis  oris  muscles,  and  between  the  latter  muscle  and  the  mucous 
membrane  close  to  the  free  margin  of  the  lip.  Its  branches  supply  the 
muscles  and  mucous  membrane  of  this  region  and  the  labial  glands, 
anastomosing,  with  its  fellow  of  the  opposite  side,  with  the  inferior 
labial,  and  the  mental  branch  of  the  inferior  dental  artery. 

The  Superior  Coronary  Artery  supplies  the  upper  lip  and  arises 
beneath  the  zygomaticus  major  muscle.  It  is  larger  and  more  tortuous 
than  the  inferior  coronary,  and  passes  transversely  between  the  mus- 
cles and  mucous  membrane  of  the  upper  lip  close  to  its  free  margin, 
inosculating  with  the  corresponding  artery  of  the  opposite  side.  It 
supplies  the  muscles,  mucous  membrane,  and  labial  glands  of  the  upper 
lip,  and  gives  oif  two  or  three  branches  which  pass  to  the  nose.  One, 
the  artery  of  the  septum,  passes  along  the  columna  nasi  as  far  as  the 
tip  of  the  nose,  and  supplies  the  septum.  Another  branch  supplies  the 
alse  of  the  nose. 

The  inferior  and  su])erior  coronary  arteries  occasionally  arise  as  a 
common  trunk.  If  either  or  both  are  smaller  than  is  generally  the 
case,  the  arteries  of  the  opposite  side  are  correspondingly  increased  in 
size.  It  is  by  reason  of  their  free  anastomosis,  with  each  other  that 
they  receive  the  name  "coronary  arteries,"  though  this  anastomosis  is 
not  always  present. 

The  Lateral  Nasal  Artery  arises  from  the  facial  as  it  ascends  along 
the  side  of  the  nose.  Occasionally  this  artery  is  replaced  by  two  or 
three  smaller  arteries.  The  branches  of  the  lateral  nasal  supply  the 
wing  and  dorsum  of  the  nose,  and  anastomose  with  the  nasal  branch  of 
the  ophthalmic,  infraorbital,  artery  of  the  septum,  and  corresponding 
artery  of  the  opposite  side. 

Vol.  I.— 1 5 


226  ANATOMY. 

The  Angular  Artery  is  properly  the  continuation  of  the  facial.  It 
ascends  between  the  inner  canthus  of  the  eye  and  the  nose,  and  its 
branches  supply  tlie  tissues  in  this  region,  including  the  lachrymal 
sac.  It  anastomoses  with  the  infraorbital  and  the  nasal  branch  of  the 
ophthalmic. 

Variations. — The  facial  artery  may  arise  in  conjunction  with  the 
lingual  and  superior  thyroid,  and  it  may  also  have  its  origin  above  the 
carotid  triangle.  When  this  is  the  case,  it  descends  to  its  normal  posi- 
tion below  the  jaw.  It  may  interchange  with  the  internal  maxillary 
(deep  facial)  artery.  It  varies  in  size  and  distribution.  Rare  instances 
are  recorded  where  the  artery  has  not  passed  upon  the  face,  but  has  ter- 
minated in  the  submental.  At  times  it  extends  in  the  face  only  far 
enough  to  supply  the  lower  lip,  and  it  frequently  fails  to  give  olf  the 
lateral  nasal  and  angular  branches.  When  the  facial  artery  is  abnor- 
mallv  short,  and  fails  to  extend  to  its  usual  termination  upon  the 
face,  the  blood-supply  is  received  through  the  enlargement  of  the  nasal 
branch  of  the  ophthalmic  and  branches  of  the  transverse  facial  (a  divis- 
ion of  the  temporal  artery),  or  through  one  or  more  of  the  terminal 
branches  of  the  internal  maxillary.  In  cases  where  any  of  these  arteries 
are  small  in  size  or  entirely  absent  the  facial  artery  may  be  increased 
in  size  to  supply  the  deficiency.  Occasionally,  while  in  the  neck  the 
facial  may  give  off  a  branch  to  supply  the  sublingual  gland,  the  gland 
in  such  case  not  receiving  its  usual  supply  from  the  lingual. 

The  Occipital  Artery. 

The  occipital  artery  is  about  3|-  mm.  (|  inch)  in  calibre,  and  arises 
from  the  surface  of  the  external  carotid,  opposite  to,  or  slightly  above, 
the  facial.  From  this  origin,  which  is  beneath  the  sterno-cleido-mas- 
toid  and  the  posterior  belly  of  the  digastric  muscle,  it  passes  upward 
and  backward,  and  is  covered  by  the  posterior  belly  of  the  digastric  and 
the  stylo-hyoid  muscle  and  a  portion  of  the  parotid  gland.  The  hypo- 
glossal nerve  crosses  it  on  its  outer  side.  It  then  passes  to  the  outside 
of  the  internal  jugular  vein,  the  pneuraogastric  and  spinal  accessory 
nerves,  to  an  interspace  between  the  transverse  process  of  the  atlas  and 
the  mastoid  process  of  the  temporal  bone.  When  it  reaches  the  base  of 
the  skull  it  is  directed  backward,  following  the  occipital  groove  situated 
to  the  inner  side  of  the  digastric  fossa  on  the  temporal  bone.  It  lies 
beneath  the  muscles  attached  to  the  mastoid  process,  and  above  the 
superior  oblique,  complexus,  and  rectus  posticus  major  muscles.  When 
it  reaches  the  extremity  of  the  groove  it  turns  upward,  passing  througli 
the  trapezius  muscle,  then  over  the  occiput,  being  distributed  to  the 
structures  in  this  region,  and  anastomoses  with  the  temporal  artery  and 
corresponding  artery  of  the  opposite  side. 

The  branches  of  the  occipital  artery  are — 

1.  The  muscular  ;  4.  Posterior  meningeal ; 

2.  The  auricular  ;  5.  Mastoid  ; 

3.  Descending  cervical ;  6.  Superficial  or  cranial. 

The  Muscular  Arteries  consist  of  several  small  branches  which  supply 
the  posterior  belly  of  the  digastric,  the  stylo-hyoid,  splenius  capitis,  and 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,   ETC.  227 

trachelo-mastoid  ;  a  branch  somewhat  hirger  tlian  the  rest  supplies  the 
sterno-cleido-mastoid  muscle.  This  branch  usually  arises  a  little  above 
the  origin  of  the  occipital  artery,  though  it  may  arise  from  the  external 
carotid. 

The  Auricular  Artery  is  a  small  branch  which  supplies  the  auricle  and 
the  tissues  near  the  mastoid  process.     This  branch  is  not  ahvavs  present. 

The  Descending  Cervical,  or  Ramus  Cerricularis  Princeps  Artery,  is 
of  large  size,  and  arises  beneath  the  splenius  capitis  muscle.  Soon  after 
its  origin  it  divides  into  two  branches,  superficial  and  deep.  The  super- 
ficial branch  perforates  the  splenius  muscle,  supplying  it  and  the  trape- 
zius. The  deep  branch  passes  beneath  the  com})lexus  and  semi-sj)inalis 
colli,  and  inosculates  with  the  vertebral  and  the  deep  branch  of  the 
superior  intercostal.  Through  the  anastomoses  of  these  arteries  a  col- 
lateral circulation  is  maintained  after  the  ligation  of  either  the  common 
carotid,  external  carotid,  or  subclavian  arteries. 

The  Posterior  or  Meningeal  Branch  arises  from  the  occipital,  passes 
up  along  the  internal  jugular  vein,  and  enters  the  brain-case  through 
the  jugular  foramen  ;  it  supplies  the  posterior  portion  of  the  dura  mater. 
This  artery  is  not  always  present. 

The  3Iastoid  Artery  is  a  small  branch  from  the  occipital,  which  enters 
the  mastoid  foramen  of  the  temporal  bone ;  it  supplies  the  diploe,  walls 
of  the  mastoid  cells  and  lateral  sinus,  and  the  dura  mater  in  the  occip- 
ital fossa. 

The  Superficial  or  Cranial  Arteries  are  terminal  branches  of  the 
occipital,  and  pass  between  the  integument  and  the  occipital  muscle, 
supplying  the  structures  in  this  region.  They  anastomose  freely  with 
each  other,  with  the  corresponding  artery  of  the  opposite  side,  and  the 
posterior  auricular  and  superficial  temporal  arteries. 

Variations. — The  occipital  occasionally  arises  from  the  internal 
carotid  or  in  conjunction  with  the  facial  or  from  the  cervical  Vn'anch 
of  the  inferior  thyroid.  Its  direction  also  may  vary :  instead  of  pass- 
ing to  the  median  side  of  the  trachelo-mastoid  muscle,  it  may  extend 
laterally.  It  occasionally  divides  into  a  larger  and  smaller  branch,  the 
smaller  assuming  the  usual  direction  of  the  artery,  whik  the  larger 
passes  superficially  to  the  sterno-cleido-mastoid  muscle.  The  stylo- 
mastoid artery  occasionally  arises  from  the  occipital  instead  of  the  pos- 
terior auricular  artery. 

The  Posterior  Auricular  Artery, 

The  posterior  auricular  artery  arises  from  the  external  carotid  nearly 
opposite  the  apex  of  the  styloid  process  of  the  temporal  bone,  above  the 
digastric  and  stylo-hyoid  muscles.  It  is  about  2  mm.  (J^  i"<^"h)  in  cali- 
bre ;  it  extends  obliquely  upward  and  backAvard  beneath  the  ]3arotid 
gland,  and  passes  up  the  styloid  process,  where  it  is  crossed  by  the 
facial  nerve.  It  then  ascends  between  the  cartilage  of  the  ear  and  the 
mastoid  process  of  the  temporal  bone,  becomes  superficial,  and  divides 
into  two  terminals,  the  auricular  and  the  mastoid. 

The  branches  of  the  posterior  auricular  artery  are  the  stylo-mastoid 
and  the  auricular. 


228  ANATOJ\IY. 

The  Stijlo-mastokl  Artery  is  long  and  slender,  and  enters  the  stylo- 
mastoid foramen  in  the  temporal  bone,  the  facial  nerve  passing  out  by 
the  same  (opening.  It  gives  off  branches  which  supply  the  mastoid  cells, 
the  stapedius  muscle,  the  tympanum,  and  the  semicircular  canals  of  the 
internal  ear.  The  continuation  antl  termination  of  the  stylo-mastoid 
artery  are  very  small ;  it  extends  forward  ^vithin  the  aquseductus  Fal- 
lopii,  anastomosing  with  the  petrosal  branch  of  the  middle  meningeal, 
which  is  itself  a  branch  of  the  internal  maxillary.  In  young  subjects 
the  artery  that  supplies  the  tympanum  comnumicates  with  the  tympanic 
branch  of  the  internal  maxillary,  thus  forming  a  vascular  circle  around 
the  tympanic  membrane,  from  which  delicate  vessels  concentrate  to 
supply  that  structure. 

The  Auricular  Artery,  the  other  branch  of  the  posterior  auricular, 
ascends  behind  the  ear  and  distributes  branches  to  the  retrahens  aurem 
muscle,  the  posterior  portion  of  the  temporal  region,  and  skin  over  the 
mastoid  process;  two  branches  to  the  auricle  supply  both  the  inner  and 
outer  surface  of  the  pinna.  Besides  these,  the  posterior  auricular  artery 
gives  off  small  muscular  twigs  which  supply  the  digastric,  stylo-hyoid, 
sterno-cleido-raastoid,  and  occipital  muscles,  the  integument,  and  the 
parotid  gland. 

Variations. — The  posterior  auricular  artery  sometimes  terminates  in 
the  stylo-mastoid.  It  is  occasionally  quite  small ;  sometimes  it  is  abnor- 
mally large,  and  takes  the  place  of  the  occi})ital  or  superficial  arteries. 
At  t'imes  it  is  given  off  by  the  occipital  artery,  and  the  transverse  facial 
may  arise  from  the  posterior  auricular. 


The  Ascending  Pharyngeal  Artery. 

TJie  ascending  pharyngeal  artery  is  the  smallest  of  the  eight  branches 
of  the  external  carotid.  It  is  long  and  slender,  and  extends  in  an  almost 
straight  course  from  its  origin  to  its  termination.  It  usually  arises  from 
the  posterior  jxirt  of  the  external  carotid,  from  a  half  to  one  inch  above 
the  origin  of  this  artery,  and  passes  upward  between  the  external  caro- 
tid artery  and  the  walls  of  the  pharynx.  The  branches  of  the  ascend- 
ing pharyngeal  artery  are  divided  into  three  sets,  as  follows : 

The  prevertebral. 

The  pharyngeal, 

The  meningeal. 
The  Prevertebral  Arteries  are  small  and  are  distributed  to  the  longus 
colli  and  rectus  capitis  anticus  muscles,  the  lymphatic  glands  of  the 
neck,  sympathetic  nerves  and  ganglia,  and  some  of  the  nerves  passing 
out  of  the  base  of  the  brain-case ;  finally  anastomosing  with  branches 
from  the  subclavian  artery. 

7V/C  P}iaryv(/eal  Arteries,  in  large  measure,  suj)ply  the  nuiscles  and 
mucous  mend)rane  of  the  pharynx.  The  middle  and  inferior  con- 
strictor muscles  are  usually  supj)lie(l  by  two  branches,  ^vhich  anastomose 
with  branches  of  the  inferior  thyroid  artery.  A  larger  and  more  con- 
stant branch  is  distributed  to  the  su])erior  constrictor  muscle  of  the 
pharynx,  and  furnishes  small  twigs  which  pass  to  the  Eustachian  tube, 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,   ETC.  229 

soft  palate,  palato-Eustaeliian,  and  levator  palati  muscles,  as  well  as  to 
the  tonsils.  The  artery  which  snp])lics  the  tonsils  and  the  soft  palate  is 
occasionally  quite  large,  and  divides  into  two  smaller  ones,  anterior  and 
posterior,  which  anastomose  with  the  corresponding  arteries  of  the  ojipo- 
site  side.  These  branches  supply  the  ])lace  of  the  inferior  palatine  artery 
when  that  is  wanting  or  abnormally  small. 

The  3Ien'mgeal  Arteries  are  two. or  three  in  number,  and  pass  into 
the  brain-case  through  the  jugular  and  anterior  condyloid  and  posterior 
lacerated  foramina  to  supply  the  dura  mater  of  the  brain. 


The  Superficial  Temporal  Artery. 

The  l^nperfickd  Temporary  Artery  is  about  3|-  mm.  (1  inch)  in  calibre.. 
It  is  the  smaller  of  the  two  terminal  branches  of  the  external  carotid, 
the  internal  maxillary  being  the  other.  It  originates  at  the  bifurcation 
of  the  external  carotid,  which  is  situated  a  little  below  the  level  of  the 
head  or  coudyle  of  the  inferior  maxilla,  and  opposite  the  upper  por- 
tion of  the  parotid  gland.  It  here  passes  u}>ward  in  a  continuous  line 
with  the  external  carotid,  over  the  posterior  root  of  the  zygomatic  pro- 
cess. This  is  a  favorite  point  to  apply  pressure  to  control  hemorrhage 
from  this  artery.  From  this  point  to  its  termination  it  lies  between  the 
skin  and  the  temporal  fascia.  It  is  usually  about  one  inch  in  length, 
and  terminates  in  tlie  anterior  and  posterior  superficial  tem2)oral  arteries, 
whicli  again  divide  into  several  branches. 

The  branches  of  the  superficial  temporal  artery  arc — 

The  glandular.  The  transverse  facial, 

The  muscular,  The  middle  temporal. 

The  articular,  The  anterior  tem])oral, 

The  anterior  auricular,  The  posterior  temjjoral. 

The  Gkvndidar  Arteries  are  several  small  branches  which  assist  in 
supplying  the  parotid  gland. 

The  3Iuscular  Arteries  are  one  or  two  small  branches  which  pass  to 
the  masseter  muscle. 

The  Articulutimi  Arteries  are  small  twigs  which  supply  the  temporo- 
maxillary  articulation. 

Tlie  Anterior  Auricular  Arteries  are  distributed  to  the  anterior  por- 
tion of  the  auricle  or  ])inna. 

The  Transverse  Facial  Artery  arises  from  the  temporal  where  that 
artery  is  imbedded  in  the  parotid  gland.  It  passes  horizontally  or  trans- 
versely forward  between  the  zygoma  and  the  parotid  duct,  and  rests  upon 
the  masseteric  fascia.  It  terminates  upon  the  fiice  by  breaking  u})  into 
three  or  four  branches,  which  are  distrilnited  to  the  orbicularis  ]ialpe- 
brarum,  zygomatici,  levator  anguli  oris  nuiscles  and  the  integument, 
anastomosing  with  the  facial,  buccal,  and  infraorbital  branches  of  the 
internal  maxillary  arteries.  It  also  sends  branches  to  the  parotid 
gland  and  masseter  muscle. 

The  3Ii(kUc  Temporrd  Artery  is  a  branch  of  the  sujierficial  temjioral, 
and  is  given  off  just  above  the  zygoma.  It  passes  inwardly  thrcnigh 
the  temporal  fascia  to  reach  a  groove  in  the  squamous  portion  of  the 


230  ANATOMY. 

temporal  bone,  in  Avhieli  it  re.^t.s.  It  gives  off  branches  to  the  temporal 
muscle^  and  communicates  with  the  deep  temporal  branches  of  the 
internal  maxillary  artery.  Occasionally  it  gives  off  an  orbital  branch, 
which  passes  along  the  superior  border  of  the  zygoma  between  the  two 
layers  of  the  temporal  fascia.  This  branch  is  distributed  to  the  orbicu- 
laris palpebrarum  muscle,  and  inosculates  with  the  lachrymal  and  pal- 
pebral branches  of  tlie  ophthalmic  artery. 

The  Anterior  Temporal  Aitery  is  the  larger  of  the  two  terminal 
brandies  of  the  superficial  temporal.  It  passes  obliquely  for\\ard  and 
slightly  upward  in  a  tortuous  manner  upon  the  temporal  fascia,  extend- 
ing slightly  above  the  orbicularis  palpebrarum  muscle,  and  terminates 
in  branches  which  anastomose  with  the  corresponding  artery  of  the 
opposite  side  and  the  supra(M'bital  and  frontal  branches  of  the  ophthal- 
mic artery.  Branches  are  also  given  off  which  supply  the  skin,  mus- 
cles, and  other  structures  in  the  anterior  temporal  region,  the  orbicularis 
palpebrarum  and  frontal  muscles. 

The  Posterior  Temporal  Artery  is  smaller,  and  its  course  is  straighter, 
than  the  anterior  temjxjral.  As  it  passes  upward  and  slightly  backward 
toward  the  vertex  of  the  skull,  it  rests  upon  the  temporal  fascia,  and 
anastomoses  with  ramifications  (jf  the  corresponding  artery  of  the  opjio- 
site  side.  It  also  gives  off  branches  posteriorly  M'hich  anastomose  witli 
the  occipital,  and  anteriorly  whicli  anastomose  with  the  anterior  tem- 
poral. It  supplies  the  skin  and  other  tissues  of  the  vertex  of  the 
skull. 

Variations. — Occasionally  the  anterior  temporal  artery  passes  verti- 
callv  over  the  vertex  of  the  skull,  giving  off  branches  which  anastomose 
with  the  occipital  artery.  The  transverse  facial  artery  may  arise 
directly  from  the  external  carotid  instead  of  from  the  superficial  tem- 
poral, and  is  sometimes  very  large,  supplying  the  place  of  the  facial 
arterv.  Occasionally  the  transverse  facial  is  double.  The  orbital 
brancli  may  be  of  large  size  and  sujiply  the  eyelids  and  part  of  the 
forehead,  and  communicate  with  the  supraorbital.  In  aged  people 
the  course  of  tlie  temporal  artery  will  be  found  to  be  more  tortuous 
than  in  early  life. 

The  Internal  Maxillary  or  Deep  Facial  Artery. 

The  Internal  3Iaxillary  (Fig.  lOll)  su])plies  all  the  deep  portions  of 
the  face,  including  the  teeth,  part  of  the  floor  of  the  mouth,  the 
palate,  the  nasal  chambers,  the  maxillary  sinus,  the  greater  portion 
of  the  ethmoidal  sinuses,  part  of  the  ])harvnx,  and  the  dura  mater 
of  the  brain.  It  is  the  larger  of  the  two  terminal  branches  of  the 
external  carotid,  being  about  5  nmi.  (1- inch)  in  calibre.  It  is  given 
off  from  the  external  carotid,  within  the  parotid  gland,  a  little  below 
and  behind  the  condyle  of  the  inferior  maxilla,  on  a  level  with  the 
lower  part  of  the  lobe  of  the  ear.  In  the  first  part  of  its  course  it 
passes  at  right  angles  to  the  external  carotid,  and  extends  forward 
in  a  tortuous  manner  between  the  inferior  maxillary  bone  and  the 
internal  lateral  ligament,  from  which  it  passes  obliquely  upward 
and  forward  upon  the  outer  surface  of  the  external  pterygoid  muscle 


BLOOD-VESSEL  SYSTE3I  OF  THE  HEAD,  ETC. 


231 


(occasionally  it  passes  on  the  inner  side),  nntil  opposite  the  space 
between  the  two  heads  of  this  nuiscle.  Here  it  tnrns  inward  between 
these  heads  into  the  spheno-maxillarv  fossa,  where  it  terminates  in 
various  branches  having  close  relation  with  the  spheno-palatine 
(Meckel's)  ganglion. 

For  facility  of  studying,  the  branches  of  this  artery  are  arranged 

Fig.  109. 


IPfffi/^c  •Palatini 

DesceneUntf  Pafafr'nt 
Falartna 


Plan  of  the  Branches 

Dee/i  TfTnfi. 

MlJdfe  MtntTtgeal 
Mmf-ng<a  Tarva 

Tvmfic 
Irjiricr  Denial- 


The  Internal  Maxillary  Artery  and  its  Branches. 

under  three  heads,  according  to  their  anatomical  relation  to  the  parts 
which  they  supply : 

Tlie  First  or  3IaxiUary  Division  extends  from  the  external  carotid  to 
the  internal  lateral  ligament,  and  gives  off  five  branches,  which  pass 
into  or  through  osseous  foramina.  These  branches  are  the  deep  auric- 
ular, tympanic,  middle  (or  great  meningeal),  small  meningeal,  and  the 
inferior  dental. 

The  Second  or  Pteryrfoicl  Division  extends  fi'om  the  internal  lateral 
ligament  to  the  point  at  which  the  artery  passes  through  the  space 


232  ANATOMY 

between  the  two  heads  of  the  external  pterygoid  muscle.  This  portion 
has  four  branches,  ^vhich  supply  the  masticatorv  and  buccinator  muscles. 
They  are  named,  according-  to  their  distribution,  the  deep  temporal, 
pterygoid,  masseteric,  and   buccal. 

The  Third  or  Spheno-maxillari/  Division  extends  from  the  inner  sur- 
face of  the  external  pterygoid  muscle  to  the  termination  of  the  artery 
in  the  spheno-palatine  fossa.  It  gives  off  six  branches,  each  passing 
into  or  througli  osseous  foramina.  They  are  likewise  named,  according 
to  their  course  or  the  parts  su])i)lied  by  them,  the  alveolar  (or  superior 
maxillary),  infraorbital,  descending  (superior)  palatine.  Vidian,  pterygo- 
palatine, and  nasal  or  spheno-palatine. 

ARTERIES   OF   THE  FIRST  DIVISION. 

The  Deep  Auricular  Branch  is  of  small  size,  occasionally  arising  in 
common  with  the  tympanic  branch,  but  usually  it  arises  just  external 
to  it,  and  perforates  the  anterior  wall  of  the  external  auditory  meatus. 
It  is  distributed  to  the  skin  and  the  external  portion  of  the  tympanic 
membrane. 

The  Ti/mpanic  Artery  is  the  second  and  one  of  the  smallest  branches 
of  tlie  internal  maxillary.  It  passes  to  the  tympanum  through  the  gle- 
noid fissure  (fissure  of  Glaser),  and  is  distributed  to  the  structures  of  the 
middle  ear  and  the  tympanic  membrane.  It  anastomoses  with  the  stylo- 
mastoid and  Vidian  arteries. 

The  Middle  or  Greed  3[eningeal  Artery  is  the  third  and  largest 
bran  ell.  It  is  also  the  largest  artery  supplying  the  dura  mater.  It  has 
a  calibre  of  about  2  mm.  (Jj  ii^t'h)  and  arises  from  the  upper  side  ol'the 
internal  maxillary,  passing  upward  behind  and  close  to  the  insertion  of 
the  external  pterygoid  muscle  through  a  loop  of  the  auriculo-teni])oral 
nerve,  and  reaches  the  brain-case  through  the  foramen  spiuosum  in  the 
spinous  process  of  the  great  wing  of  the  sphenoid  bone.  Within  the 
cranial  cavity  it  passes  in  the  direction  of  the  anterior  inferior  angle  of 
the  parietal  bones  along  a  groove  anterior  to  and  parallel  with  the 
sjiheno-scjuamosal  suture.  When  about  midway  of  the  suture  it  di- 
vides into  an  anterior  and  a  posterior  branch.  The  anterior  branch, 
the  larger  of  the  two,  passes  across  the  outer  and  upper  extremity  of 
the  great  wing  of  tlie  sphenoid  bone  to  the  anterior  inferior  angle  of  the 
parietal  l)one,  terminating  in  numerous  branches  which  extend  upward 
and  backward  toward  the  inter])arietal  suture.  Occasionally  the  grooves 
for  the  accommodation  of  this  artery  so  deeply  indent  the  bone  as  to  be 
eventually  built  over,  thus  forming  canals.  The  posterior  branch  of  the 
great  meningeal  passes  backward  and  upward  along  a  groove,  and  crosses 
the  squamous  portion  of  the  tem])r)ral  bone  to  the  posterior  half  of  the 
imrietal  bone,  where  it  usually  divides  into  two,  the  anterior  l)ranch 
ascending  toward  the  vertex,  while  the  other  branch  passes  backward 
toward  the  occipital  bone. 

The  great  meningeal  artery  before  passing  into  the  brain-case  supplies 
through  its  branches  a  portion  of  the  pterygoid  mus(^le  and  the  tissue  in 
proximity  to  the  foramen  spiuosum.  After  entering  the  cranium  it  sup- 
plies the  dura  mater,  the  bones,  the  diploe,  the  lachrymal   gland,  the 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,   ETC.  233 

ganglion  of  Gasser  of  the  fifth  pair  of  nerves,  and  passes  throngh  the 
hiatns  Fallopii  to  anastomose  with  the  stylo-mast oid  branch  of  the  pos- 
terior anricular  artery.  It  also  anastomoses  with  branches  of  the 
ophthalmic  artery. 

The  Small  3Ieningeal  Artery  is  a  branch  often  arising  from  the 
great  or  middle  meningeal  artery  before  it  enters  the  brain-case.  In 
some  instances  it  arises  from  the  upper  part  of  the  internal  maxillary 
artery,  and  passes  into  the  brain-case  through  the  oval  foramen  in  the 
great  wing  of  the  sphenoid  bone.  Before  entering  the  brain-case  its 
branches  supply  the  nasal  fossa  and  soft  palate.  After  passing  into  the 
cavity  of  the  skull  it  supplies  the  dura  mater,  bones  and  diploe  of  the 
middle  fossse,  and  the  ganglion  of  the  fifth  pair  of  nerves. 

The  Iriferio)'  Dental  Artery  arises  from  the  under  part  of  the 
internal  maxillary.  It  passes  downward  and  forward  between  the 
internal  lateral  ligament  and  the  neck  of  the  lower  jaw  to  the  posterior 
or  inferior  dental  foramen,  through  which  it  passes,  accompanied  by  the 
inferior  dental  nerve,  into  the  interior  dental  canal.  Traversing  this,  it 
terminates  at  the  anterior  or  mental  foramen  in  two  divisions,  known  as 
the  incisor  and  mental  branches.  A  small  twig  is  given  off  close  to  its 
origin  (sometimes  arising  from  the  internal  maxillary),  and,  with  the 
lingual  nerve,  is  distributed  to  the  mucous  membrane  of  the  mouth. 

TJie  Mylo-hyokl  Branch  is  given  off  from  the  inferior  dental  artery 
immediately  before  entering  the  posterior  dental  foramen.  It  descends 
into  the  mylo-hyoid  groove  with  the  nerve  and  vessels  of  the  same 
name,  and  is  distributed  to  the  under  surface  of  the  mylo-hyoid  muscle. 
The  portion  of  the  inferior  dental  artery  within  the  canal  gives  off 
numerous  small  branches  to  supj^ly  the  teeth  and  their  surroundings. 

The  Incisor  Branch  is  a  continuation  of  the  inferior  dental  artery, 
and  passes  forward  within  the  cancellated  structure  of  the  bone  to  sup- 
ply the  region  of  the  chin  and  the  anterior  teeth. 

2'he  Mental  Branch  passes  out  through  the  anterior  dental  or  men- 
tal foramen,  accompanied  by  the  nerve  of  the  same  name,  and  supplies 
the  soft  parts  in  the  region  of  the  chin,  finally  anastomosing  with 
branches  of  the  facial  artery. 

ARTERIES    OF   THE    SECOND   DIVISION. 

The  Deep  Temporal  Branches  of  the  internal  maxillary  are  two  in 
number,  anterior  and  posterior. 

The  Deep  Anterior  Temporal  is  situated  in  the  anterior  portion  of  the 
temporal  fossa,  advancing  up^\■ard  and  forward  along  the  temporo-sphe- 
noidal  suture  between  the  muscles  and  pericranium,  its  course  being 
indicated  by  the  groove  in  the  bone.  In  its  ascent  twigs  are  given  oft' 
to  the  temporal  muscle,  the  bone,  and  occasionally  to  the  di])loe.  Small 
branchlets  anastomose  with  the  other  temporal  arteries.  Oft'shoots  also 
pass  forward  through  the  small  foramina  in  the  malar  bone  to  anasto- 
mose with  the  lachrymal  branch  of  the  ophthalmic  artery. 

The  Deep)  Posterior  Temporal  passes  upAvard  and  slightly  backward, 
to  be  distributed  to  the  deep  portion  of  the  temporal  muscle,  the  peri- 
cranium, and  occasionally  the  diploe. 


234  ANATOMY. 

The  Pterygoid  Branches  are  not  constant  in  number.  They  are  small  and 
short ;  as  their  name  indicates,  they  are  distributed  to  the  pterygoid  muscles. 

The  JIasseteric  Branch  is  small  and  regular.  It  passes  outward  through 
the  sigmoid  notch  of  the  lower  jaw,  accompanied  by  the  nerve  of  the 
same  name,  and  is  distributed  to  the  masseter  muscle.  It  anastomoses 
with  the  transverse  facial  artery,  and  may  arise  conjointly  with  the  pos- 
terior deep  temporal.  Velpeau  is  of  the  opinion  that  in  dislocations  of 
the  jaw  this  vessel  is  compressed,  and  may  be  ruptured. 

the  Buccal  Brandt  is  a  small  vessel  which  passes  downward  and  for- 
ward between  the  internal  pterygoid  muscle  and  the  jaw  to  the  outer 
side  of  the  buccinator  muscle,  to  which  it  is  distributed.  It  anasto- 
moses with  the  transverse  facial  and  branches  of  the  facial  artery. 


ARTEEIES   OF   THE   THIRD   DIVISION. 

The  Alveolar  or  Superior  Ilaxillary  Branch  generally  'arises  with  the 
infraorbital  branch.  It  passes  downward  along  the  zygomatic  surface 
and  tuberosity  of  the  superior  maxillary  bone,  and  gives  oif  small 
branches,  the  posterior  dental  arteries,  which  enter  the  posterior  den- 
tal canals  ;  twigs  from  these  supply  the  superior  molar  and  bicuspid 
teeth,  and  anastomose  with  the  anterior  dental  portion  of  the  infra- 
orbital branch.  The  mucous  membrane  of  the  maxillary  sinus  is 
partly  supplied  by  the  posterior  dental  arteries,  offshoots  being  also 
distributed  to  the  alveolar  process  and  gums. 

The  Infraorbital  Branch  usually  arises  conjointly  with  the  alveolar 
branch.  It  passes  forward,  in  companv  with  the  superior  maxillary  or 
infraorbital  nerve,  along  the  infraorbital  canal,  from  which  it  finds  exit 
upon  the  face  through  the  infraorbital  foramen.  In  the  canal  offshoots 
are  su})plied  to  the  inferi(^r  rectus  and  inferior  oblique  muscles  of  the 
eye,  the  lachrymal  gland,  the  connective  tissue  in  the  floor  of  the  orbit, 
and  the  mucous  membrane  of  the  maxillary  sinus.  It  also  gives  off  the 
anterior  dental  artery,  which  descends  through  a  canal  in  the  bone  to 
supply  the  incisor,  cuspid,  and  bicuspid  teeth.  This  artery  anastomoses 
with  the  posterior  dental  of  the  alveolar  branch,  the  union,  however, 
taking  place  in  such  a  way  as  to  make  it  difficult  to  say  which  artery 
supplies  the  bicuspid  teeth.  On  the  face  twigs  from  the  infraorbital 
supply  the  lachrymal  sac  and  the  surrounding  tissue  near  its  exit.  They 
also  anastomose  with  branchlets  of  the  facial,  the  nasal  of  the  ophthal- 
mic, and  the  transverse  facial  and  buccal. 

The  Ih'scendinf/  Palatine  or  Superior  Palatine  Branch  passes  down- 
ward in  the  posterior  i)alatine  canal,  accompanied  by  the  anterior  pala- 
tine nerves  (branches  of  the  s[)lien()-palatine  (Meckel's)  ganglion),  and 
emerges  upon  the  posterior  and  lateral  part  of  the  hard  palate.  It  passes 
forward  in  a  groove  on  the  hard  ])alate  to  the  incisive  foramen,  at  which 
point  it  anastomoses  with  a  branch  of  the  naso-palatine  artery.  While 
in  the  posterior  ]>alatine  canal  small  twigs  are  given  off  to  the  mucous 
membrane  of  the  nose  and  tonsils.  It  also  supplies  the  hard  palate, 
alveolar  process,  ])alatine  nuicous  glands,  nuicous  membrane,  and  the 
gum  tissue  of  the  suj)erior  maxilla,  and  anastomoses  Nvith  the  ascending 
palatine  branch  of  the  facial. 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,   ETC.  235 

The  Vidian  Branch  passes  backward  in  the  Vidian  canal  in  the  oppo- 
site direction  to  the  A'idian  nerve.  Its  branches  are  distributed  to  the 
upper  part  of  the  pharynx,  the  opening  of  the  Eustachian  tube,  the 
levator  palati  muscle,  and  to  the  tympanum.  It  anastomoses  with  the 
ascending  pharyngeal  and  stylo-mastoid  arteries. 

The  Fterygo-palatine  Branch  is  a  small  artery  which  passes  back- 
ward and  downward  in  the  pterygo-palatine  canal,  accompanied  by  the 
pharyngeal  nerve.  It  is  distributed  to  the  sphenoidal  cells,  Eustachian 
tube,  and  upper  part  of  the  pharynx. 

The  Nasal  or  >Spheno-palatine  Branch  may  be  considered  as  the  ter- 
minal of  the  internal  maxillary  artery.  It  passes  in  a  forward  direction, 
entering  the  nasal  chamber  through  the  spheno-palatine  foramen,  which 
is  situated  at  the  back  part  of  the  superior  meatus,  dividing  into  inter- 
nal and  external  branches.  The  internal  division  is  the  continuation 
of  the  spheno-palatine,  and  holds  the  same  name,  though  sometimes 
it  is  called  the  artery  of  the  septum,  as  it  runs  downward  and  forward 
in  the  groove  of  the  vomer,  and  terminates  by  anastomosing  with  the 
descending  palatine  artery  at  the  incisive  foramen.  It  is  distributed  to 
the  bone,  cartilage,  and  mucous  membrane  of  the  nasal  septum.  The 
external  branches,  several  in  number,  are  distributed  to  the  lateral  part 
of  the  nose,  including  the  ethmoidal  and  sphenoidal  cells,  the  maxillary 
sinus,  and  the  mucous  membrane  covering  these  parts. 

Variations. — The  internal  maxillary  artery  seldom  varies  in  its  origin, 
though  it  has  been  known  to  arise  from  the  facial  (Quain).  The  num- 
ber of  branches  given  off  may  vary,  there  being  two  or  more,  which 
arise  by  one  common  trunk.  The  branches  may  also  convey  blood  to 
parts  which  are  generally  supplied  by  the  facial  and  lingual,  and  by  the 
branches  of  the  ophthalmic  and  the  temporal  arteries.  In  the  same 
way  the  cranial  branches  may  interchange  with  those  of  the  internal 
carotid. 

The  Internal  Carotid  Artery. 

The  Internal  Carotid  Artery  (Fig.  110)  is  about  6  mm,  (l  inch)  in 
calibre,  and,  as  its  name  indicates^  is  distributed  in  great  ]iart  to  the 
internal,  middle,  and  anterior  structures  of  the  brain-case.  It  also  sup- 
plies the  eye  and  the  parts  within  the  orbit,  and  partially  the  nasal 
chamber,  forehead,  and  nose.  It  is  one  of  the  terminal  •  branches  of 
the  conmion  carotid,  arising  from  that  artery  at  its  bifurcation  opposite 
the  superior  border  of  the  thyroid  cartilage,  from  which  point  it  passes 
upward,  generally  with  a  slight  curve,  to  the  carotid  foramen  in  the 
petrous  portion  of  the  temporal  bone. 

The  internal  carotid  artery  is  divided  anatomically  into  four  portions 
— cervical,  petrous,  cavernous,  and  intracranial. 

The  Cervical  Portion  is  situated  within  the  neck,  extending  from  the 
origin  of  the  internal  carotid  in  the  superior  carotid  triangle  to  the  caro- 
tid foramen.  Its  line  is  usually  slightly  curved,  though  almost  vertical, 
but  in  some  cases  it  will  be  found  to  be  quite  tortuous. 

Bekdions. — At  first  it  is  located  more  superficially  than  the  external 
carotid,  and  a  little  posterior  to  its  outer  side.     It   is  covered  by  the 


236 


ANATOMY. 
Fig.  110. 


Tho  Internal  Parotid  and  Vertebral  Arteries,  right  side. 

fascia,  the  internal  border  of  the  sterno-cleido-mastoid  muscle,  pla- 
tysnia  niyoides,  and  .skin.  U|)on  reaching  the  posterior  belly  of  the 
diirastric  muscle  it  jjasses  beneath  it  and  the  stylo-hyoid,  and  continues 
to  the  inner  side  of  the  external  carotid.     Above  this  point  it  is  deeply 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,  ETC.  237 

situatt'd  in  the  neck,  the  parotid  gland,  the  styloid  process,  and  stylo- 
pharyngeus  muscle  being  to  its  outer  side.  Its  deep  relations  are  with 
the  tonsils,  the  superior  constrictor  muscle  separating  them,  the  -walls  of 
the  pharynx,  and  transverse  process  of  the  upper  three  cervical  vertebrae, 
the  rectus  capitis  anticus  major  muscle  being  posterior  to  it.  The  artery 
is  enclosed  in  a  sheath  in  company  M'ith  the  internal  jugular  vein  and 
pneumogastric  nerve,  the  vein  lying  upon  the  outer  side  posterior  to  the 
artery.  Upon  reaching  the  skull  the  vein  separates  from  the  artery 
and  passes  through  the  jugular  or  posterior  lacerated  foramen,  the 
artery  passing  through  the  carotid  foramen.  The  glosso-pharyngeal, 
pneumogastric,  spinal  accessory,  and  hypoglossal  nerves  are  situated  be- 
tween the  two  vessels  near  these  foramina.  The  occipital  and  posterior 
auricular  arteries  cross  it  on  the  outside,  the  former  below  the  digastric 
muscle,  the  latter  above.  The  pneumogastric  nerve  and  the  upper  cer- 
vical ganglion  of  the  sympathetic  are  deeper  than,  and  situated  posterior 
to,  the  vessel.  The  hypoglossal  nerve  crosses  to  its  outer  side,  near  the 
lower  margin  of  the  digastric  muscle ;  the  glosso-pharyngeal  nerve  and 
pharyngeal  branch  of  the  pneumogastric  pass  between  the  external  and 
internal  carotids.  The  superior  and  external  laryngeal  nerves  are  inter- 
nal to  both  arteries. 

The  cervical  portion  of  the  internal  carotid  seldom  gives  off  any 
branches,  though  occasionally  its  lower  portion  supplies  the  occipital  or 
ascending  pharyngeal  arteries.     These,  however,  are  rare  variations. 

The  Petrous  Portion  of  the  internal  carotid  enters  the  carotid  foramen 
on  the  under  surface  of  the  temporal  bone,  and  passes  through  a  canal 
to  a  point  where  it  enters  the  cavernous  sinus  within  the  brain-case. 
Its  course  within  the  bone  is  at  first  upward,  passing  immediately  in 
front  of  the  tympanum  or  middle  ear  and  the  internal  ear,  being  sepa- 
rated from  them  by  a  thin  lamina  of  bone.  It  then  passes  horizontally 
forward  and  inward  to  the  middle  lacerated  foramen,  extending  across 
the  tissues  filling  in  this  aperture. 

This  portion  of  the  artery  gives  off  a  small  branch  to  the  tympanum 
which  anastomoses  with  tympanic  branches  from  divisions  of  the  exter- 
nal carotid. 

The  Chvcrnous  Portion  of  the  internal  carotid  commencies  immedi- 
ately above  the  middle  lacerated  foramen,  and  passes  upward  to  and 
along  the  sigmoid  groove  on  the  lateral  surface  of  the  body  of  the  sphe- 
noid bone.  It  terminates  in  the  intracranial  portion  of  the  artery  by 
passing  through  the  upper  wall  (which  is  membranous)  of  the  cavernous 
sinus  close  to  the  anterior  clinoid  process.  The  artery  is  situated  on  the 
inner  portion  of  the  cavernous  sinus.  It  is  surrounded  by  filaments  of 
the  sympathetic  nerve,  and  is  accompanied  by  the  sixth  nerve,  which  is 
situated  to  its  outer  side.  These  structures  are  all  covered  by  an  envelope 
derived  from  the  lining  membrane  of  the  sinus.  The  third,  fourth,  and 
oplithalmic  nerves  pass  through  the  sinus  external  to  the  envelope. 

Branches  of  this  portion  of  the  artery  are  distributed  to  the  dura 
mater,  the  pituitary  body,  Gasserian  ganglion,  and  the  walls  of  the 
cavernous  and  inferior  petrosal  sinuses.  It  also  gives  off  a  branch 
which  anastomoses  with  the  middle  meningeal  artery. 

The  Intracranial  Portion  of  the  internal  carotid  commences  after  the 


238 


ANATOMY 


artery  passes  through  the  upper  wall  of  the  cavernous  sinus.  Just 
above  this  point  the  optic  nerve  passes  to  the  inside  of  the  artery,  while 
tlie  third  nerve  passes  externally.  Near  the  anterior  clinoid  process  this 
portion  of  the  artery  gives  off  its  first  large  branch,  the  ophthalmic, 
while  near  the  iissure  of  Sylvius  it  gives  off  the  lateral  (posterior)  com- 
municating artery  of  the  circle  of  Willis.  Above  this  point  it  finally 
divides  into  the  middle  and  anterior  cerebral  arteries. 

The  branches  of  this  portion  of  the  artery  are  the  ophthalmic,  the 
anterior,  and  the  middle  cerebral. 

The  Ophthalmic  Artery  (Fig.  Ill)  is  about  2  mm.  (y^.  inch)  in  cali- 
bre. It  is  the  first  large  branch  of  the  internal  carotid,  arising  from 
that  artery  immediately  after  it  passes  through  the  dura  mater,  at  the 
last  curve  of  the  sigmoid  flexure,  just  internal  to  the  anterior  clinoid 
process.  From  this  point  it  passes  forward  and  a  little  outward  over 
the  anterior  portion  of  the  cavernous  sinus,  through  the  optic  foramen 
into  the  cavity  of  the  orbit,  passing  below  and  to  the  outer  side  of  the 

Fig. 111. 


Arteries  of  the  Orbit,  from  the  outer  side:  1,  internal  carotid  ;  2,  ojjhthahiiic  arterv ;  3,  arteria  cen- 
tralis retinie;  4,  muscular  branches;  5,  lachrymal  artery;  (i,  ciliMry  artery  ;  "7,  posterior  eth- 
moidal artery;  S,  rectus  inferior;  9.  anterior  ethmoidal  arterv;  10,  obi  iqu  us"  inferior;  11,  supra- 
orbital artery  ;  12,  facial  iirtery ;  l:i,  frontal  artery  ;  14,  palpebral  artery  ;  15,  nasal  artery. 

optic  nerve.  The  artery  and  nerve  are  enclosed  within  the  same  sheath, 
which  is  derived  from  the  dura  mater.  Within  the  cavity  of  the  orbit 
the  artery  leaves  the  sheath  and  pa.sses  obliquely  over"  (occasionally 
under)  the  nerve  to  the  inner  wall  of  the  cavity,  along  which  it  travels 
in  a  horizontal  direction  between  the  superior  oblique  and  internal  rectus 
muscles  to  tlie  trochlear  ]>rocess  or  notch.  Here  it  terminates  by  divid- 
ing into  frontal  and  external  nasal  branches. 

The  bran('he.s  of  the  o})hthalmic  artery  are  the  lachrymal,  supraorbital, 
central  retinal,  ciliary,  posterior  and  anterior  ethmoid,  muscular,  palpebral, 
frontal,  and  external  nasal. 

The  Lnrhri/mal  Artery  is  the  first  branch  given  off  by  the  ophthalmic. 
It  arises  from  its  outer  side  immediately  after  it  enters  the  cavity  of  the 
orbit,  and  frequently  while  the  artery  is  still  within  the  optic  foramen. 
Together  with  the  lachrymal  nerve  it  pas.ses  along  the  outer  wall  of  the 
orbit  below  the  external  rectus  muscle,  and  is  distributed  principally  to 
the  lachrymal  gland.     The  branches  of  the  lachrymal  artery  are  its 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,   ETC.  239 

terminal  ones,  which  pass  to  tlie  npper  eyelid  and  the  conjunctiva,  and 
anastomose  ^ith  branches  of  other  arteries  distributed  to  this  region  of 
the  face.  One  or  two  small  twigs  pass  from  the  artery  through  for- 
amina in  the  malar  bone  to  the  temporal  fossa,  anastomosing  with  the 
deep  temporal  artery.  Small  branches  also  pass  through  the  same 
bone  and  anastomose  with  the  deep  and  superficial  arteries  of  the 
check,  which  are  branches  of  the  transverse  facial.  A  branch  from  the 
lachrymal,  which  is  given  off  soon  after  its  origin,  passes  backward 
through  a  notch  in  the  margin  of  the  anterior  lacerated  foramen,  sup- 
plies the  dura  mater,  and  anastomoses  with  the  middle  meningeal  artery. 
Other  branches  are  distributed  to  the  membrane  covering  the  outer 
wall  of  the  orbit,  the  external  and  superior  recti  muscles,  and  the 
levator  palpebrse  superioris  muscles. 

The  Central  Retinal  Artery  is  a  small  branch  arising  from  the  oph- 
thalmic soon  after  it  passes  out  of  the  optic  foramen.  It  passes 
obliquely  through  the  centre  of  the  optic  nerve,  about  a  quarter  of  an 
inch  posterior  to  its  point  of  entrance  into  the  eyeball,  and  is  distributed 
to  the  retina  and  the  hyaloid  membrane.  During  embryonic  life  this 
artery  has  a  central  branch  which  passes  forward  through  the  middle  of 
the  vitreous  humor  of  the  eye  to  the  posterior  portion  of  the  lens,  upon 
which  it  is  lost. 

The  Ciliary  Arteries  are  divided  into  a  posterior  and  anterior  set,  the 
former  being  subdivided  into  short  and  long  ciliary  arteries. 

The  Short  Ciliary  Arteries  number  four  or  five,  and  arise  from  the 
ophthalmic  as  it  crosses  the  optic  nerve.  They  soon  divide  into  twelve 
or  fifteen  small  branches,  which  pass  forward  in  a  tortuous  or  spiral 
course  through  the  adipose  tissue  surrounding  the  optic  nerve  to  the 
posterior  part  of  the  eyeball,  Avhere  they  pierce  the  sclerotic  coat  in  close 
proximity  to  the  entrance  of  the  optic  nerve.  Passing  through  the 
sclerotic,  they  enter  the  choroid  coat,  and  immediately  break  up  into  a 
minute  capillary  plexus  which  forms  the  greater  part  of  the  internal 
coat  of  the  choroid.  From  the  anterior  portion  of  this  plexus  small 
vessels  are  given  off  which  pass  to  the  ciliary  processes. 

The  Lovf/  Ciliary  Arteries  are  two  in  number,  and  but  slightly  larger 
than  the  short  ciliary  vessels.  They  pass  forward,  one  on  each  side 
of  the.  eyeball,  and  enter  the  sclerotic  coat,  passing  between  it  and 
the  choroid  to  the  ciliary  ligaments,  where  they  each  divide  into  two 
branches,  superior  and  inferior.  The  four  branches  then  diverge  and 
pass  forward  to  the  periphery  of  the  iris  (circulus  major),  where  they 
reunite  and  form  an  arterial  circle.  From  this  circle  branches  are  dis- 
tributed to  the  iris,  some  of  the  concentric  extremities  uniting  to  form 
an  inner  circle  (circulus  minor)  on  the  free  or  pupillary  margin  of 
the  iris. 

The  Anterior  Ciliary  Arteries  number  six  or  eight,  and  arise  from 
the  muscular  and  lachrymal  branches.  They  communicate  freely  with 
each  other,  and  form  a  vascular  circle  around  the  anterior  portion  of  the 
eyeball  between  the  conjunctiva  and  the  sclerotic  coat  of  the  eye.  From 
tiiis  circle  small  vessels  pass  through  the  sclerotic  coat  one  or  two  lines 
posterior  to  the  margin  of  the  cornea,  and  join  the  external  vascular 
circle  of  the  iris. 


240  ANATOMT. 

The  Posterior  Ethmoid  Artery  arises  from  the  inner  side  of  the  oph- 
thabuic  nearly  opposite  the  posterior  ethmoidal  foramen.  It  passes 
through  this  foramen,  and  is  distributed,  by  a  small  meningeal  branch, 
to  the  portion  of  the  dura  mater  situated  in  the  anterior  fossa  of  the 
brain-case,  as  well  as  to  the  mucous  membrane  lining  the  posterior 
ethmoidal  cells  and  to  the  superior  portion  of  the  internal  nose. 

The  Anterior  Ethmoidal  Artery  is  larger  than  the  posterior.  It  arises 
from  the  inner  side  of  the  ophthalmic  close  to  the  anterior  ethmoidal 
foramen.  It  passes  through  this  foramen  into  the  brain-case  immedi- 
ately above  the  cribriform  plate  of  the  ethmoid  bone,  and  is  accompanied 
by  the  nasal  nerve.  The  artery  and  nerve  pass  together  through  the 
cerebro-nasal  slit  (anterior  nasal  foramen)  of  the  ethmoid  bone  into 
the  nasal  chamber,  where  the  vessel  receives  the  name  of  the  anterior 
nasal  arterv.  The  anterior  ethmoidal  artery  is  distributed  through  its 
branches  to  the  antero-ethmoidal  cells,  the  dura  mater  of  the  ante- 
rior fossa  of  the  brain-case,  the  mucous  membrane  of  the  olfactory 
portion  of  the  nasal  chamber,  including  the  superior  and  inferior  tur- 
binated ])ones,  and  to  the  roof  and  septum  of  the  nose,  the  branch 
supplying  the  septum  anastomosing  with  the  naso-palatine  artery.  It  is 
also  distributed  to  the  frontal  sinus,  a  branch  passing  between  the  nasal 
bones  and  lateral  cartilage  in  company  with  the  nasal  nerve,  and  anas- 
tomoses on  the  face  with  branches  from  the  facial  artery. 

The  Muscular  Arteries,  branches  of  the  ophthalmic,  consist  of  two 
principal  ones,  superior  and  inferior,  and  several  smaller  twigs. 

The  Superior  Muscular  Artery  is  the  smaller  of  the  two  larger 
branches  of  the  ophthalmic,  and  is  distributed  to  the  levator  palpebrre 
superioris,  superior  rectus,  and  superior  oblique  muscles.  The  existence 
of  this  artery  is  not  constant. 

The  Inferior  3Iuscular  Artery  passes  anteriorly  from  the  ophthalmic, 
and  is  distributed  to  the  external  and  inferior  recti  and  inferior  oblique 
muscles.  Its  existence  is  more  constant  than  the  superior  branch,  and 
it  furnishes  the  principal  number  of  the  anterior  ciliary  arteries. 

The  Sinaller  Muscular  Arteries  arise  from  the  ophthalmic  at  various 
points  along  its  course,  as  well  as  from  its  lachrymal  and  supraorbital 
branches.     They  are  distributed  to  the  different  muscles  of  the  eye. 

The  Supraorbital  Artery  is  the  largest  branch  of  the  ophthalmic.  It 
arises  in  the  posterior  portion  of  the  cavity  of  the  orbit  as  the  artery 
crosses  the  optic  nerve.  It  passes  above  the  muscles  of  the  eye, 
accompanied  by  the  frontal  nerve,  and  extends  anteriorly  between  tlie 
periosteum  covering  the  roof  of  the  orbital  cavity  and  the  levator  pal- 
pebral superioris  muscle  to  the  supraorbital  foramen  in  the  frontal  bone. 
It  passes  through  this  foramen  and  divides  into  two  branches,  sujierfif-ial 
and  deep.  These  branches  anastomose  with  the  temporal  and  angular 
arteries,  and  with  their  fellows  of  the  opposite  side. 

The  Superficial  Branch  is  distributed  to  the  frontal  muscle  and  to  the 
integument  over  this  region. 

The  Deep  Branch  is  distributed  to  the  periosteum  of  the  frontal  bone. 
.  The  superficial  and  deep  branches  of  the  supraorbital  artery  also  send 
branches  to  the  muscles  within  tlie  orbit,  and,  as  the  supraorbital  passes 
out  of  the  orbit,  it  supplies  the  diploe  of  the  frontal  bone  by  a  branch 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,  ETC.  241 

which  enters  a  small  foramen  often  seen  within  the  supraorbital  foramen 
or  notch. 

Tlie  Palpebral  Arteries  are  two  in  number,  superior  and  inferior. 
They  usually  arise  together  from  the  ophthalmic,  nearly  opposite  the 
pulley  of  the  superior  oblique  muscle.  From  this  point  they  diverge, 
the  sui>erior  branch  passing  above,  the  inferior  below,  the  internal  tarsal 
ligament.  They  distribute  small  branches  to  the  conjunctiva  and  the 
lachrymal  caruncle  and  sac.  They  then  pass  outward  between  the 
orbicularis  palpebrarum  muscle  and  the  trochlea,  and  encircle  the  eye- 
lids near  their  free  margins.  They  anastomose  with  branches  of  the 
lachrymal  as  well  as  with  the  orbital  branches  of  the  temporal  and 
infraorbital  arteries.  A  branch  from  the  palpebral  artery  generally 
accompanies  the  nasal  duct  into  the  nasal  chamber. 

The  Frontal  Artery  is  one  of  the  terminal  divisions  of  the  ophthal- 
mic, and  arises  in  close  proximity  to  the  trochlear  process  or  notch  on 
the  frontal  bone.  It  passes  out  of  the  orbital  cavity,  curves  around 
the  internal  angular  process  of  the  frontal  bone  or  inner  extremity  of 
the  supraorbital  arch,  and  is  distributed  to  the  superior  lid  of  the  eye, 
integument,  muscles,  and  pericranium  of  the  forehead,  as  well  as  to  the 
nasal  slip  of  the  frontal  muscle.  It  auastomoses  with  its  fellow  of  the 
opposite  side  and  with  the  supraorbital  artery. 

The  External  Nasal  Artery  is  the  other  terminal  division  of  the 
ophthalmic.  It  arises  close  to  the  trochlear  process  or  notch  on  the 
frontal  bone,  and  passes  forward  over  the  internal  tendo  palpebrarum 
and  through  the  orbicularis  palpebrarum  muscle.  It  then  extends  down- 
ward along  the  root  of  the  nose,  and  communicates  with  the  angular  and 
nasal  arteries,  branches  of  the  facial.  Occasionally  it  communicates  by 
a  small  branch  with  the  artery  of  the  opposite  side,  or  it  may  pass  down 
the  nose  and  anastomose  with  the  anterior  nasal  artery,  a  branch  of  the 
anterior  ethmoidal.  In  its  course  it  gives  off  branchlets  to  the  lachrymal 
sac,  canal,  and  caruncle  and  the  orbicularis  palpebrarum  muscle. 

Variations. — The  lachiymal  artery  may  arise  directly  from  the  middle 
meningeal.  When  it  so  arises  it  passes  out  of  the  brain-case  through, 
the  notch  in  the  border  of  the  anterior  lacerated  foramen,  and  gives  off 
a  small  recurrent  branch,  which  communicates  with  the  lachrymal  and 
middle  meningeal  arteries,  and  again  becomes  part  of  the  main  trunk 
of  the  lachrymal.  Occasionally  the  major  portion,  or  even  all,  of  the 
blood-supply  of  the  lachrymal  artery  comes  through  this  source,  "Where 
the  facial  artery  is  small  or  altogether  wanting  the  nasal  artery  is  of 
large  size  and  supplies  its  place.  The  terminal  branches  of  the  oph- 
thalmic artery  have  a  large  and  varied  communication  with  other 
arteries  in  this  region,  such  as  its  fellow  of  the  opposite  side,  the  facial,, 
infraorbital,  transverse  facial,  temporal,  middle  meningeal,  ethmoidal,, 
and  the  spheno-palatine. 

The  Cerebral  Arteries. 

The  Cerebral  Arteries,  branches  of  the  internal  carotid,  are  two  in 
number,  anterior  and  posterior,  the  posterior  cerebral  artery  being  a 
branch  of  the  basilar. 

Vol.  I.— 16 


242  ANATOiMY. 

The  Anterior  Cerebral  Artery  is  about  3^  mm.  (i  inch)  in  calibre. 
It  is  one  of  the  terminal  divisions  of  the  internal  carotid,  and  arises  at 
the  inner  extremity  of  the  fissure  of  Sylvius,  close  to  the  anterior  clinoid 
process.  It  passes  inward  and  forward  nearly  at  right  angles  with  the 
internal  carotid,  and  at  an  obtuse  angle  with  the  middle  cerebral,  to  a 
point  in  close  proximity  to  its  junction  with  its  fellow  of  the  opposite 
side,  w^iich  occurs  at  the  rostrum  of  the  corpus  callosum,  anterior  to  the 
lamina  cinerea,  where  it  gives  off  the  anterior  communicating  artery 
which  forms  a  part  of  the  circle  of  Willis.  From  this  point  it  passes 
forward  a  short  distance  from  and  nearly  parallel  with  its  fellow  of  the 
opposite  side  until  it  reaches  the  anterior  portion  of  the  corpus  callosum, 
around  which  it  curves,  and  breaks  up  into  several  branches  to  supply 
the  structures  in  the  anterior  portion  of  the  brain-case. 

The  Iliddle  Cerebral  Artery  is  about  5  mm.  {^  inch)  in  calibre,  and 
is  one  of  the  largest  of  the  terminal  divisions  of  the  internal  carotid. 
It  arises  at  the  inner  extremity  of  the  fissure  of  Sylvius,  and  passes 
obliquely  upward  and  outward  within  the  fissure  to  the  superior  surface 
of  the  island  of  Reil.  Here  it  subdivides  into  several  branches,  which 
are  distributed  to  the  brain.  It  also,  on  the  anterior  portion,  gives 
oif  the  lateral  (posterior)  communicating  artery  of  the  circle  of  Willis. 

The  Posterior  Cerebral  Artery  is  about  3|  mm.  (|  inch)  in  calibre, 
and  is  one  of  the  t^vo  terminal  branches  of  the  basilar,  hereafter  to  be 
described.  It  arises  with  the  corresponding  artery  of  the  opposite  side 
at  a  point  just  anterior  to  the  pons  varolii,  close  to  the  posterior  clinoid 
process  of  the  sphenoid  bone.  It  extends  outward,  and  then  curves  back- 
ward around  the  crus  cerebri,  and  passes  outward  and  upward  between 
the  occipital  lobe  of  the  cerebrum  and  the  cerebellum.  It  gives  off 
numerous  branches  which  supply  the  different  structures  of  the  brain, 
as  well  as  the  lateral  (posterior)  communicating  artery  of  the  circle  of 
Willis. 

The  Circle  of  Willis  is  a  system  composed  of  several  short  arteries 
which  communicate  with  each  other  and  form  a  vascular  circle  which 
surrounds  the  following  structiu^es  at  the  base  of  the  brain :  the  lamina 
cinerea,  optic  commissure,  infundibulum  and  tuber  cinereum,  corpora 
albicantia,  and  posterior  perforated  space. 

The  circle  of  Willis  is  composed  of  the  following  arteries :  the  two 
anterior  cerebral,  the  anterior  communicating,  the  upper  portion  of  the 
two  internal  carotids,  the  two  lateral  (posterior)  communicating,  and 
the  two  posterior  cerebrals. 

The  Two  Anterior  Cerebral  Arteries  form  that  portion  of  the  circle  of 
Willis  which  extends  forward  and  inward  from  their  origin,  which  is 
at  the  termination  of  the  internal  carotid,  to  the  rostrum  of  the  corpus 
callosum  just  anterior  to  the  lamina  cinerea. 

The  Anterior  Conwinnicating  Artery  is  about  two  lines  in  length,  and 
passes  from  one  anterior  cerebral  artery  to  the  other  across  the  rostrum 
of  the  corpus  callosum  anterior  to  the  lamina  cinerea.  It  forms  the 
anterior  connnunicating  branch  of  the  circle  of  Willis  between  the  two 
anterior  cerebral  arteries.  It  also  gives  oif  branches  which  supply  some 
of  the  structures  in  close  proximity  to  it. 

Variations. — This  artery  is  occasionally  represented  by  two  branches, 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,   ETC.  243 

and  at  times  it  is  absent.  When  this  is  the  case  the  two  anterior  cere- 
brals are  united  into  one  in  a  similar  manner  to  the  two  vertebrals 
which  form  the  basilar  artery. 

The  upper  portions  of  the  two  internal  carotid  arteries  are  situated 
close  to  the  anterior  clinoid  processes  of  the  sphenoid  bone,  and  in 
calibre  are  much  the  largest  of  any  of  the  arteries  which  form  the  circle 
of  Willis,  though  they  constitute  but  a  small  part  of  its  circumference. 
Anteriorly  they  give  off  the  anterior  cerebral  arteries,  while  posteriorly 
they  give  origin  to  the  posterior  communicating  arteries. 

Tlie  Lateral  (Posterior)  Commumcating  Arteries  are  situated  laterally 
instead  of  posteriorly,  as  the  generally-used  name  would  imply.  They 
are  seldom  of  equal  size,  the  right  being  most  frequently  the  larger. 
They  extend  from  the  upper  extremity  of  the  internal  carotid  backward 
and  slightly  inward,  and  pass  beneath  the  optic  tract  and  the  crus  cerebri 
to  the  posterior  cerebral  arteries.  At  their  most  anterior  portion  in  front 
of  the  pons  varolii  they  give  off  numerous  branches  to  parts  in  close 
proximity. 

Variations. — The  two  lateral  (posterior)  communicating  arteries  occa- 
sionally arise  from  the  middle  cerebral  instexid  of  the  internal  carotid. 

The  Tu'o  Posterior  Cerebral  Arteries  form  the  posterior  portion  of  the 
circle  of  Willis.  They  are  larger  in  calibre  than  any  of  the  other  ar- 
teries which  form  the  circle,  except  the  terminal  extremities  of  the  inter- 
nal carotids.  They  extend  from  the  bifurcation  of  the  basilar  artery  in 
front  of  the  pons  varolii  outward  and  slightly  forward  to  the  point  of 
junction  of  the  lateral  (posterior)  communicating  arteries. 

Variations. — Occasionally  this  portion  of  the  posterior  cerebral  artery 
is  quite  small.  When  this  is  the  case  the  corresponding  artery  of  the 
opposite  side  is  proportionately  large,  thus  equalizing  the  blood-supply. 

The  Basilar  Artery  is  formed  by  the  union  of  the  right  and  left  ver- 
tebrals, which  are  branches  of  the  subclavian  arteries  at  the  base  of  the 
neck.  This  arrangement  of  vessels,  together  with  the  external  carotids 
and  the  circle  of  Willis,  forms  such  a  continuous  communication  that 
if  the  common  carotid  be  ligated  or  entirely  obliterated  on  either  side, 
the  blood  may  yet  circulate  to  all  parts  of  the  brain,  and  also  pass  out 
of  the  brain-case  and  supply  the  external  parts  of  the  head  and  face 
through  the  anastomotic  unions  of  the  vessels  of  these  parts. 

Subclavian  Arteries. 

The  Subcfarian  Arteries  are  two  in  number,  right  and  left,  extending 
from  their  origin,  the  right  from  the  innominate,  the  left  from  the  arch 
of  the  aorta,  to  their  terminations  at  the  first  ribs.  Each  forms  an  arch, 
the  concavity  of  which  is  directed  downward,  and  the  greater  portion  of 
which  is  situated  in  the  inferior  posterior  cervical  triangle  of  the  neck. 
The  proximal  portion  rests  in  the  thoracic  cavity.  The  artery  passes 
over  the  first  rib  and  under  the  central  portion  of  the  clavicle  into  the 
axilla.  The  summit  of  the  arch  is  situated  within  the  neck  posterior  to  the 
scalenus  anticus  muscle.  The  origin  and  relations  of  the  proximal  portion 
of  the  arteries  on  either  side  are  dissimilar,  and  will  therefore  be  separately 
described.     The  subclavian  arteries  are  divided  into  three  portions. 


244  ANAT03ir. 

The  first  or  ascending  portion  of  the  right  subclavian  artery  arises  from 
the  innominate  or  brachio-cephalic  artery  at  its  point  of  bifurcation  into  the 
right  subclavian  and  right  common  carotid,  which  latter  is  situated  close 
to  the  trachea  posterior  to  the  sterno-clavicular  articulation.  From  this 
point  it  passes  upward,  outward,  and  a  little  backward  until  it  reaches 
the  proximal  border  of  the  scalenus  anticus  muscle  at  the  base  of  the 
neck. 

The  second  or  transverse  portion  is  the  shortest,  and  is  situated  higher 
in  the  neck  than  the  remainder  of  the  artery,  thus  forming  the  dome  of 
the  arch.  It  commences  at  the  termination  of  the  first  portion  of  the 
artery,  and  passes  outward  behind  the  scalenus  anticus  muscle  to  its 
distal  border. 

The  third  or  descending  portion  of  the  artery  passes  downward,  out- 
ward, and  forward  from  the  distal  border  of  the  scalenus  anticus  muscle 
to  a  point  where  it  passes  from  the  neck  over  the  first  rib  and  under  the 
clavicle  into  the  axilla,  where  it  becomes  the  axillary  artery.  The  third 
portion  of  the  subclavian  artery  is  the  most  superficial.  It  passes 
through  a  triangular  space  formed  by  the  clavicle  below,  the  omo- 
hyoid muscle  externally,  and  the  anterior  scalenus  muscle    internally. 

Relations. — The  first  or  ascending  portion  of  the  right  subclavian 
artery  is  covered  by  the  skin,  platysma  myoides,  deep  fascia,  outer 
attachment  of  the  sterno-cleido-mastoid  muscle,  the  sterno-hyoid  and 
sterno-thyroid  muscles,  and  the  sternal  end  of  the  clavicle.  The  inter- 
nal jugular  and  the  vertebral  veins  cross  it  on  their  way  to  empty  into 
the  right  innominate  vein.  The  pneumogastric  nerve  crosses  to  the  inner 
side  of  the  internal  jugular  vein,  while  the  cardiac  branches  of  the  sym- 
pathetic and  the  phrenic  nerves  also  pass  over  it.  Its  deep  surface  is 
in  close  relation  to  the  pleura,  and  behind  it  is  separated  by  a  cellular 
interval  from  the  longus  colli  muscle  and  the  transverse  process  of  the 
seventh  cervical  vertebra.  The  right  innominate  vein  is  situated  below 
and  slightly  anterior  to  the  artery,  while  the  recurrent  or  inferior  laryn- 
geal nerve  passes  over  it,  returns  upon  itself,  passes  under  the  artery, 
and  extends  upward  to  the  larynx. 

The  second  or  transverse  portion  of  tlie  subclavian  is  wholly  covered 
by  the  scalenus  anticus  muscle,  while  more  superficially  it  is  crossed  by 
the  sterno-cleido-mastoid.  The  left  phrenic  nerve  passes  over  the  second 
portion  of  the  left  subclavian  artery,  in  this  differing  from  the  right 
phrenic  nerve,  which  crosses  the  first  portion  of  the  right  subclavian. 
It  is  also  covered  by  the  integument,  platysma  myoides,  and  the  deep 
fascia.  The  deep  surface  of  the  artery  is  in  relation  with  the  middle 
scalenus  muscle  posteriorly,  the  brachial  plexus  of  nerves  above,  and 
below  with  the  pleura.  The  scalenus  anticus  muscle  is  between  the 
subclavian  artery  and  vein,  the  latter  being  anteriorly  situated. 

Eckdkmx. — The  third  or  descending  portion  of  the  subclavian  artery 
is  covered  l)y  the  integument,  platysma  myoides,  and  deep  fascia.  The 
subclavian  vein  lies  superficial  to,  though  slightly  below,  it,  while  the 
external  jugular  and  the  veins  of  the  shoulder  pass  over  it  to  enter  the 
sulx-lavian  vein.  It  is  also  in  close  relation  to  the  brachial  plexus  of 
nerves,  most  of  which  pass  over  it,  while  one  or  two  pass  under  it. 

The  first  or  ascending  portion  of  the  left  subclavian  arterv  is  some- 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,   ETC.  245 

what  longer  than  the  right,  and  is  more  deeply  situated  in  the  thoracic 
cavity.  It  usually  arises  directly  from  the  left  extremity  of  the  trans- 
verse portion  of  the  arch  of  the  aorta,  opposite  the  second  dorsal  verte- 
bra. From  this  point  it  passes  almost  vertically  upward,  though  slightly 
outward,  and  emerges  from  the  thorax  into  the  neck,  where  it  makes  a 
sharp  curve  outward  over  the  apex  of  the  left  lung  to  reach  the  prox- 
imal margin  of  the  anterior  scalenus  muscle,  from  which  point  its  direc- 
tion and  relations  correspond  to  the  artery  of  the  right  side,  and  there- 
fore need  no  special  description. 

Relations. — The  first  or  ascending  portion  of  the  left  subclavian 
artery  is  situated  at  its  origin  behind  the  pleura  and  upper  portion  of 
the  left  lung.  It  is  crossed  by  the  left  innominate  vein,  the  internal 
jugular,  and  vertebral  veins.  The  pneumogastric  nerve  passes  down 
in  front  of  it,  and  comes  in  contact  with  it  near  its  origin.  The  phrenic 
nerve  crosses  the  artery  close  to  the  anterior  scalenus  muscle  and  exter- 
nal to  the  thyroid  axis.  The  cardiac  nerves  also  pass  in  front  of  the 
artery.  Its  deep  surface  is  in  close  relation  to  the  vertebrae,  a  portion 
of  the  oesophagus,  the  thoracic  duct,  and  longus  colli  muscle.  The  cord 
of  the  sympathetic  nerve  passes  up  behind  this  surface.  Internally  are 
the  left  common  carotid  artery,  trachea,  a  portion  of  the  oesophagus,  and 
thoracic  duct.     Externally  is  the  pleura. 

The  Branches  of  the  Subclavian  Artery  are  four  in  number — vertebral, 
internal  mammary,  thyroid  axis,  and  superior  intercostal.  The  first 
three  of  these  arise  from  the  first  portion  of  the  subclavian  before  it 
reaches  the  scalenus  anticus  muscle,  while  the  last  is  derived  from  the 
second  poi'tion.  Occasionally  a  branch  arises  from  the  third  portion 
of  the  artery,  and  is  known  as  the  posterior  scapular. 

The  Vertebral  Artery. 

The  Vertebral  Artery  is  about  5  mm.  (i  inch)  in  calibre,  and  is  usually 
the  first  and  largest  branch  of  the  subclavian.  The  artery  on  the  right 
side  generally  arises  from  the  upper  and  posterior  portion,  about  three- 
fourths  of  an  inch  from  the  brachio-cephalic  or  innominate  artery;  that 
on  the  left  usually  arises  from  the  first  portion  of  the  subclavian  as  it 
curves  to  the  left  at  the  base  of  the  neck. 

Variations. — This  artery  may  arise  from  any  portion  of  the  subcla- 
vian or  the  common  carotid,  and  even  from  the  arch  of  the  aorta,  though 
this  latter  abnormality  is  rare.  Cases  are  reported  where  the  vertebral 
artery  arises  as  two  branches. 

From  its  origin  the  vertebral  artery  passes  upward  and  slightly 
backward,  and  usually  enters  the  foramen  in  the  transverse  process  of 
the  sixth  cervical  vertebra.  Occasionally,  however,  it  enters  the  fora- 
men in  the  fifth,  fourth,  third,  or  even  as  high  as  the  second,  cervical 
vertebra.  Sometimes  it  enters  the  foramen  in  the  transverse  pro- 
cess of  the  seventh  cervical  vertebra.  It  then  passes  upward  through 
the  remainder  of  the  vertebral  foramina,  curves  backward  along  the 
upper  surface  of  the  atlas,  and  enters  the  skull  through  the  foramen 
magnum  of  the  occipital  bone.  It  passes  along  the  side  of  the  medulla 
oblongata  to  its  anterior  portion,  and  joins  the  vertebral  of  the  opposite 


246  ANATOMY. 

side  at  the  posterior  inferior  extremity  of  the  pons  varolii  to  form  the 
basihir  artery. 

TAf  Branches  of  the  Vertebral  Artery  are  divided  into  cervical  and 
encranial.  The  cervical  branches  are  the  lateral  spinal  and  muscular ; 
the  encranial  branches  are  the  posterior  meningeal,  posterior  spinal, 
anterior  spinal,  and  the  posterior  cerebellar.  The  distribution  of  these 
branches  is  generally  implied  in  their  names. 

The  Basilar  Artery  is  formed  by  the  union  of  the  right  and  left  ver- 
tebral arteries,  which  takes  place  at  the  posterior  inferior  extremity  of 
the  pons  varolii.  From  this  point  it  passes  forward  and  upward  within 
a  groove  along  the  middle  of  the  superior  surface  of  the  basilar  process 
of  the  occipital  bone  to  the  anterior  extremity  of  the  pons,  close  to  the 
posterior  clinoid  processes.  Here  it  divides  into  the  posterior  cerebral 
arteries  already  described. 

The  Branches  of  the  Basilar  Artery  are  the  trans v'erse,  six  or  eight  in 
number,  which  supply  the  under  surface  of  the  pons ;  the  right  and  left 
auditory,  whicli  pass  through  the  internal  auditory  meatus  of  the  tempo- 
ral bone,  together  with  the  auditory  nerve,  and  supply  the  labyrinths  of 
the  ear ;  the  anterior  or  inferior  cerebellar,  right  and  left,  which  supply 
the  anterior  inferior  portion  of  the  cerebellum  and  other  structures  in 
juxtaposition,  and  anastomose  with  the  inferior  cerebellar  branches  of 
the  vertebral;  the  superior  cerebellar,  right  and  left,  which  supply 
through  their  numerous  branches  the  cerebellum  and  other  structures 
in  the  vicinity;  and  the  terminal  or  posterior  cerebral  arteries  previously 
described. 

The  Thyroid  Axis  is  about  6  mm.  (|  inch)  in  calibre  and  but  a  few 
lines  in  length.  It  arises  from  the  anterior  superior  surface  of  the  first 
part  of  the  subclavian  artery,  and  passes  upward  a  very  short  distance 
close  to  the  proximal  border  of  the  anterior  scalenus  muscle.  Here  it 
breaks  up  into  three  branches,  inferior  thyroid,  suprascapular,  and  trans- 
versal is  colli. 

The  Inferior  Thyroid  Artery  is  about  31  mm.  (^  inch)  in  calibre.  It 
arises  from  the  tliyroid  axis,  and  could  be  reo;arded  as  a  continuation 
of  this  artery.  From  its  origin  it  passes  directly  upward  in  front 
of  the  vertebral  artery  and  under  the  central  portion  of  the  omo-hyoid 
muscle.  Sliglitly  above  tlie  muscle,  opposite  the  fifth  cervical  vertebra, 
it  curves  inward  in  a  tortuous  manner,  and  passes  beneath  the  slieath  of 
the  large  vessels  of  the  neck  and  sympathetic  nerve  to  the  inferior  part 
of  the  thyroid  body.  Here  it  breaks  up  into  fine  branches  which  sup- 
ply tlie  gland  and  anastomose  with  brandies  of  the  superior  thyroid 
artery,  as  >vell  as  the  corresjionding  artery  of  the  opj^osite  side.  The 
other  branches  of  the  inferior  thyroid  are  the  ascending  cervical,  inferior 
laryngeal,  and  tracheal. 

The  Ascending  Ccrrical  Artery  is  ;ibout  2  mm.  (y^^-  inch)  in  calibre, 
and  arises  from  the  inferior  thyroid  just  as  it  curves  inward  behind  the 
sheath  of  the  large  vessels  of  the  neck.  It  jmsses  upward  immediately 
anterior  to  the  pln-enic  nerve  in  the  interspace  between  the  anterior  sca- 
lenus and  tlie  rectus  capitis  anticus  major  muscles,  and  is  distributed 
through  small  branches  to  these  muscles,  a  few  branches  extending 
across  the  neck  to  anastomose  with  offshoots  from  the  vertebral.     Other 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,  ETC.  247 

brandies  pass  through  the  intervertebral  foramina  in  close  relation  with 
the  cervical  nerves,  and  supply  the  bodies  of  the  vertebrae,  the  spinal 
cord  and  its  membranes,  and  anastomose  at  the  upper  portion  of  the 
cord  with  the  ascending  pharyngeal  artery. 

The  luferioi'  Laryngeal  Artery  is  not  uniform  in  size,  and  arises  from 
the  inferior  thyroid  in  close  proxijnity  to  the  thyroid  body.  It  passes 
upward,  accompanied  by  the  recurrent  or  interior  laryngeal  nerve, 
behind  the  inferior  angle  of  the  thyroid  cartilage,  and  is  distributed 
to  the  muscles  and  mucous  membrane  of  the  larynx. 

The  Tracheal  Artery  is  very  constant  in  its  existence.  It  arises  from 
the  inferior  thyroid  opposite  the  transverse  process  of  the  seventh  cervi- 
cal vertebra,  and  passes  downward  behind  the  trachea  to  a  point  in  close 
relation  to  the  bifurcation  of  the  trachea.  Here  the  artery  divides  into 
branches  which  supply  the  trachea,  bronchial  tubes,  lymphatic  glands, 
and  lower  portion  of  the  longus  colli  muscle,  and  anastomoses  with 
the  intercostal  and  bronchial  arteries. 

The  Suprascapular  Artery  (transverse  scapular  or  transverse  humeral) 
is  about  3^  mm.  (^  inch)  in  calibre.  It  arises  from  the  thyroid  axis, 
and  passes  outward  and  downward  to  the  scapula.  Its  branches  are  the 
thoracic,  acromial,  supraspinous,  and  infraspinous. 

The  Transversalis  Colli,  or  Transverse  Cervical  Artery,  arise  from  the 
thyroid  axis,  and  passes  outward  in  a  tortuous  course  to  the  superior 
angle  of  the  scapula,  where  it  divides  into  the  superficial  cervical  and 
posterior  scapular  arteries. 

The  Internal  Mammary  and  Superior  Intercostal  Arteries  are  import- 
ant to  the  head  and  neck,  as  they  by  their  relation  with  other  arteries 
complete  the  system  of  collateral  circulation.  The  supetior  gives  olf 
the  deep  cervical,  which  communicates  with  the  arteria  princeps  cervicis 
of  the  occipital  artery. 

THE  VEINS. 

The  veins  are  those  vessels  of  the  body  through  which  the  blood  is 
returned  to  the  heart.  They  originate  at  the  termination  of  the  capil- 
laries (minute  vessels  between  the  arteries  and  veins)  throughout  the 
body,  .and  unite  and  anastomose  to  form  larger  vessels  as  they  approach 
the  heart.  They  inosculate  more  freely  than  do  the  arteries,  and,  unlike 
these,  contain  throughout  their  course  numerous  valves  which  open 
toward  the  heart  and  j)revent  regurgitation  of  the  l)lood.  The  veins 
are  divided  into  two  groups — systemic  and  pulmonary. 

The  Systemic  Veins  are  those  which  collect  the  blood  from  all  portions 
of  the  body  excepting  the  lungs.  They  are  divided  into  two  sets — 
those  that  collect  the  blood  from  the  head,  upper  and  lower  extrem- 
ities, and  the  greater  ])ortion  of  the  body  ;  and  those  that  collect  the 
blood  from  the  alimentary  canal  and  its  glandular  ai)paratus  below  the 
diaphragm,  and  terminate  in  the  portal  system.  The  systemic  veins  are 
again  divided  into  superficial  and  deep. 

The  Pulmonary  Veins,  four  in  number,  tM'o  for  each  lung,  collect  the 
blood,  which  is  arterial,  from  the  capillaries  of  the  lungs  and  convey  it 
to  the  left  auricle  of  the  heart. 


248  ANATOMY. 

Superior  Vena  Cava,  Innominate,  and  Thyroid  Veins. 

The  Superior  or  Descending  Vena  Cava  (see  Fig.  106)  is  the 
large  vessel  that  receives  all  the  blood  from  the  upper  extremities,  the 
head,  and  the  walls  of  the  thoracic  cavity.  It  is  from  2  to  3  inches  in 
length,  and  commences  at  the  junction  of  the  right  and  left  innominate 
veins,  internal  to  and  just  below  the  attachment  of  the  first  costal  carti- 
lage of  the  right  side  to  the  sternum.  It  passes  almost  directly  down- 
ward, curving  slightly  to  the  left,  and  enters  the  right  auricle  opposite 
the  third  costal  cartilage  at  its  upper  anterior  portion,  its  orifice  look- 
ing downward  and  forward. 

The  Innominate  or  Brachio-Cephalic  Veins  are  two  in  num- 
ber, right  and  left.  They  each  originate  at  the  junction  of  the  subclavian 
and  the  internal  jugular  veins,  which  are  situated  posterior  to  the  sternal 
extremities  of  the  clavicles,  and  extend  downward  to  the  origin  of  the 
superior  vena  cava,  which  they  form  by  their  union.  They  are  of 
unequal  length,  and  diifer  from  mpst  of  the  other  veins  of  the  body  by 
being  destitute  of  valves. 

The  Right  Innominate  Vein  is  the  shorter  of  the  two,  being  but 
slightly  over  1  inch  in  length.  It  extends  from  its  commencement 
almost  vertically  downward  external  to  the  origin  of  the  subclavian 
and  innominate  arteries,  the  pleura  being  interposed  between  it  and  the 
lung  on  the  right  side.  The  vessels  which  empty  into  it  are  the  right 
thoracic  (lymphatic)  duct,  the  right  vertebral  vein,  right  mammary, 
right  inferior  thyroid,  and  the  right  superior  intercostal  veins. 

The  Left  Innominate  Vein  is  larger  and  longer  than  the  right, 
beiuo;  about  '4  inches  in  leny-th.  It  extends  from  its  origin  on  the  left 
side  of  the  sternum  from  left  to  right  across  the  superior  and  anterior 
portion  of  the  chest,  inclining  slightly  downward  to  its  union  with  the 
right  innominate  vein.  It  is  in  relation  with  the  sterno-clavicular  artic- 
ulation, the  ui)per  portion  of  the  manubrium,  from  which  it  is  sepa- 
rated only  by  the  lower  extremities  of  the  sterno-hyoid  and  sterno- 
thyroid muscles  and  the  thymus  gland,  or  its  remains  in  the  adult.  The 
three  arteries  arising  from  the  arch  of  the  aorta  and  the  phrenic  and 
pneumogastric  nerves  pass  down  the  neck  in  close  proximity  to  it,  the 
transverse  portion  of  the  arch  of  the  aorta  being  situated  below  it. 

The  Trihiitarie.s  of  the  Left  Id  nominate  Vein  are  the  thoracic  (lym- 
phatic) duct,  the  left  vertebral,  left  inferior  thyroid,  and  the  left  supe- 
rior intercostal  veins. 

The  Inferior  Thyroid  Veins  are  generally  two  in  number,  right 
and  left,  tinJugh  occasionally  there  are  three  or  even  four.  They  are 
formed  by  the  union  of  numerous  small  veins  which  originate  in  the 
lower  portion  of  the  thyroid  body,  and  which  anastomose  with  similar 
branches  from  the  middle  and  supi-rior  thyroid  wins.  They  jiass  down- 
ward, and  form  a  plexus  in  fi-ont  of  the  trachea  below  the  istlnnus  of 
the  thyroid  gland.  This  plexus  often  causes  trouble  from  hemorrhage 
in  the  operation  of  tracheotomy.  The  inferior  thyroid  vein  (or  veins, 
if  there  are  more  than  one)  of  the  right  side  are  situated  a  little  to 
the  right  of  the  median  line,  while  those  of  the  left  side  are  usually 
directly  in  the  median  line.     As  they  descend  in  front  of  the  trachea 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,  ETC.  249 

they  are  in  close  proximity  to  the  sterno-thyroid  muscles.  The  vein  of 
the  left  side  empties  into  the  left  innominate  vein,  while  that  of  the  right 
side  varies  in  its  termination.  It  may  empty  into  the  left  innominate 
vein  in  common  with  the  vein  of  the  left  side  or  at  the  junction  of  the 
right  and  left  innominate  veins,  or  into  the  right  innominate  vein. 
Occasionally  there  exists  a  median  vein  which  is  independent  of  the 
others,  and  which  passes  down  along  the  central  portion  of  the  trachea 
anteriorly.  These  veins  are  all  supplied  with  valves,  which  are  situated 
at  their  terminal  extremities. 

The  Tributaries  of  the  Inferior  Thyroid  Yeins  are  the  tracheal  and 
inferior  laryngeal. 

Veins  of  the  Head  and  Neck. 

The  blood  of  the  head  and  the  greater  portion  of  the  neck  is  returned 
to  the  heart  through  the  medium  of  tMO  veins  on  either  side,  the  exter- 
nal and  internal  jugular  (Fig.  112).  Close  to  their  termination  these 
large  veins  have  valves.  The  other  veins  of  the  head  and  neck  are 
generally  not  supplied  with  valves.  They  are  divided  into  external 
and  endocranial  veins. 

The  External  Veins  are  the  temporo-maxillary,  facial,  temporal,  inter- 
nal maxillary,  posterior  auricular,  occipital,  lingual,  and  pharyngeal. 

The  Facial  or  Anterior  Facial  Vein  commences  near  the  inner 
angle  of  the  eye  at  the  termination  of  the  angular  vein.  It  passes 
downward  and  outward  along  the  side  of  the  nose,  then  extends 
obliquely  to  the  facial  notch  in  front  of  the  lower  border  of  the 
masseter  muscle,  where  it  passes  inward  and  backward  under  the 
platysma  myoides  and  deep  fascia,  and  crosses  the  digastric  muscle, 
below  w^iich  it  joins  the  anterior  division  of  the  temporo-maxillary 
vein.  This  union  forms  the  common  facial  vein,  which  is  a  short  trunk 
terminating  in  the  internal  jugular  vein  on  a  level  with  the  hyoid  bone. 
The  general  course  of  the  iacial  vein  is  similar  to  the  facial  artery, 
though  it  is  more  superficially  situated  and  less  tortuous.  Upon  the 
face  it  is  imbedded  in  the  subcutaneous  fat,  and  passes  above  all  the 
facial  muscles  excepting  the  zygomaticus  major,  beneath  Avhich  it  ex- 
tends. 

The  Tributaries  of  the  Facial  Vein  are  the 
Angular,  Buccal, 

Frontal,  Masseter, 

Supraorbital,  Parotid, 

Inferior  palpebral  (two  or  three),  Submental, 

Superior  labial.  Submaxillary, 

Deep  facial,  or  Inferior  palatine. 

Anterior  internal  maxillary. 
The  Angular  Vein  is  formed  by  the  union  of  the  frontal  and  supra- 
orbital veins  at  a  point  near  the  articulation  of  the  nasal  and  frontal 
bones.  It  is  quite  superficially  situated,  and  passes  obliquely  downward 
and  outward  between  the  side  of  the  nose  and  the  inner  margin  of  the 
orbit. 

The  Tributaries  of  the  Angular  Vein  are  the  nasal  arch,  which,  when 


250 


ANAT03IY. 


present,  spans  the  root  of  the  nose  and  communicates  with  the  angular 
vein  of  the  opposite  side,  the  superior  palpebral  which  is  found  on  its 
orbital  side,  the  commencement  of  the  ophthalmic  vein  with  which  pos- 


FiG.  112. 


Lmjual 


Veins  of  the  Head  aud  Neck. 

teriorly  it  freely  communicates,  and  anteriorly  a  few  venules  from  the 
nose. 

The  Frontal  Vein  is  formed  by  the  union  of  numerous  small  branches 
situated  over  the  greater  ])art  of  the  region  of  the  frontal  bone.  It 
communicates  with  small  l)ranches  from  the  temporal  and  supraorbital 
veins,  as  well  as  with  branches  from  the  corresponding  vein  of  the 
opposite  side.     It  passes  downward  beneath  the  proximal  extremity  of 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,  ETC.  251 

the  eyebrow  and  terminates  in  the  angular  vein.  The  right  and  left 
frontal  veins  occasionally  communicate  with  each  other,  or  they  may 
unite  to  form  a  single  trunk,  separating  again  into  two  branches. 

The  Supraorbital  1  Yin  is  much  smaller  than  the  frontal.  It  is  ibrmed 
by  the  union  of  small  branches  from  the  forehead,  eyebrow,  and  eyelid, 
and  inosculates  with  the  temporal  and  ophthalmic  veins,  uniting  with 
the  frontal  to  form  the  angular  vein. 

The  Inferior  Palpebral  Veins  of  either  side  originate  in  the  lower 
eyelid,  being  formed  by  branches  from  adjacent  parts  anastomosing  with 
the  infraorbital  veins.  They  terminate  by  emptying  into  the  upper 
portion  of  the  facial  vein. 

The  Superior  Labial  Vein  commences  in  a  plexus  situated  in  the 
upper  lip,  and  anastomoses  with  the  corresponding  veins  of  the  opposite 
side.  It  passes  outward  and  upward,  and  enters  the  facial  vein  on  a 
level  with  the  ala  of  the  nose. 

The  Deep  Facial  or  Anterior  Internal  Maxillary  Vein  is  of  large 
size,  and  originates  in  the  pterygoid  plexus  formed  by  the  internal 
maxillary  veins.  It  passes  forward  and  downward  in  close  apposition 
to  the  zygomatic  surface  of  the  superior  maxillary  bone,  and  terminates 
beneath  the  malar  bone  in  the  anterior  facial  vein. 

Tlie  Buccal,  Masseteric,  and  Farotid  Veins  are  small  branches  that 
originate  in  the  structures  indicated  by  their  names.  They  terminate 
by  emptying  into  the  lateral  surface  of  the  facial  vein. 

The  Submental  Vein  is  formed  by  branches  which  originate  in  the 
submental  region.  It  passes  backward  along  the  base  of  the  inferior 
maxillary  bone,  and  terminates  by  emptying  into  the  facial  vein  just  as 
that  vessel  curves  under  the  jaw.  Its  anterior  branch  connnunicates 
with  the  anterior  jugular  vein,  and  receives  branches  which  come  from 
the  region  of  the  submaxillary  gland  and  the  mylo-hyoid  nniscle. 

The  SubmcLvillar'i/  Veins  originate  in  the  submaxillary  muco-salivary 
gland,  and  terminate  either  in  the  facial  or  submental  vein. 

The  Inferior  Palatine  Vein  originates  in  the  structures  in  and  about 
the  tonsils  and  soft  palate.  It  passes  downward  in  close  proximity  to 
the  ]:)harynx,  and  generally  terminates  by  emptying  into  the  facial  vein. 

The  following  is  from  Allen's  Human  Anatomy,  p.  417  : 

"  It  will  be  seen  that  the  venous  supply  of  the  face  differs  in  some 
important  particulars  from  that  of  the  truidv  and  limbs.  In  the  last- 
named  localities  both  deep  and  superficial  currents  flow  in  the  same 
direction  toward  the  heart.  The  facial  trunk,  however,  is  not  formed 
by  primal  venules,  as  is  commonly  the  case,  but  by  branches  communi- 
catino;  with  the  frontal  and  supraorbital  veins,  and  by  a  transverse 
branch  found  at  the  bridge  of  the  nose.  It  is  highly  probable  that 
much  of  the  blood  of  the  interorbital  space  and  of  the  locality  about 
the  inner  canthus  of  the  eye  flows  through  the  orbital  conduits  to  the 
cavernous  sinus.  Farther  down  the  face  it  is  seen  that  the  infraorbital 
artery  alone  of  all  the  vessels  of  the  face  possesses  vense  comites.  These 
jjroniptly  join  the  orbital  set  of  veins  or  aid  in  swelling  the  volume  of 
the  internal  maxillary  vein.  The  veins  corresponding  to  the  deep  parts 
of  the  face,  other  than  those  mentioned,  also  seek  an  outlet  in  the  same 
trunk,  so  that  much  of  the  superficial  blood  of  the  upper  part  and  side 


252  ANATOMY. 

of  the  face  passes  imoard  to  the  brain-case  and  to  the  interior  of  the 
facial  region,  while  the  remaining  portion  flows  doumward  to  join  the 
external  and  anterior  jugular  veins. 

"  It  is  of  interest  to  note  that  in  facial  phlebitis  the  disease  has  a  tend- 
ency to  extend  upward,  except  when  the  exciting  cause  lies  at  a  point 
in  or  about  the  lower  lip ;  in  which  case,  as  a  rule,  the  inflammation 
extends  downward.  In  a  case  reported  by  M.  Bechez,^  illustrative  of 
of  the  fact  just  stated,  a  soldier,  aged  forty-two,  was  attacked  with  fever, 
followed  bv  redness  and  slio;ht  swellino;  of  the  forehead.  This  swellino; 
soon  became  more  pronounced  along  the  temporo-frontal  veins,  which 
Avere  hard,  prominent,  and  of  a  violet  color.  The  eyelids  were  oede- 
matous  and  the  conjunctiva  chimosed.  The  patient  died  about  the 
seventh  day,  A  somewhat  similar  case,  recorded  by  Mr.  T.  H.  Sylves- 
ter, is  interesting  from  the  fact  that  the  frontal  veins  determined  the 
extent  of  the  inflamed  tract.  A  puncture  of  the  lip  excited  the  phle- 
bitis, wliich  extended  to  a  small  vein  at  the  outer  side  of  the  nose, 
thence  to  the  inner  canthus,  and  from  that  point  along  the  frontal 
vein  to  the  scalp,  which  became  extensively  inflltrated  with  pus.  The 
case  terminated  fatally  at  the  end  of  five  weeks. 

"  The  relations  existing  between  the  venous  blood  of  the  face  and  that 
of  the  brain-case  are  rendered  evident  by  the  fact  that  the  state  of  the 
circulation  of  the  external  nose  is  sometimes  an  index  of  the  condition 
of  the  vessels  of  the  brain." 

The  Temporo-maxillary  Vein  is  a  short  trunk  which  commences 
at  the  termination  of  the  temporal  and  internal  maxillary  vein.  It 
extends  downward  within  the  parotid  gland  and  along  the  outer  sur- 
face of  the  external  carotid  artery,  between  the  sterno-cleido-mastoid 
muscle  and  the  ramus  of  the  jaw,  to  a  point  near  its  angle,  where  it 
divides  into  two  brandies.  One  branch  passes  downward  and  slightly 
forward,  uniting  with  the  facial  to  form  the  common  facial  vein ;  tlie 
other  branch  passes  downward  and  backward,  terminating  in  the 
external  jugular  vein. 

The  Commox  Temporal  Yeix  is  the  medium  through  which,  in 
great  measure,  the  l)lood  is  returned  from  the  region  of  the  distribution 
of  the  temporal  artery;  the  vein,  however,  does  not  accompany  the 
artery  in  its  course.  It  originates  above  the  base  of  the  zygoma  at  the 
termination  of  the  superficial  and  middle  temporal  veins.  It  passes 
downward  and  inward  beneath  the  parotid  gland,  and  unites  with  the 
internal  maxillary  vein  at  the  point  of  origin  of  the  temporo-maxillary 
vein. 

The  Ti-ihutaries  of  the  Common  Temporal  Vein  are  the  superficial  and 
middle  temporals,  tlie  jiarotid,  the  articular,  the  anterior  auricular,  and 
the  transverse  facial  veins. 

The  Superftcial  Temporal  Vein  originates  through  the  union 
of  numerous  small  branches  in  the  form  of  a  plexus  w^hich  is  situated 
over  the  region  of  the  vertex  and  side  of  the  head.  It  anastomoses 
with  the  corresponding  artery  of  the  opposite  side,  the  frontal,  supra- 
orbital, occipital,  and  jiosterior  auricular  veins.  These  branches  pass 
downward,  converge  toward  two  central  stems  which  finally  unite,  con- 

^  Oaz.  heb.,  1863,  716. 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,   ETC.  253 

tinue  downwanl  and  pass  forward  in  front  of  the  ear  to  a  point  just 
above  the  zygoma,  where  it  joins  the  middle  temporal  vein. 

The  INIiDDLE  Temporal  Vein  originates  in  a  plexus  of  veins  situ- 
ated in  the  temjjoral  muscle.  This  plexus  communicates  with  the  deep 
temporal  veins  as  well  as  with  the  pterygoid  plexus.  The  vein  then 
passes  out  of  the  muscle  through  the  temporal  fascia,  and  joins  the 
superficial  temporal  vein  just  above  the  base  of  the  zygoma.  Its  orbital 
branch  originates  from  the  union  of  a  number  of  the  external  palpe- 
bral veins ;  it  inosculates  with  the  supraorbital  and  facial  veins,  passes 
backward,  and  terminates  in  the  middle  temporal  vein. 

The  Parotid  Veins  are  small  vessels  which  pass  from  the  parotid 
gland  and  empty  into  the  common  temporal  vein. 

The  Articular  A-^eins  pass  from  the  temporo-maxillary  articula- 
tion and  terminate  in  the  common  temporal  vein. 

The  Anterior  Auricular  Vein  passes  from  the  external  ear  and 
empties  into  the  common  temporal  vein. 

The  Transverse  Facial  Vein  returns  the  blood  from  the  region 
supplied  by  the  transverse  facial  artery,  and  inosculates  with  the  facial 
and  infraorbital  veins. 

The  Internal  Maxillary  or  Posterior  Facial  Vein  orig- 
inates in  a  large  plexus  of  veins  which  is  situated  betMeen  the  temporal 
and  external  pterygoid  muscles,  as  well  as  partly  between  the  two 
pterygoid  muscles.  It  passes  backward  and  outward,  accompanied  by 
the  internal  maxillary  artery,  enters  the  parotid  gland,  and  terminates 
by  emptying  into  the  temporo-maxillary  vein  about  halfway  between 
the  zygoma  and  the  angle  of  the  jaw.  The  plexus  from  which  the 
internal  maxillary  vein  originates  is  formed  by  numerous  tributaries 
which  arise  from  the  region  supplied  by  the  internal  maxillary  artery. 
These  tributaries  are  the  infraorbital,  which  commences  on  the  face  and 
anastomoses  with  the  veins  below  the  eye,  and  passes  backward  through 
the  infraorbital  canal  and  the  spheno-maxillary  fissure  to  join  the  ptery- 
goid plexus  ;  the  posterior  dental  or  alveolar,  which  commences  on  the 
surface  of  the  superior  maxilla  and  the  jiosterior  superior  teeth ;  the 
superior  palatine,  spheno-palatine,  and  Vidian,  which  pass  through 
the  foramina  indicated  by  their  names  to  join  the  plexus ;  the  infe- 
rior dental,  which  commences  on  the  chin,  receiving  branches  from 
the  lower  incisor  teeth,  and  passes  backward  along  the  inferior  dental 
canal,  and  emerges  from  the  jaw  at  the  posterior  dental  foramen,  AAhere 
it  is  joined  by  the  mylo-hyoid  vein.  It  then  passes  directly  upward  to 
the  plexus ;  the  deep  temporal  veins,  three  or  four  in  number,  descend 
to  the  plexus.  There  are  also  other  muscular  branches,  such  as  the 
pterygoids,  masseteric,  and  buccal,  as  well  as  a  communicating  branch 
from  the  inferior  ophthalmic  vein,  which  join  the  plexus.  The  middle 
meningeal  veins  are  also  tributaries.  They  are  two  in  number,  and  are 
the  vense  comites  of  the  middle  meningeal  artery.  They  originate 
wnthin  the  dura  mater  of  the  brain  and  inosculate  with  the  cavernous 
sinus. 

The  Posterior  Auricular  Vein  is  much  larger  than  the  artery 
of  the  same  name.  It  originates  in  a  plexus  formed  by  small  veins 
situated  at  the  posterior  portion  of  the  side  of  the  head.     This  plexus 


254  ANATOMY. 

receives  comnmnicatlng  branches  from  the  temporal  and  occipital  veins, 
and  occasionally  a  branch  from  the  mastoid  vein.  It  passes  downward 
behind  the  ear,  crosses  the  mastoid  process  of  the  temporal  bone  and  the 
npper  portion  of  the  sterno-cleido-mastoid  muscle,  and  terminates  by 
emptying  into  the  external  jugular  vein. 

The  Occipital  Vein  commences  on  the  back  of  the  head,  in  the 
region  supplied  by  the  occipital  artery.  It  is  formed  from  a  plexus  of 
small  veins  and  from  the  communicating  branches  of  its  fellow  of  the 
opposite  side,  as  well  as  from  branches  which  enter  the  posterior  auric- 
ular and  temporal  veins.  It  generally  communicates  with  the  lateral 
sinus  of  the  venous  system  of  the  brain  through  the  emissary  vein,  a 
branch  which  traverses  the  mastoid  foramen  of  the  temporal  bone.  It 
extends  downward  and  forward,  accompanied  by  the  occipital  artery, 
and  generally  terminates  by  emptying. into  the  internal  jugular,  though 
occasionally  it  joins  the  external  jugular. 

The  Lingual  Vein  arises  from  three  sources — the  ranine,  the  two 
venae  comites,  and  the  dorsal  veins  of  the  tongue. 

The  Ha  nine  or  Sublingual  Vein  is  the  largest  of  the  branches  which 
go  to  form  the  lingual.  It  commences  by  numerous  superficial  branches 
situated  on  the  under  surface  of  the  tip  of  the  tongue,  and  anastomoses 
M'ith  the  corresponding  vein  of  the  opposite  side.  It  extends  backward, 
covered  by  the  mucous  membrane  of  the  tongue,  and,  accompanied  by 
the  hypoglossal  nerve,  passes  to  the  lateral  surface  of  the  hyo-glossus 
muscle.  Small  veins  empty  into  it  from  the  mucous  membrane  of  the 
floor  of  the  mouth,  the  substance  of  the  tongue,  and  the  sublingual 
gland. 

The  Two  Vence  Comites  are  two  small  vessels  which  accompany  the 
lingual  artery,  and  terminate  by  emptying  into  the  lingual  vein. 

The  Dorsal  Vein  originates  in  a  plexus  which  is  situated  on  the 
under  surface  of  the  mucous  membrane  of  the  posterior  part  of  the 
tongue.  These  veius  occasionally  unite  to  form  one  common  trunk,  or 
they  may  break  up  into  several  independent  branches,  which  empty 
either  into  the  external  jugular  or  the  common  facial  vein.  Cases  are 
reported  in  which  they  have  emptied  into  the  pharyngeal  or  internal 
jugular  vein. 

The  Pharyngeal  Vein  originates  in  the  pharyngeal  plexus,  which 
is  formed  by  branches  wliich  pass  from  the  lateral  and  posterior  walls 
of  the  pharynx.  It  also  receives  branches  from  the  soft  pakite  and 
from  the  Vidian  and  meningeal  veins,  w^hich  pass  through  the  oval 
and  spinous  foramina  in  the  sphenoid  bone,  and  from  the  pterygoid 
plexus.  After  receiving  these  branches  it  passes  downward,  and  gener- 
ally terminates  by  emptying  into  the  internal  jugular  vein  at  the  inferior 
extremity  of  the  parotid  gland,  though  occasionally  it  passes  into  the 
common  facial  vein  or  unites  with  the  lingual  or  superior  thyroid  veins. 

VEINS   OF   THE    NECK. 

The  veins  of  the  neck  return  the  blood  from  the  external  and  internal 
portions  of  the  head  and  face,  the  neck,  and  part  of  the  region  of  the 
shoulder.     Thev  are  as  follows  : 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,  ETC.  255 

External  jugular,  Internal  jugular, 

Anterior  jugular,  Vertebral. 

The  External  Jugular  Vein  returns  the  principal  portion  of  the 
blood  from  the  internal  surface  of  the  face  and  the  external  surface  of 
the  head.  It  commences  within  the  parotid  gland  near  the  angle  of  the 
inferior  maxillary  bone.  It  is  formed  by  the  confluence  of  the  posterior 
auricular  and  the  posterior  division  of  the  temporo-maxillary  veins ; 
it  passes  almost  perpendicularly  downward.  Its  position  is  indicated 
by  a  line  drawn  from  the  angle  of  the  inferior  maxilla  to  the  middle 
of  the  clavicle.  It  is  quite  superficially  situated,  being  covered  only  by 
the  skin  and  the  platysma  myoides  muscle.  It  is  crossed  about  its  centre 
by  the  superficial  cervical  nerve.  After  leaving  the  angle  of  the  jaw  it 
passes  over  the  sterno-cleido-mastoid  muscle,  along  its  posterior  margin, 
to  a  point  just  above  the  clavicle,  where  it  pierces  the  deep  fascia  of  the 
neck.  It  then  extends  slightly  inward,  and  generally  terminates  by 
emptying  into  the  subclavian  vein  in  close  relation  to  the  external  bor- 
der of  the  anterior  scalenus  muscle.  Occasionally  it  terminates  by 
emptying  into  the  internal  jugular  vein  or  at  the  point  of  junction  of 
the  internal  jugular  and  subclavian  veins.  The  external  jugular  is 
furnished  with  two  sets  of  valves,  one  of  which  is  imperfect  and  situ- 
ated at  its  termination ;  the  other  set  is  perfect  and  located  about  an 
inch  and  a  half  above  the  clavicle. 

Tributaries. — The  tributaries  of  the  external  jugular  vein  are  the 
posterior  external  jugular,  transverse  cervical,  and  suprascapular. 

The  Posterior  External  Jugular  Vein  commences  by  numerous 
branches,  which  are  situated  in  the  muscles,  skin,  and  fascia  in  the 
region  of  the  occiput  and  posterior  portion  of  the  neck.  It  terminates 
by  emptying  into  the  external  jugular  vein  midway  between  the  clavicle 
and  the  angle  of  the  jaw. 

The  Transverse  Cervical  and  Suprascapular  ^^eins  return  the  blood 
from  the  region  of  the  shoulder,  and  closely  follow  the  course  of  the 
suprascapular  and  transversalis  colli  arteries.  These  veins  are  sup- 
plied with  valves. 

The  Anterior  Jugular  Vein  varies  considerably  in  size,  and  is 
not  constant  in  its  existence.  It  commences  below  the  chin,  nearly  in 
the  median  line,  by  branches  situated  in  the  suprahyoid  region,  the 
lower  lip,  and  the  chin.  It  also  receives  a  communicating  branch 
from  the  submental  vein.  It  passes  downward,  in  close  relation  to  the 
middle  of  the  neck,  in  a  line  with  the  sternal  extremity  of  the  clavicle. 
Slightly  above  the  clavicle  it  pierces  the  deep  fascia  of  the  neck,  passes 
outward  and  downward,  behind  the  sterno-cleido-mastoid  muscle,  and 
generally  terminates  by  emptying  into  the  lower  extremity  of  the  exter- 
nal jugular  vein,  though  occasionally  it  empties  into  the  subclavian  vein. 
Just  after  this  vein  pierces  the  deep  fascia  it  generally  receives  a  com- 
municating branch  from  the  facial  vein,  and  also  small  branches  from 
the  larynx,  and  occasionally  from  the  thyroid  body.  The  transverse 
cervical  and  suprascapular  veins  sometimes  terminate  in  the  anterior 
jugular  vein.  The  anterior  jugular  veins  of  both  sides  occasionally  com- 
municate through  small  branches  which  extend  from  the  lower  extrem- 
ities, one  branch  usually  being  of  considerable  size,  and  passing  through 


256  ANAT031Y. 

the  interfascial  space  just  above  the  sternum.     This  vein  is  not  supplied 
with  valves. 

The  Ixterxal  Jugular  Vein  is  the  largest  and  most  import- 
ant of  the  veins  which  descend  the  neck,  and  returns  the  blood  from 
the  greater  portion  of  the  brain-case  and  superficial  structures  of  the 
face  and  neck.  It  commences  at  the  termination  of  the  lateral  and 
inferior  petrosal  sinuses  in  the  enlarged  and  rounded  portion  of  the 
posterior  lacerated  (jugular)  foramen,  from  which  it  passes  downward 
almost  along  a  vertical  line,  and  then  slightly  forward,  and  becomes 
superficial  at  the  lower  portion  of  the  neck.  Its  j)osition  is  indicated 
by  a  line  drawn  from  the  anterior  portion  of  the  mastoid  process  of  the 
temporal  bone  to  the  sterno-clavicular  articulation,  beneath  which  it  ter- 
minates by  joining  the  subclavian  vein  to  form  the  innominate  vein. 
This  vein  is  not  of  uniform  calibre  throughout  its  course.  At  its  com- 
mencement is  the  dilatation  known  as  its  bulb  or  si)ius.  Opposite  the 
hvoid  bone  it  increases  in  size  through  its  confluence  with  the  common 
facial  and  several  deep  veins.  Near  its  termination  it  is  slightly  dimin- 
ished in  calibre,  and  furnished  with  a  single  or  double  valve  which  is 
situated  on  its  outer  wall.  This  vein  may  be  entirely  absent  on  the 
left  side  (Grul)er). 

Relatione. — At  its  commencement  the  internal  jugular  vein  is  situ- 
ated posterior  to  the  internal  carotid  artery,  the  ninth,  tenth,  eleventh, 
and  twelfth  nerves,  and  rests  upon  the  rectus  capitis  lateralis  muscle. 
It  then  passes  to  the  lateral  side  of  the  internal  carotid  artery,  the 
ninth  (glosso-pharyngeal),  and  the  twelfth  (hypoglossal)  nerves,  pass- 
ing between  the  vessels,  while  the  tenth  (pneumogastric)  nerve  passes 
downward  posteriorly  between  the  vein  and  the  artery,  within  the  com- 
mon sheath,  the  eleventh,  (spinal  accessory)  nerve  passing  backward  to 
the  inner  side  of  the  vein.  After  reaching  the  common  carotid  artery 
the  vein  extends  downward,  somewhat  overlapping  this  vessel.  The 
right  internal  jugular  vein  as  it  approaches  its  termination  generally 
diverges  slightly  from  the  artery,  while  the  vein  of  the  left  side  crosses 
toward  the  median  line. 

Tributaries. — In  addition  to  the  lateral  and  inferior  petrosal  sinuses, 
the  veins  that  empty  into  the  internal  jugular  ai"e  as  follows : 
The  pharyngeal,  Superior  thyroid, 

Lingual,  Middle  thyroid. 

Common  facial,  Occipital  (occasionally). 

The  pharyngeal,  lingual,  and  common  facial  veins  have  already  been 
described. 

The  Superior  Thyroid  Vein  commences  on  the  superficial  surface 
of  the  thyroid  body  by  numerous  small  branches  W'hich  extend  from 
its  surface  and  the  muscles  in  this  region.  It  receives  communicating 
l)ranchcs  from  the  superior  laryngeal  and  crico-thyroid  veins,  and  passes 
upward  and  backward  to  terminate  in  the  internal  jugular  vein.  Occa- 
sionally it  empties  into  the  common  facial  vein. 

The.  Middle  Thyroid  Vein  commences  by  branches  situated  in  the 
lateral  portion  of  the  thyroid  body,  receiving  tributaries  from  the 
larvnx  and  the  trachea.     It  passes  outward  over  the  common  carotid 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,  ETC. 


257 


artery,  and   terminates    by  emptying  into  the  internal   jugular    vein 
slightly  above  the  level  of  the  cricoid  cartilage. 

The  Vertebral  Vein  commences  by  numerous  branches  situated  in  the 
occipital  region,  these  branches  anastomosing  with  the  occipital,  the 
deep  cervical,  and  the  posterior  spinal  veins.  It  passes  downward 
along  the  vertebral  artery  through  the  foramina  in  the  transverse  pro- 
cesses of  the  first  six  cervical  vertel)r?e,  passes  over  the  subclavian 
artery,  and  terminates  by  emptying  into  the  innominate  vein  near  its 
origin :  it  sometimes  terminates  in  the  subclavian.  This  vein  is  sup- 
plied near  its  termination  by  either  a  single  or  a  double  valve.  Occa- 
sionally, as  it  passes  down  the  body  of  the  vertebrae,  it  receives  two 
branches,  one  opening  into  the  vessel  as  it  enters  the  foramen  in  the 
transverse  process  of  the  atlas,  while  the  other  is  received  oj^posite  the 
seventh  or  vertebral  prominence. 


The  Venous  Sinuses  of  the  Cranium 

are  large  canals  (Fig.  113)  analogous  to  veins,  and  into  which  the  vari- 
ous veins  of  the  brain,  the  ophthalmic  vein,  and  several  emissary  veins 

Fig.  113. 


Toreular 


Foramen  CctcurA 


Vertical  Section  of  the  Skull,  showing  the  sinuses  of  the  duia  mater. 

empty.  They  are  composed  of  two  coats,  internal  and  external.  The 
internal  coat  is  a  delicate  serous  membrane,  being  a  continuation  of  the 
lining  membrane  of  the  veins,  while  the  outer  coat  is  formed  by  the 
dura  mater.  From  this  fact  they  are  known  as  the  sinuses  of  the  dura 
mater.  They  are  fifteen  in  number,  and  are  divided  into  two  groups — 
the  supero-posterior  and  the  infero-anterior. 

The  Supero-posterior  Group  is  composed  of  six  sinuses : 
Superior  longitudinal.  Occipital, 

Inferior  longitudinal,  Eight  lateral, 

Straight,  Left  lateral. 

Vol.  I.— 17 


258  ANAT03TY. 

ToRCULAR  Herophili. — Before  passing  to  a  description  of  the 
sinuses  it  will  be  well  to  describe  what  is  known  as  the  torcular  Hero- 
phili. This  is  a  dilatation  formed  by  the  confluence  of  the  superior 
longitudinal,  the  straight,  the  occipital,  and  the  two  lateral  sinuses,  and 
is  situated  on  the  internal  surface  of  the  occipital  bone  at  the  internal 
protuberance,  where  the  superior  longitudinal  sinus  terminates  and  the 
lateral  sinuses  commence. 

The  Siqjerlor  Lo)t(/ifu(Jinal  tSi)U(s  commences  at  the  foramen  cfficum 
in  the  frontal  bone,  just  anterior  to  the  crista  galli.  In  infancy,  and 
occasionally  in  adult  life,  this  foramen  is  not  a  blind  one,  but  opens 
into  the  nasal  chambers.  AVhen  this  is  the  case  the  sinus  commences 
within  the  nose.  It  passes  upward,  backward,  and  downward  on  the 
under  surface  and  in  the  median  line  of  the  dome  of  the  brain-case,  its 
lower  wall  being  formed  by  the  upper  border  of  the  falx  cerebri.  It 
terminates  in  the  torcular  Herophili.  In  shape  it  is  triangular,  and  it 
is  crossed  by  numerous  chords  or  trabeculiTe  (chordae  Willisii).  At  its 
commencement  it  is  quite  small,  but  increases  gradually  in  size  to  its 
termination.  In  its  course  it  occasionally  deviates  from  the  median 
line,  especially  as  it  passes  along  the  occipital  bone.  It  receives  tribu- 
taries from  the  veins  of  the  brain,  Avhich  enter  the  sinus  in  a  forward 
direction  or  opposite  to  the  flow  of  blood  along  the  sinus.  Occasion- 
ally a  few  of  these  veins  which  enter  the  sinus  at  its  anterior  portion 
do  so  in  the  direction  of  the  blood-current.  The  tributary  from  the 
external  surface  of  the  parietal  bones  which  communicates  with  the 
veins  of  the  scalp  ]5asses  through  the  parietal  foramen  to  empty  into 
the  sinus.  It  is  small  in  calibre,  and  inconstant  in  existence  on  one  or 
both  sides. 

The  Infei-ior  Longitudinal  Sinus  is  shorter  and  much  smaller  than 
the  superior.  It  is  nearly  cylindrical  in  form,  and  is  often  called  the 
inferior  longitudinal  vein.  It  commences  at  the  anterior  portion  of  the 
free  or  inferior  extremity  of  the  falx  cerebri,  passes  backward  along  its 
inferior  border  to  the  tentorium  cerebelli,  and  terminates  in  the  straight 
sinus.  As  it  passes  l)ackward  it  receives  several  branches  from  the 
falx. 

The  Straight  Sinus  (sinus  tentorii)  commences  at  the  termination  of 
the  inferior  longitudinal  sinus,  which  is  situated  at  the  anterior  junction 
of  the  falx  cerebri  and  the  tentorium  cerebelli.  It  passes  backward  and 
slightly  downward  in  a  straight  line  along  the  union  of  the  falx  cerebri 
and  tentorium  cerel)elli,  increasing  in  size  as  it  extends,  and  terminates 
in  the  confluence  of  the  sinuses.  Its  transverse  section  is  triangular,  a 
few  crossing  cords  being  found  in  it.  Besides  the  inferior  longitudinal 
sinus,  its  tributaries  are  the  vense  Galeni  magnse,  the  inferior  median 
cerebri,  the  superior  cerebellar,  and  small  branches  from  the  tentorium 
cerebelli. 

The  Posterior  Occipital  Sinus  is  small  and  single,  though  occasionally 
it  is  represented  Iw  two  sinuses.  It  commences  by  l)ranches  situated 
around  the  posterior  border  of  the  foramen  magnum  which  conuiiuni- 
cate  with  the  posterior  spinal  ])lexus  ;  it  passes  backward  along  the 
inferior  border  of  the  falx  cerebelli,  and  terminates  in  the  confluence 
of  the  sinuses.     It  receives  small  branches  from  the  cerebellum. 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,   ETC.  259 

The  Lateral  Sinuses  in  either  side  are  large,  though  .seldom  of  equal 
size.  This  difference  in  calibre  is  caused  to  a  certain  extent  by  the 
deflection  of  th*e  straight  sinus  to  one  side  or  the  other  of  the  torcular 
Herophili,  and  by  its  emptying  into  one  or  the  other  sinus.  They 
begin  at  the  confluence  of  the  sinuses,  pass  outward,  forward,  and 
downward  along  the  semicircular  grooves  to  which  the  tentorium  is 
attached,  and  extend  from  the  internal  occipital  prt)tuberance  outward 
over  the  inferior  posterior  angle  of  the  parietal  bone,  thence  along 
the  sigmoid  groove  of  the  mastoid  process  of  the  temporal  bone,  over 
the  jugular  process  of  the  occipital  bone,  and  terminate  in  the  bulb  of 
the  internal  jugular  veins  situated  within  the  rounded  or  enlarged  por- 
tion of  the  posterior  lacerated  (jugular)  foramen.  The  tributaries  of 
these  sinuses  are  veins  from  the  posterior  part  of  the  cerebrum,  from 
the  cerebellum,  diploe,  superior  petrosal  sinus,  and  emissary  veins  pass- 
ing through  the  posterior  condyloid  and  mastoid  foramina,  which  are 
communicating  veins  between  the  sinuses  and  the  veins  of  the  external 
portion  of  the  cranium. 

The  Infero-anterior  Group  is  composed  of  seven  sinuses : 
Cavernous,  Superior  petrosal, 

Spheno-parietal,  Transverse, 

Circular,  Anterior  occipital. 

Inferior  petrosal. 

The  Cavenwus  Siimses  (Fig.  114),  two  in  number,  receive  their  name 
from  the  fact  of  their  being  crossed  or  interlaced  by  numerous  filaments 
of  connective  tissue,  which  give  them  the  a})pearance  of  cavernous  tissue. 
They  are  situated  one  on  each  lateral  surface  on  the  body  of  the  s})he- 
noid  bone,  and  extend  from  the  inner  portion  of  the  anterior  lacerated 
foramina  backward  to  the  apex  of  the  petrous  portion  of  the  temporal 
bones.  They  vary  in  width  and  shape,  being  narrow  and  pointed  in 
front  and  wide  behind. 

Their  tributaries  are,  anteriorly,  the  terminations  of  the  ophthalmic 
veins.  On  their  proximal  sui-face  they  conununicate  with  each  other 
through  the  circular  sinus.  A  communicating  branch  from  the  ptery- 
goid plexus  of  either  side  empties  bypassing  through  the  oval  foramina 
in  both  wings  of  the  sphenoid  bone.  They  also  receive  branches  from 
the  cerebral  veins,  and  connnunicating  branches  from  the  spheno-parie- 
tal sinuses.  Posteriorly  they  terminate  by  emptying  into  the  superior 
and  inferior  petrosal  sinuses.  The  third,  fourth,  and  the  ophthalmic 
division  of  the  fifth  nerve  on  either  side  pass  for^^•ard  along  the  outer 
walls  to  make  their  exit  through  the  anterior  lacerated  foramina.  The 
internal  carotid  arteries,  the  sixth  nerves,  and  the  parotid  sympathetic 
plexuses  pass  forward  to  the  inner  margins  of  the  floors  of  the  sinuses, 
the  arteries  and  nerves  passing  through  these  cavernous  sinuses ;  these 
nerves  and  vessels  are  separated  from  the  blood  of  the  sinuses  by  their 
thin  lining  membrane. 

The  Spheno-parietal  Si7iuses  (two  in  number)  are  situated  on  the 
under  surfaces  of  the  lesser  wnngs  of  the  sphenoid  bone.  They  receive 
communicating  branches  from  the  middle  meningeal,  anterior  temporal, 
and  diploic  veins,  and  occasionally  a  small  vein,  the  ophthalmo-menin- 
geal.     They  terminate  by  emptying  into  the  cavernous  sinuses. 


260 


ANAT03IY. 


The  Oircniar  Sinus  is  situated  around  the  pituitary  body  within  the 
sella  turcica.  Its  lateral  portions  communicate  with  the  right  and  left 
cavernous  sinuses,  while  its  anterior  and  posterior  portions  have  received 
the  name  of  anterior  and  posterior  intercavernous  sinuses.  They  are 
not  constant  in  their  existence,  one  or  both  being  sometimes  absent. 


Fig.  114. 


LONGITUDINAL    SINUS 


OPTIC    NERVE 


OPHTHALMIC    VEII 


SPHENO-PARIETAL 

SINUS 


CIRCULAR    SINUS 


CAVERNOUS    SINUS 


ANTERIOR    OCCIPITAL 
SINUS 


SUPERIOR    PETROSAL 
SINUS 


INFERIOR    PETROSAL 
SINUS 


POSTERIOR    OCCIPITAL 


LATERAL    SINUS 


TORCULAR    HEROPHILl 


LONGITUDINAL    SINUS 


The  'Miuises  ol  the  Diua  M<iter,  been  in  hoiizontal  section  of  the  skull. 

Occasionally  there  is  a  third   conununicating  sinus   in  this  situation. 
When  this  is  the  case  it  passes  under  the  ]iituitary  body. 

The  Superior  Fefrosdl  Siiim  is  a  small  canal  which  commences  at  the 
postei'ior  and  lateral  ])ortion  of  the  cavernous  sinus,  passes  outward  and 
backward  along  a  groove  situated  on  the  ridge  between  the  anterior  and 
posterior  surfaces  of  the  petrous  portion  of  the  tem]>oral  bone,  and 
within  the  attached  margin  of  the  tentorium  cerel)elli,  and  terminates 
by  emptying  into  the  lateral  sinus  as  tliis  large  canal  passes  downward 
in  the  sigmoid  groove  between  the  mastoid  and  petrous  portions  of  the 


BLOOD-VESSEL  SYSTEM  OF  THE  HEAD,  ETC.  261 

temporal  bone.  It  receives  tributaries  from  the  cerebrum,  cerebellum, 
aud  tympanum,  the  last-named  vessels  passing  through  the  petro-squa- 
mous  fissure. 

The  Inferior  Petrosal  Sinus  is  much  shorter  and  wider  than  the 
superior.  It  commences  at  the  posterior  extremity  of  the  cavernous 
sinus,  passes  downward  and  outward  along  a  groove  over  the  articula- 
tion of  the  petrous  portion  of  the  temporal  bone  with  the  basilar  process 
of  the  occipital  bone,  extends  through  the  anterior  compartment  of  the 
posterior  lacerated  foramen,  aud  terminates  by  emptying  into  the  ante- 
rior portion  of  the  bulb  of  the  internal  jugular  vein. 

The  Anterior  Occipital,  or  Transverse  JSinus  (basilar  plexus  of  Vir- 
chow)  is  a  communicating  canal  or  plexus  of  vessels  situated  between 
the  right  and  left  inferior  petrosal  sinuses  in  front  of  the  foramen  mag- 
num.    It  receives  branches  from  the  anterior  spinal  veins. 

Veins  of  the  Orbit. 

Tlie  veins  of  the  orbit  are  two  in  number,  superior  and  inferior 
ophthalmic. 

The  Supeeior  Ophthalmic  Vein  is  considerably  larger  than  the 
inferior,  and  is  by  far  the  more  important  of  the  two.  It  commences 
by  the  confluence  of  the  frontal  vein  and  a  large  communicating  branch 
from  the  angular  vein,  a  tributary  of  the  facial.  It  extends  back- 
ward through  the  orbit,  in  company  with  the  ophthalmic  artery,  to  a 
point  near  the  optic  foramen,  Avhere  it  turns  a  little  outward  to  enter  the 
proximal  extremity  of  the  anterior  lacerated  foramen.  Here  it  j)asses 
into  the  brain-case,  and  terminates  by  emptying  into  the  cavernous 
sinus. 

Its  tributaries  are  the  veins  which  return  the  blood  from  the  region 
supplied  by  the  ophthalmic  artery  as  from  the  nasal  chamber,  the 
anterior  and  posterior  ethmoidal  cells,  the  muscles  of  the  eyeball,  the 
lachrymal  gland,  the  eyeball,  etc.  These  veins  receive  names  corre- 
sponding precisely  to  the  arteries  of  the  same  region,  and  anastomose 
freely  with  each  other. 

The  Inferior  Ophthaoiic  Vein  is  an  accessory  to  the  superior. 
It  commences  at  the  terminations  of  the  posterior  ciliary  and  interior 
muscular  veins,  passes  backward  close  to  the  floor  of  the  orbit  between 
the  inferior  and  external  recti  muscles,  and  usually  leaves  the  orbit  by 
the  spheno-maxillary  fissure  to  terminate  in  the  pterygoid  plexus.  It 
occasionally  terminates  by  emptying  into  the  superior  ophthalmic  vein, 
or  it  may  pass  through  the  anterior  lacerated  foramen  to  terminate  inde- 
pendently in  the  cavernous  sinus.  It  receives  tributaries  from  the 
facial  vein,  from  the  temporal  vein  through  the  malar  bone,  and  a 
communicating  branch  from  the  superior  ophthalmic  vein. 

The  Diploic  Veins  (Fig.  115)  are  those  situated  in  the  diploe  of 
the  cranial  bones.  They  can  be  seen  to  best  advantage  by  stripping  off 
the  pericranium,  and  then  with  a  dental  or  surgical  engine  removing  the 
outer  plate  of  bone.  They  will  then  be  seen  in  great  numbers,  running 
in  various  and  tortuous  directions,  but  with  a  general  inclination  down- 
ward, and  joining  larger  main  branches  in   thpir  course.      They  are 


262  ANATOMY 


simi)ly  tubes  grooved  in  the  boue,  their  lining  membrane  being  com- 
}30sed  of  pavement  epithelium,  with  some  elastic  tissue  between  the 
epithelium  and  the  tubes.  As  they  pass  downward  and  join  other  tubes 
they  increase  in  size  and  their  lining  tissue  becomes  more  and  more 


Veins  of  the  Diploe,  as  displayed  by  the  removal  of  the  outer  table  of  the  skull. 

defined.  There  are  usually  four  of  these  veins  on  each  side  of  the 
cranium — one  frontal,  two  temporal,  and  one  occipital. 

The  Froiitd/  Diploic  Vein  is  small,  ])asses  downward,  makes  its  exit 
through  the  small  foramen  in  the  supraorbital  notch,  and  terminates  in 
the  supraorbital  vein. 

The  Anterior  Temporal  Diploic  Vein  commences  in  the  frontal  bone, 
passes  downward  into  the  great  wing  of  the  sphenoid  bone,  where  it 
divides  into  two  branches,  one  branch  jiassing  through  to  the  outer  side 
of  the  head  and  emptying  into  the  anterior  deep  temporal  vein;  the  other 
passing  through  the  internal  })late  and  emptying  into  the  spheno-parietal 
sinus. 

The  Poderior  Temporal  Diploic  Vein  commences  by  numerous 
branches  in  the  parietal  bone,  passes  downward,  and  makes  its  exit 
either  through  an  o])ening  in  the  posterior  inferior  angle  of  the  bone 
or  through  the  mastoid  fonunen,  to  terminate  in  the  lateral  sinus. 

The  ()ccij)i/(if  J)iph)ic  Vein  is  the  largest  of  the  four  named.  It  com- 
mences within  the  occipital  boue  solely,  passes  downward,  and  terminates 
either  externally  in  the  occi]Mtal  vein  or  internally  by  emptying  into  the 
confluence  of  the  sinuses  or  into  the  lateral  sinus. 

The  Emissary  Veins  are  those  which  form  communicating  branches 
between  the  veins  of  the  scalj)  and  those  at  tlie  base  of  tlie  skull  and  the 
various  sinuses  of  the  brain-case.     They  pass  through  various  foramina^ 


THE  NERVOUS  SYSTEM.  263 

and  receive  names  to  correspond  with  this  fact.  All  the  foramina  are 
not  constant  in  their  existence,  and  they  vary  in  size.  Named  in  the 
order  of  their  size  and  constancy,  they  are  as  follows : 

The  Mastoid,  which  empties  into  the  lateral  sinus  by  passing  through 
the  mastoid  foramen  in  the  temporal  bone. 

The  Parietal,  which  empties  into  the  longitudinal  sinus  by  passing 
through  the  parietal  foramen  in  the  parietal  bone. 

The  Condylar,  which  runs  through  the  cervical  plexus,  and  empties 
into  the  lateral  sinus  by  passing  through  the  posterior  condyloid  foramen 
in  the  occipital  bone. 

The  Occipital,  which  is  (][uite  inconstant,  extends  from  the  structures 
near  the  external  occii)ital  ])rotuberance  and  empties  into  the  torcular 
Herophili  by  passing  through  a  small  foramen  in  this  situation. 

There  are  several  other  small  emissary  veins  which  pass  through 
different  foramina,  such  as  the  ovale,  middle  lacerated,  anterior  con- 
dyloid, and  the  carotid  canal. 


THE  NERVOUS  SYSTEM. 

The  Nervous  System  consists  of  all  that  portion  of  the  body 
engaged  in  the  generation  and  transmission  of  nerve-force,  through 
whic-h  sensation,  volition,  and  vital  influence  are  conveyed  to  or  from 
the  brain.  It  is  made  up  of  several  organs  known  as  nerve-centres, 
nerves,  and  jjerij^heral  end-organs.  These  are  arranged  in  two  great 
systems,  the  Cerebrospinal  and  the  Sympathetic;  the  former  is  frequently 
described  as  the  nervous  system  of  animal  life,  the  latter  of  organic  or 
vegetative  life. 

The  Nerve-centres  are  found  within  the  gray  matter  of  the  cerebro- 
spinal centres,  the  ganglia  of  the  roots  of  the  spinal,  and  some  of  the  cra- 
nial nerves,  also  in  the  various  ganglia  of  the  sympathetic  system.  They 
are  composed  of  gray  matter,  white  fibrous  structure,  and  intercellular 
substance  known  as  neuroglia.  Within  the  gray  matter  are  found 
numerous  nerve-  or  ganglion-cells  (Figs.  116,  117,  118).  These  cells 
are  apolar,  unipolar,  bipolar,  or  multipolar  in  form  ;  some  investigators 
claim  those  of  the  apolar  variety  to  be  undeveloped  nerve-cells  which 
eventually  become  polar. 

The  function  of  the  nerve-cells  is  to  generate  nerve-force  in  a  manner 
analogous  to  that  of  a  galvanic  cell  or  battery  in  the  generation  of 
electricity. 

The  Nerves  are  white  fibrous  cords  of  various  sizes  extending  between 
nerve-centres  and  between  nerve-/3entres  and  peripheral  end-organs. 
They  do  not  generate  nerve-force,  but  act  as  conductors,  similarly  to  the 
wires  of  a  galvanic  cell  or  battery  in  the  transmission  of  electricity. 

The  nerves  of  the  cerebro-spinal  system  are  divided  into  three  classes : 
(1)  those  which  conduct  nerve-force  from  the  nerve-centres  outward  to 
the  muscles,  known  as  motor  or  centro-peripheral  or  centrifugal  nerves  ; 


264 


ANATOMY. 


(2)  tliose  conveying  the  impression  received  at  the  peripheral  end-organs 
to  the  nerve-centres,  known  as  the  sensory  nerves  and  nerves  of  special 
sense,  or  periphero-central  or  centripetal  nerves ;  (3)  those  which  unite 
one  nerve-centre  to  another,  as  the  wires  passing  from  one  cell  to 
another  in  the  same  battery ;  these  are  known  as  intercentral  nerves. 

The  Nerve-fibres  are  of  two  kinds,  medullated  and  non-meduUated. 

The  medidlated  or  dark-border  jihren  are  those  which  are  found  in  the 
cerebro-spinal  nerves,  with  the  exception  of  the  olfactory.     They  vary 

Fifi.  116. 


Fig. 117. 


Ganglion-cell  of  a  Frog  (highly 
magnified):  '/,«, straight  fibre; 
6,  h,  coiled  fibre ;  c,  smaller  one 
joining  it. 


fr< 


A  Ganglion-cell  within  its  sheath  from  the  Human 
Sympathethic  (highly  magnified). 


in  size  troni  ^A^tli  to  ^^ooO^^^  inch,  and  are  not  always  of  equal  size 
in  the  same  bundle.  In  fresh  condition  the  fibre  may  be  described  as  a 
bright,  glistening  cylinder  having  a  dark  double  contour,  but  after  death 
the  outline  of  the  fibre  changes  and  is  irregular,  the  result  of  decom- 
position. The  action  of  water,  reagents,  or  mechanical  disturbance  pro- 
duces the  same  ap])carance. 

By  viewing,  with  a  moderate  power,  a  cross-section  of  a  nerve-fibre, 
it  is  .seen  to  be  made  up  of  a  varying  number  of  l)undles  or  fasciculi 
of  fibres  (nerve-fibres  Fig.  119).  The  number  of  fibres  in  each  fascic- 
ulus, and  of  fasciculi  in  the  nerve,  increases  or  diminishes  the  size 
of  the  trunk.  These  fibres  and  bundles  u.sually  run  parallel  to  each 
other  in  the  .same  nerve,  except  at  points  Avhere  the  nerve  divides  or 
bifurcates.     The  whole  is  surrounded  by  connective  tissue  known  as 


THE  NERVOUS  SYSTEM. 
Fig.  118. 


265 


Nerve-cell  from  Spinal  Cord  of  Ox,  isolated  after  maceration  in  very  dilute  chromic  acid  (magnified 
l/'i  diameters).  The  cell  has  a  well-defined,  clear,  round  nucleus  and  a  bright  nucleolus.  The 
cell-processes  are  seen  to  be  finely  fibriljated,  the  fibrils  passing  from  one  process  into  another 
through  the  body  of  the  cell,    o,  axis-cylinder  process,  broken  a  short  distance  from  the  cell. 

Fig.  119. 


Section  of  the  Saphenous  Nerve  (human),  made  after  being  stained  in  osniic  ^^"^  ?"<|,^|'|'^f^".''°!!y 


are  darkly  stained  by  the  osmic  acid,  but  the  connective  tissue  of  the  nerve  is  only  sligntiy 
stained. 


266 


ANATOMY. 


the  common  sheath  or  epineurimii.  Immediately  beneath  this  sheath 
are  irregular  lymph-spaces  communicating  with  each  other.  A  fibrous 
layer,  the  perineurium,  surrounds  and  forms  a  sheath  for  the  different 
bundles,  giving  room  for  the  passage  of  blood-vessels  supplying  the 
nerves.  This  layer  is  similar  to  the  sheath  of  a  muscle  which  forms  a 
covering  to  the  bundles  of  muscular  fibres.  Within  each  bundle  can 
be  seen  the  nerve-fibres,  consisting  of  axis-cylinder,  medullary  sheath, 
and  neurilemma  or  sheath  of  Schwann,  enveloped  by  a  delicate  tissue, 
the  endoneurium.. 

The  Axis-cylinder  (axial-band,  axial-fibres)  is  the  essential  portion 
of  the  nerve-fibre ;  it  is  nearly  uniform  in  diameter,  and  undergoes  no 
interruption  from  the  nerve-centre  to  near  its  peripheral  distribution. 
It  is  either  cylindrical  or  flattened  in  shape,  and  passes  nearly  in  the 
central  axis  of  the  tube.  AVhen  in  a  fresh  condition  it  appears  pale  and 
transparent,  and  when  examined  with  a  microscope,  using  a  high  ])ower, 
it  is  demonstrated  to  be  composed  of  very  fine  homogeneous  or  more  or 
less  beaded  fibrilloe. 

These  elementary  or  primitive  fibrilke  of  Max  >SchuIfz  are  held  together 
by  a  faintly  granular  albuminous  cement  or  interstitial  substance.  At 
the  termination  of  the  axis-cylinder  it  is  observed  to  divide  up  into 
numerous  fine  filaments  or  fibrils.  Some  investigators  claim  that  the 
axis-cylinder  has  an  independent  or  elastic  sheath  composed  of  neuro- 
keratin. 

The  Medullary  Sheath  (white  substance  of  Schwann)  (Figs.  120  and 
121)  is  composed  of  a  glistening  fatty 
substance  enveloping  the  axis-cylinder, 
and  produces  the  double  or  dark  con- 
tour associated  with  the  nerve-fibres. 
Situated  between  the  axis-cylinder  and 
this  sheath  is  a  fine  lymph-space  con- 
taining a  small  quantity  of  albuminous 
fluid.  This  space  is  supposed  to  corn- 
Diagram  of  municate  with  the  lymph-space  which 
structure  of  exists  betwceu  the  sheath  and  neuri- 
lemma  (Fig.  122)  through  the  bevelled 
edges  of  the  sections  of  the  sheath.  Histologists 
hold  a  diversity  of  opinion  regarding  the  minute 
anatomy  of  the  medullary  sheath.  It  was  formerly 
considered  to  be  a  continuous  insulated  tube,  but  is 
now  claimed  by  many  to  be  made  up  of  short  seg- 
ments, each  fitting  into  the  other  by  imbricated  Kerve-substance  (magni- 
ends  (incisions  of  Schmidt)  (Fig.  123).  It  is  also  "  "  " "  " 
divided  into  the  internodal  segments  or  constric- 
tions of  Ranvier.  The  sheath  is  not  uniform  in 
thickness,  which  is  the  chief  cause  of  the  uneven 
diameter  of  a  medullated  nerve-fibre.  At  certain 
points  in  each  internodal  segment  of  Ranvier  (here- 
after described),  upon  the  outer  surface  of  the 
sheath,  are  indentations  or  depressions  for  the  lodg- 
ment of  nerve-corpuscles. 


Fig.  120. 


Fig.  121. 


fied  200  diameters) :  a, 
Kerve-tube  of  tlie  com- 
mon eel  in  water:  tlie 
delicate  line  on  its  exte- 
rior indicates  the  t  ubular 
membrane;  the  dark  in- 
ner one  is  the  white  sub- 
stance of  Schwann,  si  ijiht- 
ly  wrinkled;  b,  the  same 
in  ether.  Several  oil-glob- 
ules have  coalesced  in  the 
interior,  and  others  have 
accumulated  around  the 
exteriorof  the  tube.  The 
white  substance  has  in 
pai't  disajjpeared. 


TifA'  NERVOUS  SYSTEM. 


267 


Fig.  123. 


A,  tubular  nerve-fibres,  showing  the  sinuous  outline  and  double 
contours ;  li,  diagram  to  show  the  parts  of  a  tubular  fibre — viz. 
1,  1,  membranous  tube;  2,  2,  white  substance  or  medullary 
sheath;  3,  axis  or  primitive  band;  C,  figure  (imaginary)  in- 
tended to  represent  the  appearances  occasionally  seen  in  the 
tubular  fibres:  1, 1,  membrane  of  the  tube  seen  at  parts  where 
the  white  substance  has  separated  from  it ;  2,  a  part  where  the 
white  substance  is  interrupted;  3,  axis  projecting  beyond  the 
broken  end  of  the  tube ;  4,  part  of  the  contents  of  "the  tube 
escaped. 


Nerve-fibres,  fixed  and  stained 
by  perosmic  acid,  from  the 
posterior  wall  of  dorsal 
lymph-sac  of  frog:  1,  ], 
medullary  layer;  2,  axis-cyl- 
inder; 3,  3,  constrictions  "of 
Rauvier;  4,  4,  incisions  of 
t^chmidt. 


The  Neurilemma  or  Sheath  of  Schicann  i.s  the  outer  covering  of  a 
nerve-fibre,  and  forms  a  continuous  envelope  ;  a  narrow  lymph-space 
extends  between  it  and  the  medullary  sheath.  It  is  the  analogue  of 
the  sarcolemma  in  a  muscular  fibre,  and  appears  as  a  fine  hyaline, 
homogeneous,  elastic  membrane,  with  flattened  or  oval-shaped  nucleated 
corpuscles,  known  as  nerve-corpuscles,  situated  between  it  and  the 
medullary  sheath.  The  nucleus  is  generally  seen  in  a  depression  of  the 
medullary  membrane  surrounded  by  a  zone  of  granular  protoplasm ; 
this  is  especially  the  case  in  young  subjects.  The  optic  and  auditory 
nerves  have  no  neurilemma. 

The  Nodes  and  Internodes  of  Banvier  (Fig,  124)  are  cau.sed  by  the 
annular  constriction  or  breaks  in  the  continuity  of  the  medullary  sheath 
or  white  substance  of  Schwann.  The  axi.s-cylinder,  the  neurilenmia,  and 
the  lymph-spaces  are  not  interrupted  at  these  points,  though  the  neuri- 
lemma curves  sharply  inward  and  comes  in  close  apposition  to  the  axis- 
cylinder.  The  point  at  which  the  constriction  takes  place  is  named  the 
node  of  Ranvier,  and  the  portions  between,  the  internodes  of  Banvier  or 
interannular  segments.  Each  interiiode  or  segment  has  usually  one  or 
more  nerve-corpuscles  situated  between  the  medullary  sheath  and  the 
neurilemma. 

A  fresh  nerve  treated  with  a  solution  of  nitrate  of  silver  or  osmic 
acid  and  exposed  to  the  light  demonstrates  distinctly  the  nodes  of 
Eanvier  (Fig.   125).      After  long    exposure  the  silver  salt  penetrates 


268 


ANATOMY 


Portions  of  two  Nerve- 
Fibres  staiiiL'il  with  Os- 
mic  Acid,  from  a  Young 
Rabbit  ( til  diameters) : 
7?,  Ji,  nodes  of  Kanvier, 
witli  axi-^-cylinder  pass- 
ing tliroiigh  ;  <i,  primi- 
tive sheath  of  tlie  nerve ; 
c,  opposite  the  middle  of 
the  s  gment,  indicates 
the  nucleus  and  proto- 
plasm lying  between  tlie 
Tirimitive  sheatli  and  the 
medulbiry  sheath.  1  ii  A 
the  nodes  are  wider,  and 
the  intersegmental  sub- 
stance more  apparent 
than  in  I>. 


tlie  structure  of  the  nodes  and  passes  along  the  axis- 
cvlinder,  disclosing  transverse  markings  named  lines 
of  Froiiimann.  The  action  of  osmic  acid  will  cause 
the  nodes  to  become  almost  colorless,  while  the  me- 
didlarv  or  white  substance,  except  close  to  the  nodes, 
Avill  be  stained  a  very  dark  color. 

The  Size  of  the  S\'n-e-fibres  varies,  both  in  the 
thickness  of  the  medullated  sheath  and  the  diameter 
of  the  axis-cylinder.  This  is  dependent  up(m  the 
distance  which  it  extends  from  the  centre  of  its 
origination  :  the  greater  the  distance  covered,  the 
thicker  will  be  the  medullated  sheath,  though  to 
this  there  are  numerous  exceptions.  As  the  fibre 
approaclies  its  termination  the  medullary  sheath  be- 
comes gradually  thinner,  diminishing  until  lost 
altogether,  leaving  only  the  covering  of  the  neuri- 
lemma with  the  nerve-corpuscles  between  the  axis- 
cylinder  and  the  membrane,  thus  producing  a  non- 
medidlafed  nerve-fibre. 

The  Non-ineduU((fed  or  Pale  Fibres  (fibres  of  Be- 
mak)  (Fig.  12(3)  are  made  up  of  axis-cylinder,  neu- 
rilemma, and  the  nerve-corpuscles,  which  are  situ- 
ated at  certain  distances  between  the  other  two  struc- 
tures, the  axis-cylinder  being  faintly  striated.  These 
fibres  are  principally  found  in, 
and  compose  the  greater  part  of, 
the  sympathetic  nerves,  and  are 
the  termination  of  the  medullary 
fibres.  The  olfactory  nerve-fila- 
ments are  non-medullated,  though 
they  cannot  be  classed  as  pale  fi- 
bres, as  thoy  have  a  distinct  nu- 
cleated sheath  of  their  owji.  These 
fibres  (pale  fibres)  differ  also  from 
the  medullary  fibres  by  branching 
and  joining  offshoots  from  other 
fibres,  thus  forming  a  fine  net- 
work. Triangular  nuclei  are 
fi)nnd  at  the  nodal  points,  this 
!)eing  the  situation  at  which 
these  connections  occur. 

Before  the  final  distribution 
of  the  nerve-fibre  it  loses  its 
neuril'mma,  leaving  nothing  but 
the  axis-cylinder. 

Nerves  and 
the  nerve- 
the  centres 


The  Division  of 
Nerve-fibres.  —  As 
trunks  extend  from 
toward  the  })eri]ihery,  thev  di- 
vide and  s  u  b  d  i  v  i  d  e  ;  some 
branches    unite    with    those    of 


Nerve-libre  from  the 
Sciatic  Nerve  of  the 
Rabbit,  after  the  ac- 
tion of  nitrate  of 
silver :  n,  ring  form- 
ed by  thickened  mem- 
brane of  Schwann ;  m, 
white  substance  of 
Schwann  rendered 
transpirent  by  glyce- 
rin ;  ri/,  cylinder-axis, 
which  just  iibove  and 
below  the  leve'  of  the 
annular  constriction 
presents  the  striae  of 
Frommann. 


THE  NERVOUS  SYSTEM. 


269 


Fig. 120. 


other  trunks,  thus  forming  a  single  bundle  arising  from  two  or  more 
sources  and  possessing  two  or  more  functions ;  or  they  may  break  up 
and  unite  in  various  ways,  forming  plexuses,  as  the  brachial  or  cer- 
vical. 

The  medullary  fibres  while  in  the  nerve-cords  or  in  the  nerve-centres 
do  not  branch  or  unite  with  each  other ;  when  near  their  termination 
it  is  claimed  they  occasionally  do  so,  in  which  case 
the  branches  are  always  at  one  of  the  nodes  of 
Ranvier  (Fig.  127).  The  new  axis-cylinder  thus 
formed  has  its  own  medullary  sheath  and  neuri- 
lemma, being  a  continuation  of  the  covering  of  the 
nerve-fibre  from  which  it  originates. 

^  As  the  nerves  ai)proacIi  their  termination  they 
divide  and  subdivide  into  bundles,  until  they  be- 
come very  minute,  and  consist  of  a  single  bundle 
of  a  few  fibres  encased  in  a  perineurium  made  of 

Fig.  128. 


Fig.  127. 


Portion  of  the  Xetwork  of 
Fibres  of  Keniak,  from 
the  pneuniogastric  of 
the  dog:  7(,  nucleus:  /), 
protoplasm  surrounding 
it;  h,  striation  caused 
by  fibrils. 


Division  of  a  Nerve- 
fibre,  from  pulmo- 
nary membrane  of 
frog's  lung. 


I)ivision   of  a   Nervous    l^ranch  (a)  into  its 
ultimate  fibres,  h,  c,  d,  e. 


a  delicate  film  of  connective  tii^sue  (Fig.  128).  Finally,  the  nerve 
becomes  a  single  medullated  fibre,  which  soon  loses  its  coat,  exposing 
the  axis-cylinder  ;  this  ultimately  breaks  up  into  ])rimitive  nerve-fibrillse. 
These  become  beaded,  branching  and  uniting  with  each  other,  and  form- 
ing a  very  fine  network,  the  density  of  which  is  dependent  upon  the 
number  of  nerve-fibres  distributed  to  the  parts ;  thus,  in  some  portions 


270 


Plexus  of  fine  Non-niecTullated  Nerve-fibres  of  the  Cornea:  a,  a  thick  non-medullated  nerve-fibre; 
6,  a  fine  one;  c,  d,  elementary  fibrils,  anastomosing  into  a  network. 

of  the  body  thev  have  a  closer  woven  network  than  others,  as  in  the 
cornea,  skin,  and  mucous  membrane  (Figs.  129  and  130).  In  the  two 
latter  tissues  they  are  extremely  abundant,  forming  two  plexuses,  a  deep 
and  a  superficial,  the  latter  being  the  finer  and  closer  woven. 

Fig.  130. 


vr--^^ 


Intra-epithelial  Nerve-tcnniiiation  in  the  Anterior  Kpitheliuiii  of  the  Cornea,  as  seen  in  an  oblique 
section:  n,  an  axis-cylinder;  ?),  subcj)ithelial  ncrve-fibrilUe;  c,  intra-epithelial  network;  </, 
epithelial  cells. 

If  a  nerve  of  sensation   be  traced  from  its  network  of  distribution 
toward  its  centre,  it  will  be  first  found  composed  of  primitive  fibrils, 


THE  NERVOUS  SYSTEM. 


271 


which  form  iu  themselves  .small  axis-cylinders  without  any  membranes. 
These  unite  and  form  larger  axis-cylinders,  finally  taking  on  the  neu- 
rilemma or  white  sheath  of  Schwann,  then  the  medullary  envelope,  the 
fibres  uniting  into  bundles. 

The  Peripheral  End-organs. 

The  peripheral  end-organs  are  divided  into  two  classes,  those  of  sen- 
sation and  those  of  motion. 

The  Peripheral  End-organa  of  Sensory  or  Afferent  Nerves. — Many 
of  these  nerves  terminate  in  fine  plexuses  or  have  free  ends  (as  those 
already  described)  under  the  final  termination  of  the  medullary  nerve- 
fibres,  which  are  distributed  to  the  mucous  membrane,  cornea,  and  skin. 
Other  terminations  *are  found  in  various  organs  of  special  sense  and 
function :  amongst  the  most  important  of  these  are  the  Pacinian  and 
tactile  corpuscles  (see  Anatomy  of  the  Skin  for  description),  the  spheroidal 
end-bulbs  of  Krause,  hair-bulbs,  and  nerves  ending  in  gland-cells. 

The  small  spheroidal  oid-bidbs  of  Krause,  resembling  to  a  certain 
extent  the  Pacinian  corpuscles,  are  found  near  the  corneal  margin  of  the 
deeper  layers  of  the  conjunctiva  (Fig.  131)  of  man  and  apes ;  in  other 
animals  they  are  cylindrical.  These 
have  also  been  found  in  various  parts 
of  the  skin  and  the  mucous  membrane 
of  the  mouth.  The  spheroidal  end- 
bulbs  are  composed  of  polygonal  cells 
and  slightly  granular  substance,  sur- 
rounded or  invested  externally  by  a 
connective-tissue  capsule,  which  is  a 
continuation  of  the  sheath  of  Heide 
of  the  nerve-fibre,  and  internally  by  a 
nucleated  membrane  which  is  a  con- 
tinuation of  the  primitive  nerve-enve- 
lope. Usually  the  axis-cylinder  enters 
the    bulb    devoid    of    the    medullary 

sheath,     though     occasionally     it     passes  Knd-bulb  from  Uie  lluman  conjunctiva; 

,         1      11           •   1        1  •                    •                tj  ",  nucleated  capsule;  fc.core^the  outlines 

into    the     bulb    with    this    covering.       It  of  itscellsarenotseen;r,entennKtibre, 

■                   T     •  1     1                 •                         1  branching,  and  its  two  divisions  passing 

may    enter  ^  undivided    or    m    several       to  tenni.,ate  in  the  core  at  d.      '       ^ 

branches ;    if   the   latter,  the  branches 

twist   and    intermingle   with    each    other    before    entering,   making  a 

number  of  turns,  finally  dividing  into  fibrillse  within  the  bulb  ;  these, 

after  making  numerous   convolutions,  are  ultimately   lost  within   the 

substance. 

The  Hair-bulbs  contain  terminations  of  fibres  of  the  medullary  nerves, 
giving  extreme  sensitivity  in  cases  where  the  hair  is  used  as  a  sentinel,  as 
in  the  eyelashes  and  the  whiskers  of  cats,  dogs,  and  other  animals. 


Fig.  131. 


t^: 


d 


Nerve-endings  in  the  Gland-cells. 

As  by  mental   influences  some  glands  can  be  excited  to  secretion, 
nerve-fibres  must  be  directly  connected   A^ith  them.       Pliiger  claims 


272 


ANA  T03TY. 


Fig.  132. 


Modes  of  Termination  of  the  Nerves  in  the  Salivary  Glands :  1  and  2,  branching  of  the  nerves  between 
the  salivarj-  cells;  :>,  termination  of  the  nerve  in  the  nucleus;  4,  union  of  a  ganglion-cell  with  a 
salivary  cell;  5,  irregularly  enlarged  nerve-libres  entering  the  cylindrical  cells  of  the  excretory 
ducts. 

that  both  medullated  and  non-medullated  fibres  pass  directly  into  the 
secreting  cells  of  the  salivary  glands  of  man  (Fig.  132).    Knpifer  has 

described  the  same  connection 
Fig.  133.  ^^  nerves  in  some  of  the  in- 

sects. 

The  Peripliend  End-organs 
of  3Iofor  Nerves  are  of  two 
kinds — viz.  those  supplying 
involuntary  or  non- striated 
muscular  tissue,  and  those  sup- 
plying voluntary  or  striated 
muscular  tissue. 

Tlie  first  class,  those  of  the 
involuntary  or  non-striated  or 
smooth  muscular  tissue  (Fig. 
133),  belong  to  the  sympathetic 
nervous  system  or  non-medul- 
lary nerve-fibres.  The  fibres 
of  these  nerves  penetrate  and 
divide  in  the  connective  tissue 
which  surrounds  the  bundles 
and  muscular  fibres.  In  this 
position  the  axis-cylinder  di- 
vides into  its  ultimate  fibrillse, 
these  ending,  according  to  Elis- 
cher,  in  a  slight  bulbous  expansion  opposite  the  nucleus  of  a  contract- 
ing cell. 

The  peripheral  end-organs  of  voluntary  or  striated  muscular  tissue 
belong  to  the  medullary  nerve-fibre,  and  are  known  as  motorial  end- 
phdes  or  end-phde.s  of  Ki'dnie  (Fig.  134).  As  the  nerve-trunk  advances 
toward  its  distribution  it  divides  and  subdivides  into  its  fibres,  each 


Termination  of  Nerves  in  Non-striped  Muscular  Tissue. 


THE  NERVOUS  SYSTEM. 


273 


of  which  passes  obliquely  to  a  muscular  fibre.  Each  muscular  fibre 
receives  one  or  more  nerve-terminals  or  end-plates.  Most  authorities 
claim  that  at  this  point  the  medullary  or  white  substance  terminates, 
and  the  neurilemma  or  primitive  sheath  (sheath  of  Schwann)  becomes 
continuous  with  the  sarcolemma  of  the  nuiscular  fibre ;  others  state  that 
it  (the  medullary  sheath)  terminates  immediately  after  passing  through 
the  sarcolemma.  Ranvier  says  that  it  is  the  nucleated  sheath  of  Henle, 
and  not  the  neurilemma,  which  is  continuous  with  the  sarcolemma. 
After  the  axis-cylinder  passes  through  the  sheath  of  the  muscular  fibre, 
it  divides  and  subdivides  into  numerous  fibrillae,  forming  a  network 

Fig.  134. 


Muscular  Fibres  of  Lareria  wrWis,  with  the  terminations  of  nerves:  n,  seen  in  profile;  P,  P,  the 
nerve-end  plates;  5,  S,  the  base  of  the  plate,  consisting  of  a  granular  mass  with  nuclei;  6.  the 
same  as  seen  in  looking  at  a  perfectly  fresh  fibre,  the  nervous  ends  being  probably  still  excitable 
(the  forms  of  the  variously-divided  "plate  can  hardly  be  represented  in  a  woodcut  by  sutiiciently 
delicate  and  pale  contours" to  reproduce  correctly  wliat  is  .seen  in  nature);  c,  the  same  as  seen  two 
hours  after  death  from  poisoning  by  curare. 

which  is  imbedded  in  a  more  or  less  granular  pale  substance,  usually 
containing  a  number  of  oval  nuclei  having  bright  nucleoli.  The  sub- 
division of  the  nerve-fibres,  the  granular  substance,  and  the  oval  nuclei 
forms  the  end-plafes,  which  usually  have  only  one  fibre  terminating  in 
them,  though  occasionally  there  are  two. 


The  Cranial  Nerves. 

The  cranial  nerves  consist  of  one  of  the  two  divisions  of  the  cerebro- 
spinal system,  receiving  their  name  (cranial)  from  their  origin  within 
the  cranial  cavity,  with  the  exce])tion  of  the  spinal  accessory,  which 
originates,  in  part,  out.'^ide  the  brain-ca.'^e,  though  this  portion  passes  into 
the  cranium  at  the  foramen  magnum,  and  passes  out  in  company  with 
its  accessory  portion  through  the  posterior  lacerated  foramen. 

A  cranial  nerve  has  two  origins,  superficial  and  deep :  the  first  is 
that  portion  of  the  nerve  which  can  be  traced  to  the  circumference  or 
periphery  of  the  brain  ;  while  the  deep  origin  is  in  relation  with  the 
deeper  structure  of  that  organ. 

The  cranial  nerves  (Fig.  135)  pass  out  of  the  brain-case  through  the 
foramina  in  the  cranial  bones  at  the  base  of  the  skull.     Internally  they 

Vol.  1.-18 


274 


ANATOMY. 


are  all  f^ituated  near  the  median  line,  and  as  they  pass  out  of  the  brain- 
case  there  is  reflected  over  them  a  prolongation  of  the  dura  mater,  which 
forms  an  enclosing  sheath. 

There  are  twelve  pairs  of  cranial  nerves.     Anatomists  have  desig- 


V\a.  185. 


Dissection  of  the  Sinuses  of  the  Skull  iiiul  Cranial  Nerves— the  cavernous  sinus  dissected  on  tlie  left 
side;  1,  third  nerve;  2,  optic  nerve;  :{,  fourth  nerve;  4,  internal  carotid  artery;  5,  (iasserian 
ganglion  of  the  fifth  nerve,  with  its  three  divisions;  fi,  circular  sinus;  7,  superficial  petrosal 
nerve;  8,  cavernous  sinus;  9, sixth  nerve;  10,  transverse  or  basilar  sinus;  11,  seventh  pair;  12, 
superficial  petrosal  sinus:  13,  eighth  pair;  14,  inferior  petrosal  sinus;  Ifi,  ninth  nerve;  18,  occip- 
ital sinus ;  20,  lateral  sinus ;  21,torcular  lleiophili. 

nated  them  by  numljers  corresponding  with  their  superficial  origin, 
beginning  at  the  anterior  pair  and  passing  backward  on  the  under  or 
anterior  surface  of  the  brain  (Figs.  136  and  137).  These  nerves  arc 
known  as  motor  nerves,  sensory  nerves,  nerves  of  sjjecial  sense,  and 
compound  nerves.     Their  names  and  functions  are  as  follows  : 


Number. 
First  pair  .  . 
Second  pair  . 
Third  l)air  . 
Fdiirtli  i»air  . 
Fiftii  pair .    . 

Sixth  i)air 
Seventh  pair 
Eif^lith  pair  . 
Ninth  jiair    . 

Tentii  pair    . 
P^lcventh  pair 
Twelfth  pair 


Name.  Function. 

.  Olfactory Special  sense,  smell. 

■  0{)tic Special  sense,  sight. 

.  Motor  oculi  ......  Motion  to  five  orbital  muscles. 

.  Pathetic Motion  to  one  orbital  muscle. 

.  Trifacial Sensation    and   mcUion,  possibly  special 

sense  —taste. 

.  .\l)ducens Motion  to  one  orbital  muscle. 

•  Facial Motion  to  muscles  of  face. 

.  Auditory Special  sense,  hearing. 

.  (Ilosso-pliaryngoal  .    .  Sensation,   motion,  and    special   sense — 

taste. 
.  Pneumogastric     .    .    .  Sensation  and  motion. 
.  S])inal  accessory  .  Motion. 

.  Hypoglossal      ....  Motion  to  muscles  of  tongue. 


Nerves  of  Motion  (or  centrifugal  nerves)  are  those  which  jireside  ov^er 
the  action  of  the  mu.'^clcs  of  tlie  body.     They  have  their  origin  in  the 


THE  NERVOUS  SYSTEM. 


275 


deeper  parts  of  the  brain,  extend  outwardly,  and  terminate  in  the  mus- 
cular tissue ;  example,  the  facial  (the  nerve  of  motion  to  the  muscles  of 
the  face). 

Nei'ves  of  Sensation  (or  centripetal  nerves)  are  those  which  convey 
the  impression  received  at  their  peripheral  ends  to  the  substance  of  the 


Fig.  136. 


TAL   LOBE 


PARIETAL   LOBE 


ST°-  DIVISION   OF 
LVIAN    FISSURE 


TEMPOKO-SPHEN 
OiaAL  LOBE 


IPITAL  LOBE 


Base  of  tlie  Brain. 


brain.  (In  the  anatomical  description  of  these  and  other  nerves  their 
course  is  given  from  the  brain  outward.)  Example,  the  first  two  divis- 
ions of  the  fifth  pair,  which  gives  sensation  to  the  upper  two-thirds  of 
the  face. 

Nerves  of  Special  Sense  (centripetal)  are  those  which  convey  the  impres- 
sion made  upon  their  peripheral  ends,  conveying  such  impression  to  a 
particular  cell  of  the  brain  ;  example,  the  optic  receiving  impressions  from 
the  retina  and  conveying  them  to  certain  centres  within  the  brain. 


276 


ANATOMY. 
Fig.  137. 


j.o- 


Semi-diagraiiiniatic  View  of  a  Peep  Dissection  of  the  Cranial  Nerves  on  the  Left  Side  of  the  Head 
(Qiiain).  The  Roman  numerals  from  I  to  XII  indicate  tlie  roots  of  the  several  cranial  nerves  as 
they  lie  in  or  near  their  foramina  of  exit.  V  is  upon  the  large  root  of  the  tifth,  with  the  Gas- 
serian  ganglion  in  front;  CI,  the  suhoccipital  or  first  cervical  nerve;  CVIII,  the  eighth.  The 
branches  of  the  nerves  are — 1,  supraorbital  branch  of  the  fifth;  2,  lachrymal  passing  into  the 
gland ;  3,  nasal,  passing  toward  the  anterior  internal  orbital  canal,  and  giving  the  long  root  to  the 
ciliary  ganglion,  4';  ;i',  termination  of  the  nasal  nerve:  4,  lower  branch  of  the  third  nerve;  f>, 
superior  maxillary  division  of  the  tifth  passing  into  the  infraorbital  canal;  5',  the  .same  issuing 
at  the  infraorbital  foramen,  and  being  distributed  as  inferior  palpebral,  lateral  nasal,  and  supe- 
rior labial  nerves;  .">",  fi,  ganglion  of  >Ieckel  and  Vidian  nerve  passing  back  from  it;  6',  palatine 
and  other  nerves  descending  from  it ;  6",  large  superficial  petrosal  nerve ;  7,  posterior  dental 
nerves ;  "',  placed  in  the  antrum,  which  has  been  o))ened,  points  to  the  anterior  dental  nerve ;  S, 
inferior  ma.xillary  division  of  the  fifth;  8',  muscular  branches  coming  from  it;  Sx,  the  auriculo- 
temporal branch  cut  short,  and  above  it  the  small  superficial  petro.sal  nerve  connected  with  the 
facial ;  9,  buccal  and  external  pterygoid ;  10.  lingual  or  gustatory  ;  10',  its  distribution  to  the  side 
and  front  of  the  tongue  and  sublingual  .gland  ;  10".  submaxillary  ganglion  ;  below  10,  the  chorda 
tynipani  passing  forward  from  the  facial  to  Join  the  lingual;  11.  inferior  dental  nerve;  11',  the 
same  and  part  of  its  dental  distribution  exposed  ;  U",  its  termination  a.s  the  mental  nerve;  11'", 
its  mylo-hyoid  branch;  12,  twigs  of  the  facial  nerve  immediately  after  its  fxit  from  the  stylo- 
mastoid foramen,  distributed  to  the  posterior  belly  of  the  diitastric  and  stylo-hyoid  muscles;  12', 
teniporo-facial  division  of  the  facial ;  12",  cervico-facial  division  ;  13.  trunk  of  the  glosso-pharyn- 
geal ;  VV,  its  distribution  on  the  side  and  back  part  of  the  tongue ;  14,  spinal  accessory  nerve ;  14', 
the  same  after  having  passed  through  the  sterno-mastoid  muscle,  uniting  with  branches  from  the 
cervical  nerves;  l.'i,  hypoglossal  nerve;  l-i',  its  twig  to  the  thyro-hyoid  muscle;  l.i",  its  distribu- 
tion to  the  muscles  of  the  tongue;  Ifi,  its  descending  branch,  giving'a  branch  to  the  anterior  belly 
of  the  omo-hyoid  muscle,  and  receiving  communicating  branches  at  16x  from  the  cervical  nerves ; 
17,  pneumogastric  nerve;  17',  its  superior  laryngeal  branch;  17",  external  laryngeal  twig;  IS, 
superior  cervical  ganglion  of  the  sympathetic  nerve,  uniting  with  the  upper  cervical  nerves,  and 
giving  at  is'  the  superficial  cardiac  nerve  ;  19,  the  trunk  of  the  sympathetic;  19',  the  middle  cer- 
vical ganglion,  uniting  with  some  of  the  cervical  nerves,  and  giving  at  19"  the  large  or  middle 
cardiac  nerve:  20,  continuation  of  the  sympathetic  nerve  down  the  neck;  21,  great  occipital 
nerve;  22,  third  occipital. 


THE  NERVOUS  SYSTEM. 


277 


Fig.  138. 


Compound  Net-veH  are  those  composed  of  motor  and  sensory  filaments, 
and  in  some  instances  combining  motion,  sensation,  and  special  sense ; 
example,  the  inferior  maxillary  or  third  divis- 
ion of  the  fifth. 

With  the  exception  of  the  ninth,  tenth,  and 
eleventh  pairs,  the  cranial  nerves  are  distrib- 
uted to  the  liead  alone ;  those  excepted  have 
also  a  distribution  to  the  neck,  the  tenth  pair 
passing  to  the  thorax  and  abdomen. 

The  regions  supplied  by  the  cranial  nerves 
are  diagrammatically  represented  in  Fig.  138, 
from  which  it  will  be  seen  that  nine  of  the 
fourteen  regions  upon  the  head  and  neck  are 
supplied  with  sensation  by  some  of  the  branches 
of  the  fifth  pair  of  nerves. 


Olfactory  Nerves. 


The  olfactory  or  first  pair  of  nerves  (Fig.  139) 
are  those  concerned  in  the  special  sen.se  of  smell. 
They  are  about  twenty  in  number,  and  derive 
their  superficial  origin  from  the  under  surface 
of  the  olfactory  bulb  of  the  brain,  m  hich  is  sit- 
uated on  the  under,  proximal,  and  forward 
portion  of  the  anterior  lobe  of  the  cerebrum. 
These  bulbs  rest  upon  the  olfactory  sulcus  of 
the  cribriform  plate  of  the  ethmoid  bone,  being 
separated  from  each  other  by  the  crista  galli. 
The  nerves  pass  downward  through  the  nu- 
merous foramina  in  the  cribriform  plate  into 
the  superior  nasal  chamber.  Th^y  are  invested 
by  a  covering  derived  from  the  membranes  of 
the  brain,  and  are  distributed  to  the  mucous 
lining  of  the  superior  meatus  of  the  nose. 
The  nerves  are  divided  into  three  sets — inner,  outer,  and  middle.  The 
inner  set  is  composed  of  the  largest  nerves  :  they  are  situated  next  to  the 
median  line,  and  pass  into  delicate  gi'ooves  or  canals  which  descend  on 
either  side  of  the  perpendicular  plate  of  the  ethmoid  bone.  Some  of 
these  canals  run  obliquely  forward,  and  others  obliquely  backward. 
Those  that  arise  from  the  lateral  portions  of  the  olfactory  lobes  pass 
into  fine  canals,  which  subdivide  as  they  penetrate  the  lateral  masses 
of  the  ethmoid.  A  few  of  the  more  central  of  these  nerves  are  dis- 
tributed to  the  roof  of  the  nasal  chamber.  No  filaments  extend  to  the 
vomer  or  inferior  turbinated  bones.  The  olfactory  nerves  differ  from 
all  other  cranial  nerves  in  being  composed  of  non-medullated  fibres. 
Their  terminal  branches  communicate  freely  with  each  other  and  form 
a  plexus  beneath  the  nasal  mucous  membrane. 


The  Nervous  Distribution  of  the 
Head  (Kaiiney):  1,  region  sup- 
plied by  the  supraorbital  branch 
of  the  fifth  nerve ;  2,  supplied  by 
the  supratrochlear  branch  of  the 
fifth  nerve ;  'A,  supplied  by  the  in- 
fratrochlear  branch  of  the  fifth 
nerve;  4,  supplied  by  the  infra- 
orbital branch  of  the  fifth  nerve; 
T).  supplied  by  the  buccal  branch 
of  the  fifth  nerve ;  fi,  supplied  by 
the  mental  branch  of  the  fifth 
nerve;  7,  supplied  by  the  super- 
ficial cervical  from  the  cervical 
plexus ;  8,  supplied  by  the  great 
auricular  from  the  cervical  plex- 
us; 9,  supplied  by  the  temporo- 
malar  branch  of  the  fifth  nerve; 
10,  supplied  by  the  lachrymal 
branch  of  the  fifth  nerve;  11, 
sujiplied  by  the  auriciilo-tem- 
poral  branch  of  the  fifth  nerve; 
12,  supplied  by  the  great  occipi- 
tal (a  spinal  nerve) ;  IH,  supplied 
by  the  small  occipital  from  the 
cervical  plexus ;  14,  supplied  by 
the  supraclavicular  from  the 
cervical  plexus. 


278 


ANA  TOMY. 
Fig.  139. 


Nerves  of  the  Septum  of  the  Nose:  1,  olfactory  bulb  and  its  ramifications  in  the  septum;  2,  nasal 
nerve  of  the  ophthalmic  trunk  ;  3,  naso-palatine  nerve  from  Meckel's  ganglion  (too  large  in  the 
cut). 


Optic  Nerve. 

The  optic  or  second  pair  of  nerves  (l^'ig.  140)  are  the  special  nerves 
of  vision.  Their  encranial  portion — viz.  that  which  extends  from  the 
superficial  origin  to  where  they  pass  out  of  the  brain-case — is  divided 
into  three  parts,  the  optic  tract,  the  optic  chiasm,  and  the  optic 
nerve. 

The  Optic,  Tract  is  that  portion  which  commences  in  the  po.sterior 
part  of  the  optic  tlialamus,  the  anterior  or  superior  lobes  of  the  cor- 
])ora  quadrigemina,  and  the  corpora  geniculata.  The  fibres  from  these 
different  sources  unite  and  form  a.  flattened  or  ribbon-like  band  (with- 
out being  invested  by  neurilemma),  which  passes  obliquely  forward  and 
inward,  clo.sely  attached  to  the  under  surface  of  the  superior  portion  of 
the  cms  cerebri.  Here  it  becomes  more  cord-like  in  appearance,  and  is 
attached  to  the  tuber  cinereum  and  lamina  cinerea.  It  receives  addi- 
tional fil)res  from  these  bodies,  j^as.ses  forward,  and  joins  the  optic  chiasm 
at  its  posterior  lateral  angle. 

The  Optic  Chiasm  or  Commissure  is  an  oblong  body,  nearly  half  an 
inch  in  diameter,  formed  by  the  union  of  the  optic  tracts.  It  is  lodged 
in  the  optic  groove,  which  is  situated  u})on  the  olivary  process  on  the 
superior  surface  of  the  sphenoid  bone.  Its  extremities  are  in  close 
apjiosition  to  the  internal  carotid  artery  of  both  sides.  The  fibres  of 
each  o])tic  tra(!t  are  divided  into  three  sets — decussating,  straight,  and 
intrageniculate. 

Tiie  decu.ssating  set  is  compo.sed  of  the  greater  number  of  the  fibres  of 
each  o])tic  tract.  TIum'  fibres  cross  from  one  side  to  the  other  through 
the  chiasm,  and  thus  tiie  greater  part  of  the  optic  nerve  of  the  left  side 
is  formed  by  fibres  from  the  optic  tract  of  the  right  side. 


THE  NERVOUS  SYSTEM. 


279 


The  straight  set  form  the  outer  part  of  the  optic  tract.  They  pass 
forward,  auJ  help  to  ibrm  the  optic  nerve  of  the  same  side. 

The  iutergeniculate  set  (interior  commissure  of  Gudden)  form  the 
inner  part  of  the  optic  tract.  They  cross  from  one  side  to  the  other, 
forming  the  ])osterior  margin  of  the  chiasm,  and  luiite  the  fibres  which 
spring  from  the  geniculate  bodies.  Many  anatomists  describe  a  set  of 
fibres  which  pass  from  one  side  to  the  other  across  the  anterior  margin 
of  the  chiasm  and  form  an  inter-retinal  set.  The  existence  of  this  set  of 
fibres  is  still  a  matter  of  doubt,  though  Stilling  has  recently  claimed 
to  have  found  them. 

The  optic  nerve  is  a  rounded  cord  which  commences  at  the  anterior 
lateral  angle  of  the  optic  chiasm.     It  extends  outward  and  forward,  and 

Fig.  140. 


Diagram  of  the  Optic  Nerves  and  Tracts  in  IVraii :  1,  left  eyeball ;  2,  right  eyeball ;  3,  3,  corpora  genic- 
ulata  interna  ;  4,  4,  corpora  geniculata  externa ;  5,  tubercula  quadrigemina  ;  6,  6,  ceutres  of  vision 
in  the  cerebral  hemispheres. 

passes  from  the  brain-case  through  the  optic  foramen  in  the  sphenoid 
bone,  accompanied  by  the  ophthalmic  artery,  which  runs  along  its  outer 
and  lower  side.  Before  entering  the  optic  foramen  it  is  invested  by  a 
slender  sheath  from  the  arachnoid  membrane  of  the  brain,  but  as  it 
passes  into  the  foramen  it  is  strongly  enveloped  by  a  prolongation 
from  the  dura  mater.  Upon  reaching  the  orbit  this  covering  divides 
into  two,  the  outer  blending  with  the  periosteum,  while  the  inner  con- 
tinues to  invest  the  nerve  until  it  pierces  the  sclerotic  coat  of  the  eye. 
When  the  nerve  enters  the  orbit  it  passes  outward  and  downward 
between  the  origins  of  the  recti  muscles  to  the  posterior  aspect  of  the 
eyeball,  being  surrounded  by  the  adipose  tissue  of  the  orbit.     It  enters 


280 


ANATOMY. 


the  eyeball  about  o'lie-tenth  of  an  inch  to  the  inner  side  of  its  centre, 
passes  through  the  sclerotic  and  choroid  coat's,  and  terminates  by 
expanding  into  the  retina.  Within  the  orbit  it  is  surrounded  by  adi- 
pose tissue,  ciliary  vessels,  and  nerves,  the  central  retinal  artery  enter- 
ing the  nerve  about  one-fourth  of  an  inch  from  where  it  passes  into  the 
sclerotic  coat. 

Variation.s. — The  optic  tracts  occasionally  pass  through  the  optic 
foramina  without  decussation.  When  this  is  the  case  the  chiasm  is 
entirely  absent. 


OcuLO-MOTOR  Nerve. 

The  oculo-motor  or  third   nerve  (Fig.  142)  is  a  large,  round,  firm 
cord  which  presides  over  the  movements  of  the  eye.     It  is  the  most 

Fig.  141. 


Meter  Jtooi 
Sensorv  -flfl 

Nerves  of  the  Orbit,  seen  from  above. 


(Jleciirrent  Filament 
t       to  Dura-Mater 


anterior  motor  nerve  of  the  cerebro-spinal  axis,  and  su])plies  all  the 
nniscles  of  the  orbit,  including  the  spliincter  muscles  of  the  iris  and  the 
ciliary  muscle  of  the  eyeball,  with  the  exception  of  the  superior  oblique 


THE  NERVOUS  SYSTEM.  281 

and  the  external  rectus.  It  arises  superficially  from  the  walls  of  the 
interpeduncular  space  on  the  median  surface  of  the  cms  cerebri,  just 
above  the  pons  varolii.  It  extends  forward  and  slightly  outward  to  the 
side  of  the  posterior  clinoid  process,  soon  after  passing  which  it  enters 
the  superior  lateral  portion  of  the  cavernous  sinus,  being  invested  by  a 
sheath  from  the  dura  mater.  It  runs  through  this  portion  of  the  sinus, 
passes  below  the  anterior  clinoid  process,  and  on  to  the  proximal 
extremity  of  the  anterior  lacerated  foramen.  Here  it  enters  the  orbit 
by  passing  between  the  two  heads  of  the  external  rectus  muscle.  As 
it  extends  through  the  anterior  lacerated  foramen  it  divides  into  two 
branches,  superior  and  inferior. 

The  Superior  Division  of  the  Oculo-motor  Nerve  is  the  smaller  of  the 
two.  It  passes  inward  over  the  optic  nerve,  and  again  divides  into  two 
sets  of  branches,  one  being  distributed  to  the  superior  rectus  muscle, 
while  the  other  supplies  the  levator  palpebrse  superioris. 

The  Inferior  Division  of  the  Oculo-motor  Nerve  is  the  larger  of  the 
two.  It  divides  into  three  branches — the  internal  rectus,  inferior 
rectus,  and  inferior  oblique. 

The  Internal  Eectus  Nerve  passes  beneath  the  optic  nerve  and  supplies 
the  internal  rectus  muscle. 
.    The  Inferior  Rectus  Nerve  supplies  the  inferior  rectus  muscle. 

The  Inferior  Oblique  Nerve  is  the  longest  of  the  three  branches.  It 
passes  forward  between  the  inferior  and  external  recti  muscles  to  the 
inferior  and  anterior  portion  of  the  orbit,  and  is  mainly  distributed  to 
the  inferior  oblique  muscle.  It  also  sends  a  few  filaments  to  the  inferior 
rectus,  and  a  short,  thick  communicating  branch  to  the  ophthalmic  or 
lenticular  ganglion. 

Trochlear  Nerve. 

The  trochlear,  fourth,  or  patheticu§  nerve  (Fig.  141)  is  the  smallest 
and  the  most  slender  of  all  the  cranial  nerves,  though  it  has  the  longest 
encranial  course.  It  presides  over  the  motion  of  the  superior  oblique 
or  trochlear  muscle  of  the  eye.  It  arises  superficially  from  a  point  just 
below  the  corpora  quadrigemina  and  near  the  valve  of  Vieussens.  From 
this  point  it  passes  outward  over  the  superior  peduncle  of  the  cerebel- 
lum, then  forward,  curves  around  the  lateral  margin  of  the  crus  cerebri, 
and  penetrates  the  dura  mater  below  the  tentorium  cerebelli.  Near 
the  posterior  clinoid  process  it  enters  the  cavernous  sinus,  extends 
along  its  outer  and  upper  wall,  and  passes  through  the  proximal  por- 
tion of  the  anterior  lacerated  foramen  into  the  orbit.  It  then  passes 
forward  and  inward*  over  the  superior  rectus  and  le\'ator  palpebrse 
superioris  muscles,  and  is  distributed  to  the  upper  surface  of  the 
superior  oblique. 

Branches. — Recurrent  branches  of  this  nerve  are  given  off  as  it  ])asses 
through  the  tentorium  cerebelli.  They  are  distributed  to  the  tentorium, 
some  of  them  extending  backward  to  the  lateral  sinuses.  In  the  cav- 
ernous sinus  it  gives  off  branches  which  communicate  with  the  carotid 
plexus  of  the  sympathetic  nerve,  and  occasionally  with  the  ophthalmic 
division  of  the  fifth  nerve.     It  sometimes  sends  a  branch  which  anasto- 


282 


ANATOMY. 
Fig.  142. 


IntemaX  CarvtiJ,  As. 

A  Cairottd  Plea:uj 


Boot 


Nerves  of  the  Orbit  and  Ophthalmic  Ganglion,  side  view. 

raoses  with  the  lachrymal  nerve.     The  trochlear  nerve  is  supplied  by  a 
small  branch  from  the  anterior  cerebral  artery. 


Abducent  Nerve. 

As  the  abducent,  sixth,  or  external  oculo-motor  nerve  is  distributed 
to  a  muscle  of  the  orbit,  it  is  here  described  with  those  that  are  asso- 
ciated with  it.  This  nerve  presides  over  the  motion  of  the  external 
rectus  muscle,  and  arises  superficially  between  the  anterior  pyramids 
of  the  medulla  oblongata  and  the  pons  varolii.  Generally,  a  few 
bundles  of  its  fibres  spring  from  the  lower  margin  of  the  pons.  At 
first  it  is  flat,  but  as  it  extends  it  soon  l)ecomes  rounded.  It  passes 
forward,  and  penetrates  the  dura  mater  at  the  side  of  the  dorsum  sellse 
of  the  sphenoid  bone.  It  enters  the  cavernous  sinus,  and  passes  along 
its  outer  and  inner  portion,  covered  by  a  thin  membrane.  It  enters  the 
orbit  througli  the  anterior  lacerated  foramen,  between  the  two  heads  of 
the  external  rectus  muscle,  and  is  distributed  to  this  muscle,  entering 
its  proximal   or  orbital    surface. 

Branches. — In  the  cavernous  sinus  it  sends  communicating  filaments 
to  the  carotid  .sympathetic  ])lexus.  On  ]>asi^ing  into  the  orbits  it  gives 
off  a  branch  which  extends  between  it  :nid  the  ()])hthalmic  nerve.  This 
nerve  is  occasionally  entirely  absent.  A\'lien  this  is  the  case  the  exter- 
nal rectus  nm.scle  is  su])})lied  by  a  branch  from  the  third  nerve. 


Trifacial  Nerve. 

The   trifacial,   trigeminus,  or   fifth    nerve   is   the   largest  of  all   the 
cranial    nerves.      Through   its  wide  distribution  within   the  face  and 


THE  NERVOUS  SYSTEM. 


283 


over  the  head,  its  close  relation  to  other  nerves  and  to  the  plexuses 
and  gano;lia  of  the  sympathetic  nerve,  it  becomes  involved  in  nearly 
all  the  diseases  of  the  external  portion  of  the  head  as  well  as  the 
superhcial  and  deep  parts  of  the  face.  "  The  intimate  relations  which 
the  nerve  beai's  with  the  points  of  origin  of  the  sixth,  seventh,  eighth, 
ninth,  tenth,  eleventh,  and  twelfth  cranial  nerves  in  the  floor  of  the 
fourth  ventricle  possibly  explain  many  of  those  phenomena  which  are 
considered  as  reflex  in  character,  and  whose  starting-point  seems  to 
depend  upon  some  irritation  of  the  fifth  nerve  by  means  of  various 
branches"  (Ranney).  It  resembles  a  spinal  nerve,  in  that  it  arises  by 
two  roots,  anterior  and  posterior.  The  posterior  root  is  sensory  in 
character,  and  has  a  ganglion  upon  it,  while  the  anterior  root  has  no 
ganglion  and  is  motor  in   character. 

The  large,  sensory,  or  posterior  root  emerges  from  a  point  in  close 
l^roximity  to  the  centre  of  the  lateral  surface  of  the  pons  varolii,  but 
nearer  its  superior  than  its  inferior  border  (Fig.  136). 

Fig.  143. 


Sejtsnry  Root 
Mo-tor  Root- 


AwHcuIo-Terajtoral  N. 


nistribution  of  the  Second  and  Tliiid  Divisions  of  the  Fifth  Nerve  and  Submaxillary  Ganglion. 

The  small,  motor,  or  anterior  root  is  made  up  of  six  or  eight  rounded 
filaments  (Vulpian),  and  emerges  from  the  pons  a  little  above  the  larger 
posterior  root,  being  separated  from  it  by  a  few  transverse  fibres  of 


284  ANATOMY. 

white  substance.  It  is  entirely  distinct  and  separate  from  the  larger 
sensory  root  from  its  deep  origin  until  it  passes  out  of  the  cranial  cavity 
through  the  foramen  ovale,  when  it  becomes  closely  united  with  its  third 
or  inferior  maxillary  division,  hereafter  to  be  described. 

The  deep  origin  of  these  two  roots  is  widely  separated  from  their 
superficial  origin.  Following  them  backward  from  the  anterior  surface 
of  the  pons  varolii,  they  pass  directly  through  the  pons  to  the  medulla 
oblongata,  without  any  connection  whatever  with  its  fibres.  On  reach- 
ing the  medulla  they  form  three  main  divisions,  one  anterior  and  two 
posterior. 

The  Anterior  or  3Iotor  Division  arises  from  the  motor  nucleus  of 
the  fifth  nerve,  which  is  composed  of  large,  ramified,  and  pigmented 
cells  situated  below  the  lateral  angle  of  the  fourth  ventricle,  anterior  to 
the  inferior  facial  nucleus,  and  on  the  proximal  side  of  the  large  sensory 
nucleus  of  the  fifth  nerve.  It  also  arises  from  the  gray  matter  at  the 
anterior  portion  of  the  iter  beneath  the  corpora  quadrigemina.  As  it 
passes  toward  the  pons  it  receives  fibres  which  arise  from  the  raphe. 
The  fibres  have  their  origin  in  the  nucleus  of  the  opposite  side  or  in 
the  pyramidal  tract. 

The  Two  Posterior  or  Sensory  Divis^ions  give  general  sensibility  to  the 
face  and  head,  extending  as  far  back  as  its  vertex.  These  divisions  are 
the  superior  and  inferior. 

The  Superior  or  Larger  Division  arises  from  the  superior  sensory 
nucleus  of  the  fifth  nerve.  This  nucleus  is  situated  at  the  side  of  the 
motor  nucleus,  and  is  composed  of  nerve-cells  which  are  less  compactly 
arranged,  but  in  greater  numbers  than  the  motor  nucleus. 

The  Inferior  or  Smaller  Diinsion .  is  a  well-defined  bundle  of  nerve- 
fibres  which  arises  from  the  inferior  nucleus  of  the  fifth  nerve.  This 
is  composed  of  cells  situated  in  the  gelatinous  substance  which  consti- 
tutes the  tubercle  of  Rolando. 

From  their  sujierficial  origin  these  two  roots  extend  obliquely  upward 
and  forward  across  the  summit  of  the  petrous  portion  of  the  .temporal 
bone,  and  jwiss  through  an  oval  opening  in  the  dura  mater  into  the  mid- 
dle fossa  of  the  brain-case.  The  larger  posterior  sensory  root  terminates 
in  the  ganglion  of  Gasser,'  which  is  situated  in  a  depression  on  the  supe- 
rior part  of  the  anterior  surface  near  the  apex  of  the  petrous  portion 
of  the  temporal  bone.  This  ganglion  is  broad,  flattened,  and  somewhat 
semilunar  or  crescent-shaped,  and  from  this  fiict  is  often  called  the  semi- 
lunar ganglion  of  the  fifth  nerve.  Its  convexity  is  directed  forward  and 
slightly  upward.  The  cells  of  this  ganglion  are  unipolar  in  shape.  Its 
surfaces  are  striated,  and  it  receives  on  its  inner  side  filaments  of  com- 
munication from  the  carotid  ])lexus  of  the  sympathetic  nervous  system." 

'  The  structure  of  tliis  gantjlion  was  first  recognized  by  Gasser,  professor  of  anatomy 
in  Vienna.  His  observations,  however,  were  published  by  Hirsch,  a  pupil  of  Gasser, 
in  1765  (Hirsch,  Paria  Qiiiiiti  Nervonum  encephali,  Viennoe,  1765),  in  Ludwig  (Scrip- 
tores  Nervoinyiri  minnres  selccli,  Lipsife,  1791,  tonius  i.  pp.  244  et  seq.).  Hirsch  first  gave 
it  the  name  of  (rasserian  ganglion. 

Some  authors  call  it  ( 'asserian  ganglion,  probably  confounding  Gasser  with  Casserius. 
Casserius  in  his  anatomical  figures  describes  many  parts  of  the  brain  and  nerves,  but 
says  nothing  of  the  ganglion  of  the  fifth  (Casserius.  Anatnmische  Tofdn,  Franckfurt-am- 
Mayn,  1756).     (Flint's  Physloloyy  of  the  Nervous  iiystem,Yo\.  i.  p.  185.) 


THE  NERVOUS  SYSTEM. 


285 


Flint  claims  "this  anatomical  point  as  of  importance  in  view  of  some 
of  the  remote  effects  which  follow  division  of  the  fifth  nerve  through 
the  ganglion  in  living  animals."  A  few  small  branches  emanate  from 
the  ganglion,  and  are  distributed  to  the  dura  mater  and  the  tentorium. 

From  the  anterior  or  concave  margin  of  this  ganglion  the  three  large 
divisions  of  the  fifth  nerve  commence.  It  is  from  this  that  the  nerve 
receives  the  name  of  trifacial.  These  divisions  again  divide  and  sub- 
divide as  they  pass  forward  to  their  terminations  (Fig.  144). 

Fig.  144. 


A  Diagram  of  the  Distribution  of  the  Fifth  Nerve  (Eanney) :  1,  the  crus  cerebri;  '>,  the  sensory  root 
of  the  nerve;  3,  the  motor  root  of  the  nerve;  4,  the  (iasseriaii  ganglion,  upon  the  sensory  root 
only ;  5,  the  ophthalmic  nerve  passing  through  the  sphenoidal  fissure;  fi,  tlie  superior  maxillary 
nerve  passing  through  the  foramen  rolundum  to  enter  the  sphenomaxillary  fossa;  7,  the  inferior 
maxillary  nerve  passing  through  the  foramen  ovale  in  company  with  the  motor  root;  8,  a  fila- 
ment sent  backward  from  the  ophthalmic  nerve  to  the  tentorium  cerebelli ;  'J,  the  frontal  nerve ; 
10,  the  lachrymal  nerve ;  11,  the  nasal  nerve  ;  12,  the  supraorbital  nerve  passing  through  the  fora- 
men of  the  same  name;  13,  the  supratrochlear  nerve;  14,  the  long  ciliary  nerves  to  the  iris;  15, 
the  lenticular  or  ciliary  ganglion  ;  16,  the  temporo-malar  nerve,  dividing  into  temporal  and  malar 
branches;  17,  the  spheno-palatine  nerve,  going  to  Meckel's  ganglion;  18,  the  po>terior  dent:il 
nerves;  19,  the  anterior  dental  nerves,  given  off  in  the  antrum;  20,  the  nasopalatine  nerve, 
escaping  at  the  anterior  palatine  foramen  after  pa.ssing  through  the  antrum;  21,  the  anterior 
palatine  nerve  after  escaping  from  the  posterior  palatine  foramen  ;  22,  the  deep  temporal  nerve; 
23,  the  masseteric  branch ;  24,  the  buccal  branch,  which  also  often  supplies  the  external  jiterygoid 
musL-le;  25,  the  pterygoid  branch,  going  chiefly  to  the  internal  pterygoid  muscle;  20,  the  poste- 
rior palatine  nerves  after  leaving  the  posterior  palatine  foramen,  going  to  the  muscles  of  soft 
palate;  27,  the  auriculo-temporal  nerve,  splitting,  and  thus  embracing  the  middle  meningeal 
artery;  28,  the  gustatory  or  lingual  nerve,  distributed  to  the  anterior  two-thirds  of  tongue;  29, 
t'lie  inferior  dental  nerve,  passing  through  the  inferior  dental  canal  beneath  the  teetli  of  the 
lower  jaw  ;  30,  the  mylo-hyoid  nerve ;  31,  the  chorda  tympani  nerve,  joining  the  gustatory  nerve, 
and  possibly-bringing  to  "it  the  perception  of  taste:  -32,  the  middle  meningeal  artery;  33,  the 
fibres  going  to  the  cavernous  plexuses  of  the  sympathetic  system;  34,  the  Vidian  mrve,  going 
from  Meckel's  ganglion  to  the  Vidian  canal.— Ganglion  of  the  Fifth  Nerv?;  L,  the  lenticular 
ganglion,  sending  fibres  to  the  iris  and  ciliary  muSTcle;  C,  the  Ga.sserian  ganglion;  O,  the  otic 
ganglion,  lying  on  the  inferior  maxillary  nerve  below  the  foramen  ovale;  E,  the  submaxillary 
ganglion,  connected  with  the  gustatory  and  chorda  tympani  nerves;  jM,  Meckel's  ganglion,  lying 
in  the  spheno-maxillary  fossa. 

"  By  tracing  the  various  distributions  of  this  nerve  it  will  be  seen  that 
it  gives  motor  power  to  the  muscles  of  mastication — viz.  the  temporal, 
masseter,  and  pterygoids  ;  also  the  anterior  belly  of  the  digastric  and 
mylo-hyoid  muscles,  and  tensor  palato  "  (palato-Eustachian)  "  and  tensor 


286  ANATOMY. 

tympani,  thus  controlling  the  act  of  mastication  and  to  some  extent 
deglutition  and  hearing.  Fibres  of  the  fifth  nerve  aftbi'd  general  sensa- 
tion to  the  entire  skin  of  the  head  and  face,  except  in  the  occipital 
region  and  the  back  and  lower  part  of  the  ear,  also  to  the  mucous  mem- 
branes of  the  mouth,  with  the  exception  of  the  posterior  pillar  of  the 
fauces  and  the  posterior  third  of  the  tongue,  which  derive  their  sensa- 
tion by  means  of  the  glosso-pharvngeal  nerves  (Ranney). 

The  Ophthaliaic,  or  first  division  of  the  fifth  nerve,  is  the  smallest 
of  the  three  cords,  being  but  about  an  inch  in  length.  The  table  on 
page  287  will  show^  that  it  is  derived  wholly  from  the  sensory  root.  Its 
function  is  to  impart  sensation  to  the  eyeball,  the  lachrymal  gland,  the 
mucous  lining  of  the  eye,  and  a  portion  of  the  nose  and  of  the  eye- 
brow and  forehead.  It  commences  from  the  upper,  inner,  and  anterior 
portion  of  the  margin  of  the  Gasserian  ganglion.  It  is  a  flattened  cord, 
and  passes  forward  along  the  outer  wall  of  the  cavernous  sinus,  and 
terminates  before  or  just  as  it  is  about  to  pass  through  the  anterior 
lacerated  foramen  by  dividing  into  three  main  branches,  the  frontal, 
lachrymal,  and  nasal. 

Brandies  of  the  OpJithdhiiic  Nerve. — 

Those  within  the  cavernous  sinus.  Lachrymal, 

Frontal,  Nasal. 

The  ophthalmic  nerve  gives  off  two  small  branches  within  the  cav- 
ernous sinus. 

The  Frontdl  Nerve  is  the  largest  of  the  branches  given  off  by  the 
ophthalmic,  and  is  in  reality  its  axial  continuation.  It  enters  the  orbit 
through  the  most  superior  portion  of  the  anterior  lacerated  foramen, 
and  passes  forward  in  the  median  line  above  the  muscles  and  below  the 
periosteum.  It  terminates  midway  between  the  apex  and  base  of  the 
orbital  cavity,  above  the  levator  palpebrte  snperioris  muscle,  by  dividing 
into  two  branches  of  unequal  size,  the  su])ratrochlear  and  the  supra- 
orbital. 

The  Suprafrorhkfir  Nerve  is  nnich  the  smaller  of  the  two  terminal 
branches  of  the  frontal.  It  extends  obliquely  inward  and  forward  over 
the  trochlear  muscle,  passing  out  of  the  orbit,  and  curves  around  the 
supraorbital  arch  between  the  supraorbital  foramen  and  the  trochlear  fossa. 
It  then  extends  beneath  the  corrugator  sujicrcilii  and  frontalis  muscles, 
and  divides  into  two  terminal  branches.  These  branches  pierce  the 
orbicularis  and  frontalis  muscles,  supplying  them  as  well  as  the  integ- 
ument ;  also  the  lower  and  median  portion  of  the  forehead,  interlacing 
with  the  corresponding  nerve  of  the  o])posite  side.  This  nerve  also 
gives  off  two  distributing  branches,  one  extending  from  the  nerve  near 
the  trochlear  nuiscle,  which  passes  downward  and  joins  the  infratrochlear 
branch  of  the  nasal  nerve,  and  the  other  near  its  exit  from  the  orbit, 
which  passes  to  the  eyelid  and  bridge  of  the  nose. 

The  >Supraorhitaf  Nerve  is  really  a  continuation  of  the  frontal.  It 
passes  forward,  and  emerges  from  the  orbit  through  the  supraorbital 
notch  or  foramen.  It  then  curves  upward  on  the  forehead,  and  divides 
into  a  median  and  a  lateral  l)ranch,  which  ])ierce  the  muscles  and  become 
the  cutaneous  nerves.  Its  branches  of  distribution  are  several  small 
cords  which   descend   to  the  struc^tures  of  the  upper  eyelid,  and   one 


THE  NERVOUS  SYSTEM. 


287 


The  following;  table  will  serve  to  demonstrate  the  original  trunks  of 
this  nerve,  with  their  different  branehes  : 

Motor  Root.  Ganglion  of  Gasser  (Sensory  Root). 


O 
B 


o 

6 

•-! 

o- 

a 

ts 

rr. 

;-; 

^ 

M 

M 

T. 

3 

rr. 

a 

3-. 

'^ 

-s 

288  ANA  TOMY. 

which  passes  outward  under  the  orbicularis  palpebrarum,  interlacing 
with  the  facial  nerve.  The  muscular  branches  are  distributed  to  the 
corrugator  supercilii,  frontalis!;  and.  orbicularis  palpebrarum.  The 
cutaneous  branches  are  two  in  number,  median  and  lateral.  These 
extend  posteriorly  as  far  as  the  occiput.  The  deep  or  pericranial 
branches  are  distributed  to  the  frontal  and  parietal  bones.  This  nerve 
also  sends  a  filament  which  supplies  the  mucous  membrane  of  the  frontal 
sinus.  Occasionally  the  division  of  the  supraorbital  nerve  takes  place 
within  the  orbit,  the  larger  branch  passing  through  the  supraorbital 
foramen,  while  the  smaller  branch  extends  internally  around  the  supra- 
orl)ital  arch  or  through  the  frontal  notch,  which  is  occasionally  present. 

The  Lachri/mal  Xnnr  is  the  smallest  of  the  three  divisions  of  the 
ophthalmic.  It  passes  along  the  outer  side  of  the  frontal  nerve  into 
the  orbit  through  the  anterior  lacerated  foramen,  encased  in  an  indi- 
vidual sheath  derived  from  the  dura  mater.  It  passes  forward  and 
outward  near  the  periosteum  of  the  orbit  above  the  external  rectus 
to  the  lachrymal  fossa  of  the  frontal  bone,  accompanied  by  the  lachry- 
mal artery.  It  then  penetrates  the  external  tendo  palpebrarum  of  the 
eye  and  terminates  in  the  upper  eyelid. 

Branches  of  Distribution. — On  approaching  the  lachrymal  fossa  the 
lachrymal  nerve  sends  a  communicating  cord  to  the  orbital  branch  of 
the  second  or  superior  maxillary  division  of  the  fifth.  This  branch  is 
sometimes  called  the  inferior  division  of  the  lachrymal  nerve,  and  occa- 
sionally passes  backward  through  a  canal  in  the  outer  wall  of  the  orbit, 
its  divisions  foriiiing  an  arch  from  which  branches  are  distributed  to 
the  lachrymal  gland  and  the  conjunctiva.  Within  the  lachrymal  fossa 
it  sends  branches  to  the  lachrymal  gland  and  the  conjunctiva. 

The  Nasal  or  Oculo-xasal  Nerve  is  intermediate  in  size  between 
the  other  two  divisions  of  the  ophthalmic  nerve.  It  commences  from  the 
under  surface  of  the  ophthalmic  nerve,  and  passes  through  the  widest 
portion  of  the  anterior  lacerated  foramen  into  the  orbit  between  the  two 
heads  of  the  external  rectus  muscle,  accompanied  by  the  fourth  nerve. 
On  either  side  of  it  are  the  two  divisions  of  the  third  nerve.  From  the 
anterior  lacerated  foramen  it  passes  obliquely  inward  and  forward  over 
the  optic  nerv-e  below  the  superior  muscles  of  the  orbit  to  the  anterior 
ethmoidal  foramen  on  the  inner  wall  of  the  orbital  cavity.  It  here 
divides  into  the  internal  nasal  and  infratrochlear  nerves. 

Branches  of  the  Xa.sf(/  Xerve. — 

Branch  to  the  dura  mater,  I^ong  ciliary, 

Communicating  branches  to  Spheno-ethmoidal, 

sympathetic  nerve.  Internal  nasal. 

Ganglionic,  Infratrochlear. 

The  Branch  to  the  Dura  Mater  is  a  small  filament  which  turns  back- 
ward and  is  distributed  to  tlie  dura  mater  of  the  anterior  cerebral  fossa. 

TJie  Conimnnicating  Branches  to  the  St/nipathetie  are  a  few  distinct 
filaments  which  communiciite  with  the  sympathetic  network  about  the 
ophthalmic  artery  (Allen). 

The  Gang/ionic  Branch  is  quite  slender  and  about  half  an  inch  in 
length.  It  usually  commences  from  the  nasal  nerve  as  it  extends 
between  the  two  heads.     It  passes  along  the  outer  side  of  the  optic 


THE  NERVOUS  SYSTEM.  289 

nerve,  and  terminates  at  the  jjosterior  superior  portion  of  the  ophthalmic 
(lentieular)  ganglion,  constituting  its  long-  or  sensory  root. 

Tlie  Long  Ciliary  Nerves  are  two  or  three  in  number,  and  com- 
mence from  the  nasal  nerve  as  it  extends  across  the  optic  nerve. 
They  pass  along  the  inner  margin  of  this  nerve,  and  unite  with 
some  of  the  short  ciliary  nerves  from  the  ophthalmic  ganglion. 
They  then  pierce  the  sclerotic  coat  of  the  eye,  pass  forward  between 
it  and  the  choroid  coat,  and  are  distributed  to  the  ciliary  muscles,  the 
cornea,  and  the  iris. 

The  hipheno-eihmoidal  (Luschka)  or  Posterior  Ethmoidal  (Krause) 
Nerve  passes  from  the  nasal  nerve  to  the  posterior  ethmoidal  foramen 
(posterior  internal  orbital  canal),  and  is  distributed  to  the  mucous  mem- 
brane of  the  sphenoidal  sinus  and  the  posterior  ethmoidal  cells  in  front 
of  the  body  of  the  sphenoid  bone. 

The  Internal  Nasal  or  Ethmoid(d  Nerve  is  in  the  line  of  continuation 
of,  and  generally  described  as,  the  nasal  nerve.  It  passes  through  the 
anterior  ethmoidal  foramen,  situated  between  the  frontal  and  ethmoidal 
bones,  into  the  brain-case,  just  external  to  the  cribriform  plate.  It  then 
extends  in  a  shallow  groove  along  the  outer  wall  of  this  plate  to  the 
cerebro-nasal  slit  near  the  crista  galli,  passes  through  this  slit,  enters  the 
nasal  chamber,  and  divides  into  three  branches — the  internal  or  septal 
branch,  the  lateral,  and   the  anterior  superficial   branch. 

The  Internal  or  l^eptal  BrancJi  of  the  internal  nasal  nerve  passes 
downM'ard  and  forward,  and  supplies  the  anterior  portion  of  the  septum 
of  the  nose. 

The  Lateral  Branches  of  the  hiterncd  Nerve  usually  comprise  two  or 
three  filaments  which  are  distributed  to  the  anterior  portions  of  the  lat- 
eral walls  of  the  nasal  chambers,  including  the  extremities  of  the  middle 
and  inferior  turbinated  bones. 

The  Anterior  or  tiuperjidal  Branch  passes  dowuMard  in  a  longitu- 
dinal groove  or  canal  on  the  internal  surface  of  the  nasal  bone  until 
it  reaches  the  lateral  cartilage  of  the  nose.  Here  it  extends  between 
the  bone  and  the  cartilage,  runs  beneath  the  compressor  naris,  and 
becomes  superficial,  terminating  in  the  spine,  the  wing,  and  the  tip  of 
the  nose. 

The  Infratrochlear  Nerve  is  one  of  the  terminal  branches  of  the  nasal 
nerve,  it  being  given  off*  near  the  anterior  ethmoidal  foramen.  It  passes 
forward  along  the  inferior  border  of  the  superior  oblique  muscle  and 
parallel  to  the  supratrochlear  nerve,  and  receives  a  communicating  branch 
from  it.  As  it  approaches  the  trochlea  it  passes  to  the  inner  angle  of 
the  eye  and  divides  into  t's\^o  sets  of  branches.  Those  of  the  superior 
set  are  distributed  to  the  superficial  structures  of  the  superior  evelid ; 
while  those  of  the  inferior  set  are  distributed  to  the  superficial  struc- 
tures at  the  root  and  side  of  the  nose,  the  superficial  portion  of  the 
inferior  eyelid,  the  caruncle,  conjunctiva,  the  lachrymal  sac,  and  the 
lachrymal  duct. 

Variations. — "■  The    nasal    nerve    occasionally    (frequently,    Krause) 

gives  filaments  to  the  superior  and  internal  recti.     A  branch  to  the 

levator   palpebrse    superioris    has    been    met    with  (Fiisebeck) ;    offsets 

from  the  nasal  nerve  as  it  traverses  the  anterior  internal  orbital  canal  to 

Vol.  I.— 19 


290  ANATOMY. 

the   frontal  sinus   and  ethmoidal  cells  are  described  by  Meckel  and 
Lansrenbeck."  ^ 


Superior  Maxillary  Nerve. 

The  superior  maxillary  or  second  division  of  the  fifth  nerve  is  the 
second  in  size  of  its  three  great  divisions.  It  is  composed  entirely  of 
sensory  fibres,  and  gives  sensation  to  nearly  all  the  structures  of  and 
around  the  superior  maxillary  bone.  It  commences  in  the  centre  of  the 
conv'ex  or  anterior  margin  of  the  Gasserian  ganglion  by  a  flattened  and 
plexiform  band,  passes  horizontally  and  directly  forward,  and  leaves  the 
cranium  through  the  foramen  rotunduni  in  the  great  wing  of  the  sphe- 
noid bone.  It  then  enters  the  pterygo-maxillary  (spheno-maxillary) 
fossa,  and  becomes  more  rounded  and  firmer  in  texture.  It  passes  across 
this  fossa  surrounded  by  adipose  tissue,  and  enters  the  infraorbital  or 
superior  maxillary  canal,  and  receives  the  name  of  infraorbital  nerve.  It 
passes  through  this  canal,  and  emerges  upon  the  face  through  the  infra- 
orbital foramen.  The  branches  of  this  nerve  can  be  divided  into  lour 
groups,  according  to  the  locality   of  their  origin. 

The  Orbital  or  Temporo-malar  Branch  (subcutaneous  malse)  is  a 
small  nerve  which  arises  from  the  upper  ])ortion  of  the  superior  max- 
illary nerve  just  after  it  emerges  from  the  foramen  rotundum.  It  passes 
forward  into  the  orl)ital  cavity  through  the  spheno-maxillary  fissure, 
and  immediately  divides  into  two  branches,  temporal  and  malar. 

The  Temporal  Branch  passes  forward  in  a  groove  on  the  outer  wall 
of  the  orbit  until  it  reaches  the  temporal  canal  in  the  malar  bone.  It 
passes  through  this  canal  into  the  anterior  portion  of  the  temporal  fossa, 
ascends  between  the  bone  and  the  tem])oral  muscle  a  short  distance, 
pierces  the  muscle  and  its  aponeurosis  about  an  inch  above  the  zygoma, 
and  terminates  in  filaments  which  supply  the  cutaneous  structures  of 
the  temporal  region  and  the  side  of  the  forehead.  It  interlaces  with 
the  facial  and  occasionally  with  the  third  division  of  the  fifth  nerve. 
That  portion  of  the  nerve  within  the  orbit  sends  one  or  two  filaments 
of  communicatiiMi  to  the  lachrymal  nerve,  a  branch  of  the  ophthalmic 
division  of  the  fifth. 

TJte  Malar  Branch  at  its  commencement  ])asses  through  the  loose 
adipose  tissue  at  the  lower  angle  of  the  orbit  to  the  malar  bone,  through 
which  it  extends  in  the  malar  canal  in  its  lower  portion,  and  emerges 
upon  the  face  usually  by  two  branches.  It  is  distributed  to  the  cutaneous 
tissues  in  this  region  of  the  cheek,  and  interlaces  with  the  facial  nerve. 

TJtc  Sij/ic)io-j)alafi))P  Branches  are  usually  two  in  number,  and  are 
given  off  from  the  middle  of  the  lower  surface  of  the  pterygo-maxillary 
portion  of  the  second  division  of  the  fifth  nerve.  They  pass  downward 
to  the  spheno-palatine  or  Meckel's  ganglion. 

The  Posterior  I'^tiperior  Dental  or  Alveolo-dental  Nerve  usually  arises 
by  one  root,  though  occasionally  it  has  two,  from  the  second  division  of 
the  fifth  nerve  just  l)efi)re  it  passes  into  the  infraorbital  canal.  When 
it  arises  by  one  root  it  almost  immediately  divides  into  two,  and  forms 
a  superior  and  an  inferior  set  of  branches. 

^  From  Quain's  Anatomy. 


THE  NERVOUS  SYSTEM.  291 

The  Snperio7'  Set  passes  forward,  and  enters  canals  in  the  zygomatic 
surface  of  the  superior  maxillary  bone,  traverses  the  base  of  the  malar 
process  of  this  bone,  and  terminates  in  the  canine  fossa,  interlacing  with 
the  anterior  dental  nerves. 

The  Inferior  Set  is  somewhat  larger  than  the  superior,  and  passes 
downward,  slightly  outward  and  forward,  to  enter  the  posterior  dental 
canals.  One  of  these  canals  traverses  the  outer  wall  of  the  maxillary 
sinus,  and  joins  the  anterior  dental  canal  extending  from  the  infraorbital. 
As  the  nerve  passes  forward  in  this  canal  it  gives  off  branches  which  form 
loops  or  plexuses,  from  which  filaments  are  given  off  to  enter  the  roots 
of  each  of  the  molar  teeth,  and  are  distributed  to  their  pulps,  the  outer 
wall  and  mucous  membrane  of  the  maxillary  sinus,  the  alveolar  pro- 
cess and  the  gums,  and  a  few  fibres  to  the  bony  structure  of  the  antrum 
of  Highmore.  Occasionally  the  posterior  dental  nerve  is  of  large  size, 
and  replaces  an  absent  buccal  nerve,  a  brancli  of  the  inferior  maxillary. 

The  Middle  Superior  Dental  Nerve  is  given  off  from  the  infi-aor- 
bital  soon  after  it  enters  the  infraorbital  canal.  It  passes  outward, 
downward,  and  forward  in  a  special  canal  in  the  outer  wall  of 
the  maxillary  sinus,  interlacing  with  the  posterior  dental  nerve,  and 
forms  loops  or  plexuses  from  which  filaments  are  given  off  to  enter  the 
roots  of  the  bicuspid  teeth. 

The  Anterior  Superior  Dental  Nerve  is  larger  than  either  of  the  other 
two  divisions.  It  is  given  off  from  the  infraorbital  nerve  a  little  before 
it  emerges  from  the  infraorbital  foramen.  It  passes  in  a  special  canal 
of  its  own  which  begins  in  the  anterior  wall  of  the  maxillary  sinus, 
extends  at  first  inward,  then  downward,  and  is  reflected  upon  the  floor 
of  the  nasal  fossa.  It  then  passes  in  a  lateral  direction,  and  communi- 
cates with  the  canals  of  the  middle  and  posterior  dental  nerves.  This 
nerve  gives  off  two  sets  of  distributing  branches,  the  ascending  and  the 
descending. 

The  Ascending  Nasal  Set  is  distributed  to  the  nasal  spine  of  the  supe- 
rior maxillary  bone,  the  mucous  membrane  of  the  anterior  portion  of 
the  inferior  meatus,  and  to  the  floor  of  the  nose. 

The  Descending  or  Dental  Set  is  distributed  through  loops  or  plexuses 
to  the  incisor  and  canine  teeth,  and  interlaces  with  the  middle  and  pos- 
terior dental  nerves. 

The  three  superior  dental  nerves  interlace  or  communicate  with  each 
other  in  such  a  manner  as  to  form  loops  or  plexuses.  These  plexuses 
(superior  dental)  are  situated  above  the  roots  of  the  teeth,  and  it  is 
often,  if  not  always,  difficult  to  say  where  one  begins  and  the  other 
ends.  It  is  extremely  probable  that  filaments  from  each  of  the  three 
nerves  pass  into  the  same  tooth.  This  may  account  for  the  fact  that 
some  of  these  nerves  can  be  severed  and  the  pulps  of  the  teeth  remain 
vital. 

The  Facial  or  Terminal  Set  is  composed  of  three  nerves — the  paljje- 
bral,  nasal,  and  labial.     They  arise  from  the  infraorbital  just 
nerve  emerges  from  the   infraorbital  foramen. 

The  Inferior  Palpebral  or  Ascending  Set  is  generally  mj; 
nerves.     They  ascend  in  a  groove  or  canal,  pass  throup-^"" 
tion  of  the  proper  elevator  muscle  of  the  upper  lip, 


292  ANATOMY. 

to  the  orbicularis  palpebrarum,  the  skin,  the  conjunctiva  of  the  lower 
eyelid,  and  interlace  at  the  outer  angle  of  the  orbit  with  the  malar 
branches  of  the  orbital  and  facial  nerves.  A  branch  also  passes  inward 
and  interlaces  with  the  external  nasal  nerve,  a  division  of  the  oph- 
thalmic. 

The  Nasal  or  Internal  Branches,  two  or  three  in  number,  pass  inward 
and  outward  between  the  fibres  of  the  levator  labii  superioris  al?eque 
nasi  muscle,  and  are  distributed  to  the  skin  of  the  nose  and  the  lining 
membrane  of  the  nostril,  and  interlace  with  the  nasal  branches  of  the 
ophthalmic  nerve. 

The  Labial  or  Descending  Branches  are  more  numerous  than  the 
branches  of  the  other  sets  from  the  infraorbital  nerve.  They  pass  down- 
ward beneath  the  levator  labii  superioris  muscle,  and  are  distributed  to 
the  up])er  lip,  its  skin,  mucous  (labial)  glands,  and  mucous  membrane. 
They  also  extend  to  the  anterior  portion  of  the  gums. 

The  Infraorbital  Plexus  of  nerves  is  situated  below  the  orbit,  and  is 
composed  of  branches  from  the  infraorbital  and  facial  nerves. 

The  Inferior  Maxillary  Nerve. 

The  Inferior  Maxillary,  or  Third  Division  of  the  Fifth  Nerve,  is  the 
largest  of  its  three  divisions.  It  differs  from  the  other  two  divisions  in 
the  fact  that  its  function  is  mixed,  being  both  sensory  and  motor ;  it 
also  probably  supplies  in  a  measure  the  special  sense  of  taste.  This 
nerve  is  distributed  to  tlie  inferior  portion  of  the  face,  the  inferior 
maxillary  bone,  the  inferior  teeth,  a  portion  of  the  tongue,  and  the  mus- 
cles of  mastication.  Its  origin  is  composed  of  two  portions,  the  sensory 
and  motor. 

The  Sensory  (or  larger)  Portion  arises  from  the  inferior  lateral  and 
anterior  part  of  the  margin  of  the  Gasserian  ganglion.  It  passes  down- 
ward through  the  foramen  ovale  in  the  sphenoid  bone,  accompanied  by 
the  smaller  anterior  or  motor  root.  Immediately  after  its  exit  from 
this  foramen  the  two  portions  unite,  their  fibres  interlacing,  to  form  one 
nerve,  the  mixed  function  of  the  nerve  being  thus  accounted  for.  It 
then  descends  vertically  internal  to  the  external  pterygoid  muscle,  and 
divides  into  two  sets  of  branches,  anterior  and  posterior. 

The  Anterior  Motor  Branch  or  trunk  of  the  inferior  maxillary  nerve 
is  the  smaller  of  the  tAvo,  and  is  composed  almost  entirely  of  motor  fila- 
ments, which  are  distributed  to  the  muscles  of  mastication.  It  is  divided 
into  four  l)ranches : 

Deep  temporal,  Pterygoid, 

Masseteric,  Buccal. 

The  Deep  Temporal  Branches  are  usually  two  in  number,  though 
occasionally  thoi-e  are  three — anterior,  middle,  and  posterior. 

The  Anterior  Branch  l^efore  jiiercing  the  external  pterygoid  muscle  is 
joined,  by  a  communicating  filament  from  the  buccal  nerve.  It  ascends 
across  the  infratemporal  (pterygoid)  ridge  of  the  sphenoid  bone,  passes 
to  the  anterior  portion  of  the  temporal  fossa,  and  supplies  that  part  of 
the  temporal  muscle  situated  in  this  region. 

The  Middle  Deep  Temporal  Branch  passes  outward  above  the  exter- 


THE  NERVOUS  SYSTEM.  293 

nal  pterygoid  muscle,  then  curves  upward,  running  close  to  the  temporal 
bone,  and  is  distributed  to  the  deep  and  internal  portions  of  the  temporal 
muscle. 

The  Posterior  Temporal  Branch  is  made  up  entirely  of  motor  fila- 
ments. During  the  first  portion  of  its  course  it  is  often  associated  with 
the  masseteric  nerve.  It  passes  in  a  tortuous  manner  upward  and  out- 
ward, then  ujjward  through  the  proximal  surface  of  the  temporal  mus- 
cle ;  it  passes  out  of  this  muscle  and  through  its  fascia  from  a  half  to 
three-quarters  of  an  inch  above  the  zygoma,  and  then  turns  upAvard 
beneath  the  skin  and  interlaces  with  the  auriculo-temporal  and  facial 
nerves. 

The  Masseteric  Nerve  is  larger  than  the  deep  temporal,  and  arises  in 
close  proxiiuitv  to  it.  Occasionally  these  two  nerves  arise  as  a  common 
trunk  from  the  third  division  of  the  fifth  nerve.  It  passes  backward 
and  outward  between  the  upper  portion  of  the  zygomatic  fossa  and  the 
superior  border  of  the  external  pterygoid  muscle,  curves  slightly  down- 
ward and  outward,  and  passes  tlirough  the  sigmoid  notch  in  the  inferior 
maxillary  bone.  It  then  extends  downward  between  the  ramus  of  the 
bone  and  the  masseter  muscle,  to  which  muscle  it  is  mainly  distributed. 
Its  other  branches  of  distribution  are,  first,  a  small  communicating  fila- 
ment which  interlaces  with  the  deep  temporal  and  independent  deep 
posterior  temporal  branch,  and  an  articulating  branch  which  passes  to 
the  temporo-maxillary  articulation. 

The  Internal  Pterygoid  Nerve  is  the  shortest  branch  of  the  third 
division  of  the  fifth  nerve.  It  is  given  off  from  its  anterior  and  prox- 
imal side  on  a  level  with  the  otic  ganglion.  It  passes  backward  between 
the  ganglion  and  the  lingual  nerve,  occasionally  extending  through  the 
ganglion  to  the  inner  side  of  the  internal  pterygoid  muscle,  to  which 
it  is  mainly  distributed.  Its  other  branches  of  communication  are, 
first,  a  motor  root  to  the  otic  ganglion  ;  second,  a  filament  to  the  palato- 
Eustachian  (tensor  palati)  muscle ;  third,  a  branch  to  the  tensor  tym- 
pani. 

The  External  Pterygoid  Nerve  is  not  constant  in  its  origin  ;  it  seldom 
arises  from  the  main  trunk  of  the  inferior  maxillary,  but  generally  in 
conjunction  with  the  buccal  branch  or  from  the  internal  pterygoid 
nerve.     It  is  distributed  to  the  external  pterygoid  muscle. 

The  Buccal  Nerve,  though  described  under  the  head  of  the  motor 
branches  of  the  inferior  maxillary  nerve,  is  almost  entirely  composed 
of  sensory  fibres.  It  arises  from  the  lateral  margin  of  the  main  trunk 
of  the  inferior  maxillary  by  from  one  to  three  bundles,  and  is  usually 
joined  at  its  origin  by  the  anterior  deep  temporal  and  the  external 
pterygoid  nerves.  It  passes  outward,  either  between  the  two  heads  of 
the  external  pterygoid  or  between  the  tMO  pterygoid  muscles ;  extends 
downward  to  the  inner  surface  of  the  coronoid  process  of  the  inferior 
maxilla,  thence  forward  between  this  process  and  the  tuberosity  of  the 
superior  maxillary  bone,  occasionally  passing  between  the  fibres  of  the 
temporal  muscle  close  to  its  insertion.  Midway  between  the  lobe  of  the 
ear  and  the  angle  of  the  mouth  it  becomes  superficial,  and  terminates  by 
dividing  into  superior  and  inferior  branches. 

Branches  of  distribution  are — 


294  ANATOMY. 

(a)  Two  or  three  external  pterygoids,  which  are  given  oif  as  the  nerve 
passes  through  the  external  pterygoid  muscle. 

(6)  An  anterior  deep  temporal  branch,  which  usually  joins  the  deep 
temporal  nerve.  It  passes  upward  to  the  thick  portion  of  the  tem- 
poral muscle. 

(e)  A  descending  branch,  which  passes  to  the  insertion  of  the  tem- 
poral muscle. 

(d)  Superior  terminal  branches,  which  su]>ply  the  upper  portion  of 
the  buccinator  muscle,  the  skin  of  the  malar  and  buccal  region.  These 
branches  interlace  with  the  facial  nerve  near  the  parotid  duct. 

(e)  Inferior  termimd  branches,  which  pass  forward  to  the  angle  of  the 
mouth,  and  are  distributed  to  the  skin,  the  lower  portion  of  the  buc- 
cinator muscle,  as  well  as  the  Ijuccal  mucous  membrane  and  glands. 
These  branches,  together  with  buccal  branches  of  the  facial  nerve,  form 
a  plexus  around  the  facial  vein. 

Variations. — The  buccal  nerve  occasionally  arises  from  the  superior 
maxillary  nerve.  Turner  reports  a  case  in  which  it  arose  from  the 
inferior  dental  nerve  and  passed  through  a  foramen  in  the  alveolar 
border  near  the  ramus  of  the  inferior  maxillar\^  bone.  Gillette  has 
seen  it  arising  in  one  case  from  the  Grasserian  ganglion,  passing  through 
a  special  forameu  situated  between  the  round  and  oval  foramen  in  the 
great  wing  of  the  sphenoid  bone. 

The  posterior  or  sensory  branches  of  the  third  division  of  the  fifth 
nerv^e  are — 

Auriculo-temporal,  Inferior  dental. 

Gustatory  or  lingual. 

The  Auriculo-temporal  Nerve  usually  arises  by  two  roots,  of  unequal 
size,  situated  close  to  the  foramen  ovale.  At  first  they  pass  backward 
and  outward,  one  on  either  side  of  the  middle  meningeal  artery.  They 
then  unite  and  fi>rm  a  flattened  trunk,  which  passes  backward  beneath 
the  external  pterygoid  muscle  to  the  inner  side  of  the  neck  of  the  condyle 
of  the  inferior  maxilla.  It  curves  around  the  condyle  of  the  lower  jaw 
in  company  ^^^th  the  superficial  temporal  artery,  passes  upward  between 
the  ear  and  the  temporo-maxillary  articulation,  thence  over  the  zygoma 
and  Ijeneath  the  superficial  temporal  artery,  terminating  in  several  fila- 
ments which  are  distributed  to  the  skin  over  the  greater  portion  of  the 
temporal  region,  extending  to  its  superior  extremity.  They  interlace 
anteriorly  with  the  facial  nerve. 

Branches  of  the  auriculo-temporal  nerve  are — 

Communicating,  Parotid, 

Articular,  Anterior  auricular. 

Branches  to  external  auditory  meatus, 

The  Communicating  Branrhrs  ai'e  slender  filaments  which  pass  between 
the  otic  ganglion  and  the  third  division  of  tlie  fifth  nerve  near  its  origin. 
One  or  two  branches  which  are  given  off  near  the  neck  of  the  condyle 
of  the  lower  jaw  pass  forward  beneath  the  facial  nerve,  unite  with  it 
near  the  posterior  border  of  the  masseter  muscle,  and  form  one  of  the 
principal  communicating  branches  between  the  facial  and  trifiicial  nerves. 

The  Artiodar  Bnrnchcs  arc  one  or  two  fine  filaments  which  pass  to 
the  temporo-maxillary  articulation. 


THE  NERVOrS  SYSTEM.  295 

The  Branches  to  tlie  External  Auditory  Meatus  are  two  in  number, 
superior  and  inferior.  They  pass  between  the  bone  and  the  eartihige  to 
enter  the  meatus,  and  are  distributed  to  the  lining  of  the  ear.  The 
superior  branch  gives  oif  a  filament  to  the  membrana  tympani. 

The  Parotid  Branches  supply  the  parotid  gland.  They  are  frequently 
eonneeted  Avith  the  facial  nerve. 

The  Anterior  Auricular  Branches  are  usually  two  in  number.  They 
pass  between  the  tragus  and  helix,  and  are  distributed  to  the  concave 
-surface  of  the  auricle. 

The  Lingual  Nerve.. 

The  lingual  or  gustatory  nerve  is  second  in  size,  and  an  important 
branch  of  the  third  division  of  the  fifth.  From  its  origin  it  passes 
down  on  the  internal  surface  of  the  external  pterygoid  muscle,  anterior 
and  a  little  to  the  inner  side  of  the  inferior  dental  nerve.  These  two 
nerves  have  been  obsers'ed  arising  from  a  common  trunk  and  bifurcat- 
ing near  the  posterior  dental  foramen.  As  the  lingual  nerve  reaches 
the  hnver  border  of  the  external  pterygoid  muscle  it  curves  forward 
between  the  internal  ptervgcjid  muscle  and  the  ramus  of  the  lower  jaw, 
inclines  inward  over  the  superior  constrictor  of  the  pharynx,  under  the 
^tylo-glossus  muscle  and  above  the  deep  portion  of  the  submaxillary 
muco-salivarv  gland.  It  then  extends  forward,  crosses  Wharton's  duct, 
passes  below  the  mucous  membrane  of  the  alveolar  lingual  groove,  and 
terminates  at  the  apex  of  the  tongue. 

Branches  of  Communication. — ^ear  the  origin  of  the  lingual  nerve  a 
communicating  branch  passes  over  the  internal  maxillary  artery  to  the 
inferior  dental  nerve.  There  is  also  a  small  branch  which  passes  to 
the  hypoglossal  nerve.  This  nerve  also  forms  a  plexus,  from  which 
branches  are  distributed  to  the  walls  of  the  internal  jugular  vein,  a 
portion  of  the  sinuses  and  the  cancelli  of  the  occipital  l)one,  and  inter- 
lace with  branches  which  pass  through  the  anterior  condyloid  foramen. 
The  chorda  tympani  branch,  which  is  a  small  ner\'e,  arises  from  the 
facial,  and  descends  from  the  proximal  extremity  of  the  squamoso- 
lympanic  suture  (fissure  of  Glasserius)  to  the  acute  angle  of  the  lingual 
nerve  as  it  passes  forward  close  to  the  lower  border  of  the  external 
pterygoid  muscle.  At  first  there  is  only  a  mechanical  union  between 
these  two  nerves,  but  subsequently  they  are  intimately  associated. 
Branches  pass  directly  to  the  submaxillary  ganglion  where  it  is  in  close 
relation  with  the  submaxillary  muco-salivarv  gland.  Anterior  to  the 
last  branch,  one  or  two  communicating  filaments  descend  over  the  first 
portion  of  the  hypoglossal  muscle  to  interlace  with  filaments  from  the 
hypoglossal  nerve. 

The  branches  of  distribution  of  the  lingual  nerve  are — 

A  small  branch  to  the  palato-glossal  fold  (anterior  palatine  arch)  and 
the  tonsils. 

A  sublingual  branch,  which  is  distributed  to  the  mucous  membrane 
of  the  floor  of  the  mouth,  the  gum  tissue  on  the  inner  surface  of  the 
inferior  maxillary  bone,  and  the  sublingual  mucftus  gland. 

The  lingual  or  termimd  branches,  which  passs  upward  between  the 


296 


ANATOiMY. 


fibres  of  the  tongue,  divide  into  finer  filaments,  which  are  distributed 
to  the  mucous  membrane  of  the  anterior  two-thirds  of  the  tongue  and 
terminate  in  the  conical  and  fungiform  papillae. 

A  few  jAcxifonn  jilaiiicnts,  which  pass  beneath  the  tongue,  some  ter- 
minating on  the  under  surface  of  the  tip  and  in  the  glands  of  Niihn. 


V\a.  145. 


The  Inferior  Dental  Nerve. 

The  Inferior  Dental  Nerve  is  the  largest  of  the  branches  of  the  third 
or  inferior  maxillary  division  of  the  fifth  nerve  (Fig,  145).     From  its 

origin  it  passes  downward, 
accompanied  by  the  inferior 
dental  artery,  on  the  inter- 
nal surface  of  the  external 
pterygoid  muscle  posterior 
and  a  little  to  the  side  of 
the  lingual  nerve.  After 
reaching  the  lower  border 
of  the  external  pterygoid 
muscle  it  passes  between  the 
lateral  ligament  and  the  ra- 
mus of  the  jaw,  and  enters 
the  inferior  dental  canal 
through  the  posterior  den- 
tal foramen.  It  then  j^asses 
through  this  canal,  and  ter- 
minates opposite  the  an- 
terior or  mental  foramen 
by  dividing  into  incisor 
and  mental  branches. 

The  branches  of  the  in- 
ferior dental  nerve  are — 

A  Communicating 
Branch,  which  passes  over 
the  internal  maxillary  ar- 
tery to  the  lingual  nerve. 
A  3Ij/lo-hi/oid  Branch, 
which  is  generally  de- 
scribed with  the  inferior 
dental,  which  latter  is  a 
sensory  nerve,  while  the  former  is  in  reality  motor  in  character.  Its 
fibres  can  be  traced  from  its  point  of  distribution  backward  to  the  ante- 
rior or  motor  root  of  the  fifth  nerv^e.  It  is  given  oif  from  the  inferior 
dental  nerve  just  as  it  is  al)()ut  passing  into  the  posterior  dental  foramen, 
and  passes  (lownwaixl  and  forward,  accompanied  by  the  mylo-hyoid 
artery  in  the  mylo-hyoid  groove  of  the  inferior  maxillary  bone.  It  is 
distributed  to  the  inferior  surface  of  the  mylo-hyoid  and  the  anterior 
belly  of  the  digastric,  also  the  tensor  jjalati  and  tensor  tyrapani  mus- 
cles. A  few  filaments  from  this  branch  pass  through  the  mylo-hyoid 
muscle  and  interlace  with   the  lingual  nerve.     Branches  are  also  de- 


Pterygo-maxillary  Region  ami  Fifth  Nerve:  1,  temporal  fas- 
cia; 2,  temporal  imi.scle ;  '.i,  temporal  branches  of  auriculo- 
temporal nerve;  4,  deep  temporal  branch  of  buccinator 
nerve;  o,  deei>  temporal  nerves;  (>,  jiterygoideus  externus; 

7,  deep  temporal  l)ranch  of  masseteric  nerve  (inconstant) ; 

8,  buccinator  (or  long  buccal)  nerve  (fifth);  9,  masseteric 
nerve;  10,  buccal  briinch  of  seventh;  11,  auriculo-temporal 
nerve;  IJ,  lingual  nerve;  i:*,  facial  nerve  (seventh)  at  stylo- 
mastoid foramen;  11,  buccinator  muscle;  ll,  pterygoideus 
internus;  16,  supramaxillary  branch  of  seventh;  17,  infe- 
rior dental  nerve;  IS,  its  mental  branches;  19,  itsmylo-hyoid 
branch;  20,  inferior  dental  nerve  in  inferior  dental  canal 
(opened);  21,  masseter  (turned  down). 


THE  NERVOUS  SYSTEM.  297 

scribed  as  passing  to  the  depressor  anguli  oris  and  platysma  myoides 
muscles  (Henle),  to  the  integument  below  the  chin  (Krause  and 
Schwalbe),  and  to  the   submaxillary  gland  (Meckel,  Henle,  Curnow). 

The  Inferior  Dental  Branches  are  numerous,  and  form  loops  or  plex- 
uses beneath  the  roots  of  the  teeth  similar  to  those  found  above  the 
superior  teeth.  From  these  loops  fine  filaments  pass  through  the  apical 
foramina  in  the  roots  of  the  teeth  of  the  lower  jaw  to  supply  the  pulp 
and  tooth  with  sensation.  There  are  also  filaments  which  pass  upward 
and  supply  the  alveolo-dental   membranes  and  gum  tissue. 

The  Incisor  Branch  is  the  continuation  of  the  main  trunk  of  the 
inferior  dental  nerve.  It  jiasses  forward  under  the  inferior  canine  and 
incisor  teeth,  and  forms  loops  or  plexuses  similar  to  those  formed  by  the 
main  branch,  from  which  filaments  are  distributed  to  the  teeth  and  sur- 
rounding tissues  in  like  manner. 

The  Mental  or  Labial  Nerve  is  the  larger  of  the  two  terminal  divis- 
ions of  the  inferior  dental  nerve.  It  passes  outward  from  the  canal 
through  the  anterior  dental  (mental)  foramen,  and  immediately  breaks 
up  into  three  branches  beneath  the  depressor  anguli  oris  muscle.  The 
inferior  branch  descends,  and  is  distributed  to  the  chin.  The  two  supe- 
rior branches  ascend  to  su])])ly  the  lip,  its  mucous  membrane,  and  the 
labial  glands.  These  three  bi-anches  freely  interlace  with  the  supra- 
maxillary  branch  of  the  facial  nerve. 

The  inferior  dental  nerve  occasionally  receives  one  or  two  communi- 
cating filaments  from  other  branches  of  the  inferior  maxillary  nerve. 

The  Lenmr  Inferior  Dental  Nerve  (Sapolini)  is  frequently  present. 
It  arises  from  the  Gasserian  ganglion,  and  laiitcs  M'itli  the  inferior 
dental  nerve  after  entering  the  inferior  dental  canal. 

SYMPATHETIC   GANGLIA  CONNECTED  AYITH  THE 
FIFTH  NERVE. 

The  sympathetic  ganglia  (ganglia  of  the  fifth  nerve)  found  in  con- 
nection with  the  trifacial  nerve  belong  to  the  general  sympathetic  sys- 
tem found  throughout  the  body.  This  sym])athetic  system  is  composed 
of  a  large  number  of  ganglia,  cords,  and  plexuses. 

The  Ganglia  are  separate  centres  for  the  conveyance  and  distribution 
of  various  cords  and  filaments,  consisting  of  motor,  sensory,  and  sym- 
pathetic fibres.  They  contain  ncrvc-cclls  very  similar  to  those  found  in 
the  encephalon  and  sjiinal  cord.  These  ganglia  are  arranged  in  two 
chains  situated  on  each  side  of  the  l)ody  near  the  central  line.  They 
commence  with  the  ophthalmic  ganglion  in  the  orbit,  and  extend 
downward  along  each  side  of  the  vertebral  column,  and  terminate  below 
in  the  ganglion  impar  in  the  coccygeal  region. 

The  ganglionic  or  sympathetic  system  is  independent  and  separate 
from  the  general  nervous  system,  but  is  intimately  connected  with  it  by 
communicating  l)ranches  which  pass  from  the  motor  and  sensory  roots 
of  the  cerebro-spinal  nerves,  as  well  as  by  direct  filaments  which  extend 
between  it  and  the  cerebro-spinal  centres.  The  sympathetic  nervous 
system  is  distributed  to  the  mucous  membranes,  the  viscera,  the  coats  of 
blood-vessels,  and  to  the  non-striated  or  involuntary  muscular  fibres. 


298 


ANATOMY. 


The  nerves  of  this  system  form  plexuses  in  various  parts  of  the  body, 
especially  around  the  arteries.  They  are  not  found  in  connection  with 
striated  voluntary  nuiscular  fibres.  The  cardiac  muscle,  being  partially 
striated,  yet  involuntary,  is  an  exception.  Numerous  ganglionic  cells  are 
found  situated  at  the  terminal  ends  of  sympathetic  nerve-fibres. 

THE   CRANIAL   GANGLIA,  OR  GANGLIA  OF   THE   FIFTH   PAIR   OF 

NERVES.i 


Name. 

Situation. 

Sensory  Boot. 

Motor  Root. 

Sympathetic 
Root. 

Branches  op 
Distribution. 

Ophthalmic 
OR  Ciliary. 

Between  the  op- 
tic nerve  and 
external    rec- 
tus. 

Fifth         nerve, 
nasal   branch. 

Third  nerve. 

Cavernous 
plexus. 

To  ciliary  mus- 
cle and'  iris. 

< 
o 
< 

o 

►J 
•< 

Spheno-pal- 

TINE          OR 

Meckel's. 

Spheno  -  maxil- 
lary fossa. 

Fifth         nerve, 
spbeno-p  a  la- 
tine  brunches. 

Seventh    nerve, 
through    Vid- 
ian and  large 
petrosal 
branches. 

Carotid   plexus, 
by   means    of 
Vidian  nerve. 

Orbital,  nasal, 
naso  palatine, 
anterior  or 
large  palatine, 
middle  or  ex- 
ternal pala- 
tine. 

Otic. 

Below    the    for- 
amen ovale. 

Fifth         nerve, 
auriculo-tem- 
poral  branch. 

Seventh    nerve, 
through  small 
petrosal. 

Fifth         nerve, 
through      in- 
ternal   ptery- 
goid branch. 

Plexus    on    the 
middle     men- 
ingeal artery. 

To  tensor  tyni- 
pani  and  ten- 
sor p  a  1  a  t  i 
muscles. 

Submaxil- 
lary. 

Above  the  sub- 
maxillary 
ghiud. 

Fifth  nerve,  lin- 
sual  or  gusta- 
tory branch. 

Seventh    nerve, 
through  chor- 
da      lympani 
branch. 

Plexus    on    the 
facial  artery. 

To  submaxil- 
lary gland  and 
mucous  mem- 
brane of  the 
mouth. 

The  cranial  ganglia,  or  ganglia  of  the  fifth  pair  of  nerves  tabulated 
above,  are  four  pairs — viz.  : 

Ophthalmic,  Otic, 

Spheno-palatine,  Submaxillary. 

The  OpMhahnic,  Lenticular,  or  Ciliary  Ganglion  is  situated  in  the 
posterior  portion  of  the  orbital  cavity,  between  the  external  rectus  mus- 
cle and  the  optic  nerve,  in  close  apposition  to  the  ophthalmic  artery.  It 
is  a  small,  flattened,  and  reddish  body,  surrounded  by  adipo.se  tissue,  its 
flattened  surfaces  being  the  proximal  and  the  distal.  It  measures  about 
one  line  in  length  from  before  backward. 

Its  branches  or  roots  of  communication  are — 

1.  The  Sensory  or  Long  Boot,  which  is  a  slender  filament  arising 
within  the  cavernous  sinus  from  the  nasal  branch  of  the  ophthalmic 
division  of  the  fifth  nerve.  It  enters  the  posterior  superior  angle  of  the 
ganglion.  Occasionally  a  filament  is  found  which  extends  from  the 
lachrymal  nerve  to  the  ganglion. 

2.  'The  Motor  or  Short  Root,  which  is  shorter  and  thicker  than  the 
sensory  root,  and  occasionally  divides  into  two  branches.  It  is  derived 
from  the  inferior  oblique  branch  of  the  motor  oculi  or  third  nerve,  and 
joins  the  ganglion  at  its  posterior  inferior  angle. 

3.  The  Sympathetic  or  Middle  Boot,  which  is  derived  from  the  system 
to  which  the  ganglion  belongs.  This  root  is  smaller  than  either  of  the 
others,  and  originates  in  the  cavernous  sinus,  being  derived  from  the 

'  After  Rannev. 


THE  NERVOUS  SYSTE3I.  299 

carotid  plexus.  Through  this  plexus  it  commuuicates  with  the  cervi- 
cal ganglion.  As  it  extends  forMard  to  the  posterior  border  of  the 
ganglion,  it  occasionally  unites  with  the  long  or  sensory  root,  forming  a 
common  trunk. 

Variations  in  the  Boots. — The  ophthalmic  ganglion  may  receiye 
accessory  roots  from  the  superior  division  of  the  motor  ocnli,  the 
lachrymal,  abducens,  or  spheno-palatine  ganglion  (Henle,  Tiedemann). 

'' According  to  Reichart,  the  ophthalmic  ganglion  does  not  receive  its 
sympathetic  fibres  by  a  single  root,  but  by  several  fine  filaments,  the 
majority  of  which  accompany  the  third  nerve. 

"  It  appears  from  the  mode  of  development  and  arrangement  in  many 
of  the  lower  vertebrates  that  the  o})hthalmic  ganglion  is  morphologically 
associated  more  intimately  with  the  third  nerve,  having,  in  fact,  the  sig- 
nificance of  a  spinal  ganglion  of  that  nerve  (M.  Marshall,  Schwalbe)."^ 

Its  branches  of  distribution  are  to  the  iris  and  ciliary  muscles.  The 
short  ciliary  nerves,  ten  to  fifteen  in  number,  arise  in  two  sets,  superior 
and  inferior. 

The  Sujx'rior  Set  arises  from  the  anterior  superior  angle,  and  passes 
forward,  in  a  wave-like  manner,  between  the  optic  nerve  and  the  supe- 
rior rectus  muscle  to  the  posterior  ])art  of  the  eyeball. 

Tlie  Inferior  Set  is  more  numerous  than  the  superior,  and  arises 
from  the  anterior  inferior  angle  of  the  ganglion.  It  passes  in  a  wave- 
like manner  below  the  optic  nerve  and  above  the  inferior  rectus  nuiscle 
to  the  posterior  part  of  the  eyeball.  It  is  accompanied  by  the  long  cil- 
iary nerves  which  are  derived  from  the  nasal  branch  of  the  ophthalmic 
division  of  the  fifth.   One  or  more  of  its  fibres  join  the  short  ciliary  nerves. 

Both  the  superior  and  the  inferior  sets  pass  forward  through  the 
sclerotic  coat  of  the  eye  in  delicate  grooves  on  its  inner  sijrface,  next  to 
the  choroid  coat,  and  are  distributed  to  the  ciliary  muscle,  the  iris,  and 
the  cornea.  A  small  filament  penetrates  the  optic  nerve  to  the  arteria 
centralis  retinae  (Tiedemann). 

Spheno-palatine  Ganglion. 

The  spheno-palatine  ganglion  (ganglion  of  Meckel)  (Fig.  146)  is  the 
largest  of  the  cranial  ganglia.  It  is  situated  in  the  ])terygo-maxillary 
fossa  in  front  of  the  anterior  opening  of  the  Vidian  canal,  close  to  the 
spheno-palatine  foramen.  It  is  triangular  in  form,  with  its  apex  point- 
ing backward  in  the  direction  of  the  Vidian  canal,  and  is  surrounded 
bv  adipose  tissue.  Its  outer  surface  is  convex,  and  averages  about  one- 
fifth  of  an  inch  in  diameter.  It  is  reddish-gray  in  color,  excepting  at 
its  broadest  part,  where  it  is  composed  entirely  of  gray  matter. 

The  branches  or  roots  of  communication  of  the  spheno-palatine 
ganglion  are — 

L  The  Sensor)/  Roots,  two  in  number,  which  arise  from  the  superior 
maxillary  nerve  as  it  passes  through  the  pterygo-maxillary  fossa.  They 
enter  the  ganglion  separately,  one  at  the  anterior  and  the  other  at  the 
posterior  corner  of  the  upper  surface.  ISIany  of  the  fibres  of  these 
roots  pass  through  the  ganglion  without  becoming  incorporated  with 

^  Quain's  Anatomy. 


300 


ANATOMY. 


it,  and  receive  no  influence  from  it.     These  fibres  fi^rm  tiie  palatine 
nerves. 

2.  The  Motor  Root,  which  is  quite  long,  and  arises  from  the  facial 
nerve  or  the  large  superficial  petrosal  nerve  at  the  geniculate  ganglion 
(intumescentia  gangliaformis)  within  the  aqueduct  of  Fallopius.  From 
this  point  it  passes  forward  through  the  hiatus  Fallopii  on  the  anterior 
surface  of  the  petrous  portion  of  the  temporal  bone,  then  inward  beneath 
the  Gasserian  ganglion,  being  separated  from  it  by  a  thin  layer  of  dura 
mater.  It  then  pierces  the  fibro-cartilage  occupying  the  middle  lace- 
rated foramen,  and  passes  to  the  outer  side  of  the  internal  carotid  artery. 

Fig.  146. 


The  Spheno-palatine  Ganglion  and  its  Branches. 

At  this  point  it  is  joined  by  the  sympathetic  root  or  the  large  deep 
petrosal  nerve  of  the  spheno-palatine  ganglion,  and  the  two  conjointly 
receive  the  name  of  the  Vidian  nerve.  They  pass  into  the  Vidian  canal 
in  the  sphenoid  bone,  extend  through  this  canal,  and  at  the  exit  enter 
the  posterior  or  apicial  extremity  of  the  ganglion.  The  gray  matter  of 
the  ganglion  extends  along  the  nerve  as  far  as  the  origin  of  the  sympa- 
thetic at  the  carotid  plexus. 

3.  The  St/mpathcfic  Boot,  or  the  large  deep  petrosal  nerve,  commences 
from  the  carotid  plexus  which  surrounds  the  internal  carotid  artery. 
These  filaments  unite  and  form  a  short  branch  of  reddish  color  and  soft 
texture,  which  passes  forward  and  joins  the  motor  root  of  the  ganglion 
to  form  the  Vidian  nerve,  above  described.  Occasionally  these  two 
roots  remain  separate  throughout  their  course,  and  enter  the  ganglion 
ununited. 


THE  NERVOUS  SYSTEM.  301 

The  branches  of  distribution  of  the  spheno-palatine  ganglion  are — 

1.  Ascending  or  Orbital  Branches,  consisting  of  three  or  four  fine 
filaments  which  pass  into  the  orbit  through  the  spheno-maxillary 
fissure,  and  are  distributed  to  the  periosteum  and  mucous  membrane  of 
the  posterior  ethmoidal  and  sphenoidal  sinuses  by  passing  between  the 
sphenoid  and  ethmoid   bones. 

Some  of  the  branches  which  pass  upward  are  distributed  to  the  neu- 
rilemma of  the  optic  nerve  (Arnold  and  Longet). 

A  branch  from  the  ganglion  ascends  to  the  sixth  nerve  (Bock  and 
A^alentin). 

Also  a  branch  to  the  ophthalmic  ganglion  (Tiedemann). 

Two  or  three  branches,  spheno-ethmoidal,  ascend  to  the  superior  por- 
tion of  the  internal  orbital  wall,  pass  through  the  posterior  ethmoidal 
foramen,  and  enter  the  brain-case  (Luschka). 

2.  The  Descending  or  Palatine  Branches,  three  in  number — anterior, 
posterior,  and  external.  These  three  branches  pass  from  the  superior 
maxillary  nerve  through  that  portion  of  the  ganglion  in  which  there 
is  little  ganglionic  or  gray  matter.  They  thus  pass  to  their  distribution 
without  becoming  involved  or  influenced  by  the  ganglion,  except  it  be 
to  a  very  slight  extent. 

The  Anterior  or  Large  Palatine  Nerve  passes  downward  in  the  poste- 
rior palatine  or  palato-maxillary  canal,  and  enters  the  oral  cavity  at 
the  posterior  palatine  ft)ramen.  It  then  passes  forward  in  a  groove  on 
the  side  of  the  hard  palate  to  its  anterior  portion,  where  it  joins  the 
naso-palatine  nerve.  It  is  distributed  to  the  gums,  mucous  glands,  and 
membrane  of  the  hard  palate.  This  nerve  gives  oif  a  separate  branch 
(middle  palatine),  which  passes  downward  to  the  soft  palate  in  a  separate 
canal.  It  also  gives  oft'  branches  (inferior  nasal)  while  in  the  canal, 
which  are  distributed  to  the  middle  and  inferior  turbinated  bones. 

The  Posterior  or  Small  Palatine  Nejre  passes  downward,  accompanied 
by  a  small  artery  in  the  small  palatine  canal,  to  the  soft  palate,  and 
divides  into  two  sets  of  branches.  One  set  is  distributed  to  the  levator 
palati  and  azygos  uvula  muscles,  and  may  be  composed  entirely  of 
motor  filaments  coming  from  the  great  superficial  jjetrosal  branch  of  the 
motor,  facial,  and  the  Vidian  nerves.  The  other  set,  which  is  sensory, 
is  distributed  to  the  mucous  membrane  of  the  superior  surface  of  the 
soft  palate,  the  glands  of  the  soft  palate,  as  well  as  to  the  tonsils. 

The  External  Palatine  Nerve  is  the  smallest  of  the  three  descending 
branches,  and  is  not  always  constant  in  its  existence.  It  passes  doAvn- 
ward  through  the  external  palatine  canal,  which  is  situated  between  the 
tuberosity  of  the  superior  maxilla  and  palate  bones,  and  is  distributed 
to  the  tonsils,  uvula,  and  outer  portion  of  the  soft  palate. 

The  Internal  or  Nasal  Branches  consist  of  two  divisions,  upper  nasal 
and  naso-palatine. 

The  Upper  Nasal  Branches,  four  or  five  in  number,  are  small,  and 
pass  horizontally  inward  through  the  spheno-palatine  foramen  into  the 
posterior  superior  portion  of  the  nasal  chamber.  They  are  distributed 
to  the  posterior  superior  portion  of  the  nasal  septum,  to  the  mucous 
membrane  covering  the  superior  and  middle  turbinated  bones,  and  to 
the  posterior  ethmoidal  cells. 


302  ANATOMY. 

The  Naso-palatine  Branch  (nerve  of  Cotumnius,  Scarpa)  is  larger 
than  the  upper  nasal  branches,  and  is  an  important  division  of  the  nasal 
nerves.  It  is  long  and  slender,  and  arises  from  the  proximal  surface 
of  the  spheno-palatine  ganglion.  It  passes  through  the  spheno-palatine 
foramen  across  the  roof  of  the  nasal  chamber  to  the  septum,  where  it 
turns  downward  and  forward,  and  extends  in  a  groove  or  canal  on  the 
vomer  to  the  foramina  of  Scarpa  or  naso-palatine  foramina.  These  are 
two  in  number,  anterior  and  posterior,  and  are  situated  in  the  inter- 
maxillary suture.  The  nerve  of  the  right  side  usually  passes  through 
the  posterior  foramen,  while  the  nerve  of  the  left  side  passes  through 
the  anterior.  These  two  nerves  (right  and  left  naso-palatine),  meeting 
in  the  common  or  anterior  palatine  meatus  or  canal,  form  a  tine  plexus, 
from  which  minute  filaments  are  distributed  to  the  palate  posterior  to 
the  incisor  teeth  and  interlace  with  the  anterior  or  great  palatine  nerve. 
"  In  its  course  along  the  septum  small  filaments  are  furnished  from  the 
naso-palatine  to  the  pituitary  membrane."  ^ 

The  Poderior  Branches  generally  assume  the  name  of  the  Vidian 
nerve  (already  described)  and  the  pharyngeal  nerve. 

The  Pharyngeal  or  Pterygo-palatine  Nerve  consists  of  several  fine 
filaments  which  frequently  arise  from  the  Vidian  nerve,  instead  of  from 
the  posterior  portion  of  the  ganglion.  It  passes  downward  through 
the  ])terygo-palatine  canal,  accompanied  by  an  artery  of  the  same  name, 
and  is  distributed  to  the  mucous  membrane  of  the  upper  portion  of  the 
pharynx  and  neighborhood  of  the  Eustachian  tube. 

Otic  Ganglion. 

The  otic  ganglion  (ganglion  of  Arnold)  (Fig.  147)  is  a  reddish-gray 
body  situated  just  below  the  foramen  ovale,  and  in  close  apposition  to 
the  proximal  surface  of  the  inferior  maxillary  nerve  at  the  point  of 
union  of  its  motor  root  with  the  third  sensory  division  arising  from  the 
Gasserian  ganglion,  the  cartilaginous  portion  of  the  Eustachian  tube 
to  its  inner  surface,  while  the  middle  meningeal  artery  passes  up  into  the 
brain-case  just  posterior  to  it.  It  is  a  flattened  oval  body,  its  widest 
diameter,  which  is  about  one-sixth  of  an  inch,  being  antero-posterior. 

Its  branches  or  roots  of  comnuinication  are — 

1 .  The  Long  or  Sensory  Boot  of  Arnold  is  composed  of  the  lesser  super- 
ficial petrosal  nerve,  which  is  a  continuation  of  the  tympanic  branch  of 
the  gl()Sso-])haryngeal,  and  a  branch  from  the  geniculate  ganglion  of  the 
seventh.  The  ganglion  also  receives  an  important  sensory  branch  from 
the  auriculo-temporal  nerve  of  the  fifth. 

2.  The  Motor  or  SI  tort  Boot  of  Arnold  is  derived  from  the  internal 
pterygoid  branch  of  the  inferior  maxillary  division  of  the  fifth.  It  also 
receives  motor  filaments  through  the  lesser  superficial  petrosal  derived 
from  the  geniculate  ganglion  of  the  seventh  nerve. 

3.  The  Sympathetic  Boot,  which  is  derivecl  from  the  plexus  around 
the  middle  meningeal  artery. 

The  branches  of  distribution  of  the  otic  ganglion  supply  in  part  the 

^  Quain'ij  Anatomy. 


THE  NERVOUS  SYSTEM. 


303 


parotid  gland,  the  chorda  tympani,  tensor  tympani,  palato-Eustachian 
muscles,  and  the  mucous  membrane  of  the  middle  ear. 


The  Submaxillary  Ganglion. 

The  submaxillarv  or  lingual  ganglion  is  situated  above  the  deep 
portion  of  the  submaxillary  muco-salivary  gland,  close  to  the  outer 
portion  of  the  hyo-glossus  muscle.     It  varies  in  shape  and  size,  usually 

Fig.  147. 


The  otic  Ganglion  and  its  Branches. 

being  triangular,  but  occasionally  it  is  fusiform  or  plexiform,  or  absent 
altogether. 

Its  branches  or  roots  of  communication  are — 

1.  The  Sensori/  Boot,  which  arises  from  the  lingual  branch  of  the 
inferior  maxillary  nerve  and  enters  the  posterior  portion  of  the  gan- 
glion. 

2.  The  Motor  or  Long  Boot,  which  is  formed  from  the  motor  fila- 
ments of  the  lingual  nerve  received  from  the  chorda  tympani  branch  of 
the  facial. 

3.  The  Si/mpathetic  Boot,  which  arises  from  the  sympathetic  plexus 
around  the  facial  artery. 

The  branches  of  distribution  of  the  submaxillary  ganglion  are  prin- 
cipally those  that  supply  the  submaxillary  muco-salivary  gland  and  its 
duct  (duct  of  Wharton).  Other  branches  pass  upward,  and  interlace 
with  the  lingual  nerve,  forming  a  plexus  on  the  side  of  the  tongue,  from 
which  filaments  are  given  off  which  supply  the  mucous  membrane  of  the 
mouth.  Baldwin  and  other  anatomists  describe  a  sublingual  ganglion 
which  is  situated  on  the  branch  of  the  submaxillary  ganglion  which 


304 


ANATOMY. 


passes  to  the  lingual  nerve.  Occasionally  one  or  two  small  branches 
are  found  which  communicate  with  the  hypoglossal  nerv^e  (Meckel  and 
.  Bose).  None  of  the  branches  of  the  submaxillary  ganglion  are  dis- 
tributed to  muscles,  which  is  in  marked  contrast  with  the  branches 
from  the  otic  ganglion. 

The  Facial  Nerve. 

The  facial,  seventh,  or  nerve  of  exj^ression  (the  portio  dura  of  the 
seventh  pair  of  nerves,  according  to  the  arrangement  of  AVillis)  (Fig. 
148)  controls  the  muscles  of  expression.  This  fact  alone  would  make 
it  a  nerve  of  vast  importance  to  all  those  who  study  the  face  either  from 
a  surgical  or  an  artistic  standpoint.  It  not  only  transmits  the  motor 
stimulus  to  all  the  superficial  muscles  of  the  face,  except  the  levator 

Fig.  148. 


Diagram  of  the  I'acial  Nerve  and  its  Distribution  :  1,  Facial  nerve  at  its  entrance  into  the  internal 
auditory  meatus;  2,  its  exit  at  the  stylo-niastoid  foramen  ;  :!,  4,  temporal  and  posterior  auricular 
branches,  (listril>uted  to  th  •  muscles  of  the  external  ear  and  to  the  occipitalis;  5,  branches  to  the 
frontalis  muscle  ;  ti.  branches  to  the  stylo-hyoid  and  digastric  muscles;  7,  branches  to  the  upper 
part  of  the  philysma  niyoides;  .s,  braueh  of  communication  with  the  superficial  cervical  nerve  of 
the  cervical  plexus. 

palpcbrje  sui)erioris,  but  likewise  to  the  scalp,  the  external  ear,  platysma 
myoides,  buccinator,  ])()steri()r  belly  of  the  digastric,  and  stylo-hyoid 
muscles.     Through  communicating  branches  it  unites  the  anterior  and 


THE  JSERVOUS  SYSTEM.  305 

posterior  cranial  nerves,  and  by  so  doing  increases  the  functional  power 
of  some  of  these  nerves. 

The  following  are  some  of  its  communicating  branches  : 

It  communicates  with  the  three  divisions  of  the  tiftli  nerve ; 

With  the  spheno-palatine,  submaxillary,  and  otic  sympathetic  ganglia  ; 

A  branch  to  the  auditory  nerve ; 

A  branch  to  the  glosso-pharyngeal  nerve  ; 

Through  its  auricular  branch  it  also  conununicates  with  the  pneumo- 
p-astric  nerve.  It  will  be  seen  that  through  this  lars^e  communication  it 
supplies  other  structures,  which  will  be  described  hereafter. 

The  superficial  or  apparent  origin  of  the  facial  nerve  is  from  the 
uppermost  lateral  portion  of  the  medulla  oblongata  in  a  groove  between 
the  olivary  and  restiform  bodies,  just  below  the  pons  varolii.  The  eighth 
or  auditory  nerve  is  in  close  apposition  to  its  outer  side,  the  two  being 
separated  only  by  a  couple  of  filaments  which  are  known  as  the  inter- 
mediary nerve  of  Wrisberg  (portio  inter  duram  et  mollem). 

This  intermediary  nerve  is  more  or  less  connected  with  the  facial  and 
auditory  nerves,  but  from  the  fact  of  its  greater  connection  with  the 
facial  it  has  been  classed  as  one  of  its  roots  (accessory  root  of  Sappey). 
It  passes  between  the  two  nerves  into  the  internal  auditory  meatus,  and 
terminates  in  the  geniculate  ganglion. 

The  facial  nerve  passes  from  its  origin,  in  company  with  the  eighth 
or  auditory  nerve,  forward  and  outM-ard  between  the  pons  varolii  and 
the  middle  peduncle  of  the  cerebrum,  around  which  it  curves  to  enter 
the  internal  auditory  meatus,  situated  in  the  posterior  surface  of  the 
])etr6us  portion  of  the  temporal  bone.  It  rests  in  a  groove  on  the 
upj)er  part  of  the  meatus,  the  auditory  nerve  being  below,  while  the 
nerve  of  Wrisberg  still  retains  its  position  between  the  two.  On  reach- 
ing the  upper  extremity  of  the  meatus,  the  seventh  nerve  passes  into  and 
through  the  aqueduct  of  Fallopius.  This  aqueduct  runs  an  extremely 
tortuous  course  through  the  petrous  portion  of  the  temporal  bone.  It  is 
at  first  directed  outward  for  a  short  distance  between  the  cochlea  and  the 
vestibule  to  the  wall  of  the  middle  ear ;  then  it  b^nds  backward  over 
the  fenestra  ovalis,  then  downward  behind  the  pyramid  and  the  middle 
ear,  and  terminates  at  the  stylo-mastoid  foramen,  at  which  point  the 
nerve  makes  its  exit  on  the  face.  It  passes  from  this  point  downward 
and  forward  in  the  substance  of  the  parotid  gland,  and  breaks  up  into 
numerous  branches  to  supply  the  muscles  of  expression. 

The  branches  of  the  facial  nerve  are  tabulated  as  follows  bv  Prof. 
Allen  :  ^ 

f  The  great  superficial  petrosal  nerve. 
j   The  lesser         "  "  " 

Branches  of  the  geniculate  ganglion,    |    Branches  to  the  sympathetic  system. 

six  in  number,  1  "  "        tympanic  plexus. 

I  "  "        pneumogastric  nerve. 

[  "  "        glosso-pharyngeal  nerve. 

f   Stapedius. 
Before  escaping  at  the   stylo-mastoid    ]    (chorda  tympani. 

foramen,  I    Connecting  branches  with  pneumogastric. 

[  "  "  "     glosso-pharyngeal. 

^Allen's  Anatomy,  p.  529. 
Vol.  I.— 20 


306 


ANATOMY. 


After  escaping  from  the  stylo-mast oid 
foramen, 


Fifi.  149. 


n    ,     •  -1  f  Anricnlar. 

Posterior  aunciuar,    -,  , ,     •    ■»  i 
'     (.  (_)cfipital. 

Stylo-livoid. 

Digastric. 

Stylo-glossal. 

I  Temporal. 
Temporo-facial,  <  Malar. 

(  Intraorbital. 

f  Buccal. 
Cervico-facial,     <  fSupramaxillary. 

(  Cervical. 

The  Geniculate  Ganglion  (intumescentia  ganglioformis)  is  a  reddish 
enlargement  on  the  foremost  part  of  the  facial  nerve,  which  contains 

numerous  nerve-cells.  It  is  situ- 
ated on  the  curve  as  the  nerve 
turns  from  the  horizontal  to  the  per- 
pendicular direction  in  the  aqueduct 
of  Fallopius.  It  does  not  receive 
all  the  fibres  of  the  facial  nerve,  but 
receives  the  terminal  ends  of  the  nerve 
of  Wrisberg.  The  nerves  arising 
from  this  p;ano;lion  are  six  in  num- 
ber,  the  names  of  which  will  be  found 
in  the  ])receding  table. 

The  Great  Superficial  Petrosal  Nerve 
(Fig.  149)  arises  from  the  geniculate 
ganglion  of  the  seventh  nerve,  and  is 
the  largest  of  the  ganglionic  branc-hes. 
It  passes  forward  through  the  hiatus 
Fallopii  on  the  superior  portion  of 
the  anterior  surface  of  the  petrous 
portion  of  the  temporal  bone,  from 
which  it  passes  inward  beneath  the 
Gusserian  ganglion,  being  separated 
from  it  by  a  thin  layer  of  the  dura 
mater.  It  then  pierces  the  fibro-car- 
tilage  occupying  the  middle  lacerated 
foramen,  and  passes  to  the  outer  side 
of  the  internal  carotid  artery.  At 
this  point  it  is  joined  by  the  symjjathetic  root  or  the  large  deep  petrosal 
nerve  of  the  spiieno-palatine  ganglion,  and  passes  into  the  Vidian  canal 
in  the  s]:>henoid  bone  under  the  name  of  the  Vidian  nerve.  It  extends 
til  rough  this  canal,  and  enters  the  apex  of  the  spheno-palatine  ganglion. 
The  Le.sf<er  Snjjrrfieial  Petronal  Nerve  extends  from  the  geniculate 
ganglion  of  the  seventh  nerve  and  unites  with  a  branch  from  the  nerve 
of  Jacobson.  It  then  passes  through  a  small  foramen  and  joins  the 
otic  sympathetic  ganglion. 

The  Branch  of  Comrmoi  leaf  ion  n-if/i  flic  Si/mpafJietic  Si/stem,  or  the 
External  Superficial  Petrosal  Nerve  (Bidder),  is  not  always  jiresent 
(Ruber).  It  forms  a  connnunicating  filament  between  the  geniculate 
ganglion  and  the  sympathetic  plexus  around  the  middle  meningeal 
artery. 


'ihis  drawing  represents  the  Middle  Fossa  of 
the  Uase  of  the  Skull,  with  the  petrous  part 
of  the  temporal  bone  cut  through  so  as  to 
expose  the  nerves  joiniug  the  facial  (from 
Kidder):  '/,  external  ear;  h,  middle  fossa  of 
the  skull,  witli  the  middle  meningeal  artery 
branching  on  it ;  1,  facial  nerve  by  the  side 
of  the  auditory;  2,  large  superficial  petrosal 
nerve;  small  superficial  petrosal  nerve 
lying  over  the  tensor  tynipani  inuscle;  4, 
the  external  superficial  petrosal  nerve; 
5,  chorda  tynipani ;  S,  eighth  nerve. 


THE  NERVOUS  SYSTEM.  307 

The  Branch  of  Communication  with  the  Tympanic  Plexus  is  a  small 
nerve  which  connects  the  geniculate  ganglion  with  the  sympathetic  tym- 
panic plexus. 

Tlie  Communicating  Branch  with  the  Pneumogastric  Nerve  passes  out 
of  the  stylo-mastoid  foramen,  and  communicates  with  the  pneumogastric 
nerve  through  its  articular  branch. 

The  Commumcating  Branch  with  the  Glosso-pharyngeal  Neri^e  arises 
from  the  facial  as  it  leaves  the  stylo-mastoid  foramen.  It  communicates 
with  the  glosso-pharyngeal  nerve  below  its  petrosal  ganglion. 

The  branches  of  the  facial  nerve  before  it  escapes  from  the  stylo- 
mastoid foramen  are — 

1 .  Stapedius ; 

2.  Chorda  tympani ; 

3.  Connecting  branches  with  pneumogastric  nerve  ; 

4.  Connecting  branches  M'ith  glosso-pharyngeal  nerve. 

The  Stapedius  or  Tympanic  Nerve  is  the  most  slender  branch  given 
off  by  the  facial  nerve.  It  arises  opposite  the  pyramid  of  the  internal 
ear,  passes  through  a  fine  canal,  and  is  distributed  to  the  stapedius  nmscle. 

Tlte  Chorda  Tympani  Nerve  arises  from  the  facial  nerve  on  the  proxi- 
mal side  of  the  geniculate  ganglion,  though  apparently  it  arises  back  of 
the  tympanum  close  to  the  outer  extremity  of  the  aqueduct  of  Fal- 
lopius.  From  its  origin  it  passes  upward  in  a  special  curved  canal 
nearly  parallel  to  the  aqueduct  of  Fallopius,  and  enters  the  posterior 
wall  of  the  tympanic  cavity  close  to  the  tympanic  membrane.  It  here 
becomes  invested  by  mucous  membrane,  arches  upward  between  the 
long  handle  of  the  malleus  and  the  vertical  process  of  the  incus  to  its 
anterior  angle.  It  then  passes  out  of  the  tympanum  through  a  for- 
amen (canal  of  Hugui)  at  tlie  side  of  the  glenoid  (Glasserian)  fissure, 
extends  downward  on  the  proximal  side  of  the  internal  lateral  ligament 
of  the  inferior  maxillary  bone,  and  forms  a  union  with  the  lingual 
branch  of  the  fifth  nerve  at  a  point  where  the  nerve  forms  an  acute 
angle  by  bending  forward  under  the  inferior  border  of  the  external 
pterygoid  muscle.  It  is  then  distributed  to  the  submaxillary  muco- 
salivary  gland  and  to  the  tongue.  The  chorda  tympani  nerve  receives 
a  communicating  branch  from  the  otic  ganglion  just  before  joining  the 
lingual  nerve.  There  is  considerable  discussion  among  anatomists  and 
physiologists  as  to  the  origin  and  functions  of  this  nerve.  Some  claim 
that  it  is  a  continuation  of  the  nerve  of  Wrisberg,  while  J.  Sapolini 
claims  it  as  an  independent  cranial  nerve,  entitled  to  be  classed  as 
the  thirteenth  cranial  nerve.  Its  function  is  also  still  in  doubt,  some 
claiming  it  to  be  a  motor  nerve,  others  a  nerve  of  sensation,  while 
others  regard  it  as  a  special  nerve  of  taste. 

The  Communicating  Brcmch  with  the  Pneumogastric  Nerve  arises  from 
the  facial  nerve  a  little  before  its  exit  from  its  canal  to  join  the  upper 
ganglion  of  the  pneumogastric.     This  branch  is  not  constant. 

The  Communicating  Brcmch  with  the  Glosso-pharyngeal  Nerve  arises 
from  the  facial  just  as  that  nerve  makes  its  exit  from  the  stylo-mastoid 
foramen.     It  passes  to  the  petrosal  ganglion  of  the  glosso-pharyngeal. 

The  branches  that  arise  from  the  facial  nerve  after  it  has  passed  out 
of  the  stvlo-mastoid  foramen  are  six  in  number — viz. : 


308  ANAT03IY. 

Posterior  auricular,  Stylo-glossal, 

Stylo-hyoid,  Temporo-facial, 

Digastric,  Cervico-facial. 

The  Posterior  Auricular  Nerve  arises  from  the  facial  uear  the  stylo- 
luastoid  forameu.  It  passes  backward  in  close  apposition  to  the  lateral 
border  of  the  posterior  belly  of  the  digastric  muscle,  and  then  curves 
outward  and  upward  bet^^een  the  ear  and  the  mastoid  process  of  the 
temporal  bone,  where  it  divides  into  two  branches,  auricular  and  oc- 
cipital. 

The  Auricular  Branch  passes  upward  behind  the  ear,  and  is  distrib- 
uted to  the  retrahens  aurem,  the  small  muscles,  and  the  skin  on  the 
back  part  of  the  pinna.  Occasionally  it  sends  a  filament  to  the  atollens 
aurem  muscle. 

The  Occipital  Branch  passes  upward  in  a  curved  direction  along  the 
superior  semicircular  line,  the  posterior  boundary  of  the  base  of  the 
skull.     It  is  distributed  to  the  occipital  muscle. 

The  branches  of  communication  of  the  posterior  auricular  nerve  are 
with  the  great  auricular  and  the  small  occipital  nerve  of  the  cervical 
plexus,  and  with  the  auricular  branch  of  the  pneumogastric  nerve. 

The  Stj/ln-hi/oid  Amerce  is  a  long  slender  l)ranch  which  is  distributed 
to  the  stylo-hyoid  muscle,  and  interlaces  with  the  sympathetic  plexus 
of  the  external  carotid  artery. 

The  Dif/astric  Nerve  frequently  arises  in  conniion  with  the  stylo-hyoid. 
It  soon  divides  into  two  or  three  small  filaments  which  are  distributed 
to  the  posterior  belly  of  the  digastric  muscle  and  interlace  with  the 
glosso-pharyngeal  nerve  near  the  base  of  the  skull,  and  occasionally 
with  the  spinal  accessory  and  jjneumogastric  nerves. 

The  Sti/lo-r/lossal  Nerve  (lingual  nerve  of  Hirschfeld)  Ls  a  long  and 
exceedingly  delicate  branch  which  arises  from  the  facial  nerve  near  the 
base  of  the  styloid  jn-ocess  of  the  temjwral  bone.  It  passes  downward 
and  forward  behind  the  stylo-pharyngeus  muscle  to  the  side  of  the 
jiharynx  and  the  base  of  the  tongue.  It  receives  several  branches  of 
communication  from  the  glosso-pharyngeal  nerve,  and  is  distributed  to 
the  stylo-glossus  and  palato-glossus  muscles,  being  lost  in  the  mucous 
membrane  at  the  base  of  the  tongue. 

The  Temporo-facial  Division  of  the  seventh  nerve  is  the  larger  of  its 
two  terminals.  It  passes  forward  and  upward  in  the  substance  of  the 
parotid  gland  on  a  level  with  the  neck  of  the  lower  jaw.  The  exter- 
nal carotid  artery  and  the  temporo-maxillary  vein  are  situated  to  its 
inner  side.  At  the  neck  of  the  lower  jaw  the  nerve  breaks  up  into 
three  branches,  temporal,  malar,  and  infraorbital.  Before  it  branches, 
however,  it  receives  filaments  of  communication  from  the  auriculo- 
tem]>oral  nerve.  After  its  division  it  receives  conununicating  branches 
from  the  fifth  nerve.  The  temporo-facial  nerve  and  its  conmiunicat- 
ing  branches,  together  with  numerous  small  branches  from  its  three 
main  divisions,  form  an  irregular  network  of  nerves  known  as  the  pes 
anserinus. 

The  Temporal  Branch  ]iasses  upward  over  the  zygoma  nearly  at  right 
angles  to  it,  and  soon  breaks  u])  into  numerous  Ijranches  which  are  dis- 
tributed to  the  region  of  the  tem])le  and  side  of  the  forehead,  including 


THE  NERVOUS  SYSTEM.  309 

the  following  muscles  :  attrahens  and  attolens  aurem,  frontalis,  part  of 
the  orbicularis  palpebrarum,  and  the  corrugator  supercilii.  It  commu- 
nicates with  the  three  divisions  of  the  fifth  nerve,  the  auriculo-temporal, 
a  branch  of  the  inferior  dental,  the  temporal  branch  of  the  superior 
maxillary,  and  the  supraorbital  and  lachrymal  branches  of  the  oph- 
thalmic nerve. 

The  Malar  or  Ocular  Branch  passes  forward,  inward,  and  slightly 
upward  to  reach  the  external  portion  of  the  orbital  cavity,  and  is  dis- 
tributed to  the  orbicularis  palpebrarum  and  the  corrugator  supercilii. 
On  the  upper  eyelid  communicating  filaments  of  this  nerve  inter- 
lace with  the  lachrymal  and  supraorbital  branches  of  the  ophthalmic, 
while  on  the  lower  eyelid  they  communicate  with  branches  of  the 
infraorbital. 

The  Infraorbital  or  Tramverse  Branch  is  larger  than  the  other  two 
divisions.  It  passes  nearly  horizontally  forward  and  inward  over  the 
masseter  muscle  to  the  space  between  the  orbit  and  the  mouth,  and 
divides  into  a  superficial  and  deep  set  of  branches. 

The  Sujjerfeial  set  passes  between  the  integument  and  the  muscles  of 
the  face ;  its  filaments  are  distributed  to  the  zygomatic,  levator  labii 
superioris  alsequse  nasi,  and  the  small  nasal  muscles. 

The  Deep  Set  passes  beneath  the  levator  labii  superioris,  and  is  dis- 
tributed to  the  levator  anguli  oris  and  buccinator  muscles.  The  termi- 
nal filaments  of  this  set  of  nerves  interlace  with  the  filaments  of  the 
infraorbital  and  superior  maxillary  and  infratrochlear  nerves  to  form 
the  infraorbital  plexus,  which  is  situated  beneath  the  levator  labii  supe- 
rioris proprius. 

The  Cervico-facial  Branch  is  smaller  than  the  temporo-facial,  and 
passes  obliquely  downward  and  forward  through  the  substance  of  the 
parotid  gland  to  the  angle  of  the  inferior  maxillary  bone.  It  then 
extends  on  to  the  face  below  the  other  divisions  of  the  fiicial  nerve,  and 
passes  to  the  superior  portion  of  the  neck.  At  the  angle  of  the  jaw  it 
terminates  by  dividing  into  three  branches,  buccal,  supramaxillary,  and 
cervical.  When  this  nerve  is  within  the  parotid  gland  it  receives  a 
communicating  filament  from  the  great  auricular  nerve  of  the  cervical 
plexus. 

The  Buccal  Nerve  in  the  first  portion  of  its  course  passes  between  the 
parotid  gland  and  the  masseter  muscle,  then  extends  over  the  muscle  in 
the  direction  of  the  angle  of  the  mouth.  It  is  distributed  to  the  bucci- 
nator, palato-glossus  and  orbicularis  oris,  and  receives  communicating 
branches  from  the  buccal  and  temporo-facial  divisions  of  the  inferior 
maxillary  nerve. 

The  Supramaxillary  Nerve  is  often  double — that  is,  it  is  represented 
by  two  distinct  nerves.  It  passes  forward  along  the  deej)  surface  of 
the  depressor  anguli  oris,  and  is  distributed  to  the  muscles  of  the 
lower  lip  and  chin,  A  branch  from  this  nerve  extends  forward  along 
the  margin  of  the  lower  jaw  to  the  symphysis  inenti.  It  communicates 
with  the  mental  branches  of  the  inferior  dental  nerve  and  a  branch  from 
the  inferior  maxillary  division  of  the  fifth  nerve. 

The  Cervical  Nerve  (inframaxillary)  passes  downward  and  forward, 
pierces  the  deep  cervical  fascia,  and  breaks  up  into  slender  bi'anches 


310  ANATOMY. 

which  form  a  series  of  arches  beneath  the  platysma  rayoides  muscle, 
extending  inward  to  the  suprahyoid  region.  It  supplies  the  platysma 
myoides  and  the  skin  in  this  region,  and  communicates  with  the  super- 
ficial cervical  plexus. 

Auditory  Nerve. 

The  Auditory  or  Eighth  Nerve  (portio  mollis  of  the  seventh  nerve, 
according  to  Willis)  is  the  special  nerve  of  hearing,  and  is  distributed  to 
the  ear  alone.  It  arises  superficially  or  apparently  by  two  roots,  which 
are  situated  between  the  olivary  and  restiform  bodies  just  posterior, 
though  closely  in  apposition,  to  the  facial  or  seventh  nerve.  On  leav- 
ing the  medulla  oblongata  the  two  roots  unite,  and  the  nerve  then 
passes,  together  with  the  facial,  to  the  bottom  of  the  internal  auditory 
meatus.  Here  it  terminates  by  separating  into  superior  and  inferior 
divisions. 

The  tinperior  Division  breaks  up  into  three  branches,  which  pass  to 
the  utricle,  and  ampullae  of  the  superior  and  external  semicircular 
canals  of  the  ear. 

The  Inferior  Division  is  chiefly  distributed  to  the  cochlea,  though  it 
also  supplies  the  saccule  and  posterior  semicircular  canal. 

The  Nerve  of  Wrisberg  is  situated  between  the  auditory  and  facial 
nerves  from  their  origin  to  the  termination  of  the  auditory  nerve. 
Some  of  its  fibres  unite  with  those  of  the  auditory  nerve,  while  the 
nerve  itself  is  connected  with  the  geniculate  ganglion  of  the  facial  nerve. 

Glosso-pharyngbal  Nerve. 

The  Glosso-phari/ngeal  or  Ni)ifh  iVerve  (the  first  and  smallest  trunk 
of  the  eighth  pair,  according  to  Willis)  (Fig.  150)  is  the  sensory  nerve 
of  the  mucous  membrane  of  the  pharynx,  the  posterior  third  of  the 
tongue,  and  the  middle  ear.  It  is  also  the  nerve  which  controls  the 
motions  of  the  stylo-pharyngeal  muscle.  It  communicates  through 
the  otic  ganglion  with  the  inferior  maxillary  division  of  the  fifth 
nerve,  the  facial  and  pneumogastric  nerves,  and  the  sympathetic  sys- 
tem. Its  superficial  or  apparent  origin  is  from  the  upper  or  anterior 
surface  of  the  medulla  oblongata,  in  the  groove  between  the  olivary  and 
restiform  bodies,  and  between  the  ])nQumogastric  and  auditory  nerves. 
It  arises  by  four  or  five  filaments,  which  are  collected  into  two  bundles, 
the  anterior  being  the  larger.  It  passes  from  its  origin  outward  and 
forward  beneath  the  anterior  portion  of  the  flocculus,  and  makes  its 
exit  from  the  brain-case  through  the  middle  compartment  of  the  pos- 
terior lacerated  foramen  in  company  with  the  pneumogastric  and  spinal 
accessory  nerves.  It  has  a  se})arate  sheath  of  its  own,  however,  formed 
from  the  dura  mater.  Within  the  foramen  the  nerve  assumes  the  form  of 
a  slender  rounded  cord,  and  ]iasses  through  in  a  groove  which  is  occasion- 
ally transformed  into  a  canal,  the  most  anterior  of  the  three  nerves.  While 
in  this  groove  or  canal  tlie  nerve  is  characterized  by  two  enlargements,  the 
superficial  lieing  the  jugular,  and  the  inferior  the  petrous  ganglion.  From 
the  posterior  lacerated  foramen  the  nerve  passes  forward  between  the  inter- 


THE  NERVOUS  SYSTEM. 


311 


nal  jugular  vein  and  iiitenuil  carotid  artery,  crosses  over  the  artery  to  its 

anterior  aspect,  and  descends  behind  the  styloid  process  and  the  stylo- 

pharyngeus  muscle.     It  then  curves 

gradually  forward  over  the  lower  Fig.  150. 

])ortion  of  this  muscle  and  beneath  ^.^-^=^^ 

the  hyo-glossus,and  reaches  the  base 

of  the  tongue. 

The  Superficial  orJtif/Hfar  Gang- 
lion (ganglion  of  Ehrenritter)  is  sit- 
uated in  the  upper  portion  of  the 
])osterior  lacerated  foramen  to  the 
outer  side  of  the  nerve,  only  the  por- 
tion of  the  nerve  in  juxtaposition 
being  involved  in  the  ganglion, 
the  other  portions  passing  down  to 
join  below  with  the  fibres  that  have 
emerged  from  the  ganglion.  It  is 
from  a  half  to  one  line  in  length, 
and  sends  a  filament  of  communi- 
cation to  the  superior  cervical  gang- 
lion. 

The  Inferior  or  Petrous  Gang- 
lion (ganglion  of  Andersch)  is  larger     diagram  ff rom  Bendz)  of  tl.e  ( janglia  and  Commu- 
\*^       o    _  /  _&  nications  of  the  Divisions  oi  the  Ninth,  tenth, 

and    more  important  than  the    iug-        and  Eleventh  Pairs:  .J,  cerebellum;  7)1, medulla 
■.  -,.       ^  -,  .  i       i  •       •  i  oblongata;    C,   spinal   cord;    1,   root   of  glosso- 

nlar  ganglion,  and  is  constant  in  its        pharyngeal  nerve;  2,  roots  of  vagus  ;  8,  roots  of 

existence.  It  is  about  three  lines  in 
length,  and  involves  all  the  hbres 
of  the  nerve.  It  is  situated  in  a 
depression  near  the  lower  margin 
of  the  petrous  portion  of  the  tem- 
poral bone,  and  communicates  by 
branches  M'ith  the  auricular  liranch  of  the  pneumogastric  nerve,  with  the 
ganglion  at  the  root  of  the  pneumogastric,  though  this  branch  is  not  con- 
stant, and  frequently  the  nerve  below  the  ganglion  sends  communicating 
branches  to  the  facial  nerve. 


spinal  accessory  ;  4,  jugular  ganglion  ;  5,  petrous 
ganglion  :  6,  tympanic  arch ;  7,  ganglion  ot  the 
root  of  the  vagus  ;  8,  auricular  branch  ;  9.  gan- 
glion of  the  trunk  of  viigus ;  10,  branch  from  the 
last  to  the  petrous  ganglion  ;  11,  inner  portion  of 
spinal  accessory ;  12,  outer  portion  of  the  same  .  13, 
pharyngeal  branch  of  vagus ;  14,  upperlaryngeal 
branch;  lo,  branches  to  the  sympathetic;  16,  fas- 
ciculus of  spinal  accessory  prolonged  with  vagus. 


A    TABLE    OF    THE    BEANCHES    OF    THE    GLOSSO-PHARYNGEAL 
NERVE,  AND  THEIR   DISTRIBUTION. 


GlOSSO  -  PHARYN- 

REAL     (Ninth 
Cranial) 

Nerve. 


1.  Tympanicbranch, 
or  Jacobson's 
nerve, 


Commiinnicating  f  Large  petrosal  nerve. 
\  Care 


filaments  to 

Brandies   of  dis- 
tribution to 


olid  plexns. 
Small  petrosal  nerve. 
Fenestra  ovalis. 
Fenestra  rotunda. 
Eustacliian  tube. 


2.  Carotid. 

3.  Pbaryngeal  branches  (help  to  form  the  pharyngeal  plexus). 

4.  Muscular  branches  (to  nuiscles  of  the  pharynx). 

5.  Tonsillar  branches  (help  to  form  the  tonsillar  plexus). 

6.  Lingual  branches. 

The  Tympanic  Nerve  (nerve  of  Jacobson)  (Fig.  151)  is  a  long,  slender 
filament  which  arises  from  the  petrous  ganglion  of  the  glosso-pharyn- 
geal,  and  passes  into  a  canal,  the  opening  to  which  is  situated  on  the  ridge 


312 


ANATOMY. 


between  the  posterior  lacerated  foramen  and  the  entrance  to  the  carotid 
canal.  From  this  point  it  ascends  through  the  canal  to  the  inner  wall  of 
the  tympanum,  thence  along  a  groove  on  the  surface  of  the  promontory, 

and  leaves  the  middle  ear  at  its 
superior  and  anterior  portion.  It 
then  becomes  the  superficial  pe- 
trosal nerve,  and  passes  through 
a  small  canal  under  the  tensor 
tympani  nuiscle.    Tliis  canal  ter- 
minates in  one  of  the  small  open- 
,     iuo;s  external  to  the  hiatus  Fal- 
,%  lopii.   The  nerve  from  this  point 
^'J  extends  downward  through  the 
J   petro-sphenoidal     fissure     or    a 
■7    small  foramen  in  the  great  wing 
/     of  the  sphenoid  bone,  and  termi- 
nates in  the  otic  ganglion. 

Its  branches  of  communica- 
cation  are  two  in  number — one 
with  the  carotid  sympathetic 
plexus,  and  the  other  witli  the 
tympanic  plexus.  After  the 
nerve  assumes  the  name  of  the 
small  superficial  petrosal  it  is 
joined  by  a  filament  either  from 
the  geniculate  ganglion  of  the  fa- 
cial nerve  or  by  the  large  super- 
ficial petrosal  nerve  from  the  fa- 
cial. 

Its  branches  of  distribution  are 
to  the  tympanic  plexus,  the  fenes- 
tra rotunda,  fenestra  ovalis,  the 
promontory,  and  the  mucous  membrane  of  the  tympanum  and  Eusta- 
chian tube. 

The  pharyngeal  branches  (carotid  branches,  Henle)  are  three  or  four 
in  number,  the  largest  of  which  passes  along  the  internal  carotid  artery 
to  communicate  with  the  j)haryngeal  branch  of  the  i)neumogastric  nerve 
and  the  symi)athetic  system,  and  form  the  pharyngeal  plexus.  This 
plexus  snpi)lies  the  superior  and  middle  constrictor  muscles  and  mucous 
membrane  of  the  pharynx. 

The  Mii.scnlar  Branches  supply  principally  the  stylo-pharvngeus 
muscle,  though  filaments  pass  to  the  mucous  membrane  of  the  pharynx, 
and  occasionally  to  the  borders  of  the  base  of  the  tongue.  They  may 
connnunicate  with  the  facial  nerve  (Rudinger). 

The  ToiisiUar  Brandies  are  slender  filaments  which  pass  to  the  mucons- 
membrane  of  the  lower  portion  of  the  tonsillar  space,  where  they  form 
a  plexus  (circulus  tonsillaris).  From  this  plexus  branches  extend  to 
supply  the  mucous  membrane  covering  the  tonsils,  the  palatal  folds,  soft 
palate,  and  the  palato-glossus  muscle. 


A  drawing  of  the  Tympanic  Xerve  (from  Breschet's 
work  on  the  earj:  A,  squamous  part  of  temporal 
bone;  15,  petrous  portion  of  same;  C,  lower  maxil- 
lary nerve;  D,  internal  carotid  artery;  n.  tensor 
tympani  muscle;  1, carotid  plexus;  2, otic  ganglion  ; 
3,  glosso-pharyngeal  nerve;  4,  tympanic  nerve;  •">, 
branches  to  carotid  plexus;  li,  branch  to  fenestra 
rotunda;  7,  branch  to  fenestra  ovalis;  8,  branch  to 
join  the  large  superficial  petrosal  nerve;  9,  small 
superficial  jietrosal  nerve;  10,  nerve  to  tensor  tym- 
pani muscle;  11,  facial  nerve;  12,  chorda  tympKni; 
i;^,  petrous  ganglion  of  the  glosso-pharyngeal;  14, 
branch  to  the  membrane  lining  the  Eustachian 
tube. 


The  Lingual  or  Terminal  Branches  arc  two  in  number. 


The  larger 


THE  yERVOVS  SYSTEM.  313 

one  passes  to  the  upper  portion  of  the  posterior  third  of  the  tongue,  and 
breaks  up  into  numerous  branches  which  supply  the  circunivallate  pa- 
pilhe  and  mucous  membrane  over  this  region,  extending  back  as  lar  as 
tlie  anterior  surfiice  of  the  epiglottis.  The  smaller  branch  extends  for- 
ward to  the  posterior  half  of  the  side  of  the  tongue  and  interlaces  with 
the  lingual  nerve.  It  supplies  the  mucous  membrane  of  this  portion 
of  the  tonyi-ue. 


Pneumogastric  Nerve. 

The  pneumogastric  or  tenth  nerve  (nervus  vagus,  par  vagum,  or  sec- 
ond trunk  of  eighth  nerve,  according  to  Willis)  (Fig.  lo2)  at  its  origin 
is  purely  a  sensory  nerve,  but  through  its  communication  with  at  least 
five  motor  nerves  it  takes  on  motor  functions,  and  distributes  both  sen- 
sory and  motor  iilaments  to  different  organs  and  tissues.  It  is  the  most 
widely  distributed  of  all  the  cranial  nerves,  having  more  communicat- 
ing branches.  Its  general  distribution  is  to  the  pharynx,  cesophagUs, 
stomach,  and  alimentary  canal,  the  larynx,  trachea,  heart,  and  blood- 
vessels. It  is  thus  intijiiately  connected  with  the  digestive,  respiratory, 
and  circulatory  systems. 

Its  superficial  or  aj)parent  origin  is  from  the  anterior  surface  of  the 
upper  portion  of  the  medulla  oblongata,  between  the  olivary  and  resti- 
form  bodies,  and  also  innnediately  between  the  glosso-pharyngeal  and 
the  spinal  accessory  nerves.  It  is  made  up  of  from  fifteen  to  twenty 
filaments,  which  unite  and  form  a  flattened  band.  It  passes  transversely 
outward  across  the  flocculus  to  the  middle  compartment  of  the  posterior 
lacerated  foramen,  through  which  it  makes  its  exit  from  the  l)rain-case. 
It  is  enclosed  with  the  spinal  accessory  nerve  in  a  single  sheath  made  up 
of  dura  mater  and  arachnoid  membrane,  and  is  separated  from  the  glosso- 
pharyngeal nerve  by  fibrous  and  occasionally  by  osseous  tissue. 

The  ganglia  of  the  pneumogastric  nerve  are  two  in  number,  jugular 
and  cervical. 

The  Jugular  or  Superior  Ganglion  (ganglion  of  the  root)  is  situated 
within  the  posterior  lacerated  foramen.  It  is  grayish  in  color,  oval  or 
nearly  spherical  in  shape,  about  two  lines  in  diameter,  and  embraces  all 
the  fibres  of  the  nerve.  It  has  branches  communicating  with  the  facial 
nerve  while  the  latter  is  in  the  aqueductus  Fallopii,  and  with  filaments 
from  the  glosso-pharyngeal  nerve  and  from  the  nerve  of  Arnold — with 
the  petrous  ganglion  of  the  glosso-pharyngeal,  the  spinal  accessory 
nerve,  and  the  sympathetic  system. 

The  Cervicol  or  Inferior  Ganglion  (ganglion  of  the  trunk  or  ])lexiform 
ganglion)  is  situated  upon  the  pneumogastric  nerve  a  little  below  the 
base  of  the  skull,  a  half  inch  beneath  the  superior  ganglion.  It  is  of  a 
reddish-gray  color,  loose  or  plexiform  in  texture,  and  contains  gray 
fibres  and  nerve-cells  interspersed  between  its  white  fi!)rcs.  It  is  flat- 
tened and  cylindrical  in  shape,  and  measures  from  six  to  ten  lines  in 
length  and  two  lines  in  width.  Its  communication  with  other  nerves  is 
complicated,  all  of  its  fibres  not  passing  through  to  become  involved  in 
their  functions.     Its  branches  of  communication  are — 

1.   The  Accessory  Portion  of  the  Hpinal  Accessory. — This  is  the  most 


314 


Distribution  of  the  Ninth,  Tenth,  and  Eleventh  Pairs  of  Nerves  on  the  Left  Side:  l.Gasserian  gan- 
glion of  fifth  nerve;  2,  internal  carotid  artery,  ;i,  pharyngeal  branch  of  pueuniogastric;  4.  glosso- 
jibaryngeal  nerve;  5,  lingual  nerve  (fifth) ;  6,  spinal  accessory  nerve;  7,  middle  constrictor  of 
pharynx;  s,  intern;il  jugular  vein  (cut) ;  9.  superior  laryngeal  nerve;  10.  ganglion  of  trunk  of 
pneuniogastric  nerve;  11,  hypoglossal  nerve  (cuti  on  hyo-glossus  muscle;  12,  ditto  (cut),  commu- 
nicating with  eighth  and  tir.--t  cervical  nerve;  lo,  exteinal  laryngeal  nerve:  14,  second  cervical 
nerve,  lunping  with  first;  15,  pharyngeal  i)lexus  on  inlerioi- constrictor ;  Ki, superior  cervical  gan- 
glion of  sympathetic  :  IT,  su|)erii)i'  cardiac  nerve  of  pneuinogastric;  18,  third  cervical  nerve;  19, 
thyroid  body  ;  20,  fourth  cervical  nerve ;  21,  21,  left  recurrent  laryngeal  nerve ;  22,  spinal  accessory 
communicating  with  cervical  nerves;  2.'?.  trachea ;  24,  middle  cervical  ganglion  of  sympathetic; 
2f).  middle cardinc  nerve  of  pneuniogastric;  2(>,  phrenic  nerve  (cut);  27,  left  carotid  artery  (cut); 
28.  brachial  plexus;  29,  phrenic  nerve  (cut):  HO,  inferior  cervical  ganglion  of  sympathetic;  31,  pul- 
monary plexus  of  pneuniogastric;  :i2,  [arch  of  the]  thoracic  aorta:  3:^,  a'sophageal  plexus;  34, 
vena  azygos  superior;  3."i,  vena  azygos  minor;  'M,  gangliated  cord  of  sympathetic. 

important  branch,  and  pa.sses  over  tlie  fsnrface  of  the  ijanglion,  many  of 
its  fibres  Ixn'ominij  involved  in  the  pharvni>;eal  and  larvngeal  branches 
of  tiie  pncumojz;astric  nerve,  the  remaiiuhn-  nnitinti;  ^vitll  the  main  trunk 
and  passing  to  the  cardiac  and  inferior  laiynueal  nerves. 


THE  NERVOUS  SYSTEM.  315 

2.  With  the  hypoglossal  nerve,  by  two  or  three  filaments. 

'■>.  Generally  with  the  arcade  formed  by  the  anterior  branches  of  the 
first  and  second  cervical  nerves. 

4.  With  the  sympathetic  system  through  branches  from  the  superior 
cervical  ganglion.  (Fibres  from  this  ganglion  extend  to  join  the  main 
trunk  as  it  passes  downward.) 

The  pneumogastric  nerve  passes  from  its  inferior  ganglion  vertically 
down  the  neck  upon  the  outer  wall  of  the  pharynx,  behind  the  internal 
jugular  vein  and  internal  carotid  artery  above  and  the  common  carotid 
below,  the  nerve,  vein,  and  artery  being  enclosed  in  a  common  sheath. 
On  passing  from  the  neck  into  the  thorax  the  right  and  left  nerves  do 
not  folloM'  a  similar  course  or  bear  the  same  relations  with  the  tissue 
with  which  they  come  in  contact. 

The  Bight  Pneuiiiogadric  Nerve  enters  the  thorax  between  the  subcla- 
vian vein  and  the  first  portion  of  the  subclavian  artery.  It  then  passes 
between  the  right  innominate  vein  and  the  innominate  artery,  then 
behind  the  arch  of  the  aorta  in  a  groove  between  the  trachea  and  the 
oesophagus  to  the  root  of  the  lung,  where  it  becomes  somewhat  flattened 
and  gives  oif  numerous  branches,  which  are  joined  by  similar  branches 
from  its  fellow  of  the  opposite  side.  These  branches  together  form  the 
right  posterior  pulmonary  plexus.  The  nerve  is  then  continued  down- 
ward by  two  cords  to  the  posterior  surface  of  the  cesophagus,  where  it 
subdivides  and  communicates  with  similar  subdivisions  from  the  corre- 
sponding nerve  of  the  left  side  forming  the  oesophageal  plexus.  From 
this  plexus  the  nerve,  after  receiving  fibres  from  the  left  pneumogastric, 
is  formed  into  a  single  cord,  and  passes  down  the  neck  in  close  api)osi- 
tion  with  the  posterior  surface  of  the  cesophagus,  through  the  dia])liragm, 
and  reaches  the  posterior  surface  of  the  stomach,  "where  it  spreads  out 
and  distributes  branches  to  the  liver  and  the  solar  plexus. 

The  Left  Pneumogastric  Nerve  enters  the  thorax  between  the  left 
common  carotid  and  subclavian  arteries,  crosses  the  inner  surface  of 
the  innominate  vein,  and  passes  down  in  front  of  the  descending  portion 
of  the  arch  of  the  aorta.  It  will  thus  be  seen  that  it  holds  a  more  ante- 
rior position  in  the  thorax  than  the  nerve  of  the  right  side.  From  the 
arch  of  the  aorta  it  passes  behind  the  root  of  the  left  lung,  spreads  out 
to  receive  branches  from  the  right  nerve,  and  forms  the  left  posterior 
pulmonary  plexus.  From  this  plexus  it  descends  in  close  apposition  to 
the  anterior  surface  of  the  oesophagus,  giving  oif  branches  to  form  the 
oesophageal  plexus.  It  then  passes  as  a  single  trunk  in  front  of  the 
oesophagus,  through  the  diaphragm  to  the  anterior  surfiice  of  the  stomach, 
to  M'hich  it  is  distributed.  It  sends  branches  to  the  spleen,  pancreas, 
liver,  and  small  intestines. 

The  following  tabulated  arrangement  of  the  branches  of  the  pnemo- 
gastric  nerve  is  taken  from  Prof.  Allen's  Avato7ni/ : 

T^  -if  Auricular. 

Encranial,   {Meningeal. 

r  [Willi  the  spinal  accessory  nerve. 
T^           •  1           .        i        i-  With  the  glosso-iiharvngeal  nerve. 

Excranial,    j   Anastomotic,  I  with  the  hypoglossal  nerve. 

[  L  With  the  sympathetic  nerve. 


316  ANATOMY. 

PharviiKeal 


Excranial 

\ciiitl.l 


Pharvneeal  and  i  ^         ■      i  „  i 

,     •    '^     ,  -  Superior  lai'vnsieal. 

laryngeal,  I  t    .-    •      i      "    '     i 

•    =■      '  (  Inlenor  laryngeal. 

(  Thoracico-cardiac. 

Thoracic,  -^  Pulmonary. 

(  Q^^sophageal. 


Abdominal 


f  Hepatic. 

}  Gastric. 
(  Intestinal. 


The  Atiricnlar  Br<uu-ii  (auricularis  vagi  nerve  of  Arnold)  arises  from 
the  superior  ganglion,  or  ganglion  of  the  root  of  the  pneumogastric 
nerve,  situated  within  the  posterior  laeerated  foramen,  and  immediately 
receives  a  connnunieating  filament  from  the  petrous  ganglion  of  the 
glosso-])liaryngeal  nerve.  It  then  passes  backward  behind  the  bulb  of 
the  internal  jugular  vein,  and  enters  a  foramen  near  the  base  of  the 
styloid  process  of  the  temporal  bone,  which  is  situated  to  the  inner  side 
of  the  a(jueduct  of  Fallopius.  Within  the  canal  it  forms  a  communi- 
cation with  the  facial  nerve,  after  which  it  passes  through  a  canal  situ- 
ated close  to  the  internal  auditory  meatus  between  the  tympanic  and 
mastoid  processes  of  the  temp(jral  bone.  At  that  point  it  emerges  from 
the  Iwne,  divides  into  two  branches,  the  posterior  division  joining  the 
posterior  anricular  branch  of  the  facial  nerve,  while  the  anterior  division 
is  distributed  to  the  integument  and  cartilage  of  the  back  of  the  ear 
and  tlie  posterior  and  inferior  portion  of  the  auditory  canal, 

Vari(dion.s. — In  rare  instances  the  auricular  branch  of  the  pneumo- 
gastric nerve  is  entirely  absent,  or  it  may  have  no  communication  with 
the  facial  nerve.  Occasionally  its  individuality  is  lost  by  uniting  with 
the  facial  nerve,  in  which  case  its  fibres  are  distributed  Avith  the  poste- 
rior auricular  branch  of  the  facial. 

The  Jf('itliir/c((l  Branch  is  quite  small,  and  arises  from  the  anterior 
border  of  the  superior  ganglion  of  the  pneumogastric.  It  passes 
upward,  and  is  distributed  to  the  dura  mater  in  the  vicinity  of  the 
posterior  lacerated  foramen. 

Anadomotic  Branches. — Tiie  larger  number  of  anastomosing  branches 
of  the  pneumogastric  nerve  are  distributed  to  the  circulatory,  respira- 
tory, and  digestive  systems.  In  the  jugular  foramen  small  branches 
are  given  off  to  the  dura  mater  and  to  the  ear ;  in  the  neck  branches 
are  distributed  to  the  jiharynx,  larynx,  and  heart ;  in  the  thorax 
branches  are  supplied  to  the  heart  as  well  as  the  lungs  and  oesophagus; 
in  the  abdomen  its  terminal  branches  are  distributed  to  the  stomach, 
liver,  and  other  organs. 

The  Phari/nr/ra/  Branches  (Fig.  153)  are  the  princi]ml  motor  nerves 
of  the  ])harynx.  They  arc  usually  two  in  number,  but  there  niav  be  more 
than  two;  occasionally  there  is  but  one.  They  arise  from  the  superior 
and  inner  portion  of  the  inferior  or  cervical  ganglion  of  the  pneumo- 
gastric nerv'e,  or,  more  properly,  they  are  composed  of  fibres  which  come 
from  the  accessory  portion  of  the  s])inal  accessory  nerve,  which  passes 
over  this  ])ortion  of  tiie  ganglion.  They  pa.ss  downward  and  inward, 
generally  behind  the  internal  carotid  artery,  but  occasionally  in  front 
of  it,  to  the  superior  border  of  the  middle  constrictor  muscle  of  the 
pharynx,  where  they  divide  into  numerous  branches  which  interlace 


THE  SEE  VOL'S  SYSTEM. 


317 


larviiji'ea 
ganglion 
extremely 


and  the 

to  form 

ini])ortant, 


and 


Fig.  153. 


with  branches  from  the  glosso-pharyngeul,  superior 
sympathetic  system,  through  the  sujierior  cervical 
the   pharyngeal    plexus.      This    plexus    is 
is  situated  on  the  lateral  surface  of  the 
middle   constrictor  muscle.     It  usually 
contains  one  or  more  ganglia.     Branches 
are  distributed  from  this  plexus  to  the 
nniscles  and  nuicous  membrane  of  the 
])harynx.     It  also  gives  oif  the  lingual 
branch    of  the  vagus  nerve  (Luschka). 
They  receive  branches  from  the  glosso- 
pharyngeal   and   pneumogastric   nerves, 
pass  downward,  and  join  the  hypoglossal 
nerve  whei'e  that  nerve  curves   around 
the  occipital  artery. 

The  finperior  LaryngeaJ  Brancli  arises 
as  a  rounded  cord  from  the  middle  and 
inner  side  of  the  inferior  ganglion  or 
ganglion  of  the  trunk  of  tlie  pneumo- 
gastric nerve,  or  ''  from  the  side  oj)})osite 
to  the  point  of  junction  of  the  pneumo- 
gastric with  communicating  branches  of 
the  sjiinal  accessor}',  so  that  probably  the 
superior  laryngeal  nerve  contains  few  if 
any  motor  fibres  from  this  nerve  "  (Flint). 
Quain,  in  describing  the  lower  ganglion, 
says  :  "  The  accessory  part  of  the  spinal 
accessory  nerve  runs  over  the  surface  of 
the  ganglion,  and  is  in  a  great  measure 
continued  directly  into  the  pharyngeal 
and  superior  laryngeal  nerves." 

The  superior  pharyngeal  nerve  is  the 
important  sensory  nerve  of  the  larynx, 
especially  in  the  region  of  the  glottis. 
It  acts  as  the  sentinel  to  the  opening  of 
the  air-passage  to  guard  against  foreign 
matter,  such  as  food,  solid  or  liquid,  from 
enterinu;  duriup;  defflutition.  It  is  also 
motor  in  its  function,  and  distributes 
motor  filaments  to  the  crico-thyroid  mus- 
cle, as  well  as  small  filaments  to  the  in- 
ferior constrictor  and  arytenoid  muscles. 
It  passes  downward  and  inward  behind 
both  the  internal  and  external  carotid 
arteries,  thence  along  the  superior  margin  of  the  inferior  constrictor 
muscle  of  the  pharynx,  where  it  divides  into  tMo  brai]ches,  external  and 
internal.  Previous  to  its  division  it  receives  filaments  from  the  upjier 
cervical  sympathetic  ganglion  and  from  the  pharyngeal  plexus. 

The  External  Laryngeal  Branch  is  smaller  but  longer  than  the  supe- 
rior laryngeal.     It  passes  downward  and  forward  under  the  depressor 


Origin  and  Connections  of  Uie  Glosso- 
pharyngeal, Pneumogastric,  and  Spi- 
nal Accessory  JJerves:  1,  facial  nerve; 
2,  glossopharyngeal ;  V,,  pneumogas- 
tric ;  4,  spinal  accessory;  5,  hypo- 
glossal; n,  external  (niiisculari  branch 
of  the  spinal  accessory;  7,  superior 
laryngeal  branch  of  the  pneumogas- 
tric ;  s,  jiharyngeal  plexus;  !i,  laryn- 
geal pk'x  us  and  upper  cardiac  branches 
(if  tlie  pneumogastric;  I'l.  tympanic 
plexus,  from  a  branch  of  tlie  glosso- 
pharyngeal. 


318  ANAT03IY. 

of  the  liyoid  bone,  and  is  distributed  to  the  crico-thyroid  muscle.  It 
also  sends  branches  to  the  interior  constrictor  of  the  pharynx  and  the 
arytenoid  muscles.  It  receives  communicating  filaments  from  the 
upper  cervical  sympathetic  ganglion,  and  interlaces  with  branches  from 
the  inferior  laryngeal  nerve.  It  also  sends  communicating  or  cardiac 
branches  to  the  cardiac  plexus.  Occasionally  communicating  branches 
from  tins  nerve  pass  to  the  pharyngeal  plexus,  distributing  branches  to 
the  thyroid  body,  the  mucous  membrane  of  the  true  vocal  cords,  and 
the  depressor  muscles  of  the  hyoid  bone. 

The  Internal  Laryngeal  Brandt  is  shorter  though  thicker  than  the 
externa]  laryngeal.  It  passes  forward  along  the  thyro-hyoid  membrane 
to  the  median  line  of  the  neck,  pierces  that  membrane  in  company  with 
the  superior  thyroid  artery,  and  enters  the  internal  portion  of  the  larynx, 
being  situated  beneath  the  mucous  membrane.  Here  it  divides  into 
numerous  branches,  which  are  distributed  as  folloM's  : 

1.  A  branch  which  passes  upward  in  the  aryteno-epiglottic  fold  to 
the  posterior  surface  of  the  epiglottis.  Some  writers  claim  that  a  few 
filaments  of  this  nerve  pass  through  the  epiglottis  to  its  anterior  surface. 

2.  A  branch  which  passes  to  the  base  of  the  tongue  as  far  as  the  cir- 
cunivallate  pa})illce. 

3.  Several  small  branches  which  pass  downward  and  supply  the 
mucous  menil)rane  of  the  aryteno-epiglottic  fold  in  the  region  of  the 
glottis,  and  as  far  downward  as  the  false  vocal  cords  and  the  back  of 
the  larynx. 

4.  There  is  also  a  long  branch  which  passes  beneath  the  ala  of  the 
thyroid  cartilage,  and  unites  with  a  branch  from  the  recurrent  or  infe- 
rior  laryngeal  nerve  at  the  lower  pt)rtion  of  the  larynx. 

The  Inferior  or  Reeiwrent  Lrtrr/ngeal  Nerve  is  the  principal  motor 
nerve  of  the  larynx,  and  supplies  all  its  intrinsic  muscles  excepting  the 
crico-thyroid.  The  right  and  left  inferior  laryngeal  nerves  differ  in 
their  origin  and  in  their  relation  to  the  tissues  of  the  neck. 

The  Rif/lit  Inferior  Lariingeal  Nerve  arises  from  the  main  trunk  of 
the  pneumogastric,  close  to  the  point  where  this  nerve  crosses  the  right 
subclavian  artery.  It  curves  around  the  under  and  posterior  surface 
of  tliis  artery,  passes  obliquely  upward  and  inward  behind  the  common 
carotid  and  inferior  thyroid  arteries,  and  reaches  a  groove  between  the 
trachea  and  tlie  (esojihagus,  ascending  in  this  groove  to  the  level  of  the 
crico-thyroid  articulation. 

The  Left  Inferior  Laryngeal  Nerve  arises  from  the  main  trunk  of  the 
pneumogastri(!  as  that  nerve  ])asses  over  the  left  extremity  of  the  trans- 
verse jiortion  of  the  arcii  of  the  aorta.  It  curves  around  the  lower  sur- 
face of  tlie  arch  just  external  to  the  ductus  arteriosus  or  its  remains  after 
birth,  when  it  bec^omes  a  ligament.  It  then  passes  upward  on  its  pos- 
terior surface,  and  similarly  to  the  nerve  of  the  right  side;  extends 
Vx'hind  the  common  carotid  and  inferior  thyroid  arteries  to  the  groove 
between  the  ti-aclica  and  the  (esoj)iiagus,  terminating  on  a  level  with  the 
crico-thyroid  articulation,  where  botli  nerves  break  up  into  branches. 
Their  terminal  branches  are  distributed  to  all  the  intrinsic  muscles  of 
the  larynx  excepting  tiie  ci'ico-thvroids,  tiiese  muscles  being  supplied 
by  the  superior  laryngeal.     It  also  distributes  a  few  filaments  to  the 


THE  NEBVOUS  SYSTEM.  319 

mucous  membrane  below  the  rima  glottidis.  In  their  passage  upward 
these  nerves  distribute  small  branches  to  the  structure  and  mucous  mem- 
brane of  the  trachea  and  oesophagus  and  to  the  inferior  constrictor  mus- 
cle of  the  ]>harvnx.  As  the  nerves  pass  beneath  the  large  arteries  of 
the  neck  they  send  communicating  branches  to  the  inferior  cervical  sym- 
pathetic ganglion  and  to  the  cardiac  plexus,  which  is  formed  by  the 
interlacing  of  branches  from  the  pneumogastric  nerve  and  sympathetic 
system.  The  right  inferior  laryngeal  nerve  occasionally  sends  a  fila- 
ment to  the  pericardium. 

llie  Cardiac  Branche.^  arise  as  two  sets,  and  receive  the  name  of  cer- 
vical and  thoracic  branches. 

The  Cervical  Cardiac  Branches  are  two  or  three  in  number  (usually 
three),  two  of  which  arise  from  the  main  trunk  of  the  pneumogastric 
in  the  upper  region  of  the  neck,  and  unite  with  the  cardiac  branches  of 
the  svmpathetic  system  as  they  descend.  The  third  branch  arises  from 
the  pneumogastric  nerve  just  before  it  enters  the  thorax.  On  the  right 
side  the  nerve  passes  in  front  of  the  brachio-cephalic  artery,  and  unites 
with  the  superior  cardiac  nerve  in  its  passage  to  the  deep  cardiac  plexus, 
a  few  filaments  passing  to  the  coats  of  the  aorta.  On  the  left  side  the 
nerve  passes  in  front  of  the  arch  of  the  aorta,  and  unites  with  the  supe- 
rior cardiac  nerve  or  passes  directly  to  the  superficial  cardiac  plexus. 

TJie  Thoracic  Cardiac  Branches  of  the  right  side  arise  partially  from 
the  trunk  of  the  pneumogastric  nerve  below  the  origin  of  the  right 
recurrent  laryngeal  as  the  nerve  lies  close  to  the  trachea,  and  partially 
from  the  recurrent  branch  of  the  pneumogastric.  They  terminate  in 
the  deep  cardiac  plexus.  The  branches  of  the  left  side  usually  arise 
from  the  recurrent  or  inferior  laryngeal  nerve  and  terminate  in  the 
superficial  cardiac  plexus. 

The  Pulmonary  Brandies  are  separated  into  two  sets,  anterior  and 
posterior. 

The  Anterior  Pulmonary  Branches  are  the  smaller  of  the  two  sets, 
and  consist  of  two  or  three  slender  filaments  which  arise  from  the  pneu- 
mogastric nerve  below  its  cardiac  branches.  A  few  of  these  filaments 
pass  to  the  trachea  before  they  form,  together  with  the  sympathetic 
system  of  the  pulmonary  artery,  the  anterior  pulmonary  plexus. 
Fibres  from  this  plexus  encircle  and  pass  along  the  bronchial  tubes 
to  their  terminations  in  the  air-cells  of  the  lungs. 

The  Posterior  Pulmonary  Branches  are  larger  and  more  numerous 
than  the  anterior.  They  arise  from  the  flattened  portion  of  the  pneu- 
mogastric nerve  behind  the  root  of  the  lung.  They  unite  with  filaments 
from  the  second,  third,  and  fourth  thoracic  sympathetic  ganglia  to  form 
the  posterior  pulmonary  plexus.  From  this  plexus  a  few  filaments  are 
distributed  to  the  inferior  and  posterior  portion  of  the  trachea,  to  the 
muscular  tissue  and  mucous  membrane  of  the  central  region  of  the 
oesophagus,  and  a  few  to  the  posterior  superior  portion  of  the  pericar- 
dium. The  principal  portions  of  these  branches,  however,  surround  the 
bronchial  tubes,  and  pass  along  them  to  the  air-cells  of  the  lungs  in  the 
same  manner  as  the  branches  from  the  anterior  pulmonary  plexus.  The 
anterior  and  posterior  })ulmonary  plexuses  of  each  side  give  off  a  large 
number  of  communicating  branches  which  pass  between  each  other,  so 


320 


ANATOMY. 


that  filaments  from  both  the  right  and  the  left  pneumogastric  nerve  pass 
to  the  right  and  left  lungs. 

The  Q^fiophageal  Bra)icJies  arise  from  the  pneumogastric  nerve,  both 
above  and  below  its  pulmonary  branches.  Those  which  arise  below  are 
the  larger  and  spring  from  the  oesophageal  plexus.  The  nerves  from 
the  right  and  left  side  interlace  quite  freely,  and  are  distributed  to  the 
muscular  tissue  and  mucous  membrane  of  the  lower  third  of  the 
oesophagus. 

The  Abdotiunal  or  Terminal  Bra)H-he,s  of  the  right  and  left  sides 
differ  in  their  distribution.  Those  of  the  left  side  enter  the  abdominal 
cavity  upon  the  anterior  surfiice  of  the  oesophagus,  and  when  opposite 
the  cardiac  orifice  of  the  stomach  divide  into  numerous  branches. 
These  branches  are  distributed  to  the  muscular  tissue  of  the  walls  of 
the  stomach  and  to  the  mucous  membrane  of  its  anterior  portion,  lesser 
curvature,  and  great  cul-de-sac,  interlacing  with  branches  of  the  right 
nerve  and  the  sympathetic  system.  There  are  also  branches  (hepatic) 
which  pass  from  the  lesser  curvature  of  the  stomach,  between  the  folds 
of  the  gastro-hepatic  omentum,  reach  the  transverse  fissure  of  the  liver, 
to  be  distributed  to  the  hepatic  substance. 

The  abdominal  branches  of  the  right  side  enter  the  abdomen  on  the 
posterior  surface  of  the  cesophagus.  On  reaching  the  stomach  they 
break  up  into  branches,  some  of  which  are  distributed  to  the  muscular 
tissue  and  mucous  membrane  of  its  posterior  portion,  interlacing  with 
branches  from  the  left  nerves  ;  while  others  pass  to  the  liver,  spleen,  kid- 
neys, suprarenal  capsules,  and  to  the  whole  of  the  small  intestine,  and 
communicate  with  the  solar  plexus. 


Spinal  Accessory  Nerve. 

The  spinal  accessory  or  eleventh  nerve  (the  third  trunk  of  the  eighth 
nerve  according  to  the  arrangement  of  Willis)  (Fig.  154)  is  a  motor 
nerve,  which  is  se])arated  into  two  divisions.  The  first  division  controls 
the  action  of  the  sterno-cleido-mastoid  and  part  of  the  trapezius  muscle; 
the  second  division,  after  uniting  with  the  pneumogastric  nerve,  supplies 
motor  filaments  to  muscles,  and,  as  was  demonstrated  by  Bischoff  in 
1832,  presides  over  phonation.     This  fact  was  also  proved  by  Bernard. 

A   TABLE  OF   TIIP:  BRANCHES  OF  THE  SPINAL  ACCESSORY  NERVE. 

Branches  to  the  pharyngeal  plexus. 

"  "        superior  laryngeal  nerve. 

"  "        recurrent  laryngeal  nerve 

Accessory  portion,   |        (thus  su])plving  the  muscles  ol'  pliona- 
tioni. 
Brancli  to  the  sterno-niastoid  muscle. 

"  "       trapezius  muscle. 

Branch  to  the  stcrno-nuistoid  muscle. 
"  "       trapezius  muscle. 

I   First  cervical  nerve. 
Communicating   |    Second  cervical  nerve. 
l)ranches  to        I    Third  cervical  nerve. 
[   Fourth  cervical  nerve. 

The  name  "  spinal  accessory."  was  given  to  this  nerve  by  reason  of 
its  relations  with  the  pneumogastric  nerve,  and  also  because  of  its  origin, 


Thk  Spinal  Accks- 
soRY    OR    Elkv- 

ENTH  CkANIAL, 

Nerve. 


Spinal  portion, 


THE  NERVOUS  SYSTEM. 


J21 


which  is  quite  extensive  and  divided  into  two  portions  or  roots.  One 
root  arises  from  the  lower  portion  of  the  medulla  oblongata,  and  the 
other  from  the  cervical  portion  of  the  spinal  cord. 


Fig.  154. 


The  Side  of  the  Neck  :  1,  occipital  artery  ;  2,  facial  vein  ;  3,  spinal  accessory  nerve  ;  4,  facial  artery  ;  5, 
internal  jugular  vein  ;  (5,  hypo<,'lossal  nerve;  7,  coniniunicans  iioni  nerve;  8,  lingual  artery;  9, 
pneumogastric  nerve;  10,  superior  laryngeal  nerve;  11,  phrenic  nerve;  12,  superior  thyroid 
artery  ;  13,  sterno-cleido-niastoideus  (reflected) ;  14,  common  carotid  artery  with  descendens  noni 
nerve;  lo,  inner  end  of  clavicle  reflected  ;  Ki,  stertio-hyoid  ;  17,  subclavian  vein  (cui) ;  18,  omo- 
hyoid; 19,  subclavian  artery  giving  off  the  thyroid  axis  and  the  internal  mammary  artery  ;  20, 
inferior  cervical  ganglion  of  sympathetic;  21,  apex  of  pleura. 

The  Medullary  or  Accessor}/  Portion  or  Roof. — The  superficial  or  ap- 
parent origin  is  by  four  or  five  delicate  filaments  situated  in  the  groove 
between  the  olivary  and  restiform  bodies  on  the  side  next  the  medulla 
oblongata,  just  below  the  superficial  origin  of  the  pneumogastric  nerve. 

The  Cervienl  Portion  or  Root  arises  by  six  or  eight  filaments  from 
the  lateral  tract  of  the  entire  length  of  the  cervical  portion  of  the  spinal 
cord,  though  its  superficial  origin  is  not  generally  distinguishable  below 
the  fiiurth  or  fifth  cervical  nerve.  The  lowest  filament  is  generally 
single  ;  the  others,  however,  emerge  from  the  cord  in  pairs.  These 
filaments  ascend  along  the  cord,  increasing  in  size  as  each  additional 
filament  is  added,  and  extending  between  the  ligamentum  denticulatum 
and  the  posterior  roots  of  the  spinal  nerves.  The  first  and  second  spinal 
nerves  are  often  connected  to  these  filaments.  After  reaching  the  for- 
amen magnum,  through  wliich  it  enters  the  brain-case,  it  curves  outward 
to  the  middle  compartment  of  the  posterior  lacerated  foramen,  in  which 
it  joins  the  medullary  root.  The  two  roots  then  interchange  fibres  with 
Vol.  I.— 21 


322  ANATOMY. 

each  other,  and  occasionally  form  a  single  trnnk.  In  this  region  the 
two  roots  are  contained  in  a  single  sheath  of  the  (hira  mater  witii  the 
})nenmogastric  nerve.  A  branch  of  connnunication  extends  between  the 
accessory  and  mednllarv  j)ortions  of  the  snperior  ganglion  of  the  pneu- 
mogastric  nerve. 

The  encranial  portion  of  the  spinal  accessory  is  separated  into  two 
divisions,  internal  and  external,  which  are  almost  identical  in  origin 
with  the  two  roots  of  the  main  nerve. 

The  Interna/  ^lednllari/  or  Acce^mry  Portion,  which  contains  nearly 
all  the  fibres  arising  from  the  mednlla,  passes  over  the  inferior  ganglion 
of  the  pnenmogastric  nerve  (ganglion  plexiformis),  and  becomes  inti- 
mately associated  Avith  it.  It  is  distributed  through  the  pnenmogastric 
nerve  to  the  larynx,  pharynx,  and  other  structures.  (See  Pnenmo- 
gastric Nerv-e.) 

The  Exfernal  or  Spinal  Portion  (muscular  brancli)  is  the  longer  of 
the  two  branches,  and  contains  nearly  all  the  filaments  which  arise  from 
the  spinal  cord,  and  may  receive  all  the  fibres  of  the  posterior  root  of 
the  first  cervical  nerve.  It  passes  from  the  posterior  lacerated  foramen 
downward,  backward,  and  outward  in  front  of  the  internal  jugular  vein, 
but  occasionally  behind  the  vein,  over  the  transverse  process  of  the  atlas, 
to  the  superior  third  of  the  sterno-cleido-mastoid  muscle.  It  generally 
pierces  this  nuisi-le,  th(jugh  it  may  pass  beneath  it  and  appear  in  the  pos- 
terior cervical  triangular  s})ace  beneath  the  trapezius  muscle.  It  com- 
municates by  brandies  with  the  medullary  ])ortion  in  the  posterior  lace- 
rated foramen,  with  the  first  cervical  nerve,  and  the  superior  ganglion  of 
the  pnenmogastric  nerve,  while  beneath  the  trapezius  muscle  it  gives  off 
branches  Avhich  unite  with  branches  from  the  third,  fourth,  and  fifth 
cervical  nerves  which  assist  in  forming  the  cervical  ])lexus.  It  also 
distributes  branches  to  ])art  of  the  sterno-cleido-mastoid  muscle  and 
to  the  clavicular  portion  of  the  ti-ai)ezius  muscle. 

Hypoglossal  Nerve. 

The  hy])oglossal,  twelfth,  or  sublingual  nerve  (the  ninth  nerve  accord- 
ing to  the  arrangement  of  Willis)  (Fig.  152)  is  the  last  of  the  cranial 
nerves.  Its  chief  function  is  in  connection  Avith  the  movements  of  the 
tongue  in  deglutition  and  articulation.  It  is  also  distributed  to  all  the 
muscles  which  are  attached  to  the  hyoid  bone.  It  arises  superficially 
or  a])])ar('ntly  by  twelve  or  fourteen  filaments,  which  ])ass  from  the 
groove  situated  between  the  olivary  body  and  the  antei'ior  pyramid  of 
the  medulla  oblongata.  The  filaments  are  collected  into  two  separate 
bundles,  sujjcrior  and  inferior,  which  are  directed  outward,  pass  behind 
the  vertebral  artery,  and  extend  toward  the  anterior  condyloid  foramen; 
and  as  they  enter  this  foramen  or  foramina'  they  receive  a  separate 
sheath  from  the  dura  mater,  and  imite  into  a  single  trunk  as  they 
emerge  from  the  brain-case  and  pass  into  the  deep  ]iortions  of  the  neck. 
From  this  point  it  extends  to  the  median  side  of  the  internal  jugular 
vein  and  the   pnenmogastric  nerve,      ft  then  descends  the  neck  nearly 

'  Occasional Iv  tliere  are  two  foramina  in  tlie  ocrij)ital  l)oiie.  When  this  is  the  case 
the  bnndles  j)ass  thron.ijh  separate  openings. 


THE  NERVOUS  SYSTEM. 


323 


The  Hypoglossal  ok 
Twelfth  Crakial 
Nerve. 


Branches  of  com- 
niunicatioii. 


Branches    of    dis- 
tribution. 


in  a  vertical  (slightly  forward)  direction  on  the  median  side  ot"  the 
internal  jugular  vein,  and  between  it  and  the  internal  carotid  artery, 
to  a  level  with  the  lower  nuirgin  of  the  digastric  nuiscle.  It  here,  in 
the  snperior  carotid  triangle  of  the  neck,  becomes  snperficial,  and  curves 
around  and  under  the  occipital  artery  near  its  origin.  It  then  passes 
forward  over  the  external  carotid  artery,  above  the  hyoid  bone,  beneath 
the  tendon  of  the  digastric  and  the  lower  portion  of  the  stylo-hyoid, 
and  betAveen  the  mylo-hyoid  and  the  hyo-glossus  muscles,  terminating 
by  dividing  into  branches  in  the  genio-glossus  muscle. 

TABLE  OF   THE   BRANCHES   OF   THE   HYPOGLOSSAL   NERVE. 

To  the  ganglion  of  the  trunk  of  the 

pneumogastric  nerve. 
To  the  superior  cervical  ganglion  of 

the  sympathetic. 
To  the  loop  between  the  first  and  second 
cervical  nerves;. 
[  To  the  gustatory  nerves. 
f   Descendens  noni  nerve. 

To  thyro-hyoid  nerve. 
I    To  genio-hyoid  nerve. 
j    To  stylo-glossus  muscle. 
I    To  hyo-glossus  muscle.     • 
I   To  genio-hyo-glossus  muscle. 
[  To  the  intrinsic  nuiscles  of  the  tonjiue. 

The  branches  of  connnunication  of  this  nerve  as  tabulated  above  are — 

1.  ^^  ith  the  pneumogastric  nerve,  which  passes  between  the  interior 
ganglion  of  that  nerve  and  the  hypoglossal  nerve  immediately  after  it 
leaves  the  skull.  There  is  also  a  communicating  branch  which  passes 
between  these  two  nerves  near  to  the  point  where  they  cross  the  occipital 
artery. 

2.  With  the  sympathetic  system  by  a  filament  of  considerable  size, 
which  passes  between  the  superior  cervical  ganglion  of  that  system  and 
the  hypoglossal  nerve. 

3.  AMth  the  first  and  second  cervical  nerves,  which  pass  between  the 
loop  connecting  these  two  nerves,  the  spinal  nerves,  and  the  hypoglossal 
nerve  together. 

4.  Two  or  three  branches  of  conununication  with  the  gustatory 
nerve,  which  pass  between  the  hypoglossal  nerve  and  the  gustatory  or 
lingual  branch  of  the  fifth  nerve  in  the  region  of  the  anterior  border 
of  the  hyo-glossus  muscle. 

The  branches  of  distribution  of  the  hypoglossal  nerve  are  the — 
Recurrent,  Branches  to  the  tongue, 

Descending  thyro-hyoid,  Genio-hyoid. 

■  The  Recvrrcntr>  ranch  arises  from  the  hypoglossal  nerve  within  the 
anterior  condyloid  foramen.  It  passes  into  the  brain-case,  nnd  is  dis- 
tributed to  the  dura  mater  and  walls  of  the  vascular  sinus  close  to  the 
foramen  magnum.  It  is  also  distributed  to  the  diploe  of  the  occipital 
bone  (Luschka). 

The  Descendinr/  or  Descendens  Noni  Branch  is  a  long,  slender  fila- 
ment which  arises  from  the  hyjioglossal  nerve  as  it  curves  under  the 
occipital  arterv.  From  this  ])()int  it  descends  the  neck,  at  first  in  front 
of  the  internal  carotid  artery,  either  within  the  common  sheath  with 


324  ANA  TOMY. 

the  vessel,  or  upon  its  outer  surface,  to  a  point  just  above  the  tendon  of 
the  omo-hyoid  muscle.  In  its  descent  it  distributes  a  small  branch  to 
the  anterior  belly  of  this  muscle.  It  then  divides  into  two  or  three 
branches,  and  receives  one  or  two  communicating  branches  from  the 
second  and  third  cervical  nerves  (communicans  noni).  By  this  union  a 
plexiforni  loop  is  formed,  with  its  concavity  upward.  This  loop  occa- 
sionally receives  another  small  branch  from  the  cervical  nerves.  From 
this  plexiforni  loop  branches  are  distributed  to  the  sterno-hvoid,  sterno- 
thyroid, and  omo-hyoid  muscles,  and  sometimes  to  the  cardiac  and  phrenic 
nerves  within  the  thorax. 

The  Thyro-hijoid  Branch  arises  from  the  hypoglossal  nerve  in  front 
of  the  external  carotid  artery,  from  which  point  it  descends,  and  is  dis- 
tributed to  the  thyro-hyoid  muscle. 

The  Branches  to  the  Tone/iie  are  the  stylo-glossus,  hyo-glossus,  and 
genio-glossus,  wlii(;h  are  given  off  from  the  hypoglossal  nerve  while  it 
is  located  l)etween  the  mylo-hyoid  and  the  hyo-glossus  muscles.  They 
are  distributed  to  the  muscles  indicated  by  their  names,  and  send 
branches  to  other  muscles  in  the  substance  of  the  tongue,  as  well  as  to 
the  genio-hyoid  muscle. 

Variations. — Occasionally  the  right  and  left  hypoglossal  nerves  com- 
nnniicate  by  a  branch  wliich  passes  between  them  in  the  neighborhood 
of  the  genio-hyoid  muscle.  In  rare  cases  filaments  are  distributed  to 
the  mylo-hyoid  muscle  (Krause).  According  to  Luschka,  E.  Bischoif, 
Holl,  and  others,  the  descendens  noni  nerve  does  not  in  reality  arise 
from  the  hypoglossal  nerve,  but  is  derived  i*rom  the  upper  cervical 
nerves,  which  are  tem])orarily  associated  with  the  hypoglossal.  Holl 
states  that  the  branches  going  to  the  thyro-hyoid  and  genio-hyoid 
muscles  are  composed  of  fibres  which  arise  from  the  spinal  nerves. 


LYMPHATIC  VESSELS  OF  THE  HEAD  AND 

NECK. 

By  albert  p.  BKUBAKER,  A.M.,  M.D.,  D.D.S. 


THE  LYMPHATICS. 


The  Lymphatics,  and  the  glands  in  connection  with  tliem,  consti- 
tute a  system  of  vessels  most  important  to  the  nutrition  of  the  body. 
In  all  the  vertebrate  animals  this  system  is  superaddetl  to  the  circula- 
tory, and  is  designed  to  carry  back  into  the  general  blood-current  the 
excess  of  nutritious  fluid  which  has  been  exuded  from  the  capillary 
blood-vessels  for  the  ])urposes  of  nutrition.  The  fluid  which  the  lym- 
phatic vessels  contain  is  known  as  lymph,  and  resembles  in  its  physical 
and  chemical  constitution  the  liquor  sanguinis  or  blood-})lasma. 

The  lymphatic  vessels  have  a  very  extensive  distribution,  being  found 
in  nearly  all  the  tissues  and  organs  of  the  body  which  receive  blood. 
They  are  absent,  or  at  least  have  not  yet  been  discovered,  in  the  hair, 
nails,  epidermis,  and  other  structures  usually  regarded  as  non-vascular. 

Lymphatics  are  widely  distril)uted  throughout  the  body,  but  are  more 
abundant  in  some  situations  than  in  others.  The  inner  surfaces  of  the 
limbs  are  more  abundantly  supjflied  than  the  outer  surfaces,  while  the 
lines  of  junction  of  the  limbs  with  the  trunk  are  especially  rich  in  both 
vessels  and  glands.  In  the  thoracic  and  abdominal  cavities  they  are 
very  numerous.  In  the  majority  of  situations  in  which  the  lymphatics 
are  found  they  are  arranged  into  a  superficial  and  a  deej)  set,  the  former 
being  very  fine  and  situated  in  and  beneath  the  skin  and  nuicous  mem- 
branes, while  the  latter  are  nuich  larger  and  folloAv  the  course  of  the 
large  blood-vessels. 

The-  lymph,  when  examined  microscopically,  is  seen  to  consist  of  a 
clear  colorless  plasma,  in  which  are  imbedded  an  immense  number  of 
corpuscular  elements.  The  lymph  which  has  been  ol)tained  from  man 
and  inferior  animals  is  usually  colorless  and  transj)arent,  although  at 
times  it  presents  a  faintly  yellowish  hue.  It  is  odorless,  slightly  saline 
in  taste,  alkaline  in  reaction,  and  possesses  in  the  dog  a  specific  gravity 
of  1022.  Like  the  blood,  lymph  undergoes  a  spontaneous  coagulation 
wdien  withdrawn  from  the  body,  although  the  coagulum  is  never  so  firm 
as  in  the  case  of  the  blood.  In  its  chemical  composition  lymph  also 
resembles  the  blood.  Analyses  made  by  Lassaigne  of  the  lymph  obtained 
from  a  cow  demonstrated  that  it  contains,  in  1000  parts,  water,  964; 
fibrin,  0.9  ;  albumen,  28.0  ;  fiitty  matter,  0.4 ;  inorganic  salts,  6.7. 

The  corpuscular  elements  of  the  lymph,  known  as  lymph-corpuscles 
or  leucocytes,  are  found  floating  in  the  lymph-plasma.    When  examined 

325 


326  ANATOMY. 

microscopically  they  resemble  in  many  respects  the  white  corpuscles  of 
the  blood,  but  they  are  smaller  and  less  uniform  in  size,  varying  from 
2"TFo  ^^  soVt  ^"*^'^^  ^^^  diameter.  In  addition  to  the  lymph-corpus- 
cles there  are  present  in  almost  every  specimen  of  lymph  small  gran- 
ules, regarded  by  some  as  free  nuclei,  which  have  a  gray  color  and 
exhibit  the  Brownian  movement,  lied  corpuscles  are  also  found,  par- 
ticularly in  the  large  lymphatic  trunks  and  in  the  thoracic  duct. 

The  lymph-corpuscles  vary  much  in  size,  shape,  and  general  apjiear- 
ance.  Some  are  cpiite  small,  spheroidal  in  shape,  and  consist  of  a  single 
nucleus  surrounded  by  a  small  quantity  of  protoplasmic  matter.  Others 
are  larger,  and  frecpiently  contain  several  vesicular  or  spheroidal  nuclei 
which  are  surrounded  by  a  limiting  membrane,  while  the  enveloping 
mass  of  protoplasm  is  quite  abundant.  Many  leucocytes  contain  col- 
lections of  granules  ^v'hich  are  highly  refractive  and  impart  to  the  cor- 
puscle a  distinctly  granular  character.  The  lymph-corpuscles  are  made 
up  of  a  fine  network  of  an  albuminous  material,  in  the  meshes  of  which 
is  found  a  colorless  semifluid  substance  apparently  of  an  albuminous 
character.  There  is  no  cell-wall  present  in  any  of  the  true  lymph-cor- 
puscles. Tiiey  originate  either  by  subdivision  of  pre-existing  cells  or 
are  developed  within  the  lymphatic  glands. 

Origin  of  Lymphatics. — The  mode  of  origin  of  the  lymphatics 
has  until  recent  years  been  involved  in  the  greatest  obscnirity.  But  the 
investigations  of  Von  Recklinghausen,  Klein,  Ludwig,  and  many  others 
have  gone  far  toward  demonstrating  the  true  origin  of  these  vessels. 
The  following  modes  of  origin  are  now  well  known  : 

1.  Origin  in  Li/inpJi-i^j)ace.s  or  Jidee-canah. — Throughout  the  con- 
nective-tissue system  of  the  body  are  located  immbers  of  small,  irregu- 
lar, stellate  spaces  which  comnuniicate  very  freely  with  each  other. 
These  are  the  so-called  juice-canals  of  Von  Recklinghausen,  and  are 
su])posed  to  rej)resent  the  ultimate  radicles  of  the  lymphatic  vessels. 
They  vary  considerably  in  size,  and  their  shapes  are  determined  by  the 
nature  of  the  tissues  in  which  they  are  placed.  They  do  not  possess  an 
endothelial  lining,  but  contain  one  or  more  connective-tissue  corpuscles 
which  exhibit  chara(;teristic  amoeboid  movements.  As  these  spaces 
comuuniicate  very  freely  with  each  other,  the  movement  of  the  lymjih 
through  them  and  around  the  islets  of  tissue  readily  'takes  place. 

The  lymph-spaces  communicate  directly  with  the  Iipnph-capillnrieN, 
as  was  also  demonstrated  by  Von  Recklinghausen.  The  lym])h-ca))il- 
laries  constitute  a  jilexus  of  fine  vessels  Avhich  give  rise  to  the  smallest 
lymj)hatic  trunks  ;  they  vary  in  shape  according  to  the  tissue  in  which 
they  are  found,  and  also  in  size,  but  are  always  larger  than  the  capil- 
lary blood-vessels.  Their  walls  are  formed  by  a  lining  of  simple  endo- 
thelial cells  with  characteristic  sinuous  margins. 

2.  Origin  in  Openings  on  the  Surface  of  Serous  Membranes. — The 
large  serous  cavities,  such  as  the  peritoneal,  pleural,  pericardial,  sul)- 
arachnoid,  etc.,  have  been  shown  by  Klein,  A^on  Recklinghausen,  and 
many  others  to  comnuniicate  with  the  lymphatic  vessels.  Their  mode 
of  origin  can  best  be  studied  upon  the  peritoneal  surface  of  the  central 
tendon  of  the  diaphragm.  This  surface  is  covered  with  a  layer  of 
endothelial  cells,  whose  sinuous   margins  can  be  readily  exhibited  by 


LYMPHATIC   VESSELS  OF  THE  HEAD  AND  NECK.  327 

staining  the  surface  with  a  sohition  of  nitrate  of  silver.  At  intervals 
l)et\veen  these  cells  are  found  large  free  openings  which  have  received 
the  name  of  stomata.  These  openings  communicate  by  means  of  short 
canals  with  the  lymph-capillaries  that  are  found  among  the  fibrous 
tissue  of  \\hicli  the  diaphragm  is  composed.  Upon  the  pleural  surface 
similar  openings  have  also  been  dcnu)nstrated.  The  serous  cavities 
of  the  body  may  therefore  be  regarded  as  true  lymph-spaces,  which 
communicate  primarily  with  the  lymph-capillaries,  and  secondarily  with 
the  lymphatic  trunks.  Stomata  in  all  respects  similar  to  those  found 
on  serous  membranes  have  been  shown  to  be  present  on  the  surfaces  of 
mucous  membranes,  which  in  all  probability  are  directly  coimected  with 
the  lymph-capillaries. 

3.  Origin  in  Periv<iscu/.ar  Lymph-spaces. — Within  the  substance  of 
the  brain,  spinal  cord,  bone,  and  other  tissues  His  and  Robin  have 
shown  that  the  capillary  blood-vessels  are  surrounded  by  a  lymph-space 
bounded  and  limited  by  a  cylindrical  sheath  formed  of  endothelial  cells, 
which  is  in  frequent  communication  with  the  lymph-capillaries.  The 
blood-vessel  thus  floats  in  the  lymph-stream.  In  addition,  the  tunics 
of  the  large  blood-vessels,  both  the  intima  and  adventitia,  are  traversed 
by  lymph-channels  which  open  very  freely  into  each  other.  This 
arrangement  of  the  blood-vessels  permits  of  a  free  interchange  by 
osmosis  of  the  fluid  portion  of  both  blood  and  lymph. 

Structure  of  Lymphatic  Vessels. — The  lym])hatic  trunks  have 
their  origin  in  the  fine  plexus  of  lyniph-capillaries  prc\iously  described. 
In  their  course  toward  the  centre  of  the  body  they  pursue  generally  a 
direct  route.  They  anastomose  by  bifurcation  very  freely  with  neigh- 
boring vessels,  pass  through  the  lymphatic  glands,  and  vary  but  little 
in  size  from  origin  to  termination.  Their  walls  are  so  exceedingly  trans- 
parent and  delicate  that  when  empty  it  is  with  difficulty  they  can  be 
seen.  Their  diameter  varies  from  ^  to  yV  i"<^'l^-  ^^^^^'  ^'/^  lymphatic 
trunks  have  emerged  from  the  lymph-capillaries  they  acquire  three  dis- 
tinct coats,  which  resemble  in  their  structure  and  arrangement  the  coats 
of  the  veins. 

The  internal  coat  is  delicate  and  elastic,  and  is  composed  of  a  layer 
of  longitudinal  elastic  fibres  covered  with  a  layer  of  flattened  nucleated 
endothelial  cells'  with  wavy  or  sinuous  margins.  The  middle  coat  con- 
sists of  white  fibrous  tissue,  which  is  arranged  longitudinally,  and  of 
unstriped  muscular  and  elastic  fibres,  which  are  disposed  transversely. 
The  external  coat  is  composed  of  identically  the  same  structures,  but 
the  muscular  fibres  pursue  rather  a  longitudinal  than  a  transverse  direc- 
tion. These  three  coats  are  known  respectively  as  the  tunica  intima, 
tunica  media,  and  tunica  adventitia.  The  walls  of  the  lym])hatic 
trunks  are  abundantly  su]>plied  with  blood-vessels  {ram  vamnoii),  and 
it  is  highly  probable*  that  they  are  also  supplied  with  nerves  {)i('rvce 
vasorum),  though  the  latter  have  not  been  indisputably  demonstrated. 
On  physiological  grounds  their  existence  might  be  inferred. 

Valves. — The  lymphatics  generally  are  provided  with  valves,  which 
have  the  same  structure  and  fulfil  the  same  function  as  the  valves  with 
which  the  veins  are  furnished.  These  valves  are  very  numerous,  and 
are  located  at  such  short  intervals  along  the  course  of  the  vessel  as  to  give 


328 


ANA  TOMY. 


rise  to  a  beaded  appearance.  They  are  not  farther  apart  than  -^  to 
\  inch.  The  superficial  vessels  are  most  abundantly  supplied  with 
valves,  those  of  the  arm  containing  from  sixty  to  eighty  between  the 
fingers  and  axillary  glands,  while  the  corresponding  vessels  of  the 
lower  limbs  contain  from  eighty  to  one  hundred.  The  valves  are 
generally  arranged  in  pairs,  and  consist  of  two  semilunar  folds,  with 
their  concavities  directed  toward  the  larger  vessels.  They  are  formed 
by  a  reduplication  of  the  lining  membrane,  the  two  folds  being  strength- 
ened by  fibrous  tissue  from  the  middle  coat. 

Lipaphatic  (rlaiuh. — The  lymphatic  glands  are  small  lenticular  bodies 
placed  along  the  course  of  the  lymphatic  vessels  as  they  pass  from  their 
points  of  origin  toward  the  thoracic  duct.,  They  are  exceedingly  numer- 
ous, the  total  number  being  estimated  at  from  five  to  seven  hundred. 
They  vary  considerably  in  size,  some  not  being  larger  than  a  pin's 
head,  while  (jthers  attain  a  size  equal  to  that  of  a  kidney  bean.  As  the 
lymphatic  glands  are  in  connection  ^vitll  the  vessels,  they  may,  like  them, 
be  divided  into  a  superficial  and  a  deep  set ;  the  former  are  most 
abundant  around  the  head  and  neck  and  at  the  lines  of  union  of  the 
limbs  with  the  body;  the  latter  are  found  most  abundantly  in  the 
thorax  and  abdomen  along  the  course  of  the  deep-seated  vessels.  The 
glands  situated  between  the  folds  of  the  mesentery  are  kno\\'n  as  the 
mesenteric  glands.  The  lymphatic  vessels  as  they  approach  a  gland 
break  up,  before  entering  it,  into  a  number  of  small  branches — the 
vasa  afferentia,  which  penetrate  its  investing  membrane.  From  the 
opposite  side  of  the  gland  the  lymphatics  again  emerge,  as  the  vasa 
efferentki,  and  a  short  distance  beyond  it  unite  to  form  trunks  larger, 
but  fewer  in  number. 

The  lym])hatic  glands  present  at  one  point   a  depression  which  is 
termed  the  hilum,  through  which  the  blood-vessels  pass  into  and  out 
Pjj^,  J--  of  the  gland,  and  through  which 

also  emerge  the  efferent  vessels. 
Except  at  the  hilum  the  gland 
is  entirely  covered  externally  by 
a  membrane  composed  of  dense 
connective  tissue.  The  interior 
of  the  gland  is  soft  and  pulpy, 
of  a  dark  color,  and  mottled  in 
a])])earance.  The  superficial  })art 
of  the  gland  is  termed  the  corii- 
cdJ,  the  dee])er  \yay\  the  medullary 
])()rtion   (Fig.  loo). 

From  the  inner  surface  of  the 
investing  membrane  there  pass 
inward  partitions  or  septa  of 
lamellated  connective  tissue 
which  divide  the  outer  zone  of 
the  gland  into  small  comj)art- 
ments,  which  are  conical  in 
shape  in  consequence  of  the 
convergence  of  the  partitions  toward  the  centre  of  the  gland.     These 


Section  of  Small  Lyiiipliutic  (ilaiid,  half  cliaRrain- 
niatically  ^'nan,  with  the  course  of  tin-  lyinjih  : 
a.  the  envelope;  h,  septa  between  the  follioh's  or 
alveoli  of  the  cortical  part;  r-,  system  of  scjita  of 
the  nieduilary  portion  (h)wn  to  "the  hilum;  </,  the 
follicles;  />,  lymph-cords  of  thi'  mcilullary  mass;  f. 
atl'erent  lymph-vessels,  the  diliiMent  lymphatic 
streams  from  which  surround  the  follicles  and 
flow  throuf;h  the  interstices  of  the  medullary  jior- 
tion  ;  (/.continence  of  these  to  pass  throuf,'ii  tlie 
etferent  vessel  (h)  at  the  hilum. 


LYMPHATIC   VESSELS  OF  THE  HEAD  AND  NECK. 


329 


spaces  or  alveoli  are  from  ^  to  -^  inch  in  diameter,  and  are  con- 
nected with  each  other  thi'ough  openings  in  the  septa.  When  the 
septa  reach  the  medullary  portion  they  subdivide  and  form  bands  or 
cords  which  interlace  in  every  direction  and  constitute  a  loose  mesh- 
work,  the  spaces  of  whieh  communicate  with  each  other  and  with  the 
alveoli.  Within  the  meshes  of  the  gland  is  contained  the  proper  gland- 
substance.  In  the  conical  compartments  it  is  moulded  into  a  pear-shaped 
mass,  while  in  the  medullary  part  it  assumes  the  form  of  rounded  cords, 
which,  like  the  trabecular  meshes,  are  connected  with  each  other.  In 
both  the  cortical  and  medullary  regions,  however,  there  is  a  clear  space 
between  the  gland-pulp  and  the  trabecule,  which  is  termed  the  lymph- 
)ii)ias,  through  wliich  the  lymph  flows  as  it  passes  through  the  gland. 
This  lymph-sinus  is  crossed   by  a  f  •  TSfi 

fine  network  of  retiform  connective 
tissue  in  wliich  the  nuclei  of  the 
endothelial  plates  covering  it  are 
distinctly  seen  (Fig.  150).  This 
reticulation  offers  considerable  re- 
sistance to  the  flow  of  lymph 
through  it.  The  glandular  sub- 
stance itself  consists  of  essentially 
the  same  elements.  It  is  su])port- 
ed  by  a  framework  of  retiform  tis- 
sue, in  the  meshes  of  \\hich  are 
found  immense  numbers  of  lymph- 
corpuscles.  The  glandular  sub- 
stance is  separated  from  the  lymph- 
sinus  by  a  denser  layer  of  reticu- 
lum, although  it  is  not  so  compact 
as  to  prevent  the  lymph,  and  even 
the  corpuscles,  from  ])assing  (Hit 
into  the  lymph-sinus.  The  lym- 
phatic glands  are  abundantly  sup- 
plied with  blood-vessels.  Arteries 
enter  the  gland  at  the  liilum,  pene- 
trate into  the  medullary  substance, 
and  terminate  in  a  fine  capillary 
plexus,  which  is  surrounded  and 
sup])orted  by  the  retiform  tissue. 
The  veins  arising  from  this  plexus 
leave  the  gland  also  at  the  hilum. 

The  lymphatic  vessels  which 
enter  a  gland  ramifv  in  the  in- 
vesting membrane,  and  tlieii  open 
directly  into  the  lymph-sinus.  The  efferent  vessels  begin  l)y  fine 
branches,  which  also  communicate  directly  with  the  lym])h-sinus. 
When  the  lymphatic  vessels  enter  a  gland  they  lose  their  external  and 
middle  coats,  and  retain  only  the  endothelial,  which  lines  the  inner  sur- 
face of  the  lymph-sinus.  The  current  of  lympli,  tlierefore,  can  pass 
directly  from  the  afferent  vessel  through  the  lymph-sinus  into  the  etfer- 


Portloii  of  the  ISIedullary  Substance  of  the  INIes- 
enteric  filand  of  an  Ox,  tlie  artery  injected 
with  chroniate  of  lead  (highly  niagniiied)  :  ((, 
medullary  cylinder  with  cajjillary  network, tine 
retieuluni  of  connective  tissue, and  a  tew  lyniph- 
corpuscles;  /(,  I',  suijcrficial  lymph-path  or  me- 
dullary sinus  traversed  everywhere  by  a  retic- 
ulum of  nucleated  cells;  this  reticulum  has 
been  represented  only  at  c,  with  numerous 
anastomosing  prolongations;  the  lymph-cor- 
puscles have  for  the  most  part  lieen  removed 
with  a  camel's  hair  brush  ;  i/,  </,  trabeculic  com- 
posed almost  exclusively  of  viiistriped  muscu- 
lar tissue.  A  small  iiied'uUary  cord  or  liridge, 
contaiuingablood-vesscl  and  numerous  lymph- 
corpuscles,  is  shown  at  the  left  of  the  figure  as 
springing  from  the  medullary  cylinder. 


330  ANATOMY. 

ent  vessel.  In  addition  to  this  ])riiuaiy  current  there  is  a  secondary 
current  always  fiowing  from  the  (•a[)illary  blood- xessels  outward  into 
the  lymph-sinus  which  carries  Avith  it  immense  numbers  of  lymph-cor- 
puscles, which  enter  the  efferent  lymphatic  vessels. 

The  thoracic  duct  is  the  general  trunk  of  the  lymphatic  system,  into 
which  most  of  the  lymphatic  vessels  of  the  body  empty.  It  is  from 
eighteen  to  twenty  inches  in  length,  extending  from  the  root  of  the  neck 
downward  to  the  second  luml)ar  vertebra.  It  measures  in  diameter  about 
one-eighth  of  an  inch,  though  at  its  inferior  extremity,  where  it  expands 
into  the  receptaculum  chyli,  it  is  somewhat  wider.  Its  walls  have  the 
same  general  structure  as  the  walls  of  the  lymphatic  vessels,  consisting 
of  three  coats — an  internal,  or  endothelial ;  a  middle,  elastic  and  nnis- 
cular  ;  and  an  external,  or  fibrous.  The  inner  surface  of  the  duct  is 
abundantly  supplied  with  valves.  This  general  duct  em])ties  into  the 
venous  circulation  at  the  junction  of  the  left  internal  jugular  and  sub- 
clavian veins. 


Lymphatic  Vessels  of  the  Head  and  Neck. 

The  lymphatic  glands  and  vessels  of  the  head  and  neck  may  be 
divided  into  a  superficial  and  a  deep  set.  The  superficial  set  may  again 
be  subdivided,  according  to  their  location,  into — 

1.  ^1  Fdcial  Group,  consisting  of  two  or  three  small  glands  situated 
in  front  of  the  ear  at  the  root  of  the  zygoma  and  upon  the  outer  aspect 
of  the  parotid  gland.  A  small  gland  is  occasionally  found  near  the  side 
of  the  root  of  the  nose,  though  the  rest  of  the  facial  region  is  singularly 
free  of  glands,  none  being  found  above  the  line  of  the  mouth  (Fig.  1 57). 

2.  ^1  Post-aural  Group,  consisting  of  three  or  four  glands  situated 
slightly  above  the  insertion  of  the  sterno-cleido-mastoid  muscle,  and  one 
other  at  the  base  of  the  occipital  bone. 

3.  A  Suhtuaxi/fart/  Group,  from  eight  to  ten  in  number,  situated 
beneath  the  base  of  the  inferior  maxillary  bone.  The  largest  of  this 
grou])  is  in  close  relationship  with  the  outer  surface  of  the  submaxillary 
salivary  gland.  This  grou])  lies  cpiite  superficially,  being  only  covered 
in  by  the  skin  and  superficial  fascia. 

4.  A  Gcrvical  Group,  more  numerous  than  the  preceding,  which  is 
arranged  along  the  course  of  the  external  jugular  vein.  At  the  inferior 
boundary  of  the  neck  these  glands  are  found  in  greatest  number,  espe- 
cially in  the  s]>ace  behind  tiu»  insertion  of  the  clavicular  portion  of  the 
sterno-cleido-mastoid  muscle.  At  this  ])()int  they  penetrate  the  dee])er 
region  of  the  chest  and  become  connected  with  the  axillary  glands. 

The  deej)  glands  may  also  be  divided,  according  to  their  location, 
into — 

1.  A  Far'utl  Group,  from  six  to  eight  in  number,  situated  in  the 
spheno-maxillary  space  and  alongside  of  the  pharyngeal  wall. 

2.  A  Cervical  Group,  located  along  the  course  of  the  carotid  artery 
and  jugular  vein,  and  extending  from  the  uj)])er  limit  of  the  neck  down- 
ward as  far  as  the  thorax. 

The  lymphatic;  vessels  of  the  head  and  neck  may  be  divided  into  a 


LYMPHATIC   VESSELS  OF  THE  HEAD  AND  NECK. 


331 


superficial  and  a  deep  set.     The  superficial  may  be  subdivided,  accord- 
ing to  their  location,  into — 

1.  A  Facial  Grroup,  which  arises  from  the  central  part  of  the  forehead 
nncl  descends  oblicjuely  along  the  course  of  the  facial  vein,  and  enters  the 
submaxillarv  glands. 


Fig.  157. 


The  Superficial  Lymphatics  :\nd  (llands  of  the  Head,  Face,  and  Neck. 

2.  A  Cranial  Group,  which  consists  of  a  temporal  and  an  occipital 
set.  The  former,  arising  from  the  superior  jiortion  of  the  cranium, 
descends  in  front  of  the  "auricle,  passes  through  the  facial  glands,  and 
finally  terminates  in  the  glands  of  the  neck  ;  the  latter,  receiving  the 
lymph  from  the  occi])ital  i^gion  of  the  cranium,  converges  and  descends 
along  the  course  of  the  occipital  artery,  and  enters  the  post-aural  glands 
on  the  mastoid  process,  and  subsequently  joins  the  lymphatics  of  the 
neck  (Fig.  158). 


332 


ANA  TOMY. 


The  deep  facial  group  of  lymphatics  has  its  origin  in  the  temporal 
lossa,  the  orbital  and  nasal  cavities,  and  the  mouth.  Some  of  the  lym- 
phatic vessels  of  the  brain-case  emerge  through  the  oval  and  spinous 
foramina  in  the  sphenoid  bone  and  join  this  series  of  lymphatics.  All 
of  the  vessels  constituting  this  series  then  pass  outward  along  the  course 
of  the  internal  maxillary  vein,  and  enter  the  glands  in  the  neighborhood 
of  the  angle  of  the  inferior  maxillary  bone. 

Fig.  158. 


The  Deep  Lyiuphaticb  and  (ilaiids  of  the  Neck  and  Thorax. 

The  deep  cranial  group  of  lymi)hatics  contains  those  vessels  which 
come  from  the  brain-case,  the  pia  mater,  and  the  arachnoid  through  the 
foramen  lacerum  jiosterius. 

The  .superficial  and  deep  lymphatics  of  the  neck,  formed  by  the  union 
of  the  facial  and  cranial  vessels,  also  receive  brandies  from  the  ton2:ue, 
pharynx,  larynx,  thyroid  body,  and  other  regions  of  the  neck.     They 


LYMPHATIC   VESSELS   OE  THE  HEAD  AND  NECK.  333 

descend  the  neck  and  follow  the  conrse  of  the  veins  and  carotid  artery. 
At  the  same  time  they  [)rugressively  decrease  in  numbers.  Those  on  the 
right  side  empty  by  a  short  trunk  into  the  right  lymphatic  duct,  which 
enters  the  venous  circulation  at  the  junction  of  the  right  internal  jugu- 
lar and  subclavian  veins.  Those  on  the  left  side  enter  the  main  tho- 
racic duct. 


PART  II. 

DENTAL  ANATOMY. 


TEETH  OF  THE  INVERTEBRATES. 
TEETH  OF  THE  VERTEBRATES. 


THE  TEETH  OF  INVERTEBRATES. 

By  W.  H.  DALL. 


Almost  every  large  group  of  organisms  below  the  vertebrates,  until 
we  reach  the  Molluscoidea  and  lower  radiated  animals,  exhibits  in  some 
of  its  members  one  form  or  another  of  j)rehensile  or  raasticatory  appa- 
ratus connected  with  the  alimentary  canal.  None  of  these  exhibit  true 
homologies  with  vertebrate  teeth,  though  sometimes  presenting  remark- 
able similarity  to  the  latter  in  external  form.  Before  considering  these 
organs  in  detail  it  is  desirable  to  formulate  some  appropriate  definition 
which  shall  distinguish  between  mandibular  and  dental  appendages  in 
the  sense  in  wliich  the  latter  may  be  said  to  exist  in  the  invertebrates. 

For  our  purposes  we  shall  consider  as  teeth  only  such  appendages  as 
spring  from  the  interior  of  the  oral  orifice ;  are  clitferentiated  by  their 
chemical  constitution  and  mechanical  attachments  from  the  surrounding 
tissues ;  perform  their  functions  in  a  vertical  plane  as  distinguished 
from  a  lateral  or  horizontal  one ;  and  are  opposed  either  to  similar 
teeth,  to  a  superior  mandible,  or  to  the  roof  of  the  oral  cavity. 

This  excludes  the  modified  limbs  which  form  the  paired  and  laterally 
opposed  oral  appendages  of  insects  and  Crustacea,  and  a  great  variety  of 
other  appendages  which  are  more  naturally  classed  as  jaws,  mandibles, 
fangs,  or  stomacholiths.  While  not  homologous,  many  of  these  present 
such  striking  similarity  of  form  with  vertebrate  oral  appendages  that 
the  same  vernacular  name  seems  more  appropriate  than  a  new  desig- 
nation. No  one  would  hesitate  to  call  the  mandibles  of  a  parrot  or 
hawk  and  those  of  the  cuttlefish  by  the  same  name,  even  if  they  were 
not  aware  that  they  are  put  to  an  identical  use. 

Throughout  the  invertebrates  teeth  are  dermal  structures,  however 
much  special  modifications  may  mask  their  relations.  They  may  con- 
sist of  calcified  connective  tissue,  of  horny  matter,  or  of  chitin  or  an 
allied  substance.  Chitin  and  substances  with  very  similar  qualities  are 
almost  characteristic  products  of  invertebrate  organization.  Of  them 
are  formed  the  wing-cases  of  beetles  and  most  of  the  hard  elastic  tissues 
of  the  exterior  of  insects.  A  chitinoid  substance  is  insoluble  in  boiling 
liquor  potassoe,  and  hardly  affected  by  immersion  in  the  strongest  acids. 
Its  lightness,  elasticity,  and  strength  fit  it  remarkably  for  the  work 
required  of  the  insect  exoskeleton  and  similar  uses.  The  teeth  and 
jaws  of  mollusks,  the  nippers,  mandibles,  and  setse  of  worms,  and 
many  similar  invertebrate  organs,  are  composed  to  a  greater  or  less 
extent  of  chitinoid  material.  This  aids  materially  in  the  preparation 
of  these  structures  for  microscopical  examination  and  study.  By  heatr 
Vol.  I.— 22  337 


338 


DENTAL  ANATOMY. 


ing  in  potash  solution  tliey  can  be  freed  with  little  trouble  from  adhe- 
rent muscles  oc  other  organic  material.  Chitinous  substances  are,  how- 
ever, rather  difficult  to  stain,  and  in  time,  unless  naturally  colored,  become 
in  Canada  balsam  almost  transparent.  The  student  who  may  wish  to 
preserve  an  interesting  specimen  in  a  permanent  mount  for  the  micro- 
scope should  bear  this  in  mind,  and,  if  necessary,  use  some  other  medium. 
Part  of  the  difficulty  about  stainiug  may  be  met  by  mounting  in  a  tinted 
medium,  which  will  then  contrast  with  the  object  itself.  AVith  regard 
to  the  teeth  and  jaws  of  mollusks,  special  details  will  be  mentioned  far- 
ther on.  Many  of  these  appendages  are  so  thick  or  of  such  contorted 
form  as  to  require  a  dee])  cell  and  low  poAvers  in  order  to  bring  the 
wliole  in  focus  at  once.  The  beauty  and  multitudinous  variety  of  these 
organs,  and  the  fact  that  they  are  within  easy  reach  of  anybody,  make 
them  very  attractive  objects  for  the  microscopist,  who  has  a  wide  field 
for  investigation  in  their  study. 

In  the  annelids,  so-called  teeth  occur  in  many  groups,  but,  on  the 
whole,  partake  rather  of  the  nature  of  jaws  than  teeth,  though  fre- 
quently double  on  each  side,  or  even  more  numerous.  This  group  com- 
prises most  of  the  creatures  commonly  called  worms,  as  well  as  the 
leeches,  etc.  Their  bodies,  as  well  shown  in  the  common  earth-worm, 
are  divided  into  more  or  less  well-defined  riugs  of  muscular  tissue, 
which  correspond  internally  to  segments,  often  more  or  less  partitioned 
off  from  each  other.  These  rings  or  aunulse  for  the  most  part  contain 
successive  groups  of  similar  organs,  but  the  anterior  segments  are  usually 
modified  to  bear  sjjecial  organs. 

In  general  the  jaws  are  developed  on  the  second  or  buccal  segment, 
or  on  a  proboscis  which  is  itself  an  ajipendage  of  this  segmeut,  and  may 

be  protruded  from  the  mouth  to  a  con- 
siderable distance.  They  are  chitinous, 
most  commonly  paired,  lateral  and  oppo- 

FiG.  160. 


Fig.  159. 


Nereis  nwrrjaritacen,  head 
■n-ilh  ])rotrude<i  jaw-appa- 
ratus of  the  pharynx,  Irom 
the  dorsal  surface  ( after  M. 
Kdwards) :  A',  jaws;  /'.ten- 
tacles ;  p,  palpi ;  l-'c,  tenta- 
cular cirri  (from  Claus's 
Zoology). 


a,  cephalic  rcRion  of  the  medicinal 
leech  (the  three  jaws  are  visible) ;  //, 
one  of  the  jaws  isolated,  with  the 
finely-serrated  free  edge. 


site,  of  almost  infinitely  varied  form,  resembling  in  a  general  way  the 
maxillae  of  insects,  and  mimicking,  in  miniature,  combs,  saws,  rasps, 
claws,  etc.  etc. 

In  the  leeches  (Hiruclince)  the  mouth  is  provided  with  three  lenticu- 
lar jaws,  with  the  ])rojecting  edges  finely  serrate,  and  having  a  partly 
rotatory  motion  about   a  point  central  to  the  three.     The  medicinal 


THE  TEETH  OF  INVERTEBRATES. 


339 


leech  has  two  rows  of  serrations  on  each  jaw ;  otlier  species  doubtless 
vary  in  the  buccal  armature. 

In  all  the  annelids  reparation  of  amputated  parts,  including  the 
buccal  organs,  is  common  and  ap])arently  easy.  These  animals  have 
existed  from  very  early  geological  time,  and  small  bodies,  supposed  to 
be  the  fossilized  jaws  or  "  teeth  "  of  annelids,  have  been  found  in  the 
Palaeozoic  rocks  of  both  Europe  and  America. 

In  insects  no  true  teeth  exist.  Mandibles  and  jaws  occur  in  infinite 
variety,  usually  essentially  lateral  in  position  and  motion,  and  easily 
observed,  especially  in  such  forms  as  the  larger  grasshoppers  and  beetles. 
Among  the  spiders  teeth  are  equally  absent,  the  poisonous  fangs  being 
merely  modifications  of  limbs  or  segmental  appendages,  as,  indeed,  are 
nearly  all  the  buccal  appendages  of  the  annulated  or  articulated  inver- 
tebrates. 

Among  the  Crustacea,  lobsters,  shrimps,  crabs,  etc.,  the  maxillary 
organs  are  but  modifications  of  entire  limbs  translated  from  the  locomo- 
tive series  and  set  apart  as  special  mouth-organs.  Most  of  the  Crustacea 
have  a  suitable  masticatory  apparatus  of  this  sort,  but  in  certain  para- 
sitic forms  become  organs  of  attachment  or  are  altogether  wanting.  If 
we  examine  the  digestive  organs  of  one  of  the  higher  Crustacea,  such  as 
the  crab  or  lobster,  we  find  the  stomach  divided  into  two  regions,  the 
anterior  or  cardiac  and  the  posterior  or  pyloric  region.     These  are  sepa- 

FiG.  161. 


(From  T.  Rymer  Jones's  Outline  of  the.  Animal  Kingdom.)  Oral  Apparatus  of  Ec.hiniis:  a  a  a  a  a, 
pyramidal  pieces  forming  the  lantern  of  Aristotle ;  h  ft,  internal  projections  from  shell ;  c  c  c  c  c, 
te-th  enclosed  in  their  sockets  ;  <l  </,  interposed  osseous  pieces ;  e  e,  curved  processes ;  //,  g  g,  k  h, 
i  i,  k  k,  muscular  fasciculi  for  the  movements  of  the  jaw. 

rated  more  by  their  functions  than  by  their  form.  The  anterior  part  is 
provided  with  certain  masticatory  appendages  or  stomacholiths,  often 
termed  teeth,  though  more  analogous  to  a  sort  of  calcareous  gizzard. 
These  consist  of  several  calcareous  pieces,  moved  by  appropriate  mus- 
cles, inserted  in  the  membranous  wall  of  the  stomach,  armed  with  a 


uo 


DENTAL  ANA  TOMY. 


Fig.  162. 


smooth  median  plate  and  lateral  molar-like  organs,  whose  mimetic 
resemblance  to  the  molar  teeth  of  some  forms  of  Mammalia  affords  a 
beautiful  illustration  of  the  way  in  Nvhich,  through  the  selective  influ- 
ence of  similar  functions,  analogous  structures  may  be  built  up  in  organs 
which  have  no  homology  whatever.  Two  smaller  points,  bicuspid  in 
the  lobster,  tricuspid  in  the  crab,  complete  the  calcareous  apparatus ;  in 
the  pylorus  a  series  of  fine  hairs  is  placed,  which  doubtless  act  as  a 
strainer,  preventing  the  escape  of  coarser  particles  of  food  until  they 
have  been  sufficiently  comminuted  by  these  grinding  organs.  The 
"  lady  "  in  the  lobster,  with  which  children  amuse  themselves,  is  part 
of  this  apparatus,  which  of  course  diifers  in  detail  in  different  genera 
and  species. 

The  denticulations  on  the  claws  of  Crustacea  have  of  course  no  claim 
to  be  considered  as  teeth,  though  they  assist  in  breaking  up  the  food. 

Among  the  echinoderms,  sea-urchins,  starfish,  crinoids,  etc.  certain 
forms  possess  an  apparatus  commonly  known  as  Aristotle's  lantern, 
which  contains  what  may  fairly  be  regarded  as  true  teeth  (Fig.  161). 
Among  the  sea-urchins  the  Uchinidce  and  Ch/peastrkke  possess  such  an 
apparatus,  the  mouth  being  central ;  in  the  Hpatangkke  the  mouth  is 
at  one  side,  and  there  are  no  teeth.  Among  the  other  echinoderms, 
the  starfishes  [Astei'icke)  have  no  teeth;  the  brittle  stars  (Ophurkkc) 
have   short,   flat,    calcareous   processes  which  are   moved   by  muscles 

and  have  the  name  of  pake 
angularcs.  They  are  attached 
to  the  mouth-skeleton,  and 
are  supposed  to  be  used  for 
mastication. 

Among  the  recent  crinoids 
or  sea-lilies  the  mouth  is 
closed  by  lobes  of  the  peri- 
some,  which  may  contain 
calcareous  plates  hardly  to 
be  called  teeth.  The  other 
groups  are  edentulous. 

The  singular  and  remark- 
able mouth-apparatus  (Fig. 
1  (i2)  in  our  common  sea-urchin 
or  sea-chestnut  (Echinus)  has 
been  observed  by  every  one 
Avho  has  passed  any  time  at 
the  seaside.  It  is  frequently 
detached  from  the  test  of  the 
animal,  and  retains  its  form  for  some  time,  even  while  washed  about  by 
the  waves  on  the  l)each.  It  is  very  complicated  in  its  arrangement, 
but  in  essentials  consists  of  five  hard,  calcareous,  wedge-shaped  sockets 
or  alveoli  (Fig.  162,  b,  h),  each  containing  one  porcelainous  chisel- 
shaped  tootii.  _  The  teeth  (Fig.  162,  a,  a)  are,  like  those  of  rodents, 
softer  on  tlie  inner  than  on  the  outer  side,  and  therefore  in  wearing 
always  j)reserve  a  sharp  edge.  The  union  of  the  alveoli  produces  a 
pentagonal  cone  with  its  apex  pointing  downward,  and  formed  by  the 


(rroni  the  same  Author.)  Bental  system  of  Kc/iinnx :  1, 
represents  three  of  the  pyramidal  pieces  foriDinR  the 
"  lantern  of  Aristotle,"  in  situ:  a  a,  cutting  extremities 
of  the  incisor  teeth,  which  are  of  enamel-like  hardness; 
"',  «',  «',  fibrous  roots  of  the  same;  /*  b,  opposed  flat  sur- 
faces of  the  jaws ;  d  d,  arched  processes.  2,  an  isolated 
pyramid  :  e,  its  e.\teriial  surface ;  a,  same  as  in  1. 


THE  TEETH  OF  INVERTEBRATES.  341 

coming  together  of  the  points  of  the  five  teeth.  Each  alveokis  consists 
of  tM^o  halves  united  in  the  middle  line,  and  each  half  of  an  upper  and 
lower  portion.  In  life  the  alveolus  is  concealed  within  the  tissues,  only 
the  point  of  the  tooth  projecting.  The  socket  is  interradial  in  position 
with  relation  to  the  test  of  the  echinus,  or  opposite  the  interambulacra 
or  spaces  between  the  rows  of  walking  suckers.  Above  and  between 
the  upper  ends  of  the  alveolar  pieces  are  certain  rather  thick  radial 
pieces  called  rotulce  or  faloes,  each  of  which  in  the  Echinidce  bears  a 
bifurcated  piece  known  as  the  radius  (Fig.  162,  d,  d).  In  this  group, 
at  the  oral  end  of  the  ambulacra  (of  the  interambulacra  in  Cidaris),  are 
calcified  internal  arched  processes  called  auricalce,  each  formed  of  two 
pieces  (Fig.  161,  b,  b).  The  auriculae  are  supposed  to  be  homologous 
with  the  internal  ambulacral  ossicles  of  the  starfishes  and  ophiurans  or 
brittle  stars.  Retractor  muscles  pass  to  the  outer  edge  of  the  alveoli 
from  the  auricula ;  the  former  are  also  connected  wdth  transverse  mus- 
cular fibres.  The  oral  framework  is  also  provided  with  protractor 
muscles  proceeding  from  the  alveoli  to  the  lower  edge  of  the  corona, 
besides  special  muscles  connected  with  the  radii. 

The  food  of  the  Echinidce  consists  of  seaweed  or  small  shellfish  and 
crustaceans,  or,  in  the  case  of  those  forms  which  are  edentulous,  of  sea- 
mud  and  coral  sand,  which  contains  much  nutritive  material.  While 
the  teeth  are  useful  in  breaking  up  the  harder  parts  of  the  food,  no 
grinding  or  true  mastication  is  possible,  as  they  only  meet  near  their 
sharp  and  slender  points. 

The  study  of  this  complicated  and  wonderful  oral  apparatus,  which 
may  be  easily  indulged  in  at  any  watering-place  by  the  sea,  will  afford 
many  hours  of  amusement  and  instruction  to  the  curious  student  of 
nature. 

Among  all  the  invertebrate  animals  a  parallel  to  the  variety  in  form' 
and  importance  in  systematic  classification  of  the  teeth  of  vertebrates  is 
alone  to  be  found  with  the  Mollusca,  and  among  them  only  with  certaim 
groups. 

The  Mollusca  have  been  divided  into  two  principal  groups  by  later- 
writers — the  CepJudophora  or  Glossophora  on  the  one  hand,  and  the 
Acephala  or  Lipocephala  on  the  other.  These  have  a  general  corre- 
spondence with  the  possession  or  non-possession  of  a  "head"  or  its  con- 
comitant, a  muzzle  and  dental  apparatus.  Not  every  species  of  the 
many  thousands  which  comprise  the  Cephalophora  (whelks,  snails,  peri- 
winkles, coat-of-mail  shells,  limpets,  tooth-shells,  sea-butterflies,  nauti- 
lus, squid,  or  cuttle-  and  devil-fishes)  are  provided  with  teeth,  but  these 
special  instances  are  the  exceptions  to  the  rule.  On  the  other  hand,  no' 
single  member  of  .the  Acephala  (clams,  oysters,  mussels,  cockles,  fresh- 
water clams,  scallops,  etc.)  has  either  a  head  or  a  dental  apparatus. 

The  apparatus,  reduced  to  its  simplest  terms  (Fig.  163),  consists  of  a 
tube  entering  the  floor  of  the  gullet  in  the  median  line  behind  the  mouth, 
called  the  radulav  sac.  The  odontophore,  or  chitinous  band  upon  which 
the  teeth  are  set,  pointing  upward  and  backward  like  the  papillse  on  a  cat's 
tongue,  grows  out  of  the  radular  sac  like  a  finger-nail  from  its  sheath. 
The  odontophore  and  teeth  collectively  form  the  radula.  The  floor  of 
the  sac  is  carried  forward  by  natural  growth  in  that  direction,  bearing 


342 


DENTAL  ANATOMY. 


the  radula  upon  it,  generally  over  an  arched,  cartilaginous  mass  known 
as  the  buccal  cartilage,  and  down  to  the  front  edge  of  the  buccal  carti- 
lage immediately  behind  the  mouth.  This  serves  as  an  elastic  pad  by 
which  the  denticulate  surface  of  the  radula  may  be  pressed  against  any 
object  to  be  drilled  or  torn  with  the  teeth.  It  is  controlled  by  retractor 
and  protractor  muscles,  by  which  it  can  be  pulled  forward  into  the 
oral  opening  or  even  be  somewhat  protruded — a  fact  which  can  easily 
be  observed  by  giving  a  common  wood-snail  or  large  slug  a  bit  of  bread 

or  lettuce  to  eat.  The  tissues 
about  the  cartilage  are  so  loose 
and  flexible  as  to  offer  no  ob- 
stacle to  the  transfer.  Beyond 
this,  in  certain  groups  (as  the 
common  whelk),  the  radular 
floor,  to  which .  the  odontophore 
adheres  closely,  and  with  which 
it  moves,  may  be  so  loosely 
attached  to  the  buccal  cartilage 
as  to  slide  over  it  like  a  towel 
over  a  roller,  and,  controlled  by 
a  complicated  set  of  muscles, 
,    .  , ,   „  ,  ,     .  niay  be  made  to  move  back  and 

Sectional  Diagram  of  jNIolhiscan  Radular  Apparatus,  n     '\  i  i         • ,  i 

vertically  divided:  0,  mouth;  ?H,  jaw  or  mandible;  lortU,  Or    CVCU    gO    tliroUgll   Wltll 
/.lower  lip;  </,(/',  upper  and  lower  epidermis  of  the  •         ,  .•  .1 

iluizzle;  ff.Ruilet;  //teeth  set  on  the  odontophore,  a    SCUll-rotary    UlotlOU    UpOU    tllC 

■which   rests  on   thf^    muscular  radular  floor,  sup-  Knr>P'il     nntliinn         TIip    virlnln   in 

ported   by  the  muscular  buccal   mass,  from  which  »Jll<-<-'ti    LLlblllUll.        X  lie    ItUlUUt  HI 

extend  backward   retractor  muscles  ik,  k,).  and  in  tllis    Way    UiaV    be    made    tO    act 
■which  is  (n  imbedded  the  buccal  cartilaKe;  .v,  the        ,  "       r>   ,1  .    •  /? 

opening  of  the  radular  sac:  p,  papilla  wliich  secretes  tUC    part    Ot    the    Strip    01    Cmery 

the  teeth  and  odontophore.  ^^  ^^^^^^.^^  ^j^^j^    SOmetimeS  UScd 

in  dentistry,  only  the  rasping  effect  is  on  the  convex  and  not  on  the 
concave  side.  The  annexed  schematic  diagram  will  indicate  the  rela- 
tions of  the  parts. 

In  addition  to  the  radula,  the  mouth  of  the  cephalophorous  mollusks 
is  often  provided  with  a  chitinous'  armature  of  another  sort.  In  many 
mollusks  a  jaw  or  jaws  are  present,  which  may  be  a  strong  black  pair, 
recalling  the  jaws  of  a  parrot,  opposed  to  one  another  in  the  vertical 
line  and  largely  composed  of  a  substance  allied  to  chitin,  as  in  the 
squids  and  cuttles  (reinforced  with  calcareous  matter  in  the  case  of  the 
pearly  nautilus)  ;  or  merely  an  arch  of  delicate  chitiuous  matter  without 
a  lower  jaw,  as  in  some  ])ulmonates  ;  or  a  number  of  pieces  composing 
an  arch,  as  in  other  land-snails  ;  or  a  central  upper  piece  of  horny  mat- 
ter with  a  lateral  accessory  piece  on  each  side,  as  in  the  pond-snails 
{Limncea,   etc.).     There   are   large   groups,   however,   without  a  jaw. 


'  Tnvestifration.s  by  Tro.scliel  show  tliat  tlie  teeth  of  most  gastropods  consist  almost 
wholly  of  chitinous  matter.  The  radular  Hoor  or  ribbon  upon  which  they  are  inserted 
contains  abont  04  per  cent,  of  chitin  and  (5  percent,  phosphate  of  lime.  The  jaws  of 
JJoliiim  and  Ilrlir  pnnialia  show  a  1  or  2  per  cent,  greater  proportion  of  lime  ;  other 
helices  would  show  hardly  a  trace.  The  references  of  previous  naturalists  to  the  pres- 
ence of  iron  and  silicon  in  the  radula  is  supposed  by  Troschel  to  have  been  due  to  the 
presence  of  a  few  sand-grains  among  the  teeth  analyzed.  Slight  diflerences  doubtless 
exist  between  difi'erent  kinds  of  mollusks,  which  would  explain  the  differing  results  of 
various  analvses. 


THE  TEETH  OF  INVERTEBRATES.  343 

Some  of  the  nudibranclis,  or  naked  sea-snails,  and  cuttlefish  have  a  sort 
of  spiny  internal  collar  in  the  form  of  an  oval  ring,  as  well  as  a  well- 
marked  mandible.     The  trumpet-conch  Ym  1C4. 
(^Tiitoiilum)  has   two    heavy  black  spi- 
nous pieces  hinged  above  with  cartilage. 
The  forms  of  the  jaw  are  niitnerous  and 
afford  good  characters  for  classification, 
but  they  all  differ    from  the  jaws  of 
other  invertebrates,  in  that  the  motion 
and  action  of  the  jaws  are   essentially 
vertical,  and  not  from  the  sides  toward     jaw  of  V(/to(/7<w, showing  one  of  the  two 

,1  •  1  II  •        •  J.  1  1*  1  pieces  of  which  the  arch  is  composed. 

the  middle,  as  in  insects  and  annelids,        ^ 

though  the  accessory  pieces  may  have  a  lateral  motion.     In  some  of  the 

Glossophora  there  is  also  a  gizzard,  which  may  be  supplied  with  small 

calcareous   plates   or   stomacholiths,  recalling  the  "  gastric  teeth "  of 

Crustacea. 

Returning  to  the  radula,  we  find  in  the  innermost  extreme  of  the 
of  the  radular  sac  a  papilla  which  forms  the  matrix  of  the  teeth 
and  odontophore.  This  latter  organ,  whose  situation  has  already  been 
described  generally,  consists  of  a  ribbon  of  chitin  longitudinally  divided 
into  three  areas.  The  central  area  or  rhachls  is  bordered  on  each  side 
by  a  margin  or  pleura,  which  in  many  cases  is  bent  up  on  each  side  so 
as  to  form  a  gutter,  with  the  rhachis  at  the  bottom.  In  front  of  the 
buccal  cartilage  the  pleurpe  are  much  widened  laterally,  so  as  to  cover 
and  defend  the  front  of  the  cartilage.  In  tiie  Toxoglossa  the  teeth  are 
i'&\v  in  number,  and  appear  to  be  inserted  directly  on  the  muscular 
radular  floor  Avithout  an  odontophore.  The  teeth  are  cemented  to  or 
spring  from  the  odontophore,  in  most  cases  having  their  points  directed 
upward  and  backward.  They  are  arranged  in  longitudinal  and  trans- 
verse rows,  the  former  in  straight  lines ;  the  transverse  rows  being  gen- 
erally curved  or  angulated  symmetrically  on  each  side  of  the  median 
line  or  tooth.  Any  of  the  longitudinal  rows  may  be  absent.  In  a  very 
few  genera  the  radula  is  absent  or  the  odontophore  is  edentulous. 

The  teeth  are  composed  of  a  base,  a  shank  or  stem,  and  a  cutting  edge 
or  point,  the  latter  simple  or  variously  denticulated.  The  base  is  con- 
spicuous in  some  forms,  hardly  evident  in  others  ;  in  some,  the  surface 
of  the  odontophore  is  elevated  into  a  sort  of  boss  beneath  each  tooth, 
and  among  the  limpets,  etc.,  such  bosses  sometimes  exist  without  a  tooth 
upon  them.  The  shank  may  be  short  or  long,  simple  or  curiously  orna- 
mented, or  perforated.  The  form  of  the  cutting  points  is  very  varied, 
and  they  are  sometimes  furnished  with  a  minute  brush-like  appendage. 
As  a  rule,  the  carnivorous  forms  have  simpler  and  more  claw-shaped 
teeth. 

The  central  tooth  of  each  transverse  row  is  normally  symmetrical, 
and  the  succession  of  them  forms  the  median  longitudinal  row.  These 
teeth  are  called  median  or  rhachidian  teeth.  They  are  generally  pres- 
ent, but  are  absent  in  a  number  of  genera.  On  each  side  of  the  median 
tooth  are  the  lateral  or  pleural  teeth.  These  are  asymmetrical,  being 
rights  and  lefts,  and  having  a  tendency  to  bend  toward  the  median  line. 
The  number  of  longitudinal  rows  of  laterals  varies  a  good  deal.     They 


344  DENTAL  ANATOMY. 

are  most  numerous  in  the  land-snails,  and  may  be  wholly  absent  or 
reach  into  the  hundreds.  Outside  of  the  lateral  teeth  on  each  side  are 
frequently  several  series  of  flat,  plate-like,  or  slender  spiny  teeth,  which 
are  called  uncini.  They  too  may  be  very  numerous,  especially  in  the 
veo;etable-feedintr  sea-snails,  or  mav  be  wholly  absent.  But  in  normal 
cases,  when  one  series  is  absent  on  one  side  of  the  median  line  it  is  also 
absent  on  the  other,  so  that  the  radula  with  respect  to  the  teeth  is  bilat- 
erally symmetrical.  Abnormal  radulse  are  met  with  where  the  teeth 
will  be  deformed  or  asymmetrical  ;  in  normal  radulse  the  anterior  teeth 
are  usually  broken  and  worn  with  use,  and  those  in  the  posterior  extreme 
are  soft,  light-colored,  and  half  formed,  each  longitudinal  row  of 
teeth  being  secreted  by  the  same  })air  of  the  radular  papilla ;  if  it  is 
abnormal  at  all,  the  abnormality  extends  through  the  whole  row  during 
the  life  of  the  mollusk.  The  adult  perfect  teeth  vary  from  nearly  trans- 
parent to  an  amber-yellow  or  reddish-brown,  and  sometimes  the  cutting 
points  are  black.  In  any  large  whelk  they  are  easily  visible  to  the 
naked  eye ;  in  large  cuttlefish  the  radula  may  be  an  inch  w'ide.  On 
the  other  hand,  in  some  minute  land-shells  ( Vertigo,  etc.),  where  the 
whole  shell  is  hardly  bigger  than  a  pinhead,  high  powers  are  needed  to 
observe  them.  The  radula  may  be  quite  short,  reduced  even  to  a  single 
pair  of  teeth  in  a  few  cases,  while  in  the  limpets  it  is  very  long,  and  in 
one  periwinkle  {Tectarius pagoda)  it  has  been  found  to  be  seven  times 
as  long  as  the  len2:th  of  the  animal's  body.  Such  radulse  are  of  course 
always  coiled  up,  and  only  the  anterior  portion  comes  into  use  at  any 
one  time. 

The  form  and  arrangement  of  the  teeth  are  of  great  use  in  classifica- 
tion— a  fact  discovered  by  Prof.  S.  Loven  of  Stockholm  in  1846.  Since 
this  time  many  authors  have  studied  them,  and  great  advances  have 
thus  been  made  in  the  systematic  arrangement  of  mollusks  ;  but  the 
number  of  species  is  so  great  and  the  workers  are  so  few  that  a  vast 
amount  remains  to  be  done  before  we  can  consider  the  classification  of 
our  American  species  to  be  placed  on  a  sound  foundation.  The  great 
development  of  the  groups  of  fluviatile  and  land  snails  [Helix,  Limncea, 
Physa,  Yiripara,  Amnicola,  etc.  etc.)  in  the  woods  and  fresh  waters  of 
the  United  States  puts  it  in  the  po"\ver  of  any  one  possessed  of  a  toler- 
able microsc()])e  to  add  solid  facts  to  the  treasury  of  science.  Trusting 
that  this  brief  survey  f>f  the  subject  may  lead  some  reader  to  interest 
himself  in  it,  I  add  the  following  instructions  for  examining  the 
radula  of  mollusks: 

In  large  snails  the  radula  and  buccal  mass  may  be  easily  dissected 
out ;  in  small  ones  the  anterior  part  of  the  body,  and  in  minute  ones  the 
w^hole  body  (after  breaking  the  shell),  may  be  taken.  With  a  i)air  of 
forceps,  a  test-tube,  an  alcohol  lamp,  some  watch-glasses,  and  some 
needles  fastened  in  little  wooden  handles,  a  little  caustic  potash,  and  a 
microscope,  the  student  is  prepared  for  w'ork. 

The  radula,  or  the  part  of  the  snail  containing  it,  should  be  dropped 
into  al)()ut  a  teaspoonful  of  half-saturated  solution  of  caustic  potash  in 
water  in  the  test-tube.  This  may  then  be  gently  boiled  over  the  lamp  ; 
too  violent  boiling  may  spill  the  contents  of  the  tube.  Held  in  the 
forceps,  the  tube  may  be  moved  in  and  out  of  the  flame  as  experience 


THE  TEETH  OF  INVERTEBRATES.  345 

will  soon  indicate.  In  a  few  moments  the  soft  parts  disappear,  leaving 
the  jaw  and  radula  in  the  solution,  which  may  be  poured  into  a  watch- 
glass  and  the  radula  taken  out  on  the  point  of  a  needle,  washed  in  pure 
water,  and  then  put  under  the  microscope.  It  will  be  found  so  curved, 
except  in  very  small  mollusks,  as  to  need  the  presence  of  a  cover-glass 
to  bring  it  into  focus  :  an  ordinary  live-box  answers  well.  It  may  be 
best  examined  in  water  as  a  medium.  To  get  at  the  form  and  number 
of  the  separate  teeth,  it  will  generally  be  necessary  to  tease  the  radula 
to  pieces  with  the  points  of  two  needles.  When  the  radula  is  micro- 
scopic and  cannot  be  seen  in  the  liquor  potassse,  the  watch-glass  may  be 
put  on  the  stage  and  twirled  round  a  little,  when  all  the  solid  particles 
will  be  impelled  toward  the  centre  and  the  radula  found  and  picked  out 
under  the  microscope. 

After  drawing  the  various  parts,  so  as  be  able  to  construct  a  diagram 
of  the  teeth,  the  object  should  be  preserved  in  a  little  tube  or  vial  with 
some  weak  alcohol  and  a  tight  stopper  (rubber  is  the  best),  and  suitably 
labelled ;  or  it  may  be  mounted  on  a  slide  in  the  usual  way,  avoiding 
Canada  balsam,  which  will  soon  make  it  invisible  unless  stained. 

The  number  of  transverse  rows  of  the  teeth  is  of  slight  importance 
compared  with  the  exact  representation  diagrammatically  of  a  single 
transverse  row  or  of  the  median  tooth  and  one  side  of  the  row,  which 
is  in  most  cases  all  that  is  required. 

The  jaw  is  often  too  horny  to  bear  much  treatment  with  potash ;  the 
teeth  (except  in  some  marine  forms)  are  much  more  refractory ;  experi- 
ence will  soon  guide  the  student,  who  may  practise  on  common  species 
until  he  gains  proficiency.  The  character  of  the  jaw,  especially  of  the 
land-snails,  is  also  important  for  classification,  and  it  should  be  care- 
fully delineated. 

As  the  number  of  transverse  rows  may  be  large,  and  the  number  of 
teeth  in  each  row  sometimes  great,  the  total  number  of  teeth  is  occa- 
sionally surprising,  and  has  been  computed  for  some  species  at  .from 
twelve  thousand  to  forty  thousand. 

To  describe  the  teeth  of  mollusks  in  detail  would  require  several  vol- 
umes,^ even  in  the  present  imperfect  state  of  our  knowledge.  The 
annexed  illustrations  will  give  a  general  idea  of  their  character  in  some 
of  the  chief  groups  of  mollusks.^ 

It  is  a  remarkable  fact  that  if  we  divide  the  crawling  mollusks,  or 
Gastropoda,  into  two  great  groups,  one  containing  the  hermaphrodite 
and  the  other  the  unisexual  forms,  we  shall  find  that  in  the  former 
{Monceca)  the  auditory  sacs  contain  numerous  small  otoconia,  and  the 
form  of  the  radula  is  short  and. broad,  the  pleurae  imperfectly  distin- 
guished from  the  rhachis,  and  the  teeth  usually  numerous  and  possess- 

^  Much  assistance  may  be  gained  from  Troschel's  Gebifts  der  Schnecken,  Berlin,  1856- 
80,  and  in  tlie  works  of  Binney,  Bland,  Stimpson,  and  others  on  the  land-  and  fresh- 
water shells  of  the  United  States,  published  by  the  Smithsonian  Institution  at  Wash- 
ington. Woodward's  Munnxd  of  Eecent  ami  Fossil  Shells  may  also  be  advantageously 
consulted.  These  are  all  cheap  works.  Keferences  to  other  literatin-e  of  the  subject 
may  be  found  in  the  annual  volumes  of  the  Zooloyical  Record,  published  by  Macmil- 
lan,  London. 

^  The  figures  are  placed  in  the  text  as  if  fronting  the  observer,  with  their  cutting 
]ioints  upward  as  in  life  (except  Fig.  106, i ;  the  right  side  of  the  radula  is  the  left  side 
of  the  figure  in  each  case. 


346 


DESTAL  AXATO:iIY. 


ing  a  general  similarity  to  one  another  on  either  side  of  the  rhachidian 
row.  In  the  mollusks  where  the  sexes  are  divided  (Dioeca)  we  find 
single  otoliths  in  the  auditory  sac,  and  the  radula  tending  to  a  more 
long  and  narrow  form,  with  the  lateral  teeth,  in  general,  less  numerous 
and  showing  much  more  diversity  of  form  among  themselves.  To  these 
generalizations  there  are  a  few  exceptions,  as  in  most  laws  of  wide  appli- 
cation, but  which  may  be  accounted  for  on  other  grounds.  The  former 
type  of  dentition  has  been  termed  "  pavemental,"  as  recalling  the  uni- 
form blocks  of  a  granite  pavement,  and  the  other  "  ribbon-"  or  "  strap- 
like." 

The  highest  type  of  dentition  is  that  which  has  been  called  toxoglos- 
sate  (or  arrow-toothed),  and  which  consists  of  two  longitudinal  rows  of 
slender  hollow  or  grooved  teeth,  each  row  set  on  a  slender,  flexible  chit- 
inous  thread,  apparently  representing  the  pleurte  of  the  odontophore. 
Each  tooth  is  usually  provided  with  a  duct,  which  conveys  a  poisonous 
fluid  to  near  the  point,  and  the  latter  is  frequently  barbed  or  arrow- 
shaped,  from  which  the  name  is  derived.  Examples  of  this  group  are 
Conus  and   Bela,  both   marine  forms,  the  former  tropical,  the  latter 


Fig.  166. 


Fig.  165. 


Teeth  of  Bela. 


Teeth  of  Convs,  showing  barbs  and  poison-duct. 


northern,  in  distribution.  The  animal  of  Conns  milieus  of  the  Moluc- 
cas can  give  a  severe  bite.  Admiral  Sir  Edward  Belcher  of  the  British 
navv  was  bitten  by  one  of  them  as  he  picked  it  out  of  the  water,  and 
compared  the  acute  pain  which  followed  to  the  burning  of  phosphorus 
under  the  skin.  The  bite,  which  was  soon  followed  by  a  kind  of  blister, 
Avas  small,  triangular,  and  deep.  Troschel  ^  has  described  the  apparatus 
of  the  gland  and  duct. 

The  Toxoghssa  have  no  rhachis  or  rhachidian  tooth,  and  no  jaws  ;  in 
some  of  them  the  series  is  reduced  to  a  single  pair  of  teeth,  and  for  a 
time  these  were  supposed  to  be  edentulous. 

Next  to  the.se  come  the  Rhachiglossa,  of  which  the  typical  forms 
(  Voluta)  have  only  a  rhachidian  tooth,  but  the  larger  number,  such  as 

Fig.  167. 


Fig.  169. 


Rhachiglossate  Teeth: 2  Fig.  \C,7.  .Single  ihachidian  tooth  of  rVw/a.— Fiir.  K.R.  Transverse  series  in 
Ci/iwdu)ita.— Fig.  109.  Transverse  series  in  Fusus  antiqui'is. 

^  Gfh.  rier  Schneckrn.  ii.,  1S66.  p.  15  rf  .•'rq. 

'^  All  the  figures  of  teeth  show  single  transverse  rows,  unless  otherwise  stated. 


THE  TEETH  OF  INVERTEBRATES. 


347 


the  common  whelk  {Buccinum  ;  Fums,  and  Cijnodonta  are  also  examples) 
have  one  lateral  tooth  on  each  side  of  the  rhachidian.  These  teeth  are 
straight,  are  usnally  prettily  dentioidated  on  the  entting  edge,  and  the 
radula  is  long  and  strap-like.  The  jaw  is  represented  by  two  lateral 
rndiments,  as  in  the  next  group.  There  are  a  few  exceptional  cases 
where  the  tooth  on  the  rhachis  is  reduced  to  an  edentulous  flat  ])late. 
The  bases  of  the  teeth  point  forward  in  this  group. 

The  Tcenioglossa  (bent-toothed)  are  a  very  extensive  assembly,  which, 
amongst  others,  contains  the  largest  part  of  our  gill-breathing  fresli- 


FiG.  170. 


Fig.  171. 


Tfenioglossate  Teeth.  Fig.  170.  Teeth  o{  Rissoa— Fig.  171.  Teeth  of  Vivipara. 

water  snails.  The  teeth  are  bent  so  that  their  cutting  edges  turn  toward 
the  base  of  the  tooth,  which  is  con.se(|uently  set  on  the  odonto})hore  with 
the  base  as  well  as  the  point  turning  backward,  as  otherwise  the  crea- 
tures would  bite  out  of,  instead  of  into,  their  own  throats.  They  have 
a  rhachidian  and  three  lateral  teeth  on  each  side  of  it,  and  in  a  few 
cases  a  few  uncini,  but  these  are  very  exceptional.  Rlssoa  and  Vivipara 
are  good  examples  of  this  sort  of  dentition. 

A  small  group  which  has  been  called  Ptenoglossa  (feather-toothed) 
is  generally  supposed  to  lie  between  the  Rhachi-  and  Tcenioglossa.     Sca- 


\^AM 


Fig.  172. 


"j^^ 


Ptenoglossate  Teeth :  teeth  of  Scalaria. 

laria,  or  the  wentle-trap,  is  an  example  of  this  kind.  The  animals  are 
marine,  carnivorous,  and  have  numerous  slender  similar  lateral  teeth 
with  a  bare  rhachis  and  no  uncini. 

The  Rhiphidoglossa  (needle-toothed)  comprise  an  immense  variety  of 
marine  snails  and  a  few  operculated  land-  and  fresh- water  snails,  such 
as  Helicina,  Neritina,  Gibhula  and  Haliotis.     The  name  is  derived  from 


Rhiphidoglossate  Teeth  ;  Teeth  of  Gibbula. 

the  immense  number  of  needle-like  uncini  which  exLst  in  many  of  the 
species.  The  rhachidian  is  usually  present ;  the  number  of  laterals  is 
variable ;  the  uncini  always  numerous  and  similar.    They  are  set  on  the 


348 


DENTAL  ANATOMY. 


odontophore  as  in  the  T(eniofjlossa.  In  this  group  most  of  the  species 
have  a  well-developed  mandible  or  jaw,  usually  hinged  in  the  middle 
line  with  a  softer  cartilaginous  portion. 


Fig. 174 


Ehiphidoglossate  Teeth  :  Teeth  of  Haliotls. 


The  last  of  the  great  groups  among  the  dioecious  mollusks  is  that  of 
the  Docofjlossa  (plate-  or  chevron-toothed),  which  includes  the  limpets, 
and  is  divided  into  three  principal  subdivisions — one  [Acmcea,  etc.) 
without  a  rachidian  tooth,  and  rarely  with  uncini ;  another  (Patella, 
etc.),  with  well-developed  uncini  and  laterals,  and  generally  no  rachid- 


FlG.  1 


Fin.  175. 


Fig.  176. 


Docoglossate   Teeth:   Fig.  ITo. — Teeth  of  Leneta  fvlra.—Yig.  116.  Teeth  of  Acmasa  virginea. — Fig.  177. 

Teeth  of  Patella  vulgala. 

ian  ;  the  third  (Lepcta),  Avith  a  large  rhachidian,  without  laterals,  but 
having  uncini.  All  these  forms  have  a  well-developed  jaw,  and  all  are 
marine.     They  are  very  archaic  in  their  characters. 

It  merely  remains  to  indicate  the  types  of  dentition  among  the  her- 
maphrodite mollusks,  the  majority  of  which  are  air-breathers,  but  which 
have  also  many  marine  representatives,  and  a  few  which,  like  Limncca, 
the  conmion  pond-snail,  breathe  air,  but  live  in  the  water,  or,  like 
Siphonaria,  live  by  the  borders  of  the  sea,  and  are  prepared  with  gill 
and  lung  to  breathe  Avhatever  comes  handiest. 

The  Helices  (which  are  found  under  rotten  logs,  etc.  in  almost  any 
woodeo  place,  and  are  recognizable  by  their  depressed  sjiiral  shell  and  slug- 
like body)  have  a  tyjiically  pavement-like  dentition.  This  resemblance  is 
common  to  many  allied  groups,  such  ii'ri  AcJiafina,  SipJwnaria,  Succinea, 
etc.,  and  the  pond-snails,  Lhmum,  Planorbis,  and  others.  The  most 
interesting  and  little  known  are  the  Phj/sas,  a  group  of  beautifully  pol- 
ished pond-snails  with  a  sinistrally  wound  shell. 

The  annexed  figures  indicate  the  character  of  the  jaw  and  teeth  in 
several  of  the  air-breathing  mollusks.     In  some  others  the  jaw  is  formed 


THE  TEETH  OF  INVERTEBRATES. 


349 


of  several  pieces,  more  or  less  overlapping  and  making  the  arch  flexible, 
thus  facilitating  the  protrusion  of  the  buccal  mass  in  feeding.     The 


Fig.  178. 


Fig.  179. 


Fig.  181. 


Jaws  of  Pulmonates  :  Fig.  178.  .Taw  of  Tthonnophorns. — Fig.  179.  Jaw  of  ^riora.— Fiff.  180.  Jaw  of  G/«/)- 
tiMlonid. — Fig.  isi.  Jaw  ot  Zunites. — Fig.  182.  Jaw  (A)  of  Geomalaeus ;  B,  rachidiau  and  two  lateral 
teeth;  C,  outer  laterals. 

pieces  are  united  by  strong  muscular  tissue.     In  many  of  the  marine 
forms  the  arch  of  the  jaw  is,  as  it  were,  hinged  at  the  keystone  by  car- 

FiG.  183. 


j^..,-,aM..,v,^i.,v,o,^;v.u-L^-<-i-|-'i-ivi'i-i-i-!,i*i---   L-!:r.-i=y-' 


Fig.  184. 


2       « 


p)  \/%r'^^^'^w? 


^^ 


^^^ 


Fig.  185. 


^©S§0S^@9^9tZSS"2Q 


Fig.  186. 


'£)QiJJJM^^MWJ^ 


Teeth  of  Pulmonates:  Fig.  183.  Teeth  of  A chafhw.— Fig.  184.  Teeth  of  Siphonarin.—Tig.  IS.".  Teetn 
of  Siicclnea.— Fig.  l-«6.  Teeth  of  Linnxsn  ;  c,  rachidian  ;  /,  lateral  teeth.  In  these  figures  the  teeth 
are  represented  as  if  seen  from  above  and  behind. 

tilage,  doubtless  for  the  same  purpo.se.     In  the  pond-snails  (Limncca) 
the  arch  has  two  small,  delicately-hinged  lateral  pieces,  which  have  a 


350  DENTAL  ANATOMY. 

lateral  movement  in  connection  with  the  vertical  movement  of  the  true 
mandible. 

Having  indicated  the  character  of  the  teeth  in  divers  forms  of  mol- 
luscan  animals,  it  remains  only  to  refer  to  their  functions.  As  already 
stated,  they  are  used  for  masticating  vegetable  or  tearing  animal  matter 
on  which  the  creatures  feed,  and,  in  some  cases,  as  weapons  of  offence 
and  defence.  They  have  still  another  use — that  of  drilling  through  hard 
substances,  such  as  the  shells  of  other  mollusks  for  the  purpose  of 
devouring  the  inhabitant.  This  causes  the  small  round  holes  so  com- 
monly seen  in  dead  shells  on  the  beach.  This  process  has  been 
watched,  and  is  very  slow  in  most  cases,  two-  or  three  days  being 
required  by  a  Purpura  to  drill  through  a  small  clam-shell.  Many 
young  oysters  are  annually  destroyed  in  this  way  by  a  mollusk  known 
to  the  oyster-men  as  the  "  drill."  Some  of  the  tropical  forms  secrete 
an  acid  which  nuist  hasten  the  process  a  good  deal,  but  in  most  cases 
the  work  is  done  by  pure  friction  with  the  raclula  in  a  rotary  manner. 
After  the  hole  is  drilled  thp  destroyer  inserts  his  proboscis  and  sucks 
the  fluids  of  his  victim.  The  traces  of  the  teeth  are  perfectly  visible 
on  the  sides  of  the  perforation.  Their  action  may  be  watched  by  put- 
ting a  pond-snail  on  the  glass  walls  of  an  aquarium  where  it  has  become 
overgrown  with  green  confervoid  slime.  A  few  of  these  snails  are  fre- 
quently placed  in  aquaria  for  the  purpose  of  keeping  the  walls  clean. 


THE  COMPARATIVE  ANATOMY  OF  THE 
TEETH  OF  THE  VERTEBRATA. 

By  JACOB  L.  WOBTMAN,  A.  M.,  M.  D. 


A  STUDY  of  the  dental  organs  of  the  Vertebrata  is  one  replete  with 
much  interest  when  viewed  from  the  standpoint  of  the  naturalist.  The 
circumstance  that  their  modification  is  so  intimately  associatetl  with  the 
food-habits  of  the  animal,  being  principally  concerned  in  the  prehension 
and  comminution  of  the  food,  and  that  to  these  same  habits  we  must 
look  for  the  most  powerful  influences  and  incentives  to  modification  in 
general,  causes  them  to  assume  more  than  ordinary  importance  in  the 
estimation  of  the  philosophic  anatomist  who  earnestly  addresses  himself 
to  the  pi'oblem  of  vertebrate  evolution. 

The  fact,  too,  that  the  perfect  condition  in  which  they  have  been  so  ofter* 
preserved  in  the  fossiliferous  strata  of  the  earth's  crust  has  frequently 
furnished  the  only  evidence  which  we  possess  of  the  existence  of  forms 
long  since  extinct,  causes  them  to  be  regarded  as  objects  of  still  greater 
interest.  When  we  reflect  that  with  nothing  more  to  guide  his  judg- 
ment than  the  dental  series  of  an  animal  the  expert  palaeontologist  can, 
generally,  not  only  indicate  with  great  certainty  the  character  of  the 
food  upon  which  the  animal  subsisted,  but  its  general  characteristics 
and  relationships  as  well,  even  though  the  date  of  its  existence  be 
removed  to  a  remote  period  in  geologic  history,  but  little  surprise 
can  be  felt  that  so  much  thoughtful  attention  has  been  bestowed 
upon  this  set  of  organs. 

No  series  of  anatomical  structures  has  proved  of  greater  utility  to  the 
systematist  who  has  endeavored  to  indicate  the  exact  relationship  or 
philogenetic  history  of  mammalian  forms  than  the  teeth.  Generally, 
the  student  who  attempts  to  master  the  subject  is  discouraged  almost  at 
the  very  threshold  of  his  undertaking  by  the  apparently  great  diversity 
of  tooth-forms  to  be  met  with  in  the  mammalian  class ;  but  if  looked 
at  from  a  developmental  point  of  view,  and  if  a  little  careful  attention 
is  bestowed  upon  the  plan  of  organization  of  the  teeth  of  certain  groups, 
it  is  not  difficult  to  discover  that  there  are  certain  central  or  primitive 
types  from  which  it  is  easy  to  derive  other  related  forms  of  dentition 
by  simple  addition,  subtraction,  or  modification  of  parts  already  pos- 
sessed. 

Careful  attention  to  this  subject  for  several  years  past,  with  the  assist- 
ance of  the  light  which  American  palaeontology  is  now  able  to  throw 
n])on  the  question,  has  convinced  me  more  and  more  of  the  truth  of 
this  assertion ;  and  I  feel  well  assured  that  we  are  now  in  a  position  to 

351 


352  DENTAL  ANATOMY. 

lay  down  some  broad  principles  in  regard  to  dental  evolntion,  at  least 
among  certain  groups  of  the  Mammalia,  where  they  have  been  subjected 
to  the  greatest  amount  of  modification. 

Although  there  are  many  questions  concerning  the  origin  and  details 
of  tooth-evolution  of  many  aberrant  forms  which  remain  to  be  solved, 
yet  the  discoveries  which  have  been  made  in  palseontology  within  the 
last  twenty-five  years  leave  scarcely  a  living  group  of  animals,  the 
development  of  whose  teeth  has  progressed  beyond  the  primitive  stages, 
from  which  we  have  not  gained  some  imj)ortant  information  relative  to 
the  phases  through  which  they  have  passed  to  reach  their  present  con- 
dition. The  possibility  of  reducing  our  knowledge  of  the  dental  struc- 
tures of  the  Mammalia  to  a  broad  and  comprehensive  basis  was  long 
since  recognized  by  Prof.  Cope,  to  whom  probably  more  than  any  one 
else  we  are  indebted  for  a  genuine  philosophic  insight  into  the  forms 
and  structure  of  these  teeth.  Scarcely  less  important  are  the  contribu- 
tions of  John  A.  Ryder  and  Dr.  Harrison  Allen,  whose  learned  researches 
into  the  probable  causes  of  tooth-modification  have  marked  notable 
stages  in  the  progress  of  the  sulyect  and  have  opened  new  and  inter- 
esting fields  for  investigation.  Nor  should  we  omit  a  mention  of  the 
researches  of  Flower,  nor  those  of  Tomes,  Waldeyer,  Frey,  Hertwig, 
Magitot,  and  Legros,  into  the  histology  and  development  in  later 
times. 

Commonly,  teeth  are  defined  as  hard  bodies  attached  to  the  parictes 
of  the  mouth  or  oral  extremity  of  the  alimentary  canal,  whose  chief 
function  is  the  seizure  and  connninution  of  the  food.  ISIorphologically 
considered,  however,  they  are  specialized  dermal  appendages  situated  in 
the  buccal  cavity,  and  characterized  by  the  presence  of  certain  calcified 
tissue  developed  from  the  true  derm  or  corium  of  the  integument, 
known  as  (Icntine.  It  will  be  seen  from  this  definition  that  the  term 
"  tooth,"  strictly  speaking,  is  limited  to  those  structures  of  the  oral 
cavity  which  alone  jwssess  such  tissue,  although  it  is  a  recognized  fact 
that  to  other  epithelial  or  cuticular  structures,  found  in  many  inverte- 
brate and  some  few  vertebrate  forms,  the  term  "■  tooth "  has  likewise 
been  applied. 

While  they  all  subserve  the  same  pur})ose,  and  are  therefore  analo- 
goiis,  their  chief  distinction  consists  in  this — viz.  in  the  latter,  so  far 
as  they  have  been  investigated,  these  organs  consist  of  a  corneous  or 
hornv  substance,  which  is  invariably  derived  from  the  more  superficial 
epidermal  layer,  and  is  therefore  ecdcronic  in  origin.  In  the  former 
a  pa})illa  arises  from  the  corium,  being  sunk  into  a  fold  or  ])it,  and 
eventually  undergoes  more  or  less  calcification  from  its  summit  down- 
ward by  a  deposition  in  its  substance  of  lime  salts,  forming  dentine. 
The  dentine  thus  formed  is  a  hard,  elastic  substance,  consisting  of 
closelv-set  parallel  tubuli,  branching  as  they  go,  and  whose  crown  may 
or  mav  not  be  invested  with  an  exceediiigly  hard  and  unyielding  sub- 
stance derived  from  the  deeper  layers  of  the  epidermis,  known  as  enamel. 
These  are,  then,  endernnic  in  origin. 

Those  of  ecderonic  source  include  the  so-called  teeth  of  Annulosse, 
INIollusca,  Insectfe,  etc.  among  tlie  invertebrates,  as  well  as  the  horny 
teeth  of  Ornithorhi/nchus,  palatal  plates  of  the  Sirenia,  and  the  horny 


TEETH  OF  THE   VERTEBRA  TA. 


353 


teeth  of  the  lampreys  among  vertebrates.  If  the  term  "  tooth " 
is  applicable  to  these  structures,  then  we  must  likewise  include  the 
"  baleen  "  of  the  Cetacea  and  the  beaks  of  birds  and  reptiles,  which  by 
common  consent  are  far  removed  from  true  teeth.  For  all  such  I  think 
the  term  oral  armature  is  preferable,  from  the  fact  that  their  produc- 
tion not  infrequently  depends  upon  the  modification  of  organs  widely 
different  in  origin. 

On  the  other  hand,  those  of  enderonic  source  are  found  only  within 
the  limits  of  the  Vertebrata,  and  range  in  form  from  the  simple  cone 
usual  among  fishes  to  the  higher  complex  grinding  organs  of  certain 
herbivorous  mammals.  They  all  agree  in  being  developed  from  the 
corium  of  the  lining  membrane  of  the  mouth,  which  is  continuous  with, 
and  really  a  part  of,  the  integument,  invaginated  at  an  early  period. 
There  is  a  possible  exception  in  the  pharyngeal  teeth  of  fishes,  which 
Ryder  considers  to  be  of  liypoblastic  origin  or  developed  from  the  base- 
ment-layer of  the  mucous  membrane  of  the  alimentary  canal,  and  which 
are  practically  the  same  as  those  of  epiblastic  origin,  as  far  as  their 
relation  to  the  surface  is  concerned. 

When  we  speak  of  teeth  being  modified  dermal  appendages,  it  will 
not  be  amiss  to  cite  the  evidence  upon  which  such  a  generalization  rests. 
Tliis  is  best  afforded  by  a  study  of  the  relationship  and  development  of 
the  dermal  armature  of  certain  elasmobranch  fishes,  of  which  the  shark 
is  a  good  example  and  furnishes  us  with  one  of  the  earliest,  and  there- 
fore one  of  the  most  primitive,  conditions  of  the  Vertebrata. 

In  these  fishes  the  defensive  power  of  the  integument  is  augmented 
by  the  production  of  numerous  hard  bodies  in  its  substance,  which  have 
been  termed  "  dermal  denticles "  by  Gegenbaur.  These  structures, 
which  are  likewise  known  as  "  placoid  scales,"  are  distributed  over 
the  whole  of  the  integument  in  shark-like  fishes,  and  are  ordinarily 

Fig.  187. 


Vertical  Section  through  the  Sliin  of  an  Embryonic  Shark:  r,  corium ;  c,  p,  c,  layers  of  corium ;  d, 
uppermost  layer ;  /*,  papilla;  ^,  epidejmis  ;  e,  its  layer  of  columnar  cells;  o,  enamel  layer  (from 
Gegeubaur,  after  Uertwig). 

rhomboidal  in   form,  with  their   apices  directed  obliquely  backward. 
They  consist  of  a  solid   body,  which  is  inserted  by  its  base  into  the 

Vol.  I.— 23 


354  DENTAL  ANATOMY. 

coriiim,  with  an  exposed  part,  which  is  covered  with  a  substance  indis- 
tinguishable from  the  enamel  of  the  teeth.  The  structure  of  the  body- 
is  likewise  coincident  with  true  dentine,  and  becomes  fused  with  a  basal 
plate  of  osseous  material.  Their  development  is  as  follows  :  First,  a 
papilla  arises  from  the  uppermost  layer  of  the  corium,  being  covered  in 
by  the  epidermis  (see  Fig.  187).  From  the  deepest  layer  of  the  epi- 
dermis, or  that  which  corresponds  with  the  Malpighian  layer,  a  special 
epithelial  covering  is  furnished,  which  eventually  becomes,  by  a  process 
of  histological  differentiation,  the  enamel  of  the  exposed  part.  The 
papilla,  before  the  conversion  of  its  substance  into  dentine,  exhibits  a 
central  cavity,  from  which  fine  branched  canals  radiate  to  the  surface. 
Eventually,  calcification  takes  place,  beginning  at  the  summit,  and  the 
salts  of  lime  are  deposited  in  the  substance  of  the  papilla,  giving  rise  to 
the  dentine.  Gegenbaur  observes  : '  "  The  placoid  scale  has  therefore  the 
structure  of  dentine,  is  covered  by  enamel,  and  is  continued  at  its  base 
into  a  plate  formed  of  osseous  tissue ;  as  they  agree  with  the  teeth  in 
structure,  they  may  be  spoken  of  as  dermal  denticles." 

Now,  in  the  early  embryonic  stages  the  integument  bearing  these 
dermal  denticles  is  pushed  into  the  oral  cavity,  where  they  become 
somewhat  enlarged,  and  appear  in  the  adult  form  as  teeth.  Tomes 
says  :  ^  "  No  one  can  doubt,  whether  from  the  comparison  of  the  adult 
forms  or  from  the  study  of  the  development  of  the  parts,  that  the  teeth 
of  the  shark  correspond  to  the  teeth  of  other  fish,  and  these  again  to 
those  of  reptiles  and  mammals  ;  it  may  be  clearly  demonstrated  that 
the  teeth  of  the  shark  are  nothing  more  than  highly-developed  spines  of 
the  skin,  and  therefore  we  infer  that  all  teeth  bear  a  similar  relation  to 
the  skin."  Thus  the  generalization  is  reached  that  teeth  are  but  spe- 
cialized dermal  apj^endages. 

With  this  statement  of  the  nature  of  teeth  in  general,  we  are  now  pre- 
pared to  begin  a  more  special  inquiry  into  the  organization  of  a  single 
tooth.  For  this  purpose  I  have  selected  the  third  lower  premolar  of 
the  dog  as  an  average  and  easily-procurable  example  of  a  generalized 
type  among  the  higher  forms,  which  will  serve  to  illustrate  the  compo- 
sition and  nomenclature  of  the  several  parts  of  which  all  teeth,  w  ith  few 
exceptions,  are  made  up. 

For  convenience  of  description,  the  several  parts  of  most  teeth  can  be 
divided  into  crown,  fang,  and  neck,  although  there  are  many  in  wliich 
no  true  fangs  are  formed,  owing  to  the  persistent  and  continuous  growth 
of  the  tooth  ;  in  all  such  no  distinctions  of  this  kind  can  be  recognized. 
In  the  particular  tooth  under  consideration,  however,  we  can  distinguish 
w-ithout  difficulty  an  enamel-covered  crown,  which  corresponds  with  the 
exposed  ])art  of  the  tooth  in  the  recent  state  ;  two  more  or  less  cylindrical 
fangs  or  roots,  by  which  the  tooth  is  implanted  in  the  aveoli  and  attached 
to  the  jaw  bone ;  and  a  slight  constriction  at  the  point  where  the  fangs 
join  the  crown,  known  as  the  neck  (see  Fig.  188).  The  crown  in  form 
resembles  a  laterally  compressed  cone,  with  an  anterior  and  posterior 
cutting  edge.  It  is  covered  by  a  dense  shiny  white  substance  of  great 
hardness,  the  enamel,  which  ceases  at  the  point  where  the  fangs  com- 

^  Elements  of  Cuwparative  Anatomy.  2  A  Manual  of  Dental  Anatonui. 


TEETH  OF  THE   VERTEBRATA.  355 

mence.  At  the  base  of  the  crown  the  enamel  is  thrown  into  a  conspic- 
uous fokl  or  ridge,  which  completely  encircles  the  tooth  at  this  point,  and 
is  called  the  cincjulum.  Of  the  two  cutting  edges,  the  posterior  is  the 
more  extensive,  and  is  interrupted  in  its  descent  from  the  summit  of  the 
crown  by  a  deep  transverse  notch,  which  constricts  off  p  ■  i  s8 
a  prominent  cusp  known  as  the  'posterior  basal  taber- 
clc.  A  slight  indication  of  a  second  cusp  of  this  kind 
is  seen  immediately  behind  it  as  an  elevation  of  cingu- 
lum.  The  anterior  is  the  shorter,  and  descends  from 
the  apex  of  the  crown  to  the  cingulum  without  inter- 
ruption. It  is  placed  nearer  the  inner  than  the  outer 
border  of  the  tooth,  and  curves  somewhat  inward  at 
its  lower  extremity. 

The  fangs  are  two  in  number,  occupying  an  antero- 
posterior position,  and  give  firm  support  to  the  crown. 
They  are  covered  by  a  softer  substance,  resembling  bone-  „.,.,, 

.•',  •'  '  n  W  1  hird  Lower  rreinolar 

tissue,  known  as  cementam  or  crusta  petrosa  ot  human  of  a  Dog  (ranis  ja- 
odontography .  This  material  is  continued  over  the  ""'""  "^'  ^'^  ^"^^^^  ' 
entire  surface  of  the  crown  as  an  excessively  thin  stratum  in  the  unworn 
teeth  of  the  Carnivora  and  several  other  orders,  but  can  be  demonstrated 
only  by  the  most  delicate  manipulation  and  the  use  of  the  microscope.  It 
assumes  a  more  important  relationship  with  the  crown,  as  we  shall  pres- 
ently see,  in  the  herbivorous  species  of  mammals. 

Of  the  two  fangs,  the  posterior  is  the  larger,  but  the  shorter,  and  takes 
the  greater  share  in  the  suj)port  of  the  crown,  although  the  cleft  which 
separates  them  at  their  summits  is  placed  directly  beneath  the  summit 
of  the  crown.  It  is  broad  at  its  base,  and  tapers  somewhat  abj'uptly  to 
an  obtuse  point.  It  is  traversed  by  a  vertical  groove  upon  its  anterior 
moiety,  which  fits  into  a  corresponding  ridge  on  the  side  of  its  socket. 
The  anterior  root  is  the  more  slender  and  the  longer  of  the  two.  It 
tapers  more  gradually,  and  is  likewise  traversed  by  a  broad,  shallow 
groove  upon  its  posterior  aspect.  At  the  point  of  each  fang  will  be  seen 
a  small  aperture,  the  apical  foramen,  through  which  the  nerves  and 
nutrient  vessels  pass  to  the  pulp. 

So  far,  we  have  spoken  only  of  the  external  appearance  of  the  tooth 
and  of  those  substances  which  make  up  its  outer  coverings  ;  but  if  both 
the  cementum  and  enamel  were  removed,  it  would  still  preserve  its 
original  form,  so  great  is  the  preponderance  of  the  dentine  as  a  constit- 
uent element.  This  can  best  be  seen  in  a  longitudinal  vertical  section, 
since  at  no  part  in  an  unworn  tooth  is  the  dentine  exposed  in  these  ani- 
mals. Although  the  dentine  is  quite  thick,  and  constitutes  by  fiir  the 
greatest  part  of  the  tooth,  it  nevertheless  does  not  form  a  solid  body ; 
on  the  contrary,  a  considerable  cavity  is  hollowed  out  in  its  centre,  this 
being  largest  in  the  part  which  makes  up  the  body  of  the  crown,  and 
extending  down  each  fang.  This  cavity  lodges  the  dentinal  pulp,  the 
formative  and  nutrient  organ  of  the  tooth,  and  is  in  communication 
with  the  exterior  by  means  of  the  apical  foramina  of  the  fangs. 

While  this  structure,  in  common  examples  of  enamel-covered  teeth,  is 
observable  with  the  unassisted  eye,  a  more  minute  study  of  the  organiza- 
tion of  the  various  tissues  must  be  conducted  with  the  aid  of  the  micro- 


356  DENTAL  ANAT03IY. 

scope.  This  necessarily  requires  a  considerable  amount  of  experience 
and  skill  in  the  manipulation  and  preparation  of  material,  so  that  to 
the  unpractised  observer  a  proper  determination  of  the  things  which  one 
may  see  is  not  always  an  easy  matter.  On  this  account  I  have  chosen 
to  follow  the  conclusions  of  the  recognized  authorities,  especially  the 
excellent  treatise  on  dental  anatomy  by  Charles  S.  Tomes,  in  this  brief 
statement  of  the  histology,  rather  than  trust  the  accuracy  of  my  own 
observations  on  the  same.  Since  the  histology  of  human  teeth  has  been 
more  fully  made  out  than  perhaps  the  histology  of  those  of  any  other 
animal,  it  is  here  taken  for  illustration,  although  I  am  fully  aware  that 
important  deviations  from  the  structure  here  described  are  to  be  met 
with  among  the  Vertebrata. 

Dentine. — As  we  have  already  seen,  the  tooth  consists  of  a  dentine 
body  with  a  central  cavity  lodging  the  pulp,  an  enamel-capped  crown, 
and  cementum-covered  roots.  The  dentine  is  a  hard,  highly  elastic, 
translucent  substance  of  a  yellowish-white  tinge,  having  a  silky  lustre 
upon  fracture.  It  is  composed  of  an  organic  matrix  highly  impreg- 
nated with  calcareous  salts ;  through  this  matrix  closely-set  parallel 
tubuli  radiate  from  the  pulp-cavity  toward  the  periphery  in  a  direction 
at  right  angles  to  the  suriiice  of  the  tooth. 

Of  perfectly  dry  dentine  the  following  chemical  analysis  is  given  by 
Von  Bibra  : 

Organic  matter  (tooth-cartilage) 27.61 

Fat 0.40 

Calcium  phosjiliate  and  fluoride 66.72 

Calcium  carbonate 3.36 

Magnesium  phosphate 1.18 

Other  salts 83 

The  organic  basis  of  the  matrix,  although  closely  related  to  that  of 
bone,  is  said  not  to  be  identical  with  it,  and  is  hence  called  "  dentine"  or 
"  tooth-cartilage ;"  it  is  perfectly  structureless  and  transparent.  After  the 
tooth  has  been  decalcified  by  submitting  it  to  the  action  of  dilute  acid 
for  a  few  days,  the  matrix  will  still  preserve  the  characteristic  shape  of 
the  tooth,  and  can  readily  bo  studied. 

As  already  stated,  the  tubuli,  which  are  likewise  known  as  dental 
tubeii,  permeate  the  matrix  in  all  directions,  opening  freely  upon  the 
walls  of  the  pulp-cavity,  by  which  arrangement  all  i)arts  of  the  dentine 
are  brought  into  direct  connnunication  with  the  central  nutrient  organ, 
the  pulp.  They  are  most  nearly  approximated  and  their  diameters 
greatest  at  their  commencement  on  the  walls  of  the  pulp-cavity,  but, 
pursuing  a  somewhat  wavy  course,  gradually  diminish  in  size,  owing 
to  the  numerous  branches  Avhich  they  give  off.  These  branches,  although 
not  uniform  in  size,  anastomose  freely  with  those  of  the  neighboring 
tubuli,  and  frequently  show  varicosities  in  their  course.  They  termi- 
nate either  by  gradually  fading  out,  by  anastomosing  with  other 
branches,  by  ending  in  loops,  or  by  entering  the  enamel  and  cement- 
um  layers. 

AVhile  the  dental  tubes  may  be  said  to  be  channelled  out  in  the  sub- 
stance of  the  dentine  cartilage,  the  walls  of  the  tubidi  are  not  formed 
by  this  cartilage,  but  each  tubuli  is  furnished  with  a  structure  knoA^n  as 


TEETH  OF  THE   VERTEBRATA.  357 

the  dentinal  sheath,  which  accompanies  it  throughout  all  its  plexiform 
radiations.  The  structure  of  these  dentinal  sheaths  is  not  certainly 
known,  owing  to  the  impossibility  of  isolating  them  without  decalcifica- 
tion of  the  dentnie.  Some  histologists  believe  that  they  are  calcified, 
while  others  express  doubt  as  to  the  correctness  of  this  conclusion.  One 
very  marked  peculiarity  which  they  possess  is  their  great  indestructibil- 
ity. Dentine  when  submitted  to  the  action  of  strong  acid  for  a  suf- 
ficient length  of  time  to  completely  destroy  the  intervening  cartilage, 
or  when  boiled  in  caustic  alkali,  will  still  exhibit  these  dentinal  sheaths, 
for  it  is  indeed  only  in  this  way  that  their  presence  can  be  demonstrated 
satisfactorily.     One  writer  (INIagitot)  denies  their  existence  altogether. 

Enclosed  within  each  dentinal  sheath  is  a  soft  fibril,  the  dentinal 
fibrils,  which  take  their  origin  from  the  cells  of  the  odontoblastic  layer 
of  the  pulp,  presently  to  be  noticed,  and  of  which  there  are  sufficient 
reasons  for  believing  them  to  be  nothing  more  than  processes  or  pro- 
longations. There  is,  however,  considerable  discussion  upon  the  exact 
nature  and  relationship  of  these  fibrils.  JNIagitot  maintains  that  they 
are  continuous  with  a  layer  of  reticulate  cells  which  lie  beneath  the 
odontoblasts ;  these  freely  communicate  with  processes  of  the  odonto- 
blasts, so  that  there  is  a  very  direct  communication  between  the  den- 
tinal fibrils  and  the  nerves  of  the  pulp.  He  would  therefore  ascribe  to 
them  a  sensory  function.  Klein,  on  the  other  hand,  holds  that  the 
odontoblasts  are  concerned  only  in  the  formation  of  the  dentine  matrix, 
and  that  the  dentinal  fibrils  are  long  processes  of  deeper  cells  extended 
between  the  odontoblasts.  Whichever  of  the  various  views  now  held 
may  ultimately  prevail,  this  much  appears  to  be  settled — viz.  that  the 
dentine  is  extensively  invaded,  so  to  speak,  by  soft  plasmic  material 
derived  from  the  pulp,  by  which  it  is  not  only  nourished,  but  also  ren- 
dered highly  sensitive. 

In  the  outermost  layer  of  the  dentine,  which  underlies  the  cementum, 
numerous  globular  spaces  are  found,  in  which  many  of  the  dentinal 
tubes  end ;  these  are  filled  with  soft  living  plasma.  These  spaces, 
if  such  indeed  they  may  be  properly  termed,  give  to  this  layer  a  dis- 
tinctly granular  appearance,  whence  it  w^as  called  by  Tomes  the  "gran- 
ular layer."  Other  structures,  known  as  the  interglobular  spaces,  pos- 
sessing a  ragged  outline  and  short  pointed  processes,  may  frequently 
be  seen  in  dried  sections  of  dentine.  They  are  said  by  Tomes  to  be 
most  abundant  at  a  little  distance  below  the  surface,  and  he  believes 
them  to  pertain  rather  to  a  pathological  than  to  a  normal  condition. 

The  Tooth-pulp. — It  appears  best  to  describe  in  connection  Avith  the 
dentine  the  pulp  or  formative  organ,  in  consequence  of  the  intimate 
relation  which  exists  between  them.  As  has  already  been  stated,  it  is 
lodged  in  the  pulp-cavity,  and  is  the  principal,  if  not  the  only,  source 
of  blood-  and  nerve-supply  to  the  dentine.  In  the  young  and  growing 
tooth,  especially  about  the  time  calcification  begins,  it  is  largest  and 
assumes  its  greatest  functional  activity  and  importance,  from  the  fact 
that  it  is  through  its  mediation  that  the  dentine  is  formed  ;  in  fact,  in 
the  early  stages  of  dental  development,  as  we  shall  hereafter  see,  it  is 
coincident  with  the  dentine  organ  itself,  of  which  in  the  adult  tooth  it 
is  the  inconsiderable  remnant.   As  senile  changes  supervene  it  gradually 


358  DENTAL  ANATOMY. 

loses  its  formativ^e  energy,  and  may  become  entirely  obliterated.  Taken 
at  the  adult  stage  of  the  tooth,  it  is  seen  to  consist  of  indistinct  hnely 
fibrous  connectiye  tissue  containing  numerous  cells.  The  outermost 
layer  of  the  pulp  is  known  as  the  memhvana  eboris,  and  is  made  up  of 
a  single  layer  of  highly  specialized  cells  of  a  dark  granular  appearance, 
somewhat  elongated,  termed  ndonioblasts.  These  odontoblasts  possess 
large  oyal  nuclei,  and  are  proyided  with  three  sets  of  processes,  as  fol- 
lows :  the  dentinal  processes,  which  are  identical  with  the  dentinal  fibrils, 
and,  as  we  haye  already  seen,  enter  the  dental  tubes ;  the  latercd  pro- 
cesses, by  which  they  are  connected  with  each  other ;  and,  lastly,  the 
pulp  pjrocesses,  extending  down  to  a  deeper  layer  of  cells.  This  latter 
layer  of  cells  is  somewhat  intermediate  in  size  between  those  more  deeply 
seated  and  the  odontoblasts.  Three  or  more  arteries  enter  at  the  apical 
foramen,  and  form  a  rich  capillary  plexus  a  short  distance  beneath  the 
membrana  eboris.  The  neryes  enter  by  seyeral  trunks  along  with  the 
arteries,  and  soon  break  up  into  a  fine  network  in  the  substance  of  the 
pulp.  According  to  Boll,  nerye-fibres  penetrate  the  dentinal  tubuli  in 
company  with  the  dentinal  fibrils,  but  this  yiew  is  not  fully  accepted. 

Cementum. — The  cementum  in  human  and  many  other  teeth  of  similar 
structure  may  be  said  to  be  confined  to  the  roots,  inyesting  them  exter- 
nally, unless  the  enamel  cuticle  or  membrane  of  Nasmyth,  mentioned 
aboye,  })ertains  to  it,  which  C  S.  Tomes  and  others  belieye  to  be  the 
case.  It,  like  ordinary  bone,  consists  of  a  gelatinous  base  combined 
with  calcareous  salts,  and  is  permeated  by  yascular  canals.  Its  histo- 
logical structure  j^resents  so  many  characters  common  to  bone  that  it  is 
difficult  to  consider  it  anything  more  than  a  slight  modification  of  that 
tissue.  Just  as  in  bone,  large  irregular  spaces  (laciince),  filled  with  pro- 
toplasmic substance  and  presenting  numerous  minute  radiating  canals 
(canaliculi),  whidi  anastomose  with  those  of  neighboring  lacunae,  are 
found  in  ordinarily  thick  cementum ;  certain  differences  are,  howeyer, 
seen  to  exist. 

The  lacunte  of  cementum,  for  example,  are  more  variable  in  size 
and  are  noted  for  the  great  length  of  their  canaliculi.  The  direction, 
too,  of  the  canaliculi  is  generally  parallel  with  that  of  the  dentinal 
tubuli,  radiating  from  two  sides  only,  whereas  in  bone-tissue  they 
radiate  in  all  directions.  It  has  been  already  stated  that  the  dentinal 
tubuli  sometimes  enter  the  cementum  layer.  AYhen  this  is  the  case 
they  become  continuous  with  the  canaliculi  of  the  most  deeply  dis- 
tributed lacunre.  The  outermost  or  granular  layer  of  the  dentine  goes 
so  far  toward  establishing  a  complete  transition  in  structure  between  the 
cementum  and  the  dentine  that  it  is  generally  im]X)Ssible  to  draw  a 
diyiding-line  and  say  where  the  one  ends  and  the  other  begins.  As  to 
limit  of  distribution  of  the  cementum  on  the  surface  of  the  teeth  in  man, 
monkeys,  carniyores,  and  insectiyores,  different  yiews  haye  been  expressed, 
owing  to  the  yarious  constructions  that  haye  been  placed  upon  the  nature 
and  relationship  of  the  enamel  cuticle  or  Xasmyth's  membrane,  already 
mentioned.  AValdeyer,  Huxley,  and  K(")lliker  hold  that  it  is  no  way 
connected  with  the  cementum,  but  that  it  is  a  product  deriyed  from  the 
enamel,  and  is  therefin'e  ej)ithelial  in  origin.  C  S.  Tomes,  Magitot, 
and  AA'edl,  on  the  other  hand,  maintain  that  it  is  a  part  of  the  cementum 


TEETH  OF  THE   VERTEBRATA.  359 

extended  over  the  entire  crown  of  the  tooth,  and  becomes  continuous 
with  its  outermost  layer  in  the  vicinity  of  the  neck.  It  is  one  of  those 
excessively  thin  membranes  (not  over  -g- oto'o  ^"^^^  "^  thickness,  accord- 
ing to  Kolliker)  which  are  peculiarly  indestructible  and  resist  the  ac- 
tion of  the  strongest  acids  and  alkalies.  When  stained  with  the  nitrate 
of  silver,  it  shows  a  peculiarly  reticulated  structure  resembling  epithe- 
lium, which  is  believed  by  Tomes  to  be  due  to  the  pitted  surface  on  its 
interior,  by  which  it  is  applied  to  the  enamelrprisms.  Encapsuled 
lacunae  are  likewise  found  in  its  substance,  which  would  be  difficult  to 
explain  if  it  were  not  a  part  of  the  cementum  layer.  Tomes  has  like- 
wise traced  its  connection  with  the  outer  layer  of  the  cementum  on  sev- 
eral occasions,  and  is  therefore  firmly  of  the  opinion  that  it  is  a  continua- 
tion of  this  tissue. 

Enamel. — The  excessively  hard,  shiny  substance  investing  the  crown 
of  the  tooth  is  the  enamel.  It  is  by  far  the  hardest  tissue  to  be  met 
with  in  the  animal  body,  being  at  the  same  time  the  poorest  in  organic 
constituents.  Where  it  exists  at  all,  it  generally  forms  a  cap  of  varying 
thickness  over  the  exposed  part  of  the  tooth,  except  in  those  instances 
where  there  is  an  excessive  development  of  cementum  in  this  situation, 
which  causes  it  to  occupy  a  position  between  the  cementum  and  dentine, 
as  seen  in  the  most  exclusively  herbivorous  feeders,  of  which  the  horse, 
cow,  and  elephant  are  good  examples.  Even  here  palseontological  evi- 
dence is  quite  conclusive  in  support  of  the  proposition  that  their  earlier 
representatives  possessed  teeth  with  naked  enamel-covered  crowns.  This 
condition  of  nudity  of  the  enamel  is  coincident  with  shorter  cusps  and 
less  elevated  ridges  of  the  crown,  and,  as  we  have  good  reasons  to  infer 
from  analogy,  with  more  omnivorous  habits  of  feeding.  It  can  thus  be 
shown  that  this  anomalous  arrangement  of  the  tissues  is  one  acquired 
comparatively  late  in  the  development  of  these  forms  for  the  exclusive 
purpose  of  giving  greater  strength  to  the  lengthened  cusps,  thereby 
affording  immunity  from  fracture  during  the  act  of  mastication. 

Von  Bibra  gives  the  following  chemical  analysis  of  the  enamel  of  an 
adult  human  tooth  : 

Calcium  phosphate  and  fluoride 89.82 

Calcium  carbonate      -    .   • 4.37 

Magnesium  phosphate      '    '    ■     1-34 

Other  salts 88 

Cartilage      3.39 

Fat   . 20 

The  proportion  of  the  organic  to  the  inorganic  material  is  therefore  3.59 
to  96.41,  while  in  dentine  it  is  28.01  to  71.99.  Its  structure  consists 
of  minute  hexagonal  prisms,  known  as  enamel-fibres  or  enamel-prisms, 
whose  long  axes,  broadly  speaking,  have  a  direction  at  right  angles  to  the 
surface  of  the  tooth.  It  is  a  comparatively  rare  occurrence  to  find  the 
fibres  pursuing  a  perfectly  straight  course  from  the  dentine  to  the  sur- 
face, but  such  Is  found  to  be  the  case  in  the  enamel  of  the  manatee  or 
sea-cow  and  several  other  forms.  Usually,  they  are  tortuous,  and  fre- 
quentlv  decussate,  as  in  the  human  subject,  which  renders  it  difficult  to 
trace  the  course  of  an  individual  fibre.     A  variety  of  patterns  is  pre- 


360  DENTAL  ANATOMY. 

sented  by  the  arrangement  of  these  prisms  in  the  enamel  of  different 
animals,  especially   of  the   "gnawing  quadrupeds,"   or  rodents. 

The  prisms,  when  decalcified  and  isolated,  exhibit  slight  varicosities 
or  enlargements,  giving  them  a  distinct  transversely  striated  appearance, 
not  unlike  that  of  voluntary  muscular  fibres.  They  are  otherwise 
structureless.  It  is  maintained  by  Bodecker  that  the  prisms  are  not 
absolutely  in  contact,  but  that  minute  spaces  exist  between  them  which 
are  filled  with  active  protoplasmic  material,  which  becomes  continuous 
with  that  of  the  dentinal  tubuli,  thereby  furnishing  a  means  of  nutrition. 
Some  investigators  admit  this  interstitial  substance,  but  attribute  to  it 
no  greater  ftmction  than  that  of  simple  cementing  material,  while  others, 
again,  claim  that  the  prisms  are  in  absolute  contact,  and  that  no  inter- 
vening substance  is  demonstrable.  Owing  to  the  disparity  in  extent 
between  the  outer  and  inner  surface  of  the  enamel,  as  well  as  the  fact 
that  the  individual  prisms  do  not  decrease  in  size  nor  branch  in  their 
course  outward  to  the  surface,  considerable  spaces  would  be  left  .if  it  were 
not  that  they  are  occupied  by  numerous  prisms  which  do  not  penetrate 
to  the  dentine.  The  prisms  end  in  sharp-pointed  extremities  which  are 
received  into  corresponding  pits  in  the  enamel  cuticle  or  membrane  of 
Nasmyth. 

Development. — Next  in  order  will  be  briefly  noticed  the  develop- 
ment, so  as  to  complete  in  this  connection  an  entire  statement  of  the 
anatomy  of  a  single  tooth.  It  may  be  said  that  although  teeth  of  dif- 
ferent types  differ  to  a  wonderful  degree  in  their  forms,  which  would 
seem  to  indicate  differences  quite  as  great  in  other  respects,  yet,  in 
fact,  the  ])lan  of  their  development  is  substantially  the  same  whereyer 
found.  So  far  is  this  true  that  the  description  of  the  embryology  of 
one  tooth  will,  with  little  modification,  answer  fairly  well  for  all  teeth. 
The  more  important  of  these  modifications  in  the  details  of  development 
will  be  discussed  in  connection  ^\ith  the  teeth  of  the  various  subdivis- 
ions of  the  Vertebrata. 

We  have  already  stated  that  the  teeth  are  derived  from  the  lining 
membrane  of  the  oral  cavity,  Avhicli  blends  with  the  integument  at  the 
lips.  The  principal  differences  between  the  integument  which  covers 
the  surface  of  the  body  and  the  mucous  membrane  which  lines  the  ali- 
mentary canal  are  those  of  function  and  origin,  the  structure  being 
essentially  the  same.  In  the  one  the  indiyidual  cells  of  the  epidermal 
layer  become  devitalized  and  scale  off,  Avhile  in  the  other  they  are 
actively  engaged  in  the  secretion  of  mucous,  gastric,  intestinal,  and 
other  juices  during  alimentation.  The  devitalization  and  consequent 
"  shedding  of  the  skin  "  is  greater  in  some  forms  than  in  others.  In 
the  frogs  and  salamanders,  for  example,  the  skin  is  kept  constantly 
moist  by  an  abundant  mucoid  secretion,  and  the  epithelium  of  the  integ- 
ument may  be  said  to  be  more  "  alive  "  in  these  animals  than  in  birds, 
reptiles,  or  mammals.  The  difference  in  origin  consists  in  the  import- 
ant fact  that  the  integument  is  formed  from  the  epiblastic  or  outermost 
layer  of  primitive  embryonic  growth,  while  the  mucous  membrane  of 
the  alimentary  canal  is  derived  from  the  hypoblastic  or  innermost  layer 
of  the  same.  In  the  early  stages  of  the  development  of  the  embryo  the 
skin  is  more  or  less  invaginated  into  the  mouth-cavity,  and  partakes 


TEETH  OF  THE   VERTEBRATA.  361 

somewhat  of  the  nature  of  mucous  membrane  proper.  The  real  point 
of  blending  is,  in  the  embryo  at  least,  not  at  the  lips,  but  lies  inside  the 
borders  of  the  jaws.  If,  therefore,  we  limit  the  term  "  mucous  mem- 
brane" in  this  situation  to  that  tissue  which  is  of  hypoblastic  origin, 
then  the  teeth  of  the  jaws  cannot  be  said  to  be  developed  from  the 
mucous  membrane  of  the  mouth,  as  is  commonly  stated,  but  from  the 
invao-inated  inte(>;ument. 

In  many  fishes  teeth  are  found  far  back  in  the  pharynx,  and  are 
attached  to  the  gill-arches  and  pharyngeal  bones.  I  am  informed  by 
Mr.  J.  A.  Ryder,  whose  extensive  knowledge  of  the  embryology  of 
fishes  renders  his  statements  highly  authoritative,  that  these  teeth  lie 
beyond  the  limits  of  the  invaginated  integument,  and  are  truly  of  hypo- 
blastic derivation.  If  this  be  true,  the  generalization  that  all  teeth  are 
modified  dermal  spines  is  certainly  incorrect.  It  affords  us,  however, 
an  example  in  which  identical  structures  have  been  produced  from  tissue 
of  vastly  different  origin  in  a  similar  manner,  and  in  all  probability 
attrii^utable  to  the  same  causes — viz.  repeated  stimulation  of  a  paiticu- 
lar  point,  which  eventually  gave  rise  to  a  calcified  papilla. 

The  point  at  which  a  tooth  is  about  to  be  developed  is  marked  by  a 
proliferation  of  the  cellular  elements  of  the  tissue  in  which  it  will  ulti- 
mately appear.  These  eventually  arrange  themselves  into  three  organs, 
which  have  been  denominated  the  dentine  organ,  the  enamel  organ,  and 
the  dental  sacculus.  This  latter  organ  becomes  so  modified  in  some  ani- 
mals, in  which  coronal  cement  is  extensively  developed,  as  to  merit  the 
distinction  of  cementum  organ.  Taken  collectively,  tliey  represent  the 
tooth-germ.  C.  S.  Tomes  very  justly  remarks  that  "the  tooth  is  not 
secreted  or  excreted  by  the  tooth-germ,  but  an  actual  metamorphosis  of 
the  latter  takes  place."  The  three  principal  tissues,  dentine,  enamel, 
and  cementum,  thus  produced,  are  formed  from  their  respective  organs, 
and  consequently  separate  parts  of  the  tooth-germ.  Although  many 
adult  teeth  do  not  possess  enamel  upon  their  crowns  {e.g.  edentates  or 
sloths,  armadillos,  etc.),  yet  the  presence  of  an  enamel  organ  in  the  early 
stages  of  growth  is  believed  to  be  a  universal  feature  of  the  development 
of  all  teeth,  and  is  one  of  the  strongest  arguments  for  their  community 
of  origin,  however  much  they  may  have  been  subsequently  modified. 

The  Enamel  and  Dentine  Organs. — In  the  earliest  stages  of  the 
development  of  a  mammalian  tooth,  which  is  here  taken  for  descrip- 
tion, a  slight  longitudinal  depression  in  the  epithelium  covering  the  bor- 
ders of  the  jaws  is  noticeable ;  this  is  somewhat  augmented  in  depth  by 
the  addition  of  a  ridge  upon  either  side  of  it.  At  the  bottom  of  this 
groove  the  deepest  or  Malpighian  layer  of  the  epithelium  grows  down 
into  the  corium  as  a  continuous  fold  or  lamina,  being  directed  down- 
ward and  a  little  inward.  In  cross-section  this  fold  resembles  a  tubu- 
lar gland  and  extends  throughout  the  entire  length  of  the  jaw.  In  the 
positions  where  teeth  are  to  be  formed  the  lower  extremity  of  this 
lamina  is  considerably  enlarged  by  the  rapid  multiplication  of  its  con- 
stituent cells.  The  continuity  of  the  fold  is  now  broken  up,  and  the 
structure  which  is  destined  to  become  the  enamel  organ  appears  as  a  pro- 
cess of  epithelium  comparable  in  shape  to  a  Florence  flask  (Fig.  189). 
The  outermost  layer  of  the  organ  at  this  stage  is  made  up  of  cells  of 


362 


DENTAL  ANATOMY. 


the  columnar  variety  which  still  retain  their  connection  with  the  Mal- 
pighian  layer  above,  from  which  they  were  orignally  derived,  while  the 

interior   of    the    enlarged    ex- 
FiG- 189.  tremity  is  composed  of  polyg- 

onal cells. 

As  development  proceeds,  the 
edges  of  the  enlarged  extremity 
grow  more  rapidly  downward 
than  the  centre,  which  causes  it 
to  assume  a  bell-shaped  form, 
with  the  concavity  directed 
downward.  Synchronous  with 
this  growth,  a  papilla  arises 
from  the  corium  beneath  and 
is  closely  invested  by  the  enamel 
organ.  The  appearance  of  this 
papilla  marks  the  earliest  stage 
in  the  development  of  the  den- 
tine organ,  but  it  will  be  well 
to  examine  more  closely  at  this 
stage  the  structure  of  the  enamel 
organ.  While  it  retained  the 
shape  of  the  Florence  flask  its 
periphery  consisted  of  colum- 
nar epithelium,  the  interior  be- 
ing made  up  of  polygonal  cells. 
Coincidentally  with  its  assump- 
tion of  the  bell  shape  those  cells 
of  the  peripheral  layer  which  are 
brought  into  juxtaposition  with 
the  dentine  bulb  or  organ  un- 
dergo great  elongation  and  en- 
largement, forming  very  regular 
six-sided  prismatic  bodies,  and 
are  known  as  the  enamel-cells. 
The  polygonal  cells  of  the  interior  are  transformed  into  a  stellate  retic- 
ulum composed  of  cells  with  remarkably  elongated  processes  ;  these  pass 
through  a  series  of  unaltered  cells  known  as  the  stndinn  intermedium  into 
the  enamel-cells.  Lastly,  we  have  the  outer  layer,  which  is  little  changed, 
and  still  remains  connected  with  the  ^lalpighian  layer  by  a  slender  cord 
of  epithelium.  This  layer  is  called  the  external  epithelium  of  the 
enamel  organ. 

Before  the  dentine  papilla  makes  its  appearance  "  a  dark  halo,"  more 
vascular  than  the  surrounding  parts  and  corresponding  to  the  epithelial 
lamina  or  fold  which  gives  rise  to  the  enamel  organ,  is  to  be  seen  in  the 
submucous  tissue  or  corium.  Immediately  beneath  the  enlarged  ex- 
tremity of  the  enamel  organ  the  dentine  papilla  is  developed  at  about  the 
time  this  stage  is  reac  hed  by  the  enamel  organ.  In  its  peripheral  layer 
highly  specialized  cells  with  several  sets  of  processes,  odontohkiHtH — 
already  described  in  connection  with  the  tooth-pulj) — make  their  appear- 


Three  Stapes  in  the  Pevelopnient  of  a  Mammalian 
Tooth-germ:  o,  oral  epithelium  heaped  up  over  germ; 
/(,  younger  epithelial  cells;  c,  deep  layer  of  cells  or 
rete  Malpighii ;  rf,  inflection  of  epithelium  for  enam- 
el germ;  e\  stellate  reticulum;/',  dentine  germ;  (j, 
inner  portion  of  future  tooth-sac;  h,  outer  portion 
of  future  tooth-sac;  ?,  vessels  cut  across;  k,  bone  of 
jaw  (from  Tomes,  after  Frey). 


TEETH  OF  THE   VEBTEBRATA.  363 

ance,  while  in  the  remainder  of  the  bulb  numerous  other  cells,  identical 
with  those  of  the  tooth-pulp,  are  developed.  It  also  becomes  highly 
.vascular.  Very  soon  the  odontoblasts  nearest  the  surface  undergo 
metamorphosis  into  a  gelatinous  matrix,  and  their  nuclei  disappear; 
thev  are  next  calcified  from  the  summit  downward,  and  we  soon  recognize 
a  thin  dentine  cap  over  the  entire  bulb,  which  gradually  increases  as 
development  proceeds.  The  central  portions  of  the  odontoblasts  remain 
uncalcified  and  form  the  dentinal  fibrils,  while  the  lateral  ])rocesses  occa- 
sion the  numerous  anastomoses  of  the  dentinal  tubuli  and  fibrils  seen  in 
the  adult  tooth.  The  dentine  mass  is  gradually  thickened  by  successive 
increments  from  within  by  a  repetition  of  the  process  above  described, 
so  that  it  will  thus  be  readily  seen  that  the  configuration  of  the  dentine 
body,  and  consequently  the  entire  tooth,  is  established  as  soon  as  calcifi- 
cation has  fairly  set  in. 

Returning  to  the  enamel  organ,  we  can  now  briefly  follow  its  devel- 
opment to  completion.  We  have  already  seen  that  it  consists  of  an 
outer  layer  of  columnar  epithelium  covering  the  convex  portion,  and  is 
connected  by  a  slender  cord  with  the  INIalpighian  layer  above.  It  con- 
sists also  in  part  of  an  internal  stellate  reticulum  which  passes  by  means 
of  a  layer  of  rounded  cells  (stratum  intermedium)  into  the  enlarged, 
greatly-elongated  prismatic  cells  lining  the  concave  lower  surface,  which 
invests  the  dentine  organ  like  a  cap.  Before  the  enamel  is  completed 
the  external  epithelium,  the  stellate  reticulum,  and  stratum  interme- 
dium disappear  altogether,  but  before  this  atrophy  takes  place  the  neck 
or  epithelial  cord  of  the  enamel  organ  gives  rise  to  the  tooth-germ  of  the 
permanent  tooth  as  a  diverticulum  which  is  developed  in  the  same  way 
as  the  germ  of  the  first  or  deciduous  tooth  just  described. 

The  essential  part  of  the  enamel  organ,  or  rather  that  which  ulti- 
mately results  in  the  formation  of  enamel,  consists  of  enamel-cells. 
These,  as  we  have  said,  become  greatly  elongated  and  assume  the  form 
of  regular  hexagonal  prisms,  which  agree  in  shape  with  the  calcified 
enamel-prisms  of  the  complete  tooth.  Just  as  in  the  odontoblaf^ts  of  the 
dentine,  they  are  transformed  into  a  gelatinous  matrix,  the  nucleus  dis- 
appears, and  calcification  begins  from  above,  the  only  difference  being 
that  the  enamel-prisms  calcify  completely,  and  are  therefore  not  tubular, 
Avhile  in  the  corresponding  structures  of  the  dentine  dentinal  tubuli  are 
left.  Different  views  have  been  advanced  in  regard  to  the  exact  desti- 
nation as  well  as  the  function  of  the  several  parts  of  the  enamel  organ 
spoken  of  above  as  disappearing  by  atrophy.  As  to  the  fate  of  the 
external  epithelium,  Waldeyer  holds  that  after  the  disappearance  of 
the  stellate  pulp  it  becomes  applied  to  the  outer  surface  of  the  enamel 
as  the  membrane  of  Nasmyth,  which  Avould  certainly  seem  to  be  its 
most  natural  fate  ;  but  Kolliker,  Magitot,  and  Legros  claim,  on  the 
other  hand,  that  it  disapjiears  altogether.  Most  authors  believe  that 
the  enamel  organ  is  devoid  of  vascularity,  but  Beal  asserts  that  there  is 
a  vascular  network  in  the  stratum  intermedium.  If  it  be  non-vascular, 
then  it  is  more  than  probable  that  the  pulp  represents  stored-up  pabulum 
from  which  the  requisite  formative  energy  is  derived.  If  vascular,  it 
then  probably  subserves  a  mechanical  purpose  only,  as  some  authorities 
believe. 


364  DENTAL  A^\iT03IY. 

The  Dental  Scteculus  and  Cement  Organ. — So  far,  no  mention  has 
been  made  of  the  development  of  the  dental  sacculus.  At  an  early 
period  in  the  growth  of  the  dentine  papilla  a  process  of  the  submucous 
tissue  arises  from  its  base  and  seems  to  grow  upward  on  the  outside  of 
both  dentine  and  enamel  oi'gans,  finally  coalescing  on  top,  so  as  to  enclose 
the  growing  tooth-germ  in  a  shut  sac,  the  dental  sacculus.  AMsether 
there  is  an  actual  groMth  of  processes  from  the  base  of  the  dentine  bulb, 
or  whether  the  adjacent  connective  tissue  is  transformed  into  it,  appears 
not  to  have  been  very  accurately  determined ;  at  all  events,  the  con- 
nective tissue  immediately  in  contact  with  the  germ  soon  becomes 
distinguishable  from  that  external  to  it  by  becoming  richer  in  cells, 
vessels,  and  fibrillar  elements.  When  the  sacculus  is  fully  formed,  it 
is  made  up  of  an  outer  and  an  inner  wall,  both  richly  vascular.  The 
outer  wall  becomes  the  dental  periosteum,  while  in  the  inner  wall, 
especially  in  the  vicinity  of  the  roots,  osteoblasts  appear  and  are  calci- 
fied into  cementum,  as  in  the  formation  of  ordinary  bone-tissue.  Its 
close  application  to  the  surface  of  the  enamel,  and  ])artial  or  imperfect 
calcification  in  most  teeth,  give  rise  to  the  membrane  of  Nasmyth.  In 
those  animals,  however,  in  which  coronal  cement  is  ibrmed,  such  as  the 
Herbivora,  there  is  developed  in  connection  with  the  inner  wall,  between 
it  and  the  enamel,  a  fibro-cartilaginous  structure  containing  character- 
istic cartilage-cells.  These  undergo  calcification  in  a  manner  not  dif- 
ferent from  that  seen  in  the  formation  of  cartilage  bone,  and  produce  the 
cementum  in  the  teeth  of  these  animals.  It  is  then  known  as  the 
cementum  organ. 

We  have  now  made  clear,  we  trust,  as  complete  a  statement  of  the 
anatomy  of  a  single  tooth  as  is  consistent  with  brevity,  but  which  will 
serve  as  a  basis  for  the  comprehension  of  the  more  special  part  of  our 
subject — viz.  the  morphology  of  the  teeth  in  the  various  subdivisions  of 
the  Vertebrata. 

The  Accessory  Oegans — the  Teeth,  their  Structure,  Devel- 
opment, Replacement,  and  Attachment,  in  Fishes. 

It  will  be  impossible  to  gain  anything  like  a  concise  understanding 
of  the  dental  organs  of  this  extensive  assemblage  of  vertebrate  forms 
until  we  have  first  briefly  outlined  their  classification.  In  this  I  have 
followed  Prof  Gill,  believing  that  his  interpre<ations  more  nearly  coin- 
cide with  a  natural  arrangement. 

It  is  a  common  practice  of  naturalists  to  consider  the  Vertebrata  as 
divisible  into  five  classes,  as  follows :  Pisces,  or  fishes ;  Batrachia.  or 
frogs,  salamanders,  etc. ;  Reptilia,  or  snakes,  turtles,  lizards,  etc. ;  Airs, 
or  birds ;  and  Mammalia,  or  mammals ;  but  according  to  Prof.  Gill 
there  are  differences  quite  as  great,  if  not  greater,  betw'een  certain  mem- 
bers of  the  old  class  Pisces  as  there  arc,  for  example,  between  some  fishes 
and  frogs.  For  this  reason  he  divides  the  permanently  gill-bearing  ver- 
tebrates, or  those  which  aerate  the  blood  throughout  the  entire  life  of  the 
individual  by  means  of  specially  adapted  organs  known  as  *'  gills,"  into 
four  classes,  which  he  defines  as  follows  : 


TEETH  OF  THE   VERTEBRATA.  365 

I.  Skull  undeveloped,  witli  the  notochord  persistent  and  extending  to  the  anterior 
end  of  the  liead.     Brain  not  distinctly  ditlerentiated.     Heart  none. 

Leptocardii. 
II.  Skull  more  or  less  developed,  with  the  notochord  not  continued  forward  beyond 
the  pituitary  body.     Brain    differentiated   and  distinctly  developed.     Heart 
developed  and  divided  at  least  into  auricle  and  ventricle. 

A.  Skull    imperfectly  developed,   with   no  lower  jaw.      Paired    fins   undeveloped, 

with  no  shouldei'-girdle  nor  pelvic  elements.     Gills  purse-shaped. 

Maksipobranchii. 

B.  Skull  well  developed,  with  a   lower  jaw.     Paired   fins   developed  (sometimes 

absent  through  atropiiy),  and  with  shoulder-girdle  (lyrii'orm  or  furcula- 
shaped,  curved  forward,  and  with  its  respective  sides  connected  below),  and 
with  pelvic  elements.     Gills  not  purse-shaped Lyrifera. 

a.  Skull  witiiout  membrane  bones  ("a  rudimental  opercular  bone"  in  Cliiincera) ; 

gills  not  free,  the  branchial  openings  slit-like,  usually  several  in  number ; 
exoskeleton  placoid,  sometimes  obsolete ;  eggs  few  and  large. 

Elasmobranchii. 

b.  Skull  with  membrane  bones;  gills  free;  branchial  openings  a  single  slit  on  each 

side,  sometimes  confluent ;  exoskeleton  various,  not  piacoid  ;  eggs  compara- 
tively small  and  numerous Pisces. 

Tlie  first  of  these  classes,  Leptoeardii,  includes  a  few  small  fish-like 
animals,  such  as  the  well-known  amphioxus  or  lancelet  occurring  on  our 
coast,  in  which  no  skull  exists.  They  are  in  many  ways  most  remark- 
able f  )rms,  being  the  most  primitive  of  all  vertebrates,  but  as  they  are 
devoid  of  teeth,  this  class  can  be  dismissed  without  further  consideration. 
The  next,  Marslpohranch'ii,  embraces  the  lampreys,  whose  "horny  teeth" 
have  already  been  alluded  to.  The  relationship  as  well  as  examples  of 
each  order  of  the  remaining  two  classes  is  expressed  in  the  subjoined 
table  (p.  366),  which  is  compiled  from  Dr.  Gill's  papers  on  the 
classification  of  fishes. 

The  Accessot'i/  Organs. — A  consideration  of  these  organs  necessarily 
involves  not  only  a  study  of  the  bones  and  cartilages  taking  share  in 
the  boundary  of  tiie  oral  cavity,  but  of  all  bones  and  cartilages  in  connec- 
tion with  which  teeth  are  developed.  It  would  likewise  properly  include 
a  mention  of  the  muscles  which  move  these  parts,  together  with  the  vas- 
cular and  nervous  supply ;  but  o^viug  to  their  great  range  of  variation, 
as  well  as  the  limited  space  at  my  disposal,  these  latter  will  not  be  con- 
sidered. This,  in  my  juilgment,  is  best  accomplished  by  describing  the 
normal  arrangement  in  some  typical  fish  and  comparing  all  others  with 
it.  For  this  purpose  a  gadoid  fish,  or  one  of  the  cod  tribe,  is  most  suit- 
able, since  it  exhibits  the  structure  which  obtains  in  a  large  majority  of 
ichthyic  forms. 

If  a  well-cleaned  skull  be  examined,  it  will  be  seen  to  consist,  in  the 
first  place,  of  a  cranium  or  brain-box,  or  that  part  which  remains  intact 
after  the  skull  has  been  boiled  or  macerated  a  sufficient  length  of  time 
to  cause  the  soft  parts  to  disappear  and  the  arches  and  appendages  to 
become  disarticulated.  This  contains  the  brain,  and  becomes  continuous 
at  its  lower  back  part  with  the  vertebrae  or  axial  pieces  of  the  body  skele- 
ton into  wliicli  the  spinal  cord  jiasses.  Suspended  from  either  side  of  its 
posterior  portion  there  is  a  chain  of  bones  which  extends  down  beneath 
the  throat  and  bears  the  pectoral  fins  ;  this  is  known  as  the  shoulder-gir- 
dle or  scapular  arch  (see  Fig.  190). 

A  short  distance  in  front  of  this,  or  at  a  point  about  midway  between 
the  root  of  the  scapular  arch  and  the  eye-socket,  another  arch  springs 


366 


DENTAL  ANATOMY. 


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TEETH  OF  THE   VERTEBRATA. 


367 


from  the  side- wall  of  the  cranium  and  passes  downward  and  forward  to 
the  proximal  portion  of  the  lower  jaw,  which  is  attached  to  it ;  this  is 
known  as  the  hyo-mandibidar  arch  (see  Fig.  204).     Attached  to  the  pos- 


368  DENTAL  ANATOMY. 

terior  portion  of  this  arch  are  several  broad,  flat,  scale-like  bones  which 
cover  the  gills  and  are  called  opercular  bones.  The  upper  posterior  one 
is  the  operculum.  The  one  in  front  of  this,  presenting  a  curved  outline 
anteriorly  and  a  ])osterior  serrate  border,  is  the  preoperculum,  while  the 
two  beneath  are  the  interoperculum  and  suboperculum  respectively.  The 
arch  itself  is  composed,  first,  of  the  hyo-mcmdibular  bone  (Fig.  190, 
hy),  which  by  its  proximal  extremity  is  attached  to  the  side-wall  of  the 
cranium,  being  lodged  in  a  distinct  oblong  socket ;  secondly,  of  the 
(piadrate  (qu,  Fig.  190),  Avhich  articulates  with  it  by  suture  at  its  lower 
extremity ;  thirdly,  the  symplectic,  a  small  splint  occupying  a  groove 
in  the  inner  side  of  the  quadrate ;  and,  lastly,  the  lower  jaw,  which  is 
movably  articulated  with  the  quadrate  and  which  normally  supports 
teeth.  Each  half  is  made  up  of  the  dcntary  or  tooth-bearing  piece, 
meeting  its  fellow  of  the  opposite  side  in  the  median  line  or  symphysis, 
and  an  articular  piece  which  connects  the  dentary  with  the  quadrate. 
To  this  may  be  added  the  coronoid,  a  small  bone  superimposed  above 
the  junction  of  the  articular  and  dentary,  and  an  cnif/ular  which  lies 
just  beneath  the  articulation  of  the  quadrate  and  articular. 

From  the  region  of  the  quadrate  another  chain  of  bones  extends 
upward,  forward,  and  inward  to  the  anterior  part  of  the  roof  of  the 
mouth,  where  it  is  attached  by  ligament  to  the  side  of  the  vomer,  or 
that  bone  a\  hich  forms  the  prominent  rostrum  of  the  cranium  after  the 
removal  of  the  arches.  This  chain  is  known  as  the  pokdo-qvadj-ate 
arch,  and  the  bones  entering  into  its  composition  are  the  eido-,  mefto, 
ecto-pteryr/oid.s  and  the  palatine.  The  ento-pterygoid  is  applied  to  the 
hyo-mandibular  and  quadrate  upon  their  anterior  margins ;  the  meso- 
pterygoid  starts  out  from  the  quadrate  and  ento-pterygoid,  and  extends 
toward  the  vomer,  where  it  meets  the  palatine,  which  completes  the 
arch.  The  ecto- pterygoid  lies  above  the  junction  of  the  meso-pterygoid 
and  the  palatine  (Fig.  190). 

Immediately  in  front  of  the  vomer,  and  attached  to  it  and  to  the  pala- 
tines, are  two  considerable  bones  which  project  downward  and  backward, 
bounding  the  u}>]ier  posterior  portion  of  the  canthus  of  the  mouth — the 
superior  maxi/knies.  In  front  of  these,  again,  are  the  pre-  ovmfermax- 
illaries,  limiting  the  anterior  boundary  of  the  oral  cavity  above. 
Another  bone,  which  in  some  forms  (ex.  catfishcs)  reaches  the  roof  of 
the  mouth,  needs  to  be  noticed  in  this  connection.  The  suborbital 
ring,  or  those  bones  which  encircle  the  orbit  below,  articulates  by  its 
most  anterior  piece  (lachrymal)  with  a  bone  suturally  united  to  the 
cranium  and  taking  part  in  the  boundary  of  the  orbit  in  front  and 
above.  This  is  the  prefrontal,  and,  as  already  remarked  in  the  cat- 
fishes,  owing  to  the  width  of  the  mouth  takes  part  in  the  formation  of 
its  bony  roof,  and  in  some  species  bears  teeth.  This  bone  is  frequently 
mistaken  for  the  vomer,  but,  as  I  have  recently  ascertained,  is  certainly 
tlie  ]n-efrontal,  Avhich  must  likewise  be  added  to  the  category  of  tooth- 
sup]iorting  bones  in  fishes. 

The  several  arches  and  bones  so  far  enumerated,  with  the  exception 
of  the  sca])ular  arcli — wliich  never,  to  my  knowledge,  is  dentigerous — are 
in  direct  relation  with  the  mouth,  and  are  exclusively  concerned  in  pre- 
hensile and  crushing  functions ;  but  those  which  are  to  follow,  especially 


TEETH   OF  THE   VERTEBRATA.  369 

the  branchial  arches,  Mere  primarily  used  in  connection  with  respira- 
tion, so  that  any  relations  with  the  teeth  which  they  may  have  subse- 
quently acquired  must  be  looked  upon  as  a  secondary  modification. 
This  peculiarity,  moreover,  is  of  such  wide  application  in  the  class 
Pisces  that  a  description  of  these  parts  cannot  well  be  omitted  in  a  con- 
sideration of  the  accessory  organs. 

The  hyo-branchial  skeleton  lies  beneath  the  base  of  the  cranium,  and 
is  pretty  well  concealed  in  a  side  view  by  the  opercular,  hyo-mandibular, 
and  cpiadrate  bones.  It  is  connected  with  the  rest  of  the  skull  at  two 
points — viz.  by  the  articulation  of  the  stylo-hyal  bone  with  the  hyo- 
mandibular,  and  the  other  by  means  of  loose  connective  tissue  which 
binds  the  upper  portion  of  the  branchial  arches  to  the  base  of  the  cra- 
nium. Its  general  structure  will  be  best  understood  by  describing  it  as 
composed  of  a  series  of  transverse  bony  arches  placed  one  in  front  of  the 
other,  rising  up  from  the  floor  of  the  mouth  and  meeting  in  the  median 
line  above. 

The  most  anterior  of  these  is  the  hyoid  arch,  which  is  formed  by  two 
median  basilar  pieces  upon  either  side,  the  basi-hyals.  Passing  from 
within  outward,  we  have  first  the  cerato-hyah,  to  which  are  appended 
the  branchiostec/al  rays.  The  next  piece  in  the  arch  is  the  epi-hyal,  fol- 
lowing which  is  the  stylo-hyal.  This  latter  bone  is  a  slender  rod,  and 
serves  to  complete  the  connection  of  the  hyoid  arch  with  the  hyo-man- 
dibular bone.  From  the  interval  between  the  two  most  anterior  basi- 
hyals  there  projects  a  small  bone  forward  which  supports  the  tongue,  and 
is  hence  called  the  ento-  or  hyo-glossal.  Projecting  backward  from  the 
inferior  surface  of  these  same  basi-hyals  is  another  piece,  the  uro-hyal. 

Behind  the  hyoid,  and  similarly  composed,  are  the  five  branchial 
arches,  of  which  the  last  two  are  somewhat  modified.  The  three  ante- 
rior ones  are  made  up  of  median  basilar  bones,  the  basi-branchihyals. 
With  these  are  articulated  the  hypo-b ranch  ials  upon  the  outside,  after 
which  follow  the  cerato-branchial  and  epi-branchial  pieces.  In  the 
fourth  branchial  arch,  counting  from  before  backward,  the  hypo- 
branchials  are  absent,  and  the  uppermost  segments  are  considerably 
dilated  and  support  teeth  ;  they  are  then  known  as  the  superior  pharyn- 
geal bones.  The  fifth  arch  is  quite  rudimentary,  containing  only  the 
cerato-branchial  elements,  which  are  generally  much  enlarged  and  bear 
teeth  ;  these  are  the  inferior  pharyngeal  bones. 

The  arrangement  here  described  is  found  without  substantial  modi- 
fication except  as  regards  relative  size  and  the  degree  of  ossification  of 
the  several  parts  in  nearly  all  the  sub-class  Teleosfci.  In  the  Elasmo- 
branehii,  however,  the  skull  remains  largely  cartilaginous,  and  the  hyo- 
mandibular  arch  is  always  more  or  less  imperfectly  represented.  The 
maxillae  and  premaxill?e  are  likewise  absent.  In  the  chimeroid  division 
{Holocephall)  neither  the  hyo-mandibular  nor  quadrate  elements  can  be 
made  out,  the  mandible  being  attached  directly  to  a  broad  triangular 
cartilaginous  lamella  which  stretches  out  from  the  sides  of  the  base  of 
the  skull,  and  whose  anterior  part  bears  the  teeth  of  the  upper  jaw.  It 
will  thus  be  readily  understood  that  tliis  cartilaginous  plate,  continuous 
with  the  chondro-cranium,  represents  both  the  undifferentiated  u]iper 
portion  of  the  hyo-mandibular  and  all  of  the  palato-quadrate  arches. 

Vol.  I.— 24 


370  DENTAL  ANATOMY. 

In  tlie  Plagiostomi  (sharks  and  rays),  on  the  other  hand,  a  separate  car- 
tihiginous  element  representing  the  hyo-mandibuku*  bone  is  always  pres- 
ent, and  affords  an  articular  surface  to  the  lower  jaw  or  mandible,  which, 
moreover,  in  all  the  ela.smobranchiates  consists  of  a  single  cartilaginous 
bar,  the  primitive  Meckelian  cartilage.  The  palato-quadrate  arch  is 
likewise  present  and  forms  the  dentigerous  border  of  the  upper  jaw  (see 
Fig.  204).  Since  the  hyo-branchial  skeleton  in  these  forms  is  not  con- 
cerned in  the  support  of  teeth,  it  can  be  dismissed  without  further 
mention. 

The  principal  deviations  in  the  structure  and  relationship  of  the  den- 
tigerous apparatus  from  the  typical  teleostean  one  to  be  met  with  in  the 
sub-class  Ganoidei  are  furnished  by  the  Dipnoi  and  Chondroganoidei. 
The  former  of  these  orders  includes  the  three  living  genera  C'eratodus, 
I-'rofopfcrus,  and  Lepidosircn  of  Australia,  Africa,  and  South  America 
respectively.  They  are  most  remarkable  and  interesting  representatives 
of  types  in  some  respects  low  down  in  the  scale  of  ichthyic  organization, 
while  in  others  high,  in  that  they  furnish  many  transitional  characters 
between  true  fishes  and  the  Batrachia  (frogs  and  salamanders).  It  is 
highly  probable  that  from  some  as  yet  undiscovered  relative  of  this 
group  the  Batrachia  have  been  derived  by  descent. 

In  this  order  the  skull  is  devoid  of  both  maxillae  and  prcmaxillse, 
and,  as  in  the  chimeroid  elasmobranchiates,  the  hyo-mandibular  arch  is 
not  completely  differentiated,  the  lower  jaw  being  articulated  directly  to 
the  cranium.  There  is,  hoAvever,  a  well-defined  palato-quadrate  arch 
supporting  teeth.  The  hyo-branchial  skeleton,  although  resembling  the 
teleostean  type  of  structure  considerably,  is  edentulous.  In  the  L'hon- 
droc/anoidci  (sturgeons)  the  skull  as  well  as  the  arches  remain  largely 
cartilaginous.  The  suspensorium  (proximal  part  of  the  hyo-mandibular 
arch)  presents  two  elements,  usually  homologized  with  the  hyo-mandib- 
ular and  quadrate  pieces  of  the  teleostean  skull ;  the  latter  of  these 
pieces  affords  attachment  to  the  mandible.  There  is  also  a  palato-quad- 
rate arch.  Only  one  species  of  this  group,  the  shovel-nose  sturgeon, 
possesses  teeth,  and  these,  according  to  Owen,  apjiear  only  in  the  young. 

The  remainder  of  the  Ganoidei  agree  with  the  Telcostci  in  the  structure 
and  arrangement  of  the  accessory  organs.  The  latter  sub-class,  how- 
ever, exhibits  numerous  minor  variations,  which  are  confined  principally 
to  modifications  of  the  hyo-branchial  skeleton,  such  as  the  loss  or  atrojihy 
of  certain  of  its  component  elements;  these  are  so  numerous  and  varied 
in  their  nature  that  it  would  be  impossible,  and  quite  foreign  to  the 
object  of  the  present  article,  to  enumerate  them. 

Teetli  of  the  Elaxmohranehii. — As  already  observed,  this  class  is  divis- 
ible, not  only  by  the  differences  which  obtain  in  the  arrangement  of  the 
several  arches,  but  by  the  disposition,  structure,  and  manner  of  replace- 
ment of  tlie  teeth,  into  two  ])rimary  groups,  of  which  the  sharks 
and  ravs  constitute  one,  and  the  Chiniferce  the  other.  Of  these,  the 
former  is  the  more  primitive,  and  in  all  probability  gave  origin  to  the 
typical  fishes,  while  the  latter  rcseml)les  more  closely  the  dipnoans,  and 
may  indeed  })rove  to  liave  been  their  ancestors. 

The  teeth  of  the  sharks  are  always  numerous,  and  are  ]H^e-eminently 
adapted  to  the  predaceous  habits  of  their  possessor.     They  are  borne 


TEETH  OF  THE   VERTEBRATA.  371 

upon  the  cartilaginous  mandibuli  and  palato-quadrate  arches,  being 
attached  not  to  the  cartilages  themselves,  but  to  a  thick,  dense  fibrous 
membrane  Avhich  forms  an  external  investment.  They  are  arranged  in 
concentric  rows  on  the  summit  and  inner  surface  of  the  jaws,  being 
developed  from  the  bottom  of  a  longitudinal  fold  of  the  lining  membrane 
in  this  situation,  known  as  the  thecal  fold.  The  teeth  of  the  upper- 
most row,  or  those  occupying  the  margins  of  the  jaws,  stand  upright 
and  do  service  as  the  functional  ones  until  discarded ;  those  of  the  next 
row,  as  well  as  all  the  succeeding  ones,  usually  occupy  a  recumbent 
position,  with  their  apices  directed  downward  or  upward  according  as 
they  belong  to  the  upper  or  lower  series ;  but  it  not  unfrequently  hap- 
pens in  some  species  that  the  second,  and  even  the  third,  rows  may 
exhibit  different  degrees  of  erection.  As  a  general  rule,  but  a  single 
row  of  teeth  are  in  use  at  one  time.  The  individual  teeth  composing 
the  longitudinal  rows  may  be  disposed  with  reference  to  those  of  the 
succeeding  ones  so  as  to  be  parallel  vertically,  as  is  M^ell  exemplified 
in  the  genus  Lamna,  or  they  may  be  placed  in  such  a  manner  as  to 
alternate  with  each  other,  a  condition  seen  in  the  blue  shark  (Car- 
charias).  As  would  naturally  be  surmised  from  this  arrangement,  the 
way  in  which  succession  takes  place  is  for  the  row  beneath  to  rise  up 
and  take  the  place  of  those  in  use.  This  is  accomplished  by  the  fibrous 
gum  in  which  their  bases  are  imbedded  sliding  bodily  over  the  curved 
surface  of  the  jaws  from  within  outwaixl,  continuously  bringing  fresh 
rows  into  position,  as  was  long  since  demonstrated  by  Prof.  Owen. 

It  thus  happens,  on  account  of  this  peculiar  and,  in  my  judgment, 
remarkably  primitive  manner  of  succession,  that  large  numbers  of  teeth 
little  worn  are  cast  oif  during  the  life  of  each  individual,  and  that 
replacement  goes  on  far  in  excess  of  the  actual  requirements  of  the  ani- 
mal, and  quite  independently  of  their  temporary  use  as  organs  of  pre- 
hension and  mastication — a  fact  which  in  itself  demonstrates  their  der- 
mal relationship.  The  only  assignable  cause  for  this  extravagant  devel- 
opment of  teeth,  it  appears  to  me,  is  due  to  inequalities  in  the  rapidity 
of  growth  in  different  parts  of  the  body,  which  causes  the  integument 
invaginated  during  embryonic  development  to  be  restored  or  evaginated 
during  adult  growth.  If  this  hypothesis  be  correct,  then  the  whole 
question  of  the  force  concerned  in  the  succession  of  the  teeth  is  reduced 
to  the  simple  explanation  of  inequalities  of  growth  primarily,  however 
much  it  may  have  been  subsequently  complicated  and  obscured  in  the 
higher  forms.  Looked  at  from  this  standpoint,  it  is  not  such  an 
inscrutable  mystery  as  C.  S.  Tomes  and  others  would  have  us  believe. 

Considerable  variety  of  form  exists  in  the  teeth  of  the  different  species ; 
they  may  be  heterodonf  (that  is,  different  in  various  parts  of  the  jaws) ; 
isodont  (alike  throughout) ;  or  hemihomodont  (in  which  the  individual 
teeth  of  the  lower  jaw  are  alike,  but  different  from  those  of  the  upper 
jaw,  and  reciprocally).  In  all,  the  teeth  nearest  the  back  part  of  the 
mouth  are  smaller  than  those  in  front.  The  simplest  form  to  be  met 
with  is  the  unmodified  cone  with  a  sharp  point  and  a  broad  base.  Such 
is  found  in  the  large  Rhinodon  and  some  "dog-fishes;"  to  this  may  be 
added  basal  denticles,  as  in  the  genus  Lamna;  or  it  may  have  a  com- 
pressed triangular  outline  with  serrate  edges,  as  in  the  upper  teeth  of 


372 


DENTAL  ANATOMY. 


the  blue  shark  (Carcharias).  These  lateral  serratures  may  become  so 
strongly  developed  as  to  give  to  the  tooth  a  distinct  comb-like  appear- 
ance— e.g.  lower  teeth  oi'  Xotidanus  (Fig.  191). 

Fig.  191. 


Teeth  of  Nolidanus  (after  Gunther). 

The  most  remarkable  modification  in  the  dental  organs  of  sharks  is 
exemplified  by  the  Port  Jackson  shark  (Cestradon),  in  which  the  poste- 
rior teeth  gradually  become  broad  and  form  a  regular  pavement  on  the 
surface  of  the  jaws  similar  to  that  seen  in  many  rays.  This  structure 
exists  in  consonance  with  the  shellfish-feeding  habits  of  the  animal,  in 
the  exercise  of  which  great  crushing  and  comminuting  power  is  required 
to.  be  exerted.  These  fishes  are  of  especial  interest,  inasmuch  as  they  are 
the  only  living  representatives  of  an  extensive  and  widely-distributed 
group  which  appeared  on  the  earth  far  back  in  the  Devonian  Epoch, 
and  whose  remains,  as  Owen  justly  remarks,  "  would  have  been  scarcely 
intelligible  to  us  unless  the  key  to  their  nature  had  been  afforded  by  the 
teeth  and  spines  of  the  living  cestracionts." 

The  teeth  of  the  anterior  part  of  the  jaw  (Fig.  192)  are  the  smallest, 
and  present  a  compressed  conical  form  with  the  apex  produced  into  a 
sharp  point.  Proceeding  backward,  they  gradually  assume  an  oblong 
oval  outline,  progressively  increasing  in  size,  their  sides  becoming 
applied  to  each  other  in  such  a  manner  as  to  form  a  regular  pavement. 
The  maximum  size  is  attained  at  about  the  fourth  tooth  from  the  poste- 
rior end  of  the  series,  after  which  they  decrease  rapidly,  although  still 
preserving  their  modified  crushing  form. 

The  progressive  changes  in  size  and  form,  as  well  as  the  disposition, 
of  the  most  highly  modified  teeth  in  this  animal,  are  seen  to  be  in  direct 
accord  with  the  uses  to  which  they  are  put,  and  serve  to  illustrate,  as  so 


TEETH  OF  THE  VERTEBRATA. 


373 


many  other  dentitions  do,  the  reasonableness  of  the  view  originally  pro- 
posed by  J.  A.  Ryder,  to  the  eliect  that  mechanical  causes  have  been 
largely  instrumental  in  bringing  about  the  modifications  of  the  teeth. 
It  will  be  readily  understood  that  the  greatest  mechanical  advantage 
would  be  gained  and  the  greatest  pressure  exerted  by  passing  the  mor- 
sel to  be  crushed  to  the  posterior  part  of  the  mouth.  The  teeth  in  this 
situation  or  in  its  vicinity  have  sustained  the  greatest  amount  of  strain, 
and  are  consequently  most  modified,  while  those  of  the  anterior  part  of 
the  mouth  have  been  largely  exempt  from  such  influences,  and  are  there- 
fore little  modified.  I  will  have  occasion  to  recur  to  this  hypothesis  on 
a  future  page. 

The  teeth  of  the  rays  present  quite  as  great,  if  not  a  greater,  range  of 
variety  than  do  the  sharks.  In  general,  they  are  more  numerous,  more 
closely  crowded  together,  and  possess  forms  better  adapted  for  crushing 
than  for  seizing  and  lacerating.  They  are  developed  in  the  same  way  as 
in  sharks,  rising  up  from  the  bottom  of  a  thecal  fold  on  the  inner  sur- 
face of  the  jaw  and  being  carried  upward  by  a  rotation  outward  of  the 

Fig.  192. 


Lower  Jaw  of  Port  Jackson  Shark  {Cestracion  phiUippsi). 

membrane  in  which  they  are  imbedded.  In  Raia  stelluata,  from  the 
California  coast,  the  teeth  succeed  one  another  vertically,  as  in  Lamna 
among  the  sharks,  and  do  not  form  a  close  pavement  on  the  biting  sur- 
face of  the  jaws,  they  being  separated  from  each  other  by  slight  intervals. 
In  form  the  base  of  the  crown  represents  an  equilateral  triangle,  with 
the  apex  directed  forward;  from  this  a  prominent  ridge  passes  back- 
ward across  the  middle  line  of  the  base,  and  is  produced  into  a  sharp 
conical  point.  The  teeth  of  the  anterior  part  of  the  mouth  are  the 
largest,  and  gradually  decrease  in  size  as  the  canthus  or  angle  of  the 
mouth  is  reached.     In  the  "  barndoor  skate "  (Eaia  Icevis)  the  teeth 


374 


DENTAL  ANATOMY. 


are  more  closely  set,  but  are  not  in  absolute  contact ;  as  in  Baja  stelluata, 
those  of  the  several  rows  are  arranged  vertically,  but  their  bases  are 
more  rounded,  with  only  a  faint  indication  of  the  backwardly  project- 
ing cusp,  which  is  confined  to  the  teeth  of  the  anterior  part  of  the  jaws. 
In  the  common  "stingray"  {Trygon  centruriis)  the  teeth  are  some- 
what quadrangular,  and  have  their  sides  directly  applied  to  each  other, 
forming  a  dental  sheath  of  continuous  pavement  over  the  working  sur- 
face of  the  jaws;  those  of  the  successive  rows  are  disposed  diagonally. 
Their  crowns  are  of  an  oval  form,  well  adapted  for  crushing  and  grind- 
ing hard  substances.  The  "  eagle  rays"  or  "sea-devils"  present  a  series 
of  modifications  of  the  teeth  which  diverges  from  that  of  the  stingrays, 
and  terminates  in  the  most  unique  of  all  dentitions  to  be  found  amongst 
the  Vertebrata — viz.  that  of  Aetohaiis.  Of  this  group  the  genus  Bhi- 
noptera  possesses  tessellated  teeth  with  flat  hexagonal  crowns,  of  which 

Fig.  193. 


h  c 

Teeth  of  Rays:  a,  b,  Rhinoptera ;  c,  Mylidbatis;  d,  Aelobatis. 

the  median  or  anterior  ones  may  be  elongated  transversely.  The  fossil 
species,  M.  Woodwardi,  has  the  three  median  vertical  rows  enlarged. 
In  llyliobatis  there  is  only  one  large  median  row,  Mith  three  smaller 
ones  upon  either  side,  M'hile  in  Aelobatis  the  teeth  of  the  median  row 
alone  remain,  and  are  articulated  to  each  other  by  a  finely  serrate  border. 
These  modifications  are  well  shown  in  the  accompanying  figures.  The 
anomalous  saw^fish  (Pnstis),  although  in  no  way  peculiar  as  far  as  the 
teeth  of  the  mouth  are  concerned,  nevertheless  j)ossesses  a  remarkably 
elongated  snout,  armed  u})on  either  side  by  a  row  of  hard,  conical  liodies 
usually  referred  to  as  teeth.  In  their  histological  structure  they  agree 
with  true  teeth,  but  exhibit  the  peculiarity  of  being  lodged  in  separate 
sockets  and  growing  from  persistent  pulps — a  condition  unusual  among 
fishes.  It  is  more  than  probable  that  they  are  dermal  spines  specially 
developed  in  this  situation  for  some  important  purpose  which  is  not  at 
present  fully  determined. 


TEETH   OF  THE   VERTEBRATA.  375 

I  proceed  next  to  consider  the  teeth  of  the  Chiniserre  {HolocephaU), 
which  group  some  authors  make  equal  in  rank  with  the  Efasmohranchii, 
which  then  inchide  the  sharks  and  rays  only.  The  peculiarities  of  the 
dental  succession  alone  of  this  latter  group,  it  appears  to  me,  is  quite 
sufficient  to  separate  them  widely  from  all  others,  and  it  seems  some- 
what remarkable  that  this  character  has  never  been  utilized  by  the 
systematists  in  their  schemes  of  classification. 

The  teeth  of  the  "  ratfish  "  {CMmcera  phnnbea)  are  six  in  number,  of 
which  two  belong  to  the  lower  and  four  to  the  upper  jaw.  The  two 
inferior  ones  may  be  described  as  broad,  slightly-curved  plates  of  mod- 
erate thickness  in  the  form  of  a  right-angled  triangle.  That  border 
which  corresponds  to  the  perpendicular  is  almost  straight,  and  is  lodged 
in  a  shallow  groove  which  runs  lengthwise  along  the  inner  surface  of 
the  jaw  ;  that  which  represents  the  base  is  applied  to  the  corresponding 
surface  of  the  opposite  tooth  ;  while  the  border  representing  the  hypoth- 
enuse  forms  the  free  cutting  edge  of  the  tooth.  This  border  is  some- 
what  devious,  being  interrupted  by  three  prominences.  The  niner 
surface  is  also  slightly  ribbed.  The  two  posterior  upper  teeth  are 
similar  plates  of  a  quadrilateral  form  with  their  free  edges  roughly 
serrat^e.  The  two  anterior  teeth  above  somewhat  resemble  ordinary 
mammalian  incisors,  and  are  large  and  scalpriform.  This  peculiarity 
has  given  them  the  name  "  rabbit-fish "  or  "  ratfish."  Each  tooth 
has  a  cavity  in  the  edge  by  which  it  is  attached  and  in  which  the  pulp 
is  lodged.  But  a  single  set  of  teeth  are  developed  during  the  life  of  the 
individual,  and  these  are  of  persistent  growth.  Another  living  allied 
genus,  Callorhi/nchus,  is  found  in  Australian  seas,  in  which  the  teeth  are 
similar  to  those  of  Chimaera,  but  in  the  two  fossil  genera,  Edaphadon 
and  Passalodon,  supposed  to  belong  to  this  group,  the  teeth  are  anky- 
losed  to  the  jaw,  which  is  more  or  less  bony.  On  this  account  it  is 
more  than  probable  that  they  are  to  be  referred  to  the  dipnoans  rather 
than  to  the  chimaeroids. 

The  Teeth  in  True  FisJies. — The  teeth  of  the  class  Pisces,  although 
apparently  presenting  an  extensive  range  of  modification,  have  not, 
debarring  the  dipnoan  ganoids  and  the  plectognath  teleosts,  as  a  general 
rule,  departed  very  widely  from  the  simple  conical  pattern.  There  are 
some  forms,  however,  in  which  the  structure  and  arrangement  are  quite 
anomalous.  It  is  in  this  group  that  the  maximum  development,  as  far 
as  numbers  is  concerned,  is  reached.  The  salmon,  pike,  and  some  per- 
coids  may  be  cited  in  which  teeth  are  developed  in  almost  every  con- 
ceivable part  of  the  mouth  and  number  many  thousands ;  while  in 
others,  as  the  carps  and  suckers,  they  are  few  and  confined  to  the 
pharyngeal  bones.  In  others,  again,  as  the  pipefishes  and  sea-horses, 
teeth  are  entirely  absent. 

The  teeth  of  the  dipnoans  are  unique  among  fishes,  and,  like  those  of 
the  chimperoids,  are  limited  in  number  and  grow  from  persistent  pulps. 
The  teeth  of  the  dipnoans,  the  dental  plates  of  the  chima^roids,  and  the 
so-called  "  rostral  teeth  "  of  the  sawfish  are  the  only  examples  so  far 
known  of  permanent  teeth  to  be  met  with  among  piscine  forms. 

The  dental  armature  of  Cemtodus  Fosteri  (Fig.  J  94),  which  may  be 
taken  as  illustrative  of  this  peculiar  group,  has  six  teeth,  of  which  four 


376 


DENTAL  ANATOMY 


Fig. 


M 


tr 


L\\ 


belong  to  the  upper  and  two  to  the  lower  jaws. 
Those  of  the  upper  series  are  supported  upon  the 
palato-quadrate  arches  and  upon  a  cartilaginous 
plate  which  corresponds  in  position  with  the 
vomer.  Those  of  the  lower  series  are  set  upon 
the  inner  piece  of  each  dentary  bone,  and  be- 
come firmly  attached  thereto  by  ankylosis. 

The  two  most  anterior,  and  by  far  the  smallest 
of  the  upper  pairs  of  teeth,  form  cutting  plates 
which  resemble  somewhat  the  crown  of  a  broad 
inciscH'  with  the  posterior  border  well  rounded 
off.  They  are  arranged  in  the  form  of  a  V,  with 
the  point  directed  forward,  having  their  greatest 
extent  in  an  anterio-})osterior  direction.  After 
a  considerable  interval  the  two  large  peculiarly 
constructed  upper  back  teeth  appear,  similarly 
placed  in  the  form  of  a  V,  and  co-ossified 
with  the  bony  arches.  Their  greatest  length  is 
quite  equal  to  one-third  the  entire  length  of  the 
skull,  the  breadth  being  much  less.  Each  of 
these  dental  plates — for  such  they  may  be  prop- 
erly called — has  a  slightly  curved  internal  bor- 
der, Mith  the  convexity  directed  inward.     The 


<fT 


>\ 


v^-^ 


Ceralodus  :  a,  a,  teeth  of  same. 


TEETH  OF  THE   VERTEBRATA.  377 

lower  or  working  face  presents  internally  a  considerable  flat  pitted  surface 
reaching  the  entire  length  of  the  tooth,  whose  plane  is  directed  outward 
and  a  little  upward.  It  is  slightly  broader  in  front  than  behind.  The 
outer  border  is  indented  by  five  wide  vertical  grooves,. forming  six  verti- 
cally convex  lamelliform  projections,  M'hich  encroach  sonie\\'hat  upon  the 
flat  surface  internal  to  them  as  well-defined  parallel  ridges ;  the  anterior 
one  passes  entirely  across  the  face  of  the  tooth,  or,  rather,  skirts  its  anterior 
margin,  and  becomes  continuous  with  the  slightly  elevated  internal  bor- 
der in  this  situation.  The  grooves  are  deeper  in  front  than  behind,  leav- 
ing the  anterior  projections  the  most  pronounced,  while  the  kist  one  is 
scarcely  perceptible.  The  points  of  the  projections  describe  a  gentle 
curve  from  before  backward,  the  convexity  being  outward. 

The  two  teeth  of  the  lower  jaw  are  very  similar  to  those  of  the 
upper,  but  are  somewhat  narrower,  owing  to  a  decrease  in  width  of  the 
flat  pitted  surflice.  As  already  stated,  they  are  ankylosed  to  two  plates 
of  bone  which  cover  the  inner  and  half  of  the  lower  surface  of  INIeckel's 
cartilage  or  the  central  axis  of  the  lower  jaw.  It  will  thus  be  seen  that 
each  ramus  of  the  mandible  consists  of  an  inner  and  an  outer  bony  plate 
enclosino;  the  central  cart ilag-i nous  axis,  which  meet  in  the  median  line 
below.  To  these  is  added  a  third  piece  at  the  symphysis  on  its  lower 
surface,  so  that  the  bony  part  of  the  jaw — which  in  all  probability  corre- 
sponds with  the  single  dentary  piece  in  other  fishes — is  made  up  of 
three,  one  of  which  bears  teeth.  This  fact  is  of  great  morphological 
significance,  and  will  be  referred  to  again  when  we  come  to  discuss  the 
attachment  of  the  teeth. 

In  the  two  allied  genera  Protoptenis  and  Lepidosiren  the  teeth  are 
very  similar  to  those  of  Ceratodus,  but  in  numerous  extinct  forms  refer- 
red to  the  dipnoans  a  considerable  amount  of  variety  exists.  As  regards 
the  development  of  the  teeth  in  this  group,  very  little  is  known,  and 
until  this  has  been  studied  it  will  be  impossible  to  say  whether  the  den- 
tal j)lates  are  moulded  upon  a  single  papilla  or  represent  the  combined 
calcification  of  several.  Judging  from  their  complexity,  the  latter 
would  seem  to  be  the  case. 

The  teeth  of  the  remaining  ganoids  are  of  the  ordinary  conical  form 
which  prevails  to  so  great  an  extent  in  the  Teleostei.  In  number,  posi- 
tion, replacement,  etc.  they  likewise  agree  so  closely  with  the  average 
teleo.st  dentition  that  it  is  unnecessary  to  make  any  further  mention  of 
them. 

Among  teleosts,  however,  there  are  several  well-marked  modifications 
in  the  dental  armature  which  deserve  to  be  noticed.  One  of  these  is 
presented  by  the  Plectognathl  (plaited  jaw),  of  which  the  "trigger-fish" 
(Balistes  vetuhis)  and  the  "  swell  toad  "  (Diodon  geometricus)  represent 
the  extremes  in  dentition.  The  teeth  of  the  mouth  of  Bolides  are 
twenty-two  in  number,  of  which  fourteen  belong  to  the  upper  and 
eight  to  the  lower  jaw.  Those  of  the  superior  series  are  disposed  in 
two  rows,  one  placed  immediately  behind  the  other,  and  both  are  lodged 
in  the  premaxillary  bones.  The  most  anterior  of  these  rows  contains 
eight  teeth,  while  in  the  posterior  one  there  are  only  six.  In  the  front 
row  the  mesial  pair  are  the  largest,  of  a  subtrihedral  form,  tapering 
gradually  to  an  obtuse  point.     Those  upon  either  side  decrease  regu- 


378  DENTAL  ANATOMY. 

larly  in  size  toward  the  back  part  of  the  jaw,  and  have  notched  cntting 
extremities. 

The  teeth  of  the  posterior  row  are  applied  closely  to  those  of  the 
front  row,  and  are  completely  concealed  when  the  mouth  is  closed. 
They  have  a  broader,  more  incisiform  pattern.  The  teeth  of  the  lower 
series  are  like  the  corres])onding  ones  of  the  upper  front  row,  and  are 
lodged  in  the  dentary  bone.  They  are  attached  by  slight  ankyloses  to 
the  respective  bones  upon  which  they  are  supported  by  having  their 
bases  placed  in  a  shallow  alveolar  depression,  in  the  middle  of  which 
a  conical  process  of  bone  rises  up  and  is  received  into  the  hollow  basal 
portion  of  the  tooth.  The  successors  of  those  in  use  are  developed  deep 
clown  in  the  substance  of  the  jaws,  in  bony  crypts  which  communicate 
with  the  exterior  by  means  of  foramina  in  the  side  of  the  jaws  in  the 
vicinity  of  the  bases  of  those  in  use.  All  the  teeth  in  this  species  are 
said  by  Owen  to  be  covered  with  enamel.  There  are  likewise  small 
conical  hooked  teeth  developed  upon  the  pharyngeals. 

While  the  teeth  of  Balistes  are  more  nearly  affiliated  with  the  normal 
teleost  condition,  those  of  Dlodon,  on  the  other  hand,  show  a  much 
wider  departure.  When  the  mouth  is  closed  the  biting  surface  of  the 
jaws  seems  to  be  invested  with  a  continuous  covering  of  tooth-sub- 
stance ;  upon  close  inspection  this  is  found  to  consist  of  a  number  of 
dentine  plates  closely  incorporated  with  the  bone  of  the  jaws  and  more 
or  less  fused  together  at  the  base.  Each  one,  however,  develops  sepa- 
rately, and  takes  its  place  when  its  predecessor  has  disappeared  through 
Avear.  Just  inside  the  margin  of  each  jaw,  in  the  middle  line,  is  to  be 
seen  a  broad  rounded  mass  consisting  of  transverse  plates  of  dentine 
intimately  blended  and  ankylosed  to  the  jaw  bones.  A  faint  median 
longitudinal  suture  divides  each  into  two  parts ;  when  this  becomes 
more  distinct  and  extends  to  the  edge  of  the  jaw,  as  it  does  in  some 
species,  it  constitutes  the  mark  of  generic  distinction  of  the  genus  Tetro- 
don.  The  plates  composing  this  mass,  Mhich  is  peculiar  to  these  fishes, 
are  developed  in  the  same  manner  as  the  teeth,  and  are  strictly  homol- 
ogous with  them. 

Many  other  examples  quite  as  peculiar  as  the  last  one  could  be  cited 
among  the  dental  organs  of  fishes,  but  more  time  and  space  would  be 
required  than  is  aiforded  the  present  paper. 

The  mode  of  develo})ment  is  essentially  the  same  as  that  described 
for  the  mammal,  with  the  exception  that  the  dental  sacculus  is  generally 
simple  ;  the  dentine  papilla  arises  from  the  corium,  and  the  oral  epithe- 
lium dips  down  to  form  a  cap-like  investment,  in  both  of  M'hich  calci- 
fication takes  j)lace  in  the  manner  already  described.  AVith  regard  to 
the  succession  and  attachment  of  the  teeth  in  this  group,  as  well  as  in 
the  Batrachia  and  Rei)tilia,  some  preliminary  points  in  the  development 
of  the  jaw  bones  must  first  be  noticed. 

In  tlie  early  stages  of  embryonic  development  each  jaw  is  primarily 
made  up  of  two  cartilaginous  bars  which  meet  in  the  median  line  in 
front.  In  the  upper  jaw  these  bars  are  known  as  the  palato-ptervgoid 
bars,  and  in  the  lower  jaw  as  Meckel's  cartilage.  In  the  elasmobranchs 
these  bars  persist,  and  the  teeth  are  supported  Iw  them.  As  a  conse- 
quence of  this  condition,  as  we  have  already  seen,  succession  in  them 


TEETH  OF  THE   VERTEBRATA.  379 

takes  place  by  a  movement  of  the  fibrous  gum,  in  which  the  bases  of 
the  teeth  are  imbedded,  outward  over  the  curved  surface  of  the  jaw. 
Coincidently,  however,  witli  the  ossification  of  the  skeletal  axis  the 
osseous  bases  of  the  dermal  denticles  coalesce  to  form  the  dentary  bones, 
as  has  been  shown  by  Hertwig.  By  reason  of  the  development  of  this 
bony  envelope  of  the  primitive  axis  of  the  jaw,  any  further  movement 
of  these  denticles  is  prohibited,  being  firmly  co-ossified  with  it. 

During  the  coalescence  of  the  denticles  a  portion  of  the  primitive 
tooth-bearing  membrane  is  enclosed  beneath  the  fused  osseous  plates, 
and  retains  its  original  formative  energy,  thereby  furnishing  a  source 
of  supply  quite  equal  to  that  of  the  sharks.  Tiie  denticles  whose  basal 
plates  form  the  sides  and  under  portions  of  the  dentary  bones  disappear, 
while  those  on  the  summit  of  the  jaw  are  retained  as  teeth.  A  confor- 
mation of  this  position  by  evidence  other  than  that  afforded  by  embry- 
ology is  seen  in  the  dentary  bones  of  Ceratodus,  in  which  each  one  is 
made  up  of  three  or  four  pieces  which  have  failed  to  coalesce. 

The  attachment  of  the  teeth,  therefore,  in  this  group,  as  we  would  be 
led  to  anticipate,  is  by  ankylosis  to  the  dentary  and  other  bones  which 
support  them.  Still,  there  are  many  brush-like  structures  which  are 
identical  with  true  teeth  to  be  found  in  the  mouths  of  many  fishes, 
which  remain  imbedded  in  the  lining  membrane  and  do  not  develop 
any  connection  with  the  underlying  bones.  There  are  several  ways  by 
which  the  teeth  become  fixed  to  the  jaw  bones  in  ankylosis,  but  the  most 
common  is  for  the  central  axis  of  the  tooth  to  be  occupied  by  a  cone  of 
osteo-dentine,  which  blends  with  the  bone  of  the  jaw.  Several  fomilies 
of  fishes  have  some  of  the  teeth  attached  by  an  elastic  hinge,  by  which 
they  can  be  bent  down  in  one  direction  and  resume  an  erect  attitude.* 

Teeth  of  Batrachia  and  Reptilia. 

As  we  pass  from  the  dental  organs  of  the  more  typical  fishes  to  those 
of  frogs,  salamanders,  newts,  etc.,  constituting  the  batrachian  subdivis- 
ion, a  marked  diminution  in  the  number  of  individual  teeth  is  to  be 
observed.  With  the  appearance  of  perfected  air-breathing  organs  the 
complex  hyo-branchial  skeleton,  typical  of  the  fishes,  becomes  greatly 
reduced  and  simplified  as  the  higher  forms  are  approached ;  conse- 
quently, the  branchial  and  pharyngeal  teeth  disappear  in  all  the 
Vertebrata  above  fishes. 

In  all  those  Batrachia  in  which  teeth  exist  they  are  usually  disposed 
in  a  single  row  on  the  borders  of  the  jaws,  and  are  supported  by  the 
maxillary,  premaxillary,  and  dentary  bones  respectively.  In  addition 
to  these,  each  ^•omer  (for  there  are  two)  bears  a  single  row  of  teeth, 
between  which  and  the  maxillary  row  the  lower  jaw  bites.  As  a  rule, 
the  Reptilia,  on  the  other  hand,  lack  the  vomerine  set,  but  in  some  of 
them  (serpents,  for  example)  teeth  are  developed  upon  the  pterygoids 
and  palatines,  as  well  as  upon  the  maxillary  and  dentary  bones. 

The  teeth  of  the  Batrachia  present  so  limited  a  range  of  variation  that 
the  description  of  one  will  serve  to  give  a  general  idea  of  the  dentition 
of  the  whole  group. 

'  This  fact  was  first  noticed  by  Prof.  Gill. 


380  DENTAL  ANATOMY. 

It  slioulcl  be  stated  here  that  some  of  the  tailless  species  (toads)  are 
quite  edentulous,  M'hile  in  others  (the  frogs)  teeth  are  absent  in  the  lower 
jaw.  All  the  existing  tailed  batrachians,  however,  are  provided  with 
teeth  which  present  practically  the  same  pattern  and  disposition  which 
obtains  throughout  tlie  entire  sub-class. 

An  excellent  and  easily-obtained  example  of  this  latter  subdivision  is 
found  in  the  Alleghany  3Ienopoina,  popularly  known  as  the  "■  hell- 
bender." In  this  animal  the  skull  is  remarkable  for  its  flatness  and 
breadth,  as  well  as  the  almost  perfect  semicircular  outline  ^liich  the 
dentigerous  surface  of  the  jaws  presents.  The  mandible,  as  in  the  fishes, 
is  composed  of  angular,  articular,  and  dentary  pieces,  and  is  suspended 
to  the  cranium  by  means  of  two  bones  known  as  the  squamosals  through 
the  intervention  of  the  quadrates. 

The  palato-quadrate  or  palato-pterygoid  arch  is  not  so  well  defined, 
although  the  principal  elements  are  present.  The  vomers  are  two  in 
number,  and  occupy  their  usual  position  behind  the  maxillaries,  sharing 
in  the  formation  of  the  bony  roof  of  the  mouth.  The  maxillaries  and 
premaxillaries  also  have  the  same  position  as  in  the  fishes,  but  are  less 
mobile,  on  account  of  sutural  connections  with  the  surrounding  bones. 

The  l)iting  surface  of  each  jaw  is  produced  into  a  sharp  ridge  by  rea- 
son of  the  existence  of  a  well-marked  ledge  extending  the  full  length  of 
its  internal  face.  This  ledge  is  converted  into  a  groove  in  the  recent 
state  by  a  fold  or  flap  of  the  gum,  which  forms  its  internal  wall,  and  is 
in  all  probability  homologous  \\\\\\  a  similar  structure  (the  thecal  fold) 
found  in  the  sharks.  At  the  Ijottom  of  this  groove  the  tooth-germs  of 
the  successive  sets  of  teeth  are  developed.  It  will  be  seen,  therefore, 
that  the  general  arrangement  is  not  diiferent  from  that  of  the  sharks ; 
but  this  important  difference  is  to  be  observed  :  in  the  sharks  the  bases 
of  the  teeth  are  at  first  directed  upward,  and  it  is  only  when  they  are 
about  ready  to  take  position  on  the  working  surface  of  the  jaw  that  they 
assume  the  erect  attitude ;  this,  as  we  have  already  seen,  ife  clue  to  the 
movement  of  the  entire  gum  outward.  This  manner  of  replacement 
gives  Mcight  to  the  conclusion  that  the  teeth  in  the  sharks  are  invagi- 
nated  dermal  spines,  the  position  of  which  we  would  expect  to  find 
reversed  upon  the  inside  of  the  jaws. 

In  the  batrachians.  on  the  contrary,  the  teeth  are  said  to  have  an  erect 
position  from  the  earliest  stages  of  development,  and  it  is  less  easy  to 
see  how  they  represent  dermal  spines  or  how  the  position  came  to  be 
reversed.  Believing,  however,  that  all  the  maxillary  and  mandibular 
teeth  were  originally  of  tegumcntary  origin,  as  is  clearly  demonstrable 
in  the  sharks,  it  is  more  than  probable  that  the  arrest  of  the  outward 
movement  of  the  gum  in  the  batrachian  by  the  appearance  of  ossifi- 
cations around  Meckel's  cartilage  to  form  the  dentary  bones  is  responsi- 
ble for  this  change.  It  is  quite  possible  that  the  tooth-germs  of  the 
batrachian  do  at  first  have  the  same  position  as  those  of  sharks — that  is 
to  say,  with  the  points  directed  downward — and  that  the  formative 
energy  of  the  tissues  beneath  causes  them  to  become  erect  at  a  compara- 
tively early  period. 

We  have  already  stated,  in  connection  with  the  account  of  the  dental 
organs  of  the  elasmobl-anchs,  that  tooth-succession  is  primarily  due  to 


TEETH  OF  THE  VERTEBBATA.  381 

the  evagination  of  the  lining  membrane  of  the  oral  cavity.  Whether 
this  is  caused  by  unequal  rate  of  growth  of  the  surrounding  parts, 
whereby  this  lining  membrane  is  forcibly  pulled  outward  and  replaced 
from  within,  or  whether  the  formative  energy  inherent  in  the  membrane 
itself  causes  it,  is  difficult  to  determine.  This  primary  cause  of  succes- 
sion is  profoundly  affected  by  the  development  of  ait  osseous  sheath 
from  this  same  membrane  around  the  central  cartilaginous  axis  of  the 
jaws.  It  seems  plausible  that  secondarily  the  cause  of  tooth-succession 
is  to  be  sought  for  in  the  proliferation  of  the  cellular  elements  beneath 
the  young  and  growing  germ. 

To  the  inner  side  of  the  external  osseous  wall  of  this  groove  in  Meno- 
poma  the  functional  teeth  are  attached  ;  their  bases  are  slightly  enlarged 
and  extend  quite  to  the  bottom  of  the  groove,  while  the  tapering  crowns 
reach  considerably  above  the  level  of  the  jaw.  Attachment  takes  place 
by  the  ankylosis  of  that  part  of  the  base  which  is  in  contact  with  the 
outer  wall  to  the  bone  of  the  jaw  through  the  intermediation  of  osteo- 
dentine.  This  manner  of  implantation  is  known  as  "  pleurodont,"  on 
account  of  the  fancied  resemblance  of  the  teeth  so  attached  to  ribs. 

The  teeth  in  use  at  any  given  time  are  from  thirty  to  forty  in  num- 
ber upon  either  side  in  each  jaw ;  they  are  subequal  in  size,  and  are 
placed  with  great  regularity,  being  separated  by  spaces  about  equal  to 
the  width  of  a  single  tooth.  Their  crowns  are  sharp-pointed  and 
slightly  recurved ;  they  are  said  in  some  species  to  be  tipped  with 
enamel,  which  is  probably  true  of  all.  The  vomerine  teeth  are  fewer 
in  number  than  the  maxillary,  there  being  not  more  than  twelve  or 
fifteen  upon  either  side.  Their  line  of  direction  and  manner  of  implan- 
tation coincide  with  the  maxillary  row  external  to  them,  agreeing  with 
those  also  as  to  size  and  form. 

In  some  of  the  extinct  batrachians,  notably  the  labyrinthodonts,  there 
were  several  teeth  of  the  maxillary  and  premaxillary  set  considerably 
enlarged  and  of  a  caniniform  pattern.  The  species  of  this  section  were 
mostly  of  large  size  and  presented  a  formidable  dental  armature.  They 
likewise  differ  from  all  other  of  the  Batrachia  in  that  the  teeth  were 
implanted  in  distinct  sockets,  and  were  rarely  if  ever  attached  to  the 
body  of  the  jaw  by  ankylosis.  The  structure  of  the  teeth  is  a  curiously 
complex  one,  and  finds  no  parallel  throughout  the  entire  Yertel^rata, 
save  in  one  extinct  saurian  (Ichthyosaurus)  and  several  fishes,  which 
exhibit  a  similar  condition  in  a  less  perfected  degree. 

The  external  surface  of  the  crowms  of  the  teeth  in  the  labyrintho- 
donts is  marked  by  a  number  of  longitudinal  ridges,  separated  by  what 
at  first  sight  Mould  appear  to  be  comparatively  shallow  grooves  extend- 
ing from  the  base  to  the  apex  of  the  crown.  Upon  cross-section,  how- 
ever, these  fissures  are  seen  to  penetrate  into  the  body  of  the  tooth  to  a 
remarkable  depth — to  a  point,  in  fact,  quite  near  the  pulp-cavity  or  cen- 
tral axis  of  the  tooth,  where  they  are  separated  from  it  by  a  thin  wall 
of  dentine.  The  entire  outer  surface  is  covered  by  a  thin  layer  of 
cement,  which  is  reflected  inward  to  the  bottoms  or  internal  termina- 
tions of  the  fissures  just  mentioned.  The  cut  edges  of  this  reflected 
layer  of  cement,  which  is  of  uniform  thickness  throughout,  are  almost 
straight  for  a  short  distance  beneath  the  surface,  but  soon  become  very 


382  DENTAL  ANAT03IY. 

tortuous.  The  arrangement  of  the  dentine  is  as  follows :  The  axial 
portion  of  the  tooth  consists  of  a  central  cone  of  dentine  hollowed  out 
in  the  centre  to  receive  the  pulp.  In  cross-section  this  cone  appears  as 
a  ring  surrounding  the  pulp-cavity  ;  from  it  plates  of  dentine,  which  are 
cleft  by  the  fissures  from  without,  radiate  to  the  periphery,  pursuing  the 
same  tortuous  coarse  as  that  of  the  fissures.  These  dentinal  plates  are 
separated  from  each  other  by  fissures  which  radiate  from  the  axial  cav- 
ity, but  do  not  reach  the  exterior  of  the  crown.  Some  of  the  dentinal 
plates  do  not  arise  from  the  central  ring,  but  appear  on  transverse  sec- 
tion as  processes  from  the  periphery  of  the  crown  directed  toward  the 
central  axis,  thus  causing  the  fissures  which  radiate  from  the  pulp-cavity 
to  become  bifurcated  at  their  outer  or  peripheral  terminations.  Some 
of  these  accessory  processes  reach  but  a  short  distance  toward  the  inte- 
rior, while  others  penetrate  halfway  or  more  to  the  centre. 

This  complexity  in  the  arrangement  of  the  tooth-substances  has  sug- 
gested the  name  of  the  typical  genus,  Labyrmthodon,  which  was  orig- 
inally described  by  the  great  anatomist  Prof.  Owen.  Just  how  it  has 
been  produced  is  difficult  to  understand. 

Teeth  of  the  Reptilia. — This  class  of  vertebrated  animals  in- 
cludes snakes,  lizards,  crocodiles,  turtles,  etc.,  and,  considering  the 
extinct  as  well  as  the  recent  forms,  is  divisible  into  eleven  distinct 
orders,  according  to  Prof.  Cope's  classification.  Of  these,  but  five  are 
represented  in  the  existing  fauna,  the  others  having  become  extinct  in 
the  different  epochs  of  the  earth's  'history. 

The  batrachians  make  the  nearest  approach  to  the  permanent  gill- 
breathing  vertebrates  in  all  the  essential  features  of  their  structure ;  the 
Reptilia,  on  the  other  hand,  furnish  us  with  the  transitional  forms  lead- 
ing to  the  avian  and  mammalian  stems.  It  is  a  very  significant  fact — 
and  one  upon  Avhich  the  doctrine  of  evolution  is  primarily  based,  so  far 
at  least  as  the  Vertcbrata  are  concerned — that  the  lowest  forms  appeared 
first  in  the  order  of  time,  and  were  followed  by  those  higher  in  the 
organic  scale ;  thus  we  have  the  cartilaginous  fishes  as  the  earliest  rep- 
resentatives of  vertebrated  animals;  after  them  come  the  batrachians ; 
next  the  reptiles  and  birds,  and  finally  mammals.  It  must  be  borne 
in  mind,  however,  that  the  highest  of  one  group  is  not  always  most 
nearly  related  to  the  group  next  above  it ;  for  example,  if  Me  compare 
tlie  structure  of  a  bony  fish  with  that  of  a  salamander,  a  great  interval 
will  be  found  to  exist,  but  if  we  institute  a  comparison  betMcen  the  latter 
and  a  dipnoan  fish,  which  is  comparatively  little  removed  from  the  car- 
tilaginous forms,  this  interval  will  be  found  to  be  materially  diminished. 
Thus,  the  conclusion  is  obvious  that  the  Batrachia  sprang  not  from  the 
higher  bony  fish,  but  from  some  generalized  representative  of  the  pis- 
cine type.     The  same  reasoning  can  be  applied  to  other  divisions. 

As  regards  the  Keptilia,  the  chief  distinction  between  them  and  the 
Batrachia  consists  in  the  circumstance  that  the  latter  during  the  larval 
stages  of  their  existence  breathe  by  means  of  gills  like  the  fishes,  Avhere- 
as  the  Reptilia  breathe  by  means  of  true  lungs  from  the  time  of  birth. 
Important  osteological  differences  are  found  in  the  bones  of  the  skull. 

The  earliest  ap])earance  of  the  Reptilia  dates  back  to  the  Permian 
Epoch,  v.here  they  are  represented  by  a  group  of  peculiar  batrachian- 


TEETH  OF  THE   VERTEBBATA.  383 

like  reptiles  which  has  been  designated  the  Theromoq^ha  by  Prof.  Cope. 
This  group  includes  two  important  divisions,  one  of  which,  tlie  Anomo- 
dontia,  was  first  described  by  Prof  Owen  from  the  Triassic  (?)  deposits 
of  South  Africa  ;  the  other  is  the  Felycosauria,  which  is  so  far  known 
only  from  the  American  Permian. 

The  osteological  structure  of  this  order  furnishes  us  many  transitional 
characters  between  the  Batrachia  and  more  typical  Reptilia,  on  tlie  one 
hand,  while  on  the  other  they  seem  to  stand  in  ancestral  relationship  to 
the  prototherian  Mammalia.  Their  batrachian  affinities  are  manifested 
in  the  structure  of  the  pectoral  and  pelvic  arches,  in  the  structure  of  the 
limbs,  and  the  possession  of  teeth  on  the  vomer.  In  the  absence  of  a 
parasphenoid  bone  in  the  base  of  the  cranium  and  the  unicondylian 
condition  of  the  skull  they  are  markedly  reptilian.  The  structure 
of  the  pelvic  and  pectoral  arches  and  limbs,  together  with  the  intercen- 
tral  articulation  of  the  ribs,  allies  them  with  the  lower  Mammalia. 

Their  dental  organs  present  a  considerable  variety  of  structure — in 
some  instances  departing  widely  from  the  simple  conical  form  usual 
among  the  other  orders  of  this  class  of  the  Vertebrata.  In  one  genus 
(iJimetrodon)  there  were  two  large  caniniform  teeth  in  each  premaxil- 
lary,  implanted  in  distinct  sockets ;  these  were  followed  by  a  single  row 
of  maxillary  teeth,  whose  crowns  resemble  somewhat  the  premolars 
of  the  dog  in  general  pattern.  They  were  lodged  in  distinct  alveoli, 
and  exhibit  the  remarkable  peculiarity  of  being  implanted  by  double 
fangs,  or  rather  single  ones  deeply  grooved  upon  either  side,  otherwise 
unknown  among  the  Peptilia.  The  first  tooth  behind  the  maxillo-pre- 
maxillary  suture  is  enlarged  into  a  canine,  and  the  entire  maxillary 
series  does  not  exceed  fifteen  in  number.  The  palato-pterygoid  arch  is 
present,  and  one  of  its  elements,  probably  the  pterygoid,  is  thickly 
studded  with  small  conical  teeth  irregularly  disposed.  Another  element 
which  lies  internal  to  this  last-mentioned  bone  is  described  by  Prof. 
Cope  as  bearing  a  single  row  of  teeth.  Other  genera  related  to  this 
one  are.Theroplewa,  Clepsy drops,  etc.  of  Cope,  Avhich  present  minor 
differences  in  the  form  and  size  of  the  corresponding  teeth. 

A  nearly-allied  family  of  this  group  is  the  Diadcdidm,  likewise 
described  by  Cope.  A  typical  example  of  the  dentition  of  this  family 
is  seen  in  Empedodes  molaris,  wherein  the  pattern  of  the  crowns  of  the 
molars  is  thoroughly  unique.  The  teeth  are  disposed  on  the  borders  of 
the  premaxillary,  maxillary,  and  dentary  bones,  as  well  as  upon  the 
vomer,  which  forms  a  median  keel  in  the  roof  of  the  mouth.  The  max- 
illo-premaxillary  set  in  the  upper  jaw  describe  a  sigmoid  curve  in  their 
line  of  implantation,  and  form  an  uninterrupted  series  from  the  front 
to  the  back  of  the  mouth.  There  are  fourteen  teeth  belonging  to  this 
series,  of  which  the  first  two  are  larger  than  those  immediately  succeed- 
ing them.  They  have  obtuse  subconic  croAvns,  and  are  lodged  in  dis- 
tinct alveoli.  From  this  point  the  teeth  gradually  decrease  in  size  up 
to  the  sixth,  when  they  again  become  larger  and  more  complex  in  pat- 
tern. The  crowns  of  the  typical  molars  have  a  much  greater  transverse 
than  longitudinal  extent ;  "the  grinding  surface  is  somewhat  elliptical  in 
outline,  and  is  provided  with  a  submedian  cusp  which  stands  nearer  the 
outer  than  the  inner  border.     The  portion  of  the  crown  external  and 


384  DENTAL  ANATOMY. 

internal  to  the  median  cusp  is  horizontal,  and  has  its  surface  thrown 
into  conspicuous  folds  or  wrinkles.  The  teeth  of  the  lower  jaw  are 
essentially  like  those  of  the  upper.  The  vomerine  teeth  are  small  and 
conical,  and  are  disposed  in  two  longitudinal  rows. 

In  the  typical  genus  (Diadcdes)  there  is  a  well-developed  canine, 
while  in  another  member  of  the  family  {Helodedes)  there  are  canines 
and  a  double  row  of  maxillary  teeth  upon  either  side  in  the  dentigerous 
surface  of  these  bones. 

In  the  other  subdivision  of  this  order — viz.  Anomodontla — the  den- 
tition is  reduced  to  large  pointed,  recurved  tusks,  which  are  lodged  by 
distinct  sockets  in  the  maxillary  bones.  The  rest  of  the  jaw  is  edentu- 
lous, and  was  in  all  probability  ensheathed  in  a  corneous  substance,  as 
in  the  existing  turtles.  Other  extinct  members  of  this  subdivision, 
notably  Rhynchosaurus  and  Oudenodon,  were  entirely  edentulous,  and 
in  all  probability  were  the  ancestors  of  the  turtles. 

That  division  known  as  the  Crocodi/ia  includes  the  alligators,  croco- 
diles, gavials,  etc.,  which  are  separated  from  the  other  Reptilia  by  a 
number  of  important  osteological  characters,  prominent  among  a\  hich  is 
the  complete  development  of  the  bony  roof  of  tlie  mouth.  Teeth  are 
supported  by  the  premaxillary,  maxillary,  and  dentary  bones  only,  the 
palatines  and  pterygoids  having  appi'oximately  the  same  relations  and 
edentulous  condition  as  in  the  mammalian  skull.  In  no  crocodilian  so 
far  knoMU  are  the  teeth  ever  ankylosed  to  the  body  of  the  bones  upon 
which  they  are  borne,  but,  on  the  contrary,  they  are  set  in  distinct 
sockets  disposed  in  a  single  row  along  the  margins  of  the  tooth-bearing 
bones.  In  young  specimens  the  alveoli  are  apt  to  be  ill  defined,  more 
especially  toward  the  back  part  of  the  jaws,  but  as  age  advances  the 
bony  partitions  become  more  distinct.  On  account  of  each  tooth  having 
a  distinct  alveolus,  this  division  of  the  Eeptilia  was  formerly  known  as 
the  thecodonts,  in  contradistinction  to  the  pleurodonts — a  condition 
already  mentioned  in  connection  with  JlenojJoma — and  acrodonts,  pres- 
ently to  be  described.  • 

A  good  example  of  the  dentition  of  a  crocodilian  reptile  is  afforded 
by  the  Mississippi  alligator  (AUigcdor  J//.s.s/.ss?23p?V?Js/s),  Avhich  can  be 
found  in  almost  any  osteological  collection  in  this  country.  In  the 
upper  jaw  there  are  from  eighteen  to  twenty-two  teetli  upon  either  side, 
of  which  five  are  usually  set  in  each  premaxillary  and  the  remainder  in 
the  maxillary  bones.  The  most  anterior  of  the  premaxillary  series  is 
the  smallest,  from  which  they  gradually  increase  in  size  to  the  fourth, 
which  is  nearly  twice  as  large  as  any  of  the  others ;  the  fifth  is  about 
equal  to  the  third.  The  first  of  the  maxillary  series  is  likewise  the 
smallest ;  the  three  succeeding  teeth  gradually  increase  in  size  until  the 
third  is  rcached'(the  ninth  counting  from  the  first  tooth  in  the  premax- 
illary), which  is  known  as  the  canine  of  the  upper  jaw.  The  eighth  and 
tenth  are  frequently  as  large  as  the  canine.  Behind,  the  teeth  become 
smaller,  and  are  again  enlarged  in  the  vicinity  of  the  sixteenth  or  sev- 
enteenth from  the  first  premaxillary  tooth  ;  from  this  point  they  rapidly 
diminish  toward  the  posterior  end  of  the  tooth-line. 

In  the  lower  jaw  the  teeth  are  likewise  of  unequal  proportion,  but 
those  which  are  largest  in  the  one  series  are  opposed  by  the  smallest  of 


TEETH  OF  THE   VERTEBRATA.  385 

the  opposite  set ;  thus  that  tooth  which  is  caniniform  in  the  lower  jaw 
is  the  fourth,  and  bites  in  front  of  tlie  corresponding  tooth  above.  It  is 
received  into  a  deep  fossa  in  the  upper  jaw  just  internal  to  the  alveolar 
border  at  the  point  of  junction  of  the  maxillary  Avith  the  preraaxilkuy 
bone,  or  between  the  fifth  and  sixth  teeth  above.  It  not  unfrequently 
happens  in  old  specimens  that  this  fossa  is  converted  into  a  foramen 
leading  to  the  external  surface  of  the  skull  by  the  perforation  of  its 
base.  In  such  cases  the  point  of  the  lower  canine  passes  through  the 
upper  jaw  and  appears  upon  the  upper  surface. 

The  only  important  distinction  between  the  alligators  and  the  croco- 
diles consists  in  the  fact  that  in  the  latter  this  fossa  is  open  externally, 
causing  the  tooth-line  to  be  interrupted  by  a  deep  notch,  whereas  in  the 
latter  it  is  intact. 

Both  the  alligators  and  the  more  typical  crocodilians  are  remarkable 

for  the  breadth  of  the  palate  and  the  flatness  of  the  muzzle,  as  well  as 

the  alternate  increase  and  decrease  in  the  size  of  the  teeth  from  before 

backward  ;  but  in  the  gavials  the  snout  is  very  long,  narrow,  and  almost 

cylindrical ;  the  teeth,  too,  are  more  nearly  equal  and  of  more  regular 

proportions. 

In  the  alligator  the  anterior  teeth  have  conical  crowns  terminatino;  in 
...  .  ^ 

sharp  points,  which  are  slightly  recurved.     The  posterior  ones  have 

more  obtuse  crowns,  Avhich  terminate  below  by  a  moderately  well-defined 

neck.     In  some  species  the  anterior  and  posterior  surfaces  of  the  crowns 

are  produced  into  trenchant  edges,  which  may  be  more  or  less  serrated  ; 

in  the  alligator  this  is  but  faintly  mai'ked. 

The  manner  of  succession  is  not  different  from  that  of  the  other  lower- 
vertebrates.  If  the  root  of  a  tooth  in  place  be  exposed,  the  suceessional 
sets  in  various  stages  of  development  will  be  seen  below  and  to  the  inside^ 
of  it,  arranged  in  the  form  of  a  nest  of  crucibles.  This  arrangement; 
results  by  reason  of  the  absorption  of  the  inner  wall  of  the  root  of  the 
tooth  in  place  which  the  immediate  successor  causes.  By  this  means  the 
point  of  its  crown  comes  to  occupy  the  pulp-cavity  of  the  functional  tooth. 

In  the  order  Lacertilia,  which  includes  the  lizards  proper,  a  more 
varied  development  of  the  dental  organs  is  met  with.  As  a  general 
rule,  teeth  are  borne  upon  the  pterygoid  and  palatine  as  well  as  upon 
the  maxillary,  premaxillary,  and  mandibular  bones.  There  are,  how- 
ever, some  exceptions,  one  of  which  is  afforded  by  our  little  "  horned 
toads"  (Phrynosonut),  in  which  the  palatines  and  pterygoids  are  eden- 
tulous. The  teeth  may  be  either  "  pleurodont  "  or  "  acrodont "  in  their 
manner  of  implantation,  but  in  certain  extinct  forms  (e.  g.  3Tosof(aurus) 
l)oth  conditions  are  to  be  observed.  In  the  case  of  acrodontism  the 
bases  of  the  teeth  are  soldered  to  the  summits  of  slight  elevations  which 
arise  from  the  alveolar  border  of  the  jaMS.  Pleurodontism,  as  has 
already  been  mentioned,  consists  in  the  ankylosis  of  the  base  and  outer 
sides  of  the  teeth  to  the  outer  wall  and  bottom  of  the  dental  groove. 
Another  variety  of  implantation,  known  as  coelodontism,  has  been 
described,  in  which  the  tooth  has  a  permanent  pulp-cavity,  and  is 
attached  to  the  outer  wall,  leaving  the  base  free ;  it  should  be  men- 
tioned that  in  pleurodonts  the  pulp-cavity  is  not  permanent ;  it 
soon  becomes  obliterated,  leaving  the  tooth  solid. 
Vol.  I.— 25 


386  DENTAL  ANATOMY. 

A  fair  example  of  a  pleurodont  lacertilian  is  afforded  by  the  majority 
of  the  numerous  species  of  the  Iguanidce,  although  some  of  the  members 
of  the  iguanian  family,  such  as  Isturus,  Lophyrus,  Calotes,  and  others, 
are  acrodont.  In  the  horned  iguana  [Metopocerus  coniutus)  the  max- 
illary and  premaxillary  teeth  are  from  twenty-two  to  twenty-three  in 
number  upon  either  side.  The  central  ones  of  the  premaxillary  set, 
of  which  there  are  four,  are  smallest,  the  outer  ones  sHghtly  enlarged. 
These,  together  with  the  first  five  or  six  maxillary  teeth,  have  sub- 
conic  recurved  crowns,  while  the  crowns  of  the  posterior  maxillary 
series  are  laterally  compressed  into  anterior  and  posterior  cutting 
edges  and  terminated  by  a  principal  cusp.  Of  the  two  edges,  the 
anterior  is  the  longer  and  is  interrupted  by  three  minor  cusps,  the 
posterior  being  shorter  and  bearing  only  a  single  accessory  cusji.  The 
presence  of  these  cusps  gives  the  crown  a  serrated  appearance  when 
viewed  from  the  side. 

The  teeth  of  the  lower  jaw  are  from  t^vcnty  to  twenty-two  in  number 
upon  either  side,  and  are  similar  in  form  to  those  above,  with  the  excep- 
tion that  there  are  generally  two  accessory  cusps  upon  either  trenchant 
edge  of  the  crown.  There  is  in  addition  to  these  a  single  row  of  small 
conical  teeth  supported  by  each  pterygoid  bone ;  the  number  of  these 
varies  from  five  to  seven. 

The  only  lacertilian  which  is  known  to  be  poisonous  is  the  "  Gila 
monster "  [Heloderma  susjjcchnn)  of  our  American  fauna.  Recent 
experiments  of  Drs.  Mitchell  and  Reichart  of  Philadelphia  have 
demonstrated  beyond  doubt  the  poisonous  qualities  of  its  salivary 
secretion.  Considerable  interest  therefore  attaches  to  its  dental  organs, 
as  well  as  to  the  anatomy  of  the  poison-glands ;  this  latter  subject  I 
am,  unfortunately,  not  in  a  position  to  describe,  and  will  therefore 
limit  what  I  have  to  say  here  to  a  consideration  of  the  teeth  only. 

This  animal,  of  which  there  are  two  species,  is  confined  to  the  desert 
wastes  of  the  South-western  United  States,  where  it  is  not  of  rare  occur- 
rence. In  life  it  has  a  rather  repugnant  appearance,  which  is  no  doubt 
increased  by  our  knowledge  of  its  poisonous  qualities.  It  attains  a 
length  of  eighteen  inches  or  two  feet,  and  is  covered  with  bright  yellow 
spots,  a  circumstance  Avhieh  gives  the  name  Hdodcrma  to  the  genus, 
meaning  "  sun  skin."  Its  venomous  nature  was  not  known  until  the 
exjjeriments  above  mentioned  w^ere  made,  although  Prof.  Cope  had 
reason  to  stispect  as  much,  and  gave  the  name  '^  suspectum "  to  the 
species,  which  he  described  several  years  before. 

The  teeth  are  sup]iortcd  l)y  the  premaxillary,  maxillary,  and  dentary 
bones,  the  ])alatine  and  pterygoids  being  edentulous.  Those  of  the  pre- 
maxillary, of  which  there  arc  three  upon  each  side,  are  the  smallest  of 
the  upper  teeth.  They  increase  regularly  in  size  from  before  backward, 
and  form  a  continuous  series,  with  the  maxillary  teeth  behind,  which 
continue  to  augment  their  dimensions  up  to  the  eighth  tooth  from  the 
median  premaxillary  pair  or  the  fifth  of  the  maxillary  set.  From  this 
]ioint  backward  the  two  remaining  teeth  l)ecome  slightlv  smaller.  The 
teeth  of  the  lower  jaw  are  nine  in  numlier,  and  are  disposed  verv  much 
in  the  same  manner  as  those  above — the  smallest  in  front  and  the 
largest  toward  the  back  part  of  the  mouth.     A  considerable  disparity 


TEETH  OF  THE    VERTEBRATA.  387 

in  size  exists  between  the  inferior  series  and  the  corresponding  teeth 
above,  those  below  being  mnch  the  longer  and  more  robust. 

In  their  manner  of  implantation  tliey  cannot  be  said  to  be  either 
acrodont  or  pleurodont,  but  rather  intermediate  between  the  two.  The 
internal  aspect  of  each  jaw,  \\liicli  is  remarkable  for  its  breadth,  is  slightly- 
bevelled  internally,  causing  the  outer  edge  to  rise  a  little  above  the  inner. 
Nearer  the  outer  than  the  inner  edge  of  this  bevelled  surface  are  a  num- 
ber of  low  bony  elexations,  corresponding  to  the  number  of  the  teeth  in 
functional  use,  to  the  summits  of  which  they  are  attached  by  ankylosis. 
In  some  instances  these  elevations  are  so  faintly  indicated  that  the  teeth 
ajjpear  to  be  soldered  to  th3  bevelled  surface  of  the  jaw  directly.  Just 
internal  to  the  basis  of  the  functional  teeth  may  be  seen  the  successive 
sets  in  different  stages  of  development.  In  the  recent  state  they  are 
covered  by  a  fold  of  the  gum,  which  likewise  covers  up  the  bases 
of  the  functional  teeth. 

The  form  of  the  crown  is  that  of  a  long,  slender,  sharp-pointed  cone 
curved  inward  and  backward.  The  anterior  surface  of  each  tooth  is 
marked  by  a  well-defined  groove  extending  from  the  base  to  the  apex. 
It  is  somewhat  deeper  at  the  base  than  the  summit,  and  is  most  distinct 
in  the  teeth  of  the  lower  jaw.  The  intervals  between  the  bases  of  the 
teeth  allow  abundant  room  for  the  accommodation  of  poison-glands,  the 
secretion  of  which  is  conveyed  down  these  grooves  and  thus  injected 
into  the  wound  which  the  teeth  inflict  upon  a  prey. 

Another  group  of  curious  and  interesting  reptiles  is  the  Dinosauria, 
which  became  extinct  at  the  close  of  the  Cretaceous  Epoch.  They  are 
of  esjDCcial  interest  on  account  of  their  remarkable  bird-like  affinities, 
and,  according  to  the  views  of  many  authors,  were  the  direct  progenitors 
of  the  struthious  birds,  or  ostriches,  emus,  etc.  They  were  mostly  of 
gigantic  size,  and  some  of  them  are  remarkable  for  the  great  number 
of  teeth  contained  in  the  upper  and  lower  jaws ;  others,  again,  were 
almost  edentulous. 

In  the  iguanodonts  and  hadrosaiirs,  which  are  typical  representatives 
of  the  herbivorous  division  of  this  order,  the  crowns  of  the  teeth  are 
somewhat  expanded  and  are  marked  externally  by  vertical  ridges,  while 
the  internal  portion  is  smooth  and  rounded.  In  Iguanodon  the  external 
surface,  to  which  the  enamel  is  confined,  is  traversed  by  three  vertical 
ridges,  separated  by  vertical  grooves ;  the  anterior  and  posterior  edges 
were  serrated,  as  in  Iguana,  before  the  crown  was  abraded  by  wear. 
In  the  hadrosaurs  there  is  but  one  vertical  ridge,  which  is  external  in  tlie 
upper  and  internal  in  the  lower  teeth.  The  part  which  bears  this  ridge 
is  known  as  the  enamel  or  cementum  plate.  Prof.  Cope  has  recently 
had  the  opportunity  of  satisfactorily  determining  the  dental  peculiarities 
of  this  group  of  gigantic  saurians,  as  exemplified  by  the  genus  Diclouiiis, 
through  the  fortunate  discovery  of  an  almost  complete  skeleton  bv  Dr. 
Russel  Hill  and  the  author  in  the  Bad  Lands  of  Dakota  during  the 
summer  of  1882. 

According  to  Prof.  Cope's  description,  there  are  in  all  two  thousand 
and  seventy-two  teeth.  Of  these,  there  were  not  more  than  two  or  three 
hundred  in  use  at  one  time,  the  others  being  arranged  in  successive  rows 
beneath,  ready  to  take  the  place  of  the  functional  ones  when  they  were 


388  DENTAL  ANAT03IY. 

worn  out.  One  striking  peculiarity  which  this  reptile  presents  is  in  the 
dentigerous  character  of  the  splenial  and  the  edentulous  condition  of 
the  dentary  bones  of  the  mandible.  The  teeth  are  relatively  small,  and 
are  placed  at  some  distance  from  the  anterior  part  of  the  mouth.  This 
part  of  the  jaws  is  believed  to  have  been  occupied  by  a  kind  of  horny 
sheath  similar  to  that  found  in   birds  and  turtles. 

The  proportions  of  the  limbs  were  those  of  the  kangaroo,  the  posterior 
greatly  exceeding  the  anterior  in  size.  The  general  shape  of  the  skull 
is  very  much  like  that  of  a  bird  with  a  large  spatulate  beak  ;  it  was 
supported  upon  a  long,  flexible  neck,  which  was  doubtless  useful  to  the 
animal  in  gathering  the  soft  aquatic  vegetation  upon  which,  from  the 
character  of  its  teeth,  it  is  supposed  to  have  subsisted.  It  likewise 
had  a  powerful  tail,  much  deeper  than  thick,  which  probably  served 
not  only  as  a  fifth  limb  in  balancing  the  weight  of  the  animal,  but 
could  also  have  been  useful  as  a  swimming  organ.  The  feet  were  pro- 
vided with  true  hoofs. 

The  carnivorous  dinosaurs  were  scarcely  inferior  in  size  to  the  her- 
bivorous species,  but  were  of  a  more  slender  and  active  build.  Their 
jaws  were  provided  with  large,  powerful  conical  teeth,  better  adapted 
for  the  capture  of  living  animal  prey.  The  terminal  phalanges  were 
ensheathed  in  distinct  claws. 

Another  order  of  the  Reptilia,  and  one  which  is  probably  best  known, 
is  the  Ophklia,  or  snakes.  Especial  interest  attaches  itself  to  the  dental 
organs  of  many  of  this  group,  inasmuch  as  their  poisonous  bite  consti- 
tutes one  of  their  most  conspicuous  features  and  renders  them  particu- 
larly obnoxious  as  well  as  dangerous  to  life. 

According  to  most  systematists,  the  order  is  divisible  into  five  sub- 
orders, which  have  been  defined  as  follows : 

I.  "  The  palatine  bones  widely  separated,  and  their  long  axes  longitudinal ;  a  trans- 
verse (ecto-pterygoid)  bone;  the  pterygoids  unite  with  the  quadrate  bones." 
n.  "  None  of  the  maxillary  teeth  grooved  or  canaliculated  " Asinca. 

b.  "  Some  of  the  ])osterior  maxillary  teeth  grooved  " Torfriciiia. 

c.  "Grooved  anterior  maxillary  teeth  succeeded  by  solid  teeth"     .  Proteroglyphia. 

d.  "Maxillary  teeth  few,  canaliculated,  and  fang-like" Solenofilyphin. 

II.  "The  jialatine  bones  meet  or  nearly  meet  in  the  base  of  the  skull,  and  their  long 

axes  are  transverse.     No  ecto-pterygoid  bone ;  the  jiterygoids  are  not  con- 
nected with  the  quadrate  bones"  (Huxley)  .    .* Scalecophidia. 

""The  first  of  these  sub-orders  includes  nearly  all  of  the  harmless  or  non- 
venomous  species,  of  which  the  black  snake,  garter  snake,  boa,  etc.  are 
familiar  examples.  The  second  includes  a  single  family  with  few  species, 
said  to  be  harmless ;  they  are  confined  to  Africa.  The  third  sub-order 
embraces  such  forms  as  the  deadly  cobra,  the  coral  snake,  harlequin 
snake,  and  others.  The  fourth  includes  the  vipers,  rattlesnakes,  adders, 
etc.     The  last  is  represented  by  few  species  which  are  non-venomous. 

In  general,  the  dentigerous  elements  of  the  ophidian  skull  may  be  said 
to  consist  of  maxillary,  jxilatine,  and  jiterygoid  bones  of  the  upper  and 
the  dentary  bones  of  the  loNver  jaw,  although  in  the  pythons  and  tor- 
trices  teeth  exist  upon  the  premaxillaries  as  Avell.  In  JRachiodon,  a 
singular  African  species  of  the  Asinea,  the  teeth  of  the  jaws  are 
extremely  small  and  soon  disappear.  This  loiss  is  compensated  for  by 
an  excessive  development  of  the  hypopophyses  of  several  of  the  anterior 


TEETH  OF  THE   VERTEBRATA.  389 

vertebrae,  which  pierce  the  superior  wall  of  the  oesophagus  and  are 
tipped  with  a  layer  of  hard  ceiiieutuni.  The  food  of  this  species  con- 
sists of  the  eggs  of  small  birds,  wliicli  it  swallows  whole.  During  the 
act  of  deolutition  the  calcareous  shell  is  brouo-ht  into  contact  with  and 
crushed  by  these  oesophageal  teeth,  thus  preventing  the  escape  of  any  of 
the  nutritious  substances. 

In  the  non-venomous  species  the  maxillary  bone  is  long,  and  bears  a 
row  of  teeth  which  are  of  variable  size  in  the  ditJerent  parts  of  the  jaw 
in  different  genera.  In  some  the  teeth  are  largest  in  front  and  smallest 
behind ;  in  others  it  is  the  reverse  of  this ;  while  many  have  the  teeth 
of  equal  size  throughout ;  then,  again,  certain  teeth  of  either  jaw  may 
be  specially  enlarged  and  separated  from  the  others  by  a  diastema.  All 
these  conditions  have  received  distinct  names. 

All  serpents  are  acrodont,  and  the  crowns  of  the  teeth  consist  of  long, 
sharp-pointed,  recurved  cones  which  are  designed  more  to  prevent  the 
escape  of  a  struggling  prey  than  as  instruments  of  mastication.  The 
two  rami  of  the  lower  jaw  are  bound  together  at  the  symphysis  by 
elastic  ligaments,  which,  together  with  the  great  distensibility  of  the 
throat,  due  to  the  mobility  of  the  suspensory  bones,  allows  them  to 
swallow  objects  many  times  larger  than  the  usual  diameter  of  the  body. 
During  the  act  of  swallowing  the  recurved  and  pointed  leeth  act  as  so 
many  hooks  to  prevent  a  backward  movement  of  the  object. 

In  the  sub-order  known  as  the  Proferoglyph'ut  the  maxillary  bone  is 
shortened  somewhat,  and  the  anterior  teeth  are  enlarged  and  grooved  on 
their  anterior  faces.  One  of  these  teeth  (the  anterior)  is  the  largest,  and 
is  denominated  the  fang.  It  is  permanently  erect  in  these  serpents,  being 
ankylosed  to  the  maxillary  bone,  which  is  capable  of  comparatively  little 
movement. 

In  the  solenoglyplis,  on  the  other  hand,  of  which  the  rattlesnake  is  an 
excellent  example,  the  maxillary  bone  attains  its  maximum  of  abbrevia- 
tion and  supports  a  single  tooth,  the  fang.^  It  is  movably  articulated 
with  the  lachrymal  above  by  means  of  a  ginglymoid  joint.  The  fang  is 
canaliculated  or  perforated  in  tlie  direction  of  its  long  axis  by  a  canal 
which  opens  near  its  point.  This  canal  results  from  the  fusion  of  the 
free  edges  of  the  anterior  groove,  which  remains  open  in  the  fangs  of  the 
proteroglyphs.  When  the  mouth  is  closed,  the  maxillary  bones  are 
retracted  and  the  fangs  lie  parallel  with  the  roof  of  the  mouth ;  when 
the  animal  "  strikes,"  the  maxillary  bones  are  extended  by  special  mus- 
cles and  the  fangs  become  erect. 

The  canal  of  the  fang  receives  at  its  proximal  termination  the  duct 
of  the  large  poison-gland,  which  lies  above  it,  so  that  when  the  punc- 
tured wound  is  inflicted  the  poisonous  secretion  is  injected  into  it.  This 
is  facilitated  by  a  coincident  contraction  of  the  muscles  which  surround 
the  gland.  It  has  been  suggested  by  Owen  that  as  the  quantity  of  saliva 
and  lachrymal  secretion  is  increased  during  particular  emotions,  so  the 
rage  which  stimulates  the  venom-serpent  to  use  its  deadly  weapon  must 

'  Usually,  a  number  of  teeth  are  found  just  })ehind  the  fang  in  this  bone,  some  of 
which  are  nearly  or  quite  as  large  as  the  fang  itself.  These  are  the  teeth  which  are 
destined  to  succeed  the  functional  fang  whenever  it  shall  have  been  shed  or  lost  by 
accident. 


390  DENTAL  ANATOMY. 

be  accompanied  with  an  increased  secretion  and  great  distension  of  the 
poison-glands. 

In  reference  to  the  poisonous  character  of  this  secretion,  it  is  a  well- 
known  fact  that  the  normal  saliva  of  many  animals  is  more  or  less 
dangerous  when  injected  directly  into  the  blood,  and  that  in  a  state  of 
rage  it  is  rendered  more  so.  Prof.  Cope  has  recently  called  my  atten- 
tion to  the  possible  explanation  of  the  poisonous  character  of  this  anal- 
ogous secretion  of  the  venomous  serpents  :  that  since  their  peculiar 
method  of  locomotion  would  expose  them  most  frequently  to  injuries 
and  inconveniences  calculated  to  excite  this  state,  the  normal  salivary 
secretions  have  become  accordingly  modified. 

The  remaining  orders  of  the  Reptilia  do  not  exhibit  any  important 
modifications  of  the  dental  system  worthy  of  special  notice. 


THE  TEETH  OF  THE  MAMMALIA. 

With  a  consideration  of  the  teeth  of  the  Manmialia  we  enter  upon  a 
study  of  a  series  of  dental  organs  whose  complexity,  variety,  and  s])e- 
cialization  surpass  those  of  any  other  group  of  the  Vertebrata.  The 
wide  diversity  of  conditions  under  which  the  different  members  of  this 
great  group  exist  would  of  itself  lead  one  to  anticipate  a  corresponding 
diversity  in  dietetic  habits,  as  well  as  organs  suitable  for  the  prehension 
and  assimilation  of  the  substances  by  which  they  are  nourished.  The 
broad  grinding  surface  afforded  by  the  molar  tooth  of  the  elej)hant,  the 
sharp,  trenchant,  sectorial  dentition  of  the  lion,  the  great  scalj^riform 
incisors  of  the  beaver,  the  small  cylindrical  teeth  of  the  armadillo,  are 
a  few  examples  of  the  great  range  of  variety  which  mammals  exhibit 
in  the  form  of  their  dental  organs. 

As  already  remarked  in  the  introductory  pages,  this  study  is  greatly 
facilitated  by  considering  it  from  the  standpoint  of  evolution,  or  rather 
in  the  light  of  the  palfeontological  history  of  the  group.  If  Me  look 
upon  the  fossil  remains  of  any  given  period  of  geologic  time  as  the 
representatives  in  part  of  the  animals  which  at  that  time  inhabited  the 
earth,  it  then  becomes  of  the  utmost  importance  to  ascertain  the  exact 
relationship  Avhich  the  animals  of  each  period  bear  to  those  which  have 
preceded  and  succeeded  them  in  time.  It  is  needless  to  say  that  the 
conclusions  which  we  are  com])elled  to  draw  from  studies  of  this  cha- 
racter are  im])ortant  and  significant,  and  serve  to  bring  into  the  closest 
connection  many  isolated  facts  which  if  considered  by  themselves  would 
be  wholly  unintelligible. 

Some  objection  to  this  method  of  treatment  will  doubtless  be  raised 
by  those  who  do  not  accept  evolution  as  a  demonstrated  fact,  or  those, 
again,  Avho  consider  our  information  concerning  extinct  forms  too  meagre 
for  purposes  of  generalization.  In  answer  to  these  objections  it  must  be 
urged  that  jxdreontological  law  com]>els  us  to  recognize  the  important  fact 
that  in  every  department  of  life  the  generalized  has  preceded  the  spe- 


TEETH  OF  THE   VERTEBRATA.  391 

cializeJ  in  time ;  we  pass  from  the  simple  to  the  complex,  whether  an 
individual  organ  or  the  entire  organism  be  considered  ;  and  the  teeth 
form  no  exception  to  this  rule.  So  conclusive  is  the  testimony  which 
it  is  now  possible  to  adduce  in  support  of  this  general  proposition,  and 
so  pregnant  are  the  minds  of  modern  biologists  with  this  belief,  that  it 
seems  utterly  impossible  to  escape  the  conviction  that  life  from  its  earli- 
est inception  has  been  continuously,  and  in  many  instances  progressively, 
modified.  As  to  the  nature  of  the  causes  which  have  induced  this  modi- 
fication, there  is  much  less  unanimity  of  opinion.  It  is  a  question 
regarding  which  the  most  exhaustive  philosophic  discussion  is  now  in 
progress. 

When  we  speak  of  the  origin  of  mammalian  teeth,  it  is  necessary  to 
have  some  definite  knowledge  of  the  origin  of  this  class  of  animals  before 
we  can  be  absolutely  certain  of  just  what  constitutes  a  primitive  mamma- 
lian dentition.  Unfortunately,  the  evidence  which  would  enable  us  to 
determine  the  ancestry  of  the  mammal  beyond  dispute  has  not  as  yet 
been  found,  but  it  appears  sufficiently  evident  that  we  are  limited  in  our 
choice  to  the  Batrachia  and  Reptilia  of  the  Permian  Period.  Huxley, 
who  has  devoted  considerable  attention  to  this  subject,  concludes  that 
we  must  go  backward  past  the  Reptilia  directly  to  the  Batrachia.  This 
conclusion  is  primarily  based  upon  a  comparison  of  the  pelvic  arch  of 
the  monotremes  with  that  of  the  batrachians.  In  addition  to  the  evi- 
dence drawn  from  this  source,  upon  which  his  argument  is  principally 
founded,  the  following  reasons  are  given  for  this  view  :  "  The  Batrachia 
are  the  only  air-breathing  Vertebrata  which,  like  the  Mammalia,  have  a 
dicondylian  skull.  It  is  only  in  them  that  the  articular  elements  of  the 
mandibular  arch  remain  cartiUiginous,  while  the  quadrate  articulation 
remains  small,  and  the  squamosal  extends  down  over  the  osseous  ele- 
ments of  tlie  mandible,  thus  affording  an  easy  transition  to  the  mam- 
malian condition  of  those  parts.  Tlie  pectoral  arch  of  the  monotremes 
is  as  much  batrachian  as  it  is  reptilian  or  avian.  The  carpus  and  tarsus 
of  all  Reptilia  and  Aves,  except  the  turtles,  are  modified  away  from  the 
batrachian  tyjjc,  while  those  of  the  mammal  are  directly  reducible  to  it. 
Finally,  the  fact  that  in  all  Reptilia  and  Aves  it  is  a  right  aortic  arch 
which  is  the  main  conduit  of  arterial  blood  leaving  the  heart,  while  in 
the  Mammalia  it  is  the  left  which  performs  this  office,  is  a  great  stum- 
bling-block in  the  way  of  the  derivation  of  the  INIanunalia  from  any  of 
the  Reptilia  or  Aves.  But  if  we  suppose  the  earliest  forms  of  both 
Reptilia  and  jNIammalia  to  have  had  a  common  batrachian  origin, 
then  there  is  no  difficulty  in  the  supposition  that  from  the  first  it  Avas 
the  left  aortic  arch  in  the  one  series,  and  the  right  aortic  arch  in  the 
other,  which  became  the  predominant  feeder  of  the  arterial  system." 

If  we  had  only  the  recent  forms  to  consider,  the  argument  advanced 
by  this  learned  anatomist  would  be  specially  potent ;  but  when  we  study 
carefully  the  osteology  of  the  Reptilia  of  the  Permian  Period,  many  of 
the  arguments  here  advanced  are  invalidated.  The  structure  of  the 
pectoral  and  pelvic  arches  of  the  theromorph  Reptilia,  as  has  been  ascer- 
tained by  Cope,  resembles  that  of  the  monotremes  far  more  than  does 
that  of  any  kno\vn  batrachian.  The  carpus  and  tarsus  of  these  forms 
are  almost  identical  with  those  of  the  monotremes,  Avhile  comparatively 


392  DENTAL  ANATOMY. 

little  importance  can  be  attached  to  the  dicondylian  character  of  the 
skull,  from  the  fact  that  there  is  in  certain  members  of  this  group  a 
double  articular  surface  on  the  occipital  bone  for  the  atlas  vertebra. 
The  only  osteological  character  left  in  which  the  Batrachia  resemble 
the  Mammalia  most  is  that  of  the  quadrate  articulation ;  which  resem- 
blance is  somewhat  counterbalanced  by  the  approaches  to  the  distinctive 
peculiarities  of  the  mammalian  dentition  found  only  in  the  Theromorpha. 
The  condition  of  the  arterial  system  must  remain  inferential  for  this 
group,  since  it  became  extinct,  so  far  as  we  now  know,  at  the  close 
of  the  Permian  Period.  Upon  the  wdiole,  I  am  disposed  to  think  that 
there  are  quite  as  many  reasons  to  regard  the  theromorph  Reptilia 
as  the  ancestors  of  the  mammal  as  there  are  to  regard  in  the  same 
light  any  of  the  Batrachia  so  far  discovered. 

Accepting  the  '*  placoid  scale  "  or  the  "  dermal  denticle  "  as  the  struc- 
ture from  which  all  teeth  w-ere  primarily  derived,  we  have,  as  charac- 
ters of  a  primitive  dentition,  the  following :  (1)  the  conical  form ;  (2) 
increased  number ;  (3)  frequent  and  almost  endless  succession.  These 
conditions  we  have  fulfilled  in  many  of  the  sharks.  The  next  step  in 
specialization  consists  in  the  fusion  of  the  basal  osseous  plates  of  the 
''  dermal  denticles  "  to  form  the  maxillary  and  dentary  bones,  to  which 
the  teeth  become  attached  by  ankylosis.  This,  we  have  already  seen, 
obtains  in  a  majority  of  the  fishes,  and  is  associated  largely  with  the 
simple  conical  form.  In  the  Batrachia  the  conical  form,  this  mode  of 
attachment,  as  well  as  the  succession,  are  closely  adhered  to,  but  the 
individual  teeth  are  reduced  in  number.  In  certain  of  the  Reptilia — e.  g. 
Theromorpha — another  advance  is  made  in  the  implantation  of  the  teeth 
in  distinct  sockets,  wath  a  disposition  to  form  more  than  one  root  or 
fang.  There  are  still,  however,  many  successive  sets  of  teeth  developed. 
Lastly,  in  the  INIammalia  the  teeth  are  generally  greatly  reduced  in 
number ;  they  are  always  implanted  by  one  or  more  roots  in  a  distinct 
socket,  and  there  are  never  more  than  two  sets  developed,  the  second 
of  which  is  only  partially  complete ;  they  are  also,  as  a  general  rule, 
of  a  complex  nature  and  show  a  wide  departure  from  the  primitive 
cone. 

In  searching,  therefore,  for  a  primitive  or  generalized  mammalian  den- 
tition, the  most  important  point  to  be  taken  into  consideration  is  the 
following  :  numerous  single-rooted  teeth,  confined  to  the  maxillary  and 
mandibular  bones,  implanted  in  distinct  sockets,  with  a  complete  devel- 
opment of  one  or  more  successive  sets.  It  is  possible,  even  probable, 
that  this  stage  in  tooth-development  was  reached  in  the  ancestors  of  the 
Mammalia  before  they  assumed  their  distinctive  characteristics  as  such  ; 
but  the  nearer  any  approach  is  made  to  this  condition  on  the  part  of  the 
mammal,  in  that  proportion  it  may  be  regarded  as  primitive  in  its  den- 
tal organization. 

Having  already  spoken  of  the  probable  origin  of  the  Mammalia,  it 
now  remains  to  give  a  brief  synopsis  of  their  classification  before  pro- 
ceeding to  a  detailed  description  of  their  teeth.  The  arrangement  here 
adopted  is,  with  some  modification,  the  one  which  has  been  proposed  by 
Prof.  E.  D.  Cope,  and  is  based  upon  a  study  of  both  fossil  and  recent 
forms : 


TEETH  OF  THE   VERTEBRATA. 


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394  DE2sTAL  ANATOMY. 

It  will  be  seen,  from  the  foregoing  table,  that  the  IMammalia 
are  divisible  into  two  primary  groups,  which  hold  the  rank  of  sub- 
classes. The  first  of  these,  Protothcria,^  has  but  tv,o  living  repre- 
sentatives, both  of  which  are  confined  to  the  continent  of  Australia. 
These  are  the  Echidna,  or  spiny  ant-eater,  and  the  duck-billed  j)latypus. 
The  principal  characters  by  which  they  are  separated  from  all  other 
Mammalia  may  be  conveniently  contrasted  with  those  of  the  second 
sub-class,  Eatlieria,  as  follows  :  in  the  former  there  are  (1)  ''  large  and 
distinct  coracoid  bones,  which  articulate  with  the  sternum.  (2)  The 
ureters  and  the  genital  ducts  open  into  a  cloaca  into  which  the  urinary 
bladder  has  a  separate  opening.  (3)  The  penis  is  traversed  by  a  ure- 
thral canal  which  opens  into  the  cloaca  posteriorly,  and  is  not  continuous 
with  the  cystic  urethra.  (4)  There  is  no  vagina.  (5)  The  mammary 
glands  have  no  teats."  In  the  Eutlier'm,  on  the  other  hand,  (1)  "  the 
coracoid  bones  are  mere  processes  on  the  scapula  in  the  adult,  and  do 
not  articulate  with  the  sternum.  (2)  The  ureters  open  into  the  bladder, 
the  genital  ducts  into  a  urethra  or  vagina.  (3)  The  cystic  urethra  is 
continuous  with  the  urethral  canal  of  the  penis.  (4)  There  is  a  single 
or  double  vagina,     (o)  The  mammary  glands  have  teats  "  (Huxley). 

In  their  anatomical  structure  the  I'rotothoia  resemble  the  rc})tiles  and 
birds  more  than  does  any  other  mannnal.  This  is  particularly  conspic- 
uous in  the  pectoral  arch  and  the  repi'ocluctive  system.  On  this  account, 
De  Blainville  applied  the  name  OrnithocMjjliki  (bird  womb)  to  them, 
by  which  they  are  sometimes  known.  Strange  as  it  may  seem,  no  fossil 
remains  of  great  anti(piity  of  this  most  primitive  grouj)  of  all  Mammalia 
are  with  certainty  known  to  exist,  but  it  may.  yet  be  found  that  the 
earliest  mammalian  representatives,  which  date  as  far  back  as  the 
Triassic  Period,  and  which  are  known  from  teeth  and  jaw  bones 
only,  really  belong  to  the  Protofhcria  rather  than  to  the  Didclpliia  or 
pouched  series  of  the  Eutheria,  as  is  frequently  maintained.  Both 
the  living  forms  are  devoid  of  true  teeth. 

The  second  sub-class,  Eutheria,  has  two  principal  divisions  :  Didelphia 
(double  womb),  including  those  animals  popularly  known  as  the 
"  pouched  cpiadrupeds,"  of  Avhich  the  opossum,  kangaroo,  wombat, 
etc.  are  familiar  .examples;  and  the  MonodelpJiia  (single  womb), 
which  embraces  all  the  remaining  mammals.  The  name  of  the  first 
subdivision,  Didelphia,  was  applied  by  its  author,  De  Blainville,  with 
reference  to  the  peculiar  habit  which  these  animals  possess  of  sheltering 
their  helpless  young  in  an  abdominal  integumentary  fold.  This  is  corre- 
lated with  the  only  important  character  in  which  they  differ  from  the 
monodelph  division — viz.  the  complete  absence  of  an  allantoic  placenta 
or  any  uterine  connection  between  mother  and  foetus.  In  consequence 
of  this  peculiarity  of  gestation  the  young  are  born  in  an  exceedingly 
helpless  and  imperfect  condition,  and  are  nourished  for  a  considerable 
period  in  the  marsupium  or  pouch  of  the  mother.     This  character  is 

^  The  classification  of  tlie  jNTammalia  proposed  recently  by  Prof.  Hnxley  includes 
three  jjrincipal  subdivisions — viz. :  Prololheria,  JSIelailieria,  and  Fjilheria.  The  terms 
Pfotnlheria  and  Eutlirria  were  employed  by  Prof.  Gill  a  number  of  years  previously  t<> 
desisnate  the  two  ])rincipal  groups  of  this  class,  and  appear  to  have  been  appropriated 
bv  Huxlev  without  credit. 


TEETH  OF  THE   VERTEBRATA.  395 

considered  of  sufficient  value  by  some  to  give  the  Dldelphia  a  rank  equal 
to  that  of  the  Prototheria,  and  they  consequently  make  three  primary 
divisions  of  the  class — Ornithodelphia,  Didelphia,  and  Monoddphla,  after 
De  Blainville.  If  this  were  associated  with  any  other  characters  of 
structural  importance  it  would  be  quite  sufficient,  but  since  it  is  not, 
and  in  view  of  its  unreliability  and  inconstancy  in  the  lower  Vertebrata, 
I  am  not  disposed  to  regard  it  as  equal  in  value  to  the  strong  structural 
characters  by  which  the  Prototheria  are  deffiied. 

The  subdivision  of  the  Monodelphia  is  not  an  easy  matter,  if  indeed 
any  important  divisions  further  than  the  separation  of  the  mutilate 
series  can  be  made.  It  is  convenient,  however,  to  adopt  the  classifica- 
tion of  Lamarck,  and  divide  them  into  three  series,  as  follows :  the 
mutilate  series,  the  ungulate  series,  and  the  unguiculate  series.  The 
first  of  these  includes  the  Cetucea,  or  whales,  and  the  Sirenia,  or  sea- 
cows.  The  only  character  by  means  of  which  they  are  associated 
is  the  absence  of  hind  limbs  and  the  loss  of  the  articular  processes  of 
the  bones  of  the  manus.  The  Cetacea  form  a  i^erfectly  natural  and 
homogeneous  group,  and  are  entitled  to  a  wide  separation  from  all 
other  ^Mammalia.  We  at  present  know  very  little  concerning  their 
develo])ment  or  ancestry,  further  than  that  their  Eocene  representative, 
Zctiglodon,  resembled  the  ordinary  monodelphous  type  more  than  does 
any  other  member  of  the  order.  They  are  undoubtedly  a  very  old  and 
distinct  group,  and  it  would  not  be  at  all  surprising  if  they  are  ultimately 
found  to  have  descended  directly  and  independently  from  the  Prototlieria. 

The  Sirenia,  or  sea-cows,  on  the  other  hand,  appear  to  be  simply 
modified  ungulates  that  have  gradually  assumed  their  present  structure 
in  accordance  with  their  aquatic  environment.  The  jNIiocene  genus 
(Hulitherium)  of  this  order  had  distinct  hind  limbs,  and  in  many  ways 
resembled  the  primitive  hoofed  Mammalia.  For  this  reason  it  is 
probably  best  to  associate  them  with  the  ungulate  rather  than  with 
the  mutilate  series,  since  they  dilFer  in  almost  every  essential  feature 
from  the  Cetacea,  except  in  the  loss  of  the  posterior  members. 

The  separation  of  the  two  remaining  series,  ungulate  and  unguicu- 
late, depends  entirely  upon  the  distinctions  to  be  drawn  between  "  hoof" 
and  "  claw."  If  we  contrast,  for  example,  two  such  structures  as  the 
claw  of  the  lion  and  the  hoof  of  the  horse,  the  distinctions  are  perfectly 
obvious,  and  we  will  ex})erience  no  difficulty  in  recognizing  the  differ- 
ences ;  but  if  we  carefully  trace  the  respective  lines  of  ancestry  of  these 
two  forms  backward  to  the  Eocene  Period,  we  will  find  them  converging 
to  such  an  extent  as  to  involve  the  hoof-and-claw  question  in  almost 
hopeless  confusion. 

There  are,  however,  two  principal  lines  or  stems  which  have  terminated 
in  the  distinctly  hoof-bearing  mammals  on  the  one  hand  and  the  claw- 
and  nail-bearing  on  the  other.  The  exact  point  at  which  these  two  lines 
converge  has  not  as  yet  been  satisfactorily  determined,  but  it  is  undoubt- 
edly true  that  they  a])proached  one  another  to  a  remarkable  extent  in 
the  early  Eocene.  The  ancestry  of  the  entire  ungulate  series  is  indi- 
cated by  the  Taxeopoda  of  Cope,  to  whose  persistent  efforts  and  schol- 
arly researches  we  are  alone  indebted  for  their  discovery  and  description. 

The  primitive  or  central  stem  of  this  order  is  the  Condylarthra,  from 


39G  DENTAL  ANAT03IY. 

which  we  pass  by  easy  stages  through  the  extinct  genus  3Ieniscotherium 
to  the  little  hyrax  or  "  coney,"  whose  classification  has  long  remained 
a  puzzle  to  zoologists.  From  this  group  the  extinct  aniblypods  and 
elephantoid  animals  likewise  came,  while  the  Ferissodadyla  and  the 
AHiodaciyla  are  traceable  directly  to  it. 

The  unguiculate  series  also  has  a  generalized  order,  from  which  all 
the  others  radiate  in  dilierent  directions.  This  order  has  been  called  the 
Bunothcria  by  Cope,  and  exhibits  a  central  axis  in  the  sub-order  Insecf- 
ivora,  the  representatives  of  which  are  among  the  oldest  of  monodelph 
mammals.  From  the  Insectivora  we  derive  the  Creodonta,  a  group  of 
extinct  insectivoro-carnivorous  animals  which  terminates  in  the  Car- 
nivora.  In  another  line  come  the  lemuroids,  monkeys,  and  man,  while 
in  still  another  are  the  Cheiroptera  or  bats,  which  are  simply  insectivores 
modified  for  flight. 

One  other  order,  the  Edentata,  or  sloths,  armadillos,  ant-eaters,  etc., 
remains  to  be  accounted  for.  Some  authors  believe  them  to  be  affiliated 
with  the  unguiculate  series,  and  to  have  sprung  from  the  central  insect- 
ivorous group.  Palaeontology  has  so  far  given  us  very  few  if  any  hints 
concerning  the  origin  of  this  order,  and  it  is  probable  that  it  will  not 
be  until  the  Eocene  and  Miocene  Tertiaries  of  South  America  are  more 
fully  explored  that  any  important  information  Mill  be  had  upon  this 
subject.  At  present  I  consider  the  evidence  too  meagre  to  hazard  an 
opinion. 

Divisions  of  the  Mammalian  Dentition. — Many  years  ago 
Prof.  Owen  called  attention  to  the  fact  that  in  many  of  the  Entheria 
there  are  two  sets  of  teeth  developed  during  the  life  of  the  individual — 
a  deciduous  or  milk  set  and  a  permanent  set — while  in  others  but  a  single 
set  appears.  The  former  of  these  two  conditions  he  designated  by  the 
term  diphyodont,  and  to  the  latter  he  gave  the  name  monophyodont  den- 
tition. It  likewise  so  happens  that  generally,  in  those  that  have  tM'O 
sets  (diphyodonts),  the  teeth  in  the  various  parts  of  the  mouth  are  dif- 
ferent in  form  and  complexity,  while  in  those  that  have  but  a  single  set 
(monophyodonts)  the  teeth  are  alike  throughout.  The  diphyodont  den- 
tition is  therefore,  as  a  general  rule,  hcterodont,  that  is,  there  are  many 
kinds  of  teeth,  and  the  monophyodont  dentition  is  homodont,  or  all 
the  teeth  are  alike.  It  was  therefore  originally  supposed  by  Owen  that 
diphyodont  and  heterodont  and  monophyodont  and  homodont  were  cor- 
relative and  interchangeable  terms,  but  it  has  since  been  discovered  that 
there  arc  many  exceptions  to  this  rule. 

It  must  be  borne  in  mind  that  the  terms  diphyodont  and  monophyo- 
dont are  simply  conveniences  by  which  we  are  enabled  to  express  briefly 
the  conditions  of  replacement,  and  are  not  in  any  way  to  be  looked  upon 
as  definitive  of  a  natural  group.  The  degree  to  which  the  second  den- 
tition is  developed  in  the  various  sections  of  the  INIammalia  is  subject  to 
extreme  variation,  and  it  is  not  always  an  easy  matter,  if  not  frequently 
an  utter  impossibility,  to  determine  whether  certain  teeth  belong  to  the 
deciduous  or  permanent  set,  or  in  the  monophyodonts  to  say  whether 
it  is  the  permanent  or  deciduous  set  which  has  been  lost.  There  are, 
however,  as  will  appear  later,  several  important  series  in  which  the 
replacement  and  position  are  sufficiently  constant  to  enable  us  to  divide 


TEETH  OF  THE   VERTEBRATA. 


397 


the  teeth  into  several  categories,  the  convenience  of  which,  to  say  the 
least,  if  not  the  real  importance,  is  undeniable.  The  question  of  the 
nature  and  relationship  of  the  milk  dentition  to  the  permanent  one 
will  be  discussed  after  the  teeth  of  the  several  groups  have  been 
considered. 

The  Teeth  and  their  Accessory  Organs  in  the  Dog. — I  have 
thought  best  to  next  present  a  detailed  des(!ription  of  the  adult  structure 
of  an  average  diphvodont  dentition,  together  with  the  accessory  organs, 
in  order  that  the  student  may  become  familiar  with  the  technicalities 
before  proceeding  to  consider  the  teeth  of  the  various  sections  of  the 
Mammalia  The  dog  has  been  selected  as  an  example  of  this  kind, 
])artially  on  account  of  the  generalized  condition  of  the  teeth,  but 
principally  on  account  of  the  readiness  with  Avhich  the  student  will 
be  enabled  to  provide  himself  with  the  necessary  material. 

The  teeth  of  the  dog  (Figs.  195  and  196)  are  forty-two  in  number, 
of  which  twenty  belong  to  the  upper  and  twenty-two  to  the  lower 
jaw.  The  most  anterior  teeth  of  the  upper  series  are  relatively  small, 
and  are  imjjlanted  in  the  free  edge  of  the  premaxillary  bones  in  such  a 
manner  as  to  describe  the  arc  of  a  circle.  These  are  known  as  the 
incisors  {ic,  Figs.  195,  196).     Behind  these,  after  a  slight  interval,  are 

Fig.  195. 


Vertical  View  of  tlie  Upper  Jaw  of  a  T)og  {Ornis  familiaris) :  ic,  incisors;  e.  canine  ;  pm,  premolars  ; 
111,  molars;  .«,  sectorial ;  pmz,  premaxillary  bone;  mx,  maxillary  bone;  pi,  palatine  ;  <(///,  anterior 
p  ilatine  foramen  ;  ppf,  posterior  p.ilatine  foramen.  The  position  of  the  third  premolar  is  slightly 
abnormal. 

a  pair  of  strong,  laterally  compres.sed  curved  teeth,  the  canines,  which  are 
lodged  deeply  in  the  sub.stance  of  the  maxillary  bone,  immediately  behind 
the  maxillo-premaxillary  suture.  Behind  the  canines,  again,  are  six 
teeth  on  each  side,  wliich  progressively  increase  in  size  and  complexity 
as  we  proceed  backward  until  the  penultimate  tooth  is  reached,  the  last 
one  being  somewhat  smaller.  These  are  termed  molws  and  premolars. 
The  tooth-line  of  each  moiety  of  the  upper  ja^v  presents  three  curves, 
the  most  anterior  of  which  is  formed  by  the  three  incisors  and  canine, 
with  a  strong  convexity  outward ;  the  line  of  tlie  next  four  describes  a 
gentle  curve  whose  convex  surface  is  inward  ;  while  that  of  the  la.st  two 
curves  boldly  inward  toward  the  median  line. 

The  number  of  teeth  in  the  lower  jaw  is  one  in  excess  of  that  of  the 
upper,  which  is  caused  by  the  addition  of  a  small  single-rooted  tooth  at 


398 


DENT  A  L  A  NA  TO  MY. 


the  posterior  end  of  the  series.  They  describe  the  same  curves,  so  as  to 
oppose  those  of  the  upper  series.  The  incisors  of  the  upper  jaw,  as  has 
already  been  stated,  are  lodged  in  the  pre-  or  intermaxillary  bones, 
which  limit  the  anterior  part  of  the  oral  cavity  above.  The  definition, 
therefore,  of  an  incisor  tooth  of  this  series  is  one  tchich  has  a  pre-  orinter- 
maxilku'ij  imphtntatlon  irrespedlce  of  its  size  or  form.  The  incisor  teeth 
of  the  lower  jaw  are  the  corresponding  ones  whieli  are  brouf/ht  info  opjposi- 
tion  with  those  of  the  upper  jaw  ichen  the  mouth  is  dosed.  The  teeth  thus 
defined  are  three-in  number  upon  each  side  above  and  below  in  this  animal, 
and  are  implanted  by  single  slightly  recurved  fangs  in  distinct  sockets  or 
alveoli.  In  the  upper  series  the  median  pair  is  the  smallest,  the  outer 
ones  gradually  increasing  in  size.  The  base  of  the  crowns  of  the  four 
middle  teeth  is  somewhat  trihedral  in  form,  with  the  apex  flattened  from 
before  backward  and  produced  into  three  cusps,  of  which  the  central 
one  is  the  largest.  The  entire  apex  of  the  crown  is  slightly  recurved. 
Upon  its  inner  aspect  the  crown  presents  a  basal  ledge  or  cingulum, 
M'hich  sends  out  a  low  ridge  to  each  of  the  lateral  cusjis.  The  lateral 
incisors  are  the  largest  and  are  somewhat  caniniform.  Like  the  median 
ones,  their  crowns  have  a  strong  basal  cingulum  posteriorly,  but  the 
lateral  cusps  a"re  absent ;  the  apex  terminates  in  a  strong  hooked  point. 

The  iiicisors  of  the  lower  jaw  are  similar  to  those  of  the  upper,  with 
the  exception  of  the  median  pair,  which  is  much  the  smallest  and  occu- 
pies a  more  anterior  position  than  the  others.  The  intf^rnal  lateral  cus])s 
of  these  teeth  are  very  faintly  indicated,  if  indeed  they  can  be  at  all 
made  out,  while  the  external  lateral  cusp  is  present  and  situated  high 
up  in  the  two  median  pairs.  In  the  lateral  ones  it  has  a  position  nearer 
the  base  of  the  crown,  and  is  separated  from  the  median  cusp  by  a  deep 
fissure. 

Between  the  lateral  incisors  and  canines  of  the  upper  series  there  is  a 
space  or  diastema  about  equal  to  the  width  of  the  lateral  incisor.  This 
space  serves  to  receive  the  lower  canine  when  the  mouth  is  closed.  At 
the  back  part  of  it  upon  the  outside  may  be  seen  the  suture  by  which 

Fig.  190. 


Vertical  Vie«"  of  the  Lower  .Taw  of  a  Dor  {C.  /nmiHuris) :  ic,  incisors;   r,  canine;  pm,  premolars; 

m,  molars;  .«,  sectorial. 

the  premaxillary  bone  joins  the    maxillary  in  the  dentigerous  border 
of  the  jaw.     Just  behind  this  suture  the  .superior  canine  is  lodged. 

The  definition,  then,  of  a  superior  canine  tooth  is  one  which  is  situated 
in  the  maxillary  bone  immediately  behind,  the  maxillo-prcmaxiJlarg  suture, 
pr^ovided  it  be  not  too  far  back,  whatever  may  be  its  form,  size,  or  func- 


TEETH  OF  THE   VERTEBRATA.  399 

tion,  while  the  canine  of  tJie  lower  jaw  is  the  tooth  which  closes  just  in  front 

The  canines  of  the  dog  are  large,  recurved,  pointed  teeth,  projecting 
far  above  the  level  of  tlie  others,  with  slightly  trenchant  anterior  and 
posterior  edges.  They  are  almost  equal  in  size  and  very  similar  in 
shape.  A  very  useful  means  by  which  they  can  be  distinguished  from  each 
other,  if  at  all  worn  and  isolated  from  the  rest  of  the  teeth,  is  to  note 
the  point  at  which  the  worn  surface  exhibits  itself.  It  must  be  remem- 
bered that  the  lower  canine  closes  in  front  of  the  upper,  in  consequence 
of  which  the  posterior  face  of  the  lower  impinges  against  and  abrades 
the  anterior  face  of  the  upper ;  the  anterior  face  of  the  lower  canine  also 
comes  in  contact  with  the  lateral  incisor,  and  an  abrasion  takes  place  at 
this  point ;  but  the  posterior  face  of  the  upper  canine  is  seldom  worn 
except  by  long-continued  use,  so  that  ordinarily  these  points  of  Avear 
serve  as  a  useful  guide  in  distinguishing  between  them.  There  is  a 
slight  difference  in  form,  which  can  be  ascertained  only  by  close  and 
careful   comparison. 

Behind  the  canines  are  four  teeth  which  have  been  designated  premo- 
lars. The  reason  for  this  distinction  is  founded  upon  the  circumstance 
that  these  are  the  teeth  situated  behind  the  canine  wliich  vertically  suc- 
ceed the  corresponding  ones  of  the  deciduous  or  milk  set.  The  defini- 
tion, therefore,  of  a  premolar  tooth  is  one  ichich,  being  situated  behind 
the  canine,  displaces  in  a  vertical  direction  a  deciduous  or  milk  tooth;  all 
others  behind  these  are  true  molars.  This  is  the  definition  which  was 
originally  proposed  by  Owen,  to  whom  we  are  greatly  indebted  for  this 
nomenclature  :  it  would  appear  to  be  entirely  satisfactory  and  sufficient, 
Avere  it  not  for  the  fact  that  the  first  tooth  counting  from  before  back- 
ward, which  is  generally  enumerated  in  the  premolar  series,  does  not 
have  any  deciduous  predecessor.  If  we  adhere  strictly  to  this  definition, 
it  cannot  be  justly  considered  a  premolar,  but  common  usage  has  so 
Icng  given  it  a  place  in  this  category  that  it  appears  advisable  to 
still  call  it  such.  It  should  be  remembered,  however,  that  this  is  by 
no  means  an  isolated  case,  but  that  other  animals  exhibit  similar 
peculiarities. 

The  first  premolar,  so  called,  of  the  superior  series  is  the  smallest  of 
the  four,  and  is  implanted  rather  obliquely  in  the  maxillary  bone ;  its 
single  fang  is  sliglitly  compressed  laterally,  and  joins  the  crown  at  a 
moderately  well-defined  neck.  The  crown  has  an  elongated  oval  form, 
terminated  by  a  prominent  obtuse  cusp  and  surrounded  by  a  well- 
marked  ledge  or  cingulum,  which  is  most  conspicuous  upon  its  inner 
face.  From  the  summit  of  the  main  cusp  two  well-defined  ridges 
descend  to  the  cingulum,  one  on  the  posterior  and  the  other  upon  the 
anterior  border,  giving  to  the  tooth  a  slightly  trenchant  appearance. 
The  hindmost  of  these  two  ridges  divides  the  posterior  half  of  the 
crown  into  two  equal  parts,  and  terminates  with  a  very  slight  enlarge- 
ment in  the  cingulum,  while  the  anterior  one  has  a  more  internal  direc- 
tion, and  terminates  in  a  distinct  tubercle  ^hich  occupies  a  position  at 
the  base  of  the  antero-internal  portion  of  the  crown.  The  two  ridges 
and  the  cingulum  below  enclose  a  shallow  triangular  depression  inter- 
nally, the  outer  face  being  convex. 


400  DE^'TAL  ANATOMY. 

The  second  and  third  premolars  are  considerably  larger  than  the  first, 
and  are  implanted  by  two  roots,  of  which  the  posterior  is  the  larger. 
These  two  teeth  resemble  one  another  very  closely,  the  only  appreciable 
difference  being  their  slight  disparity  in  size.  Their  crowns,  like  that  of 
the  first,  are  of  greater  longitudinal  than  transverse  extent,  and  are  pro- 
duced into  a  prominent  cusp  situated  a  little  anterior  to  the  centre.  The 
posterior  ridge  is  interrupted  shortly  before  it  joins  the  cingulura  by  a 
deep  transverse  notch  which  gives  rise  to  a  distinct  cusp,  the  jjosferior 
baml  tubercle,  situated  over  the  hinder  root.  A  faint  indication  of  a 
second  cusp  is  seen  just  behind  this  as  an  elevation  of  the  cingulum. 
The  antero-internal  tubercle  is  present,  and  occupies  relatively  the  same 
position  as  it  does  in  the  first  premolar.  The  cingulum  is  more  promi- 
nent on  the  inner  than  on  the  outer  side  of  the  crown,  and  Avith  the  two 
ridges  encloses  a  triangular  space. 

The  fourth  premolar  is  by  far  the  largest  and  strongest  tooth  of  the 
premolar  series.  It  is  commonly  known  as  the  "  flesh  tooth,"  or  supe- 
rior sectorial,  for  reasons  presently  to  be  given.  It  is  implanted  by 
three  roots,  two  external  and  one  internal.  The  crown  is  comjiosed  of 
tw^o  principal  lobes  supported  by  the  two  external  roots,  and  a  small 
antero-internal  one  supported  by  the  internal  fang  The  tAvo  prin- 
cipal lobes  have  an  antero-posterior  position,  and  are  separated  from 
each  other  by  a  deep,  narroAv  fissure.  Of  these,  the  anterior  is  the 
larger  and  higher  of  the  two ;  when  viewed  externally  it  resembles  a 
cone  with  the  anterior  contour  produced.  Internally  it  is  flattened 
somewhat,  so  as  to  correspond  with  the  flattened  inner  surface  of  the 
posterior  lobe.  Posteriorly  it  is  produced  into  a  strong  blade-like  ridge, 
which  is  terminated  by  the  vertical  fissure,  while  its  anterior  surface  is 
marked  by  a  moderate  vertical  ridge.  The  posterior  lobe  is  essentially 
chisel-shaped  in  form,  with  the  bevelled  edge  external ;  its  apex  forms 
a  blade-like  crest  which  extends  the  entire  length  of  the  lobe.  The 
internal  lobe  is  small,  and  occupies  a  position  at  the  antero-internal 
angle  of  the  croAvn,  being  connected  w-ith  a  faintly-marked  cingulum 
which  surrounds  the  base  of  the  crown.  When  we  attempt  to  homol- 
ogize  the  component  lobes  of  this  tooth  with  those  of  the  premolars'  in 
advance  of  it,  it  is  not  difficult  to  see  that  the  anterior  lobe  is  the  prin- 
cipal cone,  that  the  posterior  one  is  merely  an  exaggerated  posterior 
basal  tubercle,  while  the  internal  lobe  is  strictly  homologous  with  the 
structure  which  has  a  similar  position  in  the  others.  The  three  anterior 
premolars  are  not  in  as  close  contact  as  the  teeth  in  the  back  part 
of  the  jaw,  but  are  separated  from  each  other  by  slight  intervals,  which 
are  most  conspicuous  between  the  first  and  second. 

The  premolars  of  the  lower  jaM"  are  similar  in  form  to  those  of  the 
upper,  with  the  important  exception  of  the  fourth  or  last,  wherein 
there  is  to  be  found  a  wide  difference  both  in  size  and  structure. 
The  first  of  the  lower  series  is  smaller  than  the  corresponding  tooth 
above,  and  has  a  simpler,  more  conical  crown.  It  is  separated  by  a 
considerable  diastema  from  the  canine  in  front  of  it,  but  is  almost  in 
contact  with  the  second  behind.  The  second  and  third  resemble  those 
"vvhich  are  in  a  like  position  in  the  upper  jaw,  while  the  fourth  is  also 
similar  to   the   corresponding  tooth   above,  with  the   exception    of  a 


TEETH  OF  THE   VERTEBRATA.  401 

slightly  increased  size  and  the  possession  of  a  well-defined  second 
posterior  basal  lobe.  It  slightly  overlaps  the  great  first  true  molar 
behind  it. 

The  true  molars  of  the  superior  series  are  two  in  number  upon  each 
side,  and  are  placed  directly  behind  the  premolars.  The  definition  of  a 
true  molar  tooth  is  one  which,  being  situated  behind  the  premolars,  does 
not  displace  a  deciduous  or  milk  predecessor.  The  two  molars  above 
are  three-rooted,  with  broad  tuberculated  crowns  imperfectly  quadran- 
gular in  outline.  The  first,  which  is  more  than  twice  the  size  of  the 
second,  has  two  strong  obtuse  conical  tubercles  on  the  external  portion 
of  the  crown,  situated  directly  over  the  anterior  and  posterior  external 
roots ;  they  are  subequal  and  separated  from  each  other  by  a  transverse 
notch.  Internal  to  these  there  is  a  broad  ledge,  well  rounded  oif  inter- 
nally, bearing  three  cusps.  The  one  most  internal  is  lunate  in  form,  and 
is  closely  connected  with  the  cingulum,  which  surrounds  the  base  of  the 
tooth.  The  cusp  situated  near  the  antero-internal  angle  is  the  largest, 
and  has  a  subtrihedral  form.  A  distinct  ridge  passes  outward  and  for- 
ward from  it  to  join  the  cingulum.  Posterior  to  this  last-mentioned 
cusp,  and  separated  from  it  by  a  wide  open  notch,  is  the  third  tubercle, 
less  distinctly  marked  than  either  of  the  others.  An  analysis  of  the 
various  cusps  of  which  the  crown  is  composed  leaves  little  room  to 
doubt  that  the  two  external  cusps  are  strictly  homologous  with  the  two 
external  ones  of  the  sectorial  in  advance  of  it — that  the  internal  ledge 
which  bears  the  three  tubercles  represents  the  greatly  enlarged  internal 
lobe  of  the  sectorial,  Avhich  has  been  removed  to  a  more  posterior 
position,  and  has  acquired  an  important  addition  from  the  cingulum. 
That  part  of  it  which  is  exactly  homologous  Avith  the  internal  lobe 
is  the  principal  cusp  at  the  antero-internal  angle,  which  in  some  car- 
nivorous animals  is  continued  outward  and  backward  as  a  prominent 
ridge,  and  does  not  develop  the  third  tubercle.  If  the  lunate  cingular 
cusp  be  subtracted,  the  crown  will  be  seen  to  resemble  that  of  the 
sectorial  in  its  general  features. 

The  second  true  molar  is  like  the  first,  except  that  the  internal  ledge 
exhibits,  instead  of  three  tubercles,  two  crescentiform  ridges. 

The  first  true  molar  of  the  lower  jaw  is  the  largest  tooth  in  the  entire 
dentition  of  the  dog,  and  is  the  sectorial  of  the  inferior  series.  It  is 
implanted  by  two  powerful  roots  at  a  point  about  midway  between  the 
anterior  extremity  and  the  condyle  of  the  lower  jaw,  and  occupies  a 
position  near  the  canthus  or  angle  of  the  mouth.  Its  crown  may  be 
described  as  composed  of  two  anterior  blade-like  cusps,  a  small  inter- 
nal tubercle,  and  a  low  tubercular  heel.  Of  the  two  anterior  cusps,  the 
posterior  is  the  larger,  and  rises  gradually  above  the  level  of  the  one 
anterior  to  it ;  both  are  convex  internally,  but  somewhat  flattened  exter- 
nally to  correspond  with  the  internal  flattened  surface  of  the  two  blades 
of  the  superior  sectorial.  They  are  separated  from  each  other  by  a  deep, 
narrow  fissure.'  The  heel  is  low,  and  occupied  by  two  cusps  disposed 
transversely,  of  which  the  outer  one  is  the  larger,  A  faint  ridge  con- 
nects them,  enclosing  a  shallow  basin  in  front ;  on  this  account  the  heel 
is  said  to  be  basin-shaped.  The  internal  tubercle  is  small,  and  is  placed 
at  the  inner  posterior  part  of  the  median  lobe.     In  many  carnivores  it 

Vol.  I.— 26 


402 


DENTAL  ANATOMY. 


completely  disappears,  as  does  also  the  heel,  as  we  shall  presently  see. 
The  fourth  superior  premolar  and  the  first  inferior  true  molar  are  called 
sectorial,  on  account  of  their  scissor-blade  structure  and  the  manner  in 
which  they  oppose  each  other.  If  the  macerated  skull  of  a  dog  be  care- 
fully examined,  it  will  be  seen  that  the  incisors  of  each  series  oppose 
each  other  almost  exactly,  while  the  lower  canines  close  in  front  of  the 
upper.  As  a  consequence  of  this,  the  first  premolar  below  closes  in 
advance  of  the  first  premolar  above ;  the  second  below  in  the  interval 
between  the  first  and  second  above,  etc.,  but  always  upon  the  inside,  on 
account  of  the  unequal  width  of  the  two  jaws.  Now,  the  inferior  sec- 
torial bites  against  the  superior  in  such  a  manner  that  its  blades  exactly 
oppose  those  of  the  tooth  above  after  the  manner  of  a  pair  of  shears,  so 
that  when  the  mouth  is  closed  the  inferior  sectorial  is  completely  hidden 
from  view ;  the  heel  opposes  the  first  true  molar  above.  Those  who 
have  ever  studied  the  habits  of  dogs  or  wolves  must  have  noticed  that 
when  they  wash  to  divide  a  tough  animal  membrane  or  ligament  they 
pass  it  back  to  the  canthus  of  the  mouth  on  one  side  and  make  several 
short  quick  strokes  of  the  jaw ;  this  is  the  shearing  movement  of  the 
sectorials. 

The  remaining  two  true  molars  are  much  smaller,  the  last  being  one 
of  the  smallest  of  all  the  teeth,  and  is  implanted  by  a  single  root.  It  is 
said  to  be  permanently  absent  in  some  races  of  the  domestic  dog,  espe- 
cially the  "  pugs"  and  "Japanese  sleeve  dogs."  The  second  molar  is 
two-rooted,  with  a  tuberculate  crown  of  a  more  or  less  quadrate  form. 
Two  transverse  cusps  occupy  the  anterior  part,  while  a  third  is  placed 
at  the  postero-external  angle  of  the  crown  on  the  edge  of  a  broad  flat 
heel.     A  basal  cingulum  is  also  present.     The  last  tooth  has  an  obtusely 


Fig.  197. 


Side  View  of  the  Skull  of  a  Dog  (C.familiaris). 

conical  crown.  The  homologies  of  the  cusps. of  the  inferior  true  molars 
are  not  evident  in  the  dog,  but  when  we  come  to  examine  allied  forms 
it  will  be  found  that  the  two  blades  of  the  sectorial  represent  the  primi- 
tive cone,  and  the  anterior  basal  lobe  of  the  ordinary  premolar  greatly 
enlarged  and  specialized,  while  the  heel  represents  the  two  posterior 


TEETH  OF  THE   VERTEBRATA.  403 

basal  tubercles  arranged  transversely ;  the  internal  tubercle  is  an  extra 
outgrowth  from  the  cinoulum. 

In  the  case  of  many  extinct  animals  the  succession,  and  consequently 
the  discrimination,  of  the  molars  and  premolars  would  be  attended  with 
considerable  difficulty  were  it  not  for  the  fact  that  in  a  majority  of  the 
Mammalia  the  first  true  molar  is  the  first  of  the  permanent  set  of  the 
molar  and  premolar  series  which  comes  into  place.  By  the  time  the 
last  or  fourth  premolar  is  cut,  which  is  usually  one  of  the  last,  the  first 
true  molar  immediately  behind  it  is  considerably  worn  down  by  use,  so 
that  this  disparity  of  wear  will  of  itself  frequently  serve  to  locate  the 
exact  limits  of  each  series.  It  is  a  rule  which  is  often  employed  by 
palaeontologists  to  determine  the  dental  formula  of  an  animal  the  suc- 
cession of  whose  teeth  is  unknown.  When  the  anatomist  wishes  to 
indicate  briefly  the  number  of  the  various  teeth  of  any  particular  ani- 
mal, he  employs  what  is  called  a  dental  formula.  By  this  method  the 
permanent  dentition  of  the  dog  would  be  expressed  as  follows  :  I.  |,  C. 
\,  Pm.  1^,  M.  1^  ;  which  means  that  there  are  three  incisors  upon  each 
side  above  and  below,  that  there  is  one  canine  upon  each  side  above  and 
below,  that  there  are  four  ])remolars,  and  that  there  are  two  true  molars 
above  and  three  below.  This  manner  of  abbreviation  is  convenient  and 
easily  understood,  and  saves  both  time  and  space  in  descriptions. 

The  division  of  the  teeth  into  incisors,  canines,  premolars,  and  molars, 
although  open  to  some  objection,  is  nevertheless  useful,  since  it  serves  to 
locate,  in  the  case  of  addition  or  subtraction  of  a  tooth  to  or  from  the  nor- 
mal dijihyodont  number,  the  exact  position  in  which  the  change  has 
taken  place.  In  the  marmoset  monkeys  of  South  America,  for  exam- 
ple, the  total  number  of  teeth  is  thirty-two,  the  same  as  in  man.  An 
inspection  of  their  formula,  however,  wdiich  is  I.  |-,  C.  \,  Pm.  |,  M.  ^ 
=  32,  will  show  that  there  is  an  important  difference  between  the  num- 
ber of  molars  and  premolars,  the  formula  in  man  being  I.  f,  C.  \,  Pm. 
f ,  M.  f .  In  the  former  it  is  a  molar  vchicli  is  lost ;  in  the  latter  it  is  a 
premolar.  Another  example  of  this  kind  is  seen  in  the  upper  and  lower 
teeth  of  the  otter,  in  which  they  are  equal  in  total  number,  but  unequal 
as  far  as  the  respective  kinds  are  concerned.  The  dental  formula  in  this 
animal  is  I.  f ,  C.  \,  Pm.  f^  M.  l  -  36. 

The  Accessory  Organs. — This  subject  properly  embraces  a  considera- 
tion of  the  bones  by  which  the  teeth  are  supported,  the  muscles  con- 
cerned in  their  movement,  the  blood-vessels  by  which  they  are  supplied 
with  nutriment,  and  the  nerves  distributed  to  them.  The  bones  in 
which  the  upper  teeth  are  implanted  are  the  maxillce  and  prem.nxill(je, 
which  are  usually  enumerated  as  bones  of  the  face.  The  maxillary  bone 
(Fig.  195,  mx)  is  by  far  the  largest  one  belonging  to  this  category,  and 
forms  the  greater  part  of  each  moiety  of  the  upper  jaw.  It  likewise 
contributes  to  the  formation  of  the  cheek,  orbit,  and  palate,  and  also 
takes  the  principal  share  in  forming  the  boundary  of  the  nasal  cham- 
ber. The  maxillary  bones  do  not  meet  in  the  median  line  above,  on 
account  of  the  interposition  of  the  nasals  and  premaxillaries,  but 
below  they  send  inward  two  thin  horizontal  plates  which  meet  in 
the  middle  of  the  roof  of  the  mouth. 

For  descriptive  purposes  it  is  convenient  to  divide  each  bone  into 


404  DENTAL  ANATOMY. 

three  external  surfaces,  the  facial,  palatine,  and  orbital.  The  facial  sur- 
face, ^vliich  is  the  largest  of  the  three,  is  directed  outward,  and  is  irregu- 
larly triangular  in  form,  with  the  apex  directed  forward.  The  superior 
border  of  this  surface  is  considerably  curved,  and  joins  the  premaxillary 
in  front  and  the  nasal  behind.  The  posterior  border  is  irregular,  and  is 
in  contact  from  within  outward  with  the  frontal,  lachrymal,  and  malar 
bones  respectively,  being  excluded  by  these  bones  from  the  rim  of  the 
orbit.  The  inferior  border  is  known  as  the  dental  or  alveolar  border, 
on  account  of  its  affording  support  to  the  canine,  premolar,  and  molar 
teeth  of  the  upper  jaw.  It  is  in  contact  with  the  premaxillary  in  front, 
and  terminates  behind  in  a  free  extremity  beneath  the  orbital  fossa. 

The  surface  thus  bounded  is  uneven,  being  interrupted  by  elevations 
and  depressions.  At  the  anterior  angle  the  superior  canine  is  implanted, 
and  the  course  of  its  powerful  curved  root  is  indicated  by  a  well-marked 
ridge  or  swelling  of  the  external  surface.  Behind  and  above  the  pos- 
terior termination  of  this  is  a  broad,  shallow  depression,  while  behind 
and  below  is  another  depression,  the  canine  fossa,  ending  posteriorly  in 
a  large  foramen,  the  infraorbital  foramen,  situated  above  the  interval 
between  the  third  and  fourth  premolars.  Behind  the  infraorbital  for- 
amen a  strong  process  is  thrown  up  to  meet  the  malar ;  this  is  known 
as  the  malar  jyroccss  of  the  maxillary.  The  posterior  superior  angle  is 
produced  into  a  considerable  rounded  process,  which  passes  as  far  back- 
ward as  the  centre  of  the  orbit  to  articulate  with  the  frontal.  This  is 
the  nasal  process  of  the  maxillary,  and  is  the  homologue  of  a  corre- 
sponding process  in  the  human  skull  bearing  this  name. 

The  posterior  or  orbital  surface  is  relatively  small,  convex  from  before 
backward,  and  concave  from  side  to  side.  It  is  somewhat  triangular  in 
shape,  and  forms  the  greater  part  of  the  floor  of  the  orbit,  being  directed 
upward  and  backward.  It  is  bounded  above  and  externally  by  the 
malar,  directly  above  by  the  lachrymal,  and  internally  by  the  palatine 
bones  respectively,  terminating  in  a  free  rounded  border  behind.  The 
internal  portion  of  this  last-mentioned  border  is  separated  from  the 
palatine  by  a  notch,  and  forms  a  conspicuous  eminence  known  as  the 
maxillary  tuberosity.  At  the  anterior  extremity  of  this  surface  is  seen 
the  posterior  opening  of  the  infraorbital  canal,  which  traverses  the  max- 
illary bone  and  serves  for  the  transmission  of  the  second  division  of  the 
trigeminal  or  fifth  nerve,  as  well  as  a  part  of  the  external  carotid  artery, 
which  terminates  in  this  situation  as  the  infraorbital.  This  surface  is 
perforated  by  small  foramina  for  the  entrance  of  the  su^jerior  dental 
nerves  and  arteries. 

The  inferior  or  palatal  surface  forms  a  considerable  part  of  the  bony 
roof  of  the  mouth  as  well  as  the  floor  of  the  nasal  chamber.  It  is  limited 
in  front  by  the  premaxillary  bone,  externally  by  the  free  alveolar  border, 
posteriorly  in  part  by  the  palatine  and  in  part  by  a  free  edge,  and  inter- 
nally by  the  suture  with  which  it  joins  its  fellow  of  the  opposite  side.  It 
is  slightly  concave  from  side  to  side,  the  alveolar  border  being  consider- 
ably elevated.  Posteriorly  it  sends  backward  a  narrow  strip  which  ter- 
minates in  a  free  edge  behind  ;  anterior  to  this,  at  a  point  opposite  to  the 
anterior  part  of  the  sectorial,  it  widens  rapidly.  From  this  point 
to  its  anterior  termination  it  gradually  narrows  ai^ain.     Just  internal 


TEETH  OF  THE   VERTEBRATA.  405 

to  the  sectorial  is  seen  a  deep  depression,  the  sectorial  fossa,  which 
serves  to  accommodate  the  blades  of  the  inferior  sectorial  when  the 
mouth  is  closed.  Internal  to  this,  again,  are  usually  two,  sometimes 
three,  foramina,  the  posterior  palatine  foramina,  which  transmit  the  pos- 
terior palatine  vessels  and  nerve.  From  the  largest,  most  anterior  of 
these  a  shallow  groove  is  continued  forward  in  which  the  palatine  ar- 
tery is  lodged.     This  is  the  palatine  groove. 

The  line  of  junction  of  the  two  palatal  plates  of  the  maxillaries  is 
marked  by  a  longitudinal  ridge,  the  sutiirai  ridge,  which  gives  support 
to  the  vomer  above.  The  maxilla  articulates  with  the  premaxilla  and 
nasal  in  front,  with  the  frontal  above,  and  with  the  lachrymal,  malar, 
and  palatine  behind. 

The  premaxilhe  are  small  bones  placed  in  front  of  the  maxillte,  the 
two  together  forming  the  anterior  termination  of  the  upper  jaw.  Each 
consists  of  a  thickened  anterior  portion  meeting  in  the  median  line, 
together  with  an  ascending  or  vertical  process  and  a  horizontal  process. 
The  thicke]ied  body  forms  the  lower  boundary  of  the  anterior  nares, 
and  by  its  free  alveolar  border  lodges  the  incisor  teeth.  The  ascending 
or  vertical  process  is  a  long,  sharp  spicule  of  bone  which  springs  from 
the  outer  side  of  the  body  and  furnishes  the  external  wall  for  the  narial 
opening.  It  is  directed  upward  and  backward,  and  insinuates  itself 
between  the  nasal  above  and  the  maxilla  below.  This  is  known  as  the 
nasal  process  of  the  premaxilla.  Upon  either  side  of  the  median  line 
the  horizontal  or  palatine  processes  pass  backward  to  the  maxillie,  form- 
ing the  anterior  portion  of  the  bony,  palate.  These  processes  are  in  con- 
tact with  each  other  in  the  middle  line,  but  each  is  separated  from  its 
body  by  a  wide  hiatus,  which  is  converted  into  a  foramen  by  the  inter- 
position of  the  palatal  plate  of  the  maxillary  beliind.  These  large  oval 
foramina  are  conspicuous  features  in  the  macerated  skull,  and  are  known 
as  the  incisive  or  anterior  palatine  foramina.  They  transmit  the  ante- 
rior palatine  vessels  and  nerve. 

The  next  and  last  bony  structure  to  be  noticed  in  connection  with  the 
teeth  is  the  mandible  or  lower  jaw.  This  part  of  the  skeleton  in  human 
anatomy  is  known  as  the  inferior  maxilla,  and  consists,  in  the  adult  state 
at  least,  of  a  single  bone  (the  two  halves  co-ossified),  as  is  also  the  case 
in  the  monkeys  and  several  other  mammals.  In  the  majority  of  them, 
however,  it  is  made  up  of  two  more  or  less  persistent  pieces,  which  may 
unite  in  extreme  old  age  to  form  a  single  bone.  The  mandible  of  the 
dog  consists  of  two  symmetrical  elongated  halves,  the  rami,  diverging 
behind  and  coming  in  contact  in  front  in  the  median  line  by  two  rough- 
ened surfaces,  the  symphysis.  They  are  bound  together  by  the  inter- 
position of  fibro-cartilage  at  this  point,  and  are  movably  articulated  to  the 
skull  behind  by  two  transversely  elongated  processes,  the  mandibular  con- 
dyles, placed  near  the  middle  of  the  posterior  border.  Each  ramus  is 
laterally  flattened,  with  the  inferior  border  considerably  curved  in  an 
antero-posterior  direction.  In  front  this  border  slopes  gradually  upward 
to  meet  the  alveolar  or  dentary  border,  while  behind  it  is  terminated  by 
a  prominent,  slightly-inflected  process,  the  angle.  The  dentary  border  is 
nearly  straigiit,  and  is  prevented  from  reaching  the  posterior  border  by 
the  intervention  of  a  broad  flat  recurved  plate  of  bone,  the  coronoid  pro- 


406  DENTAL  ANATOMY. 

cess,  which  rises  high  above  the  level  of  the  surrounding  parts.  The 
posterior  border  is  interrupted  by  two  notches,  between  which  is  situ- 
ated the  condyle.  Immediately  in  front  of  the  condyle  is  a  wide  and 
deep  depression,  the  masseteric  fossa,  for  the  insertion  of  the  powerful 
masseter  muscle.  In  front  of  and  below  the  condyle,  on  the  inner  side, 
is  a  conspicuous  opening,  the  inferior  dental  canal,  which  gives  passage 
to  the  inferior  dental  artery  and  nerve.  On  the  external  surface,  behind 
and  below  the  root  of  the  canine,  is  another  opening,  the  mental  foramen, 
through  which  a  part  of  the  nerve  makes  its  exit  to  be  distributed  to  the 
lower  lip. 

The  Muscles. — The  principal  muscles  concerned  in  the  movement  of 
the  lower  jaw  are  the  temporal,  masseter,  external,  and  internal  ptery- 
goids, the  digastric,  genio-hyoid,  and  mylo-hyoid. 

The  Temporal  is  a  broad,  thick,  fleshy  muscle  which  covers  the  side 
wall  of  the  brain-case  from  the  post-orbital  process  in  front  to  the  lamb- 
doidal  or  occipital  crest  behind,  reaching  as  high  up  as  the  sagittal  crest 
above,  and  completely  filling  up  the  temporal  fossa,  to  which  it  gives  its 
name.  Its  fibres  converge  fan-wise  to  be  inserted  into  tlie  summit  of 
the  coronoid  process  of  the  ramus  of  the  mandible.  Its  principal  action 
is  to  elevate  the  lower  jaw.  By  its  leverage  and  great  strength  the  ani- 
mal is  enabled  to  take  a  firm  grip  upon  its  prey. 

The  3Iasseter  is  a  short,  thick  muscle  arising  from  the  under  and  a 
part  of  the  outer  surface  of  the  malar  bone^  as  well  as  the  posterior  part 
of  the  maxillary,  and,  passing  downward  and  backward,  is  inserted  into 
the  masseteric  fossa  of  the  ramus.  .  Its  action  is  similar  to  that  of  the 
preceding  muscle. 

The  Interned  Pterygoid  muscle  consists  of  a  strong  bundle  of  muscu- 
lar fibres  which  takes  its  origin  from  the  pterygoid  fossa  in  the  base  of 
the  skull,  and  passes  doAvnward  and  outward  to  its  insertion  in  the  lower 
part  of  the  angular  process.  By  its  contraction  the  lower  jaAV  is  drawn 
upward  and  inward,  but  owing  to  the  manner  in  which  the  teeth  inter- 
lock no  extensive  lateral  movement  is  possible.  The  most  reasonable 
view  of  the  action  of  this  muscle,  as  well  as  the  succeeding  one,  is, 
that  by  the  contraction  of  those  of  one  side  the  sectorial  apparatus  of  the 
side  op])osite  is  enabled  to  perform  a  more  perfect  shearing  movement, 
just  as  the  blades  of  a  pair  of  scissors  nuist  be  pressed  closely  togetlier 
in  order  to  make  them  cut.  From  the  direction  of  its  fibres  it  likewise 
assists  in  elevating  the  jaw. 

The  External  Pterygoid  arises  from  the  pterygoid  plate  of  the  sphe- 
noid bone,  and  is  inserted  into  the  base  of  the  condyle,  and  as  far 
forward  as  the  inferior  dental  canal.  Its  action  has  already  been 
alluded  to. 

The  Digastric  is  a  large  muscle  M-hich  arises  from  the  skull  behind 
the  auditory  bulla  in  a  strong  bony  prominence,  the  paramastoid  pro- 
cess, and  passes  forward  to  its  attachment  on  the  inferior  margin  of  the 
ramus  in  front  of  the  angular  process.  Its  action  is  to  depress  the  jaw 
and  open  the  mouth. 

The  Genio-  and  3Iylo-hyoid  muscles  are  broad  muscular  sheets  which 
lie  between  the  rami  forming  the  floor  of  the  mouth  in  the  recent  state, 
being  attached  to  the  hyoid  bones  and  the  "  fork  "  of  the  jaw.     They 


TEETH  OF  THE   VERTEBRATA.  407 

assist  in  depressing  the  mandible,  and  conseqnently  in  opening  the 
mouth. 

Vessels  and  Nerves. — Tlie  blood-vessels  by  which  the  teeth  and  the 
muscles  described  above  are  supplied  are  derived  from  the  external 
carotid  artery,  which  passes  forward  along  the  side  of  the  neck,  giving 
off  branches  to  the  various  structures  in  this  situation.  This  artery  does 
not  terminate,  as  in  man,  in  the  temporal  and  internal  maxillary  arteries 
— at  least  it  is  so  generally  considered  by  anatomists.  Both  the  right 
and  left  common  carotids  spring  from  the  innominate,  as  in  the  Carniv- 
ora  generally.  After  giving  off  the  thyro-laryngeal  branch,  remarkable 
for  its  large  size,  to  the  thyroid  gland  and  larynx,  it  passes  forward  in 
front  of  the  transverse  process  of  the  atlas  vertebra,  where  it  gives  off 
the  occipital  artery,  which  goes  to  the  back  of  the  head  and  the  deep 
muscles  of  the  neck.  Upon  the  base  of  the  skull  in  the  vicinity  of  the 
carotid  canal  it  bifurcates  into  two  principal  branches,  the  external  and 
internal  carotids,  the  latter  entering  the  skull  through  this  canal  to  be 
distributed  to  the  brain,  the  latter  continuing  forward  through  the  ali- 
sphenoid  canal,  giving  off  in  its  course  the  laryngeal,  lingual,  facial, 
posterior  auricular,  and  superficial  temporal  branches.  Near  the  con- 
dyle of  the  lower  jaw  it  describes  a  remarkable  sigmoid  curvature  be- 
tween this  structure  and  the  internal  pterygoid  muscle,  thence  passing 
forward  to  the  infraorbital  canal,  where  it  receives  the  name  of  the 
infraorbital  artery.  Between  the  condyle  and  the  infraorbital  canal  the 
following  principal  branches  are  emitted  by  this  arterial  trunk  :  the 
inferior  dental  artery,  M'hich  enters  the  inferior  dental  canal  and  sup- 
plies the  teeth  of  the  lower  jaw ;  the  deep  posterior  temporal,  which 
furnishes  a  masseteric  branch  passing  through  the  sigmoid  notch,  or  that 
between  the  condyle  and  coronoid  process  of  the  ramus,  to  enter  the 
masseter  muscle ;  several  pterygoid  arteries,  which  go  to  the  pterygoid 
muscles;  the  ophthalmic  artery,  distributed  to  the  eye;  the  deep  ante- 
rior temporal ;  the  palatine,  buccal,  and  alveolar  arteries ;  lastly,  the 
superior  dental  artery,  which  supplies  the  teeth  of  the  upper  jaw. 

The  nerves  supplying  the  teeth  and  accessory  organs  are  derived 
principally  from  the  trigeminal  or  fifth  pair  of  cranial  nerves.  This 
is  essentially  a  mixed  nerve  in  function,  arising  by  two  roots,  a  large 
sensory  and  a  small  motor  root.  At  a  short  distance  from  its  origin  the 
sensory  root  swells  out  into  ganglionic  enlargement,  the  Gasserian  gan- 
glion, after  which  it  divides  into  three  branches — the  ophthalmic  or  first 
division,  the  superior  maxillary  or  second  division,  and  the  inferior  max- 
illary or  third  division. 

The  first  of  these  makes  its  exit  from  the  cranial  cavity  through  the 
sphenoidal  fissure,  and  supplies  by  its  subdivisions  the  eyeball,  mucous 
membrane  of  the  eyelids,  the  skin  of  the  nose  and  forehead,  dividing  into 
frontal,  lachrymal,  and  nasal  branches. 

The  second  of  these  branches,  the  superior  maxillary,  issues  from  the 
skull  through  the  foramen  rotundum,  and  supplies  the  side  of  the  nose, 
upper  teeth,  and  the  upper  part  of  the  mouth  and  pharynx.  It  crosses 
from  the  foramen  rotundum  directly  to  the  infraorbital  canal,  in  the 
vicinity  of  which  it  gives  off  the  anterior  and  posterior  dental  nerves 
which  supply  the  teeth. 


408  DENTAL  ANAT031Y. 

The  third  division,  inferior  maxinary,  passes  out  of  the  skull  through 
the  foramen  ovale,  just  outside  of  which  it  is  joined  by  tlie  motor  root. 
It  then  divides  into  two  branches,  a  small  anterior  one  distributed  to 
the  muscles  of  mastication,  and  a  large  posterior  branch,  which  supplies 
the  ear,  side  of  the  head,  lower  lips,  gums,  teeth,  salivary  glands,  and 
inside  of  the  mouth.  The  posterior  branch  divides  into  the  auricido-tem- 
jjoral,  which  passes  backward  to  the  temporal  region  ;  the  inferior  dental, 
which  supplies  the  teeth  of  the  lower  jaw  ;  and  the  c/nstatory,  or  the  nerve 
of  taste,  which  goes  to  the  mucous  membrane  of  the  tongue. 

The  lips,  tongue,  and  salivary  glands  should  also  be  mentioned  in 
connection  with  the  accessory  organs,  since  they  serve  an  important 
purpose  in  preventing  small  particles  of  the  food  from  escaping  during 
mastication,  as  well  as  supply  the  requisite  moistening  fluid  Avherebv 
comminution  is  more  readily  accomplished  and  the  food  rendered  more 
digestible. 

Teeth  of  the  Edentata,  or  Bruta. 

Although  this  group  is  by  no  means  the  most  primitive  of  the  INIam- 
nialia,  as  will  be  seen  by  reference  to  the  table  of  classification,  yet  the  cha- 
racters which  we  have  assigned  to  the  ideal  primitive  mammalian  dentition 
are  most  nearly  approached  in  certain  members  of  this  order.  Whether 
the  comparatively  simj)le  form  and  absence  of  enamel  in  the  adult  tooth, 
which  is  characteristic  of  all  the  animals  of  this  order,  pertain  to  a  prim- 
itive state,  or  whether  this  condition  has  been  reached  by  a  process  of 
retrogression  or  degradation,  as  many  believe,  we  are  not  at  present  pre- 
pared to  say,  in  the  absence  of  any  knowledge  of  their  paleeontological 
history  beyond  the  latest  Tertiary  epoch.  There  is  one  character,  how- 
ever, in  which  one  at  least  is  more  decidedly  primitive  than  any  other 
known  Eutherian  mammal,  and  that  is  the  succession  of  all  the  teeth  bid 
one  (the  last)  by  a  second  set.  I  refer  to  the  nine-banded  armadillo 
(Tcdusia  peba).  It  is  not  certainly  known  whether  this  condition  exists 
in  any  other  of  the  edentates  or  not,  with  the  exception  of  the  sloths, 
which  are  truly  monophyodont. 

The  term  Edentata  is  inappropriate,  inasmuch  as  one  would  be  led  to 
suppose  from  the  name  that  they  have  no  teeth.  The  original  term, 
Bruta,  Avas  applied  to  this  order  by  IJnnpeus,  which  he  defined  by  the 
absence  of  incisor  teeth.  It  was  afterward  changed  to  Edenteda  by 
Cuvier — a  name  which  has  been  extensively  adopted  by  subsequent 
authors.  It  was  formerly  supposed  that  no  incisor  teeth  are  ever  pres- 
ent in  this  group,  but  the  discovery  of  new  forms  proved  this  to  be 
erroneous.  The  median  incisors,  however,  are  wantine;  in  all  cases  so 
far  known.  The  definition  of  the  order  now  most  commonly  given 
is  "  absence  of  enamel  on  the  teeth."  This  peculiarity  appears  at  first 
sight  striking  and  quite  sufficient  to  separate  them  froni  all  other  mono- 
delphous  mammals,  but  C.  8.  Tomes  has  shown  ^  that  the  tooth-germs 
of  the  nine-banded  armadillo  have  distinct  enamel  organs,  which  are 
subsequently  aborted  as  the  tooth  comes  to  maturitv.  This  discovery  is 
important,  since  it  indicates  pretty  clearly  that  the  loss  of  enamel  is  a 

^  Philos.  Trans.,  1876. 


TEETH  OF  THE   VERTEBRATA. 


409 


mark  of  degeneracy,  and  leads  indirectly  to  the  conclusion  that  the 
armadillos  at  least  are  descended  from  ancestors  with  enamel-covered 
teeth,  who  in  all  probability  were  the  possessors  of  a  completely  devel- 
oped second  set. 

The  only  assignable  cause  for  this  degenerate  condition  of  the  dental 
organs  is  the  peculiarity  of  their  food-getting  habits.  Many  of  them 
feed  upon  insects,  which  they  capture  by  means  of  a  long  whip-like 
tongue  covered  with  the  viscid  secretion  of  the  submaxillary  glands,  and 
swallow  whole.  This  manner  of  feeding  would  occasion  little  demand 
for  nuisticatory  organs,  which  from  disuse  would  gradually  fall  into  a 
rudimentary  condition  and  eventually  disappear.  Those  in  which  the 
entomophugous  habit  is  exhibited  in  its  greatest  perfection  are  edentu- 
lous, and  have  small  mouths  with  extremely  long  tongues.  All  the 
Edentata  in  which  this  structure  exists  at  all  show  a  tendency  toward 
such  a  habit — even  the  arboreal  sloths,  which  are  said  to  be  exclusively 
vegetable  feeders. 

Flower  has  recently  shown  that  the  sloths  are  intimately  connected 
with  the  ant-eaters  and  armadillos  of  South  America  through  the  extinct 
megatheroids,  and  that  all  the  American  forms  have  probably  descended 
from  a  common  ancestor,  while  the  Old  World  forms  are  likewise  closely 
related  and  descended  in  another  line.  It  is  prol^ably  true  that  the  arma- 
dillos are  most  nearly  related  to  the  ancestral  form,  and  that  the  sloths 
represent  an  offshoot  which  was  derived  from  them  after  they  had  lost 
the  enamel  of  the  teeth  in  the  manner  indicated. 

The  teeth  of  the  armadillos  are,  with  one  exception,  relatively  small 
cylindrical  bodies  implanted  in  the  dentigerous  borders  of  the  lower  jaw, 
m  ixiljary,  and  sometimes  premaxillary  bones.  They  are  entirely  devoid 
of  enamel,  and  grow  continuously  throughout  the  life  of  the  animal,  in 
consequence  of  which  no  roots  are  formed. 

Fig.  198. 


Side  View  of  the  Skull  of  a  Seven-bamled  Anuadillo  {Tatusin  hybrUhisf) 

In  the  seven-banded  armadillo  (Ta/u-s/rt  hybrid  us,  Fig.  198')  there  are 
seven  teeth  above  and  eight  belo^v  upon  each  side.     So  little  is  known 

'  The  specimen  here  figured  is  in  the  U.  S.  Army  Medical  Museum,  and  is  labelled 
Tatuxia  st'plemcindiis.  It  exhibits  tlie  peculiarity  of  liaving  eight  teeth  upon  one  side 
and  seven  upon  the  other  in  the  ui)per  jaw.  Tliere  is,  however,  a  con.siderable  space 
between  the  first  and  second  tooth  of  the  right  side,  wliich  would  indicate  tiiat  a  tooth 
is  missing.  Tlie  number  ascribed  to  this  species  by  Owen  is  seven  above  and  eight 
bek)w  upon  each  side.     Its  e.xact  identification  is  therefore  diflScult. 


410  DENTAL  ANATOMY. 

about  their  succession  that  it  is  impossible  to  say  Avhether  there  are 
mohirs  and  premolars  represented  or  not.  The  teeth  of  the  upper  series 
are  lodged  in  the  maxillary  bones,  and  begin  at  a  considerable  distance 
behind  the  maxillo-premaxillary  suture.  They  progressively  increase 
in  size  up  to  the  fifth  or  sixth  tooth,  the  last  being  quite  small.  They 
are  not  in  contact  with  each  other,  but  are  separated  by  slight  spaces 
about  equal  to  the  width  of  a  tooth.  The  teeth  of  the  lower  jaw  are 
similar  to  those  of  the  upper  jaw  in  size  and  shape,  Avitli  the  exception 
of  the  last,  which  is  much  larger  than  the  corresponding  tooth  above. 
The  teeth  of  the  inferior  series  close  in  the  intervals  between  those  of 
the  upper  and  conversely,  causing  the  summits  of  the  crowns  to  wear, 
as  Prof.  Owen  puts  it,  **  into  two  facets  divided  by  a  median  transverse 
ridge."  The  form  of  the  working  surface  of  the  tooth  is  therefore 
wedge-shaped.  The  first  two  teeth  of  the  lower  jaw  shut  in  front  of 
the  first  tooth  above,  and  the  last  three  teeth  above  behind  the  last  one 
of  the  lower  series,  leaving  them  with  little  or  no  opposition.  Each 
tooth  continues  its  cylindriform  shape  to  the  bottom  of  the  alveolus  in 
which  it  is  implanted,  having  its  base  excavated  into  a  large  pulp- 
cavity.     It  consists  of  dentine  and  cementum  only. 

In  another  species,  the  nine-banded  armadillo,  the  number  and  form 
of  the  teeth  are  the  same.  The  teeth  of  this  animal,  as  has  already  been 
stated,  have  a  successional  set.  According  to  the  definition  laid  down 
for  premolar  and  molar  teeth  in  the  diphyodont  Mammalia  generallv, 
there  would  be  one  molar  and  six  pi'cmolars  in  the  dentition  of  this 
animal.  The  rooted  appearance  of  the  deciduous  teeth,  according  to 
Tomes,  is  not  due  to  the  possession  of  true  roots,  but  to  the  absorp- 
tion set  up  by  the  approach  of  the  successors. 

The  genus  Priodon  of  this  group  has  as  many  as  one  hundred  teeth, 
the  greatest  number  exhibited  by  any  land  mammal.  Thev  are  rela- 
tively small  and  simple  in  form,  and  are  confined  to  the  maxillary  and 
mandibular  bones.  They  vary  in  number  from  twenty-four  to  twenty- 
six  upon  each  side  in  the  upper,  and  from  twenty-two  to  twenty-four 
upon  each  side  in  the  lower  jaw.  In  the  living  genus  Dasi/pus  there  is 
one  tooth  upon  each  side  implanted  in  the  premaxillary  bone,  which, 
according  to  the  definition,  becomes  an  incisor,  while  in  still  another 
extinct  genus,  Cli/ami/fJofhcrium,  almost  equalling  in  size  the  rhinoceros, 
there  were  two  incisors  above  and  three  which  oj^posed  them  below.  In 
GlijpfofJon  the  teeth  are  more  complex  in  pattern,  being  laterally  com- 
pressed and  divided  by  two  vertical  grooves  upon  each  side,  which  are 
opposite  to  each  other.  The  resulting  structure  from  this  arrangement 
is  three  transverse  vertical  plates  connected  in  the  centre  by  an  isthmus. 
There  were  teeth  in  the  premaxillaries  in  this  genus. 

The  megatheroids  affV)rd  another  example  of  moderate  complexity  in 
the  enamelless  teeth  of  the  Brufa.  In  the  gigantic  extinct  Megatherium 
there  are  five  molars  above  and  four  l)elow  u})on  each  side.  They  are 
very  deeply  implanted  in  tiie  substance  of  the  jaw  bones,  and  have 
remarkably  elongated  pulp-cavities,  which  communicate  with  the  grind- 
ing surface  by  means  of  a  narrow  fissure.  The  pulp-cavity  is  inmie- 
diately  surrounded  by  soft,  more  or  less  vascular  dentine-^the  vaso- 
dentine  of  Owen — which  is  covered  by  a  thin  layer  of  unvascular,  much 


TEETH  OF  THE   VERTEBRATA.  411 

liarder  dentine.  Upon  the  outside  of  this  comes  the  cementum,  which 
lias  a  great  thickness  upon  the  anterior  and  posterior  face  of  the  tooth. 
Owing  to  the  unequal  })owers  of  resistance  which  these  substances  offer, 
the  teeth  wear  in  such  a  manner  as  to  present  two  transverse  crests  each, 
and  are  therefore  spoken  of  as  lophodont.  They  are  confined  to  the 
maxillary  and  mandibular  bones  and  grow  from  persistent  pulps. 

In  another  extinct  allied  genus,  3Iegalonyx,  the  teeth  are  oval  in  sec- 
tion, and  did  not  wear  into  transverse  crests  as  in  3Ier/atheriuia,  but  have 
slightly  concave  grinding  faces.  The  first  tooth  of  the  upper  series  also 
is  considerably  enlarged  and  caniniform  in  shape,  as  in  one  of  the  liv- 
ing sloths.  Another  nearly-related  form  is  Mylodon,  likewise  extinct, 
which  exceeded  the  rhinoceros  in  size.  The  first  tooth  above,  instead 
of  being  enlarged  and  caniniform,  is  smaller  than  the  succeeding  ones, 
and  otherwise  like  them  in  pattern. 

The  dental  formula  of  the  three-toed  sloth  (Brady pus  tridndyhts)  is 
I.  ^,  C.  ^,  M.  |^z|  =  18.  It  has  been  observed,  however,  that  there  is 
in  some  young  examples  of  this  species  a  small  extra  tooth  in  the  lower 
jaw  just  in  front  of  the  first  permanent  one,  which  is  shed  before  the 
animal  attains  to  the  adult  state.  The  teeth  are  relatively  small,  of  a 
columnar  form,  and  implanted  to  a  moderate  depth  in  the  substance  of 
the  jaws  by  a  deeply-excavated  base  for  the  accommodation  of  the  per- 
sistent pulp.  The  grinding  surface  presents  a  central  depression  in  the 
vaso-dentine,  surrounded  by  a  raised  rim  on  its  outer  margin  composed 
of  the  harder  dentine,  which  usually  wears  unequally  into  one  or  two 
prominent  points.  The  teeth  of  the  upper  and  lower  jaws  do  not 
oppose  each  other  exactly,  but  alternate  when  the  mouth  is  closed. 

In  the  two-toed  sloth  [Choloepus  didactylus)  the  dental  formula  is  the 
same.  The  first  tooth  in  each  series,  which  in  the  edentates  generally 
is  the  smallest,  is  here  greatly  increased  in  size,  of  a  subtrihedral  form, 
and  of  a  caniniform  pattern.  They  are  separated  by  a  considerable 
diastema  from  the  rest  of  the  teeth,  and  are  implanted  above  in  the 
maxillary  bones  a  short  distance  behind  the  maxillo-])remaxillary 
suture.  It  will  be  seen,  therefore,  that  as  far  as  the  definition  of  a 
canine  tooth  is  concerned,  all  the  conditions  are  fulfilled ;  but  the 
tooth  in  the  lower  series,  which  has  undergone  a  similar  modification, 
violates  the  definition  of  a  canine,  inasmuch  as  it  closes  behind  the 
upper  caniniform  tooth  instead  of  in  front  of  it.  It  is  therefore  a 
matter  of  uncertainty  whether  these  teeth  are  strictly  homologous  with 
the  canines  of  the  diphyodont  Mammalia  or  not.  From  the  manner  in 
which  they  oppose  each  other  the  posterior  surface  of  the  upper  and  the 
anterior  surface  of  the  lower  are  extensively  abraded,  and  their  summits 
worn  into  sharp  points,  which  would  render  them  efficient  weapons  of 
offence  or  defence  should  the  animal  choose  to  use  them  as  such. 

The  next  tooth  of  the  upper  series  is  relatively  small,  and  is  implanted 
rather  obliquely,  with  the  summit  inclined  backward  and  inward.  The 
two  following  teeth  are  larger,  with  a  central  depression  upon  the  grind- 
ing face,  and  having  the  external  and  internal  portions  of  the  rim  pro- 
duced into  sharp  points.  The  last  tooth  is  about  equal  to  the  second  in 
size,  which  it  also  resembles  in  form. 

The  teeth  of  the  lower  series  resemble  those  of  the  upper,  with  the 


412  DENTAL  ANATOMY. 

exception  that  the  three  posterior  ones  are  more  robust  and  gradually 
decrease  in  size  from  the  second  to  the  last.  Viewing  the  teeth  and 
accessory  bony  structures  of  this  animal  as  a  whole,  the  premaxilke  are 
remarkable  for  their  small  size,  little  extension  anteriorly  beyond  the 
maxilla?,  and  the  complete  absence  of  the  ascending  or  nasal  process,  as 
well  as  their  edentulous  condition.  The  palatal  plates  of  the  maxillae 
are  Ayidest  in  front  and  gradually  narrow  posteriorly,  causing  the  dental 
series  of  opposite  sides  to  conyerge  behind.  In  the  lower  jaw  the  two 
halyes  are  completely  co-ossified,  as  in  monkeys  and  man ;  the  anterior 
part  of  the  symphysis  is  produced  into  a  peculiar  spout-like  termination, 
at  the  base  of  which  the  jaw  widens  rapidly  ;  and  the  rami  are  little 
diyaricated  posteriorly.  The  posterior  teeth  are  implanted  in  a  strong 
inwardly  projecting  "ledge,  in  consequence  of  which  the  dentigerous 
border  gradually  approaches  the  median  line  as  it  proceeds  bac.k\\ard. 
The  mental  foramen  is  placed  below  the  interyal  between  the  third  and 
fourth  teeth  near  the  middle  of  the  ramus. 

With  respect  to  thg  teeth  themselyes,  Owen  giyes  the  following  com- 
mon and  constant  characters  of  both  recent  and  extinct  sloth-like  ani- 
mals, which  would  include  the  megatheroids  :  "  Teeth  implanted  in  the 
maxillary,  neyer  in  the  intermaxillary  bones ;  few  in  number,  not  ex- 
ceeding f  zf ;  composed  of  a  large  central  axis  of  vascular  dentine, 
with  a  thin  inyestment  of  hard  or  unvascular  dentine,  and  a  thick  outer 
coating  of  cement.  To  these,  of  course,  may  be  added  the  dental  cha- 
racters connnon  to  the  order  BruUi — viz.  uninterrupted  growth  of  the 
teeth,  and  their  concomitant  implantation  by  a  simple  deeply-seated  exca- 
vatecl  base,  not  separated  by  a  cervix  from  the  exposed  summit  or  crown." 

Of  the  two  Old  Workl  genera  now  living,  but  one  has  teeth.  This 
is  the  aard-vark  (Orycterojms),  or,  as  it  is  sometimes  called,  the  Cape 
ant-eater.  Its  dental  formula  is  M.  |^z|=^26,  of  which  the  anterior 
ones  of  each  series  are  not  unfrequently  wanting  or  concealed  by  the 
gum.  The  teeth  of  the  superior  set  progressively  increase  in  size  from 
before  backward  up  to  the  last  tooth,  which  is  smaller.  They  are  oval 
in  section,  M'ith  the  exception  of  the  fourth  and  fifth,  and  have  Avedge- 
shaped  triturating  surfaces,  like  the  armadillos.  The  fourth  and  fifth 
above  and  the  last  two  below  have  two  vertical  grooves,  one  upon  each 
side,  which  give  to  them  an  hour-glass  shape  upon  section. 

The  teeth  of  this  animal  do  not  exhibit  the  customary  excavated  base 
of  the  Edentata  generally,  but  are  continued  solid  to  the  bottom  of  the 
sockets.  Their  minute  structure  is  peculiar,  and  resembles  that  found  in 
3Ii/Uohatrs  among  the  elasmobranch  fishes  ;  the  dentine  is  of  the  variety 
known  as  plici-dentine.  This  consists  of  a  series  of  small  vertical  par- 
allel tubnli  which  ])ass  up  from,  and  are  virtually  prolongations  of  the 
pulp-cavitv.  From  these  the  dentinal  tnbuli  radiate  toward  the  per- 
iphery, just  as  they  do  from  the  single  ])ulp-cavity  <»f  the  human  tooth 
already  described.  Owing  to  this  peculiarity,  Prof.  Owen  regarded  the 
tooth  of  Orycferopu^  as  an  aggregate  of  many  denticles,  each  with  its 
proper  pulp-cavity  and  dentinal  tubes. 

In  Eurojie  fossil  remains  of  edentates  are  known  from  the  ISIiddle 
Miocene  of  Sansan  in  France  and  the  upper  INIiocene  deposits  of  Piker- 
mi  in  Greece.     Two  genera,  3Iacrotherium  and  Ancylotherium,  have  been 


TEETH  JOF  THE   VERTEBRATA.  413 

described  by  Lartet  and  Gaudry,  from  feet  and  limb  bones  principally, 
nothing;  beino-  known  of  the  skull  or  teeth.  In  South  America  fossil 
remains  of  this  order  are  very  abundant  in  the  Pampean  or  Pliocene 
deposits.  Older  deposits  on  the  Parana  River  have  furnished  M. 
Ameghino  with  numerous  f(jrms  which  stand  in  ancestral  relation  to 
those  of  the  Pampean  beds,  and  which,  it  is  interesting  to  observe, 
have  more  or  less  enamel  on  the  teeth.  In  North  America,  Prof. 
Marsh  has  described  a  genus  under  the  name  of  3forotherium,  from 
the  Loup  Fork  or  Upper  Miocene  strata,  from  feet  bones  only.  The 
teeth  are  not  known. 

Teeth  of  the  Cetacea. 

According  to  Dr.  Theo.  Gill's  arrangement,  the  cetaceans  are  divisible 
into  three  groups  or  sub-orders,  as  follows :  Mysticete,  including  the 
"  whalebone  whales  ;"  Denticete,  or  the  "  toothed  whales,"  and  Zeuglo- 
dontia,  a  division  which  includes  Zeuglodon  and»  several  other  extinct 
genera.  In  the  3Iysticete,  teeth  are  present  in  a  foetal  state  only,  being 
absorbed  before  birth.  This  loss  of  the  teeth  is  compensated  for  by  the 
development  of  large  corneous  plates,  the  "  baleen  plates,"  which  depend 
from  the  roof  of  the  mouth.  The  more  important  of  these  are  of  a  tri- 
angular form,  and  are  arranged  along  each  side  of  the  palate  in  such 
a  manner  as  to  be  transverse  to  the  axis  of  the  skull,  the  centre  being 
occupied  by  smaller  ones,  also  placed  transversely.  Altogether,  they 
form  by  their  extremities  a  vaulted  surface  into  which  the  large  tongue 
fits  accurately,  their  edges  being  broken  up  into  numerous  stiff  hairs 
which  project  into  the  mouth.  The  animal  feeds  by  taking  large  quan- 
tities of  water  into  the  mouth  and  expelling  it  again  through  the  nos- 
trils ("  spouting  ") ;  any  small  aquatic  animals  Avhich  may  have  been 
contained  in  it  are  entangled  in  the  fringes  of  the  baleen  plates,  and 
subsequently  collected  by  the  tongue  and  swallowed.  It  will  thus  be 
seen  that  the  baleen  acts  as  a  sort  of  sieve  or  strainer,  and  is  pre- 
eminently adapted  to  the  capture  of  the  small  aquatic  forms  with  which 
the  sea  in  certain  places  literally  swarms.  Each  baleen  plate  possesses 
a  pulp  situated  in  a  cavity  at  its  base,  from  which  it  is  developed,  and 
through  which  it  is  regenerated  as  fast  as  worn  away.  According  to 
Tomes,  each  hair-like  fibre  has  within  its  base  a  vascular  filament  or 
papilla;  "in  fact,  each  fibre  is  nothing  more  than  an  accumulation  of 
epidermic  cells  concentrically  arranged  around  a  vascular  papilla,  the 
latter  being  enormously  elongated.  The  baleen  plate  is  composed 
mainly  of  these  fibres,  which  constitute  its  frayed-out  edges ;  and  in 
addition  to  this  there  are  layers  of  flat  cells  binding  the  whole  together 
and  constituting  the  outer  or  lamellar  portion." 

All  the  whalebone  whales  possess  rudimentary  teeth,  or  rather  dentine 
and  enamel  organs,  which  undergo  very  little  calcification  before  absorp- 
tion sets  in.  In  the  fin-backs  (Bakenopfera)  these  dentine  organs  are 
simple  in  the  front  part  of  the  mouth,  bifid  in  the  middle,  and  trifid  in 
the  back  part  of  the  jaw.  They  are  placed  in  an  open  groove  along  the 
jaw,  as  in  all  other  Mammalia  at  this  stage  of  embryonic  growth,  and 
do  not  differ  from  them  in  any  important  particular. 


414  DENTAL  ANATOMY. 

In  tlie  second  sub-order  (Denticetc)  no  baleen  plates  are  developed  ; 
teeth  are  always  present,  and  are  more  or  less  persistent.  They  are 
implanted  by  single  roots,  and  are  in  some  instances  very  numerous. 
No  second  dentition  has  ever  been  observed  in  any  member  of  this 
group,  and  they  are,  so  far  as  known,  truly  monophyodont.  In  the 
common  porpoise  of  our  coast  (Delphinus  chymene),  which  is  an  average 
example  of  this  sub-order,  the  teeth  are  about  ninety-four  in  number, 
and  are  lodged  in  the  premaxillary,  maxillary,  and  mandibular  bones. 
They  are  implanted  by  single  sligh'tly  enlarged  fangs  in  ill-defined 
sockets  incompletely  partitioned  otf  from  each  other,  and  in  what  at 
first  sight  seems  to  be  a  wide-open  groove.  Their  crowns  taper  grad- 
ually to  a  sharp  point,  which  is  strongly  incurved.  The  first  two  teeth 
in  the  upper  ja\v  are  small  and  implanted  in  the  premaxillary  bone, 
Avliich  furnishes  a  very  small  part  of  the  dentigerous  border  of  the  upper 
jaw.  Behind  these  the  maxillary  teeth  rapidly  increase  in  size  up  to  the 
seventh  or  eighth  tooth,  after  which  they  continue  to  the  fifteenth  or  six- 
teenth almost  equal  in  size,  and  then  gradually  diminish  in  size  toward 
the  posterior  j^art  of  the  jaw.  The  teeth  of  the  inferior  series  are  like 
those  of  the  upper,  except  that  the  posterior  ones  are  more  robust. 
The  jaws  are  remarkable  for  their  great  length  and  narrowness,  and  the 
arrangement  of  the  bones  of  the  face  when  compared  with  other  mam- 
mals is  also  peculiar.     The  coronoid  process  of  the  lower  jaw  is  obsolete. 

In  other  members  of  the  DelpJiinidcv — the  dolphin,  for  exam])le — the 
teeth  are  often  as  many  two  hundred,  the  greatest  number  exhibited  by 
any  mammal,  or  they  may  be  reduced  to  a  single  functional  tooth,  as  in 
the  narwhal  [3Ionodon).  In  this  latter  species  four  teeth  are  found  in  a 
foetal  state,  but  the  two  lateral  ones  are  lost  or  absorbed  before  birth. 
In  the  male  narwhal  the  left  of  the  two  anterior  ones,  which  is  placed 
in  the  premaxillary  bone^  grows  from  a  persistent  pulp  and  attains  a 
length  of  ten  or  twelve  feet.  This  formidable  tusk  is  almost  straight, 
and  is  marked  by  spiral  ridges  which  wind  forward  from  left  to  right. 
The  corresponding  tooth  of  the  opposite  side  sometimes  reaches  a  devel- 
opment equal  to  that  of  the  left,  but  more  frequently  its  growth  is 
arrested  and  it  remains  buried  beneath  the  gum,  as  do  both  in  the 
female.  Owing  to  this  circumstance,  it  has  been  thought  that  it 
serves  as  a  sexual  weapon  similar  to  the  antlers  of  the  deer,  but  until 
the  habits  of  the  animal  are  better  known  this  explanation  of  its  use 
must  remain  conjectural. 

The  great  bottle-nosed  whale  {Hyperoddon  bidens)  is,  to  all  outward 
appearances,  edentulous,  but  careful  examination  reveals  the  presence  of 
two,  sometimes  four,  well-calcified  conical  teeth  in  the  front  jiart  of  the 
jaw,  which  remain  more  or  less  completely  hidden  by  the  gum.  In 
addition  to  these,  there  are  usually  twelve  or  thirteen  small  rudimentary 
teeth  imbedded  in  the  gums  of  both  jaws,  which  soon  disappear. 

In  the  sperm  whale  {Physdcr  macrocephcdufi)  the  exposed  and  func- 
tional teeth  are  confined  to  the  lower  jaw.  These  are  about  twenty- 
seven  in  number  in  each  ramus,  loosely  implanted  in  a  wide-open  gutter, 
with  the  alveoli  or  sockets  scarcely  pci'ceptible.  They  are  at  first 
sharply  conical,  but  by  attrition  wear  down  into  obtuse  cones,  biting 
into  pits  or  cavities  in  the  gums  of  the  upper  jaw.     In  this  jaw  there 


TEETH  OF  THE   VERTEBRATA.  415 

are  a  number  of  persistent  rudimentary  teeth  concealed  in  the  thick 
gums,  one  pair  of  which  is  exposed  in  the  small  pug-nosed  sperm  whale 
(P.  simus). 

In  the  dolphin  of  the  Ganges  (Platynista  gangetica)  the  total  number 
of  teeth  is  one  hundred  and  twenty- four,  of  which  there  are  thirty  upon 
each  side  above  and  thirty-two  upon  each  side  below.  In  the  young 
animal  their  crowns  are  produced  into  sharp  cones,  but  by  attrition  the 
posterior  teeth  are  worn  down  to  such  an  extent  as  to  become  molari- 
ibrm  in  shape.  The  last  tooth  in  this  species  not  unfrequently  develops 
a  double  root  or  fang,  and  is  the  only  example  of  the  kind  to  be  met 
with  in  living  cetaceans. 

The  teeth  of  the  dolphins  of  the  Amazon  are  surrounded  at  the  bases 
of  their  crowns  by  a  well-marked  ledge  or  cingulum,  which  throws  up 
a  strong  internal  cusp.  On  this  account  Dr.  Gill  elevates  the  genus 
Inia  to  the  rank  of  a  family. 

The  sub-order  Zeuglodontla  is  extinct,  and  includes  a  number  of  fossil 
cetaceans,  some  of  which  are  estimated  to  have  attained  a  length  of 
seventy  feet.  They  differ  from  living  representatives  of  the  order  in 
many  important  osteological  characters,  but  not  more  prominently  than 
in  their  dental  organization.  Besides  being  heterodont  and  having  the 
])osterior  teeth  implanted  by  two  or  three  roots,  some,  if  not  all,  were 
diphyodont  as  ivell.  The  exact  extent  of  the  replacement,  however,  is 
not  fully  known,  but  it  is  certainly  true  that  two  sets  of  teeth  were 
developed.      In  Zeuglodon   cetoldes   (Fig.    199),    from   the    Claiborne 

Fig.  199. 


Side  View  of  the  Skull  of  Zi-uytudon  celoides  (after  Gaudry). 

Eocene  deposits  of  Louisiana,  Alabama,  and  Mississippi,  the  teeth 
are  divisible  by  their  form  and  position  into  incisors,  canines,  and 
molars.  Three  teeth  with  conical  recurved  crowns  are  implanted  by 
single  roots  in  each  premaxillary  bone,  which  in  this  animal  contributes 
a  considerable  part  of  the  tooth-bearing  border  of  the  upper  jaw.  Of 
these  the  anterior  is  the  smallest  and  placed  at  some  distance  behind  the 
extreme  anterior  border,  the  posterior  ones  gradually  increasing  in  size. 
Behind  these,  near  the  maxillo-jiremaxillary  suture,  is  a  strong  recurved 
single-fanged  tooth  of  a  caniniform  pattern,  and  one  which  both  by 
position  and  form  becomes  the  homologue  of  the  canine  in  the  ordinary 
heterodont  dentition.  The  rest  of  the  alveolar  border  is  occupied  by 
four  rather  large  more  or  less  trenchant  teeth,  referable  to  the  molar 
and  premolar  series.  Each  of  these  is  implanted  by  two  roots,  and  has 
a  laterally  compressed  crown  of  a  triangular  form  with  the  apex  of  the 
triangle  at  the  summit.     Each  of  the  anterior  and  posterior  edges  are 


41 G  JJESTAL  ANAT03IY. 

interrupted    by  three  well-marked   cnsps,  Mliicli  give  to  the  tooth  a 
strongly-serrated  appearance. 

The  heterodont  and  diphyodont  character  of  the  teeth  of  this  cetacean 
serves  to  bring  the  anomalous,  and  in  many  respects  degenerate,  dental 
organs  of  this  order  into  the  closest  relationshi})  with  the  teeth  of  the 
ordinary  diphyodont  ^Mammalia,  and,  being  the  oldest  member  of 
the  group  so  far  known,  goes  far  toward  filling  the  wide  gap  between 
these  aquatic  and  the  terrestrial  mammals. 

Teeth  of  the  Unguiculate  Series. 

In  considering  the  dental  organization  of  this  vast  assemblage  of 
mammiferous  animals  it  is  necessary  to  have  at  the  very  outset  a  correct 
conception  of  the  primitive  or  ancestral  stock  from  which  all  of  them 
have  been  derived,  if  such  can  be  found  to  exist.  This  can  be  learned 
only  by  a  careful  study  of  the  successional  history  of  the  various  orders 
composing  it.  In  searching,  then,  for  this  original  stem  we  can  by  this 
method  exclude  many  of  the  groups  from  this  position  by  fixing  the 
date  of  their  appearance,  and  thereby  establishing  their  exact  limit  in 
time.  We  know,  for  example,  that  the  Primates  could  not  be  the 
ancestral  group,  for  the  obvious  reason  that  they  do  not  extend  beyond 
Miocene  time  ;  nor  the  Carnivora,  which  appeared  about  the  same  time; 
nor  the  Rodentia,  which  date  from  the  Middle  Eocene ;  nor  the  Cheir- 
optera, which  can  be  traced  back  no  further  than  the  Upper  Eocene. 
AVe  are  therefore  restricted  in  our  choice  to  the  insectivores,  lemuroids, 
creodonts,  or  tillodonts,  which  alone  of  the  entire  series  continue  back- 
ward to  the  base  of  the  Eocene  Period.  AVith  reference  to  the  creodonts, 
I  do  not  believe  that  any  important  distinctions  exist  between  them  and 
the  insectivores,  while  the  line  between  this  latter  group  and  the  lem- 
uroids and  tillodonts  becomes  extremely  shadowy  at  this  point. 

Prof.  Cope  unites  the  insectivores,  lemuroids,  tillodonts,  creodonts, 
and  tfeniodonts  into  one  order,  which  he  calls  Bunotheria,  and  defines 
the  several  sub-orders  as  follows  :  ^ 

I.  Incisor  teeth  groAvinc:  frnm  persistent  pnlps: 

[a)  Canines  also  growing  from  less  persistent  pulps,  agreeing  with  external 

incisors  in  liaving  niolariform  crowns 'Jcrniodmita. 

[b)  Canines  riulimental  or  wanting  ;  hallux  not  opposable    ....  Tillodonta. 

[c)  Canines  none  ;  hallux  opposable Daubenton ioklea. 

II.  Incisor  teeth  not  growing  from  persistent  pulps: 

(")  Superior  true  molars  quadritubercular;  hallux  opposable       .    .   Pro<imi<z. 

(b)  Superior  true  molars  quadritubercular ;  hallux  not  ()})posable.     Inseclivora. 

(c)  Superior  true  molars  tr'.tubercular  or  bitubercular;  hallux  not  opposable. 

Creodoida. 

I  believe,  with  this  author,  in  classifving  tliose  forms  in  which  the 
incisors  grow  from  jjersistent  pulps  as  a  distinct  group  from  those  in 
which  the  incisors  are  normal,  as  far  at  least  as  their  growth  is  con- 
cerned. In  the  first  division  there  are  three  well-defined  sub-orders.  In 
the  second  division  it  is  extremely  questionable  whether  more  than  two 
sub-orders  should  be  made.  If  we  use  the  opposable  and  non-opposable 
condition  of  the  hallux  as  a  character,  we  Avill  have  two  perfectly  natural 

'  Proceedings  Academy  yutural  Sciences  Phllada.,  1883. 


TEETH  OF  THE   VERTEBRA  TA.  417 

series — the  prosimian  or  lemuroicl  and  the  insectivorous  ;  but  if  we  go 
further,  and  establish  another  sub-order  upon  the  tritubercular  or  quad- 
ritubereular  character  of  the  superior  mokir  teeth,  it  will  necessitate  the 
wide  separation  of  forms  closely  related  to  each  other  by  every  import- 
ant feature  of  their  anatomical  structure — a  course  which  I  do  not  deem 
advisable  nor  in  keeping  with  our  present  knowledge  of  the  subject. 

According  to  Prof  Cope's  definition,  the  only  character  in  which  the 
Crei)donta  differ  from  the  Insectivora  is  the  tritubercular  superior  molars 
as  distinguished  from  the  quadritubercular ;  and  in  order  to  make  the 
Creodonta  homogeneous  he  is  compelled  to  take  out  of  the  old  group 
Insectivora  the  Taupa'iadce,  Centetidce,  Chrysiochloridce,  and  Talpidce,  and 
place  them  in  the  Creodonta.  Aside  from  the  inadvisability  of  such  a 
course,  these  teeth  in  many  of  the  above-named  families  are  altogether 
intermediate  between  the  tritubercular  and  quadritubercular  pattern,  the 
postero-internal  tubercle  being  represented  often  by  a  rudimentary  cingu- 
lum,  which  may  be  entirely  absent  or  produced  into  a  strong  cusp. 
Then,  again,  the  superior  molar  teeth  of  the  prosimian  division  are 
indifferently  tritubercular  or  quadritubercular ;  and  if  we  adhere  to 
this  practice  in  the  one,  why  not  in  the  other?  In  consequence  of 
these  facts,  I  propose  to  unite  the  Creodonta  with  the  Insectivora  into 
a  single  division,  fjr  which  the  old  name  Insectivora  may  be  retained. 

Thus  constituted,  palteontological  history,  in  my  judgment,  points 
strongly  to  the  fact  that  this  group  stands  in  the  important  relationship 
of  ancestors  to  a  large  part,  if  not  the  whole,  of  the  unguiculate  Mam- 
malia. Working  upon  this  hypothesis,  it  will  be  desirable  to  describe 
the  more  important  types  of  dental  structure  to  be  met  with  in  this  sub- 
order, after  which  they  can  be  followed  out  to  their  respective  termina- 
tions in  the  various  orders  and  sub-orders  which  make  up  the  series. 

Insectivora. — The  simplest  form  of  dental  structure  in  this  sub-order 
is  exhibited  by  the  extinct  genera  Mesonyx  and  Dissacus  of  Cope,  from 
the  American  Eocene  strata.  The  teeth  of  Mesonyx  (Figs.  200,  201) 
are  forty-four  in  number,  disposed  as  follows :  I.  f ,  C.  \,  Pm.  |-,  M.  f 
=  42.  The  incisors  are  relatively  small,  with  subconic  crowns,  which 
are  closely  approximated.  The  superior  canines  are  large,  recurved,  and 
pointed,  being  placed  at  a  considerable  distance  from  the  incisors  to 
accommodate  the  crown  of  the  inferior  canine.  The  three  anterior  pre- 
molars of  the  upper  jaw  are  two-rooted,  with  the  exception  of  the  first, 
which  is  probably  single-rooted.  They  have  comparatively  simple  com- 
pressed crowns,  with  a  principal  cusp  and  a  posterior  basal  lobe,  sur- 
rounded by  a  basal  cingulum.  The  fourth  is  more  complex,  and  resem- 
bles the  true  molars  posterior  to  it.  Like  them,  it  has  three  principal 
cusps,  of  which  two  are  external  and  one  internal,  giving  to  the  crown 
a  triangular  shape.  In  the  first  true  molar  the  postero-external  angle 
of  the  crown  is  produced  into  a  strong  blade-like  process,  a  develop- 
ment of  the  cingulum  which  is  conspicuous  in  all.  The  last  molar  of 
this  series  is  bicuspid,  the  posterior  of  the  two  external  cusps  being 
absent. 

In  the  lower  jaw  both  the  premolars  and  molars  are  remarkable  for 
their  simplicity.  The  first  premolar  is  single-rooted,  and  has  a  sub- 
conic  crown,  as  in  the  dog.     The  teeth  behind  it  are  two-rooted,  and 

Vol.  I.— 27 


418 


DENTAL  ANATOMY. 


have  a  general  premolariform  appearance,  the  true  molars  exhibiting  but 
little  departure  from  the  conical  pattern  of  the  lower  Vertebrata.  As  in 
the  premolars  of  the  dog,  their  crowns  are  laterally  compressed,  of  a 


Fig.  200. 


Mandible  of  Mesonyxossifragns,  Cope,  from  tlie  Wasatch  Epoch  of  the  Big  Horn  River,  Wyoming,  one- 
third  uaturiil  size  (after  Cope). 

triangular  form  when  viewed  from  the  side,  having  a  principal  median 
cusp,  to  wliich  are  added  an  anterior  and  posterior  smaller  one  from  the 
cingulum. 

It  is  a  matter  of  considerable  interest  to  find  in  this  ancient  represen- 
tative of  the  unguiculate  series  so  simple  and  generalized  a  dentition, 
inasnuich  as  it  furnishes  a  key  to  an  interpretation  of  the  lobes  and 
cusps  of  the  teeth  of  many  of  the  succeeding  forms.  It  is  more  than 
probal)]e  tliat  tin's  ])nrticular  species  is  not  the  original  ancestral  form 
from  which  the  otlicrs  have  l)een  derived,  on  account  of  certain  charac- 
ters presented  by  the  skeleton,  but,  as  far  as  the  teeth  of  the  lower  jaw 
are  concerned,  they  exhibit  just  such  a  transitional  condition  between 
the  primitive  cone  of  the  theromorjih  R,e]itilia  and  the  lowest  forms 
of  mannnalian  teeth  as  we  would  most  reasonably  expect  to  find  in 
the  ]irimitive  ancestor. 

The  various  steps  in  this  jirocess  of  dental  evolution  I  conceive  to 
have  been  as  follows:  (1)  additions  to  the  anterior  and  posterior  edges 
of  the  cone  and  tlie  formation  of  a  cingulum  ;  (2)  division  of  the  single 


TEETH  OF  THE    VERTEBRATA. 


419 


root  into  two ;  (3)  addition  of  basal  cnsps  from  the  cingulura.  It  is  a 
fact  worthy  of  notice  that  in  the  conical  dentition  the  teeth  of  one  series 
do  not  exactly  oppose  those  of  the  other,  but  close  in  the  intervals  be- 
tween them.  This  in  animals  that  attempted  to  crush  a  morsel  of  food 
would  cause  stimulation  of  the  anterior  and  posterior  edges  of  the  tooth, 
thereby  determining  the  point  of  the  greatest  nutritive  activity  and  con- 
sequent growth.  Long-continued  vertical  pressure  I  believe  to  be  an 
adequate  cause  for  the  appearance  of  the  wrinkle  or  fold  of  the  enamel 
covering  at  the  base  of  the  tooth  which  is  designated  as  the  cingulum. 


Skull  of  Mesonyx  ossifnigus,  anterior  to  post-glenoid  process,  one-third  natural  size,  from  the  Wasatch 
beds  of  Wyoming  (after  Cope). 

The  formation  of  two  roots  I  believe  to  have  been  the  result  of  the  in- 
equality of  pressure  exerted  upon  each  tooth  during  the  act  of  mastication, 
whereby  there  was  an  eifort  to  displace  the  tooth  in  an  antero-posterior 
direction,  or,  in  other  words,  to  give  it  a  forward  and  backward  rocking 


420 


DENTAL  ANATOMY. 


movement,  as  the  greatest  pressure  was  in  front  of  or  behind  it.  This 
would  cause  the  stimulation  of  the  anterior  and  posterior  faces  of  the  root, 
and  as  a  consequence  of  this  a  vertical  groove  was  first  formed  upon  each 
side,  which  eventually  coalesced,  dividing  the  root  into  two.  As  we 
have  already  seen,  this  condition  is  found  in  a  theromor})h  reptile, 
and  is  likewise  to  be  found  in  the  premolars  of  many  existing  animals. 
The  development  of  basal  cusps  would  naturally  follow  at  those  points 
where  the  crown  sustained  the  greatest  amount  of  resistance,  which 
would  be  at  the  base  of  the  triangle. 

It  is  a  rule  of  pretty  general  application  in  heterodont  teeth  that  the 
molars  are  more  modified  than  the  premolars.  This,  in  all  probability, 
results  from  the  greater  mechanical  advantage  which  is  gained  by  bring- 
ing the  morsel  to  be  crushed  or  divided  to  the  posterior  part  of  the 
mouth ;  that  is  to  say,  the  resistance  as  near  to  the  power  as  possible. 
The  power  in  this  case  is  the  muscles  which  close  the  mouth,  which, 
being  attached  to  the  posterior  part  of  the  jaw,  exert  the  greatest 
influence  upon  those  teeth  in  the  vicinity  (3f  their  attachment. 

The  next  step  in  dental  complication  is  seen  in  the  genus  Dlssacus, 
from  the  lowest  Eocene,  the  lower  teeth  of  which  are  represented  in 
Fig.  202.     They  are  very  similar  in  general  appearance  to  those  of 

Fig.  202. 


Bissncus  naviijoviiis,  Cope.    Right  Alandibulnr  Pianius,  three-fourths  natural  size:  a,  external ;  6,  supe- 
rior view,  Iroui  the  Puerco  Beds  of  New  Mexico  (after  Cope). 

Mesonyx,  with  which  they  also  agree  in  number.  There  is,  however,  an 
additional  cusp  developed  upon  the  inner  side  of  the  median  cone  near 
its  summit,  which  is  the  homologue  of  the  internal  tubercle  of  the  infe- 
rior sectorial  of  the  dog,  as  well  as  that  of  many  other  animals  of  the 
unguiculate  series.  The  upper  teeth  are  not  known.  The  genera  in 
which  tlie  mandibular  teeth  ]n'esent  this  premolariform  structure  are 
associated  by  Cope  into  a  family  which  he  calls  the  Jlcsonj/cJiiflce. 

As  a  probable  derivative  of  this  family  we  have  the  extinct  family 
Ui/cenodontidce,  of  which  the  teeth  of  the  single  genus  Hycenodon  are 
represented  in  Fig.  20.3.  This  animal  is  known,  so  far,  from  the  Mio- 
cene dc])osits  of  this  country  and  Europe  only,  and  has  been  shown  by 
Prof  AV.  B.  Scott  of  Princeton  College  to  be  a  near  relative  of  Mesonyx. 
The  dental  formula  is,  according  to  Gaudry,  I.  |,  C.  -f,  Pm.  ^,  M.  f 
=  42.     The  incisors  resemble  those  of  the  dog,  the  median  pair  being 


TEETH  OF  THE   VERTEBRATA. 


421 


the  smallest,  the  outer  pair  the  largest.  The  canines  are  large,  pointed, 
and  recurved.  The  anterior  premolars  above  are  two-rooted  and  have 
premolariform  crowns.     The  third  and  fourth  are  three-rooted,  with 


Fig.  203. 


Hywnodon  horridus,  Leidy.    Skull,  one-half  natural  size  (from  Cope,  after  Leidy). 

three  external  and  one  internal  cusp,  which  in  the  third  premolar  is 
small  and  placed  far  back ;  in  the  fourth  it  is  large  and  has  a  position 
nearer  the  middle  of  the  tooth ;  while  in  the  first  and  second  molars  it 
is  anterior  and  more  or  less  rudimental.    The  anterior  cusp  and  median 


422 


DENTAL   ANATOMY. 


cone  in  these  latter  teeth  form  cutting  blades  and  are  truly  sectorial  in 
their  nature. 

In  the  lower  jaw  the  first  premolar  is  t^vo-rooted,  with  a  coni})ressed 
crown  without  basal  lobes.  The  second,  third,  and  fourth  have  well- 
developed  posterior  basal  lobes,  with  the  anterior  al)sent.  The  first  true 
molar  has  three  lobes,  which  form  an  imperfect  trilobed  sectorial  blade. 
The  second  is  also  trilobed,  having  the  anterior  cusp  and  median  cone 
developed  into  a  true  sectorial,  while  the  posterior  lobe  forms  a  cutting 
heel.  In  the  third  the  heel  is  rudimental  or  absent,  and  the  anterior 
lobe  and  median  cone  are  modified  into  a  perfect  trenchant  blade. 

From  the  Me^onychidce  we  pass,  through  Dissacus  and  Triitiodon,  to 
another  extinct  family,  which  Prof.  Cope  calls  the  Leptldidce.     In  an 

Fig.  204. 


Skull  and  Part  of  the  Posterior  Foot  of  two  individuals  of  Shipulophvs  whi/ice,  Cope,  two-thirds  nat- 
ural size:  a,  b,  side  and  under  views  of  the  skull;  c,  portion  of  lower  jaw,  <i,  ankle-joint  (after 
Cope). 

Eocene  genus  of  this  family,  Stj/poIopJms,  Cope  (Fig.  204),  the  dental 
formula  is  I.  f ,  C,  \,  Pm.  ^,  M.  f  =  44.  The  incisors,  canines,  and 
premolars  are  very  like  the  corresponding  teeth  in  3Iesonyx.  The  last 
superior  premolar  is,  like  the  true  molars,  tritubercular,  with  the  pos- 


TEETH  OF  THE   VERTEBRATA. 


423 


con- 
The 
two 

wsal 


terior  external  angle  produced  into  a  prominent  process,  which  is 
nected  with  the  postero-external  cusp  by  a  sharp  cutting  ridge, 
cingulum   also   furnishes  a  broad  ledge  upon  the  outside  of  the 
external  cusps. 

In  the  three  inferior  true  molars  the  median  cone,  the  anterior 
lobe,  and  the  internal  tubercle  are  all  well  developed,  and  are  disposed 
in  such  a  manner  as  to  form  an  equilateral  triangle,  with  the  apex 
directed  forward  and  the  base  backward.  Of  these,  the  anterior  basal 
lobe  occupies  a  position  at  the  apex  of  the  triangle,  the  median  cone 
and  internal  lobe  being  placed  at  the  external  and  internal  angles  of 
tlie  base  respectively.  The  posterior  basal  lobe  is  also  present  in  the 
form  of  a  low  heel,  which  may  in  some  genera  retain  a  simple  cutting 
form  or  may  be  broken  up  into  several  and  become  ''  basin-shaped." 
This  form  of  tooth  Prof.  Cope  proposed  some  years  ago  to  designate  by 
the  name  of  ^^  tuherculo-sectorial."  There  can  be  little  doubt  that  it 
furnishes  the  point  of  departure  for  the  sectorial  teeth  of  the  lower  jaw 

Fig.  205. 


Left  Mandibular  Ramus  of  Triisodnn  quivirensis,  three-fourths  natural  size,  from  the  Puereo  of  Xew 
Mexico  ;  «,  external  view,  displaying  last  tempnrary  molar  in  place  ;  h,  the  same  from  above;  c,  the 
same,  internal  side,  the  temporary  molar  removed  and  the  permanent  Iburth  premolar  displayed 
in  ihe  jaw  ;  d,  the  fourth  premolar  seen  from  above  (after  Cope). 

of  the  modern  Carnivora  on  the  one  hand,  and  the  quadritubercular 
lower  molar  of  the  entire  unguiculate  series  on  the  other. 

As  will  be  seen,  it  displays  the  same  elements  that  are  found  in  the 
inferior  sectorial  of  the  dog,  the  only  difference  being  in  the  relatively 


424 


DENTAL  ANATOMY. 


Fifi.  20fi. 


smaller  size  of  the  internal  tubercle  and  the  modification  of  the  primi- 
tive cone  and  anterior  ba.'^al  lobe  into  a  more  perfect  sectorial  form  in 
the  dog.  The  quadritul)er('ular  tooth  has  been  derived  from  this  bv  the 
suppression  of  the  anterior  basal  lobe,  the  reduction  in  size  of  the  median 
cone  and  internal  tubercle,  and  the  division  of  the  heel  into  two  cusps, 
whereby  the  median  cone  becomes  the  antero-external  tubercle,  the 
internal  tubercle  the  antero-internal,  and  the  heel  the  two  posterior 
ones. 

The  genus  Triisodon  of  Cope  (Fig.  205)  affords  a  perfect  transition 
between  titypolophus  and  Dlssacus,  as  far  as  the  pattern  of  the  infe- 
rior teeth  is  concerned.  In  another  genus,  C)iriacus,  Cope,  from 
the  Lower  Eocene,  which  is  provisionally  referred  to  this  family,  the 
upper  molars  are  tritubercular  with  a  strong  internal  cingulum,  which 
develops  a  riidimental  fourth  cusp  behind.  This  forms  one  of  the 
examples  referred  to  in  which  it  is  difficult  to  say  whether  the  teeth 
in  question  are  tritubercular  or  quadritubercular,  and  goes  far  toward 
invalidating  the  definition  of  the  Creodonta  as  given  by  Cope. 
This  author  says  in  reference  to  this  family,  and  more  especially  to 
this  genus :  "  Two  groups  are  easily  recognized  among  the  Leptididce. 
In  the  first  of  these  tlie  last  or  fourth  inferior  premolar  is  a  simple  pre- 
molariform  tooth,  different  from  the  inferior  true  molars  and  without 

any  internal  cusp.  In  the  second 
division  the  fourth  inferior  premo- 
lar is  either  like  the  first  true  mo- 
lars or  approximates  their  form  by 
the  jiresence  of  an  internal  tubercle. 
To  tlie  latter  group  belongs  the  ge- 
nus C/iy'mc(/.s',  which,  from  the  slight 
development  of  the  fourth  inferior 
premolar,  approximates  the  first  di- 
vision. This  genus  may,  however, 
be  improperly  referred  to  the  C^reo- 
donta."  ' 

Still  another  genus  of  this  family, 
Miockcnus,  also  from  the  Eocene, 
presents  truly  quadritubercular 
lower  molars.  The  premolars  are 
sim])le  and  conical,  and  differ  widely 
in  tlieir  structure  from  the  molars. 
The  superior  true  molars  are  sim- 
ilar to  those  of  the  preceding  genus, 
with  the  exception  that  the  fourth 
tubercle  is  better  defined  and  fur- 
nishes another  example  of  the  tran- 
sition between  the  tritubercular  and 
quadritubercular  condition. 

In  the  typical  genus  Leptidis  of 
Leidy  (Fig.  206)  the  dental  formula  is  probably  the  same  as  that  of 
Stypolnphus,  the  lower  jaw  being  imperfectly  known.     The  upper  teeth 

^  "  The  Creodonta,"  Avierican  Naturalist,  April,  1884,  p.  348. 


Lepiictis  hnydevi,  Leidv,  Skull  natural  size,  from 
the  White  River  beds  of  Xehraska  i  from  Cope, 
after  Leidy). 


TEETH  OF  THE   VERTEBRATA. 


425 


are  like  those  of  Stypolojjhus  in  having  the  fonrth  premolar  and  all  the 
true  molars  tritubercular.  There  is  no  broad  ledge  external  to  the  outer 
cusps,  however,  as  in  that  genus,  and  the  posterior  external  angle  of  the 
crown  is  not  produced.  It  is  from  the  White  River  Miocene  of  this 
country,  as  is  also  a  nearly-related  genus,  Ictops  of  Cope.  The  only 
difference  between  these  two  genera  is  the  more  complex  form  of  the 
fourth  superior  premolar  in  the  latter. 

The  living  genus  Centetes,  or  tenrec  of  ]Madagascar,  is  closely  related 
to  this  family,  and  differs  only  in  the  incomplete  condition  of  the  zygo- 
matic arch.  The  number  and  form  of  the  teeth  are  very  like  those  of 
Leptktis,  and  it  is  highly  probable,  as  Cope  suggests,  that  Centetes  is 
the  living  descendant  of  this  genus. 

Another  quite  remarkable  genus  which  Cope  places  in  this  family  is 
from  the  Eocene,  and  was 

described  by  him  under  the  Fig.  207. 

name  of  Esthoni/x.  Its 
dental  formula  (Fig.  207) 
is  1.1  C.i-,Pm.|,  M.f 
=  34.  The  single  superior 
incisor  of  each  side  is  great- 
ly enlarged,  and  exceeds  the 
canine  in  size.  The  first  pre- 
molar is  small  and  has  a 
simple  crown.  The  next  is 
larger,  and  is  tritubercular. 
The  third  is  like  the  true 
molars,  with  the  exception 
that  it  lacks  the  internal 
cingulum.  The  true  molai's 
have  two  external  cusps, 
bordered  npon  the  outside 
by  a  broad  ledge  which  is 
produced  anteriorly  into  a 
marginal  cusp.  There  is 
a  large  internal  cusp,  from 
which  is  developed  at  its 
inner  posterior  extremity 
a  strong  cingulum,  the  representative  of  the  fourth  cusp,  which  is  con- 
tinued thence  around  the  base  of  the  crown  behind  to  join  its  broad 
external  portion.  This  is  another  case  wherein  the  tritubercular  and 
quadritubercular  question  is  involved  in  uncertainty. 

In  the  lower  jaw  the  median  incisors  are  small,  the  outer  pair 
enlarged,  almost  equalling  the  canines.  The  first  two  premolars  are 
small,  the  third  larger,  resembling  the  true  molars  somewhat  in  form. 
The  molars  support  two  Vs,  of  which  the  anterior  is  most  elevated. 
An  analysis  of  the  crown  shows  it  to  be  of  a  modified  tuberculo-secto- 
rial  nature,  wherein  the  three  anterior  cusps  are  connected  by  ridges 
that  extend  quite  to  their  summit  and  form  the  anterior  V.  The  broad 
heel  displays  two  cusps  connected  by  a  strong  ridge ;  from  the  outer  of 
these,  again,  another  ridge  passes  obliquely  forward  to  join  the  internal 


Esihonyx,  burmeisteri,  Cope:  a,  b,  c,  parts  of  upper  and  lower 
jaws,  two-thirds  natural  size  (after  Cope). 


426 


DENTAL  ANATOMY. 


cusp,  thereby  completing  the  second  V.     The  last  molar  has  a  fifth  cusp 
behind,  in  this  respect  resembling  many  of  the  lemuroids. 

The  family  most  nearly  approximated  to  this  genus  is  that  including 
the  shrews  (Sorickke),  Avhich  always  have  two  incisors  both  above  and 
below,  greatly  enlarged.  In  Blarina  talpouJi'S,  a  living  species  of  this 
country,  the  teeth  (Figs.  208,  209)  are  thirty-two  in  number,  of  which 

Fig.  208. 


Fig.  209. 


Side  View  of  a  Portion  of  a  Skull  of  Blnrina  ialpoides  (much  enlarged). 
The  si.xth  tooth  of  the  upper  series  is  placed  somewhat  interDal  to 
the  others,  and  is  not  repiesented  in  the  drawing. 


Vertical  View  of  Grinding 
Surface  of  o,  a  lower  mo- 
lar, and  b.  an  upper  mo- 
lar (eularged) 


twenty  belong  to  the  upper  and  twelve  to  the  lower  jaw.  Owing  to  the 
very  early  co-ossification  of  the  premaxillae  with  the  maxillse  and  the 
paucity  of  suitable  material,  I  am  at  present  unable  to  give  the  proper 
dental  formula  of  this  animal.  Neither  can  I  find  any  statement  upon 
the  subject  further  than  that  of  Owen,  in  M'hich  he  refers  to  the  European 
species,  Sorex  arcouvns,  with  only  eight  teeth  u])on  each  side  in  the  ujiper 
jaw,  and  says:^  "  The  determination  of  the  small  teeth  between  the  large 
anterior  incisors  and  the  niulticus]>id  molars  dejiends  upon  the  extent  of 
the  early  ankylosed  intermaxillaries  ;  the  incisors  being  defined  by  their 
implantation  in  these  bones,  the  succeeding  small  and  simple  crowned 
molars  must  be  regarded  as  premolars,  not  any  of  them  having  the 
development  or  office  of  a  canine  tooth  :  their  analogues  in  the  lower 
jaw  are  implanted  by  two  roots."  If  he  confines  his  statement  to  this 
species,  it  is  probably  correct  to  refer  all  those  teeth  between  the  large 
incisors  and  the  anterior  one  of  the  last  three  to  the  premolar  .series ;  but 
in  Blarina  there  are  six  teeth  to  be  disposed  of.  Allowing  the  normal 
number  of  premolars  (four),  we  have  either  three  incisors  and  no  canine, 
or,  as  is  most  pro])able,  two  incisors  and  a  canine,  which  would  give  the 
following  formula  :  I.  ^,  C  1,  Pni.  |-,  M.  |.  This  determination  of 
course  may  prove  to  be  incorrect. 

^  Odontofjyfiphi.;  p.  41S. 


TEETH  OF  THE   VERTEBRATA.  427 

The  two  large  incisors  above  are  hook-shapecl,  with  a  prominent  pos- 
terior ledge  at  the  base,  which  in  some  species  of  this  tamily  is  produced 
into  a  strong  basal  cusp.  The  next  two  teeth  are  much  smaller  and  sub- 
equal,  while  the  three  following,  rapidly  decrease  in  size,  the  last  becom- 
ing very  small.  Exclusi\'e  of  the  large  hook-shaped  incisor,  the  above- 
mentioned  teeth  display  a  principal  cone  with  an  internal  lolje  and 
an  external  cingulum,  which  is  most  distinct  in  the  fourth,  fifth,  and 
sixth.  The  next  tooth,  which  I  take  to  be  the  last  premolar,  marks  an 
abrupt  change  both  in  the  character  and  size  of  the  teeth  of  the  ujiper 
series.  It  is  almost  equal  in  size  to  the  first  true  molar,  which  it  resem- 
bles very  closely  in  structure. 

The  crowns  of  the  molars  may  be  described  as  consisting  of  four 
principal  cusps  or  tubercles,  of  which  two  are  external  and  two  internal, 
and  are  therefore  quadritubercular.  The  two  external  cusps  stand  at  the 
apex  of  two  Vs,  which  open  externally,  giving  to  this  part  of  the  tooth  a 
distinct  W  pattern.  At  the  extreme  antero-external  angle  of  the  crown 
there  is  a  considerable  cingular  cusp,  which  is  connected  with  the  main 
antero-external  tubercle  by  a  prominent  ridge,  thereby  forming  the  first 
downward  stroke  of  the  W.  From  this  main  tubercle  another  well- 
marked  ridge  passes  outward  and  backward  to  another  small  cusp  of 
the  cingulum,  situated  at  a  point  midway  between  the  two  main  exter- 
nal tubercles  on  the  outer  edge  of  the  crown,  forming  the  first  upward 
stroke  of  the  W  and  completing  the  first  V.  The  second  downward 
stroke  of  the  W  is  furnished  by  a  ridge  connecting  the  small  median 
marginal  cusp  ^vith  the  postero-external  tubercle,  while  the  second  upward 
stroke  of  the  W  is  formed  by  a  ridge  continued  outward  and  backward 
to  the  postero-external  angle  of  the  crown,  where  it  terminates  in  as  light 
enlargement. 

From  the  apex  of  each  of  the  Vs  a  high  ridge  passes  inward,  meeting 
at  the  antero-internal  angle  of  the  crown,  forming  a  distinct  U.  The 
inner  part  of  this  crest  is  the  antero-internal  tubercle.  The  postero- 
internal tubercle  stands  just  behind  it,  and  exhibits  a  somewhat  cres- 
centiform  pattern.  It  will  be  seen  that  the  tooth  just  described  does 
not  differ  materially  from  those  of  some  other  insectivores  already 
noticed,  especially  Esthonyx.  The  principal  differences  are  to  be  found 
in  the  greater  development  of  the  marginal  cingular  cusps  and  connect- 
ing ridges  upon  the  external  part  of  the  crown,  which  we  have,  in  a 
measure,  foreshadowed  in  Esthonyx  and  others. 

In  the  lower  jaw  the  single  pair  of  incisors  are  large,  scalpriform,  and 
procumbent.  The  two  succeeding  premolars  are  small,  single-fanged, 
and  have  simple  crowns.  The  first  two  true  molars  are  the  largest  of 
the  molar  and  premolar  series,  and  exhibit  a  structure  identical  with 
that  of  Esthonyx.  The  last  is  very  small,  and  corresponds  with  the  last 
tooth  of  the  upper  jaw,  which  frequently  disappears.  The  crowns  of 
all  the  teeth  are  stained  a  deep  wine-color  by  a  pigment  which  pene- 
trates the  substance  of  the  enamel,  this  tissue  being  remarkable  for  its 
thickness  in  all  the  Insectivores. 

Considerable  discussion  has  taken  place  in  regard  to  the  nature  of  the 
external  Vs  and  the  exact  homology  of  the  two  external  tubercles.  Since 
this  W-structure  is  common  to  the  superior  true  molars  of  all  the  moles, 


428  DENTAL  ANATOMY. 

shrews,  and  insectivorous  bats,  as  well  as  some  others  of  the  imgnicnlate 
series,  it  is  desirable  to  have  a  thorough  understanding  of  it.  Cope 
maintains  ^  that  the  median  and  anterior  marginal  cusps  are  the  homo- 
logues  of  the  two  external  tubercles  of  the  teeth  of  such  a  form  as  H'ty- 
po/ophus  (Fig.  204),  and  that  the  two  cusps,  which  are  here  homolo- 
gized  as  the  representatives  of  the  two  external  tubercles  of  this  genus, 
he  proposes  to  call  intermediate  tuljercles.  JNIivart,  on  the  other  hand, 
holds"  that  all  the  marginal  cusps  are  developed  from  the  cingulum,  and 
that  the  true  external  tubercles  have  come  to  occupy  a  more  and  more 
internal  position  on  the  crown — a  view  which  I  believe  to  be  correct. 

The  evidence  upon  which  I  base  my  opinion  is  to  be  found  bv  exam- 
ining the  teeth  of  such  genera  as  >Sfi/poIup}ius,  Esthouy.r,  and  Scapanus 
of  the  unguiculate  series,  and  TJri/laeinuH,  DkJe/pJtys,  Fhdscogale,  and 
DasyiD-us  among  the  marsupials.  In  the  genera  StypolopJnis  and  Ksfho- 
nyx,  as  we  have  already  seen,  the  way  is  paved,  so  to  speak,  for  the 
formation  of  the  two  Vs  by  the  appearance  of  a  broad  ledge  external  to 
the  two  main  outer  cusps  and  the  elevation  of  the  cingulum  into  a  small 
cusp  at  the  antero-external  angle  of  the  crown,  as  well  as  the  backward 
prolongation  of  the  postero-external  angle  and  its  connection  with  the 
postero-external  tubercle  by  a  strong  ridge.  This  latter  ridge  I 
regard  as  the  strict  homologue  of  the  last  upward  stroke  of  the  W.  In 
these  two  genera  the  only  modifications  necessary  to  produce  the  W 
would  be  greater  separation  of  the  two  external  tubercles  and  the  pres- 
ence of  a  median  marginal  cusp  connected  with  them  by  ridges. 

In  the  genus  Scapanus,  or  hairy-tailed  moles,  of  this  country  the  fourth 
superior  premolar  does  not  exhibit  the  W-shaped  arrangement  in  the 
same  perfection  that  the  true  molars  do,  the  anterior 
V  being  rudimental  or  absent.  The  cusp  at  the  an- 
tero-external angle,  however,  i.s  present,  and  can  be 
clearly  shown  to  be  of  a  cingular  origin.  It  cannot 
therefore,  as  Cope  supposes,  represent  the  true  antero- 
external  tubercle,  in  this  tooth  at  least.  In  the  sec- 
ond unworn  true  molar  of  Basyurvs  (Fig.  210)  all 
the  marginal  cusps  are  present,  but  the  median  one 
is  not  connected  with  the  two  main  external  tuber- 
cles by  ridges,  leaving  the  W  imperfect.  In  this 
View  of  the  GrindiTig     tootli  nothing  is  morc  ai)iiarent  than  the  cingular 

Surlace    of     an     Un-  •    •  r.      ;/    ,i  •       i  i 

worn  aroiar  Tooth  of  Origin  ot  all  the  marginal  cusps ;  and  no  one  can 
J°internair&!"efter-  tloubt,  it  apjjcars  to  me,  that  they  are  strictly  homol- 
n'ai;-,  anterior  aspect     ogous  witli  thc.cusps  in  a  like  positiou  iu  the  molars 

of  the  crown.  <p  •i-i-ii^.  ,ii> 

ot  those  animals  in  which  the  W  is  perfectly  formed. 
A  careful  consideration  of  the  teeth  of  the  genera  above  mentioned  in 
my  judgment  effectually  disposes  of  the  whole  question,  and  demon- 
strates beyond  doubt  the  correctness  of  the  position  here  maintained, 
notwithstanding  the  conclusions  of  so  high  an  authority  as  Prof.  Cope 
to  the  contrary. 

Galeopithecus,   or   the   so-called  flying  lemur,   constituting  another 

'  "Mutual  Relations  of  tlie  Bunotherian  Mammalia,"  Proceed.  Acad.  Nat.  Sciences 
Philadelphia,  1883,  pp.  81-83. 

^  Journal  of  Anatomy  and  Phyaiolocjy,  ii.  138,  figures,  1868. 


TEETH  OF  THE   VERTEBRATA. 


429 


Fig.  211. 


Two  Incisors  of  the  Lower 
Jaw  of  Galeopil/iecus,  ex- 
ternal view  (enlarged). 


family  (Galeojjithecldce),  is  quite  aberrant  in  the  form  of  its  incisors 
and  some  of  the  premolars.  The  incisors  are  two  in  number  upon 
each  side  in  the  upper  jaw,  and  those  of  the  opposite  sides  are  separated 
by  a  wide  edentulous  space ;  the  first  is  minute  and  comparatively 
simple ;  the  second  is  relatively  large,  two-rooted,  and  in  every  way 
similar  to  the  tooth  behind  it,  which  is  lodged  in  the  maxillary  bone. 
The  form  of  the  crown  is  that  of  a  greatly  flattened  cone  with  anterior 
and  posterior  cutting  edges.  The  anterior  edge  is  interrupted  by  one 
minor  denticle,  the  posterior  by  four,  making  it  dis- 
tinctly serrated.  The  next  tooth  behind  this  one  is 
sometimes  called  a  canine,  but  it  is  more  probably 
a  premolar ;  if  this  be  the  case  the  premolars  are 
three  in  the  upper  jaw.  The  last  premolar  is  like 
the  molars,  with  three  principal  cusps  and  two  small 
intermediate  ones. 

In  the  lower  jaw  the  incisors  (Fig.  211)  form  a 
continuous  arch  around  the  alveolar  margin,  and 
are  of  a  mo.st  remarkable  pattern.  They  are  four  in 
all,  of  which  the  outer  pair  is  somewhat  the  larger  ; 
they  have  broad  incisive  crowns,  which  are  cleft  to 
the  base  by  deep  vertical  fissures  like  the  teeth  of  a  comb.  In  the 
middle  pair  there  are  seven  such  fissures,  dividing  off  eight  slender  col- 
umns, whereas  in  the  lateral  pair  there  are  ten. 

The  next  tooth  has  a  somewhat  similar  shape,  but  there  are  only  four 
fissures,  ^vhich  do  not  penetrate  so  deeply  ;  its  cro^vn  cannot  therefore  be 
said  to  be  more  than  serrate.  The  true  molars  are  quintitubercular, 
Avitli  very  elevated  cusps. 

In  the  European  mole  (Talpa  europca),  which  may  be  taken  as  a  fair 
representative  of  the  family  Talpidce,  the  dental  formula  is  I.  |^,  C.  \, 
Pm.  |-,  M.  f  =  44.  The  incisors  of  the  upper  series  are  normal  both  in 
size  and  structure.  The  upper  canine  is  large,  recurved,  and  jiointed, 
and  exhibits  the  remarkable  peculiarity  of  being  implanted  by  two 
fangs.  The  premolars  are  simple  compressed 
teeth,  increasing  progressively  in  size  from  the 
first  to  the  fourth.  The  true  molars  are  tritu- 
bercular,  with  the  W-shaped  structure  externally. 

In  the  lower  jaw  the  first  four  teeth  are 
small  and  incisiform ;  the  next  is  large,  two- 
rooted,  and  caniniform,  performing  the  func- 
tion of  the  inferior  canine.  It  is,  however, 
really  a  premolar,  since  it  closes  behind  the 
superior  canine,  and  not  in  front  of  it.  The 
tooth  immediately  in  front  of  it  is  the  true 
canine,  notwithstanding  its  small  size  and  in- 
cisive office.  The  three  succeeding  premolars 
are  similar  to  the  corresponding  teeth  above. 

rrii       ,  1  1    • ,     1  1  ,1         Vertical  View  of  a,  the  upper 

ihe  true  molars  are  quadritubercular,  or  rather  jaw,  and  ft,  the  lower  jaw,  of 
intermediate  between  the  tuberculo-sectorial  and  ^ZT^""  hedge-hog  iEnna- 
the  quadritubercular  patterns. 

In  the  hedge-hogs  [Erinacidxje)  (Fig.  212)  and  the  elephant  shrews 


Fig.  212. 


430 


DENT  A  L  ANA  TOM  Y. 


(IlacrosceHdce)  the  molars  are  quadritubercular  both  above  and  below, 
and  exhibit  no  traces  wliatever  of  the  complex  W-structure.  If  it  is 
imperative  to  make  any  division  of  the  Insectivora  upon  the  characters 
of  the  teeth,  I  would  suggest  that  the  W-arrangement  of  the  cusps 
of  the  superior  true  molars  be  considered  as  available  for  the  purpose, 
although  I  would  be  seriously  disposed  to  question  this  character  alone 
as  indicative  of  community  of  descent. 

Another  family  of  the  Insectivora  which  in  all  probability  stands  in 
ancestral  relationship  to  the  Carnivora  is  the  one  which  Cope  calls  the 
Miacidce.  It  is  represented  by  two  genera,  Dklymiciis  and  Miaci.s,  both 
from  the  Eocene  of  North  America.  In  this  family  we  have,  as  Cope 
remarks,^  "the  point  of  nearest  approximation  of  the  Creodonta  and 

Carnivora.  This  is  indicated  by  the  fact  that 
the  sectorials  are  sectorials  both  by  position 
and  form,  such  as  are  not  elsewhere  met  ^^■ith 
in  the  Creodonta.  The  genera  might  readily 
be  taken  for  members  of  the  Canidfe  and  Vi- 
verridte  (dogs  and  civets)  but  for  the  struc- 
ture of  the  astragalus,  which  is  thoroughly 
creodont." 

The  genus  Didymictm  may  be  certainly  re- 
garded as  the  ancestor  of  the  civets,  while  it  is 
more  than  probable  that  Miach  (Fig.  213)  was 
the  immediate  progenitor  of  the  dogs.     In  the 
teeth  of  Didymidis  (Fig.  214)  the   dental  formula  is  not  comj^letely 

Fig.  214. 


Fragment  of  the  Lower  .Inv.-  of  a 
species  of  Jfincis :  a,  external,  /<, 
internal,  and  c,  vertical  views. 


Two  Species  of  Didt/micfis :  ft,  h,  c,  internal,  vertical,  and  external  views  ol  lower  jaw  of  D.  dawhin- 
sianiis,  from  I'ig  Horn  Beds ;  il,  e,  /,  I),  /ini/cleniami.s ;  d,  upper-jaw  fragment,  vertical  view ;  e,  frag- 
ment of  lett  ramus,  inner  side;  /,  vertical  view  of  same, — all  natural  size  (after  Cope). 

known,  but  mo.st  probably  it  is  I.  f ,  C.  \,  Pm.  f ,  M.  f  =  40.  The 
fourth  premolar  above  is  sectorial  in  form,  the  two  true  molars  tuber- 
cular. 

In  tlie  lower  jaw  the  tirst  true  molar  has  lost  much  of  its  typical 
tuberculo-sectorial  structure,  which  is  best  seen  in  the  decreased  size  of 
the  internal  tubercle  and  the  tendency  of  the  anterior  basal  lobe  and  the 

^  "The  Creodonta,"  American  Naturaliftt,  May,  1884,  p.  483. 


TEETH  OF  THE   VERTEBBATA.  431 

primitive  cone  to  fuse  into  a  cutting  blade.  A  single  tubercular  molar 
follows  the  sectorial,  which  exhibits,  as  does  the  second  lower  true  molar 
in  the  dog,  a  reduced  or  degraded  condition  of  the  tuberculo-sectorial 
pattern. 

Miacis  has  three  true  molars  in  the  lower  jaw,  of  which  the  first 
is  sectorial,  in  this  respect  resembling  very  closely  the  lower  jaw  of  the 
dog ;  its  complete  dental  formula  is  not  known. 

Tp:eth  of  the  Prosimi.e. — With  this  group  we  enter  that  division 
of  the  Ijuiiotheria  which  leads  out  to  the  monkeys  and  man.  Its  palteon- 
tological  history  reveals  an  antiquity  quite  equal  to  that  of  any  other 
of  the  Monodelphia,  continuing  backward  to  the  lowest  Eocene.  It 
is  customary  with  most  naturalists  to  regard  the  Proshnke  as  widely 
separated  from  the  Insedh-ora  on  account  of  the  higher  order  of  brain- 
structure  which  the  living  representatives  of  the  lemurs  display,  and 
they  are  accordingly  placed  near  the  Primates.  Owing  to  the  perish- 
able condition  and  non-preservation  of  the  soft  parts  in  the  extinct 
forms  generally,  we  will  never  be  able  to  know  the  exact  structure 
of  their  brains,  but  must  be  content  to  judge  of  its  generalized  or 
specialized  character  by  the  mould  of  the  cranial  cavity,  which  in 
many  respects  is  unsatisfactory. 

It  can  be  shown  in  the  ungulate  series  that  the  lowest  Eocene  repre- 
sentatives possessed  brains,  judging  from  the  cranial  casts,  almost  as  low 
in  the  scale  of  organization  as  that  of  the  lowest  known  mammals,  and 
it  is  likewise  true  that  the  brains  of  the  Eocene  prosiraians  were  more 
generalized  than  those  now  living.  I  do  not  think  there  can  be  any 
radical  differences  shown  to  exist  between  the  structure  of  the  brain 
of  such  forms  as  the  squirrel  shrews  [Taupaiadce),  the  elephant  shrews 
{]\IacrosGelidcB),  and  the  (Taleopithecidce  of  the  insectivores,  and  the 
true  lemurs  (^Lemnridce),  the  fossil  Adapts,  and  others  of  the  Pro- 
simice.  The  very  fact  of  their  remote  antiquity  and  appearance  in  an 
age  when  the  brain-development  of  all  the  Mammalia  was  small  would 
of  itself  lead  to  the  supposition  that  they  too  at  first  possessed  brains  of 
lowly  organization.  It  should  be  here  stated  that  very  few  skulls  of 
the  Eocene  prosimians  are  known. 

The  dental  formula  of  the  spectrum  lemur  (Tarsius  spectrum)  is 
I.  y,  C  ^,  Pm.  1^,  M.  f.  Of  the  two  pairs  of  incisors  in  the  upper  jaw, 
the  median  is  much  the  larger ;  they  are  closely  approximated,  long, 
pointed,  and  conical,  and  are  surrounded  at  the  base  by  a  prominent 
cingulum,  which  is  well  defined  upon  the  anterior  face  of  the  crown. 
The  next  pair  are  much  smaller,  and  also  have  pointed  crowns  and 
basal  cingul-a.  The  upper  canines  are  about  equal  in  size  to  the 
median  incisors,  which  they  resemble  both  in  the  form  of  their 
crowns  and  the  cingulum  at  the  base. 

The  first  premolar  is  the  smallest  of  the  three,  and  is  placed  just 
behind  the  canine  ;  its  crown  is  simple  and  pointed.  The  next  two  are 
larger  and  imperfectly  two-lobed,  the  internal  lobe  being  represented  by 
a  strongly-developed  cinguhnii  which  continues  around  upon  the  outer 
face  of  the  tooth.  The  true  molars  are  subequal  in  size  and  tritubercu- 
lar.  The  two  external  cusps  are  well  developed,  and  jilaced  at  the 
external  border  of  the  crown.     The  internal   lobe  is  relatively  large. 


432  DENTAL  ANAT03IY. 

and  occupies  a  position  opposite  the  interval  of  the  two  external.  A 
moderate  cingulum  is  developed  on  its  internal  aspect,  and  continues 
around  to  the  outside  of  the  tooth. 

In  the  lower  jaw  the  single  pair  of  incisors  come  close  together  above 
the  symphysis,  and  completely  fill  the  space  between  canines  ;  they  have 
conic  crowns  and  are  smaller  than  the  median  pair  above.  The  canines 
are  larger  than  those  above,  and  like  them  have  pointed,  slightly  re- 
curved apices.  The  premolars  resemble  those  above,  with  the  exception 
that  the  internal  lobe  is  absent.  The  true  molars  are  quadritubercular, 
with  the  two  anterior  slightly  elevated.  A  trace  of  the  anterior  basal 
lobe  is  visible,  and  is  best  marked  in  the  first,  ^^^hich  brings  the  struc- 
ture of  the  tooth  into  close  correspondence  with  the  tuberculo-sectorial 
of  the  Insectivores,  and  strongly  suggests  its  derivation  from  it,  as  so 
many  other  examples  of  a  similar  kind  do.  The  last  molar  displays  a 
fifth  lobe  behind  the  two  posterior  ones,  and  is  therefore  quintituber- 
cular.     This  species  is  the  sole  representative  of  the  family  Tarsiidce. 

In  the  typical  lemurs  of  the  family  Lemuridce  the  two  pairs  of  upper 
incisors  are  separated  from  each  other  by  a  wide  space  in  the  centre,  both 
being  small  and  subequal.  The  superior  canines  are  large ;  the  pre- 
molars, with  the  exception  of  the  first,  have  a  small  internal  cusp. 
The  molars  are  quadritubercular  by  reason  of  the  internal  cingulum 
rising  up  into  a  cusp  at  the  postero-external  angle  of  the  crown. 
Various  intermediate  conditions  betMcen  the  perfect  development  of 
this  cusp  and  its  almost  complete  absence  are  to  be  seen.  The  fourth 
premolar,  too,  is  in  some  genera  like  the  true  molars,  in  which  case  the 
last  molar  is  small. 

The  incisors  of  the  lower  jaw  are  two  in  number  upon  each  side,  and 
are  long,  slender,  laterally  compressed  teeth,  having  a  procumbent 
implantation.  The  canines  resemble  them  very  much  both  in  shape 
and  position,  being  a  little  larger.  The  first  premolar  is  large  and 
caniniform,  and  would  be  readily  taken  for  the  canine  at  the  first 
glance.  The  two  following  are  smaller,  and  usually  have  simple 
crowns.  The  molars  are  truly  quadritubercular,  the  anterior  basal 
lobe  being  entirely  absent.  The  last  molar  may  or  may  not  have 
a  fifth  posterior  tubercle. 

Teeth  of  the  Tillodoxta,  Tvexiodoxta,  and  Daubentoni- 
oiDEA. — The  aye-aye  (Chiromys)  of  Madagascar  is  generally  associated 
with  the  lemurs  in  the  sub-order  Prot^imicc,  but  naturalists — notably 
Profs.  Cope  and  Gill — have  seen  fit  to  give  it  a  rank  equal  to  that  of 
the  lemuroids  and  j^lace  it  in  a  distinct  sub-order,  Dmtbcntonioidea,  on 
account  of  the  aberrant  character  of  its  teeth  as  compared  with  the  lemurs. 
There  are  two  other  Eocene  groups  which  go  ^vith  it  and  constitute  the 
first  division  of  the  order  Buuotheria,  according  to  Cope. 

The  dental  formula  of  the  adult  aye-aye  is,  according  to  Owen,  I.  ]-, 
C.  I",  P.  \,  M.  f  =  18.  The  upper  incisors  are  curved  as  in  the  Roden- 
tin,  and  deejily  implanted  in  the  jaw.  Their  exposed  portions  are  con- 
tiguous, their  widely-excavated  fangs  diverging  as  they  proceed  back- 
ward. The  incisors  of  the  lower  jaw  are  similar  in  shape  to  the  upper 
ones,  and  are  implanted  as  far  back  as  the  coronoid  process.  They 
are  all  covered  with  enamel,  both  in  front  and  behind,  and  grow  from 


TEETH  OF  THE   VERTEBRATA.  433 

persistent  pulp?.  In  the  entire  investment  of  enamel  tliey  offer  an 
important  (litfercnee  from  the  incisors  of  the  rodents,  which  they  other- 
wise closely  resemble.  The  enamel  being  thicker  upon  the  anterior  than 
upon  the  posterior  face  of  the  tooth  causes  them  to  wear  into  chisel- 
shaped  extremities,  whereby  the  same  effective  gnawing  instruments 
are  produced  as  in  the  typical  gnawing  quadrupeds.  The  molar  and 
premolar  teeth  are  four  in  number  upon  each  side  in  the  upper,  and 
three  upon  each  side  in  the  lower,  jaw.  They  are  implanted  after  a 
considerable  interval  behind  the  incisors,  leaving  a  wide  space  or 
diastema,  as  in  the  Rodentla.  The  first  and  last  molars  of  the  upper 
series  are  the  smallest,  and  have  single  roots ;  the  second  and  third 
larger,  and  implanted  by  three  fangs  each.  Their  crowns  have  simple 
subelliptical  grinding  surfaces.  The  molars  of  the  lower  jaw  are  similar, 
the  first  being  implanted  by  two  roots,  the  second  and  third  by  one  each. 

The  deciduous  or  milk  dentition  is  I.  y,  C.  ^,  Pm.  ^  =  12.  In  the 
milk  set  a  small  incisor  appears  upon  each  side  of  the  median  pair,  and 
is  not  replaced  by  a  permanent  one.  Two  teeth  in  this  set  occupy  the 
spaces  between  the  premolars  and  incisors  above,  and  have  been  con- 
sidered canines,  they  having  no  permanent  successors.  The  single  decid- 
uous molar  in  each  jaw  is  succeeded  by  the  permanent  premolar. 

The  TUlodonta  is  a  group  which  was  discovered  and  described  by 
Prof.  O.  C.  jSIarsh  from  the  Upj^er  Eocene  deposits  of  Wyoming  Ter- 
ritory. In  the  typical  genus,  TUlotherium,  the  dental  formula,  as  given 
by  this  author  is,  I.  |,  C.  \,  Pm.  f ,  M.  f  =  34.  The  median  pair  of 
incisors  in  each  jaw  are  large  and  scalpriform,  being  faced  with  enamel, 
as  in  the  rodents.  They  grew  from  persistent  pulps,  as  is  indicated  by 
the  large  pulp-cavities  at  the  base.  The  outer  pair  are  small  and  did 
not  grow  persistently.  The  canines  are  much  reduced,  and  placed  well 
back  in  the  alveolar  border.  The  first  of  the  three  premolars  of  the 
up])er  jaw  is  small  and  simple,  the  other  two  being  larger  and  of  a  more 
complex  ])attern. 

The  structure  of  the  crowns  of  the  superior  molars  is  not  very  differ- 
ent from  that  of  KsfJtoni/x.  Two  external  cusps  are  present,  which  are 
not  well  separated  from  each  other  ;  external  to  them  is  a  broad  cingu- 
lar  portion  which  is  produced  anteriorly  into  a  process  more  marked 
than  in  Esthonyx.  Internally  two  cusps  are  present,  the  posterior  being 
lunate  and  consisting  of  a  highly-developed  cingulum.  In  the  anterior, 
or  that  wliicli  corresponds  with  the  antero-internal  cusp  of  the  quadri- 
tubercular  molar,  two  well-developed  ridges  pass  outward  from  its  sum- 
mit, one  toward  the  anterior,  and  the  other  toward  the  posterior  external 
angle  of  the  crown,  giving  it  a  rounded  U-shaped  appearance.  The 
pattern  of  the  lower  molars  is  identical  with  that  of  Esthony.v} 

In  a  general  survey  of  the  dentition  of  this  genus  I  am  compelled  to 
dissent  from  the  views  expressed  by  Mr.  Tomes,  wherein  he  says  that 
tlie  molar  teeth  are  of  the  ungulate  type,  and  that  the  order  combines 
characters  of  the  Carnivora,  Ungulata,  and  Rodentia.  While  it  is  true 
that  the  scalpriform  incisors  faced  with  enamel  is  a  condition  exhil)ited 
by  the  rodents,  a  condition    also  found  in  the   Toxodonfia,  I  fail   to 

^  See  Professor  Marsh's  monograph  of  this  group,  American  Journal  of  Science  and 
Arti,  vol.  xi.,  ]876,  p.  249. 
Vol.  I.— 28 


434  DENTAL  ANAT03IY. 

discover  the  faintest  trace  of  either  carnivorous  or  ungulate  relation- 
ship. On  the  other  hand,  it  seems  to  me  that  the  evidence  points 
strongly  to  the  fact  that  this  group  is  the  direct  descendant  of  Esthonyx, 
which  preceded  it  in  time.  This  is  especially  seen  in  the  increased  size 
of  the  mesial  pair  of  incisors,  the  reduction  of  the  canines,  loss  of  one 
premolar  in  the  upper  jaw,  and  the  remarkable  similarity  in  the  pattern 
of  the  molar  teeth.  That  Esthonyx  is  an  insectivore  allied  to  the  shrews 
there  is  scarcely  any  doubt.  It  is  also  probable  that  this  group  gave 
origin  to  the  toxodonts,  but  the  exact  connections  between  them  are 
not  now  apparent. 

Another  family,  Sfylinodontidce  of  Prof.  Marsh,  makes  approaches  in 
this  direction  in  the  growth  of  the  molars  as  well  as  the  incisors  from 
persistent  pulps. 

In  the  Tceiiiodontia  the  incisors  are  large  and  scalpriform,  and  were 
of  persistent  growth ;  the  molar  and  premolar  series  are  not  separated 
from  them  by  any  diastema,  in  the  lower  jaw  at  least,  and  the  canines, 
or  those  teeth  regarded  as  such,  in  the  inferior  set  also  grew  from  per- 
sistent pulps,  and  have  grinding  crowns.^ 

Teeth  of  the  Primates  oe  Quadeumana. — The  teeth  of  this 
order  are  closely  affiliated  with  those  of  the  typical  lemuroids  in  the 
structure  of  the  molars,  and  when  compared  with  that  of  the  other 
groups  the  amount  of  dental  variation  is  comparatively  insignificant. 
The  order  is  naturally  divisible  into  five  families,  of  which  the  mar- 
mosets and  platyrrhines  of  South  America  and  the  catarrhines  and 
anthropoids  of  the  Old  World,  as  well  as  man,  constitute  the  respective 
divisions.  Of  these  families,  the  marmosets  (HapalkJce)  are  the  most 
generalized  and  approach  nearest  to  the  lemurs  in  several  important 
characters,  prominent  among  which  are  the  relatively  smooth  cerebral 
hemispheres,  want  of  opposability  of  the  thumb  and  its  termination  by 
a  distinct  claw  instead  of  a  nail,^  and  the  possession  of  tritubercular 
instead  of  quadritubercular  molars.  Since  they  are  found  only  in  the 
New  World,  and  as  lemuroids  were  very  abundant  in  this  country  in 
the  Eocene  Period,  it  seems  probable  that  they  are  the  derivatives  of 
some  member  of  this  group.  It  is  a  fact  worthy  of  notice  that  in  the 
curious  Eocene  genus  Anaptomorphus  we  have  a  near  approach  to  the 
anthrof)oid  condition  of  the  teeth.  In  the  shortness  of  the  jaw  and  cer- 
tain cranial  peculiarities  it  also  resembles  the  higher  monkeys.  For  this 
reason  Cope  believes  that  the  simians  have  descended  directly  from  this 
lemur. 

The  dental  formula  of  the  genus  Midas  is  I.  f,  C.  \,  Pm.  f ,  M.  |-  = 
32,  which  obtains  in  the  one  other  living  genus.  The  upper  incisors 
have  longitudinally  flattened  incisive  crowns,  with  a  prominent  inter- 
nal ledge  at  the  base.     The  median  pair  is  the  larger,  as   is   gener- 

^Prof.  Cope  has  established  this  sub-order  upon  the  peculiar  condition  of  the  canine 
teeth  of  the  lower  jaw,  or  at  least  those  which  he  supposes  to  be  such  ;  the  only  know- 
ledge we  liave  of  tlie  teeth  of  the  upper  jaw  is  confined  to  the  large  scalprii'orm  incisors. 
This  sub-order  must  be  regarded  as  provisional  until  we  know  more  of  the  upper  teeth, 
as  well  as  the  relationship  of  some  genera  api)arently  intermediate  between  it  and  the 
TiUodonia. 

^Many  of  the  lemurs  are  provided  with  an  opposable  thumb,  which  is  terminated  by 
a  distinct  nail.     In  this  respect  the  marmosets  are  even  below  the  lemurs. 


TEETH  OF  THE   VERTEBRATA.  435 

ally  the  case  in  all  the  Primates,  and  are  in  contact  in  the  median 
line.  The  smaller  outer  incisors  follow  closely  in  the  dentigerous 
border  of  the  premaxillaries,  after  which  there  is  a  wide  space,  almost 
equal  to  the  width  of  the  two  incisors,  for  the  passage  of  the  lower 
canine.  The  canines  of  the  upper  jaw  are  comparatively  strong  for  the 
monkeys,  and  have  pointed,  slightly  recurved  croAvns  which  project  far 
above  the  level  of  the  other  teeth ;  there  is  a  deep  groove  upon  their 
anterior  faces. 

The  premolars  or  bicuspids  are  three  in  number,  and  completely  fill 
the  interval  between  the  canines  and  molars.  The  first  is  the  smallest, 
and  has  a  prominent  pointed  external  cusp  on  the  grinding  surface,  to 
which  tlie  cingulum  adds  a  low  U-shaped  internal  portion  ;  the  second 
and  third  are  similar,  except  that  the  internal  lobe  is  no  longer  cingular, 
the  cingulum  furnishing  a  second  internal  ledge.  The  true  molars  are 
two  in  number  upon  each  side,  in  this  respect  differing  from  all  known 
Primates.  The  only  approach  to  this  condition  to  be  met  with  else- 
where in  the  order  is  in  the  dentition  of  man,  in  whom  it  appears,  as 
we  will  hereafter  see,  that  the  last  molar,  or  the  "  wisdom  tooth,"  is 
gradually  becoming  rudimentary  or  defective  in  the  higher  races.  A^ari- 
ous  causes  have  been  assigned  in  explanation  of  this  fact,  one  of  which 
is  that  the  greater  development  of  the  brain  necessitates  the  expenditure 
of  smaller  amount  of  growth-force  upon  the  maxillary  bones,  whereby 
insufficient  room  is  allowed  and  the  tooth  stunted.  If  this  be  the  real 
cause,  it  is  difficult  to  understand  why  in  the  lowest  representatives  of 
the  order — and  those,  too,  in  which  the  cerebral  hemispheres  are  pro- 
portionally the  smallest — the  complete  suppression  of  the  last  molar 
should  have  occurred. 

The  two  pairs  of  lower  incisors  are  small  and  of  the  usual  incisiform 
pattern,  being  consideralily  smaller  than  the  canines.  The  lower  incisors 
of  the  allied  genus,  Hapale,  are  proclivous,  the  canines  being  relatively 
small  and  approximated  to  them,  as  in  the  lemurs,  although  not  to  so 
great  an  extent.  The  canines  are  almost  equal  to  the  upper  ones  in  size, 
and  follow  the  outer  incisors  without  interruption.  The  three  lower 
premolars  are  subequal,  the  summit  of  the  first  being  elevated  above 
the  level  of  the  succeeding  teeth.  In  the  first  the  anterior  basal  lobe,  the 
principal  cone,  and  an  imperfect  heel  can  be  indistinctly  made  out,  while 
in  the  second  and  third  the  internal  tubercle  is  present.  In  the  true 
molars  there  are  four  indistinct  cusps;  the  anterior  basal  lobe  has  almost 
completely  disappeared,  and  all  the  cusps  are  of  equal  height.  A  care- 
ful study  of  unworn  teeth  will  show  them  to  be  a  still  further  modifica- 
tion of  the  tuberculo-sectorial  type,  whereby  the  perfect  quadrituber- 
cular  has  been  produced. 

The  next  division,  Platyrrhines,  or  flat-nosed  monkeys,  constitute  the 
family  Cebidce,  in  which  the  dental  formula  is  I.  |,  C.  \,  Pm.  |,  M.  | 
=  36.  They  belong  to  the  continent  of  South  America,  and  have  pre- 
hensile tails  and  generally  rudimentary  thumbs.  The  canines  are  usually 
strong  and  prominent,  and  the  superior  molars  have  a  well-defined  ridge 
connecting  the  antero-internal  with  the  postero-external  cusps,  a  rem- 
nant of  the  tritubercular  condition.  This  ridge  is  found  with  varying 
constancy  in  the  superior  molars  of  all  the  Primates,  and  marks  the 


436  DENTAL  ANATO^IY. 

connection  between  the  internal  cu:^p  and  the  postero-external  tubercle, 
which  generally  exists  in  the  tritubercular  tooth.  The  postero-internal 
cusp,  which  lies  inside  and  behind  this  ridge,  is  the  last  one  which  has 
been  added  to  complete  the  quadritubercular  tooth  in  the  upper  jaw.  In 
the  squirrel  monkeys  of  this  family  the  lower  incisors  have  a  tendency 
to  be  proclivous,  as  in  Hapale  of  the  marmosets,  thus  retaining  the 
lemurine  character  of  these  parts.  Xo  fossil  remains  of  this  family  are 
known  except  from  very  late  geological  time,  and  these  do  not  difller 
materially  from  those  now  living. 

The  teeth  of  the  Catarrhines  {Semnopithecidce)  show  a  reduction  in 
the  number  of  premolars,  whereby  the  tbrnnda  I.  f,  C.  \,  Pm.  |-,  M.  f 
=  32,  the  same  as  that  of  man,  is  reached.  The  incisors  are  of  the 
same  shape  as  in  man,  the  central  pair  being  considerably  larger  than 
the  outer  pair.  The  canines  are  always  strong  and  powerful  teeth,  and 
their  apices  are  always  elevated  above  the  other  teeth.  They  reach  their 
maximum  of  development  in  the  baboons,  more  especially  in  the  dog- 
headed  baboon,  Ci/nocephalus,  in  which  they  are  deeply  grooved  ante- 
riorly. In  this  group  the  first  premolar  below  is  implanted  by  a  double 
fang,  with  its  apex  directed  upward  and  backward.  The  anterior  root 
is  naked  for  some  distance,  and  presents  in  front  a  blunt  edge  Avliich 
bites  against  the  posterior  edge  of  the  powerful  superior  canine,  giving 
to  this  part  of  the  jaw  a  peculiar  and  characteristic  appearance.  The 
second  lower  premolar  of  Cynocephalus  is  quadritubercular,  with  all  the 
cusps  well  developed,  but  in  the  macaques  the  posterior  tubercles  are 
not  well  defined.  Both  the  ujiper  and  lower  true  molars  increase  in  size 
from  the  first  to  tlie  last,  the  last  lower  one  being  distinctly  five-lobed. 

In  the  semnopithiques  the  incisors  are  more  nearly  equal  in  size ;  the 
canines  are  smaller  and  less  deeply  grooved  than  in  the  baboons  ;  the  first 
and  second  molars  are  subequal,  while  the  last  lower  molar  is  propor- 
tionally narrower,  but  still  retains  the  fifth  lobe.  The  typical  cerco- 
pithiques  have  the  last  lower  molar  quadritubercular  and  all  the  molars 
subequal.  Fossil  remains  of  this  family  are  known  from  the  Miocene 
and  Pliocene  deposits  of  Europe  and  Asia,  but  no  characters  of  unusual 
importance  occur  in  their  dentition. 

The  next  family  of  this  order  includes  the  anthropoid  or  tailless  apes, 
which  are  also  confined  to  the  tropics  of  the  Old  World.  They  consti- 
tute the  family  Simiidcp,  and  are  distinguished  from  the  preceding  fam- 
ily, CcrcopitheclcJcc,  principally  by  the  absence  of  the  tail ;  from  the  suc- 
ceeding family,  Homimdce,  by  the  circumstance  that  the  hallux  is  oppos- 
able, whereas  in  the  latter  it  is  in  a  line  with  the  other  digits  and  is  not 
opposable.  Other  characters  of  considerable  anatomical  importance  are 
also  found  which  distinguish  them  from  man. 

The  teeth  of  this  family  are  the  same  in  number  as  those  of  man, 
but  considerable  differences  are  found  in  the  relative  size  of  the  canines 
and  the  last  molar  when  compared  M'ith  that  which  obtains  in  the 
human  subject.  Although  they  are  organized  substantially  upon  the 
same  plan,  the  teeth  are  larger  and  stronger  than  in  man.  The  orang 
(Simla  i^afjfnts)  is  j)robably  the  most  human-like  in  its  dentition,  although 
in  other  respects  the  gorilla  and  chimpanzee  most  resemble  man.  The 
molar  teeth  in  this  animal  are  remarkable  for  the  straight  line  in  which 


TEETH  OF  THE    VERTEBRATA.  437 

they  are  implanted  in  both  jaws,  and  contrast  with  tlie  graceful  curve 
they  pursue  in  the  normal  human  mouth. 

The  median  pair  of  incisors  are  larger  both  above  and  below ;  in  the 
upper  jaw  they  are  more  than  twice. the  size  of  the  lateral  pair,  Avhile  in 
the  lower  jaw  they  are  more  nearly  equal.  Between  the  lateral  pair 
and  the  canine  above  there  is  a.  considerable  space,  into  which  the  lower 
canine  bites.  The  canines  are  relatively  large,  and  their  apices  rise  far 
above  the  level  of  the  surrounding  teeth.  They  are  imperfectly  trihe- 
dral in  form,  with  a  trenchant  edge  behind.  These  teeth  are  larger  in 
the  male  than  in  the  female. 

The  premolars  or  bicuspids  differ  from  those  of  man  in  the  upper 
jaw  in  being  implanted  by  three  roots  like  the  molars ;  their  crowns 
are  very  similar  to  those  of  man,  presenting  essentially  the  same  ele- 
ments. The  pattern  of  the  crowns  of  the  molars  is  like  that  of  the 
human  subject  both  above  and  below,  but  the  last  molar  is  as  large  as 
the  others ;  it  is  implanted  by  three  roots,  and  is  always  perfectly  formed. 
In  the  lower  jaw  the  two  posterior  molars  slightly  exceed  the  first  in 
size,  and  the  last  is  distinctly  five-lobed.  The  first  lower  premolar  is 
two-rooted,  and  has  a  faint  resemblance  to  the  corresponding  tooth  in 
the  baboons.  The  second  is  also  implanted  by  two  roots,  and  its  crown 
agrees  with  that  of  man. 

In  the  other  genera  minor  differences  only  are  to  be  met  with  in  the 
form,  pattern,  and  arrangement  of  these  organs. 


The  Human  Dentition. 

In  this  connection  we  come  next  to  consider  the  teeth  of  man  ;  and 
before  so  doing  I  am  constrained  to  make  some  general  remarks  in 
regard  to  the  position  he  occupies  in  the  zoological  scale.  While  it  is 
undeniable  that  by  virtue  of  his  superior  brain-capacity  and  intellectual 
development  man  is  to  be  accorded  a  place  at  the  head  of  the  animal 
kingdom,  it  is  nevertheless  true  that  much  of  his  anatomical  structure 
has  not  been  specialized  beyond  that  of  many  of  the  lower  forms.  The 
fact  that  different  members  of  the  mammalian  sub-class  have  been  mod- 
ified in  different  directions,  some  to  fit  one  environment  and  some 
another,  has  led  to  the  specialization  of  different  sets  of  organs,  and 
that,  moreover,  in  different  ways  as  the  surrounding  conditions  and 
particular  exigencies  of  the  case  have  required. 

It  is  these  differences  which  enable  the  naturalist  to  construct  zoologi- 
cal definitions  of  the  major  or  minor  groups,  such  as  orders,  sub-orders, 
families,  genera,  etc.  The  impracticability  of  determining  which  ani- 
mal is  highe.^^t  or  lo^west  in  the  scale  of  organization  is  thus  rendered 
apparent  from  the  fact  that  a  comparison  of  different  sets  of  organs  is 
involved.  Thus,  in  their  dental,  digestive,  and  limb  structure  the 
ungulates  surpass  all  other  Mammalia  in  complexity  and  specialization, 
and  in  these  respects  may  be  said  to  be  highest,  wdiile  in  the  matter  of 
brain-development  they  are  much  inferior  to  others.  The  monkey  line 
or  Primates,  on  the  other  hand,  of  which  man  is  at  the  head,  retain  a 
comparatively  generalized  structure  of  the  limbs,  teeth,  and  digestive 


438  DENTAL  ANAT03IY. 

organs,  but  have  outstripped  all  others  in  the  development  of  the  cere- 
bral nervous  system. 

It  is  only  upon  an  evolutionary  basis  that  we  are  enabled  to  compre- 
hend the  significance  and  import  of  the  manifold  modifications  with 
which  the  morphologist  is  called  upon  to  deal,  and  it  is  not  at  all  un- 
natural that  in  the  consideration  of  the  human  or  any  other  dentition 
the  student  should  first  of  all  bend  his  energies  to  the  discovery  of  the 
relative  position  which  his  subject  holds  in  the  system.  All  the  evi- 
dence which  anatomical  and  pala?ontological  science  can  now  bring  to 
bear  on  the  question  tends  to  show  that  man  is  the  legitimate  product 
and  highest  expression  of  the  evolutionary  forces  in  that  line  of  devel- 
opment which  began  with  the  Eocene  lemuroids,  however  objectionable 
this  conclusion  may  be  to  many.  No  adequate  conception  of  his  place 
in  nature  or  the  structure  of  any  set  of  his  organs  can  be  had  without 
a  comparison  with  the  other  members  of  the  stem  to  which  he  naturally 
belongs.  This  reason  alone  has  induced  me,  somewhat  contrary  to  cus- 
tom, to  give  an  account  of  the  human  dentition  in  this  situation,  rather 
than  at  the  latter  part  of  the  present  article. 

Looked  at  from  the  point  of  view  of  the  comparative  odontologist, 
these  organs  present  little  of  general  morphological  interest  beyond  that 
displayed  by  other  Primates ;  but  from  the  practical  standpoint  of  the 
operative  dentist  they  are  of  the  greatest  importance.  In  the  course 
of  this  account  many  questions  in  connection  with  this  latter  phase  of 
the  subject  will  doubtless  suggest  themselves  to  the  reader  which  are  not 
within  the  scope  of  the  present  ]>art  of  the  work  to  discuss,  its  object 
being  merely  to  outline  the  anatomy. 

The  dental  formula  of  the  human  subject  is,  normally,  I.  f,  C.  \, 
Pm.  I,  M.  I  =  if  =  32,  the  same  as  that  found  in  the  Old  World 

monkeys.     Much  variation  from  this  num- 
"  ber  exists,  however,  by  reason  of  the  failure 

of  development  of  the  superior  lateral  inci- 
sors and  of  the  third  molars,  the  wisdom 
teeth  or  denies  mpientkv;  these  molars  may  be 
present  in  the  upper  or  lower  jaw  only,  or  they 
may  fail  to  develop  on  one  side  in  one  or 
both  jaws,  or,  again,  they  may  be  completely 
aborted.  These  variations  are  most  fre- 
quently met  with  in  the  higher  races  of  man- 
kind, and  are  said  to  be  of  rare  occurrence  in 
the  inferior  races.  The  teeth  are  implanted 
in  the  alveolar  process  in  such  a  manner  in 
both  jaws  as  to  describe  a  regular  parabolic 
curve,  being  uninterrupted  at  any  point  by 
the   intervention   of  diastemata    or    spaces. 

Superior  Maxillary  Bone  of  Man.         —,,  -^  i^    ji  i  i_ 

Ihe  summits  ot  the  crowns  have,  when 
normally  developed,  approximately  the  same  level,  the  canines  not 
excepted,  thereby  aifording  a  marked  contrast  with  the  apes  and  mon- 
keys, in  which  the  crowns  of  the  canines  are  always  more  elevated  than 
the  other  teeth. 

The  incisors  are  four  in  number  in  each  jaw,  those  of  the  upper  being 


TEETH  OF  THE   VERTEBRATA.  439 

implanted  in  the  premaxillary  bones,  which  at  an  early  period  coalesce 
with  the  maxillaries.  Of  these,  the  central  pair  is  the  larger  and  has  a 
slightly  more  anterior  position  than  the  lateral  ones,  on  account  of  the 
curve  of  the  alveolar  border.  Their  incisive  nature  is  manifested  by 
the  possession  of  a  crown,  which  is  bevelled  on  its  palatine  or  lingual 
surface  ^  to  a  cutting  edge,  being  broader  at  the  extremity  than  at  the 

Fig.  216. 


luferior  Maxillary  Bone  of  Man. 

base.  The  adjacent  teeth  are  in  contact  at  their  coronal  extremities,  but 
on  account  of  the  narrower  base  a  slight  interval  appears  between  them 
at  the  margin  of  the  gum.  The  root  joins  the  crown  without  any 
marked  constriction,  so  that  a  neck  can  scarcely  be  said  to  exist ;  from 
this  point  it  tapers  gradually  to  an  obtuse  termination,  being  imperfectly 
trihedral  in  form  and  slightly  recurved. 

In  newly-erupted  teeth  the  cutting  edge  of  the  crown  is  divided  into 
three  inconspicuous  cusps,  which  soon  disappear  through  wear,  leaving 
it  smooth.  The  basal  termination  of  the  crown  is  indicated  by  the  limit 
of  the  enamel  covering,  which  is  of  greater  vertical  depth  on  the  labial 
and  palatine  or  lingual  than  on  the  lateral  faces,  so  that  if  a  line  be 
drawn  around  the  tooth  at  the  most  extreme  basal  portion  of  the 
enamel,  it  will  touch  only  the  labial  and  palatine  prolongations,  and 
not    mark  its  exact  limit  on  the   mesial  and   distal    surfaces.     These 

^  Tlie  nomenclature  of  tlie  various  surfaces  of  a  tooth  as  it  stands  in  position  in  the 
jaw,  it  seems  to  me,  is  simplified  by  employing  terms  with  tlie  following  signification : 
if  the  tooth-line  were  straightened  out  upon  each  side,  the  surface  which  looks  away 
I'rom  the  condyle  would  be  anterior,  and  that  which  is  directed  toward  it  would  be  pos- 
ierior  ;  the  surface  directed  toward  the  median  line  of  the  mouth  would  be  internal,  and 
that  directed  away  from  it  external.  In  this  system  some  confusion  may  arise  with 
respect  to  the  incisors  and  canines,  in  whicli  tlie  anterior  surface  is  internal  and  con- 
versely, owing  to  the  curvature  of  tlie  tootli-line ;  but  while  it  has  appeared  to  me  best 
to  speak  of  the  surfaces  as  if  tlie  tooth-line  were  straight,  I  have  in  this  paper  adopted 
terms  now  most  familiar  to  the  dental  profession,  which  are  represented  by  the  follow- 
ing: The  sui-face  looking  toward  the  anterior  part  of  the  mouth  and  median  line  is 
called  the  mesial  surface;  its  opposite,  looking  toward  tlie  condyle,  the  distal  surface. 
In  the  superior  row  the  surface  which  has  been  designated  the  internal  I  shall  term 
the  palatal  ,  and  in  the  inferior  row  tlie  lingual,  while  the  external  surface  is  the  buccal 
for  the  molars  and  bicusi)ids,  and  labial  for  the  incisors  and  cuspids  or  canines. 
The  triturating  surfaces  of  the  molars  and  bicuspids  are  termed  the  masticating  snrfiices, 
while  the  incisive  surfaces  of  the  incisors  and  cuspids  or  canines  are  denominated  the 
catting  edges. 


440 


DENTAL  ANATOMY. 


Fig.  21 ; 


A  Left  L'pper  Central  In- 
cisor of  Man  :  a,  external 
or  labial  aspect ;  b,  inter- 
nal or  lingual  aspect. 


projections  of  the  enamel  present  convex  outlines  basally,  and  are 
separated  from  each  other  by  two  wide  V-shaped  notches  occupying 
the  mesial  and  distal  faces. 

The  labial  aspect  of  the  crown  is  convex  from  side  to  side,  as  well 
as  from  above  downward,  and  is  of  great'cr  vertical  than  transverse 
extent.  Upon  either  side  the  crown  is  triangular 
in  form,  with  the  apex  of  the  triangle  terminating 
at  each  free  angle  of  the  cutting  extremity,  and  the 
base  directed  toward  the  root ;  the  basal  part  of  the 
triangle  is  interrupted  by  the  V-shaped  notch  already 
alluded  to.  That  lateral  surface  which  is  directed 
toward  the  median  line  (mesial)  is  comparatively 
flat  and  most  produced  at  the  extremity,  while  the 
one  which  looks  away  from  the  median  line  (distal) 
is  more  rounded,  having  its  terminal  angle  less  pro- 
duced. The  interior  or  palatine  surface  is  also  tri- 
angular, but  the  base  is  formed  by  the  free  cutting 
edge  and  the  apex  turned  toward  the  root.  Usually,  this  surface  is 
nearly  flat,  but  in  some  examples  it  presents  a  broad  central  concavity 
whose  depth  may  be  considerably  augmented  by  the  presence  of  two 
marginal  ridges  meeting  at  the  radicular  extremity  or  apex  of  the  tri- 
angle. These  ridges,  which  are  homologous  with  the  cinguhim  of  other 
teeth,  sometimes  develop  a  small  cusp  at  their  point  of  junction,  in  front 
of  which  there  is  usually  a  deep  i)it  in  the  enamel — "  a  favorite  site  for 
caries."  As  a  general  rule,  the  cingulum  is  but  faintly  marked,  and  the 
posterior  or  palatine  face  is  slightly  concave. 

The  lateral  incisors  of  the  upper  jaw  are  smaller  than  the  median  pair, 
but  have  approximately  the  same  form.  The  labial  face  is  more  convex 
from  side  to  side,  and  the  outer  or  distal  angle  of  the  cutting  edge  is 
much  more  rounded  off  than  in  the  median.  The  lingual  surface  may 
be  slightly  concave  from  above  downward,  and  convex  in  the  opposite 
direction,  without  any  trace  of  the  cingulum,  or,  as  is  most  generally 
the  case,  it  is  concave,  with  the  cingulum  present,  and  elevated  into  a 
small  cusp  at  the  point  of  junction  of  the  two  lateral  ridges.  The 
basilar  contour  of  the  enamel  covering  is  the  same  as  in  the  preced- 
ing tooth.  The  root  is  more  compressed  laterally,  of  relatively  greater 
length,  and  tapers  more  gradually  to  its  termi- 
nation, giving  to  the  tooth  a  more  slender  and 
less  robust  appearance. 

The  ])ulp-cavities  of  these  two  teeth  have  sub- 
stantially the  same  shape,  and  the  description  of 
one  will  answer  for  that  of  both.  Its  form  is 
that  of  an  elongated  tube,  gradually  increasing 
in  diameter  from  the  apical  foramen  in  the  apex 
of  the  root  to  a  point  which  nearly  coincides 
with  the  summit  of  the  V-shaped  notch  in  the 
enamel  on  the  lateral  surface  of  the  crown,  where  it  becomes  contracted 
in  an  antero-posterior  direction,  but  enlarged  in  its  transverse  diameter. 
It  is  ]irolonged  upon  either  side  into  a  slight  cornua,  which  reaches  but  a 
short  distance  bevond  the  level  of  the  general  cavitv  :  the  one  which  cor- 


A    Lower    Incisor    of   Man: 
anterior,  and  ft,  lateral  view 


*  TEETH  OF  THE    VERTEBRATA.  441 

responds  to  the  internal  or  mesial  angle  of  the  cutting  edge  of  the  crown 
is  a  little  the  longer  of  the  two. 

The  two  pairs  of  lower  incisors  reverse  the  condition. of  the  superior 
set,  in  that  the  central  ones  are  the  smallest.  Their  crowns  have  sub- 
stantially the  same  pattern  as  those  in  the  upper  jaw,  with  the  exception 
that  an  internal  or  lingual  cingulum  is  never  developed.  They  are  readily 
distinguished  from  those  above  by  their  smaller  size  and  greater  lateral 
flattening  of  the  roots.  The  pulp-cavity  and  basal  enamel  contour  are 
like  the  corresponding  teeth  above. 

The  cuspids,  canines,  or  "  eye  teeth,"  are  the  next  in  order  behind  the 
incisors  ;  in  both  jaws  they  completely  fill  the  gap  between  these  latter 
teeth  and  the  bicuspids,  being  in  contact  with  yig.  219. 

them  at  the  mesial  and  distal  extremity  of  the 
crown.  They  are  in  every  way  stronger  and 
more  robust  than  the  incisors,  and  are  im- 
planted by  roots  W'hose  length,  proportionate 
to  that  of  the  crown,  is  much  greater.  In  the 
upper  jaw  these  are  indicated  on  the  external 
surface  of  the  maxillary  bone  by  a  vertical 
ridge  or  swelling  which  in  many  skulls  extends 
quite  as  high  as  the  lower  border  of  the  ante- 

^.     ^  ^  A  Left  Superior  Human  Canine: 

nor    nareS.  «,    external,    and    h,   internal 

The  crown  is  terminated  by  an  obtuse  point,  ^'^"'' 
which  has  a  position  in  a  line  with  the  longitudinal  axis  of  the  root. 
Upon  either  side  of  this  cusp  the  terminal  extremity  slopes  away,  but 
still  retains  a  blunt  cutting  edge.  When  the  median  cusp  is  reduced  by 
wear  the  crown  does  not  look  very  much  unlike  that  of  an  incisor ;  its 
labial  or  external  face  is  broader  above  than  below, ^  and  convex  in  both  a 
transverse  and  a  longitudinal  direction,  as  in  the  incisors  ;  the  palatal  or 
internal  surface  is  also  bevelled,  and  the  lateral  surfaces  (mesial  and 
distal),  or  those  which  lie  adjacent  to  the  contiguous  teeth,  are  likewise 
somewhat  triangular  in  form,  but  more  rounded.  In  the  superior 
canines  a  slight  ridge  descends  upon  the  external  or  labial  face  from 
the  summit  of  the  terminal  cusp  to  the  neck,  but  is  absent  in  the 
corresponding  teeth  below. 

The  internal  or  palatine  aspect  is  slightly  convex  from  side  to  side, 
but  concave  from  above  downward.  The  palatine  convexity  is  occa- 
sioned by  a  well-marked  vertical  ridge  which  extends  from  the  summit 
of  the  terminal  cusp  to  the  cingulum  below ;  this  latter  structure  is 
usually  well  defined,  being  stronger  in'the  upper  than  in  the  lower  teeth. 
There  is,  as  a  general  rule,  a  prominent  basal  cusp  at  the  junction  of 
the  two  lateral  ridges  which  connects  with  the  vertical  ridge,  leaving  a 
deep  pit  upon  either  side — a  spot  where  caries  very  frequently  occurs. 

As  already  stated,  the  extremity  of  the  crown  slopes  away  upon  either 

^  When  the  terms  above,  below,  superior,  and  inferior  are  used  in  connection  with  a 
single  tooth,  they  refer  to  the  free  as  opposed  to  the  implanted  extremities :  in  the 
upper  jaw  the  part  of  the  crown  which  is  really  above  is  that  which  joins  the  root,  but 
in  tlie  lower  jaw  it  is  the  reverse  of  this.  It  is  convenient  to  use  these  terms  for  all 
teeth,  as  they  correctly  apjily  to  tlie  lower  teeth,  so  that  when  we  s[)eak  of  the  superior 
extremity  of  the  crown,  the  free  or  terminal  part  is  meant,  whether  it  belong  to  the 
upper  or  lower  jaw. 


442  DENTAL  ANATOMY. 

side  of  the  median  cusp ;  that  side  which  lies  next  to  the  premolars  or 
bicuspids  is  longer  than  that  which  is  directed  toward  the  incisors,  so 
that  the  distal  or  posterior  moiety  is  greater  than  the  mesial  or  anterior. 
This  inequality  of  the  two  sides  exists  in  both  pairs  of  the  canines,  being 
less  marked  in  the  lower  than  in  the  upper ;  it  furnishes  a  very  useful 
rule  by  which  a  canine  can  be  referred  without  difficulty  to  its  proper 
side  of  the  mouth. 

The  inferior  cuspids  or  canines  differ  principally  from  those  above  in 
the  shorter  root,  blunter  median  cusp,  and  less-marked  posterior  or  lin- 
gual cingulum  and  basal  cusp.  The  roots  of  both  are  thicker  labially 
than  lingually,  and  are  generally  traversed  by  a  vertical  groove  upon 
either  side. 

The  bicuspids  or  premolars  are  four  in  number  in  each  jaw,  and  afford 
a  further  complication  of  the  pattern  of  the  crown  by  reason  of  the  ele- 
vation of  the  basal  cingulum  into  a  strong  in- 
FiG.  220.  ternal  cusp.     In  proportion  as  this  part  of  the 

crown  is  well  marked  and  complicated,  there  is 
a  corresponding  disposition  to  increase  in  the 
number  of  roots  or  fangs.  These  teeth,  as  their 
name  implies,  are  provided  with  two  cusps  to  the 
crown ;  those  of  the  superior  set  are  of  subequal 
dimensions  and  considerablv  exceed  the  lower 

First  Upper  Bicuspid  or  Pre-  .  .  ^tm  <•   ji       i  •  •  i         i 

molar  of   Wan:   o,  vertical       OUCS    lU    SlZC.        illC    CrOWU  ot    tllC   blCUSpid,  whCU 

view  of  the  crown;  6,  lateral  ^,-^^^,^^1  vertically,  prescuts  au  imperfectly  quad- 
rate outline,  which  is  most  distinct  in  the  second, 
and  are  broader  than  long.  Two  strong  cusps,  of  which  one  is  exter- 
nal and  the  other  internal,  occupy  the  grinding  face,  and  are  separated 
by  a  deep  notch  or  valley,  deepest  in  the  centre.  The  anterior  and  pos- 
terior margins  of  this  valley  are  bordered  by  slight  ridges  which  con- 
nect the  anterior  and  posterior  extremities  of  the  cusps ;  the  anterior  of 
these  is  a  little  more  elevated  than  the  posterior,  and  forms  a  useful 
guide  in  determining  the  mesial  and  distal  surfaces  of  the  tooth,  and 
consequently  the  side  of  the  jaw  to  which  it  belongs.  In  some  instances 
the  enamel  forming  the  floor  of  the  valley  and  adjacent  sides  of  the 
cusps  and  ridges  is  quite  smooth,  but  most  frequently  it  is  considerably 
wrinkled  and  thrown  into  a  number  of  minor  cusps  and  ridges,  -with 
intermediate  indentations  which  offer  receptacles  for  the  lodgment  of 
food. 

Of  the  two  cusps,  the  external  is  slightly  the  larger  and  more  ele- 
vated ;  it  likewise  has  a  greater  'antero-posterior  extent.  Its  form  is 
very  much  like  the  entire  crown  of  the  cuspid,  terminating  superiorly 
in  a  median  cusp,  from  which  the  cutting  edge  gradually  slopes  away 
upon  either  side.  The  internal  vertical  rib  is  also  present,  but  the 
external  is  absent.  The  internal  or  palatine  cusp  is  thicker  transversely 
than  the  buccal,  and  is  more  rounded.  On  account  of  the  connecting 
ridges  it  has  somewhat  of  a  crescentic  pattern. 

Commonly,  there  is,  to  all  a])])earance,  but  a  single  root,  which  is 
traversed  upon  the  mesial  and  distal  faces  by  vertical  grooves  which 
may  unite  near  the  apex,  causing  it  to  become  divided.  These  vertical 
grooves  are  the  external  indication  of  two  pulp-cavities  in  the  implanted 


TEETH  OF  THE   VERTEBRATA. 


443 


Fig.  221. 


Second  Lower  Human  Hicus- 
pid :  n,  li,  vertical  and  lat- 
eral views. 


extremity,  which  unite  about  midway  of  the  root,  and  are  thence  con- 
tinued upward  into  the  crown  as  a  common  cavity.  The  cavity  thus 
formed  is  of  greater  transverse  than  antero-posterior ^  extent;  in  the 
vicinity  of  the  neck  it  is  httle  more  than  a  narrow  transverse  fissure, 
which  widens  somewhat  above,  and  is  prolonged  into  two  cornua  corre- 
sponding to  the  two  cusps.  The  external  of  these  is  the  larger  and  most 
elevated. 

While  this  condition  of  the  roots  and  pulp-cavity  is  the  one  usually 
to  be  met  with,  nevertheless  two  roots  are  frequently  found  in  the 
first  bicuspid,  and  three  roots  are  occasionally 
developed,  two  of  which  support  the  outer  cusp  ; 
the  pulp-cavity  has  then,  of  course,  three  divis- 
ions. 

The  principal  differences  between  the  upper 
and  lower  bicuspids  or  premolars  are  seen  in  the 
size  of  the  internal  cusp  as  compared  with  the 
external,  the  more  cylindrical  form  of  the  root, 
and  the  almost  complete  absence  of  the  vertical 
grooves,  on  account  of  which  the  pulp-cavity 
is,  as  a  general  rule,  single.  The  crown  con- 
sists of  a  large,  somewhat  conical  external  cusp,  very  convex  without, 
to  which  is  added  a  low  lunate  internal  cingular  ridge.  The  internal 
vertical  ridge  of  the  external  cusp  joins  this  cingulum  near  its  central 
portion,  leaving  a  deep  pit  upon  either  side  where  the  destructive  agen- 
cies of  decay  on  the  crowns  of  these  teeth  exhibit  themselves  most  fre- 
quently. The  degree  to  which  this  vertical  rib  is  developed  is  subjected 
to  great  variation  ;  it  may  be  almost  entirely  absent  in  some  individuals 
or  strongly  developed  in  others.  The  crown  of  the  second  or  posterior 
bicuspid  or  premolar  is  more  quadrate  in  outline  than  the  anterior  or 
first ;  the  internal  cusp  is  better  developed,  and  frequently  shows  a  tend- 
ency to  form  two. 

The  normal  number  of  true  molars  is  twelve,  three  on  either  side  in 
each  jaw,  but,  as  already  remarked,  the  last  in  both  series  may  be  absent. 
In  a  series  of-  adult  skulls  of  various  civilized  races  which  I  have 
examined,  twelve  out  of  forty  had  one  or  both  of  these  teeth  wanting 
from  the  upper  series,  and  in  the  lower  jaw 
the  proportion  was  ten  to  thirty.  It  is  highly 
probable  that  in  many  of  these  cases  these 
teetli  had  been  j^resent,  but  had  disappeared 
early  in  life.  Many  examples  could  be  cited 
in  which  the  last  or  third  molars  wholly  fail 
to  be  erupted,  and  it  is  established  upon  good 
authority  that  in  many  families  one,  two,  or 
all  of  these  teeth  are  habitually  absent  from 
generation  to  generation. 

In  the  lower  jaw  the  three  molars  in  the 
more  typical  lower  races  are  equal  in  size  and  sub.stantially  alike  in  pat- 
tern ;  their  crowns  are  quadrangular  in  section,  with  the  angles  consider- 

^  By  antero-posierior  in  this  connection  is  meant  the  diameter  whicli  corresponds  with 
ihe  long  axis  of  the  jaw. 


Fig. 


I'irst  Lower  Human  Molar  :  a,  verti- 
cal view  of  the  crown  ;  1.  anterior; 
2,  postal ioi-  aspect;  l>,  side  view. 


444-  DENTAL  ANATOMY. 

ai)ly  rounded  off.  They  support  four  principal  cusps,  as  in  the  quadri- 
tubereular  molar  generally,  together  Mith  a  hfth  one  behind,  which  is 
strictly  homologous  with  the  heel  of  these  teeth  in  the  more  generalized 
members  of  the  Primate  section.  These  are  separated  by  four  distinct 
fissures  arranged  in  the  form  of  a  cross  ;  where  the  two  limbs  cross  each 
other  they  widen  out  into  a  median  valley  deepest  in  the  centre.  The 
longitudinal  of  these,  or  the  one  which  separates  the  external  from  the 
internal  principal  cusps,  terminates  in  a  posterior  bifurcation  which  con- 
stricts off  the  tifth  cusp  or  heel.  The  enamel  lining  this  valley  is,  in 
perfectly  unworn  teeth,  much  corrugated,  so  that  it  is  sometimes  difficult 
to  distinguish  the  principal  cusps. 

They  are,  with  the  exception  of  the  last  or  third  molar,  implanted  by 
two  antero-posteriorly  flattened  roots,  which  join  the  crown  at  the  mod- 
erately well-defined  neck.  These  may  be  connate,  having  the  two  roots 
indicated  only  by  a  vertical  groove  upon  either  side.  Each  root  is  hol- 
lowed out  in  the  centre  to  receive  the  radicular  portion  of  the  pulp,  the 
cavity  corresponding  with  the  external  form  of  the  root.  These  unite 
into  a  common  cavity  above,  Mhich  at  about  the  time  the  tooth  is  erupted 
is  relatively  very  large,  but  which  becomes  smaller  with  age,  and  is  final- 
ly in  old  age  obliterated  through  progressive  calcification.  The  body 
of  the  cavity  is  terminated  superiorly  by  cornua  corresjjonding  k)  the 
fiv^e  cusps  of  the  crown ;  of  these  the  tAvo  anterior  are  most  prolonged, 
and  reach  slightly  above  the  inferior  limit  of  the  outer  enamel  covering. 

In  the  higher  races  the  last  or  third  molar  is  usually  smaller  than  the 
first  and  second,  and  does  not  have  the  cusp  so  well  defined ;  but  in 
many  of  the  negro  skulls  I  have  examined  it  is  nearly  as  large,  and 
quite  as  well  formed,  as  the  two  anterior  to  it.  This  tooth  is  more 
constant,  both  as  regards  presence  and  form,  than  the  corresponding 
tooth  above.  It  is,  as  .a  rule,  two-rooted,  but  these  roots  may  be 
confluent,  in  which  case  two  vertical  grooves  mark  a  tendency  in  this 
direction. 

The  superior  molars,  like  those  in  the  lower  jaw,  are  three  in  num- 
ber, and  have  quadritubercular  crowns  normally,  but  many  examples 
can  be  found  in  which  the  postero-internal  cusp,  the  last  one  added  in 
the  quadritubercular  molar,  is  little  more  than  a  cingulum,^  and  is 
scarcely  entitled  to  the  appellation  of  a  cusp.  In  such  cases  it  fre- 
quently lias  a  position  internal  to  the  antero-internal  cusp,  and  all 
stages  between  that  and  its  normal  position  are  to  be  met  with. 

The  grinding  face  of  the  crown  is  of  a  squarish  form,   bearing  a 

^  It  is  probable  that  this  condition,  of  which  I  have  seen  a  number  of  examples  in 
the  liigher  races,  is  a  degenerate  one,  and  is  an  effort  to  return  to  the  tritubercular 
stage.  Dr.  Harrison  Allen,  in  a  communication  to  the  Academy  of  Natural  Sciences 
of  Philadeli)hia,  has  recently  called  attention  to  the  fact  that  in  senile  changes  those 
structures  which  hare  l)een  added  last  in  the  course  of  evolutionary  growth  are  the 
first  to  disappear.  Although  this  condition  cannot  be  said  to  be  in  any  way  depend- 
ent upon  individual  senility,  it  is  in  all  probability  the  residt  of  senility  of  the  race, 
Avherein  retrogressive  modifications  of  any  set  of  organs  are  first  apparent  in  those 
parts  which  were  the  last  to  appear.  It  should  be  stated  here  that  to  Dr.  Allen  is  due 
the  credit  of  liaving  prcjiarcd  the  way  for  all  the  more  important  generalizations  that 
liave  been  made  in  regard  to  the  evolution  of  the  quadritubercular  tooth  from  the  more 
primitive  ty})es.  He  demonstrated  that  the  postero-internal  cusp  of  the  human  molar 
is  an  outgrowth  from  the  cingulum. 


TEETH  OF  THE   VERTEBRATA.  445 

cusp  at  each  angle.  Of  the  two  external,  the  anterior  is  slightly  the 
larger,  and  is  usually  connected  with  the  antero-internal  by  a  strong 
ridge  which  skirts  the  anterior  margins  of  the  crown.  The  posterior 
is  separated  from  it  by  a  fissure  which  terminates  internally  in  the 
median  valley ;  it  is  also  connected  with  the  antero-internal  cusp  by  a 
rido;e,  the  oblique  ridge.     From  its  posterior 

•  11     1         11-  1  •  Fif    '''^^ 

margin  a  well-developed  cmgulum  passes  in-  "" 

ward  on  the  posterior  border  of  the  crown  to 
join  the  postero-internal  cusp,  of  which,  as 
already  remarked,  this  latter  is  a  part. 

The  antero-internal  cusp  is  the  largest  of 
the  four,  and  by  reason  of  its  union  with 
the  cross-ridges  above  mentioned  has  a  some- 
what crescentic  appearance.     It  is  placed  at  ^""■''eS';nd""™S°vie\v."^^ 
the  apex  of  a  V  which  opens  externally  and 

encloses  the  median  valley.  The  postero-internal  cusp  in  the  sjiecimen 
figured  stands  a  little  posterior  and  internal  to  the  last  mentioned,  being 
separated  from  it  by  a  deep  groove  ;  it  is  little  more  than  an  enlargement 
of  the  strong  posterior  (unguium. 

The  roots  are  three  in  number,  of  which  two  are  external  or  buccal, 
and  support  the  two  outer  cusps,  and  one  internal  or  lingual,  supporting 
the  two  internal  cusps.  The  two  outer  are  not  unfrequently  connate, 
in  which  case  the  line  of  separation  of  the  radicular  portions  of  the 
j)ulp-cavities  is  indicated  by  a  vertical  groove.  The  palatine  is  the 
largest  and  longest  root  of  the  three. 

While  the  structure  here  described  usually  obtains  in  the  first  and 
second  molars,  the  last  is  more  simple  and  variable.  In  the  more  civil- 
ized races  it  is  exceptional  for  these  teeth  to  be  regular  either  in  form  or 
position,  so  great  is  their  variability.  The  crown  resembles  in  a  gen- 
eral way  those  of  tlie  first  and  second  molars,  except  that  the  oblique 
ridge  is  generally  absent  and  the  two  internal  cusps  are  blended  together. 
The  roots  are  connate  and  somewhat  curved  at  their  implanted  extrem- 
ity, and  the  pulp-cavity  is  single. 

Occlusion  of  the  Teeth. — Tlie  diagram  (Fig.  224)  on  p.  446  represents 
the  occlusion  of  the  teeth.  It  has  been  previously  stated  that  in  a  well- 
formed  denture  no  one  tooth  rises  higher  than  its  fellows  ;  that  is,  if 
the  crowns  of  the  teeth  in  position  be  turned,  cusps  and  cutting  edges, 
upon  a  plain  or  even  surface,  each  tooth  rests  upon  this  surface.  From 
this  arrangement  there  is  nothing  to  interfere  with  a  perfect  occlusion. 
Still,  the  fact  must  be  recognized  that  while  the  above-described  arrange- 
ment is  true  of  a  perfectly-developed  jaw  and  teeth,  yet  so  rarelv  is  it 
found  that  it  may  be  considered  an  ideal  denture. 

It  has  also  been  stated  that  the  superior  arch  or  row  of  teeth  describes 
the  segment  of  a  larger  circle  than  does  the  inferior  row ;  this  being  the 
case,  when  the  two  are  brought  in  contact,  as  in  normally  closing  the 
mouth,  the  anterior  superior  teeth  are  thrown  slightly  over  and  anterior 
to  the  corresponding  inferior  teeth.  Also  with  the  bicuspids  and  molars, 
the  external  cusps  of  the  superior  ones  are  in  closing  slightlv  external  to 
the  corresponding  cusps  of  the  inferior.  Another  serviceable  peculiarity 
is  the  noticeable  absence  of  an  exact  opposition  of  tooth  to  tooth  in  clos- 


446 


DENTAL  ANATOMY. 


ing,  as  will  be  seen  by  the  diagram  :  the  greater  width  of  the  superior 
central  covers  the  wudth  of  the  inferior  central  and  a  small  portion  of 
the  inferior  lateral ;  this  brings  the  superior  lateral  over  the  remainder 
of  the  inferior  one  and  the  mesial  fourth  of  the  inferior  cuspid,  while 
the  cusp  of  the  superior  cuspid  fits  into  the  concave  space  between  the 
cusp  of  the  inferior  cuspid  and  the  first  bicuspid.     In  like  manner,  this 

Fig.  224. 


irregularity  of  opposition  is  maintained  in  all  the  teeth,  so  as  to  give 
each  tooth  a  bearing  on  two  teeth,  except  the  superior  third  molar, 
which  has  but  the  corresponding  tooth  in  the  lower  jaw  for  an  antag- 
onizer.  This  irregularity  of  opposition  contributes  to  the  efiiciency  of 
the  teeth  in  mastication,  and  is  a  valuable  feature  when  a  tooth  is  lost 
from  the  arch  in  either  jaw,  for  by  this  arrangement  the  tooth  in  partial 
antagonism  with  the  one  lost  still  maintains  a  portion  of  its  usefulness 
by  its  occlusion  with  yet  another  tooth. 

The  Deciduous  or  Temporary  Teeth  (Fig.  225),  twenty  in  number,  are 


Fig.  225. 


rf^ 


smaller  than  the  permanent  set,  though  tliey  resemble  them  in  their  gen- 
eral conformation  of  crown  and  root,  the  bicuspids  of  the  permanent  set 


TEETH  OF  THE   VERTEBRATA. 


447 


not  being  represented  in  the  deciduous  dentine.  The  formula,  wlien  they 
are  normally  developed,  is  I.  f,  C.  \,  M.  |=^  =  20,  the  premolars  or 
bicuspids  being  confined  to  the  permanent  set.  A  marked  point  of  dis- 
similarity, as  compared  with  their  successors,  is  in  the  termination  of  the 
enamel  on  the  neck  of  the  tooth.  In  the  permanent  teeth  the  gradual 
completion  of  the  enamel  on  the  border  of  the  cement  marks  but  indis- 
tinctly the  point  of  union  of  these  two  structures,  while  at  the  base  of 
the  deciduous  crown  the  terminatino-  enamel  on  the  buccal  and  labial 
surfaces  is  recognized  by  a  ridge  or  well-defined  border  which  unmis- 
takably marks  its  limitation  and  develops  a  well-constricted  neck.  This 
ditfereuce  is  often  of  importance  in  deciding  as  to  whether  a  tooth  in 
question  belongs  to  the  deciduous  or  permanent  series.  These  teeth, 
from  the  fact  that  their  crowns  are  largely  calcified  before  birth,  are 
much  less  liable  to  vices  in  conformation  than  their  successors,  but  from 
deficient  nutrition,  want  of  use,  and  neglect  not  unfrequently  become  an 
easy  prey  to  the  ravages  of  deutal  caries.  In  common  with  a  large  class 
of  the  order  to  which  man  is  closely  allied,  the  difference  in  number 
betw^een  the  deciduous  and  permanent  set  is  twelve,  the  additional 
teeth  being  without  predecessors. 

The  accompanying  figure  (226)  represents  the  denture  of  a  child  about 

Fig.  226. 


seven  years  of  age.  Twenty  deciduous  teeth,  ten  in  each  jaw,  and  the 
four  first  permanent  molars,  are  erupted.  The  second  permanent  molar 
is  seen  in  the  crypt  in  the  posterior  part  of  each  maxilla.  Commencing 
with  the  median  line,  to  the  right  of  it  and  just  above  the  erupted  decid- 
uous central  incisor,  we  observe  the  permanent  central  with  its  crown 
fully  calcified  and  the  root  partially  so.  In  this  case  the  crown  of  the 
permanent  tooth  stands  in  front  of  or  on  the  labial  side  of  the  partially 
absorbed  root  of  the  deciduous  central.  This  is  not  its  constant  relative 
position  ;  not  unfrequently  the  deciduous  root  is  in  front  of  the  crown, 
as  is  seen  in  the  adjoining  lateral  incisor.     In  this  case  the  crown  of 


448  DENTAL  ANATOMY. 

the  permanent  lateral  has  the  position  which  it  invariably  maintains. 
The  crown  of  the  permanent  cuspid  is  here  normally  located  quite  above 
the  root  of  its  predecessor,  and  at  the  side  of  and  in  close  proximity  to 
the  wang  of  the  external  nares.  Next  in  position,  a  little  below  and 
slightly  posterior  to  this  cuspid  crown,  is  that  of  the  first  l)icuspid,  this 
and  its  lellow,  the  second  bicuspid,  are  located  between  the  roots  of 
their  respective  predecessors,  the  first  and  second  deciduous  molars. 
The  same  is  true  of  those  on  the  other  side  of  the  jaw,  and,  with  slight 
variation,  the  same  relative  positions  of  the  deciduous  roots  and  perma- 
nent crowns  are  observed  in  the  inferior  maxilla.  It  is  above  stated 
that  the  figure  represents  the  teeth  of  a  child  about  seven  years  of  age. 
The  first  permanent  molars,  it  should  be  noted,  are  at  this  age  erupted 
and  in  position,  though  their  roots  are  not  quite  completed.  The  per- 
manent central  incisors  will  be  the  next  to  take  their  position  at  about 
the  age  of  eight,  followed  by  the  laterals  at  nine,  the  first  bicuspids  at 
ten,  the  second  bicuspids  at  eleven,  the  cuspids  from  twelve  to  thirteen, 
and  the  second  molars  from  twelve  to  fourteen,  which  completes  the 
eruption  of  the  permanent  teeth,  with  the  exception  of  the  third  molars 
or  wisdom  teeth,  these  may  take  their  position  at  eighteen  or  some  years 
later.  The  anatomy  of  human  dentition  is  further  illustrated  in  plates 
placed  at  the  end  of  this  paper  (see  p.  505). 

Teeth  of  the  Oabnivora. 

Our  knowledge  of  the  philogenetic  history  of  the  unguiculate  series 
has  so  increased  within  the  last  few  years  that  it  is  now  a  matter  of  great 
difficulty  to  say  just  Avhat  forms  should  be  included  in  the  order  Carniv- 
ora,  as  at  present  defined.  If  we  take  into  account  the  living  forms  only, 
no  one  will  hesitate  in  fixing  its  limit  and  giving  to  it  a  moderately  good 
definition ;  but  when  the  fossil  representatives  are  considered,  the  interval 
between  it  and  some  of  the  contiguous  orders,  especially  the  Insedivora, 
is  brought  down  to  extremely  small  limits.  We  have  already  seen  that 
the  Miacidce  approach  the  dogs  and  civets  in  the  Carnirora  on  the  one 
hand,  and  the  Lcpfididce  of  the  Insedivora  on  the  other.  If  a  dog, 
bear,  cat,  and  seal,  all  of  which  are  admitted  to  belong  to  the  Carnivora, 
be  selected,  and  a  careful  comparison  of  their  anatomical  structure  insti- 
tuted, the  differences  between  them  will  be  found  to  be  much  greater 
than  between  such  forms  as  Styjoolophus,  Ccntetes,  Miacis,  and  the  dogs 
and  civets. 

Every  increment  to  our  knowledge  of  the  more  exact  relationship 
of  the  various  groups  seems  to  bring  us  nearer  to  the  conclusion  that  our 
present  classification  is  largely  a  matter  of  convenience,  and  often  fails 
utterly  to  express  the  deeper  and  more  important  facts  of  origin  and 
ancestry.  Such  reflections  bring  us  abreast  of  the  question.  What  is  an 
order,  a  fiimily,  or  a  genus,  etc.  ?  And  just  here  M'e  approach  a  prob- 
lem as  to  the  solution  of  which  no  two  naturalists  agree. 

It  appears  to  me  that  the  only  way  out  of  these  difficulties  is  to  con- 
sider the  test  of  ancestry  the  only  true  basis  of  aflfinity.  If  it  can  be 
shown,  for  example,  that  any  given  assemblage  of  organic  forms  have 
descended  from  a  common  ancestor,  however  much  they  may  differ 


TEETH  OF  THE    VERTEBRATA.  449 

among  themselves,  siu-li  a  line  or  branch  constitutes  a  natural  division. 
Viewed  from  this  standpoint,  there  can  be  little  doubt  that  the  order 
Oirnivoni  represents  the  terminal  extremities  of  several  distinct  branches, 
Avhich  arose  not  from  one,  but  from  two  or  perhaps  three  points  in  the 
Insectivora.     The  same  reasoning  holds  good  for  many  other  orders. 

The  order  Garnivora,  as  at  present  understood,  is  divisible  into  two 
sub-orders — Fissipedia,  or  the  land  carnivores,  and  the  P'uinipedia,  or 
aquatic  flesh-eaters.  The  latter  division  includes  the  seals,  sea-lions, 
and  walruses,  and  is  distinguished  bv  the  fiippei-like  modification  of 
the  feet  for  progression  in  the  water,  as  well  as  bv  several  important 
cranial  characters.  They  are  all  known  to  be  diphyodont,  but  the  milk 
teeth  disappear  early  ;  in  some  cases  this  occurs  before  birth,  and  in 
others  a  few  weeks  after.  The  teeth  always  possess  comparatively 
simple  crowns,  which  are  either  simple  cones,  as  in  the  majority  of 
the  Cetacca,  or  laterally  compressed,  like  the  premolars  of  the  dog, 
with  smaller  cusps  along  the  edge,  giving  a  well-defined  serrated 
structure. 

There  are  three  families  of  this  group,  viz.  the  Phocidce  or  seals,  the 
Otaridce  or  sea-lions  and  sea-bears,  and  the  Trichecidce,  or  walruses. 
In  the  common  seal  [Phoca  ritiUina),  which  is  a  good  exara])le  of  the 
first,  the  dental  fonnula  is  I.  f ,  C.  |,  Pni.  f ,  M.  |  =  34.  The  central 
pair  of  incisors  above  (Fig.  227)  are  the  smallest,  with  sharp-pointed, 

Fig.  227. 


Vertical  View  of  the  Upper  Jaw  of  a  Harbor  Seal  {I'Uoca  vituiinn). 

slightly  hooked  crowns ;  the  next  are  similar  in  shape,  but  a  little 
larger,  while  the  outer  pair  are  abruptly  increased  in  size.  These  are 
separated  from  the  canine  by  a  diastema  to  admit  the  lower  canine. 
The  canine  is  a  powerful  tooth,  with  a  conical  recurved  crown,  and  is 
deeply  implanted  in  the  maxillary  bone.  In  the  specimen  figured,  which 
is  a  young  individual,  it  is  remarkable  for  the  very  large  size  of  the 
pulp-cavity,  which  extends  nearly  to  the  apex  of  the  crown.  The  first 
premolar  follows  just  inside  and  behind  the  canine,  giving  a  crowded 
appearance  to  the  first  two  premolars,  the  longitudinal  axes  of  wliich 
are  directed  very  obliquely  to  that  of  the  succeeding  teeth  :  it  has  no 
deciduous  predecessor,  as  the  corresponding  tooth  in  the  dog,  and  is  one 
of  the  many  examples  in  which  it  is  difficult  to  say  whether  it  should 
be  relegated  to  the  milk  dentition  as  a  persistent  milk  molar  or  whether 
it  should  be  referred  to  the  permanent  set.  It  is  implanted  bv  a  single 
root,  also  remarkable  for  the  size  of  the  pulp-cavity,  and  has  a  crown 

Vol.  I.— 29 


450  DENTAL  ANATOMY. 

with  a  principal  hook-shaped  cusp,  a  small  posterior  basal  cusp,  and  a 
strong  internal  cingulum. 

The  next  three  premolars  are  similar,  except  that  they  are  larger, 
implanted  by  two  roots,  and  have  two  posterior  accessory  cusps,  the 
hindermost  of  which  is  very  small.  The  single  molar  diliers  from  the 
rest  of  the  teeth  in  advance  of  it  in  having  an  anterior  basal  cusp,  being 
relatively  thicker  at  the  base  of  the  crown,  and  with  a  moderately  well- 
defined  internal  cingulum,  which  displays  a  tendency  to  develop  inter- 
nal cusps. 

The  incisors  and  canines  of  the  lower  jaw  are  like  those  above,  but 
the  two  incisors  of  each  side  are  separated  at  the  median  line.    The  first 

premolar  is  single-rooted  and 
somewdiat  larger  than  its  fellow 
above.  The  crown  displays  a 
median  cone  with  three  poste- 
rior accessory  cusps,  and  one 
very  minute  anterior  one.  The 
following  teeth,  including  the 
molar,  are  all  similarly  con- 
structed, but  have  the  anterior 

Vertical  View  of  the  Lower  Jaw  of  a  Harbor  Seal.         ■,  ■,  i     j..  ^    n        a 

basal  cusp  better  denned. 

In  the  hooded  seals  (Ci/stophora)  the  incisors  are  two  upon  each  side 
above,  and  one  upon  each  side  below.  The  canines  are  comparatively 
large  and  powerful,  while  the  molars  and  premolars  are  small  and  reduced 
to  simple  conical  bodies,  similar  to  the  teeth  of  the  cetaceans.  In  another 
genus  (Stenorhynchii.s)  the  teeth  are  remarkable  for  the  great  length  of 
the  cusps,  and  in  one  species,  Lepfonyx,  for  the  curvature  of  the  acces- 
sory cusps  toward  the  principal  one,  thereby  resembling  the  trident 
of  a  fishing-spear. 

A  good  example  of  the  dentition  of  the  Otaridce  is  furnished  by  the 
fur  seal  {Callorhynns  urs^nus),^\\\\Q\\  can  usually  be  found  in  museums. 
Tlie  dental  formula  is  I.  f ,  C.  },  Pm.  f ,  M.  f  =  36.  The  two  median 
pairs  of  incisors  above  are  subequal  and  laterally  compressed.  They 
each  present  a  deep  transverse  notch  in  the  summit  of  the  crown,  into 
which  the  incisiform  extremities  of  the  lower  incisors  bite ;  the  outer 
pair  are  larger  and  sharp-pointed.  The  canines  are  relatively  longer 
and  more  slender  than  in  the  seals,  and  have  a  well-defined  posterior 
trenchant  edge.  The  succeeding  teeth  are  all  alike  in  form  and  size, 
being  imi)lanted  by  single  fangs.  Their  crowns  are  of  a  triangular 
shape  when  viewed  from  the  side,  and  present  a  single  cusp.  It  fre- 
quently happens  that  the  bases  of  these  teeth  just  where  they  emerge 
from  the  gums  are  very  much  eroded,  the  cause  of  which  is  not  at 
present  well  understood. 

Both  the  PJiocidce  and  OtarirJcc  are  remarkable  for  their  comparatively 
weak  and  slender  jaws,  the  backward  dii-ection  of  the  coronoid  process, 
and  the  great  distance  intervening  between  its  base  and  the  last  tooth. 
In  the  seals  the  palate  is  very  broad  posteriorly,  and  the  last  tooth  does 
not  extend  behind  the  anterior  root  of  the  zygoma,  whereas  in  the  sea- 
lions  the  ]xalate  is  long  and  narrow,  and  the  last  tooth  is  placed  consid- 
erably behind  the  anterior  termination  of  the  zygomatic  arch. 


TEETH  OF  THE   VEBTEBRATA.  451 

The  Trk'hechidw  or  walruses  exhibit  the  most  anomalous  condition 
of  the  dental  organs  of  any  pinniped  carnivore  so  far  known,  in  that 
two  enormous  tusks  are  developed  in  the  upper  jaw,  which  occupy  the 
position  and  fulfil  the  functions  of  canines.  Owing-  to  the  transitory 
character  of  some  of  tlie  other  teeth,  it  is  difficult  to  assign  a  definite 
dental  formula  to  this  animal.  Prof.  Flower  makes  it  out  to  be  I.  ^, 
C.  \,  Pm.  I,  M.  ^.  Besides  these  there  are,  according  to  Tomes,  sev- 
eral other  small  teeth  to  be  found  frequently  in  the  position  of  the  inci- 
sors, and  he  is  disposed  to  regard  them  as  the  rudimentary  representatives 
of  the  permanent  normal  ones  in  other  animals  ;  there  can  be  little  doubt 
that  he  is  correct.  Rudiments  of  true  molars  are  also  not  unfrequently 
present  in  the  back  part  of  the  jaws.  The  incisors  and  molars  are  small 
and  simple,  and  are  soon  worn  down  even  with  the  gums  into  obtuse  oval 
grinding  surfaces.  The  canines  of  the  upper  jaw  protrude  far  below  the 
level  of  the  symphysis,  and  grow  from  persistent  pulps.  They  are  com- 
posed of  dentine  with  a  thin  investment  of  cementum.  Tomes  says  of 
them  :  "  These  great  tusks  are  employed  to  tear  up  marine  plants  and 
turn  over  obstacles,  the  walrus  feeding  upon  Crustacea  and  also  upon  sea- 
weed, etc. ;  they  are  also  used  to  assist  the  animal  in  clambering  over 
the  ice ;  as  they  are  of  almost  equal  size  in  the  female,  they  cannot  be 
regarded  as  weapons  of  sexual  offence,  but  they  are  undoubtedly  used 
in  the  combats  of  the  males." 

The  walruses  and  sea-lions  agree  with  respect  to  the  use  of  the  hind 
limbs  for  progression  on  land,'  being  able  to  walk  on  all  fours  fairly 
well ;  in  the  seals,  on  the  other  hand,  tlie  posterior  members  are  rotated 
backward,  and  permanently  fixed  in  this  position,  so  as  to  be  of  little 
or  no  use  in  walking.  In  this  respect  they  approach  nearer  to  the 
cetacean  condition. 

Viewing  the  Pinnipedia  as  a  whole,  I  am  inclined  to  think  that  the 
relationship  existing  between  them  and  the  Finsipedia  is  more  apparent 
than  real ;  and  although  paloeontology  does  not  at  present  permit  us  to 
judge,  I  am  of  the  opinion  that  they  will  ultimately  be  found  to  have 
been  derived  from  an  entirgly  different  ancestry.  Fossil  remains  are 
known  as  far  back  as  the  Miocene,  but  all  that  have  so  far  been  found 
are  typically  pinniped.  The  simple  structure  of  the  teeth  finds  a  par- 
allel in  the  Insectivora  in  the  teeth  of  the  lower  jaw  of  the  genus 
3Iesgni/i',  already  described,  which  Cope  believes  to  ha\^e  been  more  or 
less  aquatic  from  the  evidence  afforded  by  some  of  the  limb  bones.  This 
genus  or  an  allied  one  may  have  been  the  progenitor  of  the  pinnipeds, 
but  too  little  is  known  of  the  skull -structure  to  say  anything  about  the 
affinities  between  them. 

The  fissiped  Carnivora  are  more  extensive,  both  in  number  and 
variety,  than  the  pinnipeds,  and  enjoy  a  wider  range  of  distribution. 
Some  of  them  are  almost  exclusively  aquatic  in  habit,  while  others  are 
arboreal,  fossorial,  or  terrestrial.  It  is  in  this  group  that  we  meet  with 
the  highest  specialization  of  the  dental  organs  for  the  purpose  of  seiz- 
ing, lacerating,  and  devouring  living  prey.  In  many  the  claws  are 
extremely  sharp  and  hookrshaped,  and  are  provided  with  a  special 
apparatus  by  which  they  are  made  retractile,  thereby  rendering  them 
efficient  organs  of  destruction  and  prehension  as  well.     The  feet  are 


452 


DENTAL  ANATOMY. 


Fig.  229. 


not  modified  into  flippers,  as  in  the  pinnipeds,  but  constitute  distinct 
*'  paws,"  M'hicli  in  the  aquatic  forms  have  webbed  toes.  The  canines 
are  always  present  and  generally  of  formidable  proportions,  while  the 
sectorial' or  shearing  ai)i)aratus  is  present  only  in  those  that  subsist 
exclusively  on  an  animal  diet. 

They  have  been  divided  by  Prof  Flower  into  three  groups,  which  he 
has  called  the  Ci/noidea,  Ailuroidea,  and  Arctoidea,  defining  them  by  the 
characters  of  the  otic  bullse  and  the  base  of  the  skull.  The  first  of 
these  includes  the  dogs,  wolves,  and  jackals,  etc.,  and  in  all  ])rol)ability 
represents  the  central  group.  From  it  the  civets,  cats,  etc.,  consti- 
tuting the  Ailuroidea,  branch  oli'  on  the  one  hand,  while  the  bears, 
weasels,  raccoons,  etc.  are  closely  connected  on  the  other.  The  Oynoidea 
comprises  two  families — according  to  most  authors  only  one  ;  these  are 
the  Canidce,  or  dogs,  wolves,  foxes,  etc.,  and  the  3Ie(/alotid(c,  including 
the  single  genius  MegulotiH,  or  the  fennec  of  Africa,  which,  for  reasons 
which  will  a])pear  hereafter,  I  am  strongly  disposed  to  regard  as  an 
entirely  distinct  family. 

A  typical  dentition  of  the  Canidcc  has  already  been  described  in  that 
of  the  dog.     About  the  only  dental  variations  of  importance  to  be  seen 

in  this  family  consists  in  the  re- 
duction of  the  number  of  premo- 
lars, addition  or  subtraction  to  the 
number  of  upper  true  molars  to  or 
fniiu  that  of  the  dog,  subtraction 
from  the  lower  molar  series,  and 
slight  modification  in  form  of  the 
sectorials.  Upon  these  variations 
principally  some  thirteen  or  fifteen 
genera  have  been  defined.  The 
dental  formula  for  many  of  the 
genera  is  the  same  as  that  of  the 
dog,  I.  I,  C.j,  Pm.f,  M.|  = 
42,  but  the  extinct  Miocene  genus 
Amphicyon  (Fig.  229),  found  both 
in  this  country  and  Europe,  had 
three  true  molars  in  the  ujiper  jaw. 
In  another  extinct  genus  [Enhy- 
drocyo)i),  described  by  Cope  from 
the  iSIiocene  of  the  John  Day  beds 
of  Oregon,  the  premolars  are  re- 
duced to  three  in  each  jaw.  Olif/o- 
bumts  is  the  name  given  by  this 
author  to  another  extinct  genus 
from  the  same  locality,  in  which 
^.     The  principal  part  of  the  skull  is 


Skull   of    AwjiliKii-ii   (ii\i  ir/niis    (  (i])e 

supi'iior  molar  lost,  one-half  natural  size,  from 
the  John  Day  beds  of  ()ret;on  (after  Cope). 


molar  fin'nuda  is  Pm.  |,  M. 


the 

represented  in  Fis;.  280 


Still  another  genus  of  this  family  has  been 
described  by  the  same  author  from  the  rich  fossiliferous  deposits  of  that 
region  under  the  name  of  Hycenocyon,  which  has  three  premolars  above 
and  below,  with  only  a  single  true  molar  above. 

The  sectorials  of  the  more  typical  Canidw  are  like  those  described  in 


TEETH  OF  THE   VERTEBRATA. 


453 


the  dog,  but  in  some  genera — notably  Temnocyon  of  Cope — the  heel  of 
the  lower  sectorial,  instead  of  being  basin-shaped,  retains  the  more  primi- 
tive structure,  and  consists  of  a  single  trenchant  cusp  (see  Fig.  231). 

In  the  extinct  genus  AUurodon  of  Leidv  the  dental  fornuda  is  the 
same  as  in  the  dog,  but  it  approaches  the  cats,  and  especially  the  hysenas, 


Fig 


Portiuu  of  ^kull  of  Olif/ubnuiis  crits.siimlliix.  Cope,  one-half  n-.itural  size  :  In,  right  maxiUary  bone  from 
below ;  2,  Mght  maudibulur  ramus  from  above  (after  Cope^ 

in  having  three  cusps  to  the  blade  of  the  superior  sectorial,  whereas  the  dog 
has  only  two.  The  premolars  too  are  more  robust  than  in  the  dog,  consti- 
tuting another  approach  to  the  ^la  -y-^i 
condition  of  the  Uj/ceuida'.  The 
skull  is  represented  in  Fig.  232. 
The  genus  Ichtifhcriam  of  Gau- 
dry  (Fig.  233),  from  the  Miocene 
of  Pikermi,  Greece,  is  an  allied 
genus,  but  the  third  molar  of  the 
lower  jaw  is  absent,  leaving  a  for- 
mula, I.  f ,  C.  I,  Pm.  f ,  M.  I  =  40. 
In  one  species  (/.  robuHium)  the 
last  superior  molars  have  nearly 
the  same  proportions  as  in  the 
dog,  while  in  anotlier  (J.  hippa- 
rionum)  the  last  molar  is  consid- 
erably reduced  in  size.  It  will 
thus  be  seen  that  these  two  genera 
depart  from  the  central  or  typical 
Cankke,  and  establish  close  con- 
nections with  the  Hycenidce,  which 
are  closely  affiliated  with  the  cats 
and  belong  to  the  Ailuroidea. 
Cope  has  suggested  that  AUu- 
rodon  is  the  ancestor  of  the  hysenas ;  and  there  is  undoubtedly  much 
evidence  to  support  this  opinion. 

The  second  family  of  the  Cynoidea  is  the  Megalotldce,  which  is  dis- 


Temnocyon  altiqenis,  Cope:  part  of  Right  Jlandibulnr 
Eamus,  one-half  natural  size,  viewed  from  without, 
within,  and  above  (after  Cope). 


454 


DENTAL  ANATOMY. 


tinguishecl  from  the  Canidce — and,  for  that  matter,  from  all  other 
diphyodont  monodelphous  mammals — by  the  possession  of  four  true 
molars  in  the  lower  jaw,  thereby  giving  the  formula  J.  f,  C.  \,  Pm. 
1^,  M.  f  —  46.  The  only  other  cases  in  which  there  are  more  than 
three  true  molars  normally  are  found  in  the  marsupials,  edentates,  and 
cetaceans  ;  and  in  these  two  latter  orders  we  have  already  seen  that  the 
teeth  are  not  generally  divisible  into  incisors,  canines,  premolars,  and 
molars,  on  account  of  the  development  of  only  a  single  set.  In  the 
marsupials,  however,  as  we  shall  presently  see,  the  normal  number  of 

Fig.  232. 


Skull  of  Ailnrodon  sceviis,  Leidy,  three-eighths  natural  size  (after  Cope). 

true  molars  is  four,  just  as  the  number  three  is  most  common  to  dip- 
hyodont monodelphs.  Reduction  of  the  normal  number  is  to  be  fre- 
quently observed  in  the  monodelphs,  and,  as  we  have  just  seen  in  the 
Canidce,  occurs  in  genera  otherwise  nearly  related  ;  it  cannot  therefore 
be  regarded  as  of  more  than  generic  imjjortancc,  but  there  are  no  cases 
known  to  me  in  which  teeth  have  been  added.  On  the  contrary,  I  am 
firmly  of  the  opinion  that  not  so  much  as  a  single  tooth  has  ever  been 
added  to  the  diphyodont  mammalian  dentition  in  the  course  of  develop- 
ment, but  that  specialization  has  invariably  gone  in  the  opposite  direc- 


TEETH  OF  THE    VERTEBRATA. 


455 


Fig.  233. 


tion,  as  almost  all  evidence  of  palaeontology  goes  to  show.  The  teeth 
are  not  otherwise  remarkable,  resembling  distantly  those  of  the  dog  in 
general  pattern.  The  sectorials  are  not  well  defined,  and  the  crowns 
generally  have  a  tendency  to  the  tubercular  structure. 

The  second  division  of  the  Fissipedia  (^Ailuroidea)  includes  five  fam- 
ilies, the  exact  definitions  of  which  the  increasing  knowledge  of  the 
extinct  forms  is  tending  every 
day  to  break  down  into  hopeless 
confusion.  The  definitions  are 
already  very  unsatisfactory  and 
in  many  cases  fiiil  to  define. 

The  families  which  approach 
nearest  to  the  Canklce  are  the 
Hycenidce  or  hysenas,  and  the 
Viverridce  or  civets.  The  evi- 
dence already  cited  brings  the 
former  of  these  families  into  the  closest  relationship  with  the  central 
cynoid  group.  The  dental  formula  of  the  existing  hyaenas  (Fig.  234) 
is,  I.  f ,  C.  \,  Pm.  ^,  M.  \  =  34.  The  incisors  and  canines  have  very 
much  the  same  pattern  as  the  corresponding  teeth  in  the  dog,  as  do 
also  the  premolars,  with  the  exception  of  their  more  robust  proportions 

Fig.  234. 


Superior  Dental  Series  of  IcIUherhnn  robiixfuni,  two- 
thirds  natural  size  (from  Cope,  alter  Oaudry). 


Skull  of  Striped  Hyrena,  Ifycena  striata. 


and  the  addition  of  an  anterior  cutting  lobe  to  the  superior  sectorial. 
In  the  lower  sectorial  the  heel  is  very  rudimental  and  the  internal 
tubercle   is    wanting.     The    single  superior   true    molar  is  small   and 


456 


DENTAL  ANAT03fY. 


lower  juw,  giving  the  formula  1. 1,  C.  y,  Pm.  ^,  M. 


Fig.  235. 


Fig.  236. 


situated  just  internal  to  the  posterior  part  of  the  great  superior  sec- 
torial, so  as  to  be  completely  hidden  in  an  external  view  of  the  ja\v. 
In  an  extinct  species  [Hi/irna  exhnia)  there  were  four  premolars  in  the 

'    "   "  ~        '   "  ^  =  3G.     The  infe- 

rior sectorial  also  has  a  well-defined  heel. 
In  the  more  ancient  or  Miocene  represent- 
ative of  this  family  {Hycenidh  (jrccca, 
Fig.  235)  the  superior  molar  is  nmch 
larger  and  has  a  more  posterior  position  ; 
the  inferior  sectorial  (Fig.  236)  has  a  rela- 
tively large  basin-shaped  heel.,  and  there  is 
a  small  second  true  molar  behind  it.  It  is 
through  this  genus  that  the  transition  is 
effected  from  the  Hyai\i(]w  to  the  (MnUke 

Superior  Sectorial  and  First  Molar  of    bv  W'ay  of  IditherivDl  and  AUuVodon. 

Hyanictisgra.caX^iterV.^nAry).  ^  ^j^^     ^^^^^^^^     fomuda     of    the      Vk€rkJ(B 

varies  somewhat  by  reason  of  decrease  in  number  of  the  premolars 
and  molars.  The  more  important  of  these  will  be  noticed  after  we  have 
first  described  the  dentition  of  a  typical  example  of  the  family,  which  is 
found  in  the  genus  Herpedes,  or  the  mongoose.     The  dental  formula  is 

I.  1  c.  x.]  Pni.  4^  M.  I  =  40.  The  in- 
cisors of  the  upper  series  have  flattened 
oval  crowns  without  lateral  lobes,  in- 
creasing in  size  from  first  to  third ;  the 
canines  are  long,  pointed,  and  recurved  ; 
the  first  three  premolars  have  the  usual 
pattern,  but  are  devoid  of  accessory 
cusps.  In  the  fourth  premolar  or  su- 
perior sectorial  the  blade  is  composed 
of  the  usual  two  posterior  cusps,  sepa- 
rated l)y  a  fissui'e  remarkable  for  its 
depth.  There  is  also  a  rudimental  an- 
terior basal  lobe,  which  arises  from  the 
cingulum.  The  internal  lobe  is  unusually  strong,  and  sends  a  trenchant 
ridge  backward  and  outward  to  join  the  principal  cone.  The  next 
tooth,  or  first  true  molar,  is  tritubercular,  with  two  external  and  one 
internal  cusp  ;  the  crown  is  remarkable  for  its  transverse  extent.  The 
last  molar  is  relatively  small,  and  has  a  more  internal  position,  possess- 
ing a  bicuspid  crown.  The  decrease  in  size  of  the  true  molars  from  that 
of  the  great  sectorial,  and  the  strongly  inward  curvature  of  the  tooth-line 
behind,  are  more  i)ronounced  than  in  the  dog,  and  altogether  interme- 
diate between  that  of  the  latter  animal  and  the  cats. 

The  incisors  of  the  lower  jaw  are  smaller  than  the  corresponding 
teeth  above,  and  the  sununits  of  their  crowns  are  distinctly  notched  ; 
the  canines  are  like  those  of  the  nj)per  jaw,  while  the  premolars  have 
basal  cusps  which  are  largest  behind.  The  first  true  molar  or  inferior 
sectorial  furnishes  a  pattern  intermediate  between  the  tuberculo-sectorial 
and  the  well-defined  sectorial.  The  ])rimitive  cone  and  anterior  basal 
l()b(\s  are  connected  into  a  blade,  the  internal  tubercle  being  large  and 
furnishing  the  characteristic  triangular  appearance  of  this  portion  of  the 


Frastnient  of  Lower  Jaw  of  //.  ijra'ca,  show- 
ing sectorial  and  second  molar  (after 
Gaudry). 


TEETH   OF  THE   VERTEBRATA.  457 

crown.  The  heel  consists  of  a  raised  margin  bearing  several  small  tuber- 
cles. The  last  molar  is  quadritubercular,  and  seems  to  have  retained 
the  anterior  triangle  of  the  preceding  tooth,  together  with  one  cusp  of 
the  heel.  If  this  be  so,  it  is  an  exception  to  the  general  rule,  according 
to  which  the  anterior  cusp  becomes  obsolete. 

In  the  two-spotted  paradoxure  [Nandinia)  of  West  Africa  the  molar 
series  is  frequently  reduced  to  M.  ^,  while  in  the  bintourong  {Arctkiis) 
the  last  molar  above  and  the  first  })remolar  below  are  often  absent.  The 
premolar  formula  of  the  genus  GaUdea  is  normally  f ,  which  likewise 
obtains  in  the  kusimanse  (Crosscn-chiisi)  from  the  West  Coast  of  Africa. 
The  form  of  the  inferior  sectorial  of  the  genus  Ctjiio(/a/e,  a  Bornean 
representative  of  this  family,  is  nearer  that  of  a  tubercular  than  a  sec- 
torial tooth.  The  three  anterior  cusps  which  go  to  make  up  the  tri- 
angular portion  are  very  much  reduced,  and  have  altogether  lost  their 
sectorial  character ;  the  superior  sectorial,  however,  is  much  better  de- 
fined as  such.  In  another  genus  (^Eaph'rcx)  the  teeth  are  very  small 
and  the  incisors  stand  far  apart,  on  account  of  which,  together  with 
several  cranial  peculiarities,  Dr.  Gill  gives  it  a  distinct  family  rank. 

It  will  thus  be  seen  in  a  survey  of  the  dental  organs  of  this  family 
that  they  are  almost  identical  with  the  genus  Didymictis  of  our  American 
Eocene,  which  has  already  been  described,  and  I  think  there  can  be  little 
doubt  that  they  are  the  derivatives  of  this  or  some  nearly  related  genus. 

Another  family,  which  stands  intermediate  between  the  civets  and 
cats,  is  represented  by  the  single  living  genus  Ci')jptoprocta,^\\\\Q\\  is 
limited  in  its  distribution  to  the  island  of  Madagascar.  Some  authors 
classify  it  as  a  sub-family  of  the  cats,  others  as  a  sub-family  of  the 
civets,  while  others  again  make  it  a  distinct  family.  No  better  argu- 
ment, it  seems  to  me,  could  be  advanced  in  support  of  its  intermediate 
nature.  It  undoubtedly  has  strong  affinities  with  l)oth  families,  and 
goes  far  toward  bridging  over  the  interval  between  them.  The  recent 
discoveries  of  Cope  and  Filliol  have  shown  it  to  be  the  surviving  rem- 
nant of  an  extensive  group  which  lived  in  this  country  and  Euro]:)e,  and 
which  were  the  ancestors  of  the  cats,  and  in  all  probability  the  deriva- 
tives of  the  more  generalized  civets.  In  distinguishing  between  the 
Fed  dee,  Viverridre,  and  Cri/pfoproctidce.  the  foramina  at  the  base  of  the 
cranium  afford  the  best,  if  not  the  only,  grounds  for  separation.  Pre- 
vious to  our  knowledge  of  the  extinct  forms  the  number  of  the  molar 
teeth  was  also  used  for  this  purpose,  but  owing  to  the  intermediate 
condition  of  this  latter  character  in  many  of  the  fossils  it  must  be  aban- 
doned as  altogether  worthless.  In  the  Crypfojyrodldcv  the  alisphenoid 
bone  is  perforated  by  a  canal — the  alisphenoid  canal — for  the  passage 
of  the  external  carotid  artery  in  its  course  forward.  The  foramen  for 
the  entrance  of  the  internal  carotid  in  its  passage  to  the  brain  is  also  well 
defined,  and  of  a  considerable  size.  In  the  Felidce  there  is  no  alisphe- 
noid canal,  and  the  carotid  canal  is  minute  or  absent.  In  the  Viverridce 
the  alisphenoid  canal  is  generally  present,  but  not  invariably  so  ;  the  for- 
amen for  the  entrance  of  the  internal  carotid  is  of  moderate  proportions, 
as  in  the  Cryptoproctidce,  from  which  I  can  see  no  very  good  reasons  for 
distinguishing  them  as  a  family.  Cope  associates  a  number  of  extinct  genera 
together  under  the  name  of  Nhnravidce,  and  defines  them  from  the  Felidce 


458 


DENT  A  L   A  XA  TOM  Y. 


by  a  number  of  characters  in  ^\■hicll  they  agree  with  the  Cryjjtoproctidce  ; 
the  distinctions  betAveen  them  and  this  latter  family  are  not  so  apparent. 

The  dental  formula  of  CtYptoproda  is  I.  -|,  C.  \,  Pm.  f ,  M.  \  =  34. 
The  incisors  and  canines  resemble  those  of  the  cats  generally ;  the  first 
premolar  in  the  upper  jaw  is  caducous,  and  does  not  usually  appear  in 
the  adult  skull.  The  superior  sectorial  has  a  rudimental  anterior  basal 
lobe,  an  internal  tubercle,  and  a  well-defined  blade.  The  molar  is  a 
much  smaller  tooth,  and  has  an  internal  position,  as  in  the  hyaenas.  In 
the  lower  jaw  the  sectorial  has  a  faint  heel  and  lacks  the  internal  tuber- 
cle, and  is  altogether  feline  in  its  appearance. 

The  following  extinct  genera  are  enumerated  and  defined  by  Cope  as 
belono-ino;  to  the  faxmly  Nimravidce  •} 

I.  Lateral  and  anterior  faces  of  mandible  continuous ;  no  inferior  flange. 

a.  No  anterior  lobe  of  suj^erior  sectorial ;  inierior  sectorial  with   a  heel ; 
canines  sniootli. 
Pm.  I,  M.  I ;  inferior  sectorial  with  internal  tubercle  ,    ....    .  Procelurus. 
Pm.  f ,  M.  y ;  inferior  sectorial  without  internal  tubercle      ....  Pseudceiurus. 
Pm.  |,  M.  j-;  inferior  sectorial  without  internal  tubei'cle      .    .    .     Q-yptoprocta.'^ 
II.  Lateral  and  anterior  laces  of  mandible  separated  by  a  vertical  angle;  no  infe- 
rior flange ;   incisors  obspatulate. 
((.  Xo  anterior  lobe  of  superior  sectorial  ;  inferior  sectorial  witli  a  heel  land 
no  internal  tubercle)  ;  incisiors  truncate. 

Pm.  I,  j\I.  2  ;  canine  smooth Arclicdurus. 

Pm.  f,  M.  ^  ;  canines  denticulate ^Inrogale. 

Pm.  I,  ^L  I  ;  canines  denticulate Nimravus. 

III.  Lateral  and  anterior  faces  of  mandible  separated  by  vertical  angle  ;  an  inferior 
flange  ;  canines  denticulate. 
«.  No  or  a  small  anterior  basal  lobe  of  superior  sectorial  ;  interior  sectorial 
with  a  heel.     No  posterior  lobes  on  crown  of  premolars. 

Pm.  I,  M.  ^ Dinictis. 

Pm.  f,  ^L  Y Pogonodon. 

Pm.  '^  M.  I Hophplioneus. 

Pm.  y,  M.  X ■ Emmilm. 

Prolceurus.  is  known  to  have  possessed  five  digits  in  each  foot,  as 
Cryptoproda,  and  it  is  probable  that  two  sub-families  should  be  made, 

since  others  had   only  fotu"  in   the 
^"^*^^  -'^''  pes.     The    dentition    of  Procdwus 

(Fig.  237)  is  more  primitive  than 
Cryptoproda  in  the  following  cha- 
racters :  there  are  four  premolars  in 
the  lower  jaw  ;  the  superior  sectorial 
has  no  anterior  basal  lobe ;  the  in- 
ferior sectorial  has  a  strong  heel  and 
an  internal  tubercle ;  and  there  are 
ivio  true  molars  below. 
k^i^         Pseudceiurus  agrees  more  nearly 
with    Cryptoproda,   but    lacks    one 
premolar  in  the  upper   series.     As 
/i^^fir     already  ol)!^erved,  the  first  premolar 
is  caducous  in  this  latter  genus,  and 
P/w/?«M.siw/v>»/,  Fiiii., two-thirds  natural  size,    they  may  be  the  same.     In  the  sec- 

^  "On  the  Extinct  Cats  of  America,"  Amn-iran  KalnrdUft,  Dec,  1880. 
-  I  have  combined  the  yimravid'r  and  the  driipioproclidce,  and  have  inserted  this 
genus  where  it  seems  to  most  appropriately  belong. 


TEETH  OF  THE   VERTEBRA  TA. 


459 


Fig.  238. 


ond  section  the  anterior  and  lateral  faces  of  the  mandible  are  separated 
by  an  angle  or  vertical  ridge,  which  gives  to  the  jaw  the  appearance  of 
having  a  square  chin. 

The  genera  of  this  section,  with  the  exception  of  ^liir or/ate,  are  from 
the  Miocene  beds  of  the  John 
Day  Valley,  Oregon,  and  were 
described  by  Cope ;  the  pre- 
molar series  shows  a  gradual  re- 
chiction  in  number,  but  they  all 
retain  the  heel  to  the  inferior 

sectorial     and     the     generalized    Prmrhnn^  lal,  m   J  illi,  two-thirds  natural  size:  «,  inner 

,  ,,  °  -.  .  view  of  niandilile    />,  superior  view  of  inferior  teeth; 

character  ot   two  true  molars  in        r,  mU-nor  ^ectoiial,    natural   size    (fioni    Cope    after 

thelowerjaw.  ArcJudm'u.s and     ^'i''^"''- 

Nhnravus  are  represented  in  the  acconipanyii;g  figures,  239  and  240. 

Fig.  239. 


'^^'^S^i'^^^^ 


Archfiehinis  debilis,  Cope,  Skull,  one-half  natural  size  (after  (ope). 

Fig.  2J0. 


Skull  ot  Nimravus  gornjjhodnx.  Cope,  two-fifth-^  natural  size  Cafttr  Copei:   1,2,  first  and  second  true 
molars;  .-,,  4,  third  and  fourth  premolars  of  lower  jaw. 


460  DENTAL   ANATOMY. 

In  the  third  section  the  mandible  possesses  a  strong  inferior  flange 
upon  each  side  to  protect  the  powerful  canines  of  the  upper  jaw,  which 
in  some  forms  project  far  below  the  level  of  the  symphysis.  They  are 
therefore  known  as  the  "  sabre-tooth  division."  In  the  hrst  of  these 
genera,  Dinidis  (Fig.  ^-11),  the  true  molars  are  ^,  the  inferior  sectorial 

Fig.  24] . 


Skull  of  Dincitis  Cyclops,  one-half  natural  size  (after  Cope). 

has  a  heel,  and  the  true  molar  above  is  a  moderately  well -developed 
tooth,  as  in  the  preceding  genera.  The  genera  Hoplojihoneus  and  Pogon- 
odon  carry  dental  specialization  several  steps  further,  while  in  Eusmilus 
we  have  the  highest  point  reached  by  any  of  this  group,  which  is  in 
many  respects  superior  to  the  living  cats. 

Cope,  in  commenting  upon  the  dentition  of  this  group,  says  :  "  It  is 
readily  perceived  that  the  genera  above  enumerated  form  an  unusually 
simple  series,  representing  stages  in  the  following  modifications  of  parts  : 
(1)  In  the  reduced  number  of  molar  teeth  ;  (2)  in  the  enlarged  size  of 
the  superior  canine  teeth  ;  (3)  in  the  diminished  size  of  the  inferior 
canine  teeth  ;  (4)  in  the  conic  form  of  the  crowns  of  the  incisors;  (5) 
in  the  addition  of  a  cutting  lobe  to  the  anterior  base  of  the  superior 
sectorial  tooth  ;  (6)  in  the  obliteration  of  the  inner  tubercle  of  the  lower 
sectorial,  and  (7)  in  the  extinction  of  the  heel  of  the  same ;  (8)  in  the 
development  of  an  inferior  flange  at  the  latero-anterior  angle  of  the 
front  of  the  ramus  of  the  hnver  jaw  ;  (9)  in  the  development  of  cutting 

lobes  upon  the  ])osterior  border  of  the  large  premolar  teeth 

The  succession  of  the  genera  above  pointed  out  coincides  with  the  order 

of  geologic  time  very  nearly The  relations  of  these  genera  are 

very  close,  as  they  differ  in  many  cases  by  the  addition  or  subtraction 
of  a  single  tooth  from  each  dental  series.  Tliese  characters  are  not 
even  always  constant  in  the  same  species,  so  that  the  evidence  of 
descent,  so  far  as  the  genera  are  concerned,  is  conclusive.  No  fuller 
genealogical  series  exists  than  that  A\hich  I  have  discovered  among  the 
extinct  cats." 

The  last  family  of  the  Ailuroidea  is  the  Felidcp,  in  -svhich  we  meet 
with  the  highest  |)oint  in  specialization  that  has  been  reached  in  the  flesh- 


TEETH  OE  THE    VERTEBRATA. 


461 


eating  Mammalia.  It  includes  two  divisions — one  in  which  the  superior 
canines  are  normal  and  without  the  vertical  angles  and  inferior  flanges 
to  tlie  mandible ;  and  another,  "  sabre-tooth  division,"  wherein  the 
superior  canines  are  enormously  enlarged,  denticulate,  and  protected 
by  inferior  flanges  of  the  rami. 

The  first  of  these  groups  or  sub-families  is  the  more  generalized,  and 
embraces  all  the  existing  cats  or  those  animals  popularly  known  as  lions, 

Fif4.  242. 


Pogiinodon  plaiyeopis,  Skull,  less  than  two-fifths  natural  size  (^after  Cope):  2,  ",  4,  second,  third,  and 
fourth  premolars,  and  1,  first  lUoUir  of  lower  jaw  ;  F  G,  post-glenoid  foramen  ;  P  JP,  post-parietal 
foramen. 


tigers,  leopards,  panthers,  etc.  Five  genera  have  been  established  in  this 
division  on  characters  of  the  teeth  and  orbit.  It  is  here  that  the  domestic 
cat  belongs,  and  its  dentition  may  be  taken  as  a  good  average  represen- 
tation of  that  of  the  sub-family. 

The  dental  formula  in  this  animal  is  I.  f ,  C.  y,  Pm.  |^,  M.  ^  =;  30. 
The  incisors  are  rehitively  small,  and  are  disposed  almost  transversely 
across  the  front  of  the  jaw.  The  first  premolar  above  is  a  small,  single- 
rooted  tooth,  and  is  situated  at  a  considerable  distance  from  the  canine, 
which  has  tlie  usual  form  and  proportions  of  that  tooth  in  the  C'arnivora 
generally.  The  second  is  larger  and  two-rooted,  while  the  fourth 
or  upper  sectorial  is  decidedly  the  largest  tooth  of  the  superior  series ; 
it  has  three  external  cusps  united  into  a  blade,  and  a  small  internal 
tubercle.  The  single  mokir  is  very  small  and  functioidess,  being 
placed  internal  to  the  posterior  part  of  the  large  sectorial.  In  the 
lower  jaw  the  premolars  are  proportionately  large,  having  two  fangs 
and  posterior  accessory  cusps.  The  sectorial  is  specialized,  and  con- 
sists simply  of  two  cusps  forming  a  trenchant  blade ;  both  the  heel 
and  internal  tubercle  are  absent. 

The  lynxes  have  one  less  premolar  upon  each  side  above  than  the  cat, 
and  for  this  reason  are  ])Iaced  in  a  distinct  genus.  In  the  flat-headed 
cat  and  the  fishing  cat  the  orbit  is  completely  encircled  by  bone — an 
unusual  occurrence  in  this  familv.     In  both,  the  number  of  teeth  is  the 


462 


DENTAL  ANATOMY. 


same  as  in  the  domestic  cat,  but  in  the  former  the  first  premolar  in  the 
upper  jaw  has  a  single  fimg,  whei-eas  in  the  latter  this  tooth  is  two- 
rooted.  Upon  these  characters  two  genera  have  been  established.  The 
clouded  tiger  of  India  has  a  dental  formula  like  that  of  the  lynxes,  and 
approaches  the  "  sabre-tooth  division  "  in  the  enlargement  of  the  supe- 
rior canines,  by  reason  of  which  it  has  also  been  given  a  generic  rank. 
The  hunting   leopard,  or  cheetah,  forms  another  genus,  and  is  distin- 

FiG.  243. 


Cranium  of  Smilodon  necalor,  (lervais,  one-third  natural  size  (after  Cope). 

guished  by  the  absence  of  the  internal  tubercle  of  the  superior  sectorial. 
All  the  other  cats  are  very  much  alike,  and  can  be  distinguished  from 
one  another  only  specifically,  being  classified,  therefore,  under  the  genus 
Felis. 


TEETH  OF  THE    VERTEBRATA.  463 

The  second  division  is  extinct,  despite  the  fact  that  they  reveal  to  us 
the  most  perfect  laniary  dental  apparatus  yet  known  within  the  limits 
of  the  Carnivora,  and  were  of  the  most  formidable  size.  Two  genera 
are  known,  of  which  the  cranium  of  one  [Smilodon)  is  represented  in 
Fig.  243.  In  this  animal  the  dental  formula  is  I.  |,  C  y,  Pm.  2'W\, 
M.  ^  =  24  or  26,  and  marks  the  extreme  point  in  dental  specialization  in 
this  order,  as  far  as  reduction  is  concerned.  The  canines  of  the  upper  jaw 
are  of  prodigious  size  in  comparison  with  those  of  the  lower  series,  having 
compressed  crowns  with  serrulate  edges.  The  superior  molar  has  disap- 
peared, and  the  first  premolar  in  the  lower  jaw  in  some  species  is 
wanting.  The  exact  use  of  the  great  superior  canines  is  not  very 
clearly  understood.  The  possession  of  retractile  claws,  the  reduction  of 
the  molar  and  premolar  series,  together  with  the  general  perfection  of 
the  sectorial  apparatus,  are  strictly  in  keeping  with  a  most  carnivorous 
habit ;  but  with  all  this  it  must  have  been  impossible  for  the  animal  to 
open  its  mouth  wide  enough  to  take  a  firm  grip  upon  a  living  prey,  on 
account  of  the  great  length  of  the  upper  canines. 

Seeing  that  in  the  existing  cats  their  chief  destructive  powers  reside 
in  their  biting  qualifications,  it  is  difficult  to  understand  how  these 
animals  inflicted  wounds  sufficient  to  destroy  their  prey,  unless  they 
did  so  with  that  part  of  the  tusk  which  projected  below  the  level  of  the 
s}anpliysis  when  the  mouth  was  closed,  just  as  the  walrus  uses  his  tusks 
to  clamber  over  the  ice.  They  may  also  have  been  used  to  assist  the 
animal  in  climbing,  and  in  this  way  attained  their  great  size. 

The  animals  composing  the  last  group,  Ardoidea,  are  the  least  car- 
nivorous, and  do  not  as  a  general  rule  display  as  trenchant  and  sectorial 
dental  organs  as  the  two  preceding ;  in  two  families  the-  almost  exclu- 
sively carnivorous  habits  are  manifested  by  sectorials  of  moderate  per- 
fection ;  this  condition  is  associated  wdth  a  reduction  of  molars  and 
premolars  from  the  number  possessed  by  the  dog.  In  the  otliers  the 
molars  are  more  or  less  tubercular — a  structure  better  fitted  for  the 
mastication  of  the  mixed  diet  upon  which  they  subsist — and  usually 
exceed  the  premolars  in  size  and  strength.  The  extremes  of  dental 
variation  in  this  group  are  exhibited  by  the  bears  and  Aveasels,  of 
which  the  former  are  the  farthest  and  the  latter  the  least  removed 
from  the  more  typical  carnivores  in  the  structure  of  the  teeth. 

In  the  bears  the  dental  formula  is  the  same  as  in  the  dog,  but  in 
most  of  the  living  species  the  three  anterior  premolars  are  very  small, 
and  frequently  disappear  in  old  age,  leaving  a  ^vide  space  between  the 
fourth  and  the  canine.  In  the  upper  jaw  the  teeth  progressively 
increase  in  size  from  the  fourth  premolar  to  the  last  molar,  which, 
besides  being  quadritubercular,  is  provided  with  a  large  posterior 
heel  rounded  off  behind ;  by  the  addition  of  this  heel  the  crown  is 
rendered  elliptical  in  transverse  section,  the  antero-posterior  diameter 
being  twice  that  of  the  transverse.  The  first  true  molar  has  four 
cusps  on  its  triturating  face,  and  is  subquadrate  in  outline  ;  the  fourth 
premolar  is  tricuspid,  as  in  the  dog,  but  the  two  outer  cusps  are  not 
united  into  a  perfect  blade,  and  the  internal  lobe  is  large  and  has  a 
median  position.  This  tooth  is  relatively  small,  and  is  situated  consid- 
erably in  advance  of  the  canthus  or  angle  of  the  mouth ;  it  is  doubtful 


464  DENTAL  ANAT031Y. 

whether  its  possessor  ever  makes  use  of  it  as  a  sectorial  organ,  but 
rather  prefers  to  tear  the  tough  animal  membranes  than  to  divide  them 
with  the  sectorials,  as  the  dogs  and  cats  do. 

In  the  lower  jaw  the  first  true  molar  betrays  the  same  lack  of  car- 
nivorous specialization  as  the  upper  teeth,  being  essentially  tubercular 
in  structure,  although  the  proper  elements  of  tlie  sectorial  of  the  dog 
can  be  easily  made  out ;  the  crown  is  nuicli  elongated,  and  is  narrower 
in  front  than  behind,  the  heel  composing  at  least  half  of  the  crown. 
The  next  tooth  behind  it  is  the  largest  of  this  series,  and  is  perfectly 
quadritubercular ;  the  last  molar  is  smaller,  with  a  subcircular  grinding 
face,  upon  which  the  tubercles  are  poorly  defined. 

While  the  structure  here  described  is  found  in  all  the  northern  more 
carnivorous  bears,  the  tropical  frugivorous  S])ecies  retain  to  a  greater 
extent  the  integrity  and  more  normal  condition  of  the  anterior  premo- 
lars. This  is  especially  apparent  in  a  genus  recently  discovered  in  the 
mountains  of  oriental  Thibet  and  described  under  the  name  of  ^Eluro- 
pus.  In  this  animal  the  first  premolar  only  is  small,  while  the  others 
gradually  increase  in  size  to  the  last  molar,  which  has  a  comparatively 
small  heel. 

The  palseontological  evidence  is  as  yet  too  meagre  to  demonstrate 
with  any  considerable  degree  of  certainty  the  evolution  of  this  group  of 
the  Chrnivora,  but  some  suggestive  liints  of  their  former  connection  with 
the  Oynoidea  are  afibrded  by  the  extinct  genus  Hi/a'narctos,  which  was 
originally  described  by  Dr.  Falconer  from  the  Sewalik  Hills  in  India. 
This  genus  displays  three  premolars  of  normal  proportions  and  a  large 
sectorial,  together  with  a  last  superior  molar  in  which  the  heel  is  absent. 
In  one  species  in  particular,  H.  hemicyon,  from  the  Miocene  of  Sansan 
in  France,  which  is  provisionally  referred  to  this  genus,  the  two  true 
molars  in  the  u])per  jaw  have  about  the  same  proportions  as  in  the  dog, 
and  otherwise  resemble  them  very  nuich.  The  sectorial,  as  is  indicated 
by  the  roots,  was  large,  with  the  internal  tubercle  placed  opposite  the 
middle  part  of  the  crown.  If  it  were  not  for  this  latter  fact,  the  frag- 
ment of  the  up})er  jaw  upon  which  the  species  was  established  would 
readily  pass  for  that  of  a  member  of  the   Can  idee. 

In  the  weasels,  which  constitute  the  family  Afudelida',  the  sectorials 
are  well  defined  as  such,  and  some  of  them,  notably  the  typical  weasels, 
possess  retractile  claws.  In  none  does  the  molar  formula  exceed  ^, 
except  a  fossil  genus,  Lidridis,  a  near  ally  of  the  otters,  in  which  the 
molars  are  two  in  the  upper  jaw;  it  may,  however,  be  reduced  to  \,  as 
in  the  case  of  the  Cape  ratel  [MeUivora  capenfiis).  The  premolars  vary 
in  number,  as  do  also  the  sectorial  in  structure. 

The  dentition  t)f  the  American  pine  marten  (Fig.  244)  will  serve 
as  an  illustration  of  this  family,  althougli  it  is  somewhat  more 
specialized  in  a  ciu-nivorous  direction  than  most  of  them.  Its  dental 
formula  is  I.  f ,  C.  y,  Pm.  ^,  M..  ^  =  38.  The  incisors,  canines,  and 
premolars  have  approximately  the  same  structure  as  those  of  the  dog, 
except  that  the  fourth  premolar  or  superior  sectorial  has  the  two  outer 
cus])s  blended  together,  with  the  vertical  notch  absent.  The  true  molar 
is  tubercular,  and  has  a  greater  transverse  than  longitudinal  extent. 
In   the  lower  jaw  the  sectorial   is  very  much   like  that  of  the  dog. 


TEETH  OF  THE    VERTEBRATA. 


465 


Fig.  244. 


while  the  second  molar  i.s  small,  single-rooted,  having  a  crown  with 
one  cusp. 

The  teeth  of  the  raccoons  and  allied  forms  are  intermediate  between 
those  of  the  bears  and  weasels  in  many  respects,  with  a  stronger  tend- 
ency to  the  tubercular  than  to  the  sectorial  pattern. 

Teeth  of  the  Cheiroptera, — The  modification  of  the  anterior 
members  for  flight  distinguishes  this  order  from  all  other  unguiculates 
at  once.  Excluding  this  peculiarity,  which  is  univ^ersal  among  them, 
they  are  closely  related  to  the  Insectivora, 
and  without  doubt  have  been  derived 
from  some  arboreal  representative  of 
this  order.  It  is  conceivable  that  in 
jumping  from  branch  to  branch  they 
have  first  developed  a  lateral  fold  of 
integument,  similar  to  that  seen  in  the 
flying  squirrels,  which  later  involved 
the  fore  limbs  and  extended  to  the  neck. 
The  flying  lemur  (^(jr(deopitJu'cn.s)  fur- 
nishes such  a  transitional  condition,  both 
in  the  possession  of  the  membrane  and 
the  elongated  and  slender  fore  limbs,  al- 
though it  is  highly  improbable  that  the 
bats  have  descended  through  this  genus. 

The  incisors  are  never  more  than  two 
upon  each  side  above,  while  the  lower 
jaw  is  usually  provided  wath  the  same 
number,  but  may  be  increased  to  three. 
Canines  are  always  present  in  both  jaws, 
but  are  of  variable  proportions.  In  the  insect-eating  forms  (Animalivora), 
which  includes  the  great  bulk  of  the  species,  the  upper  molar  teeth  invari- 
ably display  the  peculiar  W-pattern  of  the  moles,  shrews,  etc,  of  the  Insec- 
tivora, already  noticed.  The  premaxillary  bones  are  always  small,  and 
seldom  meet  in  the  median  line  so  as  to  leave  the  tooth-border  inter- 
rupted in  front.  In  the  W-pattern  of  the  superior  molars,  the  absence 
of  the  median  pair  of  upper  incisors,  and  the  small  premaxillaries  it  is 
interesting  to  note  the  resemblances  they  bear  to  the  squirrel  shrews 
[Taiipaiada'),  the  only  other  insectivores  besides  the  flying  lemur  which 
are  known  to  be  arboreal  in  habit.  Ignorance  of  the  rest  of  the  anat- 
omy of  this  genus  does  not  permit  me  to  state  whether  it  strengthens 
this  resemblance  or  otherwise,  but  upon  the  whole  I  am  inclined  to 
believe  that  some  such  arboreal  insectivore  was  the  ancestor  of  the  bats. 

The  dentition  of  the  l)lood-sucking  vampires  is  modified  in  accord- 
ance with  their  habits,  as  is  also  the  entire  alimentary  canal,  and  devi- 
ates quite  extensively  from  the  normal  condition  of  that  of  the  insect- 
eaters.  The  alimentary  tract  consists  of  little  more  than  a  straight  tube 
from  mouth  to  anus,  and  is  thus  adapted  to  the  assimilation  of  the 
blood  of  living  animals,  upon  which  it  feeds. 

The  large  incisors  of  the  upper  jaw  are  two  in  number,  one  upon  each 
side,  whose  roots  extend  into  the  maxillary  bone,  and  whose  compressed, 
sharp-pointed,  hook-shaped  crowns  are  specially  fitted  to  puncture  the 

Vol.  I.— 30 


Vertical  View  of  the  Upper  and  I^ower 
Jaw  of  American  Pine  Marten  (Mustela 
umericana). 


466  DENTAL  AKAT03fY. 

skin  of  an  animal  sufficiently  to  cause  the  blood  to  flow  freely.  The 
canines  are  almost  equal  in  size  and  similar  in  shape,  while  the  lower 
incisors  and  canines  are  small.  The  molars  are  reduced  to  two  in  the 
upper  and  three  upon  each  side  in  the  lower  jaw ;  the  upper  molars  are 
implanted  by  single  fangs  and  have  simple  conical  crowns ;  in  the  lower 
jaw  the  first  two  are  like  those  above,  but  the  third  has  two  fangs  and 
a  bilobed  crown,  and  is  considered  by  Owen  to  be  homologous  Avitli  the 
last  premolars  of  insectivorous  bats.  The  dental  formula  is  thus  re- 
duced to  I.  1,  C.  {,  Pm.  I  =  20. 

The  frugivorous  bats,  which  are  popularly  known  as  "■  flying  foxes," 
offer  another  deviation  from  the  usual  structure  in  the  pattern  of  the 
molar  teeth ;  those  in  the  upper  jaw  have  crowns  of  a  subcircular  form 
in  outline  with  a  central  longitudinal  depression,  upon  each  side  of 
which  the  edge  is  elevated  into  a  cusp.  Those  of  the  lower  series  are 
similar  but  smaller,  with  the  cusps  more  pronounced  and  the  median 
groove  narrower. 

Teeth  of  the  Rodentia. — The  amount  of  minor  variation  in  the 
dental  organs  of  this  order  is  so  extensive  that  their  complete  elucida- 
tion is  hardly  within  the  scope  of  the  present  work ;  a  description  of 
the  leading  types  must  suffice.  That  which  most  conspicuously  distin- 
guishes the  rodents  from  all  other  mammals  is  the  possession  of  two 
powerful  curved  incisors  in  each  jaw,  M'hich  grow  from  persistent  pulps 
and  are  faced  with  enamel.  The  roots  are  implanted  deeply  in  the  sub- 
stance of  the  jaw  bones  in  the  lower  jaw,  often  reaching  as  far  back  as 
the  coronoid  process.  In  consequence  of  the  distribution  of  the  enamel 
upon  the  front  face  of  the  tooth,  leaving  the  dentine  naked  behind,  the 
inequality  of  Avear  between  the  two  surfaces  is  always  marked,  and  con- 
stantly preserves  a  chisel  point  to  the  crown — a  structure  pre-eminentlv 
adapted  to  the  gnawing  habits  of  its  possessor.  Concomitant  with  this 
modification  the  canines  are  always  absent,  the  premaxillarv  bones  are 
large  to  support  the  roots  of  the  incisors,  and  there  is  a  wide  space 
between  the  first  molar  or  premolar  and  the  incisor,  in  which  no  teeth 
appear.  The  mandibular  condyle,  moreover,  is  globular  in  form  and 
never  transverse,  thereby  allowing  excursion  only  in  an  antero-poste- 
rior  direction. 

The  order  thus  distinguished  is  divisble  into  four  sub-orders,  of 
which  the  rat,  squirrel,  porcupine,  and  rabbit  are  typical  representatives 
of  each. 

The  dental  formula  of  the  common  rat  (Fig.  245)  is  I.  \,  C.  -§-,  Pm.  ■^, 

M. -1  =  16.      Deciduous  teeth   are  entirely 
"  "  '^'  wanting,  and  it  is  therefore  monophyodont 

— a  condition  which  we  would   be  led  to 
anticipate,  as  far  as  the  molar  and  premolar 
series  is  concerned,  in  view  of  the  subtrac- 
tion of  the  latter.     The  absence  of  any  de- 
cnuiium  of  conunon  Kat,  Mu.s       ciduous  prcdcccssors  of  the  two  iiairs  of  in- 
cisors  IS  said  to  be  a  constant  feature  of  all 
rodents  except  the  hares,  so  that  monophyodontism  of  this  highly  heter- 
odont  animal  need  not  occasion  surprise. 

The  incisors  are  of  the  usual  pattern  displayed  by  the  order — large. 


TEETH  OF  THE   VERTEBRATA. 


467 


curved,  compressed  teeth,  with  chisel-shaped  crowns,  which  are  stained 
a  deep  orange  color  on  the  anterior  face  ;  the  pigment  which  produces 
this  color  is  intimately  incorporated  with  the  enamel  itself,  as  in  the 
shrews,  and  serves  to  sharply  define  the  limits  of  the  enamel  covering. 

In  both  the  upper  and  lower  jaws  the  first  molar  is  the  largest  and 
the  third  the  smallest.  They  are  implanted  by  distinct  roots,  the  oppo- 
site rows  of  teeth  being  nearly  parallel.  The  crowns  are  made  up  of 
three  curved  transverse  ridges,  with  the  convexity  in  front  and  the  con- 
cavity beliind ;  the  two  anterior  of  these,  in  the  upper  teeth,  are  termi- 
nated internally  by  well-marked  cusps,  which  rise  above  the  summits 
of  the  ridges.  In  tlie  last  tooth  the  anterior  and  posterior  of  these 
ridges  are  less  distinctly  marked,  and  are  reduced  to  little  more  than 
internal  tubercles.  The  second  molar  of  the  lower  jaw  has  tlie  last 
crest  rudimental,  and  in  the  third  it  is  entirely  wanting. 

While  this  structure  j^revails  in  the  teeth  of  tlie  more  typical  murines, 
others  possess  molars  with  crowns  of  much  greater  complexity  and 
witliout  roots.  Such  is  exemplified  by  the  arvicoline 
section  of  tlie  Muridce,  in  which  the  crown  is  (;left  to 
the  median  line  by  vertical  fissures  upon  each  side 
placed  alternately.  The  structure  of  the  grinding  sur- 
face which  results  from  tliis  arrangement  is  a  system 
of  alternate  triangular  prisms  connected  in  the  middle 
of  tlie  cro^vn  by  a  narro\v  btuid  of  dentine.  This  is 
well  shown  in  the  accompanying  figure. 

In  the  S(}uirrel  division  premolars  are  always  pres- 
ent, in  consequence  of  which  there  are  deciduous  teeth, 
tioii  of  the  beaver  family,  the  teeth  are  very  similar  in  the  different  spe 
cies,  the  only  important  variation  occurring  in  the  number  of  premolars. 


Fig.  246. 


Vertical  Mew  of  the 
('.rinding Surface  of 
the  First  Lower 
Molar  of  a  Muskrat 

(Fiber  zibethicus). 

With  the  excep- 


In  the  common  fox 
M.  #  =  20.     The 


squirrel  the  dental   formula  is  I. 


P 


ai   rormuia  is  i.  \,  C.  ^, 
f  =  20.     The  incisors  (Fig.  247)  are  not  so  robust  as  in  the 
and,  like  them,  are  colored  upon  the  anterior  face. 

Fig.  247. 


m. 


rat, 


Vertical  View  of  the  Teeth  of  Fox  Squirrel  {Sciurus  carol inensis). 

The  first  and  onlv  premolar  is  smaller,  implanted  by  three  roots,  and 
has  a  triangular  tricuspid  crown.     The  three  true  molars  in  the  upper 


468  DENTAL  ANATOMY. 

jaw  are  larger  and  subequal  in  size.  Tlieir  crowns  are  imperfectly  quad- 
rate in  outline,  and  provided  with  two  transverse  crests  which  join  a 
large  marginal  cusp  on  the  internal  border.  There  is  in  addition  an 
anterior  and  posterior  cingulum,  which  becomes  continuous  with  the 
large  marginal  cusp.  The  inferior  molars  have  the  same  quadrate  out- 
line as  those  above,  but  the  crowns  present  a  central  depression  sur- 
rounded by  a  slightly  elevated  margin  bearing  a  cusp  at  each  angle. 
In  this  sub-order  is  to  be  found  the  nearest  approach  to  the  quadri- 
tubercular  condition  of  the  molar  teeth  in  any  of  the  Rodcntia,  in  con- 
sequence of  which  there  is  little  difficulty  in  comprehending  their  organ- 
ization ;  but  when  we  come  to  analyze  the  highly  complex  form  of 
molar  which  some  of  the  porcupines  exhibit,  we  naturally  seek  for  a 
key  to  a  solution  of  their  structure  on  the  basis  of  the  quadritubercular ; 
this  is  all  the  more  natural  when  we  remember  that  the  squirrels  present 
the  oldest  known  representatives  of  the  order  in  the  genus  Plesiarctomys 
of  Middle  Eocene  Age,  which  scarcely  differs  generically  from  the  living 
forms.  The  teeth  of  the  American  porcupine  (JEref/iizon),  while  possess- 
ing in  general  the  molar  pattern  of  the  squirrel,  nevertheless  differs  from 
it  sufficiently  in  the  direction  of  the  more  specialized  hystricine  teeth  to 
let  us  into  the  secret  of  how  these  complex  forms  have  arisen  from  that 
of  the  squirrel. 

In  the  description  of  the  molars  of  the  squirrel  we  have  already  seen 
that  the  face  of  the  crown  is  marked  by  three  transverse  ridges,  enclos- 
ing two  valleys,  which  open  externally  and  are  bound- 
ed internally  by  a  thick  marginal  cusp.  Now,  in  the 
first  premolar  of  the  porcupine  (Fig.  248)  which  is  un- 
usually instructive,  the  three  transverse  ridges  are  pres- 
ent, but  considerably  augmented  in  height,  together 
with  a  fourth  ridge  behind  added  from  the  cingulum. 
The  valleys  separating  the  three  anterior  crests  open 
externally,  while  the  fourth  coalesces  externally  with 
the  third,  so  as  to  enclose  a  deep  pit  or  fossette ;  the 
C  strong  internal  marginal  cusp  is  likewise  present,  but 

^i^f*  Lower  Pjtnioiar    j^  iiiterrui)ted  ou  its  inner  side  bv  a  deep  wide  vallev 

of  Porcupine  [Eifthi-  1         .  .  1 

zon  d(jrs(iii.s),  vertical    Avliich  opcus  internally,      ihe  succeeduig  molars  are 
porterior;r,  internal;    like  it  in  structure,  cxccpt  that  the  first  and  second 
facts 'oAllrcrown"''    trausversc  ridges  unite  at  their  extremities  to  form 
a  second  fossette  in  front. 
In  other  genera  of  this  group  the  valleys  are  still  further  dee])ened  by 
the  elevation  of  the  ridges,  and  other  indentations  are  added  from  within. 
As  a  protection  against  fracture  of  the  now  laminar  crests,  cementum  is 
added,  which  completely  fills  up  the  valleys,  leaving  the  grinding  surface 
approximately  smooth.     This  is  the  condition  attained  by  the  beaver 
among  the  sciuromor])h  or  squirrel  sub-order,  as  well  as  a  majority  of  the 
hystricomorphs  or  porcupines.     As  a  further  comjilication  in  this  series, 
the  external  and  internal  valleys  unite  across  the  face  of  the  crown,  leaving 
transverse  laminae  connected  only  at  the  base  and  bound  together  above 
by  cementum ;  of  which  the  guinea-pig  is  an  example.     Finally,  the 
extreme  of  specialization  is  reached  in  the  cajiybara,  wherein  these  trans- 
verse laminae  are  as  many  as  thirteen  or  fourteen    in  a  sinarle  tooth. 


TEETH  OF  THE   VERTEBBATA.  469 

This  point  of  perfection  rivals  that  of  the  elephant,  and  is  undoubtedly 
a  long  way  removed  from  the  quadritubercular  structure.  On  account 
of  this  highly  complex  molar  dentition  and  certain  cranial  peculiarities 
Dr.  Gill  has  proposed  to  give  this  genus  a  distinct  family  rank. 

The  last  sub-order  of  the  Bodentia  is  the  Lagoiiiorphd,  which  includes 
the  hares  and  rabbits.     The  dental  formula  in  this  group  is  constantly 
I.  \,  C.  ^,  Pm.  I,  M.  f  =  28,  in  addition  to  which  in  very  young  spe- 
cimens there  is  another  or  third  pair  of  inci- 
sors in  the  upper  jaw  to  be  added  to  the  per-  ^^^-  ^"^*'-. 
manent  set.     Huxley  has  recently  shown  that 
the  deciduous  dentition  is  D.  I.  |-,  D.  M.  |^, 
which  brings  this  group  of  the  Rodentia  into 
strict  accord  with  other  Mammalia  in  the  re- 
placement of  the  teeth.                                                       Last   Molar  of  Capybaia   {Hf,dro- 
i     ^                                   .                          ...             ,                    cnoerus  capyoara),  vertical  view. 

The  median  pan'  of  superior  incisors  depart 
from  the  usual  pattern,  inasmuch  as  they  are  indented  upon  their  anterior 
faces  by  a  vertical  groove  near  the  middle  of  the  tooth ;  they  are  other- 
wise as  in  the  genera  already  noticed,  except  that  they  lack  the  orange 
color  of  the  enamel.  Immediately  behind  each  of  these  incisors,  and 
applied  closely  to  them,  is  to  be  seen  a  small  cylindrical  tooth,  the  second 
pair  of  incisors.  In  the  very  young  state  a  third  pair  can  usually  be 
found  imbedded  in  the  gum  external  to  the  two  median  ones,  which  fall 
out  soon  after  birth.  The  single  pair  of  the  lower  jaw  are  not  grooved 
and  have  the  usual  form  common  to  the  order. 

The  molars  are  remarkable  for  their  great  length  in  a  vertical  direc- 
tion, as  well  as  their  antero-posterior  compression ;  they  grow  contin- 
uously and  do  not  form  roots.  With  the  exception  of  the  first  premolar 
and  the  last  molar,  the  molars  and  premolars  of  the  upper  jaw  are"  alike, 
and  consist  of  two  vertical  transverse  laminse  closely  united  in  the  middle 
line,  the  division  of  which  is  indicated  both  on  the  inner  and  outer  sides 
of  the  tooth  by  a  vertical  groove.  The  first  premolar  and  last  molar  are 
made  up  of  a  single  lamina,  the  enamel  being  thrown  into  two  vertical 
folds  upon  the  anterior  part  of  the  first  premolar.  In  other  respects  the 
rabbits  are  remarkable  for  the  entire  absence  of  the  coronoid  process 
and  the  very  small  bony  palate,  which  forms  little  more  than  a  bridge 
across  the  roof  of  the  mouth. 


Teeth  of  the  Ungulate  Series. 

So  far,  excluding  the  rodents,  our  attention  has  been  confined  to  those 
dental  organs  in  which  the  molars  have  not,  with  few  exceptions,  passed 
beyond  the  quadritubercular  stage  of  development ;  this  condition,  we 
have  the  best  of  reasons  to  conclude,  was  preceded  by  the  tritubercular 
in  the  upper  and  the  tuberculo-sectorial,  or  at  least  a  tooth  possessing 
its  elements,  in  the  lower  jaw.  When  one  compares  these  short-crowned 
rooted  tubercular  molars  with  the  complex  rootless  molars  of  a  horse, 
cow,  or  elephant,  he  might  spend  hours  and  days  in  thoughtful  contem- 
plation without  discovering  the  faintest  relationship  existing  between 
their  respective  patterns ;  nor  would  we  be  any  nearer  a  solution  of 
the  difficulty  had  not  the  researches  of  palaeontologists  brought  to  our 


470 


DENTAL  ANATOMY. 


understanding  a  knowledge  of  these  organs  before  they  had  assumed  those 
distinctive  characteristics  and  speciaHzed  patterns  which  they  now  display. 

There  are  few  students  of  odontography  who  are  acquainted  M'ith  the 
facts  of  mammalian  palneontology  as  they  now  stand  who  have  not  had 
repeatedly  forced  upon  their  attention  the  gradual  decrease  in  complexity 
of  the  molar  teeth  of  the  ungulates  as  we  go  backward  in  time.  Cope 
has  recently  shown  that  the  earliest  ungulates  had,  as  a  general  rule, 
tritubercular  molars — a  condition  which  is  as  primitive  as  that  of  many 
insectivorjes  ;  and  in  no  instance  do  we  meet  with  highly  specialized  teeth 
until  the  latest  geological  periods  are  reached. 

The  ungulate  series  is  divisible  into  four  orders,  which  have  been 
characterized  and  defined  by  Cope  upon  the  structure  of  the  limbs.  The 
oldest  of  these  orders,  Taxeopoda,  is  remarkable  f(3r  the  generalized  cha- 
racter of  the  limbs  as  compared  with  the  later  ungulates ;  they  possess  live 
toes  upon  each  foot,  and  in  one  family,  the  Periptychida',  the  superior 
true  molars  are  tritubercular — a  fact  which  brings  the  ungulate  stem  to 
a  point  not  far  removed  from  the  Insectivora  of  the  unguiculates.  This 
order  includes  three  sub-orders,  two  of  which  are  extinct,  and  one,  the 
Hyracoidea,  being  represented  by  two  living  genera,  popularly  known 
as  the  coneys.  The  most  ancient  of  these  three  sub-orders  is  the  (hn- 
dylarthra,  a  group  thus  far  known  only  from  the  American  Eocene.  A 
careful  study  of  their  osteology  leads  to  the  conclusion  that  they  are  the 
ancestors  of  all  succeeding  ungulates,  furnishing  just  such  a  generalized 
type  in  the  proper  geological  position  as  is  necessary  to  satisfy  the 
demands  of  the  development  hypothesis ;  they  likewise  enable  us  to 
comprehend  more  clearly  the  mutual  relationship  and  evolution  of  the 
entire  series. 

Teeth  of  the  Taxeopoda. — As  the  Condylarthra  are  the  oldest 
of  this  order  and  the  most  primitive  in  their  organization,  it  will  be  best 

Fig.  250. 


Dentition  of  Periptychvs  rhnbdmlnn,  Cope,  two-thirds  natural  size:   a,  superior  molars  from  below; 
//    inferior  molars  from  above — from  the  New  Mexican  Puerco  (alter  Cope). 

to  commence  with  a  consideration  of  their  teeth.  Three  families  are 
referred  to  it,  one  of  which,  the  Per iptych idee,  is  confined  to  the  lowest 
Eocene  deposits.^     In  the  typical   genus,  Periptychu.s  (Fig.   250),  the 

'  When  the  lowest  Eocene  is  mentioned,  reference  is  made  to  the  Pnerco  beds,  which 
•were  formerly  considered  to  belong  to  the  Tertiary  ;  Prof.  Cope  now  considers  tliat  they 
are  of  Cretaceous  age. 


TEETH  OF  THE   VERTEBBATA. 


471 


dental  formula  is  I,  |,  C.  \,  Pm.  ^,  M.  f  =  44,  the  normal  diphyodbnt 
number.  The  incisors  are  relatively  small  and  of  the  usual  pattern  ;  the 
canines  are  large,  powerful  teeth,  and  resemble  those  of  many  carniv- 
orous and  insectivorous  animals.  The  premolars  gradually  increase  in 
size  from  the  first  to  the  fourth,  which  considerably  exceeds  the  true 
molars  in  size  ;  the  crowns  of  the  last  three  premolars  in  the  upper  jaw 
have  a  large  external  conical  cusp  and  a  strong  internal  ledge ;  those  of 
the  lower  jaw  have  a  strong  outer  cusp,  with  a  small  accessory  one  at 
the  antero-internal,  and  two  at  the  postero-internal,  angle  of  the  crown. 
The  true  molars  of  the  upper  series  appear  at  first  sight  to  be  com- 
plex and  multicuspid,  but  upon  analysis  it  is  found  that  they  are  essen- 
tially tritubercidar,  with  minor  cusps  added.  The  two  usual  external 
cusps  are  present,  together  with  one  large  internal  tubercle  somewhat 
crescentic  in  horizontal  transverse  section.  The  three  principal  cusps 
iu*e  homologous  with  the  three  cusps  of  the  molar  teeth  of  many  of  the 
Insectivora  already  mentioned,  and  like  them  are  placed  in  the  form  of 
a  triangle,  but  the  two  horns  of  the  crescent  are  interrupted  by  the 
development  of  two  intermediate  cusps ;  to  these  are  added  two  small 
interior  cingular  marginal  cusps,  making  seven  in  all.  The  lower 
molars  are  quadritul)ercular,  with  a  faint  representation  of  the  anterior 
basal  cusp  of  the  tuljerculo-sectorial  still  remaining.  The  postero- 
external cusp  is  connected  ^\•ith  the  antero-internal  by  a  ridge  which 
crosses  the  face  of  the  crown  obliquely ;  this  ridge  is  found  in  some  of 
the  insectivores,  notably  Esthonyx,  and  is  what  remains  of  the  former 
connection  of  the  heel  with  the  anterior  or  triangular  part  of  the  tuber- 
culo-sectorial.  The  enamel  of  both  the  molars  and  premolars  of  this 
genus  is  curiously  sculptured,  owing  to  the  presence  of  a  number  of 


Fig 


Ectoconits  dilrigdiiiis,  Cupt',  two-tliuds  natural  size:  ",  maxillary  and  jiitni  i\ill  n  \  Ixint-  \i  mi  lulon, 
retaining  a  good  deal  ol'  the  matrix;  h,  last  two  interior  molars,  worn  bj  use,  (,  thiee  deciduous 
with  first  permanent  molar  of  a  young  animal  (after  Cope). 

vertical  grooves  and  ridges,  it  being  the  only  case  of  the  kind  known  in 
the  Mammalia.  In  an  allied  genus,  Edoganus  (Fig.  251),  the  molars 
are  larger  than  the  premolars,  and  their  crowns  are  further  complicated 
by  the  addition  of  an  outer  cingular  cusp,  giving  a  total  of  eight  of  the 


472  DENTAL  ANATOMY. 

most  complex  trituberciilar  teeth  yet  known.  This  figure  displays 
more  clearly  than  that  of  Periptych  us  the  relationship  of  the  component 
cusps. 

Other  genera  of  this  family,  of  which  there  are  seven  in  all,  display 
simple  tritubercular  molars,  which  resemble  the  corresponding  teeth  of 
the  insectivores  to  a  remarkable  extent. 

The  second  family  of  this  sub-order  is  the  Phenacodontkkc ,  which 
continues  to  the  Upper  Eocene  Period.  Fragmentary  remains  of  the 
typical  genus  Phenacodus  were  known  as  long  ago  as  1873,  but  very 
little  was  known  of  its  true  nature  until,  some  nine  years  later,  the 
writer  was  fortunate  enough  to  discover  two  almost  complete  skeletons, 
representing  two  distinct  species,  in  a  fine  state  of  preservation  while 
exploring  the  AVasatch  deposits  of  the  Big  Horn  Basin,  AVvoming  Ter- 
ritory. This  material  has  afforded  Prof.  Cope,  at  whose  instance  the 
exploration  was  undertaken,  the  opportunity  of  not  only  determining 
the  position  and  affinities  of  this  remarkable  genus,  but  a  key  to  a  cor- 
rect interpretation  of"  many  of  his  later  discoveries,  as  well  as  a  basis  for 
one  of  the  most  important  generalizations  yet  introduced  in  relation  to 
the  hooted  Mammalia.^ 

The  dentition  of  this  genus  (Fig.  252)  approaches  nearer  to  that  of 
the  higher  ungulates  than  the  preceding  family,  although  the  interval 
between  them  is  comparatively  small.  Its  formula  is  1. 1^,  C  \,  Pm.  ^, 
M.  1^  =  44.  The  premolars  are  of  a  simpler  pattern  than  the  molars, 
the  posterior  ones  becoming  tritubercular.  The  superior  molars  have 
quadrate  crowns  bearing  four  principal  cusps,  placed  at  each  angle,  tg 
which  are  added  several  minor  cusps,  the  rudiments  of  structures  which 
assume  considerable  importance  in  the  later  and  more  specialized  gen- 
era. The  four  principal  cusps  are  the  usual  ones  of  the  quadritubercular 
molar,  two  external  and  two  internal,  and  are  low,  more  or  less  conic, 
obtuse  structures.  Between  the  outer  and  inner  ones  are  two  isolated 
tubercles,  which  are  later  developed  into  cross- ridges  connecting  the 
outer  and  inner  cusps,  thereby  producing  the  lophodont  molar  which 
is  so  characteristic  of  some  groups  of  the  ungulates.  At  a  point  mid- 
way between  the  two  outer  cusps,  on  the  external  margin  of  the  crown, 
the  cingulum  is  produced  into  a  small  tubercle,  which  in  most  of  the 
specialized  ungulates  becomes  connected  with  and  unites  the  two  Vs 
formed  by  the  crescentic  structure  of  the  two  external  cusps,  just  as  in 
some  of  the  insectivorous  genera  already  described. 

In  the  lower  molars  four  tubercles  are  present,  of  which  the  postero- 
external is  connected  with  the  antero-internal  by  a  well-marked  ridge. 
The  anterior  basal  lobe  is  reduced,  but  still  present  in  the  form  of  a  low 
cingular  ridge. 

The  molar  teeth  of  this  animal  display  a  tyjiical  bunodont  dentition, 
and  upon  a  correct  understanding  of  their  organization  depends  a  proper 
com]>rehension  of  all  the  succeeding  s]iecialized  molars  of  this  series. 
It  is  l)y  sini])le  additions  to,  and  modifications  of,  the  component  lobes 
and  crests  of  this  pattern  that  all  the  comiilex  ungulate  molars  have  been 
produced;  if  the  advocate  of  the  evolution  hypothesis  had  no  other  evi- 

'  See  Prof.  Cope's  valuable  memoir  of  this  group,  American  Naturolkt  for  August 
and  September,  1884. 


TEETH  OF  THE    VERTEBRATA. 


473 


474 


DENTAL  ANATOMY. 


dence  upon  which  to  base  his  belief  than  that  afforded  by  the  gradual 
complication  of  the  molar  teeth  from  this  point  upward  in  the  hoofed 

Fig.  253. 


Meniscotherium  terrcerubrce,  Parts  of  Cranium,  Diree-fourths  natural  iize— fiom  ^\  asatch  Beds  of  New 
Mexico:  «,  cranium  from  above;  b,  from  below;  r,  portion  ot  upper  jaw,  displaying  deciduous 
molars  (after  Cope). 

]\Iammalia,  this  alone,  it  appears  to  me,  would  be  sufficient  to  gain  for 
it  a  respectful  consideration  at  the  hands  of  its  opponents. 

Fig.  254. 


Lower  Jaw  ot  M.  terrcerubrx,  three  views  (after  (  ope). 

The  last  family  of  this  sub-order  is  the  Memscothenidce,  whose  den- 
tition  is  represented   in  Figs.  253,  254,     The  dental  formula  of  the 


TEETH  OF  THE   VERTEBRATA.  475 

single  genus  3Ieniscotherium  is  given  by  Cope  as  follows  :  I.  |,  C.  ]-, 
Pni.  |,  M.  f  =  44.  As  compared  with  Phenacodns,  the  canines  are 
relatively  smaller  and  the  molars  more  complex ;  the  same  elements  are 
readily  recognized  as  in  the  molars  of  that  genus,  but  the  two  exter- 
nal cusps  are  crescentic  and  elevated,  the  two  contiguous  horns  being 
connected  with  the  median  external  cusp,  which  now  forms  a  vertical 
ridge  or  rib  on  the  external  part  of  the  crown.  The  intermediate  tuber- 
cles are  also  present,  and  are  greatly  enlarged  ;  the  anterior  is  crescentic 
and  the  posterior  oblique  and  elongate.  Of  the  two  internal  cusps,  the 
anterior  is  conic,  while  the  posterior  is  crescentic. 

The  lower  molars  exhibit  two  Vs,  by  reason  of  the  development  of 
cross-ridges  connecting  the  external  with  the  internal  cusps  and  tlie 
increase  in  height  of  the  oblique  ridge.  The  tooth-line  is  uninterrupted 
by  a  diastema,  and  the  incisors  did  not  grow  from  persistent  pulps. 

The  second  sub-order,  Hyracoidea,  has  long  remained  a  puzzle  to 
zoologists,  and  has  been  associated  at  different  times  near  the  rodents, 
at  others  with  the  perissodactyle  ungulates,  and  latterly  has  been  made 
the  type  of  a  distinct  order.  The  discovery  of  the  Condylarthra  leaves 
no  doubt  of  its  relationship  with  these  forms,  and  the  propriety  of 
making  it  a  sub-order  of  the  Taxeopoda  is  at  once  apparent.  The 
dental  formula  of  the  two  living  genera,  Hyrux  and  Dendrohi/rax,  is 
given,  I.  f ,  C.  ^,  Pm.  ^,  M.  |  =  36,  although  DeBlainville  in  his  figures 
of  the  diifercnt  species  represents  some  of  them  with  only  two  incisors 
in  the  upper  jaw  instead  of  four. 

The  incisors  grow^  from  persistent  pulps  and  have  large  pointed 
crowns ;  the  canines  are  entirely  absent  from  both  jaws ;  the  molars 
and  premolars  have  complex  crowns — in  one  genus,  Hyrax,  being 
almost  identical  with  those  of  the  rhinoceros ;  on  account  of  this  com- 
plexity Cuvier  placed  it  in  the  same  group  with  tliat  animal.  In  the 
other  genus,  Deudrohyrax,  the  molar  teeth  are  quite  different,  and  upon 
careful  comparison  with  those  of  3Ienlscotherlum  betray  unmistakable  evi- 
dence of  near  relationshii).  This  resemblance  is  „  «-- 
not  confined  to  tlie  molar  teeth  alone,  but  is  strik- 
ingly sliown  in  the  general  form  of  the  skull, 
and  especially  in  the  great  enlargement  of  tlie 
angular  portion  of  the  mandible.  The  upper 
molars  of  this  genus  (Fig.  255),^  like  Menisco- 
therium,  have  two  crescentic  external  cusps  con- 
nected by  a  vertical  rib,  and  two  intermediate  ^^°!^6L-.T'rverficai'fi'^wf ''r^ 
tubercles,  which  are  more  or  less  blended  with        superior  moiar;  i.extemaij 

-  '.  -  1  M         1        1  1  '  interior,  3,  internal,  and 

the  two  internal  cusps,  wliile  the  lower  molars       4,   posterior    surfaces    or 

1  J-    11        j1  ij_  J.1  r  crown;    &,    inferior    molar; 

nave  essentiallv  the  same  pattern  as  those  ot        1,  external,  2,  internal  sur- 
this  genus.     The  whole  structure  of  the  molars       ^^'^'  '^"^''  ^'  Bi'''""i"e)- 
represents  just  such  an  advance  over  that  of  the  extinct  Eocene  genus 
as  we  should  be  led  to  anticipate  on  a  priori  grounds. 

It  is  true  that  the  canines  are  absent  in  Dendrohyrax,  and  incisors 

grow  from  persistent  pulps ;  but  this  is  not  at  all  remarkal^le  w^hen  we 

consider  the  great  interval  of  time  between  them  and  an  approach  to 

this  condition,  as  far  as  the  canines  are  concerned,  in  their  reduced  size, 

'  This  figvire  does  not  represent  the  structure  of  the  grinding  face  very  clearly. 


4 7(5  DENTAL  ANATOMY. 

in  the  extinct  genus.  Altogether,  I  am  disposed  to  regard  llenisco- 
therium  as  the  direct  ancestor  of  the  Hyracoidca,  notwithstanding  their 
wide  separation  in  both  time  and  space. 

As  a  further  complication  in  the  molar  pattern  of  this  line,  we  have 
the  complete  fusion  of  the  intermediate  tubercles  with  the  internal  cusps 
in  Hijra.v,  which,  as  already  stated,  gives  the  pattern  of  the  molars  of 
the  rhinoceros. 

It  is  believed  by  Cope,  from  evidence  aifbrded  by  the  structure  of  the 
limbs,  that  the  Toxodontia,  a  group  of  curious  extinct  ungulate  forms 
found  in  the  later  geological  horizons  of  kSouth  America,  belong  to  this 
order.  I  am  unable  to  find  any  confirmation  of  this  position  from  a 
study  of  the  teeth,  but  it  may  be  that  they  have  been  derived  from  a 
condvlarthrous  source.^ 

The  dentition  of  the  typical  genus  Toxodon  contains  incisors,  pre- 
molars, and  molars  only,  the  canines  being  absent,  and  all  were  of  per- 
sistent growtii.  The  two  pairs  of  incisors  above  are  large  and  scalpri- 
form,  as  in  the  rodents,  of  which  the  outer  greatly  exceed  the  mesial 
pair  in  size.  In  the  lower  jaw  these  teeth  are  three  in  number  upon 
each  side,  and  were  also  of  persistent  growth.  They  are  subequal  in 
size,  and  have  imperfectly  prismatic  crowns  similar  in  shape  to  the  tusks 
of  the  boar  in  transverse  section,  being  covered  with  enamel  only  upon 
the  anterior  convex  surface. 

The  molars,  of  which  there  are  seven  upon  each  side  above,  gradually 
increase  in  size  fr(^m  the  first  to  the  last.  It  is  highly  probable  that 
the  first  four  of  these  teeth  are  premolars,  but  in  the  absence  of  any 
knowledge  of  the  milk  dentition  and  the  manner  of  its  replacement, 
this,  of  course,  is  inferential.  They  have  remarkably  long  crowns, 
with  an  altogether  unique  pattern,  and  did  not  develop  roots.  In 
section  thevare  triangular,  with  the  apex  of  the  triangle  directed  forward 
and  outward.  Upon  the  inner  side  there  is  a  deep  indentation  or  fold 
reaching  to  a  point  near  the  centre  of  the  crown,  which  may  be  the 
valley  separating  the  two  internal  cusps.  The  only  arrangement  sim- 
ilar to  this  is  seen  in  the  last  upper  molars  of  many  of  the  Ungulata, 
of  which  ]\[(nmcothennm  furnishes  an  average  example.  Here  the  pos- 
tero-internal  cusp  is  absent,  and  the  two  outer  cusps  are  intimately 
blended.  In  the  rhinoceros  (Fig.  257)  the  last  molar  goes  even  further 
in  this  direction  by  reason  of  the  fusion  of  the  elements  and  the  obliter- 
ation of  the  external  rib.  It  is  conceivable  that  some  such  structure  as 
this  preceded  the  present  one  in  Toxodoyi,  but  until  the  palseontological 
evidence  of  the  philogcny  of  this  group  is  more  fully  known  this  is  the 
onlv  explanation  \\hicli  can  now  be  offered  to  account  for  their  aberrant 
pattern.  The  ])attern  of  the  lower  molars  is  very  like  that  of  Menis- 
cotherium — a  fiict  wliich   lends  countenance  to  the  above  hypothesis. 

Teeth  of  the  True  Ungut.ata. — This  order  includes  nearly  all 
the  modern  and  many  extinct  ungulate  animals,  and  is  conspicuously  dis- 
tinguished from  all  other  hoofed  forms  by  the  interlocking  character  of 
the  proximal  and  distal  rows  of  the  carj)al  and  tarsal  bones.  Cope  has 
called  it  the  Diplarflirn,  in  allusion  to  the  double  articular  surface  af- 
forded bv  the  ankle-bone  (astragalus)  to  the  cuboid  and  navicular  below, 
'I  have  elsewhere  spoken  of  tlieir  relutionsliip  to  the  Tillodontia. 


TEETH  OF  THE   VERTEBRATA. 


477 


whereas  in  the  Condylarthra  the  astragakis  articulates  distally  with  the 
navicular  or  scaphoid  only — a  condition  which  obtains  in  nearly  all 
Mammalia.  Two  prominent  divisions  of  this  order  can  be  recognized 
— the  Artiodactyln,  or  "  split  hoofs,"  of  which  the  hog,  cow,  and  deer, 
etc.  are  familiar  examples,  and  the  Perissod((cti/l((,  whose  only  living 
representatives  are  the  horse,  tapir,  and  rhinoceros. 

The  latter  sub-order  is  divisible  into  a  number  of  sections,  which, 
when  we  consider  the  extinct  forms  constituting  at  least  nine-tenths  of 
the  species,  we  are  not  able  to  separate  by  any  characters  of  very  great 
anatomical  importance,  notwithstanding  the  fact  that  the  extremes  of 
the  several  stems  are  different  enougli.  That  family  which  stands 
nearest  to  the  Condylurtlira  is  the  Lopluodontidcv,  a  group  ol"  extinct 
generalized  perissodactyls  from  the  Middle  and  Lower  Eocene  beds. 
The  digital  formula  is  not  so  great  as  in  the  Condylarthra,  being  only 
4 — 3,  and  in  one  instance  3 — 3  ;  that  is  to  say,  four  toes  on  the  anterior 
and  three  on  the  posterior  limbs.' 

Hyracotherium  (Fig.  256)  is  a  typical  example  of  this  family,  or  at 

Fig.  25(5. 


Skull  of  Hyracotherium  augustidens,  Cope,  from  the  \Vind  River  Beds  of  Wyoming  (after  Cope). 


least  that  section  of  it  whose  dentition  approaches  nearest  to  Phenacodus  ; 
and  if  it  were  not  known  that  the  carpal  and  tarsal  articulations  were 
different,  they  might  easily  be  mistaken  for  the  same  family,  so  great  is 
the  resemblance  of  their  teeth.  The  dental  formula  of  this  animal  is 
I.  3.  C.  J-,  Pm.  ^,  M.  f  =  44,  the  same  as  Fhniacodns.  The  ]>remolai-s 
are'^'different  from  the  molars,  being  simpler  in  form,  and  the  first  in 
both  jaws  is  separated  from  the  others  by  a  diastema.     Tlie  molar  pat- 

iProf.  Marsh  has  described  several  genera  of  this  group,  wliich  he  has  called  Eohip- 
pus,  Orohippux,  etc.,  but  the  descriiitions  are  so  brief  that  it  is  impossible  to  form  any 
correct  estimate  of  their  true  relationship.  Enhippii.^.  he  says,  has  five  toes,  but  further 
than  this  its  osteology  has  not  been  described.  It  would  be  interesting  to  know  in  what 
respects  it  diflers  from  the  phenacodonts,  Hyracotherium,  Pliolophus,  etc. 


478  JJESTAL  ANATOMY. 

tern  is  substantially  the  same  as  in  Plienacodus,  with  the  slight  excep- 
tion that  the  cusps  are  more  elevated  and  laterally  flattened,  and  the 
external  rib  is  very  small  or  absent  in  Hyrucotherium.  In  the  nearly 
allied  genus  PHolopIius,  which  I  suspect  to  be  the  same  as  Orohippus  of 
Marsh,  the  last  or  fourth  premolar  below  is  like  the  true  molars  in  form, 
and  is  (piadritubercular,  while  the  genus  Lopldotlierium  has  the  third 
and  fourth  premcjlars  below,  like  the  true  molars. 

In  the  second  section  of  this  family  the  external  lobes  of  the  superior 
molars  are  laterally  flattened  and  intimately  blended  together,  so  as  not 
to  be  well  distinguished.  Of  these  the  anterior  .is  much  the  smaller,  and 
is  convex  externally,  whereas  the  posterior  is  large  and  concave  without. 
The  intermediate  tubercles  no  longer  exist  as  such,  but  form  jjrominent 
crests  which  connect  the  external  with  the  internal  cusps,  crossing  the 
crown  somewhat  obliquely.  In  the  lower  molars  the  external  and  inter- 
nal cusps  are  also  connected  by  crests,  giving  the  typical  lophodont  pat- 
tern. As  a  rule,  the  premolars  are  trilobed,  and  the  molar  formula  is 
Pm.  ^,  M.  f ,  but  in  one  genus  (Dilophodou),  recently  described  by  Prof. 
Scott,  there  are  only  three  premolars  in  the  lower  jaw.  In  another 
genus,  lately  described  by  the  same  author  under  the  name  of  JJcsina- 
totherium,  the  third  and  fourth  upper  premolars  are  like  the  molars, 
and  are  four-lobed. 

The  tapirs  form  another  nearly  related  family  (Tapiridce),  which  no 
doubt  sprang  fr<jm  some  member  of  the  preceding  group.  The  incisors 
and  canines  are  like  those  of  the  Lophiodoiitklce,  but  the  canines  in  the 
lower  jaw  of  the  living  forms  are  somewhat  procumbent.  Tlie  third  and 
fourth  premolars  in  the  upper  jaw  are  like  the  true  molars,  which  dis- 
play the  four  cusps  connected  by  cross-ridges  remarkable  for  their  trans- 
verse direction  in  contrast  with  the  oblique  crests  of  some  of  the  preced- 
ing family.  The  two  external  lobes  are  likewise  different  in  their 
subequal  pro})ortions,  both  being  convex  externally  and  well  separated 
from  each  other. 

The  lower  premolars  except  the  first  are  like  the  molars.  The  exter- 
nal and  internal  lobes  are  connected  by  strong  cross-crests,  which  are 
as  much  elevated  as  the  cusps  themselves,  and  there  is  no  ridge  crossing 
from  the  postero-external  to  the  antero-internal  lobe,  as  in  Ht/racothe- 
rium  and  Phcndcodns. 

From  this  family  we  pass  to  the  rhinoceros  section  of  the  sub-order. 
In  accordance  with  what  the  philosopliic  student  of  the  living  forms 
would  be  led  to  anticipate,  this  section  pertains  to  a  later  geologic  period 
than  the  preceding,  and  not  unnaturally  would  he  seek  for  the  connect- 
ing linkb'  between  them  and  that  section  of  the  Lopthiodontidce,  in  which 
the  external  lobes  are  flattened.  Thi-ough  the  researches  of  American 
palaeontologists  we  are  now  in  a  position  to  fully  comprehend  all  the 
more  important  steps  in  the  evolution  of  this  group,  and  I  fail  to  recall 
in  the  whole  range  of  vertebrate  palaeontology  an  instance  in  which  the 
demands  of  the  evolution  hypothesis  are  more  completely  satisfied  than 
in  the  present  one. 

The  molar  formula  of  the  rhinoceros  is  Pm.  ^,  M.  f,  the  usual  num- 
ber in  jK-rissodactylcs  ;  but,  as  regards  the  incisors  and  canines,  the  great- 
est variability  is  to  be  observed.     In  the  two-horned  African  species 


TEETH  OF  THE   VERTEBBATA. 


479 


neither  canines  nor  incisors  exist  in  the  adult  animal,  they  having 
completely  disappeared  in  the  course  of  development.  On  the  other 
hand,  in  the  remarkable  and  interesting  Eocene  genus  Orthocynodon 
of  iScott  and  Osborn,^  the  canines  are  of  normal  size  and  erect  in  posi- 
tion, as  the  name  implies.  The  number  of  incisors  has  not  been  defi- 
nitely determined,  o^ving■  to  the  imperfect  condition  of  the  single  specimen 

Fig.  257. 


Skull  of  Aphelops  me^alodiis,  Cope,  an  extinct.  American  rliinoceros. 


known,  but  it  certainly  had  two,  and  probal)ly  three,  in  the  lower  jaw, 
as  there  is  abundance  "of  room  between  the  canine  and  the  second  incisor 
for  another  tooth.  If  the  number  is  three  in  the  lower  jaw,  it  would 
imply  a  like  number  in- the  upper,  which  would  luring  it  very  near  to 
the  LophiodontidcE.  From  this  condition  of  the  dentition,  which  is  very 
nearly  that  of  the  Lophiodontidce,  we  pass  to  the  genus  Amynodon  of  Prof. 
Marsh,  in  which  the  lower  canine  is  much  smaller  and  procumbent, 
with  tiie  incisors  reduced  to  two  pairs  in  each  jaw.     Following  this 

1  See  BvUetin  No.  3  Cnntribntiom  from  E.  M.  Museum  of  Geology  and  Archaeology 
of  Princeton  College,  May,  1883. 


480 


DENT  A  L   A  NA  TO  MY. 


genus  in  time  comes  the  Lower  Miocene  representative  Acerathenum,  in 
which  the  incisors  are  two  upon  each  side  in  the  upper  and  one  in  the 
lower  jaw,  with  the  upper  canine  absent.  The  Middle  Miocene  fur- 
nishes a  genus,  Ceratorhinus,  in  which  the  incisors  are  one  upon  each 
side  above  and  below,  and  a  canine  in  the  lower  jaw  only.  Finally, 
we  have  a  complete  disappearance  of  both  incisors  and  canines  in  some 
species  now  living.  The  reduction  of  the  incisors  and  canines  from 
Orthocynodon  to  Coelodonta,  a  living  species,  can  be  summarized  as 
follows  :  I.  I,  C.  I,  Orthocynodon  ;  I.  |,  C.  \,  Amynodon  ;  I.  \,  C.  f , 
Acerathenum;  I.  {,  C.  f ,  Ceratorhinus;  I.  ^,  C.  f,  Coelodonta. 

Fig.  258. 


Superior  Molar  Dentition  of  lUiinoceros  :  «,  anterior;  6,  posterior  end  of  series, 
indicate  molars  and  premolars. 


The  figures  1,  2,  3 


In  the  earliest  forms  the  molars  are  more  complex  than  the  pre- 
molars, but  in  the  later  and  living  species  the  premolars  are  as  highly 
organized  as  the  molars,  and  like  them  in  form ;  this  is  well  shown  in 
the  accompanying  figure. 

About  twelve  genera  have  been  described,  seven  of  which  come  from 
the  fo.ssil  beds  of  North  America.  Through  Orthocynodon,  as  was 
pointed  out  by  Profs.  Scott  and  Osborn,  they  inosculate  with  the  Lo- 
phiodoniidm,  after  which  they  branch  into  several  distinct  lines.  While 
the  rhinoceroses  have  perpetuated  the  type  of  molar  which  began  with 
the  la.st  .section  of  the  lophiodonts,  other  forms  inherited  the  pattern  of 
the  hyracotheroids,  and  from  this  ])()int  tlie  dentition  was  gradually  .spe- 
cialized, not  so  much  through  subtraction  of  the  number  of  teeth  as 
addition  and  complication  of  the  different  lobes  and  crests  of  the 
crowns  of  both  molars  and  premolars.  The  culminating  point  of 
this  line  is  found  in  the  living  horses. 

The  first  .step  beyond  Hyracotherinin  in  this  series  is  seen  in  the 
Eocene  genus  Ectoc'uvm  of  t/ope,  in  which  the  external  rib  is  better 
defined,  the  external  cusps  more  crescentic,  and  the  cusps  and  oblique 
ridge  of  the  lower  molars  are  more  prominent.  In  the  next  geological 
stage  (Upper  Eocene)  we  meet  with  the  family  Challcotheri'idcB,  abun- 
dantly represented  in  the  Wind  River  deposits  by  the  genus  Lamhdothe- 
rium,  likewi.se  des(n-ibed  by  C^ope.  In  this  form  (Fig.  259)  the  external 
cusps  of  tlie  u[)|K!r  molars  are  considerably  elevated,  of  a  crescentic  form, 
and  connected  with  an  external  median  rib.  The  anterior  cro.s.s-crest 
still  has  a  tubercular  form,  while  the  posterior  is  cre.st-like  and  blended 
with  the  postero-internal  lobe.  Tlie  four  cusps  of  the  inferior  molars 
are  connected  by  cro.ss-ridges  and  the  oblique  cre.st,  .so  as  to  form  two  Vs, 
opening  internally.  The  tooth  here  rej)resented  is  the  la.st  one,  which  in 
many  of  the  perissodactyls  has  a  i)roimnent  heel  (A).     In  this  animal 


TEETH  OF  THE   VERTEBRA  TA. 


481 


j^tti'tii 


ace 


the  antero-internal  cusp  (a I)  becomes  bifid  at  its  summit,  and  the  ante- 
rior basal  lobe  (k)  again  assumes  considerable  importance. 

Following  the  chalicotherioids,  and  as  a  probable  derivative  of  them, 
we  meet  with  the  pakeotherioids,  in  which  the  molar  pattern  makes  a 
considerable  advance  in  complexity 
over  that  of  the  preceding  family, 
and  the  premolars  are  now  like  the 
molars.  Anchitherium  is  a  erood 
representative  of  this  group,  and 
is  here  taken  for  illustration.  This 
genus  is  of  especial  interest,  in  view 
of  its  ancestral  relation  with  the 
horses ;  it  is  here  that  we  get  the 
first  distinctive  traces  of  equine 
peculiarities,  although  several  gen- 
era intervene  between  it  and  the 
modern  Equidse  or  horses.  The 
species  were  numerous,  most  of  them 
equalling  the  sheep  in  size,  and  had 
three  subequal  toes  on  each  foot 


Upper  and  Lower  Molar  Tei'th  ol'  Larnhdolhirmm, 
vertical  view,  natural  size:  a,  su|  erior;  6,  last 
inferior  molar.  In  the  upper  molar,  at-,  antero- 
external ;  pe,  postero-external;  at,  antero-in- 
ternal; /j(',  posterointernal  or  principal  cusps 
respectively  ;  //,  external  vertical  rib  ;  x,  an  an- 
terior cingular  cusp ;  ace-pcc,  anterior  and  pos- 
terior cross-crests.  In  the  lower  molar  the 
principal  cusps  are  lettered  the  .same :  A-,  ante- 
rior basal  lobe;  «/',  accessory  cusp;  A,  heel. 

The  incisors,  as  in  all  the  preceding 


genera,  are  plain  incisiform  teeth,  without  the  pits  or  "mark"  found  in 
the  corresponding  teeth  of  the  horses.  Well-developed  canines  are  like- 
wise present. 

The  superior  molars  (Fig.  260)  display  the  same  elements  as  those  of 
Lambdotheriuin ;  the  external  cusps  are  very  much  flattened  and  cres- 
centic,  having  their  vertical  dimensions  considerably  augmented.  The 
cross-crests  form  laminar  ridges  connected  with  the  two  internal  cusps  at 
the  base,  and  separated  from  them  above  by  open  notches ;  they  reach 
quite  across  the  face  of  the  crown.  The 
two  internal  cusps  almost  equal  the 
external  ones  in  height,  but  have  a 
more  conical  form ;  they  are  sepa- 
rated from  each  other  by  a  deep 
fissure  or  valley  opening  internally. 
On  the  posterior  border  of  the  crown 
the  cingulum  develops  an  accessory 
cusp,  which  has  a  tendency  to  form 
a  cross-crest  in  this  situation  and  enclose  a  valley  between  it  and  the 
posterior  cross- crest. 

In  the  molars  of  the  lower  jaw  the  same  elevation  of  the  lobes  and  crests 
is  to  be  observed ;  their  pattern  is  substantially  that  of  Lambfhfherium. 

In  a  later  geological  epoch  the  genus  Hippotherium  carries  dental 
modification  a  step  farther  toward  that  of  the  existing  horses.  The 
outer  toes  are  much  reduced,  the  incisors  possess  the  peculiar  pits  of 
the  horse,  the  molars  are  more  complicated,  and  the  entire  appearance 
is  decidedly  equine.  A  strict  comparison  of  the  elements  of  the  molars 
with  those  of  Anchitherium  is  generally  difficult,  on  account  of  the  thick 
deposit  of  cement  which  fills  up  the  valleys  and  spaces  between  them. 
To  obviate  this  difficulty  and  bring  out  more  clearly  the  relationship 
between  them,  I  have  represented  in  Fig.  261  an  unworn  molar  in 
Vol.  I.— 31 


Upper  and  Lower  Molars  of  Right  Side  of  a 
species  of  A7tc/iil/ieriu)ii  :  1,  upper;  2,  lower 
tooth;  (/,  anterior ;  ft,  posterior  border. 


482  DENTAL  ANATOMY. 

which  the  cementuiii  has  been  removed.  AUhough  the  respective  pat- 
terns are  very  much  alike  in  their  general  structure,  the  differences  con- 
sist in  this :  the  external  cusps  of  the  superior  molars  are  relatively- 
larger,  more  perfectly  crescentic,  and  strongly  inclined  inward  in  Hip- 
potherium.  The  anterior  cross-crest  is  better  developed  and  joins  the 
posterior  cross-crest,  so  as  to  enclose  a  deep  pit  or  valley  between  it  and 
the  antero-external  cusp,  which  is  tilled  with  cement  in  the  natural 
Fig.  261. 

Fig.  262. 
jt         ai    ai'  P} 


OB 

i 

A  Superior  Molar  Tuutli  of  a  species  of  ////)-         Lower  Molar  of  same.    Letters  as  in  Fig.  259. 
pollmrmm,  withcementum  removed  :  a,  an- 
terior; 6,  posterior;  c,  internal;  </,  external 
borders.    Vertical  view,  natural  size. 

state ;  this  is  called  the  anterior  lake  in  the  worn  tooth.  The  posterior 
cross-crest  bends  around  to  join  the  posterior  cingular  cusp,  which,  with 
the  postero-external  cusp,  furnishes  the  boundary  of  the  posterior  lake. 
To  these  w'oss-crests  are  added  a  greater  or  lesser  number  of  vertical 
folds,  which  give  the  borders  of  the  lakes  a  crenate  appearance  when 
the  crown  is  much  worn.  The  internal  cusps  are  relatively  small,  the 
posterior  being  connected  with  the  corresponding  cross-crest,  the  ante- 
rior isolated.  To  all  these  must  be  added  the  increased  height  and  the 
presence  of  cementuni. 

The  lower  molars  (Fig.  2(32)  do  not  exhibit  such  marked  diiference 
from  the  Anchitherium  type  as  do  those  above,  but  they  are  neverthe- 
less more  complex  in  their  increased  dej^th,  complete  isolation  of  the 
accessory  antero-internal  cusp,  and  the  addition  of  cementum.  The  grind- 
ing surface  of  the  teeth  resulting  from  this  arrangement  of  the  enamel, 
dentine,  and  cement  is  kept  constantly  rough  by  reason  of  the  inequalities 
in  the  rate  of  wear  which  these  substances  sustain  during  mastication. 
Coincident  with  this  structure  of  the  crown  the  roots  disappear  and  the 
tooth  grows  continuously — a  condition  necessary  to  compensate  for  the 
great  waste  of  the  tooth-substance. 

Ijastly,  we  come  to  the  modern  horse,  in  which  digital  reduction  has 
reached  the  extreme  ]ioint  in  this  series,  or  that  furthest  removed  from 
the  pcntcdactyle  Condi//(irfJira.  As  is  well  known,  the  digital  formula 
in  this  family  is  1  —  1  in  functional  use,  with  the  second  and  fourth 
represented  by  the  rudimentary  metapodials  commonly  known  as  the 
"  splint  bones." 

The  incisors  are  peculiar  and  characteristic,  inasmuch  as  the  working 
face  is  interrupted  by  a  deep  ])it  caused  by  the  upward  growth  of  the 
posterior  cingulum.  Previous  to  extrusion,  the  posterior  wall  of  this 
cavity  is  incom])lete  and  does  not  rise  so  high  as  the  anterior.^     After 

1  Ryder,  "On  the  Origin  and  Homologies  of  the  Incisors  of  the  Horse,"  Proc.  Acad. 
Nat.  Sci.,  Philada.,  1877. 


TEETH  OF  THE   VERTEBRATA. 


483 


the  tooth  has  been  in  use  for  a  Httle  while,  lio\\ever,  the  lace  is  worn 
down  smooth,  and  the  central  depression  appears  bounded  by  a  layer 
of  enamel,  between  ^liich  and  the  enamel  covering  the  outer  surface' of 

Fig.  263. 


Skull  of  Ilippotherium  srversum,  Cope  (after  Cope). 

the  tooth,  may  be  seen  the  dentine.     The  incisors  are  not  all  cut  at  the 
same  time,  the  last  appearing  at  the  age  of  five  years,  on  account  of 
which  the  central  pit  disappears  through  wear  sooner  in  those  teeth 
which  are  first  extruded  than  those  which 
are  cut  last.     By  observing  carefully  the 
date  of  appearance  of  the  various  inci- 
sors, and  the  consequent  difference  in  time 
at  which  the  pits  are  obliterated  in  the 
different  teeth,  veterinarians  have  estab- 
lished some  very  useful  rules  by  which 
the  age  of  a  horse  can  be  approximately 
told  wdth  considerable  certainty  up  to  ten 
or  twelve  years. 

Canines,  or  the  "  bridle  teeth,"  are  pre- 
sent, but  they  are  of  smaller  size,  and  some- 
times disappear  in  the  female.  The  first 
premolars  in  both  jaws  are  normally  ab- 
sent, but  there  are  many  cases  on  record  in  which  they  are  present. 
Hippothenum  they  are  normally  present  and  functional. 

The  molars  present  essentially  the  same  pattern  as  those  of  the  pre- 
ceding genus,  the  only  difference  of  importance  being  found   in  the 


ace 


pee 


Molar  Tooth  of  a  species  of  Horse.    Let- 
ters as  in  the  preceding  tigures. 


In 


484  DENTAL  ANATOMY. 

enlargement  of  the  antero-internal  lobe  and  its  connection  by  a  ridge 
with  its  corresponding  cross-crest.  Some  species  of  Hippotherium  show 
a  gradual  advance  from  the  conic  isolated  condition  of  this  element  to 
its  enlarged  and  sub-connected  form. 

Thus  it  is  that  palaeontology  has  enabled  us  to  fully  comprehend 
the  different  steps  in  the  production  of  these  complex  and  specialized 
organs  from  the  simple  bunodont  pattern.  To  say  that  such  evidence 
is  witliout  its  special  bearing  on  tlie  great  problem  of  biology,  or  that 
evolution  or  development  has  not  taken  place,  is  to  deny  the  truth  of 
the  assertions  herein  made.  Many  intermediate  steps  between  those 
given  could  be  cited,  but  time  and  space  have  compelled  me  to  limit 
tlie  examples  to  the  most  salient. 

The  remaining  perissodactyles  exhibit  different  degrees  of  modification 
of  the  bunodont  type,  none  having  reached  the  same  stage  of  perfection 
as  the  horse. 

The  second  sub-order  of  the  ungulates,  Artiodacti/la,  attained  its 
greatest  development  at  a  later  geological  period,  and  it  is  probably  in 
the  present  epoch  that  the  genera  and  species  are  the  most  numerous. 
A  few  genera  are  found  in  the  Lower  Eocene,  but  they  are  of  rare 
occurrence  as  compared  with  the  perissodactyles.  It  is  probable  that 
they  two  came  off  the  condylarthrous  stem,  but  the  direct  evidence  to 
substantiate  this  supposition  is  wanting.  They  are  primarily  divisible 
into  two  groups,  Bunodontia  and  Selenodontia,  characterized  by  the 
pattern  of  the  molar  teeth  and  the  consequent  condition  of  the  posterior 
termination  of  the  maxillary  bones.  In  the  former  division,  of  which 
the  hog  is  an  excellent  example,  the  molars  have  approximately  the 
same  pattern  as  PJicnacodns ;  the  tooth-line  is  little  curved,  and  the 
posterior  extremity  of  tlie  maxillary  is  apjilied  closely  to  the  pala- 
tine and  pterygoid  bones,  whereas  in  the  Sc/cnodontia  the  molar  teeth 
have  crescentic  cusps,  and  the  posterior  borders  of  the  maxillaries  are 
separated  by  a  wide  sinus  from  the  palatines  and  pterygoids.  These 
characters  at  first  appear  insignificant  and  inadequate  to  establish  and 
define  two  such  great  groups  as  the  foregoing ;  but  when  we  remember 
that  they  express  a  very  important  structural  modification,  and  that  the 
two  are  correlated,  we  cease  to  express  surprise. 

Of  these  two  divisions,  the  Bunodontia  is  the  older,  and  as  a  conse- 
quence the  more  generalized.  Their  generalized  characters  are  most 
conspicuously  displayed  in  the  increased  number  of  digits,  bunodont 
teeth,  absence  of  horns,  non-complexity  of  the  stomach,  and  separate 
condition  of  all  the  limb  bones.  In  fact,  the  suilline  artiodactyles  are  as 
primitive  in  many  respects  as  the  (hndi/faiihrd,  but  in  the  arrangement 
of  the  carpal  and  tarsal  elements  they  are  specialized  and  far  removed 
from  their  ])rimitive  ancestrv. 

In  the  hog  the  dental  fornmla  is  I.  |,  C.  |,  Pm.  f ,  M.  f  =  44.  The 
outer  pair  of  incisors  are  small,  and  sometimes  fall  out  in  old  age.  The 
canines  are  relativ'cly  large — dis))n)])()rtionally  so  in  the  male — and  in 
the  upper  jaw  curve  round  in  such  a  manner  that  the  point  of  the  crown 
is  directed  upward.  The  enamel  of  these  teeth  does  not  uniformly 
invest  the  crown,  but  is  disposed  in  three  bands  corresponding  with  its 
trihedral  form.     The  canines  of  the  lower  jaw  are  more  slender  and 


TEETH   OF  THE   VERTEBRATA.  485 

have  a  normal  direction.  It  is  said  that  castration  arrests  the  excessive 
development  of  the  tusks  of  the  boar,  just  as  this  operation  profoundly 
affects  the  growth  of  the  antlers  of  the  deer — a  circumstance  which  at 
once  relegates  the  cause  of  this  condition  to  sexual  influences. 

The  first  premolar  has  no  deciduous  predecessor,  and  disappears  soon 
after  the  adult  stage  is  reached.  The  rest  of  the  premolars  increase  in 
complexity  and  size  from  front  to  rear,  but  none  of  them  are  quadri- 
tubercular.  The  first  and  second  molars  are  quadrate  in  section,  with 
four-lobed  crowns.  The  last  molar  is  greatly  elongated  in  an  antero- 
posterior direction,  which  is  occasioned  by  the  possession  of  an  enormous 
heel,  much  as  in  the  bears,  and  its  crown,  as  in  the  others,  besides  pre- 
senting the  normal  four  cusps,  has  an  immense  number  of  subsidiary 
tubercles,  giving  to  it  a  decidedly  wrinkled  appearance. 

In  the  wart-hogs  (Phacochcenis)  a  very  peculiar  modification  of  the 
molar  pattern  is  to  be  seen  in  the  last  tooth.  In  the  unworn  state  the 
crown  of  this  tooth  presents  about  thirty  small  tubercles,  arranged  in 
three  rows  in  a  direction  longitudinal  to  the  axis  of  the  body,  the  inter- 
mediate spaces  between  them  being  occupied  by  cementum.  When  wear 
takes  place,  the  summits  of  these  cusps  are  abraded,  leaving  as  many 
little  dentine  islands  bordered  by  enamel;  they  are  strengthened  by  the 
addition  of  cement. 

The  canines  are  of  enormous  size,  devoid  of  enamel,  and  grow^  from 
persistent  pulps  ;  the  suj)erior  ones  are  directed  upward  at  first,  piercing 
the  upper  lip,  and  then  curve  backward  toward  the  eye;  their  length  is 
sometimes  as  much  as  eight  or  ten  inches.  All  the  molar  teeth  are  gen- 
erally shed  in  old  age,  with  the  exception  of  the  fourth  premolar  and 
the  last  true  molar,  so  that  the  molar  dentition  is  practically  reduced  at 
this  time  to  four  upon  each  side  in  both  jaws,  and  is  the  only  case  of 
the  kind  known  in  the  Mannnalia. 

The  peccaries  constitute  another  family  of  this  division,  and  are 
known  from  the  lowest  Miocene,  if  not  from  the  Upper  Eocene  depos- 
its. Their  molar  dentition  is  more  nearly  like  that  of  the  Condylarthra 
and  ])rimitive  perissodactyles  than  other  suillines,  lacking,  as  a  rule,  the 
great  development  of  the  minor  tubercles  of  the  molars  of  the  hog  as 
well  as  the  elongated  heel  of  the  tooth.  The  canines,  moreover,  are  nor- 
mal in  direction,  and  the  great  disparity  in  size  between  these  teeth  does 
not  exist  in  the  sexes.  The  incisors  are  of  the  usual  pattern,  although 
the  outer  pair  is  absent  from  both  jaws  in  some  genera. 

From  this  family  the  transition  is  easy  to  the  earlier  forms  of  the 
selenodonts,  in  Avhich  the  feet  were  multidactyle  ;  in  one  genus,  Oreodon, 
as  has  been  recently  shown  by  Prof  W.  B.  Scott,  the  anterior  limb  was 
provided  with  the  normal  number  of  toes,  five.  That  family,  which 
almost  completely  bridges  the  chasm  between  these  divisions,  is  the 
extinct  Anthracotheridce,  whose  remains  are  abundant  in  the  Miocene 
strata  of  Europe,  but  less  so  in  this  country. 

It  is  somewhat  uncertain  how  many  genera  should  be  referred  to 
this  family,  and  by  what  character  or  characters  it  should  be  defined. 
Palceoclioeru^,  which  by  common  consent  is  a  suilline,  has  four  lobes  upon 
the  crowns  of  the  superior  molars,  which  are  conic  and  not  connected 
with  an  external  rib,  together  with  two  small  intermediate  cusps,  repre- 


486  DENTAL  Ay  ATOMY. 

senting  the  cross-crests  very  much  as  in  Phenaeodus.  Oiceropotamits, 
another  genus  from  the  Eocene  of  France,  is  akogether  intermediate 
between  Falceochcerus  and  Anthnieotherium,  the  typical  representative 
of  this  family,  in  the  pattern  of  the  superior  molars ;  the  external 
cusps  are  somewhat  crescentic,  but  the  external  rib  is  rudimentary  or 
absent.  In  the  first  molar  the  anterior  of  the  two  intermediate  tuber- 
cles only  is  present,  while  in  the  other  two  molai*s  it  is  very  small 
and  insignificant ;  the  two  internal  lobes  are  conic. 

Following  this  genus  in  time  come  Anthracotherium,  Hyopotamus,^ 
Ancodus,  and  others  in  which  the  anterior  of  the  two  intermediate 
tubercles  is  the  only  one  which  is  present  in  the  upper  molars.  This 
character,  I  am  therefore  disposed  to  believe,  defines  a  natural  group, 
and  should,  in  connection  with  the  external  rib  and  crescentic  form  of 
the  external  cusps,  be  the  test  of  limitation  of  this  family. 

Two  derivatives  of  the  Eocene  Hi/ojxjtaiai,  Xiphodon,  and  Anoph- 
therium  soon  became  specialized  in  their  limb  structure,  but,  strangely 
enough,  disappeared  in  the  Early  Miocene.  Another  line  was  com- 
menced contemporaneously  with  that  of  the  anthracotheroid  in  the 
genus  Dichohune,  wherein  the  jjosterior  intermediate  tubercle  only  w^as 
retained.  It  continues  forward  through  the  genus  Cainofheritun  into 
the  Upper  Miocene  deposits  of  Sansan,  where  it  gradually  faded  from 
existence,  leaving  no  modified  descendants.  This,  it  appears  to  me, 
constitutes  another  family,  definable  by  the  above  character. 

From  the  Anthracotheriddo  have  sprung  all  the  modern  artiodactyles, 
with  the  possible  exception  of  the  cameloids  and  the  existing  suillines, 
together  with  other  stems  which  are  extinct.  Many  extinct  genera 
complete  the  connections  with  the  living  forms  in  all  the  osteological 
and  dental  details,  which  it  is  scarcely  witliin  the  scope  of  the  present 
article  to  discuss. 

In  the  production  of  a  perfected  double  crescentic  pattern  of  the 
superior  molars  in  this  sub-order  from  the  short-crowned  semi-buno- 
dont  anthracotheroids,  the  anterior  intermediate  tubercle  has  gradually 
usurped  the  function  of  the  true  antero-internal  cusp,  it  having  been 
reduced  to  a  small  cusp  situated  internal  to  the  mesial  horns  of  the 
inner  crescents  on  the  inner  basal  portion  of  the  crown  (see  Fig,  265).^ 

Specialization  of  the  dental  organs  of  the  Selenodontia  is  seen  in  the 
following  characters  :  (1)  Formation  of  double  crescents  in  the  superior 
and  inferior  molars  ;  (2)  great  elevation  of  the  cusps  and  deposit  of  a 
thick  layer  of  cementum,  filling  up  the  valleys;  (3)  loss  of  the  roots  of 
the  molars  and  premolars,  and  their  growth  from  persistent  pulps ;  (4) 
reduction  of  the  premolars  to  three  in  each  jaw ;  (5)  subtraction  of  the 
canines  and  incisors  from  the  upper  jaw  ;  (6)  the  reduction  in  size  and 
approximation  of  the  lower  canine  to  the  incisors;  and  finally  (7),  the 

'  Gaudry  places  the  appearance  of  this  sonns  in  the  sands  of  Beauchanip.  wliioh 
probably  corres|)()nds  with  our  Bridirer  Beds  or  Upper  Eocene.  He  also  fixes  the  date 
of  appearance  of  Palrporhfrriia  in  Europe  in  the  deposits  of  Saint-Geraud-le-Piiv,  Middle 
IMiocene.  In  this  country  Jhjfipril(im>iA  does  not  apuear  until  the  Lower  Miocene, 
whereas    PnUp/tclKmix  protiably  extends  into  the  Bridtrer  epoch. 

^For  a  further  knowledtre  of  the  fossil  forms  of  these  families  the  reader  is  referred 
to  the  important  worl<  of  Prof  Albert  (Jaudry,  "  Les  Enchainements  du  Monde  animal 
dans  les  Temps  geolo>i:i(pies,"  in  which  tiie  more  important  genera  are  figured. 


TEETH  OF  THE    VERTEBRATA. 


487 


488  DENTAL  ANATOMY. 

development  of  a  long  diastema  in  front  of  the  premolars.  While 
the  complete  assumption  of  these  characters  is  reached  only  in  the 
bovine  ruminants,  others  exhibit  all  the  intermediate  stages  of  modi- 
fication tending  in  that  direction. 

The  common  Virginia  deer  (Cariacus  virginianus)  has  been  selected 
as  an  average  example  of  the  higher  selenodont  dentition  ;  although 
in  its  family  (Cervidte)  canines  are  sometimes  found  in  the  upper 
jaw,  there  is  little  or  no  cementura  on  the  crowns  of  the  molars,  and 
they  have  well-defined  roots.  It  will  therefore  be  observed  that  it  does 
not  fulfil  all  the  requirements* of  the  most  highly  specialized  selenodonts 
in  its  dental  organization.  The  dental  formula  of  this  species  (Fig. 
265)  is  I.  -|,  C.  {,  Pm.  |,  M.  |  =  32.  The  incisors  have  long 
spatulate  crowns,  the  median  pair  being  the  larger,  the  outer  ones 
decreasing  gradually  in  size.  The  canines  are  smaller  than  the  outer 
pair  of  incisors,  which  they  resemble  very  much  in  shape,  being  applied 
closely  to  them.  After  an  immense  interval  follow  the  premolars,  the 
first  two  in  the  lower  jaw  being  comparatively  simple,  the  third  four- 
lobed  like  the  succeeding  molars.  The  molars  display  two  perfect 
double  crescents,  of  which  the  outer  are  convex  externally.  The  last 
molar  has  a  fifi:h  lobe.  In  the  upper  jaw  the  premolars  are  bilobed, 
the  internal  being  convex  internally  and  enclosing  a  deep  valley  between 
it  and  the  external  cusp.  The  true  molars  have  double  crescents  enclos- 
ing two  valleys.  The  antero-internal  of  these  crescents  is  made  up  of 
the  anterior  intermediate  tubercle,  which  has  become  greatly  enlarged 
and  developed  into  a  crescentic  form,  the  true  antero-internal  cusp  being 
situated  internal  to  and  behind  it.  The  proper  evidence  to  support  this 
determination  is  to  be  found  by  examining  the  superior  molars  oi  Hyopot- 
amus,  Anoplotherium,  and  Xiphodon,  it  which  it  will  be  seen  that  the 
antero-internal  cusp  becomes  gradually  smaller. 

Teeth  of  the  Proboscidea. 

The  last  order  of  the  ungulate  series  whose  dental  organs  remain  to 
be  noticed  is  that  including  the  elephants,  mastodons,  etc.  The  animals 
composing  this  group  are  the  largest  of  terrestrial  mammals,  and  display 
many  curious  modifications  of  the  primitive  ungulate  tyjie.  Probably 
no  ]mrt  of  their  organization  has  been  more  profoundly  affected  in  their 
gradual  evolutionary  growth  than  the  teeth,  and  were  it  not  for  the  fact 
that  abundant  evidence  is  at  hand  to  demonstrate  the  successive  steps  in 
the  progressiv^e  modification  from  a  more  simple  type,  we  would  be  at 
a  loss  to  comprehend  tiie  manner  of  production  of  these  most  complex 
of  all  teeth. 

Two  genera  of  ]irobosci deans  are  fi)und  in  the  existing  faunae  of  Asia 
and  Africa,  but  tliese  are  only  tlie  inconsiderable  remnant  of  a  once 
greater  and  nnich  more  widely  distributed  representation,  as  is  indicated 
by  their  fossil  remains.  During  the  later  Tertiaries  proboscideans  were 
not  unknown  in  both  the  northern  and  southern  hemispheres  in  all  the 
extensive  land-areas ;  in  some  parts  of  the  northern  hemisphere,  where 
thev  are  now  extinct,  judging  from  their  fossil  remains  immense  herds 
and  droves  must  have  at  one  time  existed. 


TEETH  OF  THE   VERTEBRATA.  489 

In  the  African  elephant  {Loxodon  africanu.s)  the  dental  formula  is 
I.  ^,  C.  ^,  Pm,  and  ]\I.  |-.  The  two  incisors  are  greatly  enlarged, 
inn)lanted  in  deep  sockets,  and  grow  from  persistent  pulps.  They  are 
preceded  by  small  deciduous  teeth,  and  when  first  protruded  are  tipped 
with  enamel,  which  soon  Avears  off.  The  tooth  then  consists  mainly 
of  dentine  covered  by  a  thin  layer  of  cement,  the  dentine  presenting 
a  slightly  modified  form  known  as  "  ivory."  This  substance,  as  is  well 
known,  is  extensively  used  in  the  arts  and  has  a  fixed  commercial  value. 
Although  not  exclusively  confined  to  the  tusks  of  the  elephant,  never- 
theless the  chief  source  of  supply  of  this  material  is  derived  from  them. 
Tomes  cites  an  example  in  A\hich  a  pair  of  tusks  of  this  species  were 
exhibited  in  England  that  Meighed  three  hundred  and  twenty-five 
pounds  and  measured  eight  feet  six  inches  in  length  and  twenty-two 
inches  in  circumference ;  the  average  weight,  however,  does  not  exceed 
from  twenty  to  fifty  pounds.  The  female  of  this  species  has  tusks  quite 
as  large  as  the  male,  but  in  the  Indian  species  the  tusks  of  the  male 
exceed  those  of  the  female  in  size. 

The  molar  teeth  of  the  living  elephants  are  very  much  alike  in  gen- 
eral pattern  and  mode  of  replacement,  which  is  unique ;  the  description 
of  one  will  therefore  suffice  to  convey  an  intelligent  understanding  of 
the  entire  subject. 

Both  existing  species  have  a  molar  formula  of  f ,  which  are  divided 
into  milk  molars  f ,  true  molars  f .  There  is  sometimes,  in  addition  to 
these,  a  small  rudimentary  milk  molar  in  front,  which  increases  the 
total  number  to  seven  upon  either  side  in  each  jaw. 

Although  the  total  number  of  molars  is  normal  or  nearly  so,  they  are 
not  all  in  place  nor  in  existence  at  the  same  time.  Barring  the  occa- 
sional rudimentary  one,  the  first  molar  in  the  Indian  s])ecies  cuts  the 
gum  at  a  considerable  distance  from  the  front  of  the  jaw  about  the 
second  week  after  birth.  It  is  implanted  by  two  fangs,  and  disj^lays 
a  subcompressed  crown  bearing  four  cross- ridges,  and  is  therefore  lopho- 
dont  in  pattern.  The  upper  tooth  corresponding  to  this  one  cuts  the 
gum  a  little  earlier,  and  possesses  five  cross-crests.  These  teeth  are  shed 
at  about  the  age  of  two  years. 

Before  the  disappearance  of  the  first  tAvo  teeth  the  second  molars 
come  into  place  from  behind.  They  are  considerably  larger  than  the 
first,  being  on  an  average  two  and  a  half  inches  in  length  by  one  inch 
in  breadth.  Their  crowns  are  of  similar  form,  but  have  the  number  of 
cross-ridges  increased  to  eight  or  nine.  They  are  implanted  by  two 
fangs,  and  are  shed  before  the  beginning  of  the  sixth  year. 

Bv  the  time  the  second  molar  has  been  worn  out  the  third  molar, 
averaging  four  inches  in  length  by  two  in  breadth,  makes  its  appear- 
ance. Its  crown  has  from  eleven  to  thirteen  cross-plates  on  its  working 
face,  and  is  also  supported  by  two  fangs,  of  which  the  posterior  is  much 
the  larger.     It  is  said  to  be  Avorn  out  and  shed  about  the  ninth  year. 

The  teeth  so  far  enumerated  are  taken  to  be  homologous  with  the 
second,  third,  and  fourth  milk  molars  of  the  ordinary  diphyodont  den- 
tition, which  have  in  this  case  failed  to  develop  permanent  successors. 
This  conclusion  is  rendered  reasonably  certain,  as  we  shall  presently  see, 
by  the  fact  that  their  ancestors  had  a  more  or  less  complete  permanent 


490  DENTAL  ANATOMY. 

premolar  system,  which  underwent  progressive  subtraction  as  they 
approached  the  modern  proboscideans. 

Three  teeth  which  are  homologous  with  the  permanent  true  molars 
are  developed  behind  these  in  a  similar  manner.  They  increase  in  size 
and  complexity  from  before  backward  :  the  first,  or  fourth  of  the  entire 
series,  bears  fifteen  or  sixteen  plates  ;  the  second  has  from  seventeen  to 
twenty  plates  ;  while  the  last  supports  from  twenty  to  twenty-five.  The 
first  true  molar  disappears  between  the  twentieth  and  twenty-fifth  years 
of  the  animal's  life,  the  second  somewhere  about  the  sixtieth,  while  the 
last  is  retained  until  the  termination  of  the  animal's  natural  existence, 
which  is  said  to  be  more  than  one  hundred  years. 

The  structure  of  these  teeth  is  complex,  and,  as  we  have  said  on  a 
former  page,  resembles  that  of  some  of  the  hystricine  rodents,  such  as  the 
capybara,  for  example.  The  cross-ridges  near  their  summits  are  broken 
up  into  a  number  of  conical  projections,  which,  when  abrasion  first  takes 
place,  present  so  many  dentine  islands  surrounded  by  a  rim  of  enamel : 
these  are  arranged  in  rows  across  the  face  of  the  crown  in  the  position 
of  the  future  plate  (see  Fig.  266).     As  wear  goes  on  these  islands  unite 

Fig.  2G6. 


Molar  Teeth  of  Indian  Elephant  (Elcplms  indiciis),  after  Tomes:  a,  anterior;  /;,  posterior  border. 

below,  and  form  transverse  lamellre  composed  of  a  narrow  strip  of  den- 
tine surrounded  by  enamel.  Between  these  much-elongated  lamellae, 
which  are  all  blended  together  at  the  base  of  the  crown,  a  thick  deposit 
of  cementum  is  found ;  it  also  invests  the  lateral  surfaces  of  the  crown 
and  prevents  fracture  of  the  cross-plates. 

In  the  growth  of  the  tooth  the  anterior  plates  or  crests  are  first 
formed,  and  come  into  ]>osition  and  use  long  before  the  posterior.  As 
a  consequence  of  this,  the  most  anterior  plates  wear  out  and  disappear 
while  the  posterior  ones  are  still  being  formed.  This  is  well  shown  in 
the  accompanying  figure.  As  new  plates  are  added  from  behind,  the 
whole  tooth  moves  forward,  which  probably  exerts  some  influence  in 
the  removal  of  the  tooth  in  front  of  it.  Finally,  before  the  tooth  dis- 
appears altogether,  it  ])resents  an  oval  area  of  smooth  dentine  sur- 
rounded by  enamel  and  cenientum.  It  is  then  no  longer  efficient  as  a 
grinding  organ,  and  is  consequently  discarded. 

It  will  be  seen  by  this  arrangement  of  the  three  tooth-substances  on 
the  working  surface  of  the  crown,  and  by  reason  of  the  varying  rate  of 
their  wear,  the  teeth  of  the  two  jaws  when  brought  into  ojiposition 
afford  most  perfect  machinery  fi)r  the  grinding  up  of  the  coarse  herba- 
ceous substances  upon  which  the  elephant  feeds. 

The  two  genera  of  existing  proboscideans  may  be  readily  distinguished 


TEETH  OF  THE    VERTEBRATA.  491 

by  the  character  of  the  plates  of  the  molar  teeth.  In  the  African  species 
they  are  fewer  in  number  on  the  corresponding  teeth  than  in  the  Indian, 
and  they  have  a  distinct  lozenge-shaped  pattern  upon  cross-section, 
whereas  in  the  Indian  species  they  present  an  oval  outline  upon  cross- 
section  and  the  enamel  border  is  crenate.  In  the  number  and  succes- 
sion of  the  teeth  the  two  genera  are  alike. 

The  genus  Deinothenum  includes  a  few  species  whose  remains  have 
been  found  in  the  Miocene  deposits  of  Europe,  and  which  Mere  but 
little  if  any  inferior  to  the  living  proboscideans  in  bodily  proportions. 
They  are  the  oldest  representatives  of  this  order  so  far  discovered,  and 
especial  interest  attaches  to  their  teeth,  inasmuch  as  their  structure  fur- 
nishes a  clue  to  a  more  perfect  understanding  of  the  later  and  more 
complex  types. 

The  premaxillary  bones  were  edentulous,  but  the  front  part  of  the 
lower  jaw  was  provided  with  two  large  decurved  tusks.  What  particu- 
lar use  the  animal  made  of  these  teeth  is  difficult  to  imagine.  The 
molar  formula  is  Pm.  |-,  M.  f .  The  structure  of  these  teeth  is  not  very 
diiferent  from  that  of  the  tapir,  consisting  of  a  moderately  short  crown 
bearing  two  or  three  cross-crests.  Both  the  premolars  had  deciduous 
predecessors,  just  as  in  the  diphyodonts  generally.  These  animals, 
however,  were  very  elej)hantine  in  every  other  feature  of  their  anatomy, 
and  were  in  all  probability  provided  with  a  trunk. 

From  this  condition  of  the  dental  organs  we  pass  to  the  mastodons, 
in  which  there  is  a  marked  approach  to  the  elephants.  In  some  species 
there  were  two  tusks  in  each  jaw,  but  the  lower  ones  were  small,  and  in 
many  cases  disappeared  early  in  life.  The  molars  increase  in  complex- 
ity and  size  from  before  backward,  the  posterior  ones  bearing  in  some 
species  as  many  as  ten  cross-crests,  which  were  unsupported  by  a 
cementum  deposit ;  in  others  the  cross-ridges  are  much  fewer  in  num- 
ber. Many  species  are  known,  and  when  all  are  considered  a  complete 
transition  between  the  comparatively  simple  lophodont  and  the  extreme 
lamellate  patterns  is  afforded.  Many  of  them  had  deciduous  teeth, 
which  were  vertically  succeeded  by  two,  and  probably  three,  permanent 
premolars.  As  the  elephantine  molar  pattern  was  acquired,  however, 
these  were  gradually  lost. 

Altogether,  it  is  imi)ossible  for  a  student  of  odontography  to  study 
carefully  the  teeth  of  this  order,  and  not  be  thoroughly  convinced  in  the 
end  that  the  complex  pattern  has  gradually,  but  none  the  less  certainly, 
arisen  from  the  simpler  one.  If  this,  therefore,  is  true  of  one  series,  it 
must  be  of  all. 

The  Amblypoda. 

Another  order  of  hoofed  mammals  which  became  extinct  at  the  close 
of  the  Eocene  Period  has  been  described  from  the  fossil-bearing  deposits 
of  this  country.  They  were  mostly  of  gigantic  proportions,  and  exhibit 
affinities  with  both  the  proboscideans  and  the  Perissodactyla.  They  are 
most  nearly  related,  however,  to  the  Toxeopoda,  with  which  they  were 
contemporary  in  the  Eocene. 

Nearly  all  of  them  have  the  full  complement  of  incisors,  canines,  pre- 


492 


DENTAL  ANATOMY. 
Fig.  267. 


Skull  of  Lnrolophorion  ,omi,tns.   Cope,  a  species  of  amhlypod  from  the  American  Eocene  (after  Cope). 

molars,  and  molars,  and  in  some  the  canines  were  greatly  enlaro-ed     The 
molar  pattern  js  of  moderate  complexity,  and  shows  a  considerable 


TEETH  OF  THE   VERTEBRATA.  493 

departure  from  the  primitive  tritubereular  ancestry.  In  the  lower  jaw 
the  molars  are  lophodont,  while  in  the  upper  they  have  a  single  cres- 
cent of  moderate  perfection.  Owing  to  their  near  relationship  with  the 
Toxeopoda,  it  is  highly  probable  that  their  teeth  represent  an  extreme 
modification  of  the  tritubereular  pattern,  but  of  the  different  steps  in 
their  production  lack  of  space  i)revents  me  from  speaking  here.  1  nuist 
refer  the  reader  to  the  papers  of  Profs.  Cope  and  Marsh  for  a  more 
complete  description  of  the  dentition  of  this  order. 

Teeth  of  the  Marsupials. 

I  have  indicated  on  a  preceding  page  that  this  division  of  the  Mam- 
malia is  sharply  defined  from  the  monodelphs  by  the  circumstance  that 
no  connections  are  formed  between  the  foetal  envelopes  and  the  walls  of 
the  uterine  cavity  during  gestation,  so  that  no  placenta  is  developed. 
They  are  therefore  known  as  the  implacental  division  of  the  Eutheiia  ; 
they  are  likewise  known  as  the  Didelphia  and  Marmpialia.  The  young 
are  born  in  an  exceedingly  helpless  and  imperfect  condition,  and  are 
transferred  to  the  pouch  or  marsupium  of  the  mother,  where,  by  a  special 
arrangement,  the  nourishment  is  forced  into  their  months  until  such  time 
as  they  are  enabled  to  help  themselves. 

In  the  majority  of  the  lower  Verlebrata  very  little  devektpment  of 
the  young  takes  place  in  the  body-cavity  of  the  mother ;  the  ovum  is 
relatively  large,  by  reason  of  the  addition  of  an  abundant  supply  of  pab- 
ulum suflticient  to  nourish  the  embryo  until  the  later  stages  of  develop- 
ment are  reached.  It  has  been  recently  ascertained  that  the  monotremes 
reproduce  in  the  same  way;  that  is,  they  lay  eggs  like  birds  and  rep- 
tiles, which  are  hatched  in  a  similar  manner.  The  whole  plan  of  devel- 
opment moreover,  is  like  that  of  the  bird  (mesoblastic) — a  condition 
which  would  be  reasonably  suggested  by  a  study  of  their  reproductive 
system. 

As  the  monotremes  furnish  the  connecting  link  between  the  higher 
mammal  and  the  reptile,  so  do  the  marsupials,  as  far  as  reproduction  is 
concerned,  afibrd  a  transitional  stage  between  the  monotremes  and  the 
monodelphs.  For  this  reason  we  Avould  naturally  be  led  to  look  for 
primitive  and  transitional  characters  in  their  teeth.  Unfortunately, 
these  organs  do  not  in  many  particulars  go  beyond  the  lowest  forms  of 
the  monodelphs  sufficiently  to  give  us  any  clear  insight  into  the  inter- 
mediate structures  and  patterns  which  must  have  preceded  the  (li])hyo- 
dont  monodelph  dentition  ;  still,  some  of  the  earliest  representatives  of 
mammalian  existence  AA'hich  have  been  referred  to  in  this  group  possess 
a  greater  number  of  heterodont  molar  and  premolar  teeth  than  any 
known  mammal. 

In  the  small  living  marsupial  genus  Myr'wecobivs  the  dental  formula 
is  I.  ^,  C.  \,  Pm.  I,  ^I.  f  =  54.  The  incisors  are  small,  subconic  teeth, 
implanted  in  the  premaxillary  bones  above,  and  followed  by  the  canines, 
which  have  the  usual  laniary  form.  The  premolars  have  laterally-com- 
pressed, unicuspid  crowns,  and  are  implanted  by  two  roots.  The  molars 
exceed  in  number  those  of  any  other  marsupial,  reaching  the  unusual 
number  of  six  in  each  jaw.     Owing  to  the  imperfect  descriptions  of 


494  DENTAL  ANAT03IY. 

the  crowns  of  these  teeth,  and  never  having  seen  a  specimen  myself,  I 
am  at  present  unable  to  say  just  M'liat  the  pattern  of  the  crown  is.  From 
the  best  information  at  my  command  I  suppose  it  to  be  somewhat  after 
the  style  of  a  modified  tuberculo-sectorial.  I  further  do  not  know 
\vhether  the  succession  has  been  observed,  and  whether  a  proper  distri- 
bution of  the  molars  and  premolars  expressed  in  the  above  formula  has 
been  made;  but,  judging  from  the  condition  in  marsupials  generally,  I 
am  induced  to  believe  it  to  be  correct.  It  is  so  given  by  Owen  and 
Waterhouse. 

Some  fragmentary  remains,  consisting  principally  of  jaws  and  isolated 
teeth,  of  a  number  of  small  mammals  have  been  discovered  from  time 
to  time  in  the  Jurassic  and  Triassic  deposits  of  this  country,  Europe, 
and  South  Africa,  in  which  the  teeth  behind  the  canines  reach  as  high 
a  number  as  twelve  in  each  lower  jaw  in  some  species.  These  are  some- 
what arbitrarily  divided  into  an  equal  number  of  molars  and  premolars, 
but  whether  any  or  all  of  them  had  deciduous  predecessors  is  not 
known.  The  reason  for  this  division  is  that  the  first  six  behind  the 
canine  are  premolariform  in  shape,  while  the  others  possess  a  number  of 
sharp  cusps.  They  have  been  referred  to  the  marsupials  and  assigned  a 
position  near  to  Jli/rmecobins,  but  until  their  osteology  is  better  known 
this  is  doubtful.  Inasmuch  as  they  are  the  oldest  known  mammals,  we 
should  anticipate  on  a  priori  grounds  that  they  really  belong  to  the 
monotremes  instead  of  the  marsupials.  The  great  number  of  teeth  cer- 
tainly constitutes  an  approach  to  the  Reptilia,  and  if  they  possessed  a 
complete  development  of  a  second  set,  which  is  not  at  all  improbable, 
the  transition  between  reptile  and  mammal  would  be  in  a  measure  com- 
plete as  regards  the  teeth. 

Another  strange  and  remarkal)le  genus,  P/ar/inulax,  together  with  a 
number  of  allies,  comes  from  these  ancient  horizons.  In  this  animal 
the  molar  pattern  is  complex  for  so  early  a  representative  of  the  Mam- 
malia, and  is  difficult  to  understand.  In  the  loAver  jaw  of  Plagiaulax 
there  are  seven  teeth,  of  which  the  first  is  large,  curved,  and  pointed, 
and  is  probably  an  incisor.  This  is  followed  after  a  considerable  space 
by  four  teeth,  all  of  which,  except  the  first,  are  implanted  by  two  roots 
and  increase  gradually  in  size.  Their  crowns  are  terminated  superiorlv 
by  a  wedge-shaped  crest  directed  antero-posteriorly,  which  is  rendered 
subserrate  by  the  presence  of  a  number  of  oblique  vertical  grooves. 
Behind  tliese  are  two  smaller  teeth  with  tubercular  crowns,  which 
have  been  supposed  to  represent  true  molars. 

The  remaining  marsupials  whicli  are  really  known  to  be  such  are 
divisible  into  the  Polj/protodontia,  or  those  of  predaceous  habits,  having 
many  incisors,  and  the  Diprofodontia,  vegetable  feeders,  having  onlv 
two  incisors,  in  the  lower  jaw.  As  far  as  dental  characters  go,  thev  all 
agree  in  the  possession  of  fi)ur  true  molars;  there  are  never  more  than 
three  premolars,  and  the  deciduous  molars,  ^vhich  are  succeeded  at  a 
comparatively  late  jx'riod  by  tlie  last  premolars,  are  reduced  to  one  in 
eacli  jaw.  This,  therefore,  furnishes  another  example  wherein  the  defi- 
nition of  a  premolar  is  violated. 

Three  families  are  included  in  the  polyprotodont  division,  one  of 
which,  the  opossums,  is  confined  to  North  and  South  America,  and  the 


TEETH  OF  THE    VERTEBRATA.  495 

other  tM'o  to  the  continent  of  Australia.  As  the  common  A^irsinia 
opossum  IS  a  good  representative  of  this  division,  it  is  liere  taken  for 
ilhistration  and  description.  The  dental  formula  is  I.  |,  C.  ]-,  Pm.  |, 
M.  ^  =  50.     The  incisors  (Fig.  268)  have  a  truncate  cylindroid  pattern, 


Fig.  2G8. 


Dentition  of  Virginia  Opossum  {Didelphis  virginianuK) :  a,  upper;  b,  lower  jaw. 

implated  by  single  fangs,  and  diifer  considerably  from  the  correspond- 
ing teeth  of  the  carnivores,  which  they  exceed  in  number  by  two  upon 
each  side  in  the  upper,  and  by  one  upon  each  side  in  the  lower,  jaw.  The 
canines  have  relatively  the  same  size  and  form  as  in  the  dog,  and  indi- 
cate clearly  the  carnivorous  habits  of  their  possessor.  The  premolars 
are  simple  premolariform  teeth  implanted  by  two  roots,  the  first  being 
smallest  and  separated  from  the  other  tAvo  by  a  diastema. 

The  molars  of  the  lower  jaw  are  essentially  tuberculo-sectorial  in  pat- 
tern, with  the  external  cusp  of  the  anterior  triangle  largest.  The  heel  is 
tritubercular  and  of  large  size.  The  molars  of  the  upper  jaw  are  inter- 
esting, inasmuch  as  they  furnish  a  transitional  stage  in  the  formation  of 
the  W  pattern  described  in  the  moles,  shrews,  etc.  The  first  molar  has 
the  folloM'ing  structure :  The  crown  is  triangular  in  transverse  section, 
with  the  apex  directed  inward,  at  which  is  situated  the  antero-internal 
cusp  or  the  one  corresponding  with  the  single  internal  tubercle  of  the 
tritubercular  molar.  At  the  antero-external  angle  is  situated  a  cusp  of 
moderate  dimensions,  which  in  perfectly  unworn  specimens  is  more  or 
less  blended  with  the  cingulum  ;  just  internal  to  this,  upon  close  inspec- 
tion, can  usually  be  seen  the  rudiment  of  another  cusp,  which  becomes 
better  defined  in  the  second  molar.  The  exact  homologies  of  these  two 
cusps  are  not  clear,  but  it  seems  very  probable  that  the  external  is  of 
cingular  origin,  and  that  the  one  internal  to  it  is  the  true  homologue  of 
the  antero-external  cusp  of  the  tritubercular  tooth.  On  the  outer  edge 
of  the  crown,  ])osterior  to  the  two  just  described,  is  another  cusp,  which 
disappears  in  the  last  two  molars,  but  which  is  well  defined  in  the  first 
and  second.  This  cusp  is  homologous  with  the  one  which  terminates 
the  median  external  part  of  the  W  in  the  molars  of  the  shrew  and  mole. 
A  little  posterior  to  a  line  drawn  between  this  last-mentioned  cusp  and 
the  one  most  internal  is  another  large  well-defined  tubercle,  from  which 


496  DENTAL  ANATOiMY. 

a  conspicuous  ridge  passes  outward  and  backward  to  the  produced  pos- 
tero-external  angle  of  the  crown. 

It  will  thus  be  seen  that  all  the  requisite  cusps  are  present  in  the  first 
and  second  molars  for  the  production  of  the  W-structure,  and  that  it 
would  only  require  the  presence  of  connecting  ridges  to  complete  it. 

A  distinctive  characteristic  of  this,  as  well  as  most  other  marsupials, 
is  seen  in  the  strong  inflection  of  the  angle  of  the  jaw  and  the  vacuities 
caused  by  failure  of  ossification  in  the  posterior  part  of  the  palatine  bones. 

Another  family  of  this  group  includes  the  Phascogales,  Tasmanian 
devil,  the  dog-headed  opossum,  etc.  of  the  Australian  continent  and 
neigh boriug  islands.  This  family  is  known  to  naturalists  as  the 
Dasi/w'idce,  and  is  distinguished  from  the  opossums  proper  {^Didelphi- 
d(e)  by  having  the  incisor  formula  |.  In  the  genus  Phascogale  there 
are  three  premolars  in  the  upper  jaw  and  two  in  the  lower ;  in  jDastjurus, 
or  the  Tasmanian  devil,  there  are  only  two  premolars  in  each  jaw,  which 
number  also  obtains  in  the  dog-headed  opossum  (Thylacuius). 

The  pattern  of  the  molar  teeth  of  this  latter  animal  is  very  much  like 
that  of  Mesoni/x,  consisting  in  the  lower  series  of  a  principal  cone,  to 
which  are  added  anterior  and  posterior  basal  cusps.  The  npper 
molars  are  tritubercular,  as  in  that  genus,  but  there  is  a  consider- 
able cingular  ledge  external  to  the  t^\•o  outer  cusps. 

The  lower  molars  of  the  other  two  genera  are  very  similar  to  those 
of  the  opossum,  already  described.  The  pattern  of  the  upper  molars 
of  Dasyurus  have  been  alluded  to  in  connection  with  those  of  the  shrew, 
and  need  no  further  description  ;  those  of  Phascogale  are  essentially  the 
same. 

The  bandicoots,  constituting  the  family  Peramelidce,  are  distinguished 
by  an  incisor  formula  |-.  The  canines  are  reduced,  and  placed  relatively 
far  back  in  the  dentigerous  border  of  the  jaws.  The  molar  and  pre- 
molar formula  is  the  same  as  in  the  opossum,  and  there  is  a  similar- 
ity of  pattern  in  the  corresponding  teeth  of  the  two  families. 

In  the  second  division,  Dipvotodoniki,  the  incisors  are  reduced  to  two 
in  the  lower  jaw  ;  the  canines  are  always  small,  and  in  many  cases  alto- 
gether wanting,  while  the  molars  are  more  complex,  being  better  adaj)ted 
to  the  mastication  of  a  vegetable  diet,  upon  which  they  principally  feed. 

The  kangaroo  furnishes  a  typical  example  of  this  group,  and  is  here 
described.  The  dental  formula  of  Bennett's  wallabv  (Halmafurus 
hmmiti)  is  I.  f ,  C.  fi-,  Pm.  \,  U.  f  =  28.  The  three  pairs  of  incisors 
in  the  upper  jaw  (Fig.  269)  are  subequal  and  closely  a])proximated, 
except  in  the  middle  line,  where  those  of  the  opposite  side  are  separated 
from  each  other  by  a  consideral)le  sjiace.  They  have  incisiform  crowns, 
and  are  implanted  by  enlarged  roots  caused  by  an  unusually  thick  coat 
of  cement.  These  are  opposed  by  a  single  tooth  on  each  side  below, 
whose  direction  is  almost  a  continuation  of  the  long  axis  of  the  jaw, 
so  procumbent  is  its  implantation.  They  are  long  teeth  with  enamel- 
covered  crowns,  slightly  compressed  from  side  to  side,  so  as  to  present 
cutting  edges  on  the  sui-faces  which  would  correspond  to  the  anterior 
and  posterior  faces  if  the  tooth  were  erect,  but  which  in  its  present 
position  are  superior  and  inferior.  The  superior  edge  bites  against 
the  three  upper  incisors,  opposing  them  exactly. 


TEETH   OF  THE   VERTEBRATA. 


497 


After  a  long  interval  come  the  premolars,  which  have  approximately 
the  same  structure  in  the  two  jaws  as  do  the  molars  behind  them.  The 
premolars  are  implanted  by  two  roots,  and  have  crowns  whose  longitu- 
dinal diameter  greatly  exceeds  the  transverse.  The  summit  of  the  crown 
terminates  in  an  antero-posterior  ridge,  which  is  bordered  at  the  base 


Fig.  269. 


Dental  Series  of  Kangaroo  ( Halmaturns  bennetti) :  a,  upper,  fe,  lower  jaw. 

internally  in  the  upper  ones  by  a  well-marked  cingulura  bearing  several 
small  cusps ;  this  cingulum  is  absent  from  the  inferior  teeth. 

The  crowns  of  the  molars  are  highly  lophodont,  consisting  of  two 
strong  transverse  crests  connected  in  the  median  line  by  an  antero-]:>os- 
terior  ridge.     Tliey  are  all  nearly  equal  in  size  and  alike  in  both  jaws. 

In  the  phalangers,  which  constitute  another  iamily  of  this  division, 
the  incisors  are  the  same  as  in  the  kangaroo.  Small  canines  are  usually 
present,  and  the  premolars  may  be  increased  to  three  in  the  upper  jaw. 
The  third  premolar  has  substantially  the  same  structure  as  that  of  the 
kangaroos,  but  the  molar  pattern  is  selenodont,  resembling  in  this  resjjcct 
the  artiodactyle  ungulates.  They  are  quadritubercular,  the  four  cusps 
being  crescentic  in  section,  with  the  crescents  reversed  in  the  lower  jaw, 
just  as  in  the  artiodactyles. 

Still  another  family  is  represented  by  the  wombat,  whose  dentition 
exhibits  a  modification  in  the  same  direction  as  the  rodent  monodelphs 
in  the  reduction  of  the  incisors  to  a  single  pair  in  each  jaw  and  their 
growth  from  persistent  pulps.  The  canines  are  absent,  the  premolars 
are  ^,  and  the  molars,  as  well  as  incisors  and  premolars,  grow  contin- 
uously during  the  life  of  the  animal.  The  molar  pattern  consists  of 
transverse  laminpe,  greatly  elongated  and  united  by  cement,  much  as  in 
capybara,  one  of  the  rodents. 

A  gigantic  extinct  marsuj)ial  animal  (Thylocoleo)  has  been  described 
from  the  late  Tertiary  deposits  of  Australia,  whose  affinities  and  prob- 
able habits  have  provoked  a  good  deal  of  discussion  among  English 
palaeontologists.  In  each  jaw  there  is  a  pair  of  enlarged,  hooked,  and 
pointed  teeth  in  the  position  of  the  median  incisors ;  these  are  followed 
in  the  upper  jaw  by  three  small  teeth,  the  posterior  of  which  probably 
Vol.  I.— 32 


498  DENTAL  ANATOMY. 

represents  a  canine ;  in  the  lower  jaw  but  a  single  tooth  of  this  kind 
exists.  Next  follows  a  relatively  enormous  tooth,  corresponding  in 
pattern  with  the  single  premolar  of  the  kangaroo,  and  is  therefore  tren- 
chant. Behind  these  are  one  small  tooth  in  the  upper  and  two  of  like 
nature  in  the  lower  jaw. 

From  the  trenchant  nature  of  the  large  premolariform  .teeth,  Prof. 
Owen,  its  describer,  has  considered  it  to  have  been  carnivorous  in  habit, 
while  Prof.  Flower  concludes,  from  the  enlarged  incisors  and  general 
resemblance  of  the  enlarged  teeth  to  that  of  the  premolars  of  the  kanga- 
roos, that  it  is  really  affiliated  with  this  group  and  was  a  vegetal)le  feeder. 

Other  marsupials  might  be  mentioned,  but  the  principal  modifications 
of  the  dental  organs  of  this  group  have  already  been  set  forth  in  the 
types  selected. 

The  Milk  Dentition. 

In  the  preceding  pages  we  have  spoken  of  the  deciduous  or  milk  den- 
tition of  the  diphyodont  Mammalia  so  far  only  as  they  relate  to  the 
permanent  set  in  matters  of  definition.  It  now  remains  to  discuss  the 
more  important  question  of  their  true  nature  and  relationship  to  the 
permanent  teeth  in  a  philosophic  sense.  Are  they  superadded  embry- 
onic structures  similar  to  the  amnion  and  allantois,  which  subserve  a 
temporary  purpose  and  disappear  with  approaching  maturity,  or  are 
thev  to  be  homologized  with  the  first  set  of  teeth  of  the  lower  Verte- 
brata  ? 

Before  proceeding  to  a  discussion  of  these  questions,  it  will  first  be 
necessarv  to  give  a  general  statement  of  the  more  important  features  of 
their  anatomy,  as  well  as  the  principal  characters  in  which  they  differ 
from  the  permanent  teeth. 

As  regards  their  development,  it  nuist  be  borne  in  mind  that  their 
enamel  organs  are  originally  derived  from  the  lining  membrane  of  the 
oral  cavity,  or  at  least  that  jiart  of  it  which  immediately  covers  the  axes 
of  the  jaws,  by  a  dipping  down  of  the  epithelium,  while  the  dentine 
organ  is  devcloi)ed  from  the  underlying  end^ryonic  tissue.  The  enamel 
organs  in  this  case  are  said  therefore  to  arise  (h>  novo.  After  a  time  the 
enamel  organs  of  the  ]X'rmanent  incisors,  canines,  and  premolars  appear 
bv  a  process  of  budding  from  the  necks  of  the  enamel  organs  of  the 
deciduous  teeth,  but  that  of  the  first  molar  in  the  human  subject  arises 
de  novo,  just  as  those  of  the  temporary  teeth  do  from  the  ])rimitive 
epithelial  layer  of  the  mouth. 

From  the  neck  of  the  enamel  organ  of  this  tooth  the  enamel  organ 
of  the  second  true  molar  buds  out,  Avhile  the  third  is  derived  from  the 
second  in  a  like  maimer.  Whether  tliis  order  of  development  is  true 
of  all  di])hyodont  mammals  is  not  known,  and  is  a  subject  which  very 
much  needs  further  investigation. 

The  form  of  the  milk  teeth  resembles  that  of  the  permanent  ones 
which  succeed  them,  as  a  general  rule ;  an  important  exception  to  this, 
however,  is  to  be  observed  in  the  last  milk  molar,  which  in  the  majority 
of  cases  is  more  complex  than  the  permanent  tooth  which  succeeds  it.  In 
the  ungulates  the  last  milk  molar  in  the  lower  jaw  resembles  the  last 


TEETH   OF  THE   VERTEBRATA.  499 

true  molar  in  having  three  lobes,  while  in  the  upper  jaw  the  last  two 
milk  molars  have  the  complex  pattern  of  the  permanent  molars.  It  is 
a  rule  of  pretty  general  application  that  the  last  milk  molar,  and  in  many 
instances  the  last  two,  are  succeeded  by  teeth  of  a  simpler  pattern. 
They  may  be  well  developed  and  retained  in  the  jaw  for  a  consider- 
able period,  as  in  the  dog,  or  they  may  be  extremely  small,  and  shed,  or 
rather  absorbed,  before  birth,  as  in  some  of  the  seals.  There  may  be  as 
many  as  six  in  each  jaw,  as  in  the  case  of  the  nine-banded  armadillo,  or 
they  may  be  reduced  to  a  single  one  in  each  jaw,  as  in  the  marsupials. 
The  usual  nundjer  of  milk  molars  is  four  in  what  may  be  called  the 
typical  diphyodont  dentition,  in  which  there  are  forty-four  permanent 
teeth  in  all.  Subtractions  from  this  number  are  of  conmion  occurrence 
by  reason  of  the  first  milk  molar  failing  to  develop  a  permanent  succes- 
sor or  its  complete  disappearance.  This,  as  we  have  seen,  occurs  in  the 
dog  and  many  other  animals  in  which  the  number  of  premolars  is  nor- 
mal. That  this  tooth  is  a  persistent  milk  tooth  is  suggested  by  the  fact 
that  its  enamel  organ  arises  <Je  novo,  like  those  of  the  milk  teeth  generally. 

In  the  monophyodonts  one  set  has  been  lost,  and  the  question  nat- 
urally suggests  itself.  Which  one  is  it?  The  very  rudimentary  con- 
dition of  the  milk  teeth  in  the  seals,  which  reaches  an  extreme  point  in 
the  elephant  seal,  has  led  Prof.  Flower  to  conclude  that  the  single  set 
of  the  monophyodonts  is  homologous  with  the  permanent  set  of  the 
diphyodonts,  the  first  set  having  become  rudimental  and  finally  disap- 
peared. He  further  concludes  that  the  milk  dentition  generally  is  some- 
thing superadded,  and  cannot  therefore  be  homologized  with  the  first 
set  of  the  lower  vertebrates.  These  conclusions  are  adopted  by  many 
authors. 

In  the  first  place,  as  regards  the  homology  of  the  single  set  of  teeth 
of  the  monophyodonts,  there  is  nuich  plausibility  in  Prof  Flower's 
position  ;  but,  u])on  the  whole,  our  information  respecting  the  exact 
limits  of  monophyodontism  is  too  meagre  to  reach  any  satisfactory  results 
in  a  solution  of  this  question.  It  may  yet  turn  out  that  many  of  the 
Cetacea,  in  which  it  is  thought  to  be  universal,  really  have  rudimentary 
deciduous  teeth  in  the  early  stages  of  growth,  as  has  been  suggested  by 
Tomes.  Among  the  edentates  the  nine-banded  armadillo  has  already 
been  cited  as  having  two  sets  of  teeth,  and  it  does  not  seem  at  all  improba- 
ble that  all  armadillos  will  ultimately  be  found  to  be  diphyodont. 

It  should  also  be  remembered  that  an  approach  to  monophyodontism 
is  made  in  many  diphyodonts ;  and  in  all  cases  in  which  there  is  a  par- 
tial loss  of  one  set  there  can  be  little  doubt  that  it  is  the  second  which 
has  been  subtracted.  An  example  of  this  is  afforded  by  the  jn-obos- 
cidean  series.  In  Deinotherium  there  were  two  and  probably  three  per- 
manent premolars ;  in  some  species  of  mastodons  they  are  reduced  in 
number  to  two  or  three ;  while  in  the  existing  elephants  they  have  com- 
pletely disappeared.  The  teeth  which  remain  in  the  position  of  the  pre- 
molars in  these  animals  are  certainly  persintent  milk  molars.  The  first 
premolar  of  the  dog,  hippopotamus,  and  others  is  a  case  of  the  same 
kind.  If  monophyodontism  has  been  produced  in  this  way,  then  the 
single  set  which  remains  is  not  homologous  with  the  permanent  set  of 
the  diphyodontSj  but  combines  the  two,  the  molar  dentition  being  made 


500  DENTAL  ANAT03rY. 

up  of  the  true  molars  and  persistent  milk  rnolars,  ^^'itll  the  permanent 
premolars  subtracted. 

With  reference  to  the  second  conclusion,  that  the  milk  dentition  is 
something  superadded,  Dr.  Tomes  very  justly  raises  objection  on  the 
ground  that  the  history  of  the  development  of  the  permanent  teeth 
interposes  a  difficulty.  He  says  : '  "  The  tooth-germ  of  the  milk  tooth 
is  first  formed,  and  the  tooth-germ  of  the  permanent  is  derived  from  a 
portion  (the  neck  of  the  enamel  germ)  of  the  formative  organ  of  the 
milk  tooth.  Again,  in  most  of  those  animals  in  which  there  is  an  end- 
less succession  of  teeth,  suc:h  as  the  snake,  the  newt,  or  the  shark,  each 
successive  tooth-germ  is  derived  from  a  similar  part  of  its  predecessor ; 
the  natural  inference  from  whicdi  would  be  that  the  permanent  set,  being 
derived  from  the  other,  was  the  thing  added  in  the  diphyodonts." 

Aside  from  the  inherent  improbability  of  this  hypothesis  of  super- 
addition  of  the  milk  teeth,  if  the  mammal  has  been  derived  from  the 
reptile  or  batrachian — which  is  true  if  evolution  is  true — it  is  not  at 
all  remarkable,  but,  on  the  contrary,  quite  in  keeping  with  the  nature  of 
the  case,  that  the  descendants  should  have  retained  some  of  their  ancestral 
features.  In  the  Batrachia  and  Reptilia  there  are  many  sets  of  teeth 
developed  during  the  life  of  the  individual,  of  which  the  first  arises  de 
novo,  and  all  the  succeeding  ones  are  derived  from  that  which  precedes 
it.  Altogether,  I  am  disposed  to  regard  the  diphyodont  manmialian 
dentition  in  the  same  light :  those  teeth  which  take  their  origin  pri- 
marily from  the  epithelial  lining  of  the  mouth  are  strictly  homologous 
with  the  first  set  of  the  lower  vertebrates.  This  would  include  in  the 
first  set  the  deciduous  incisors,  canines,  molars,  and  the  first  true  or 
permanent  molars.  The  second  set  of  the  batrachian  and  reptile  would 
be  represented  by  the  permanent  incisors,  canines,  premolars,  and  sec- 
ond true  molar.  The  third  succession  would  be  represented  by  the  last 
molar  of  the  diphyodont  dentition. 

This  view,  of  course,  is  based  upon  the  presumption  that  the  devel- 
o])ment  of  the  true  molars  is  the  same  in  all  diphyodonts  as  it  is  in 
the  human  subject — viz.  that  the  enamel  germ  of  the  first  is  derived 
from  the  ejiithelial  lining  of  the  mouth  ;  that  that  of  the  second  is 
derived  from  the  neck  of  the  first;  and  that  of  the  third  from  the 
second. 

If  it  shall  be  found,  however,  on  further  investigation,  that  in  any 
diphyodont  the  enamel  germs  of  all  the  molars  arise  fJe  novo,  then  they 
nnist  in  all' such  cases  be  added  to  tlie  first  set.  This  objection  may  be 
urged  against  the  view  that  there  are  three,  or  even  two,  successions 
re])resented  in  tiie  molars  of  the  diphyodont — viz.  that  they  do  not  suc- 
ceed each  other  vertically,  as  in  the  case  of  the  reptile  and  batrachian  ; 
but  this  I  do  not  consider  of  vital  importance.  There  is  one  thing  upon 
which  I  would  strongly  insist,  and  that  is  that  the  first  true  molar  in 
the  human  dentition  is  a  persistent  milk  tooth. 

'  Manual  of  Dental  Analoimj,  p.  302. 


TEETH  OF  THE   VERTEBRATA.  501 

CONCLUSIONS,  ACKNOWLEDGMENTS,  ETC. 

Throughout  the  foregoing  pages  I  have  endeavored  not  only  to 
give  the  leading  eharaeteristics  of  the  principal  niodiiieations  of  the 
dental  organs  of  the  A'ertebrata,  bnt  have  in  many  oases,  so  far  as  our 
knowledge  of  the  extinct  forms  would  permit,  endeavored  to  trace  the 
leading  steps  in  the  production  of  the  complex  from  the  simple  form. 
In  so  doing  I  have  been  made  aware  of  the  difficulties  which  beset  such 
an  undertaking:  the  principal  burden  of  these  difficulties  lies  in  the  com- 
paratively imperfect  knowledge  we  possess  of  the  palffiontological  history 
of  certain  groups.  In  others  the  ancestry  is  more  clearly  indicated,  and  in 
my  judgment  the  evidence  is  sufficient  to  demonstrate  with  a  reasonable 
degree  of  certainty  the  more  important  steps  in  their  dental  evolution. 

The  modification  of  an  organ  from  a  simple  to  a  complex  structure 
necessarily  implies  a  cause  or  force,  adequate  to  the  production  of  such 
result.  What,  then,  is  the  nature  of  the  force  or  forces  involved,  and 
what  is  their  method  of  operation  ?  To  simply  say  that  this  or  that  is 
so,  that  this  tooth  is  simple  and  that  is  complex,  without  giving  any 
reason  why  it  is  so,  conveys  little  information.  If  one  tooth  is  sim- 
ple and  another  complex,  there  are  reasons  for  it,  and  it  is  not  only 
within  the  province,  but  is  clearly  the  duty,  of  the  odontologist  to  dis- 
cover and  p(jint  out  these  reasons  if  they  can  be  found  to  exist. 

Two  explanations  for  all  such  phenomena  have  been  offered.  One 
of  these  presumes  that  they  were  created  so  by  supernatural  forces,  but 
as  to  the  nature  of  these  forces  we  are  not  informed  ;  much  less  do  we 
know  about  the  manner  in  which  it  was  done.  The  other  assumes  that 
the  natural  or  physical  forces,  operating  through  distinct  and  well-known 
physiological  laws,  are  alone  responsible  for  the  resulting  modifications. 

Between  these  tAvo  explanations  the  naturalist  experiences  little  diffi- 
culty in  deciding  which  is  most  in  accordance  with  the  observed  facts 
at  his  command.  While  the  one  rests  solely  upon  the  vaguest  assump- 
tion, unsupported  by  so  much  as  a  single  fact,  the  other  rests  upon 
observed  scientific  truth,  which  any  one  can  verify  who  will  take  the 
pains  to  investigate.  When  we  ascribe  these  modifications  to  the  physi- 
cal forces,  the  conclusion  seems  inevitable  that  those  of  a  mechanical 
nature  have  been  most  largely  concerned  in  the  modification  of  form. 

The  change  in  form  or  size  of  any  organ  is  principally  due  to  addi- 
tion, subtraction,  or  transposition  of  the  histological  elements  of  which 
it  is  composed ;  these,  as  is  well  knoAvn,  are  directly  dependent  on  the 
amount  of  physiological  waste  and  repair  which  the  organ  sustains,  or, 
in  other  words,  the  extent  of  use  and  disuse.  In  pro])ortion  as  an  organ 
or  a  part  of  an  organ  is  used,  in  that  proportion  will  there  be  increased 
destruction  of  its  substance  and  a  corresponding  determination  of  the 
nutritive  fluids  to  supply  the  loss.     The  reverse  is  true  of  disuse. 

In  the  harder  tissues  of  the  animal  body  strain  and  pressure  have 
likewise  been  potent  factors  in  the  determination  of  form.  Recognizing 
the  importance  of  these  influences,  Mr.  J.  A.  Ryder  has  constructed  a 
most  ingenious  and  far-reaching  hypothesis  in  regard  to  the  teeth,  which 
he  terms  ''the  mechanical  genesis  of  tooth-forms."'     In  this  he  satis- 

'  Proceedings  Acad.  Nat.  Sciences,  Philada.,  1878. 


502  DENTAL  ANATOMY. 

factorily  accounts  for  the  forms  and  patterns  of  the  molar  teeth  of  the 
ungulates  by  the  manner  in  which  they  have  used  their  jaws.  He  has 
shown  that  in  the  bunodonts  the  mouth  is  simply  opened  and  closed 
during  mastication — a  movement  which  is  associated  M'ith  a  short- 
crowned  tubercular  molar — while  in  the  selenodonts  the  lower  jaw 
makes  an  extensive  lateral  sweep,  and  is  associated  with  long-crowned 
crescentic  molars.  The  conclusion  is  therefore  obvious  that  as  the  buno- 
donts were  compelled,  through  force  of  circumstances,  to  live  upon  a 
diet  which  required  more  extensive  comminution  before  it  could  be 
properly  assimilated,  they  gradualy  develop  greater  mobility  of  the 
lower  jaw  ;  as  a  consequence  of  this,  the  patterns  of  the  molar  teeth  were 
modified  through  pressure  in  accordance  with  this  movement.  If  this 
proposition  be  true  of  the  teeth  of  the  ungulates,  it  must  likewise  be  true 
of  all  other  animals.^ 

Dr.  Tomes  in  his  JIanual  of  Dental  Anatomy  criticises  Mr.  Ryder's 
conclusions,  as  follows :  "  The  simple  mechanical  explanation  that  the 
teeth  are  drawn  out  into  these  forms  hardly  conveys  much  information, 
seeing  that  the  tooth,  before  it  is  subjected  to  these  influences,  is  quite 
finished,  and  its  form,  such  as  it  is,  is  unalterable  ;  while  to  effect  an  alter- 
ation in  the  form  of  a  masticating  surface  an  influence  must  be  brought 
to  bear  upon  the  tooth-germs  at  an  exceedingly  early  period.  It  might 
with  equal  justice  be  said  that  the  crown  of  the  tooth,  being  formed 
thus,  had  influenced  the  excursions  of  the  jaw,  and  so  modified  the 
condyle." 

It  is  evident  that  Dr.  Tomes  has  either  failed  to  grasp  the  mean- 
ing of  Ryder's  reasoning,  or  else  denies  one  of  the  most  important 
principles  of  the  evolution  doctrine.  I  am  not  aware  that  Rvder  has 
anywhere  asserted  that  the  production  of  the  selenodont  pattern  of 
the  ungulate  molar  took  place  in  a  single  generation,  as  Dr.  Tomes's 
criticism  would  seem  to  imply.  As  a  matter  of  course,  the  tooth  of  a 
modern  ungulate  when  it  comes  into  position  is  "  quite  finished,"  but 
were  the  teeth  of  the  ancestors  of  the  modern  ungulates  quite  finished 
when  they  came  into  position  ?  Ryder  has  attempted  to  show  that  this 
finishing  process  was  a  gradual  one,  which  took  many  generations  to 
accomplisli,  and  the  facts  of  palaeontology  bear  out  this  view.  The 
bold  assertion  of  Dr.  Tomes,  to  the  effect  that  the  masticating  surface 
of  a  tooth  wlien  it  comes  into  position  is  unalterable,  is  open  to  very 
grave  and  serious  doubts.  If  the  firm  of  a  bone  or  any  other  organ 
of  the  animal  body  can  be  influenced  by  imjiact  and  strain,  as  all  evolu- 
tionists believe,  then  I  can  see  no  reason  why  a  tooth  is  not  amenable 
to  the  same  influences. 

The  sugge.stion  which  Dr.  Tomes  offers,  to  the  effect  that  tiie  crowns 
of  the  teeth  have  determined  the  direction'  of  tlie  jaw  movements, 
and  so  modified  the  condyle,  is  somewhat  absurd.  It  is  equal  to 
assuming  that  structure  has  determined  habit — a  most  remarkable 
conclusion  foi-  an  evolutionist  of  the  ])ronounced  tvpe  of  Dr.  Tomes. 
The  fact  of  the  matter  is,  the  evolution  hypothesis  assumes  the  very 
opposite  of  this.     I  have  always  believed  it  to  be  one  of  the  cardinal 

'  Dr.  C.  N.  Pierce  ha.s  elaborated  the  views  of  Ryder  and  made  important  additions 
to  this  mechanical  hypothesis. 


TEETH   OF  THE   VERTEBRATA.    '  503 

principles  of  that  great  doctrine  to  consider  that  structure  is  largely  the 
result  of"  habit.  Upon  the  whole,  I  find  it  quite  impossible  to  harmonize 
such  a  suggestion  with  what  this  author  holds  on  page  268  of  the  same 
work,  in  which  he  says  :  "  It  would  be  impossible  in  these  pages  to  go 
through  the  arguments  by  which  Mr.  Darwin  has  established  his  main 
propositions ;  it  must  suffice  to  say  here  that  he  has  fully  convinced  all 
those  who  are  not  in  the  habit,  from  the  fixity  of  early  impressions,  of 
putting  many  matters  upon  another  footing  than  that  established  by  the 
exercise  of  reason,  tliat  any  modification  in  the  structure  of  a  plant  or 
animal  which  is  of  benefit  to  its  possessor  is  capable — nay,  is  sure — of 
being  transmitted  and  intensified  in  successive  generations  until  great 
and  material  differences  have  more  or  less  masked  the  resemblances  to 
the  parent  form." 

As  a  result  of  palseontological  investigation  we  know  that  the  form 
of  the  mandibular  condyles  has  been  very  little,  if  any,  modified,  while 
the  teeth  have.  We  know,  moreover,  that  it  was  a  gradual  process,  and 
that  all  com])lex  patterns  had  their  origin  in  simj)le  ones. 

I  feel  well  satisfied  that  there  is  not  a  single  dentition  of  a  complex 
nature  that  has  not  been  profoundly  modified  by  these  same  mechanical 
influences.  If  evolution  has  taken  place  as  a  result  of  the  physical 
forces,  it  is  impossible  to  discover  any  forces  sufficient  to  produce  such 
results  other  than  those  of  strain,  impact,  and  jiressure.  These  have  in 
some  instances  })robably  been  exerted  upon  the  young  and  growing  tooth- 
germs  ;  in  others  they  have  o]>erated  upon  the  adult  tooth,  thereby  fur- 
nishing the  causes  for  individual  variation  and  determining  the  direction 
of  the  hereditary  energies. 

In  the  preparation  of  the  present  article  my  grateful  acknowledgments 
are  due  to  the  following  gentlemen  :  to  Prof.  E.  D.  Cope  of  Philadelphia, 
who  has  kindly  accorded  me  free  access  to  his  large  and  valuable  collec- 
tion of  fossil  vertebrates,  without  which  it  would  have  been  impossible 
to  include  the  extinct  forms.  He  has  likewise  placed  at  ray  disposal  all 
the  illustrations  in  his  jjossession  which  relate  to  his  labors  in  this  field. 
To  Mr.  J.  A.  Ryder  for  many  wise  and  valuable  suggestions  in  the 
developmental  history  of  the  teeth  and  other  kindred  subjects.  To 
Dr.  Theo.  Gill  for  the  loan  of  illustrations  and  much  important  infor- 
mation ;  and,  finally,  to  Prof.  C.  N.  Pierce,  at  whose  instance  I  was 
led  to  undertake  the  present  work.  I  also  wish  to  express  my  obliga- 
tions to  this  gentleman  for  much  kindly  advice  and  assistance. 

Of  the' works  consulted  I  have  made  free  use  of  C.  S.  Tomes's  Manual 
of  Dental  Anatomy,  a  most  useful  and  important  work  ;  also,  of  the  pub- 
lished writings  of  Profs.  Owen,  Huxley,  Gegenbaur,  Flower,  Cope,  Leidy, 
Allen,  Ryder,  Marsh,  and  others. 


504  DENTAL  ANATOMY. 

Descriptions  of  Plates.^ 

Plate  I.— Figs.  1  and  ■_'  represent  the  deciduous  incisors  and  cuspids,  with  their  labial  surfaces, 
and  the  molars  with  their  buccal  surfaces  facing.  Also  the  noinial  number  of  roots  for  these  teeth 
in  situ. 

Figs.  3  and  4  represent  the  superior  incisors,  cuspids,  and  molars  with  their  palatine  surfaces,  and 
the  full  inferior  set  with  their  lingual  surfaces  facing. 

Figs.  0  and  6  represent  the  mesial  surfaces  of  the  full  deciduous  set,  aud  both  mesial  and  distal 
surfaces  of  the  molars. 

Plate  II. — Figs.  1  and  'i  represent  the  full  permanent  set  of  thirty-two  teeth,  sixteen  in  each  jaw, 
with  the  labial  surfaces  of  the  incisors  and  buccal  surfaces  of  bicusjjids  and  molars  exposed:  a  a,  the 
central  incisors,  right  and  left;  b  h,  the  laterals;  c  c,  the  cuspids  or  canines;  (/ rf,  the  first  bicuspids; 
e  e,  the  second  bicuspids ;  ff^  the  first  molars ;  g  tj,  the  second  molars ;  li  A,  the  third  molars. 

Figs.  2  and  4  repre.sent  the  anterior  teeth,  incisors,  and  cuspids,  with  their  cutting  edges  notched, 
as  they  are  usually  seen  in  the  newly-erupted  teeth,  this  uneven  or  notched  appearance  usually  dis- 
appearing in  a  few  months,  or  at  most  in  a  year,  after  eruption. 

Plate  III. — Figs.  1  and  2  represent  the  deciduous  or  temporary  teeth  divided  longitudinally 
through  their  lateral  diameter. 

Figs.  3  and  4  represent  the  same  teeth  divided  through  their  antero-posterior  diameters.  These 
cuts  give  a  very  accurate  idea  of  the  relative  size  of  the  crown  and  roots,  aud  of  the  position  occupied 
by  the  pulp-chamber  in  the  same. 

Plate  IV.— Fig.  3  gives  in  contrast  a  sectional  view  of  deciduous  and  permanent  upper  teeth 
divided  through  their  lateral  diameters. 

Fig.  4,  a  sectional  view  of  the  corresponding  lower  teeth  divided  through  their  antero-posterior 
diameters.  «,  6,  c,  represent,  respectively,  the  deciduous  and  permanent  front  incisors  in  contrast; 
d,  e,f,  the  lateral  incisors ;  g,  h,  i,  the  cuspids ;  k;  deciduous  molars,  upper  and  lower ;  and  /,  in,  the  suc- 
cessors to  the  deciduous  molars,  the  bicuspids;  ii,o  represent  i)ermanent  molars.  c,J',i,m,o  have 
dotted  lines,  indicating  the  thickness  of  enamel  removed  l)y  wear,  atrophy  of  the  cementum,  and  reduc- 
tion in  the  size  of  the  pulp  due  to  progressive  calcification,  these  changes  being  incident  to  old  age. 

Plate  V.  represents  in  Fig.  1,  letters  a  to  k  and  ^  to  A,  the  longitudinal  or  vertical  sections  of  the 
sixteen  superior  teeth,  showing  the  labio-palatine  diameter  of  the  pulp-chamber  and  canal  in  crown 
aud  roots,  the  section  of  the  molars  being  through  the  anterior  buccal  and  palatine  roots,  while  the 
bicuspids  d  e  a.udd_e  illustrate  the  result  of  such  a  compression  of  the  fang  or  root  as  to  divide  the 
pulp-chamber  into  two  canals — a  condition  which  .so  frequently  exists  in  these  flattened  roots. 
The  double-lettered  series,  (/'/  to  h/i  and  ihi  to  hji,  represent  in  the  molars  a  section  through  the  pos- 
terior buccal  and  the  palatine  roots,  from  which  is  quite  readily  recognized  the  slightly  greater  lateral 
diameter  of  the  pulp-chamber  in  the  crown  and  the  larger  canal  in  the  posterior  buccal  root  over  that 
in  the  anterior  buccal  root,  while  the  bicuspids  lettered  e  e  dd  and  d  d  <;  f  illustrate  a  modified  pulp- 
chamber  and  canal,  with  bifurcation  of  the  root  in  one,  these  being  cut  through  a  diflereut  axis  or  plane 
from  the  single-lettered  series. 

Fig.  2,  letters  a  to  h  and  ato  h,  represents  the  sixteen  inferior  teeth  with  the  section  through  their 
long  diameters,  as  in  the  superior  series.  These  incisors  illustrate  the  compressed  or  flattened  con- 
dition of  their  roots  in  contrast  with  the  cylindrical  character  of  the  roots  of  the  superior  incisors, 
while  the  bicuspids  d  e  and  d_e  illustrate  the  siuglene.ss  of  their  pulp-chamber  and  the  cylindrical  con- 
dition of  their  roots  as  in  contrast  with' the  flattened  or  compressed  condition  of  the  roots  of  the  supe- 
rior bicuspids.  The  molars  /,  g,  //,  and  f",  g,  h  represent  sections  through  the  anterior  root,  illustrating 
its  compressed  condition  and  divided  pulp-chamber  in  the  first  and  second  molar,  and  a  somewhat 
flattened  one  in  tlie  anterior  root  of  the  third  molar  ;  ff,  g  g,  k  )i,  and/'/,  g  g,  h  li  represent  the  single 
and  cylindrical  pulp-chamber  in  the  posterior  root  of  the  inferior  molars,  while  b  h,  c  c  and  a  n.h  b 
represent  the  incisors  and  cuspids  of  the  same  series,  with  modified  pulp-chambers  arising  from  modi- 
fied development. 

Plate  VI. —Fig.  1,  from  a  to  h  and  «  to^,  represents  the  superior  teeth,  with  transverse  or  horizon- 
tal section  through  the  base  of  the  pulp-chamber  in  the  crown,  viewing  the  entrance  to  the  canals  of 
the  .several  roots,  while  the  same  letters  in  Fig,  2  represent  the  inferior  series  in  the  same  manner. 

Fig.  8  represents  the  superior  teeth,  with  the  transverse  or  horizontal  section  made  below  the 
largest  diameter  of  the  pulp-chamber  and  through  the  canals  after  they  have  diverged  from  the  cen- 
tral chamber,  but  before  the  roots  into  which  they  run  have  in  the  molars  bifurcated. 

Fig.  4  in  like  manner  represents  the  inferior  series,  well  illustrating  the  flattened  or  compressed 
coiidition  of  the  canal  in  anterior  roots  of  the  molars  and  the  division  of  the  chamber,  as  is  frequently 
found  in  the  roots  of  the  inferior  incisors. 

The  letters  <i  a,  b  b,  c  c,  d  d,  ff,  d  d  and  e  e  (Fig.  '■'>)  represent  the  relative  shapes,  whether  circular, 
oval,  or  flattened,  of  the  pulp-canal  in  the  roots  of  the  sni)erior  centrnl  and  lateral  incisors,  the  cuspids, 
the  first  and  second  bicuspids,  and  the  first,  second,  and  third  molars,  while  the  same  letters  in  Fig. 
4  represent  the  relative  shapes  of  the  pulp-canal  in  similar  teeth  in  the  inferior  series. 

1  These  plates  are  taken  from  v.  Carabelli's  Anatomic  des  Mtmdes. 


PLATE  I. 

For  (lescriptiou,  see  page  51)4. 


T.j.^. 


fry-S 


rv^.s. 


^&-^- 


r<^,s. 


jf^.ff. 


505 


-^1^ 


PLATE    II. 

For  description,  see  page  504. 


■^1  "'L' ■.".ii!Mi|ftfl"""''"l''\ 


\ 0iMmm 


•4" 


^ 


^ 


'■k 


'<i 


507 


PLATE  III. 

For  de.-criptioii,  isee  page  504. 


F'^.^. 


h'hiBB 


Fia.  ^ 


Jflf.J. 


JF^A.i 


I  i  I) 


'■/     \\ 


509 


PLATE  IV. 

For  description,  see  page  504. 


511 


PLATE  V. 

For  description,  see  page  504. 


Vol.  I.— 33 


PLATE  VI. 

For  description,  see  page  504. 


0^ 


.^^ 


,o^ 


Uo.'®.^ 


K^ 


I^K") 


FQ 


u/ 


^ 

'^) 


^ 


^^ 


^^ 


«^.. 


^„(i 


515 


PART   III 


EMBRYOLOGY  AND  DENTAL  HISTOLOGY. 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

By  W.  XAVIER  SUDDUTH,  M.  D.,  D.  D.  S. 


Physiological,  Consideration  op  Life-Force. 

What  is  the  nature  of  life?  is  a  question  which  man  is  ever  asking 
of  the  universe  of  wiiieh  he  is  so  wondrous  yet  so  infinitely  small  a 
part.  From  the  earliest  times  the  ultimate  purpose  of  all  scientific 
research  has  been  to  elicit  a  sufficing  reply  to  this  inquiry.  The  deepest 
thinkers  and  most  devoted  searchers  after  truth  have  speculated  and 
investigated  in  the  hope  of  making  up  something  like  a  satisfactory 
answer.  But,  though  knowledge  has  been  augmented  and  phenomena 
explained,  the  great  life-mystery  remains  unrevealed.  The  question 
still  is  asked,  What  is  that  vital  or  living  principle  which  we  call  life? 

Scientists  and  philosophers  have  ventured  various  and  widely  diver- 
gent theories  in  explanation  of  the  nature  and  powers  of  vital  phenom- 
ena. Setting  aside  opinions  that  are  so  manifestly  based  upon  fallacies 
as  to  carry  with  them  no  inkling  even  of  definite  signification,  the  great 
variety  of  theories  advanced  in  our  own  day  may  be  for  the  most  part 
reduced  to  two  or  three  classes. 

In  the  early  part  of  the  present  century  Lorenz  Oken,  a  devotee  of  the 
physical  school,  proclaimed  "primordial  slime"  to  be  the  original  source 
of  life  and  the  material  basis  of  all  living  bodies.  This  "  primordial 
slime"  possessed  in  all  essentials  the  same  qualities  and  the  same  import- 
ance now  ascribed  to  the  substance  known  as  protoplasm.  The  proto- 
plasm theory — varied  in  many  ways  as  to  the  first  vitality  on  earth — 
has  occupied  the  attention  of  the  most  earnest  scientists  and  profoundest 
thinkers  of  the  age. 

It  is  not  mv  intention  to  notice  to  any  extent  the  diiferent  phases 
which  this  theory  has  assumed,  but  I  wish  to  be  understood  as  antag- 
onizing that  interpretation  of  it  which  aims  to  make  the  beginning  of 
life  in  the  individual  solve  the  great  mystery  of  the  beginning  of  life 
in  the  world.  I  desire,  at  the  outset,  to  forestall  any  misapprehension 
of  facts  I  may  state  hereafter,  and  to  impress  upon  my  readers  the  wide 
difference  between  accepting  protoplasm  as  the  fird  formative  substance 
and  ascribing  to  it  the  power  of  spontaneous  generation,  since  it  by  no 
means  follows  that  because  it  is  the  essential  and  active  agent  in  the 
formation  of  every  tissue,  in  the  construction  of  every  organ  and  of 
every  form  of  mechanism  existing  in  a  living  being,  it  is  in  any  sense 
self-originating. 

Perhaps  the  most  plausible  theory  advanced  by  speculators  concerning 

619 


520  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

life-formation  is  that  of  evolution,  but  evolutionists  themselves  assign 
several  meanings  to  the  term.  One  class  maintains  that  the  develop- 
ment hypothesis  is  restricted  to  the  living  world — that  it  simply  teaches 
that  all  grades  of  life  have  arisen  from  the  simplest  beginnings,  the 
higher  being  derived  from  the  lower  by  a  long  course  of  organic  devel- 
opment solely  through  the  operation  of  such  forces  and  laws  as  belong 
to  matter.  Another  class  holds  that  the  hypothesis  includes  not  only 
the  evolution  of  living  forms  from  pre-existing  living  forms,  but  the 
spontaneous  production  of  living  from  non-living  material.  A  vast 
majority  of  the  practical,  working  scientists  in  Europe  and  America — 
those  who  report  not  what  they  wish  nor  hope  nor  imagine,  but  only 
what  they  see,  who  are  seeking,  not  the  mere  sujjport  of  cherished 
hypotheses,  but  the  uncolored  truth  from  Nature, — refuse  to  accept  the 
doctrine  of  evolution,  while  at  the  same  time  they  fully  allow  the  value 
of  many  of  the  facts  gathei'ed  by  its  followers. 

In  regard  to  the  "transmutation  of  species,"  that  part  of  the  theory 
of  evolution  which  undertakes  to  show  how  the  higher  grades  of  life 
came  by  a  series  of  natural  changes  from  the  lower,  Agassiz  has  written 
thus : 

"  I  wish  to  enter  my  earnest  protest  against  the  transmutation  theory. 
It  is  my  belief  that  naturalists  are  chasing  a  phantom  in  their  search 
after  some  material  gradation  among  created  beings  by  which  the  whole 
animal  kingdom  may  have  been  derived  by  successive  development  from 
a  single  germ  or  from  a  few  germs.  I  confess  that  there  seems  to  me  a 
repulsive  poverty  in  this  material  explanation  that  is  contradicted  by 
the  intellectual  grandeur  of  the  universe.  I  insist  that  this  theory  is 
opposed  to  the  processes  of  Nature  as  we  have  been  able  to  apprehend 
them ;  that  it  is  contradicted  by  the  facts  of  embryology  and  palaeon- 
tology, the  former  showing  us  forms  of  development  as  distinct  and 
persistent  for  each  group  as  are  the  fossil  types  of  each  period  revealed 
to  us  by  the  latter ;  and  that  the  experiments  on  domesticated  animals 
and  cultivated  plants,  on  which  its  adherents  base  their  views,  are 
entirely  foreign  to  the  matter  in  hand." 

From  the  side  of  geology — on  which  evolutionists  very  largely  de- 
pend for  the  support  of  their  scheme — we  have  many  an  earnest  pro- 
test, of  which  the  following  may  serve  as  an  illustration: 

"Were  all  the  anatomists  of  the  earth  against  us,  we  should  not  one 
jot  abate  our  confidence.  For  we  have  examined  the  old  records,  but 
not  in  cabinets,  where  things  of  a  different  age  are  put  side  by  side,  and 
so  viewed  might  suggest  some  glimmering  notions  of  a  false  historical 
connection.  We  have  seen  them  in  spots  where  Nature  placed  them, 
and  we  know  their  true  historical  meaning.  We  have  visited  in  suc- 
cession the  tombs  and  charnel-houses  of  these  old  times,  and  we  took 
with  us  the  clue  spini  in  the  fabric  of  development;  but  we  found  this 
clue  no  guide  through  these  ancient  labyrinths,  and,  sorely  against  our 
will,  we  were  com])elled  to  snap  its  thread,  and  now  dare  to  affirm, 
with  all  the  confidence  of  assured  truth,  that  geology — not  seen  through 
the  mists  of  any  theory,  but  taken  as  a  ])lain  succession  of  monuments 
and  facts — offers  one  firm  cmnulative  argument  against  the  hypothesis 
of  development"  (Sedgwick). 


PHYSrO LOGICAL   CONSIDERATION  OF  LIFE-FORCE.  521 

Still  stronger  words  than  these  have  been  spoken  against  the  doctrine 
of  spontaneous  generation.  It  is  even  admitted  by  nearly  all  the  fore- 
most evolutionists  themselves  that  as  yet  not  an  instance  of  life-forma- 
tion without  seed  has  been  made  out.  "It  is  true,"  say  they,  "that 
the  knowledge  of  man  has  not  yet  enabled  him  to  make  a  vegetable  or 
animal  germ,  but  the  time  may  come  when  it  will  be  done." 

"'To-morrow,  and  to-morrow,  and  to-morrow,'"  says  Dr.  Beale, 
"  has  always  been  the  refuge  of  the  philosophers  who  have  faith  in  the 
dogma  that  matter  alone  is  competent  to  develop  every  form  of  life. 
But  the  'to-morrow'  of  Lucretius  has  not  yet  dawned;  and  how^  many 
thousand  years,  I  would  ask,  may  be  expected  to  pass  away  before  the 
prophecies  of  those  who  would  now  go  along  with  Lucretius  shall  be 
fulfilled?"  Again,  speaking  directly  of  the  theory  of  spontaneous 
generation,  he  says:  "I  cannot  but  remark  that  the  more  minutely 
investigation  is  carried  out,  the  more  thoroughly  and  intently  facts 
bearing  upon  the  matter  are  examined,  the  more  improbable,  in  my 
judgment,  does  it  appear  that  any  living  form  should  be  derived  directly 
from  the  non-living.  Notwithstanding  all  that  has  been  recently  written 
upon  this  subject,  I  cannot  but  feel  surprised  that  at  this  time  many 
good  reasoners  should  decide  in  favor  of  the  de-novo  origin  even  of 
bacteria.  Whether  we  consider  the  matter  from  the  experimental  side 
only,  or  study  the  evidence  obtained  in  a  general  survey  of  Nature,  or 
carefully  reflect  upon  the  facts  learned  from  investigations  concerning  the 
properties  of  living  and  non-living  matter  with  the  aid  of  the  most 
perfect  instruments  of  minute  research  now  at  command  or  from  other 
standpoints,  the  conclusion  seems  to  me  irresistible  that  the  verdict  of  a 
jury  of  well-educated  men  would  be  against  the  direct  origin  of  any 
form  of  living  from  any  form  of  non-living."  ^ 

Pasteur  asserts  decisively,  "There  is  no  circumstance  now  known 
that  permits  us  to  affirm  that  microscopic  beings  have  come  into  the 
world  without  germs,  without  parents  like  themselves.  Those  who 
affirm  it  have  been  victims  of  illusions,  of  experiments  badly  made, 
and  infected  with  errors  which  they  have  not  been  able  to  perceive  or 
avoid.     Spontaneous  generation  is  a  chimera." 

Did  our  limits  allow  we  might  multiply  quotations  almost  indef- 
initely to  show  that  the  most  thoughtful  among  working  scientists,  both 
at  home  and  abroad,  deny  that  there  have  been  proved  cases  either  of 
transmuted  species  or  of  spontaneous  generation.  On  the  contrary, 
experimental  investigation  is  constantly  furnishing  positive  proof  of  the 
permanence  of  species,  and  so  intensifying  the  vast  dissimilarities  be- 
tween the  living  and  the  non-living  as  to  preclude  the  possibility  of 
drawing  even  an  analogy  between  the  properties  peculiar  to  living  mat- 
ter and  any  properties  known  in  connection  with  the  non-living. 

The  distinctive  characteristic  of  non-living  matter  is  rest;  the  dis- 
tinctive trait  of  living  matter  is  motion,  life.  The  non-living,  once 
formed,  never  changes  from  internal  causes ;  its  parts  invariably  pre- 
serve the  position  which  they  have  once  taken  in  respect  to  each  other, 
unless  endowed  with  the  properties  of  life  by  the  aid  of  organisms 
already  living.  Living  bodies,  on  the  contrary,  from  the  very  lowest  in 
'  On  Life  and  on  Vital  Action  in  Health  and  Disease. 


522  DENTAL   EMBRYOLOGY  AND  HISTOLOGY. 

the  vegetable  kingdom  to  those  concerned  in  the  development  of  man, 
are  continually  in  action.  This  capacity  of  movement  is  the  broad  essen- 
tial character  which  distinguishes  living  matter  absolutely  from  all  other 
matter,  and  makes  a  clear-cut  boundary  bet\veen  it  and  the  non-living. 
It  has  been  claimed  that  the  phenomena  of  the  minute  organisms  which 
lie  on  the  very  verge  of  the  vast  area  of  what  we  know  as  the  living 
are  not  essentially  different  from  those  of  the  highest  points  in  the  area 
of  the  non-livino-  which  thev  touch.  The  wonderful  revelations  of  the 
lowest  forms  of  life  made  by  the  modern  microscope  have  shown  that 
not  only  is  the  assertion  entirely  groundless,  but  the  highest  form  of 
living  matter  is  not  more  unlike  non-living  than  is  the  lowest — that 
"one  is,  in  fact,  just  as  near  and  just  as  far  from  inorganic  matter  as 
the  other." 

With  all  our  study,  we  must  admit  that  at  best  we  have  only  been 
able  to  demonstrate  life  in  its  concrete  form.  It  is  a  correlation  of 
forces  that  our  present  knowledge  does  not  enable  us  to  separate  into 
ultimate  principles.  We  know  the  elements  that  compose  the  vital  stuff; 
we  know  their  physical  properties.  But  Jiow  these  elements  can  be  so 
combined  as  to  acquire  the  wonderful  properties  of  life  is  as  great  a 
mystery  now  as  when  God  first  "  breathed  into  man  the  breath  of  life, 
and  he  became  a  living  soul."  Humanity  stands  to-day,  as  in  the 
remotest  past,  with  the  same  question  on  its  lips  :  What  is  life  ?  What 
is  it  to  be  f 

But  whatever  may  be  the  essential  nature  of  the  central  force  which 
determines  the  form  and  action  of  living  bodies,  it  cannot  be  denied 
that  some  power  does  exist  and  act  in  every  organism  independent  of 
the  physical  and  chemical  forces  of  Nature.  "  Besides  the  material  sub- 
stance of  which  a  living  body  is  constructed,  there  is  also  an  immaterial 
principle,  which,  thougli  it  eludes  detection,  is  none  the  less  real,  and  to 
which  we  are  constantly  obliged  to  recur  in  considering  the  phenomena 
of  life.  It  originates  with  the  body,  and  is  developed  with  it,  while  yet 
it  is  totally  apart  from  it."  We  are  as  certain  that  this  inscrutable  prin- 
ciple does  exist  as  we  are  of  the  constancy  of  species — a  phenomenon 
depending  on  its  operation.  Every  living  thing  tells  of  some  wonder- 
ful power  which  is  capable  of  controlling  matter  and  its  forces — "a 
power  which  we  cannot  isolate  and  physically  examine,  but  the  effects 
of  the  actions  of  which  we  may  study." 

Let  us  use  a  familiar  illustration  :  If  one  grain  of  copper  be  dissolved 
in  three  pints  of  water,  a  distinctly  blue  tint  is  imparted  to  the  volume 
of  water.  AVe  cannot  see  the  finely-triturated  j^articles  which  by  their 
minute  subdivisions  have  given  the  blue  tint  to  the  water — they  do  not 
reveal  themselves  even  to  the  microscope — but  we  know  that  they  exist, 
and  that  by  the  j^rocess  of  evaporation  we  may  receive  back  our  one 
grain  of  coj)per.  But  you  ask.  How  can  this  illustration  be  applied  to 
the  question  of  ultimate  life-force?  We  answer:  In  all  our  study  of 
life  we  see  the  "  blue  tint,"  as  it  were.  Especially  is  this  the  case  in 
the  microscopic  study  of  the  formative  material  which  we  designate  pro- 
to])lasm.  Beyond  the  protoplasm  we  see  the  manifestations  of  a  uni- 
versal power  by  virtue  of  which  all  formation,  whether  vegetable  or 
animal,  takes  place.     AVe  see  how  protoplasmic  atoms  act  under  the 


STRUCTURE  OF  CELLS.  523 

direction  of  this  indwelling  principle  just  as  plainly  as  we  see  the  blue 
tint  of  the  water ;  and  we  feel  as  sure  that  there  is  a  force  outside  the 
properties  of  matter,  which  pervades  and  vivifies  every  living  particle, 
as  we  do  of  the  grain  of  copper  left  after  the  evaporation  of  its  men- 
struum. It  is  only  as  man  contemplates,  at  the  same  time,  matter  and 
mind  that  he  is  able  to  master  the  first  data  of  life-science  or  form  even 
a  dim  conception  of  that  Infinite  Spirit  "  whom  none  by  searching  can 
find  out." 

But  we  must  now  leave  the  question  of  how  life  begins,  and  consider 
life  as  it  presents  itself  to  our  eyes  when  seen  in  its  minutest  forms  and 
at  its  earliest  known  stage  of  existence — i.  e.  as  an  aggregation  of  trans- 
parent cells. 

The  unit  of  life,  as  we  are  able  to  demonstrate,  is  expressed  in  small 
bodies  denominated  cells,  and  "  the  life-history  of  the  hidividual  cell  is 
the  first  important  and  indispensable  basis  whereon  to  found  the  true 
physiology  of  the  life-history  of  all  the  orders  of  creation."  We  shall 
therefore  take  our  starting-point  from  the  simple  cell,  which  is  the  same, 
in  respect  to  its  chief  characters,  in  animal  and  vegetable  life. 

Structure  of  Cells. 

A  mature  cell  is  composed  of  a  nucleus,  a  cell-body,  and  a  cell-limit, 
or  wall.  The  nucleus  is  that  part  of  the  cell  which  is  first  formed  from 
the  germinal  matter,  and  is  the  first  to  be  affected  when  a  change  in  form 
occurs.  The  nucleus  may  assume  various  shapes,  as  round,  oval,  rod- 
like, or  irregular.  It  generally  encloses  central  dots,  termed  nucleoli, 
which  are  thought  by  some  histologists  to  be  the  enlargements  of  por- 
tions of  an  irregular  network  of  fibres  which  can  be  seen  inside  the 
nucleus.  The  cell-body  is  the  formed  material  which  surrounds  the 
nucleus.  The  cell-wall  is  the  limit  of  this  formed  material.  When  we 
speak  of  a  cell-wall,  we  do  not  mean  that  there  is  any  abrupt  demarca- 
tion between  the  cell-body  and  its  outer  edge  ;  the  one  passes  gradually 
into  the  other.  Cells  draw  their  nourishment  from  a  protoplasmic  sub- 
stance which  circulates  in  the  intercellular  spaces.  This  supply  of  cell- 
pabulum  is  inert  until  acted  upon  by  the  living  principle  resident  in  the 
cell.  Such  are  the  visible  parts  of  a  cell  when  seen  in  its  early  stage  of 
existence. 

Ziegler,  speaking  of  the  youngest  embryonal  cells,  says  :  "  The  cell 
by  itself  appears  originally  as  a  microscopic  mass  of  pale,  slimy,  finely- 
granular  matter — the  so-called  protoplasm.  It  usually  contains  within 
it  a  nucleus — that  is  to  say,  a  structure  like  a  tiny  vesicle,  whose 
form  may  be  round,  oval,  rod-like,  or  irregular,  and  in  whose  interior 
we  can  make  out,  by  proper  handling — 1,  small  definite  bodies,  the 
nucleus-corpuscles  ;  2,  a  net-like  framework  of  nucleus  substance  ;  and, 
3,  a  clear  fluid,  the  nucleus  juice.  The  young  cell  is  at  first  naked. 
Only  in  its  raaturer  stages  does  it  develop  on  its  surface  an  oj^tically 
distinct  membrane  or  other  structure  according  to  the  special  tissue 
of  which  it  forms  a  part."  This  accords  with  my  own  observation. 
For  example,  in  studying  sections  from  the  mucous  membrane  of  the 
mouth  it  is  found  that  the  deepest  part  of  the  epithelial  layer  of  the 


524  DENTAL  E3IBB.Y0L0GY  AND  HISTOLOGY. 

mucous  membraue  of  the  mouth  in  the  embryo  is  formed  of  a  layer  of 
protoplasm,  which  is  conspicuous  in  preparations  stained  with  hsema- 
toxylon  and  eosin  in  that  it  stains  more  darkly  than  the  surrounding 
tissue.  In  this  protoplasmic  basis-substance  are  found  small  spheroidal 
cells  (nuclei),  sometimes  arranged  in  regular  layers  ;  in  other  cases  the 
dark-stained  layer  of  protoplasm  is  wider,  and  several  layers  of  sphe- 
roidal cells  exist — not  arranged  in  strata,  but  presenting  an  irregular 
appearance,  and  in  some  instances  being  four  or  five  cells  deej).  These 
spheroidal  cells  have  no  distinct  cell-body  or  membrane,  and  the  sur- 
rounding protoplasm  presents  no  characteristic  feature.  The  youngest 
cells  of  the  Malpighian  layer  take  the  stains  similarly  to  the  embryonal 
connective-tissue  cells  lying  immediately  beneath  in  the  submucous 
layer,  and  at  this  stage  present  the  same  shape,  and  can  be  seen  in  the 
pig  embryo  1 —  centimeter  in  length,  and  in  the  human  embryo  at  the 
thirty-fifth  day. 

As  the  nuclei  are  crowded  up  from  this  bed  of  protoplasm,  they  carry 
with  them  a  certain  portion  of  protoplasm  which  surrounds  the  nucleus 
as  a  cell-body,  and  as  they  approach  the  surface  of  the  epithelium  they 
apparently  develop  a  cell-wall ;  in  this  state  they  present  an  imbricated 
border  Avliich  unites  them  to  their  fellows.  (For  further  description  and 
figures  see  section  on  Mucous  Membrane  of  the  Mouth,  p.  611.) 

The  shape  of  cells  depends  to  a  great  extent  upon  the  reci})rocal 
pressure  of  fellow-cells.  This  is  specially  noticeable  in  cells  developed 
from  the  epiblast  and  hypoblast :  these  may  be  round,  oval,  cylindrical, 
columnar,  prismatic,  hexagonal,  or  tessellated  in  form.  The  cells  devel- 
oped from  the  mesoblast — viz.  the  connective-tissue  group — vary  from 
round  or  oval  to  fusiform  with  numerous  fibrillee.  The  size  of  a  cell 
may  be  -g-g-oth  part  of  an  inch  in  diameter ;  some  are  larger,  some 
smaller ;  the  nucleus  may  be  gQ^Q^th  of  an  inch  in  diameter  ;  the  nucle- 
olus 10  000^^^  ^^  ^^  "^^^^  ^^  diameter,  more  or  less. 

Physiological  Consideration  of  Cells. 

Dependent  upon  an  inherent  principle,  the  nature  of  which  we  have 
never  been  able  to  divine,  cells  have  a  threefold  character :  the  power 
of  self-preservation,  of  multiplication,  and  of  functional  activity. 

In  the  first  place,  out  of  the  common  stock  of  cell-])abulum  each  cell 
has  the  power  to  assimilate  such  constituents  as  are  needed  to  prolong 
its  existence.  That  different  cells  require  diiferent  kinds  of  food,  and 
are  able  to  convert  the  same  into  matter  like  themselves,  is  evidenced 
by  the  fact  tliat  chemical  reagents  give  manifestly  different  results  on 
the  various  cells.  A  simple  demonstration  is  found  in  the  action  of 
staining  agents  upon  different  tissues.  Cells  have,  within  a  certain 
limit,  the  power  of  overcoming  deleterious  agents  or  conditions.  This 
limit  is  not  great  as  regards  the  cell  itself,  but  for  the  tissue  of  which 
it  is  a  comjMnient  part  the  range  is  much  more  extended. 

Recovery  after  the  loss  of  a  portion  of  the  cellular  elements  that  com- 
pose a  tissue  is  generally  very  rapid,  and  depends  upon  that  attribute 
of  cells  we  term  muUiplicaiion.  Increase  of  cells  is  accomjjlished  by 
segmentation,  which,  beginning  in  the  nucleus,  results  in  the  division 


PHYSIOLOGICAL   CONSIDERATION  OF  CELLS.  525 

of  the  parent  into  two  equal  parts,  each  of  which  when  detached  absorbs 
nutrient  matter,  and,  soon  attaining  the  same  size  as  the  mother-cell, 
multiplies  in  turn.  The  principle  enunciated  by  Virchow  twenty  years 
ago,  Omnk  cdlula  e  celluld,  is  as  much  in  force  now  as  then.  Discov- 
eries regarding  the  methods  of  cell-multiplication  have  been  made,  but 
no  instance  of  metaplasia  between  members  of  different  groups  or  fam- 
ilies has  been  demonstrated.  That  the  repair  of  tissues  depends  upon 
the  multiplication  of  cells  of  like  families  is  the  accepted  belief  of  his- 
tologists  to-day.  A  surface  denuded  of  its  epithelium  does  not  recover 
itself  from  the  connective  tissue  beneath,  but  from  the  edges  of  the 
wound  by  tlie  extension  of  the  borders  toward  the  centre,  thus  gradu- 
ally forming  a  complete  skin.  It  is  true  that  the  regeneration  of  con- 
nective tissue  is  through  granulation-tissue,  but  granulation-tissue  is 
developed  from  the  escaped  white  blood-cells ;  and  I  think  we  can 
place  white  blood-cells  in  the  list  of  connective  tissues  developed  from 
the  mesoblast.  The  change  from  white  blood-cells  to  plasma-cells  and 
fixed  connective-tissue  cells  is  simply  a  matter  of  adaptation  to  environ- 
ment. 

We  come  now  to  the  consideration  of  the  third  attribute  of  cells — 
that  of  functional  activity.  The  life  of  the  individual  rests  in  the  life 
of  the  individual  elements  that  compose  it.  The  human  body  is  made 
up  of  millions  of  individualities  which  are  dependent  upon  a  special 
localized  principle  for  their  functional  activity.  These  units  of  life  not 
only  have  the  power  of  individual  cellular  activity,  but,  united,  they 
form  organs  which  are  but  the  expressions  of  their  aggregation.  A 
tissue  is  what  it  is  by  reason  of  the  elements  that  constitute  it,  and  the 
function  it  performs  is  only  the  united  expression  of  its  component 
parts.  Cellular  activity,  then,  is  the  basal  principle  that  underlies  all 
visible  life-functions. 

The  limit  of  duration  as  regards  the  life  of  an  organism  is  in  adverse 
ratio  to  the  scale  it  occupies  in  the  order  of  being.  A  perversion  of 
physiological  action  in  the  individual  organism  gives  rise  to  a  patho- 
logical condition  known  as  disease.  Total  and  permanent  cessation  of 
functional  activity  is  that  state  of  being  which  we  recognize  as  death. 
Death  may  result  from  outside  influences  or  by  reason  of  the  cells  hav- 
ing performed  their  life-office. 

Cells  are  developed  to  perform  well-known  physiological  actions, 
and  when  a  pathological  result  is  produced  it  has  its  origin  in  some 
outside  influence.  Cells  have  not  the  power  to  produce  pathological 
results  unless  stimulated  by  some  agent  which  lies  without  the  bounds 
of  physiological  action ;  and  when  so  stimulated  they  act  through  their 
original  channels.  Thus,  we  see  that  pathological  conditions  are  only 
perverted  physiological  conditions.  Many  physiological  processes  pre- 
sent pathological  ajjpearances,  but  when  we  study  their  deeper  expres- 
sions we  find  that  they  are  purely  physiological.  For  instance:  in  the 
development  of  bone,  giant-cells  or  osteoclasts  are  always  present  taking 
down  the  first-formed'  bone  from  the  inner  side,  while  the  osteoblasts 
are  adding  to  its  circumference.  In  the  resorption  of  the  roots  of  tem- 
porary teeth  we  find  another  excellent  example  of  physiological  action 
which  bears  upon  its  face  the  stamp  of  a  pathological  process.     In  this 


526  DENTAL   EMBRYOLOGY  AND  HISTOLOGY. 

case  giant-cells  are  Nature's  physiological    agents,  by  whose  aid   she 
removes  tissues  that  have  performed  their  life-oifice. 

There  can  be  no  doubt  that  cellular  activity  can  be  induced  by  dif- 
ferent agents,  but  the  action  of  a  given  tissue  is  always  the  same — pro- 
vided the  other  conditions  remain  unchanged — whatever  may  be  the 
nature  of  the  outside  irritant.  Too  little  stress  is  laid  upon  the  character 
of  the  irritant,  and  too  much  on  the  visible  expression  of  Nature's  effort 
to  remove  it. 

The  close  intimacy  existing  between  physiological  and  pathological 
processes  is  very  clearly  seen  in  the  action  of  giant-cells.  In  one 
instance  they  are  the  expressions  of  normal  action ;  in  another  they  are 
actively  engaged  in  producing  pathological  results.  Let  us  study  them 
in  their  several  conditions. 

Giant-cells  are  found  in  connection  with  a  perversion  of  the  equili- 
brium of  the  circulation  which  results  in  increased  nutrition.  In  most 
instances  where  such  disturbance  is  found  it  can  be  directly  traced  to 
some  local  irritant.  We  see  a  hypersemic  condition  of  some  organ  or 
part  of  the  body,  which  state  is  quickly  followed  by  congestion  and 
the  exudation  of  white  blood-corpuscles.  These  tend  to  form  granula- 
tion-tissue. The  increased  nutrition  does  not  sufficiently  account  for 
increased  cellular  activity,  either  as  regards  multiplication  or  function — 
congestion  not  always  resulting  in  cell-multiplication.  There  is  back 
of  all  that  can  be  observed  some  force  inherent  in  the  cell  itself  that 
leads  to  these  special  attributes — an  ego  which  has  the  power  to  turn 
the  local  irritant  into  a  cellular  stimulant.     - 

Ziegler,  writing  on  this  subject,  says  :  "  The  proposition,  often  enun- 
ciated as  if  it  were  self-evident,  'the  stronger  the  external  stinudus 
the  greater  the  proliferation,'  cannot  be  accepted  as  true.  We  can,  at 
most,  admit  that  slight  stimuli,  sufficient  merely  to  excite  the  cell  with- 
out injuring  it,  may  perhaps  call  into  play  its  powers  of  multiplication  ; 
but  nothing  has  been  experimentally  established  concerning  the  nature, 
the  action,  or  the  mode  of  application  of  such  stimuli.  If,  then,  it  be 
true  that  external  injurious  agencies  are  not  competent  to  induce  multi- 
plication of  cells,  we  must  have  recourse  to  the  normal  vital  stimuli  if 
we  are  to  explain  the  process  of  pathological  cell-growth.  For  the 
due  growth  and  multiplication  of  a  cell  certain  external  conditions  must 
be  fulfilled.  Above  all,  it  is  necessary  to  provide  for  a  certain  degree 
of  warmth  and  a  certain  modicum  of  proper  nutritive  material.  In 
addition  to  this  there  must  be  no  obstacle  in  the  way  of  multiplication. 
These  are  the  external  requirements.  The  internal  condition  is  the 
inherent  faculty  of  the  cell  to  assimilate  the  nutriment  offered  to  it.  In 
a  tissue  not  undergoing  transformation  the  factors  favoring  proliferation 
and  those  which  inhibit  it  must  be  in  a  state  of  balance.  If  this  bal- 
ance be  disturbed  toward  the  side  of  the  proliferous  forces,  the  cells 
proceed  to  grow  and  to  multiply.  The  factors  in  question  resolve  them- 
selves on  analysis  into  three.  In  the  first  place,  it  is  conceivable  that 
the  capacity  of  the  cell  to  assimilate  nutriment  may  be  increased.  Such 
increase  can  only  be  conditioned  by  an  increase  in  the  normal  stimuli 
required  for  the  preservation  of  the  cell.  Such  stimuli  are  warmth ; 
for   many  cells,  light;    for  the   muscles,  motor   impulses;    for  glands, 


PHYSIOLOGICAL   CONSIDERATION  OF  CELLS.  b21 

special  excitations  from  the  nervous  system,  etc.  Increased  stimula- 
tion of  this  kind  may,  as  a  fact,  lead  not  only  to  intensified  functional 
metabolism  in  the  tissue  concerned,  but  even  to  hypertrophy  of  its 
elements.  Such  hypertrophies,  which  we  may  call  functional  hyper- 
trophies or  hypertrophies  of  action,  are  specially  common  and  remark- 
able in  muscles  and  glands  (heart-muscles,  bladder-muscles,  kidneys, 
etc.).  As  we  have  said,  they  are  referable,  in  part  at  least,  to  increased 
vital  activity  in  the  cells,  consequently  upon  increased  physiological 
stimulation.  A  second  possible  factor  is  increase  in  the  supply  of  nutri- 
ment. This  plays  a  chief  part  in  hyperplastic  processes,  at  any  rate. 
A  third  is  the  removal  of  the  normal  checks  to  growth.  Its  effect  is 
most  evident  in  the  processes  described  as  regenerative.  If  we  attempt 
in  particular  cases  to  make  out  to  which  of  these  factors  cell-multipli- 
cation is  due,  we  are  led  to  see  that  it  is  rare  for  any  one  factor  alone  to 
be  the  efficient  cause. 

"  The  remarkable  regulating  mechanism  of  the  vessels  is  so  adjusted 
that  when  the  function  of  a  tissue  is  increased,  its  blood-supply  is 
increased  to  correspond.  In  like  manner,  when  the  smallest  fragment 
of  tissue  is  removed,  the  slight  loosening  of  the  surrounding  texture  is 
enough  to  augment  the  stream  of  transudation  from  the  vessels.  In 
consequence  of  these  adjustments  increased  supply  of  nutriment  plays 
a  great  part  in  all  the  formative  disturbances  of  nutrition. 

"  Cohnheim,  in  his  Allyeiiieine  Fdthologie,  has  insisted  on  the  import- 
ance of  increased  sup})ly  of  nutriment  ev^en  more  strongly  than  we  have 
done.  According  to  his  view,  it  is  the  sole  influential  factor,  compared 
with  which  the  intrinsic  activity  of  the  cell  is  quite  secondary.  We  are 
unwilling  to  condemn  the  cell  to  play  so  passive  a  part,  but  rather  agree 
with  Virchow,^  who  affirms  that  '  the  cell  is  not  nourished,  but  nour- 
ishes itself.'  Functional  hypertrophy  is  therefore  not  to  be  looked 
upon  as  the  mere  consequen(;e  of  the  increased  blood-supply  to  the 
active  organ. 

"  If  the  assimilative  activity  of  the  cells  were  not  augmented,  the 
mere  presence  of  a  greater  supply  of  nutriment  would  be  valueless.^ 

''  We  shall  more  readily  comprehend  the  activity  of  the  tissue-cells — 
i.  e.  their  behavior  under  various  conditions  and  the  changes  they  pass 
through,  now  at  rest  and  now  manifesting  intense  formative  energy — 
if  we  consider  first  the  vital  manifestation  of  an  organism  that  is  uni- 
cellular, micro-organisms  of  bacteria  and  yeast-])lants,  and  their  mode 
of  life.  If  we  reflect  on  the  conditions  essential  for  the  multiplication 
of  such  organisms,  we  note  that  the  nature  of  the  nutrient  fluid  is  (next 
after  the  adjustment  of  the  temperature)  the  factor  of  liigher  import- 
ance. In  suitably  composed  fluids  the  fungi  develop  much  more  luxu- 
riantly than  in  those  that  are  ill-suited.  But  we  are  not  thereby  justi- 
fied in  assuming  that  the  cell  plays  a  merely  passive  part — that  all  it 
has  to  do  is  to  take  up  the  nutriment  offered  to  it.  The  cell  is,  on  the 
contrary,  active,  and  its  activity  has  a  special  influence  on  the  liquid 
itself.  It  has  the  power  to  induce  certain  chemical  changes  in  the 
liquid,  to  decompose  certain  substances  contained  in  it,  and  to  change 

'  Cellular  Palholngy. 

^See  Samuel's  Al'lg.  Path.,  1879;  Paget's  Surgical  Pathology,  Lect.  3. 


528  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

this  condition  so  as  to  adapt  them  for  assimilation  by  itself.  The  cell 
does  not  merely  take  in  and  give  out  material ;  it  acts  '  catalytically ' 
on  its  environment.  This  is  proof  at  least  that  the  cell  possesses  a  high 
degree  of  spontaneity — that  it  has  the  power  of  making  more  available 
for  its  own  sustenance  the  various  forms  of  nutriment  that  come  in  its  way. 

"  It  is  also  of  great  interest  to  note  that  the  cell  is  ultimately  limited  in 
its  formative  activity  by  its  own  products.  When  the  amount  of  nutri- 
ment present  is  abundant,  the  activity  of  the  cell  comes  to  an  end,  not 
through  the  exhaustion  of  the  supply,  but  through  its  contamination 
with  certain  products  of  cell-metabolism. 

"  Many  of  the  substances  engendered  in  fermenting  liquids  by  the 
action  of  fungi  tend  to  check  the  growth  and  nndtiplication  of  the 
fungi  themselves ;  \\hen  present  in  quantity  they  may  put  a  stop  to 
multiplication  altogether. 

''  The  alcoholic  lermentation,  and  the  multiplication  of  the  yeast-plant 
which  produces  it,  come  to  an  end  when  a  certain  proportion  of  alcohol 
has  been  generated  in  the  fermenting  liquid.  In  septic  putrefaction  the 
bacteria  generate  compounds,  such  as  carbolic  acid,  which  are  destructive 
to  themselves.  If  we  may  apply  these  facts  of  fungus  physiology  to 
the  cell  physiology  of  higher  organisms,  M'e  find  that  they  illustrate, 
first  of  all,  this  principle  :  that  the  quantity  and  quality  of  the  nutritive 
material  at  the  disposal  of  the  cell  have  a  profound  influence  upon  its 
behavior ;  and,  secondly,  this  other :  that  the  cell  has  nevertheless  an 
intrinsic  power  of  utilizing  this  material,  and  of  appropriating  what  is 
suitable  to  itself  out  of  various  combinations.  Lastly,  the  limits  im- 
posed on  the  midtiplication  of  fungi  by  the  products  of  their  o\\n\ 
activity  may  help  us  to  understand  how  the  formative  activity  of  the 
cells  of  complex  organism  may  be  temporarily  checked. 

"  We  cannot,  indeed,  regard  the  intercellular  substance  of  the  connec- 
tive tissues  as  equivalent  in  significance  to  the  products  of  the  chemical 
changes  induced  by  the  bacteria.  Yet  the  comparison  may  at  least 
enable  us  to  conceive  how^  cell-growth  may  tend  to  limit  and  to  check 
itself  without  the  interposition  of  extensive  resistance.  In  the  connec- 
tive tissues  the  formation  of  the  intercellular  substance  is  the  limiting 
factor ;  in  the  epithelia  it  is  the  cohesion  or  cementation  of  the  individ- 
ual cells  into  a  firm  and  single  whole,  just  as  in  yeast  fermentation  it 
is  the  formation  of  alcohol.  When  the  alcohol  is  withdrawn  in  the 
latter  case,  the  nudti])lication  of  the  yeast-fungus  goes  on  again.  So, 
likewise,  if  the  intercellular  substance  be  dissolved  away  from  a  connec- 
tive tissue,  or  if  the  continuity  of  the  epithelial  mosaic  be  loosened  or 
interrupted,  the  faculty  of  multiplication  is  again  awakened  in  the  con- 
stituent cells ;  or  if  (as  in  the  epithelia)  it  has  never  been  dormant,  it  is 
at  once  intensified." 

Cellular  activity,  as  found  in  normal  development,  depends  upon  some 
force  which  cannot  be  explained  by  chemistry  and  physics  or  ^vithout 
calling  in  the  aid  of  the  hypothesis  of  vita/  fimcHons.  Cells  stimulated 
by  the  indwelling  vital  power  proliferate  until  the  typal  demands  of  the 
tissues  are  reached.  In  many  tissues  this  growth  is  so  adjusted  as  to  be 
self-limiting,  as  in  the  Plaversian  system  of  bones,  in  which  the  devel- 
opment is  centripetally  arranged,  thus  lessening  the  calibre  of  the  enclosed 


PHYSIOLOGICAL   CONSIDERATION  OF  CELLS.  529 

capillary  vessels,  and  so  diminishing  the  supply  of  cell-food.  The 
innate  governing  principle  in  normal  development  decides  that  cellular 
activity  shall  set  in  at  one  point  and  not  at  another.  This  is  beautifully 
illustrated  in  the  development  of  the  hair,  glands,  and  the  enamel  organ 
of  the  teeth.  These  organs  are  formed  by  an  infolding  of  the  super- 
imposed epithelium.  This  process  begins  in  localized  cellular  activity  ; 
rapid  cell-multiplication  follows,  and  the  new-formed  cells  sink  into  the 
subepithelial  tissue.  The  point  of  greatest  activity  is  always  found  in 
the  deepest  portions  of  the  ingrowing  tissue ;  and  this  activity  continues 
until  the  typal  demands  of  the  special  organ  are  met,  Avhen  it  ceases. 
No  other  satisfactory  explanation  of  the  action  of  cells  can  be  given 
than  that  an  independent  life-principle  resides  in  them  which  directs 
their  growth  and  function.  As  we  investigate  more  minutely  we  find 
that  insuperable  difficulties  present  themselves  to  any  physical  interpre- 
tation of  the  facts  connected  with  living  cells. 

Fleming  has  established  beyond  dispute  that  cell  division  is  depend- 
ent upon  nucleus  division.  In  some  instances,  however,  the  nucleus 
divides  and  a  subsequent  division  of  the  cell  does  not  follow.  In  this 
case  multinuclear  cells  are  formed.  We  do  not  know  positively  why 
cellular  activity  results,  but  it  is  probable  that  the  cells  are  stimu- 
lated to  an  increased  assimilation  of  cell-pabulum,  as  an  increased  sup- 
ply of  nutrition  does  not  always  produce  giant-cells.  Some  authors 
hold  that  giant-cells  or  osteoclasts  found  in  connection  with  resorption 
of  bone  are  produced  by  the  liberated  bone-cells ;  but  the  fact  that 
giant-cells  appear  in  connection  with  the  resorption  of  other  hard  tis- 
sues which  do  not  contain  bone-cells  seems  to  establish  for  them  an 
independent  identity.  When  speaking  of  erosion  of  bone,  Ziegler  uses 
the  terms  osteoclasts,  giant-cells,  and  resorption-cells  as  synonymous, 
and  asserts  that  they  arise  from  multiplication  of  exuded  white  blood- 
cells.  Resorptive-cells  in  some  cases  contain  but  one  nucleus.  They 
are,  however,  considerably  larger  than  ordinary  cells,  so  we  will  use  the 
term  giant-cells  in  the  sense  of  larger  cells  having  a  specialized  func- 
tion, whether  they  be  multinuclear  or  not. 

Giant-cells  are  found  in  diseases  where  great  cellular  activity  exists, 
as,  for  example,  in  miliary  tuberculosis,  syphilis,  myeloid  sarcoma,  and 
hyperplastic  granulation-tissue ;  they  are  also  found  in  connection  with 
the  resorption  of  bone  in  normal  development,  and  in  the  roots  of 
temporary  teeth  and  other  bodies  that  Nature  desires  to  remove.  They 
are  developed  in  all  the  above-named  cases  unless  the  exuded  cells  are 
destroyed  and  a  purulent  condition  produced. 

Ziegler,  writing  of  the  resorption  of  tissue,  says  : 

"  Tiie  first  stage  is  the  formation  of  a  zone  of  inflammatory  infiltra- 
tion around  the  foreign  body.  This  is  followed  by  the  development  of 
granulation-tissue,  and  at  length  of  fibrous  tissue.  If  the  foreign  body 
is  not  meanwhile  absorbed,  it  thus  becomes  encapsuled.  Only  insoluble 
and  compact  bodies  can  remain  quite  unaltered,  for  resorption  is,  as  it 
were,  attempted,  even  though  it  be  in  vain.  Bodies  which  are  at  all 
assailable  are  sure  sooner  or  later  to  undergo  changes.  These  ensue  as 
follows  :  The  migratory  leucocytes,  transformed  into  uninuclear  or  mul- 
tinuclear formative  cells,  attach  themselves  to  the  surface  of  the  object. 

Voi,.  I.— 34 


530  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

If  this  be  made  up  of  smaller  parts,  or  if  particles  of  necrosed  tissue  be 
mingled  with  it  (such  as  decomposed  blood  in  hemorrhagic  patches), 
these  are  taken  up  by  the  cells  and  carried  off  by  the  white  blood-cells 
which  migrate  froni  the  blood-vessels.  These  migratory  cells  appro- 
priate the  foreign  substances  lying  in  the  tissue.  They  let  their  proto- 
plasm flow  romid  them,  and  so  take  them  up  into  their  interior.  By 
frequent  repetition  of  this  process  granule-carrying  cells  are  produced. 
According  to  their  contents  these  have  been  variously  described  as  fat- 
granule  carriers,  blood-cell  carriers,  pigment-granule  cells,  cinnabar- 
carrying  cells,  etc.  If  the  foreign  body  be  compact  and  not  to  be 
broken  up,  the  cells  cling  to  its  surface.  If  there  be  accessible  cavities 
or  clefts  in  it,  they  penetrate  into  these.  If  the  cells  be  insufficiently 
nourished,  they  become  fatty  and  die.  If  new  vessels  are  formed  to 
supply  them,  they  develop  as  granulations.  Very  often,  indeed,  multi- 
nuclear  or  giant-cells  are  found  in  such  circumstances." 

"A  dead  piece  of  bone  inserted  under  the  skin  of  an  animal  and 
examined  a  few  weeks  after  will  be  found  interpenetrated  with  vascular 
granulations,  and  the  trabeculse  will  be  beset  in  many  places  with  giant- 
cells.  The  whole  process  is  very  similar  to  that  of  physiological  bone 
resorption."  .... 

"  This  process  is  peculiarly  modified  when  the  foreign  substance  is 
firmly  connected  with  the  surrounding  tissue — when  it  is,  in  fact,  a 
necrosed  fragment  of  the  tissue  itself,  such  as  bone  or  kidney.  In  this 
case  the  first  step  is  the  separation  of  the  living  from  the  dead."  .... 

"  Langhans  was  the  first  to  describe  minutely  the  process  by  which 
larger  foreign  bodies  are  absorbed.  He  pursued  the  subject  experimen- 
tally by  producing  extravasations  of  blood  in  various  animals.  He 
thus  discovered  the  giant-cells.  Heidenhain  also  found  them  in  pieces 
of  elder-pith  which  he  had  inserted  in  the  abdominal  cavity  of  animals. 
Ziegler  always  met  them  in  connection  with  his  experiments  in  placing 
cover-glasses,  slightly  separated,  under  the  skin  of  a  dog.  I^ater  exper- 
iments with  sponge-grafting  have  demonstrated  their  presence  and  active 
agency  in  the  absorption  of  the  pieces  of  sponge." 

Resorption  of  tissues  or  foreign  substances  is  a  purely  physiological 
process.  The  pathological  phase  is  found,  not  in  the  removal  of  the 
offending  substance,  but  in  the  irritant  which  brought  about  the  resorp- 
tive  process.  Hitherto,  too  much  stress  has  been  laid  upon  the  visible 
expression  of  Nature's  effort  to  remove  the  irritant,  and  too  little  on  the 
character  of  the  irritant  itself.  Pathological  results  may  attain  to  the 
resorptive  process  through  the  action  of  giant-cells  by  reason  of  the  jux- 
taposition of  healthy  tissue,  but  such  conditious  are  incidental,  and  not 
the  direct  point  of  attack.  Cells  have  not  the  power  to  produce  path- 
ological results,  except  they  be  pathologically  stimulated,  and  when  so 
stinudated  they  act  through  their  own  peculiar  channels.  I  look  upon 
giant-  or  resorjition-cells  as  Nature's  physiological  agents,  by  whose 
aid  she  removes  tissues  which  have  performed  their  life-office,  and 
substances  which  by  their  presence  are  hurtful  to  the  animal  economy. 
The  action  of  giant-cells  in  this  process  belongs  to  the  third  attribute 
ascribed  to  cells — viz.  that  of  function.  They  secrete  a  fluid  which  has 
the  power  of  digesting  the  tissues  in  their  immediate  neighborhood.    In 


MORPHOLOGICAL  APPEARANCE  OF  CELLS.  531 

claiming  this  attribute  for  them  we  do  not  go  beyond  the  physiological 
action  of  cells.  The  process  of  digestion  is  well  known  to  every  student 
of  physiology.  In  the  stomach  glands  secrete  certain  fluids,  by  whose 
action  that  which  we  call  food  is  so  chang-ed  that  it  can  be  taken  into 
the  blood  and  assimilated  by  different  parts  of  the  body.  A  failure  on 
the  part  of  these  glands  to  produce  their  normal  fluid  results  in  what 
we  term  indigestion.  Foocl-stuflfs,  unless  prepared  and  dissolved  by 
the  fluid  secreted  by  the  glands  of  which  we  have  been  speaking,  cannot 
be  assimilated.  We  find  that  what  is  true  of  the  digestion  of  food- 
stuffs is  also  true  of  the  resorption  of  tissues.  In  order  that  a  tissue 
may  be  removed  it  must  first  be  digested  by  the  cell-fluid,  after  which 
it  can  be  taken  up  by  the  lymphatic  system.  It  is  true  that  very  small 
particles,  by  reason  of  their  minute  subdivision,  do  enter  the  lymph- 
channels,  but  they  are  not  assimilated  into  the  general  system ;  they  are 
deposited  in  the  first  gland  into  which  the  lymphatic  empties.  In- 
stances of  this  kind  are  found  in  cases  of  respired  particles  of  coal-  and 
stone-dust,  and  as  a  consequence  we  have  the  pathological  condition 
known  as  the  "  coal-miner's "  and  the  "  stone-hewer's "  lung. 

As  I  have  already  said,  in  order  that  any  tissue  may  be  assimilated 
it  must  first  be  digested.  In  the  cases  above  mentioned  the  soluble 
ferment  is  secreted  by  the  giant-cells  at  the  point  of  irritation.  The 
juxtaposition  of  the  secreting  cells  and  the  tissue  to  be  resorbed  is  a 
matter  of  essential  import.  The  ferment  or  fluid  in  question  is  not  an 
exuded  fluid  of  the  blood ;  it  is  as  truly  a  specialized  fluid  as  are  the 
secretions  of  the  peptic  glands  of  the  stomach.  The  nature  of  the  body 
to  be  resorbed  has  no  more  influence  in  the  production  of  the  secretions 
than  have  various  food-stuffs  which  are  taken  into  the  stomach  over 
the  secretions  of  the  stomachic  glands.  Then,  again,  resorbed  and 
resorber  must  be  in  actual  contact,  as  is  seen  in  every  instance  where 
tissues  are  removed.  The  secretion  acts  upon  the  tissues  found  in  its 
immediate  neighborhood,  whether  they  be  living  or  dead.  This  fact  is 
well  illustrated  in  the  resorption  of  the  roots  of  temporary  teeth.  It 
matters  not  whether  the  pulp,  the  life  of  the  root,  be  alive  or  dead,  so 
long  as  the  surrounding  j^arts  do  not  become  purulent. 

Resorption,  then,  is  the  result  of  the  physiological  action  of  cells 
stimulated  by  irritation  to  increased  cellular  activity  ;  but  in  order  that 
they  may  so  act  the  irritation  must  not  be  too  severe.  If,  when  the 
pulp  of  a  temporary  tooth  dies,  a  chronic  abscess  results,  physiological 
resorption  of  the  root  cannot  occur.  Its  removal  is  then  accomplished 
by  necrosis,  and  gicmt-cells  are  not  found.  Resorption  by  giant-cells,  as 
we  have  seen,  can  only  occur  when  the  cells  are  stinmlated  to  an  increased 
assimilation  of  the  over-supply  of  nutrition  which  is  produced  by  the 
local  irritant. 

Morphological  Appearance  of  Cells. 

Under  this  head  we  will  briefly  consider  blood-corpuscles,  epithelial 
and  connective-tissue  cells. 

The  physical  appearance  of  blood  is  that  of  a  red  fluid  somewhat 
thicker  than  water.     When  examined  under  the  microscope  we  find 


532 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 


FiC4.  270. 


suspended  in  the  fluid  (serum)  of  the  blood  small  spheroidal  and  disc- 
shaped bodies  known  as  blood-corpuscles.  These  blood-corpuscles  or 
cells  vary  not  only  in  form,  but  also  in  color  and  action.  One  of  the 
disc-shaped  corpuscles,  seen  by  itself,  looks  slightly  yellow  in  color,  but 
when  seen  in  a  mass  the  mass  is  clearly  red ;  and  it  is  to  the  presence 
of  these  cells  that  the  blood  owes  all  its  color,  the  other  blood-cells 
and  the  serum  being  alike  colorless.  Upon  the  warm  stage  or  when 
subjected  to  the  action  of  a  strong  salt  solution  they  become  crenated 
in  form  (see  Fig.  270,  c,  c) ;  if  the  salt  solution  be  displaced  by  distilled 
water,  they  assume  their  original  shape  for  a  short  time,  but  soon 
bcome  swollen  and  decolorized,  the  luemoglobin  which  gives  them  their 
color  being  freely  soluble  in  water. 

In  different  animals  the  corpuscles  vary  both  in  size  and  form.  In 
Mammalia  they  exist  in  general,  like  those  of  man,  as  circular  discs, 
larger  or  smaller,  but  without  nuclei.  In  birds  and  cold-blooded 
animals  nuclei  are  found,  but  the  cells,  instead  of  being  circular,  are 
oval  and  larger.  "  The  size  of  the  corpuscles,"  says  Foster,  "  seems  to 
bear  no  relation  to  the  size  of  the  body,  but,  as  has  been  pointed  out 
by  Milne-Edwards,  there  occasionally  exists  a  relation  between  the  size 
and  the  muscular  activity  of  the  animal.  Thus  it  was  found  that  in 
deer  and  other  fleet-footed  animals  the  corpuscles  were  relatively  small ; 
in  Amphibia,  which  are  comparatively  sluggish,  the  corpuscles  were 

relatively  larger.  The  relation, 
then,  that  the  diameter  of  the 
corpuscle  would  bear  to  the 
muscular  activity  would  be  in 
an  inverse  ratio.  It  has  also 
been  found  that  the  higher  the 
scale  of  life  is  advanced  the 
smaller  the  diameter  of  these 
bodies  becomes." 

Besides  the  red  blood -cells, 
there  are  others  slightly  larger, 
not  colored  at  all,  and  not  cir- 
cular and  flat,  like  those  above 
described,  but  round  like  a  ball ; 
these  are  termed  colorless  or  white 
corpuscles.  When  watched  un- 
der the  microscope — care  being 
taken  to  keep  the  temperature 
the  same  as  that  of  the  body — 
they  are  seen  to  have  a  peculiar 
amoeboid  movement,  by  means 
of  which  they  are  able  to  trans- 
port themselves  from  place  to 
place;  it  is  owing  to  this  ca- 
pacity of  movement  that  they 
have  received  the  name  of  wan- 
dering leucocytes.  Their  activity  varies  with  the  rise  and  fall  of  the 
temperature  and  the  amount  of  oxygen  present  in  the  tissue.     Under 


Human  Blood  as  seen  on  the  Warm  Stage  (magni- 
fied abuut  I'-'OO  diiuneters) :  r,  r,  single  led  corpus- 
cles seen  lying  flat;  r',  r',  red  corpuscles  on  their 
edge  and  viewed  in  profile;  r",  red  corpuscies 
arranged  in  rouleaux;  r,  r,creiiate  red  corpuscles; 
;<,  a  finely  granular  pale  corp\iscle ;  (/,  a  coarsely 
granular'pale  corpuscle.  Hoth  have  two  O'  three 
distinct  vacuoles,  and  were  undergoing  changes 
of  shape  at  the  moment  of  observation ;  iu  1/  a 
nucleus  also  is  visible. 


MORPHOLOGICAL  APPEARANCE  OF  CELLS. 


533 


Fig.  271. 


favorable  circuiustaiices  they  may  be  seen  migrating  from  the  sides  of 
blood-clots.  When  at  rest  the  white  corpnscles  are  spheroidal,  bnt  in 
a  state  of  activity  they  are  continually  changing  in  shape.  Sometimes 
they  assume  an  irregular  form,  throwing  out  pseudopodia  or  prolonga- 
tions (Fig.  270,  |j),  such  as  are  found  in  the  amcieba ;  in  fact,  so  strong 
is  their  resemblance  to  that  minute  animal  that  they  have  been  called 
the  human  amoebtTe. 

The  white  blood-cells  are  lighter  than  the  red,  and  traverse  the 
vascular  channels  upon  the  periphery  of  the  vessels.  They  also  pass 
through  the  walls  of  the  capillaries,  and  are  found  normally  in  the 
various  tissues  of  the  body ;  in  pathological  conditions  they  migrate 
in  vast  numbers.  Each  pale  corpuscle  has  one  or  more  nuclei,  which 
are  surrounded  by  a  mass  of  protoplasm  unconfined  by  a  cell- wall  {g). 
By  certain  methods  of  staining,  the  nuclei  are  demonstrable. 

In  size  the  white  corpuscles  are  somewhat  larger  than  the  red,  aver- 
aging about  3  aVo"  ^^  ^^^  ^^^*^'^  "^  diameter,  and  they  always  retain  al)out 
the  same  measurement  in  different  species  of  animals.  They  bear  to 
the  red  the  proportion  of  1  to  500. 

Besides  these  red  and  white  cells  or  corpuscles  there  may  also  be  seen 
in  the  blood  free  granules  and  fine  filaments  (Fig.  271).  Some  of  the 
granules  are  round  (B),  others  angular.  In 
some  instances  the  angular  granules  are  con- 
nected with  the  fine  filaments  (A),  as  if  they 
formed  the  nucleus  from  which  the  filaments 
radiate. 

The  blood-corpuscles  and  granules  can  be 
washed  out  from  a  small  quantity  of  blood 
that  has  been  allowed  to  clot  upon  a  slide, 
and  there  will  be  nothing  left  but  an  opaque, 
stringy  substance.  This  white  stringy  sub- 
stance is  fibrin,  which  may  now  be  stained 
and  examined. 

The  physiology  of  the  blood  is  perhaps 
less  understood  than  any  other  part  of  the 
animal  organism.  Many  theories  have  been 
advanced  as  to  its  origin.  It  seems  most 
rational  to  believe  that  one  which  teaches 
that  the  lymph-corpuscles  become  altered  by 
contact  with  pre-existing  white  blood-cor- 
puscles, and  that  these  in  turn  are  changed  into  red  corpuscles,  which  in 
time  disintegrate,  their  pigment  being  taken  up  by  their  successors. 

Prudden,  speaking  of  the  origin  of  blood-cells,  says :  "  Direct  observa- 
tion has  shown  that,  in  some  animals  at  least,  the  white  blood-cells  can 
multiply  by  division.  Whether  the  cells  which  supply  the  place  of 
those  which  seem  to  be  used  up  in  the  process  of  growth  and  reparation 
are  produced  in  this  way,  and,  if  so,  whether  the  division  occurs  in  the 
blood-  or  lymph- vessels,  or  in  the  cell-spaces  of  the  connective  tissue, 
or  in  certain  special  organs,  or  whether  they  are  produced  in  a  manner 
entirely  unknown  to  us, — these  are  questions  not  only  of  theoretical  but 
of  practical  interest;  but  in  spite  of  much  research  and  the  accumula- 


Fibrin-filaments  and  Blood-tablets: 
A,  network  of  fibrin,  shown  after 
washing  away  the  corpuscles  from 
a  preparation  of  blood  that  lias 
been  allowed  to  clot;  many  of 
the  filaments  radiate  from  small 
clumps  of  blood-tablets.  B  (from 
Osier ),  blood-corpuscles  and  ele- 
mentary particles  or  blood-tablets- 
within  a  small  vein. 


534  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

tion  of  many  observations  bearing  on  the  matter,  we  are  still  unable  to 
give  them  a  detinite  answer.  Still  more  obscure,  if  possible,  is  the 
origin  of  the  red  blood-cells.  Although  in  the  adult  man  they  seem  to 
possess  no  nucleus,  yet  in  embryonic  life  they  certainly  are  furnished  with 
that  structure;  we  find  nucleated  red  blood-cells.  Now,  it  has  been 
recently  shown  that  in  certain  parts  of  the  body  in  adult  life  cells  occur 
which  in  many  respects  resemble  the  nucleated  red  blood-cells  of  the 
embfyo;  such  cells  are  found,  for  example,  in  the  spleen,  in  the  red 
marrow  of  bones,  etc.  The  most  plausible  theory  in  regard  to  the 
matter  is  that  in  certain  parts  of  the  body — spleen,  marrow,  lymph- 
glands,  and  liver — white  blood-cells  are  produced,  a  part  of  which  are 
changed  into  the  red  blood-cells.  The  so-called  nucleated  red  blood- 
cells  are  supposed  to  be  intermediate  forms.  It  must  be  remembered, 
however,  that  this  view  is  not  established  as  yet,  and  many  observers 
do  not  ascribe  to  the  so-called  nucleated  red  blood-cells  the  significance 
upon  which  the  advocates  of  this  theory  insist." 

Klein  says  that  "  at  an  early  stage  of  embryonic  life,  when  blood 
makes  its  appearance  it  is  a  colorless  fluid,  containing  only  white  cor- 
puscles (each  with  a  nucleus),  which  are  derived  from  certain  cells  of 
the  mesoblast.  These  white  corpuscles  change  into  red  ones,  which 
become  flattened,  and  their  protoplasm  becomes  homogeneous  and  of  a 
yellowish  color.  All  through  embryonic  life  new  white  corpuscles  are 
transformed  into  red  ones.  In  the  embryos  of  man  and  mammals  these 
red  corpuscles  retain  their  nuclei  for  some  time,  but  ultimately  lose  them. 
Kew  nucleated  red  blood-corpuscles  are,  however,  formed  by  division  of 
old  red  corpuscles.  Such  division  has  been  observed  even  in  the  adult 
blood  of  certain  lower  vertebrates  (Peremeschko),  as  well  as  in  the  red 
marrow  of  mammals  (Bizzozero  and  Torre).  An  important  source  for 
the  new  formation  of  red  corpuscles  in  the  embryo  and  adult  is  the  red 
marrow  of  bones  (Neumann,  Bizzozero,  Rindfleisch),  in  which  numerous 
nucleated  protoplasmic  cells  (marrow-cells)  are  converted  into  nucleated 
red  blood-corpuscles.  The  protoplasm  of  the  corpuscles  becomes  homo- 
geneous and  tinged  with  yellow,  the  nucleus  being  ultimately  lost.  The 
spleen  is  also  assumed  to  be  a  place  for  the  formation  of  red  blood-cor- 
puscles. 

"  Again,  it  is  assumed  that  ordinary  white  blood-corpuscles  are  trans- 
formed into  red  ones,  but  of  this  there  is  no  conclusive  evidence.  In 
all  these  instances  the  protoplasm  becomes  homogeneous  and  filled  with 
haemoglobin,  while  the  cell  grows  flattened,  discoid,  and  the  nucleus  in 
the  end  disap]wars.  SchiifPer  described  intracellular  (endogenous)  forma- 
tion of  red  blood-corpuscles  at  first  as  small  haemoglobin  particles,  but 
soon  growing  into  red  blood-corpuscles  in  certain  cells  of  the  subcu- 
taneous tissue  of  young  animals.  Malassez  describes  the  red  blood- 
corpuscles  originating  by  a  process  of  continued  budding  from  the 
marrow-cells.  The  white  corpuscles  appear  to  be  derived  from  the 
lymphatic  organs,  whence  they  are  carried  by  the  lymph  into  the  cir- 
culating blood." 

Notwitlistanding  these  differences  of  opinion  regarding  the  origin  of 
blood-cells,  there  is  almost  universal  agreement  as  to  the  function  per- 
formed by  the  blood;  and  it  is  to  be  hoped  that  with  improved  means 


EPITHELIAL   CELLS. 


535 


for  observation  we  shall  soon  be  able  to  solve  the  enigma  of  its  deriva- 
tion. That  there  must  of  necessity  be  some  means  for  renewing  aged 
cells  or  supplying  lost  ones  is  admitted  by  all,  but  as  to  the  special 
mode  of  their  origin  there  seems  to  be  considerable  doubt.  The  white 
blood-corpuscles  are  probably  the  main  source  of  supply  for  the  regen- 
eration of  lost  tissues,  osteoblasts,  and  the  other  members  of  the  connec- 
tive-tissue group.  This  part  of  the  subject  will  be  considered  in  detail 
later  on. 


Epithelial  Cells. 

A  very  delicate  membrane  forms  the  outer  covering  of  the  derma  or 
true  skin  of  animals,  and  enters  also  into  the  structure  of  glandular 
organs;  to  it  the  name  epithelium  is  given. 

The  microscope  has  shown  this  tissue  to  be  an  aggregation  of  epithelial 
cells,  differing  in  different  situations  in  form  and  function. 

Epithelial  cells  are  derived  from  both  epiblast  and  hypoblast.  We 
will  dismiss  the  consideration  of  those  which  have  their  origin  in  the 
hypoblast,  and  confine  ourselves  to  the  epithelium  of  the  mucous  mem- 
brane of  the  mouth,  premising  that  it  is  derived  from  the  same  source 
as  the  skin.  It  is  certainly  analogous  in  foi'm,  being  only  slightly 
modified  by  constant  immersion  in  the  fluids  of  the  mouth,  which 
does   not   permit   the   oldest 


or 
outer  layer  to  assume  the  cor- 
neous nature  found  in  the  most 
superficial  layer  of  the  skin. 

The  epithelium  of  the  mouth 
belongs  to  the  stratified  epithelial 
group:  it  may  be  considered  as 
transitional  epithelium,  and  is 
composed  of  several  layers  of 
cells  which  are  constantly  un- 
dergoing the  process  of  desqua- 
mation. These  layers  of  cells 
are  held  together  by  an  inter- 
cellular cement-substance,  which 
exists  in  small  quantities. 

We  divide  the  layers  into 
three  kinds  :  the  infant,  older, 
and  oldest.  The  oldest  layer 
can  readily  be  studied  by  exam- 
ining microscopically  the  saliva 
or  scrapings  from  the  tongue. 
Under  examination  this  layer 
very  plainly  appears  to  be  made 
up  of  flattened  discs  containing 
nuclei.  The  cells  of  the  corne- 
ous layer  of  the  skin,  however, 
as  a  rule,  do  not  contain  nuclei. 


Fig.  272. 


EpiUielial  Cells  in  the  Oral  Cavity  of  ISIan  :  a,  large; 
6,  middle-sized ;  c,  the  same  with  two  nuclei  (high 
power). 


definite  measurement  can  be  given. 


The  cells  vary  so  much  in  size  that  no 


536 


DENTAL  EMBRYOLOGY  AND  HLSTOLOGY. 


Fig 


Columnar  Ciliated  i:\n- 
thelium  Cells. 


In  some  of  the  cold-blooded  animals  the  palate 
is  covered  with  ciliated  cells.  These  are  for  the 
most  part  spheroidal  in  form,  and  do  not  differ 
greatly  from  the  cells  above  described.  The  most 
remarkable  circumstance  in  connection  with  them 
is  the  movements  of  their  cilia,  which  arise  from 
the  broad  side  of  the  cell.  These  hair-like  append- 
ages are  supposed  to  be  prolongations  of  the  cell- 
protoplasm.  They  can  be  seen  in  the  frog,  and  ex- 
amined while  yet  in  motion  by  scraping  the  surface 


Fig.  274. 


/?•    ^'^^a^         -^— ^       ^^ 


Epitheliuin-cells  of  Snlatnander  Larva  in  Dift'erent  Thases  of  Pivision :  a,  normal  cell,  by  con)pari- 
son  with  which  the  following  changes  may  lie  noted :  I.  The  network  of  filaments  of  the  resting 
nucleus  becomes  formed  into  a  sort  of  xkein,  formed  apparently  of  one  long  coiivoluted  filament; 
the  nuclear  membrane  and  the  nucleoli  disappear  or  are  merged  into  the  skein  (/<.  c,  rfi.  II.  The 
skein  becomes  arranged  in  the  form  of  a  ri/xr/fi',  the  filaments  looping  in  and  out  to  and  from  the 
centre  ('-).  Ill  The  outer  loojjs  of  the  rosette  separate  so  that  the  filament  breaks  into  a  lum- 
ber of  V-shaped  fibres  arran-ed  like  a  star  {(i.ttfr./,  g,  /i).  IV.  The  V-shaped  fibres  separate  into 
two  groups,  the  ends  of  which  are  for  a  time  interlocked  (/,./.  k).  V.  The  two  groups  pass  to  the 
opposite  poles  of  the  now  elongated  nucleus  and  form  a  star-shaped  figure  /)  at  each  pole  ulynsli-r). 
Each  of  the  stars  represents  a  daughter-nucleus.  VI.  Each  star  of  the  d vaster  i;oes  through  the 
same  changes  as  the  original  nucleiis,  but  in  the  reverse  order— viz.  rosette  im).  skein  (??),  and  net- 
work (fi,  p,  91— passing  finally  into  the  condition  of  a  lypal  resting  nucleus.  The  jirotoplasm  of 
the  r-ell  divides  soon  after  the  formation  of  the  dyaster  (/;/ 1.  Sometimes  fine  lines  may  be  seen  in 
the  i>rotoplasm,  during  the  i>rocess  of  division,  radiating  from  the  poles  cf  the  nucleus,  and  others 
uniting  the  two  daughter-nuclei. 


EPITHELIAL   CELLS. 


537 


X 


Fk;.  27'). 


E^^-'rf 


.rJ/  ("^ 


Two  Flattened  and  Branched  Cnnuective-tissue  Corpuscles  from  the  subcutaneous  areolar  tissue. 
Opposite  /  a  secondary  liunella,  projecting  toward  the  observer,  is  seen  in  optical  section  as  a 
dark  line. 


From  a  Preparation  of  the  Omentum  of  (Juinea-pig:  n,  artery;  c,  vein;  c,  j'oung  capillary  blood- 
vessel ;  d,  fat-cells  formed  by  infiltration  of  ordinary  connective  cells  with  fat-globules. 


Fig.  278. 


Fig.  277. 


Bundles  of  the  White  Fibres  of  Areolar  Tissue,  partly 
unravelled. 


A,  Elastic  Fibres  of  Areolar 
Tissue,  from  the  subcutane- 
ous tissue  of  the  rabbit. 


of  the  mucous  membraue  and  transferring  the  substance  thus  obtained 
to  a  slide,  adding  tepid  water. 


538 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 


Ciliated  cells  are  also  found  in  the  nasal  passages  of  man,  an  illustra- 
tion of  which  may  be  seen  in  Fig.  273. 

The  middle  or  older  layer  of  cells  of  the  buccal  epithelia  are  more  or 
less  polyhedral  in  shape,  and  have  an  imbricated  border  :  they  are  some- 
times called  "prickle  cells,"  and  generally  extend  beyond  the  oral  cavity 
into  the  pharynx. 

The  deepest  or  infant  layer  of  the  epithelium  of  the  mouth  is  com- 
posed of  spheroidal  or  slightly  cylindrical  cells  placed  vertically  upon 
the  dividing-line  between  the  epithelium  and  the  dermal  layers.  It  is 
in  this  layer  of  the  rete  Malpighii  that  cell-multiplication  occurs ;  the 

Fig.  279. 


Articular  Cartilage  from  Head  of  ^Metatarsal  Bone  of  Man  (osraic-acid  preparation) :  the  cell-bodies 
entirely  fill  the  spaces  in  the  matrix  CilO  dianieter.s) :  a,  group  of  two  cells;  6,  group  of  four  cells; 
h,  protoplasm  of  cell,  with  ;/,  fatty  granules;  >i,  nucleus. 

changes  "whereby  tiie  cells  undergo  division  appear  first  in  the  nucleus 
(see  Fig.  274,  after  Fleming,  from  Schaefer's  Histology),  afterward 
extending  to  the  cell-body  in  adult  tissues. 

The  method  of  cell-growth  in  embryonal  tissues  will  be  considered 
later  on,  in  the  section  on  the  development  of  the  mucous  membrane  of 
the  mouth. 

Connective-tissue  cells  of  the  dermal  layer  of  the  mouth  are  of  two 
kinds,  jxxed  and  imnderinfi  cells.  The  first  are  fibrillated,  and  have  a 
definite  relationship  to  the  basement-substance,  although  varying  in 
form  and  number  in  different  positions.  The  second  are  spheroidal, 
and  have  been  considered  in  our  study  of  the  white  blood-corpuscles. 
The  fixed  cells  may  have  one  or  more  processes,  and  when  infiltrated 
with  fat,  constitute  fat-tissue. 


EMBRYOLOGY.  539 

The  intercellular  substance  is  broken  up  into  fibres,  both  yellow  and 
white.  The  yellow  fibres  are  ela>iiic  (Fig.  278),  and  are  more  or  less 
abundant  in  areolar  tissue.  The  Nvliite  fibres  form  the  interlacing  net- 
work which  binds  the  tissues  together  throughout  the  body.  They  are 
joined  in  bundles,  as  may  be  seen  by  referring  to  Fig.  277. 

There  yet  remains  to  be  considered  hyaline  cartilage,  which  belongs 
to  the  connective-tissue  group.  In  this  tissue  spheroidal  flattened  or 
angular  cells,  containing  one  or  more  nuclei,  are  seen  lying  in  a  homo- 
geneous basement-substance  (see  Fig.  279),  which  is  said  to  yield  chon- 
drin  upon  being  boiled.  The  cells  are  sometimes  finely,  at  other  times 
coarsely,  granular.  Both  the  capsule  which  surrounds  the  cell  and  the 
hyaline  intercellular  substance  possess  higher  refractive  power  than  does 
the  cell  itself. 

Having  thus  brought  our  brief  examination  of  a  few  of  the  more 
important  characteristics  of  cell-action  and  morphology  to  a  close,  it 
only  remains  to  express  the  hope  that  it  will  stimulate  the  student  to 
a  better  and  more  careful  survey  of  the  whole  subject.  The  import- 
ance of  such  a  survey  cannot  be  too  strongly  urged  upon  his  attention, 
for  without  definite  knowledge  of  cellular  structure  it  is  impossible  to 
prosecute  histological  inquiries  with  any  degree  of  success. 

We  are  now  better  able  to  enter  upon  the  subject  of  Embryology,  a 
subject  in  regard  to  which  what  we  know  at  present  is  so  little  in  com- 
parison to  what  we  do  not  know  that  there  remains  an  illimitable  field 
for  our  inquiries  and  discoveries. 

Embryology. 

Down  to  our  own  century,  though  many  important  truths  bearing 
upon  embryology  were  known  to  anatomists  and  physiologists,  nothing 
could  have  been  farther  from  their  conception  than  the  fact  now  uni- 
versally admitted  that  all  animals,  without  exception,  arise  from  eggs. 

Aristotle  and  his  followers  recognized  three  modes  of  generation — 
viz.  oviparous,  viviparous,  and  spontaneous  generation.  By  the  prog- 
ress of  investigation  the  last  mode  of  generation  was  shown  to  be  a 
thing  unknown  in  Nature,  and  in  1651,  Dr.  William  Harvey  announced 
that  there  is  no  essential  difference  in  the  mode  of  generation  between 
oviparous  and  viviparous  animals,  but  that  "all  animals  whatsoever, 
even  the  viviparous,  and  man  himself  not  excepted,  are  produced 
from  ova."  A  little  later  Linnteus  expressed  this  great  truth  in  the 
sentence  so  often  quoted,  "  Omne  vivum  ex  ovo  ;"  but  neither  he  nor 
Harvey  appreciated  the  full  significance  of  these  statements,  for  the  exist- 
ence of  the  mammalian  e^g  was  not  then  dreamed  of.  Since  then  the 
discoveries  of  Von  Baer,  Negrier,  Pouchet,  and  others  have  shown  not 
only  that  "  the  egg  is  common  to  all  living  beings  without  exception, 
from  the  lowest  radiate  to  the  highest  vertebrate,  but  that  its  structure 
is  at  first  identical  in  all,  composed  of  the  same  primitive  elements  and 
undergoing  exactly  the  same  process  of  growth  up  to  the  time  when  it 
assumes  the  special  character  peculiar  to  its  kind  ;"  and  the  only  real 
diiference  between  oviparous  and  viviparous  animals  is  that  in  the  Ovip- 
ara  the  fecundated  egg  is  discharged  from  the  body  of  the  female  and 


540  DENTAL   EMBRYOLOGY  AND  HISTOLOGY. 

deposited  in  some  suitable  receptacle,  in  -which  it  is  afterward  hatched, 
while  in  the  Vivipara  it  is  retained  in  the  body  of  the  female  and  there 
nourished  till  it  develops  into  a  perfect  organism. 

In  common  parlance,  we  understand  by  an  egg  a  spheroidal  body 
composed  of  a  mass  of  yolk,  surrounded  by  what  is  known  as  the 
ivhite  of  the  egg,  and  an  outer  covering  or  shell.  But  to  the  embryolo- 
gist  the  envelopes  of  the  eg^  are  mere  accessories,  while  the  true  egg — 
or,  as  it  is  called,  the  ovctrian  egg — with  which  the  life  of  every  organ- 
ism begins,  is  a  minute  globule  of  protoplasm.  The  undeveloped  ova- 
rian Qgg  immediately  after  its  fertilization  is  uniform  in  appearance 
throughout  the  animal  kingdom,  the  human  ovum  at  this  stage  corre- 
sponding in  structure  to  those  which  stand  at  the  very  foot  of  the  zoo- 
logical scale. 

The  ovarian  egg  is  at  first  a  mere  speck  of  living  protoplasm,  but 
through  the  processes  of  nutrition  development  proceeds,  antl  presently 
there  appears  a  bright,  transparent  spot  on  the  upper  side  of  the  egg 
near  the  wall  or  outer  membrane — the  nucleus,  as  it  is  called.  When 
this  albuminous  spot  becomes  a  little  larger  there  arises  in  its  centre  a 
minute  speck  of  matter  slightly  more  opaque  than  the  surrounding 
matter  :  this  is  called  the  germinal  spot.  At  this  stage  of  its  existence, 
when  the  egg  consists  of  a  protoplasmic  body  containing  in  its  interior 
a  nucleus  which  in  turn  envelops  a  nucleolus,  its  resemblance  to  a  cell 
is  unmistakable ;  and,  in  fact,  an  egg  when  forming  is  a  perfect  cell- 
structure.  But  while  closely  resembling  the  cell  in  structure  there  is, 
nevertheless,  in  this  ovarian  mass  of  protoplasm  a  wonderful  power 
which  separates  it  from  the  cell  by  diiferences  too  great  to  be  bridged 
over — an  inherent  force  by  which  its  destiny  as  a  distinct  individual 
is  assured.  Agassiz  has  described  this  difference  better  than  most 
embryologists : 

"  While  we  recognize  the  identity  of  cell-structure  and  egg-structure 
at  this  point  in  the  history  of  the  egg,  we  must  not  forget  the  great  dis- 
tinction between  them — namely,  that  while  the  cells  remain  component 
parts  of  the  whole  body,  the  egg  separates  itself  and  assumes  a  distinct 
individual  existence.  Even  now,  while  still  microscopically  small,  its 
individuality  begins ;  other  substances  collect  around  it,  are  absorbed 
into  it,  nourish  it,  serve  it.  Every  being  is  a  centre  about  which  many 
other  things  cluster  and  converge,  aud  which  has  the  power  to  assimi- 
late to  itself  the  necessary  elements  of  its  life.  Every  egg  is  already 
such  a  centre,  differing  from  the  cells  around  it  but  by  the  principle  of 
life  in  which  its  individuality  consists,  which  is  to  make  it  a  new  being, 
instead  of  a  fellow-cell  with  those  that  build  up  the  body  of  the  parent 
animal  and  remain  comjwnent  parts  of  it.  This  intangible  something 
is  the  subtle  element  that  eludes  our  closest  analysis  ;  it  is  the  germ  of 
the  immaterial  principle  according  to  which  the  new  being  is  to  develop. 
The  physical  germ  we  see ;  the  spiritual  germ  we  cannot  see,  though 
we  may  trace  its  action  on  the  material  elements  through  which  it  is 
expressed." 

At  this  period  of  its  growth  the  microscopic  cell  is  as  truly  an  inde- 
pendent organism  as  it  ever  becomes ;  it  is  itself  the  young  animal,  and 
the  action  of  the  vital  principle  is  manifest  in  it  from  the  earliest  moment 


EMBRYOLOGY.  541 

of  its  career,  guid'uuj  and  directing  a  series  of  changes  which  result  at 
last  in  the  complete  development  of  an  individual  perfect  in  its  adapta- 
tions and  wonderful  in  its  mechanism.  The  physicist  and  chemist  are 
utterly  unable  to  explain  the  energy  and  power  which  throb  with 
unceasing  pulse  in  every  atom  of  living  matter  which  enters  into  the 
formation  of  the  several  parts  that  make  up  the  complete  organism,  or 
tell  us  in  what  way  the  multitudes  of  cells  which  exist  in  connection 
with  its  various  tissues  live,  grow,  and  form,  so  that  at  length  are  pro- 
duced the  many  textures  of  the  living  thing,  each  perfectly  fulfilling  the 
object  of  its  formation. 

In  all  our  study  of  the  })henomena  of  embryonic  development  from 
the  tiny  cell  we  shall  see  how  this  vital  power,  ''  unlike  any  physical 
agency  yet  discovered,  manifests  a  remarkable  capacity,  so  to  say,  of 
prevision.  The  changes  effected  by  living  matter  at  one  time  are  carried 
out,  as  it  were,  in  anticipation  of  future  change,  as  if  the  conception  of 
what  loas  to  be  had  been  acted  upon  even  while  the  etu'ly  changes  were 
proceeding."  We  shall  see  how  this  vital  force,  though  it  imprints 
upon  the  ])rotoplasmic  germ  no  trace  l)y  which  it  can  be  distinguished 
from  a  fellow-germ,  unfailingly  clears  the  way  for  its  onward  devel- 
opment according  to  prearranged  forms,  controlling  and  directing  its 
growth  into  the  perfect  structure  having  the  capacities  and  powers  of 
the  parent  germ.  It  is  impossible  to  ex])ress  in  any  force-terms  the 
inherent  principle  by  which  one  germ  develops  into  an  oak,  and 
another  into  the  bird  which  seeks  shelter  amid  its  foliage,  or  explain 
how  typal  forms  and  peculiarities  are  handed  down  from  generation  to 
generation,  so  that  each  plant  and  animal  reproduces  its  own  kind. 
Consider  for  a  moment  the  immense  number,  the  perfect  separation,  of 
the  different  kinds  of  animals  and  plants,  their  power  of  life  and  repro- 
duction, and  their  wonderful  fruitfulness. 

Consider  first  their  number.  In  the  animal  kingdom  the  number  of 
living  species  which  have  been  satisfactorily  made  out  and  descril^ed  is 
more  than  one  hundred  thousand,  and  botanists  reckon  about  as  many 
diflFerent  kinds  of  plants.  Not  one  of  this  great  multitude  of  plants 
and  animals  has  ever  produced  a  structure  unlike  its  kind.^  No 
seed  of  wheat  has  ever  yielded  barley,  or  seed  of  alder  grown  up  into 
an  oak.  The  egg  of  the  hen  has  never  been  made  to  produce  any 
other  animal  than  the  chick,  and  the  egg  of  the  frog  produces  only  the 
frog.  It  is  true  that  the  young  frog  or  tadpole  when  first  hatched 
from  the  egg  is  unlike  its  parent  in  external  appearance  and  habits  of 
life.  But  in  this  and  other  instances  the  process  of  development  goes 
on  after  the  young  embryo  has  left  the  &g'^,  till  at  last  the  perfect  like- 
ness to  the  parent  is  established.  Here,  again,  we  see  how  the  vital 
power  transcends  physical  forces,  for  it  controls  the  successive  forma- 
tion and  disappearance  of  different  organs  adapted  to  the  different 
modes  of  infant  life,  but  w^hich  would  be  useless  when  the  adult  state 
is  reached.  For  my  own  part,  the  more  I  look  into  the  phenomena  of 
embryonic  development  the  more  am  I  convinced  that  they  determine 
"  the  unity  of  the  authorship  of  a  wonderfully  complicated  design,  exe- 

'  It  is  true  that  hybrids  have  been  produced  from  the  mixture  of  two  species,  but  they 
have  never  been  known  to  perpetuate  themselves. 


542  DENTAL   EMBRYOLOGY  AND  HISTOLOGY. 

cuted  on  a  groundwork  broad  as  time  and  whose  scope  and  bearing  are 
deep  as  eternity."  In  them  we  find,  "not  a  material  connection  by 
which  blind  laws  of  matter  have  evolved  the  whole  creation  out  of  a 
single  germ,  but  the  clue  to  that  intellectual  conception  which  spans 
the  whole  series  of  the  geological  ages  and  is  perfectly  consistent  in  all 
its  parts." 

General  Account  of  Embryonic  Development. 

In  our  investigations  into  the  first  stages  of  embryology  we  are  of 
necessity  confined  to  the  lower  animals.  It  is  not  possible  to  secure 
well-preserved  human  embryos  in  sufficient  numbers  to  enable  us  to 
formulate  even  a  theory  of  development,  except  as  we  arrive  at  our 
conclusions  by  reason  of  such  knowledge  of  the  processes  of  develop- 
ment as  we  are  able  to  glean  from  the  field  of  comparative  embryology. 
I  have  found  the  rabbit  and  pig  more  easily  obtainable  than  other  ani- 
mals, and  have  therefore  devoted  most  of  my  time  to  the  study  of  their 
embryos. 

The  human  embryos  of  which  I  have  had  the  fortune  to  become  pos- 
sessed have  been  two  months  or  more  old ;  a  great  many  have  not  been 
in  a  good  state  of  preservation ;  consequently,  I  have  been  obliged  to 
seek  other  sources  for  my  supply  of  microscopical  material.  Judging 
from  the  paucity  of  illustrations  drawn  from  human  embryos  under 
tM'o  months,  I  conclude  that  other  observers  have  found  the  same  diffi- 
culty. Very  valuable  specimens  are  being  constantly  lost  through  neg- 
lect or  lack  of  knowledge  as  to  the  methods  necessary  to  preserve  them. 
Noticeable  as  this  is  regarding  embryos,  it  is  much  more  so  in  the  case 
of  the  ova.  No  studies — at  least  so  far  as  I  am  conversant  with  the 
literature  upon  the  subject — have  been  made  upon  the  segmenting 
human  ova  or  the  first  stages  in  the  development  of  the  blastoderm. 
There  is  a  vast  field  yet  open  for  study  in  this  direction.  The  exact 
nature  of  impregnation  has  not  been  definitely  settled,  and  even  the 
processes  of  segmentation  have  not  been  sufficiently  studied. 

The  most  convenient  and  easily-obtained  mammalian  eggs  are  from 
the  rabbit.  The  variations  between  them  and  human  ova  are  no  doubt 
considerable,  but  by  reason  of  the  imjwssibility  of  obtaining  human  ova, 
and  the  difficulty  attending  the  study  of  those  more  closely  allied  to 
them,  we  are  obliged  to  accept  those  of  the  rabbit  as  a  compromise. 
Many  observers  have  noted  the  changes  occurring  in  the  egg  of  the 
fowl  in  its  early  stages ;  these  very  closely  resemble  those  which  occur 
in  the  mammalian  egg.  The  former  eggs  are  oviparous — that  is,  the 
ova  are  ])roduced  and  developed  by  incubation  outside  the  body; 
wiiile  the  latter  are  rivipni-ou.s,  brought  forth  alive,  the  period  of 
incubation  being  within  the  body. 

Mammalian  eggs  come  from  two  ovaries,  M'hich  are  said  to  produce 
ova  alternately.  In  the  development  of  the  ovaries  the  cylindrical  epi- 
thelium which  covers  their  surface  is  by  a  process  of  involution  enclosed 
in  the  connective-tissue  substance  of  the  ovary  at  many  points  in  the 
form  of  solid  buds  or  cords.  These  soon  become  detached  from  the 
surface  epithelium,  and  set  up  a  rapid  process  of  cell-proliferation,  in  a 


GENERAL  ACCOUNT  OF  EMBRYONIC  DEVELOPMENT.       543 

short  time  breaking  up  into  small  oval  or  irregularly-formed  masses  of 
cuboidal  or  polyhedral-shaped  cells.  These  are  surrounded  by  the  con- 
nective tissue  of  the  ovary,  which  by  condensation  forms  one  of  the  coats 
of  the  Graafian  follicles,  as  the  points  in  which  the  ova  are  developed  are 
called. 

Kapid  differentiation  now  occurs  inside  the  connective-tissue  envelope, 
until  the  ovum  which  occupies  the  central  portion  is  surrounded  by 
several  distinct  layers  of  cells.  As  development  progresses  the  Graafian 
follicles  approach  the  surface  and  rupture  at  regular  periods.  The  ripe 
ovum,  when  set  free  by  the  rupture  of  the  mature  Graafian  follicle,  is 
taken  up  by  the  fimbricated  ends  of  the  Fallopian  tube.  Impregnation 
generally  occurs  in  the  upper  third  of  the  Fallopian  tube :  unimpreg- 
nated  eggs  soon  perish. 

Before  proceeding  to  a  study  of  the  more  complicated  development 
of  the  embryo  of  the  rabbit,  human,  and  pig,  we  will  consider  that  of  the 
tadpole.  The  ovum — by  a  process  of  segmentation — consists  of  a  vast 
number  of  cells  which  form  a  double  membrane  within  the  vitelline  mem- 
brane. This  is  called  the  blastoderm.  In  the  fresh-laid  egg  the  blasto- 
derm consists  of  two  layers  of  cells,  an  internal  and  an  external.  Shortly 
after  incubation  in  the  region  of  the  jyrimitive  trace  there  appears  a  thick- 
ening of  the  blastoderm,  which  results  in  the  formation  of  a  middle  layer. 
The  blastoderm  now  consists  of  three  layers  :  the  external,  or  epiblast ; 
the  internal,  or  hypoblast;  and  the  middle,  or  mesoblast. 

If  at  this  stage  of  development  we  examine  a  longitudinal  section  of 
the  Qgg  of  a  frog,  the  blastoderm  will  be  seen  in  profile  (see  Fig,  280). 
The  anterior  portion  (2),  which  occupies  the  position  of  the  head,  is 
thicker  than  the  posterior  part,  or  tail  (3),  As  development  progresses 
the  ovum  more  nearly  approximates  the  shape  of  the  tadpole,  and  the  tail 
assumes  the  more  prominent  part  (Figs.  281,  282,  and  283),  Concomitant 
with  the  changes  seen  in  profile,  other  changes  are  occurring.  These 
can  be  demonstrated  by  making  cross-sections  of  the  body  (Fig.  284), 
Arising  at  A,  A  are  two  processes  which  extend  longitudinally  the 
entire  length  of  the  tadpole,  occupying  a  dorsal  position.  Between 
these  two  plates  or  ridges  (b)  a  groove  is  seen,  which,  as  the  plates 
develop,  naturally  deepens  (Fig.  285,  b).  The  plates  grow  rapidly, 
and,  folding  together,  form  a  canal  in  which  is  developed  the  spinal 
cord  and  nerve-centres  (Fig,  286,  b).  Around  this  canal  are  developed 
the  vertebrse,  which  appear  first  as  cartilaginous  matrices,  but  which 
afterward  become  ossified  (c,  c). 

About  the  time  the  dorsal  plates  are  seen  the  abdominal  plates  arise 
from  the  under  side  of  the  blastoderm,  and,  growing  rapidly,  com- 
])letely  enclose  the  hypoblastic  layer  within  the  abdominal  cavity  (Fig, 
287),     Within  the  latter  cavity  the  remains  of  the  vitellus  are  enclosed. 

The  hypoblast  gives  rise  to  the  lining  membrane  of  the  alimentary 
canal.  At  first  this  is  a  closed  sac  or  pouch,  without  either  anterior 
or  posterior  outlet.  As  development  progresses,  an  involution  of  the 
epiblastic  layer,  which  finally  unites  with  the  hypoblastic  layer  of  the 
intestinal  canal,  gives  rise  to  the  mouth  at  the  anterior  part,  while  a 
similar  indipping  at  the  posterior  end  forms  the  rectum  (Fig.  283). 

Having  thus  briefly  considered  the  stages  of  development  in  the  tad- 


544 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY 


Fig.  280. 


Fig.  284. 


Diagram  of  Frog's  Egg,  in  an  Early  .Stage 
of  IJevelopuient,  longitudinal  section:  1, 
thickened  portion  of  external  blas^todermic 
layer;  2,  anterior  extremity  of  the  embryo; 
3,  "posterior  extremity,  4,  internal  blasto- 
dermic layer;  5,  cavity  of  vitellus. 


Fig.  281. 


Cross-section  of  Frog's  Egg, 
showing  blastoderm  same  age 
as  I-Mg.  280:  a,  a,  lateral  folds 
situated  upon^  either  side  of 
groove  B. 

Fig.  285. 


Egg  of  Frog  iu  Process  of  Development. 


Fig.  282. 


Cross-section  of  Frog's  I'^gg,  same 
stage  of  development  as  seen 
in  Fig.  281 :  a,  a,  lateral  pro- 
cesses ;  B,  neural  groove. 

Fig.  286. 


Egg  of  Frog,  farther  advanced. 


Fig.  283 


Cross-section  of  Tadpole,  showing 
same  stage  of  development  as 
seen  in  Fig.  282:  B,  neural 
canal ;  v,  c,  lateral  processes  of 
spinal  column. 

Fig.  287. 


Tadjiole,  fully  developed. 


Cross-section  of  Fully-developed 
Tadpole :  letters  same  as  seen 
in  Fig.  286. 


GENERAL  ACCOUNT  OF  EMBRYONIC  DEVELOPMENT.       545 


pole,  we  are  better  prepared  to  take  up  the  study  of  the  more  compli- 
cated processes  as  seeu  iu  the  evolution  of  the  ovum  of  the  rabbit  as  it 
develops  into  the  embryo. 

After  leaving  the  ovaries  the  ovum  of  the  rabbit  passes  slowly  down 


Fig.  288. 


Three  Stages  in  the  Segmentation  of  the  Rabbit's  Ovum  'from  Quain's  Anatomy,  after  Bischoff ) : 
A  Nhows  the  division  of  the  ovum  into  two  nearly  equal  masses;  H,  the  formation  of  four  spheres 
by  division  of  the  two  of  the  preceding  stage;  C,  the  stage  with  eight  segmentation-spheres. 


Fig.  2 


Optical  Section  of  Rabbit's  Ovum  at  the  Close  of  Segmentation  (from  Balfour,  after  Ed.  van  Beneden)  : 
ep,  epiblast;  hy,  primitive  hypoblast;  bp,  spot  where  the  epiblast  has  not  yet  grown  over  the 
hypoblast. 

the  Fallopian  tube,  where  it  meets  the  spermatozoa,  impregnation  taking 
place  in  the  upper  third  of  that  tube,  and  the  ovum  reaching  the  uterus 

Vol.  I.— 35 


546 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 


about  the  fourth  day.  In  their  course  through  the  Fallopian  tube 
nearly  all  ova  become  coated  with  albumen,  this  covering  attaining  its 
greatest  thickness  in  the  egg  of  the  tbwl,  where  it  is  commonly  known 
as  the  white  of  the  egg. 

Segmentation  in  the  ovum  of  the  rabbit  occurs  throughout  the  whole 
structure,  but  in  the  egg  of  the  fowl  it  is  less  complete,  being  confined 
to  one  point  on  the  surface.  In  the  mammalian  egg  the  process  of  seg- 
mentation is  in  all  probability  by  segmentation  of  the  nucleus  first, 
division  following  in  the  cell-bodv,  as  in  the  division  of  cells  in  gen- 
eral.   (See  Fig.  274,  p.  536.) 

The  ovum  of  the  rabbit  first  divides  into  two  parts,  these  again  into 
four,  then  into  eight,  and  so  on  until  the  ovum  has  become  infinitely 
subdivided  into  hundreds  of  minute  cells.  These  myriad  cells  are 
in  fact  the  component  parts  of  the  young  rabbit  that  is  to  be.  They 
will  undergo  certain  modifications  to  become  muscle-cells,  bone-cells, 
blood-cells,  and  so  on,  adapting  themselves  to  the  very  different  tissues 
and  organs  they  are  to  build  up.  All  these  cells  have  descended  from 
a  common  protoplasmic  mass,  yet  they  have  as  much  "  their  definite 
and  appointed  share  in  the  formation  of  the  body  no^^'  as  at  any  later 
stage  of  its  existence." 

After  segmentation  the  larger  cells  arrange  themselves  upon  the  per- 
iphery, enclosing  the  smaller  ones  in  the  central  portion.  The  outer 
layer  of  cells  is  called  the  epihlast,  and  the  inner  the  Jiijpoblast. 

The  ovum  has  by  this  time  reached  the  uterus,  and  consists  of  a 
spherical-shaped  vesicle  (Figs.  290,  291).     Development  now  proceeds 

Fig.  290. 


Rabbit's  Ovum  between  Seventy  and  Ninety  Hours  after  Impregnation :  hi;  cavity  of  blastodermic 
vessels ;  ep,  epiblast ;  lij/,  primitive  hypoblast ;  zp,  zona  pellucida. 

very  rapidly.  The  hypoblastic  layer  of  cells,  which  occupied  only  a 
small  spot  upon  the  inner  side  of  the  epiblastic  layer,  gradually  spreads 
in  such  a  manner  as  to  form  an  inner  layer  to  the  epiblast,  which  in 
turn  encloses  the  former  as  a  blind  sac  or  pouch,  within  which  is  found 
the  remains  of  the  vitellus. 


GENERAL  ACCOUNT  OF  EMBRYONIC  DEVELOPMENT.       547 

Outside  these  two  layers  the  zona  pellucida  forms  another  coating. 
It,  however,  does  not  play  any  essential  part  in  the  further  develop- 

FiG.  291. 


Diagrammatic  views  of  tlie  Blast  ode  iiiiic  Vesicle  of  a  Rabbit  on  the  Seventh  Day  (from  Balfour,  after 
Kd.  V.  Beneden) :  lu  the  left-hand  figure  the  vesicle  is  seen  from  above;  in  the  right-hand  figure, 
from  the  siile.  The  white  iiatch  (a//)  is  the  germinal  area,  and  the  slight  constriction  {ge)  marks 
the  limit  to  which  the  hypoblast  has  extended. 

ment  of  the  embryo,  at  least  in  so  far  as  we  are  to  con.sider  the  subject ; 
and  henceforth  we  will  not  mention  it. 

This  embryonic,  area  is  the  result  of  the  thickening  of  the  hypoblast 
at  the  point  where  the  development  of  the  primitive  streak  will  pres- 

FiG.  292. 


Embryonic  area  of  a  Rabbit's  Ovum  on  the  Seventh  Day  (from  Kolliker):  The  shaded  part  (ag)  is  the 
embryonic  area;  oo  is  the  region  of  the  blastodermic  vesicle  immediately  surrounding  the  embry- 
onic area,  into  which  the  mesoblast  has  already  spread,  and  in  which  blood-vessels  will  shortly 
appear;  jir,  primitive  streak;  rf,  medullary  groove. 


548 


DENTAL  EMBRYOLOGY  AND   HISTOLOGY. 


ently  appear.  Previous  to  the  formation  of  the  latter,  however,  there 
is  formed  a  third  layer,  which  locates  itself  between  those  already 
developed,  and  is  known  as  the  mesoblast.  It  is  mainly  produced  by 
the  proliferation  of  the  cells  of  the  epiblast  (Fig.  292). 

The  cellular  activity  of  the  epiblast  proceeds  rapidly,  and  results  in 
the  formation  of  two  medullary  plates  which  arise  in  parallel  rows, 
between  which  lie  the  medullary  groove  or  primitive  streak.  At  the 
anterior  portion,  in  the  very  first  differentiation  of  the  groove,  a  dark 
spot  is  seen,  known  as  the  ''  nodal  point  of  Hensen,"  which  subse- 
quently marks  the  front  part  of  the  groove.  Its  signification  is  not 
exactly  known. 

The  medullary  plates  develop  rapidly,  expanding  at  their  anterior 
portion  into  a  spatula-shaped  crescent  (Fig.  293).     This  gives  rise  to 


\iiil)|"M"  ■ iiiiii.""iiiilwiii' 


^.,_ 


h 
'f 


Fig.  293. 


^mmmm^^"^ 


Rabbit  Embryos  of  about  tbe  Ninth  Day,  seen  from  the  doisal  side  (from  Kcilliker) :  «6,  optic  vesicle; 
nf,  amnion  ;  "/),  area  pellueida;  A  and  hz,  heart:  hf,  lueduilary  plate  in  region  of  future  fore-brain  ; 
/('",  medullary  plate  in  region  of  future  mid-brain  ;  ///(  and  Ii"\  hind-brain  ;  vth.  mid-brain  ;  ]ili, 
pericardial  section  of  body-cavity ;  //,-,  lateral  zone;  pr,  primitive  streak;  ;/,  medullary  groove; 
.sir,  vertebral  zone;  iiu\  protovertebne ;  vh,  fure-brain  ,  ro,  vitelline  vein. 

the  ce]ihalic  end  of  the  embryo.  The  first  indication  of  the  vertebral 
column  is  seen  about  the  eighth  day,  in  the  formation  of  the  first  pair  of 
somites.  Tlicy  are  located  in  the  region  of  the  neck,  and  mark  the  line 
of  union  of  head  and  trunk.  The  latter  gradually  elongates  by  the 
addition  of  other  pairs  of  somites,  the  growth  in  length  being  from  the 
first-formed  somites  caudal-ward.      The  medullary  groove  deepens  as 


GENERAL  ACCOUNT  OF  EMBRYONIC  DEVELOPMENT.       549 


the  embryo  grows  older ;  the  medullary  folds  become  higher,  and  finally 
unite  over  the  medullary  groove,  which  they  have  made  by  their  growth. 
The  union  of  the  sides  begins  at  the  anterior  part.  The  canal  thus 
formed  is  called  the  neural  canal,  and  locates  the  spinal  cord.  The 
caudal  end  grows  rapidly,  pair  after  pair  of  somites  being  added,  until 
at  the  twelfth  day  the  embryo  presents  the  appearance  seen  in  Fig.  294. 


Fig.  294. 


^?io 


md 


am 


Itabbit  Embryo  ol"  ab'Hit.  the  Twelfth  Day  (liom  Balfour,  after  Weldou)  :  ce,  cerebral  hemisphere;  fl, 
to  e  limb;  ///,  liind  limb;  /(//,  hyoid  arch;  u\  n,  fourth  ventricle;  mb,  mid-brain  ;  mx,  maxillary 
arch;  md,  mandibular  arch;  op,  eye;  l/i,  thalamencephaloii  ;  nm,  umbilical  stalk. 

The  embryo  rabbit  of  twelve  days  has  reached  about  the  stage  of 
the  human  embryo  of  four  weeks  and  tlie  pig  1  cm.  in  length. 

In  describing  the  rabbit  embryo  of  twelve  clays  Foster  and  Balfour 
say:  "The  latter  stages  in  the  development  proceed,  in  the  main,  in  the 
.same  manner  as  in  the  bird.  The  cranial  flexure  soon  becomes  very 
marked,  the  mid-brain  forming  the  end  of  the  long  axis  of  tlie  embryo 
(Fig.  294,  mb).  The  sense-organs  have  the  usual  development.  Under  the 
fore-brain  appears  an  epiblastic  involution  giving  rise  both  to  the  mouth 
and  to  the  pituitary  body.  Behind  the  mouth  are  three  well-marked 
pairs  of  visceral  arches.  The  first  of  these  is  the  mandibular  arch 
(Fig.  294,  md),  which  meets  its  fellows  in  the  middle  line  and  forms 
the  posterior  boundary  of  the  mouth.  It  sends  forward  on  each  side 
a  superior  maxillary  process  (nix),  which  partially  forms  the  anterior 
margin  of  the  mouth. 

As  the  embryo  increases  in  length,  the  convexity  of  the  spine  be- 
comes greater,  and  the  head  and  tail  ends  approximate  each  other.  The 
chin  rests  hard  upon  the  breast,  and  the  caudal  convexity  comes  in  con- 
tact with  the  forehead.  The  limbs  are  seen  as  buds  springing  off  from 
the  sides  of  the  body  {fl  and  hi).  The  umbilical  stalk  (nm)  arises  from 
the  concave  surflice  of  tlie  embryo  and  extends  posteriorly. 

As  we  have  before  said,  a  sufficient  number  of  human  embryos  under 
four  weeks  of  age  have  not  been  obtained  to  establish  any  definite 
description  of  development  prior  to  that  age.  The  earliest  authenticated 
observations  were  made  by  Allen  Thomson  (see  Fig.  297,  human  embryo 


550 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY 


of  four  weeks,  somewhat  enlarged).     The  mandibular  arch  (c)  and  the 
maxillary  arch  (d)  are  quite  plainly  shown. 

The  proportion  of  the  cephalic  as  compared  with  the  caudal  end  of 
the  human  embryo  is  not  as  great  as  that  seen  in  the  rabbit.  Our  next 
illustrations  (Fig.  295)  show  the  human  embryo  in  various  stages  of 


Fig.  295. 


Figures  illustrating  the  Formation  of  the  Face  in  the  Human  Embryo  (from  (IwtdWs  Anatomy) :  A, 
he:  d  of  ;m  embryo  of  about  four  -neeks  (after  Allen  Thomson) ;  1,  mandibular  arch;  a,  ear.  B^ 
head  of  an  embryo  of  about  six  weeks  (after  Kcker):  1,  mandibular  arch;  1',  hyomaudibular 
cleft.     C,  head  of  an  embryo  of  about  nine  weeks  (after  Ecker}. 

development:  ..I,  four  ^\•eeks,  corresponding  to  pig  embryo  1  centimeter 
in  length;  B,  six  weeks,  shows  the  same  progress  in  development  aft 
seen  in  foetal  pigs  1^  centimeters;  while  the  last,  C,  equals  in  length  a 
pig  embryo  2^  centimeters. 

Having  tlms  shown  the  comparative  ages  and  stages  of  development 
in  foetal  life,  we  will  confine  ourselves  in  our  further  study  largely  to 
pig  embryos,  the  supply  of  which  in  a  good  state  of  preservation  is 
unlimited. 

Development  of  the  Jaws  and  Buccal  Cavity. — The  first  indication  of 
the  formation  of  the  oral  cavity  is  seen  very  early  in  the  life-history  of 
the  embryo.  Considerable  difference  of  opinion  is  recorded  regarding 
the  exact  time  of  its  formation  in  the  human  embryo.  In  Fig.  296, 
representing  the  twenty-fifth  or  twenty-eighth  day  of  foetal  life,  the  wide 
cavity  seen  at  (6)  represents  the  })osterior  portion  of  the  buccal  cavity. 
The  growth  of  the  maxillary  arches  closes  this  cavity  anteriorly.  Its- 
floor  is  formed  by  the  inferior  maxillary  arches  (4).  These  arise  from 
the  first  pharyngeal  arches.  The  superior  maxilla  arises  from  three 
separate  points.  On  either  side  of  the  face  a  ]>rocess  springs  off  from 
the  first  jiharyngeal  arch  (one  side  of  which  is  shown  at  d  in  Fig.  297). 
Tlu!  processes  pass  downward  and  Ibi'ward,  and  unite  with  the  sides  of 
the  nasal' ]irocess. 

From  the  frontal  prominence  (1)  the  third  process,  the  incisive,  grows^ 
downward,  and  fills  in  the  space  between  the  ends  of  the  two  preceding 
processes.  By  the  union  of  these  three  proces,^es  the  superior  maxilla  is 
completed.  Failure  of  union  between  the  middle  and  two  lateral  pro- 
cesses gives  ri.se  to  the  (lefi)rmity  known  as  hare-lip.  This  may  be 
simple,  and  occur  on  either  side  at  the  juncture  of  the  intermaxillary 
bones  with  the  lateral  processes,  or  in  the  median  line  at  the  point  of 


GENERAL  ACCOUNT  OF  EMBRYONIC  DEVELOPMENT.       551 


union  of  the  two  intermaxillary  bones  themselves ;  or  it  may  be  double, 
by  reason  of  the  non-union  on  both  sides. 

Development  of  the  Palate. — The  plates  which  form  the  hard  palate 
arise  from  the  lateral  processes  of  the  superior  maxilla  and  grow  toward 

each  other,  uniting  in  the  median 
FiG^96.  lii^e.     Previous  to  their  develop- 

ment and  union  the  buccal  cavity 
and  nose  are  as  one  cavity.  The 
separation  is  usually  completed  by 
the  end  of  the  second  month. 

When  for  any  reason  union  does 

not  occur  between  the  t\vo  plates, 

there  results  what  is  known  as  clejit 

it        palate.    This  is  very  apt  to  accom- 

Face  of  an  Embryo  of  Twenty-five  to  Twenty-  - — : — ^^^^^S^^?y^ 
eight  Days  imagjiified  fifteen  times):  1,  frontal 

promiuence;  2,  S,  right  and  left  olfactory  fossse  ;  Embryo  removed  from  the  Ovum,  and  magni- 

4,  inferior  maxillary  tubercles,  united'  in  the  fied:  a,  amnion;   6,  yolk-sac;   c,  mandibular 

middle  line;   5,  superior  maxillary  tubercles;  arch;    d,  maxillary  arch;    e,  hyoidean   arch; 

6,  mouth  or  fauces:  7,  second  pharyngeal  arch  ;  behind  this  are  the  first  and  second  branchial 

8,  third;   9,  fourth;    10,  primitive  ocular  ves-  arches  ;/.  rudiment  of  fore  limb;  </,  auditory 

icle;  11,  primitive  auditory  vesicle.  vesicle;  h,  eye;  /,  heart  (X  5)- 

pany  hare-lip,  the  same  causes  which  give  rise  to  the  latter  operating  to 
prevent  the  normal  development  of  the  palate  bones,  which,  as  we  have 
seen,  follow  the  development  of  the  intermaxillary  bones. 

Turning  our  attention  now  to  the  inferior  maxilla,  we  see,  by  refer- 
ring to  Fig.  294,  that  the  inferior  or  mandibular  arch  also  arises  from 
the  first  pharyngeal  arch  (?)icZ).  In  the  human  embryo  these  processes 
are  said  to  have  been  seen  as  early  as  the  fifteenth  to  the  eighteenth  day 
of  foetal  life.  They  arise  in  pairs,  as  do  the  lateral  processes  of  the 
superior  maxilla,  and  grow  very  rapidly,  union  occurring  in  the  median 
line  at  about  the  twenty-eighth  day.     (See  Fig.  296.) 

The  maxillae  arise  as  solid  buds  from  the  mesoblastic  layer,  and  are 
covered  externally  by  the  epiblast.  The  maxillary  bones  belong  to  the 
class  of  splint  bones,  and  are  not  preformed  in  cartilage,  but  ossify  by 
what  I  term  interstitial  ossification.^ 

With  the  development  of  the  maxillae  the  anterior  boundaries  of  the 
oral  cavity  are  formed.  Posteriorly,  there  is  seen  a  "  foetal  septum  " 
between  the  forming  cavity  and  the  upper  end  of  the  intestinal  canal ; 
as  the  buccal  cavity  and  the  upper  end  of  the  intestinal  canal  near  each 
other  the  septum  diminishes  in  width,  and  finally  disappears  entirely. 

'^  My  own  classification.     See  section  on  Calcification. 


552 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 


In  the  viviparous  family  the  perforation  of  the  foetal  septum  occurs, 
in  most  cases,  before  birth  ;  when,  however,  it  does  not  occur,  there 
arises  a  pathological  condition  known  as  impervious  oesophagus. 

Of  necessity,  the  lining  membrane  of  the  mouth  is  formed  from  the 
involution  of  the  epiblast.  The  point  of  union  between  the  epiblastic 
and  hypoblastic  layers  is  located  at  variable  distances  from  the  upper 
end  of  the  oesophagus,  even  to  the  union  of  the  latter  with  the  cardiac 
end  of  the  stomach. 

Meckel's  Cartilage. — The  central  portion  of  the  inferior  maxilla,  very 

soon  after  the  union  of  the  two  lateral  processes,  becomes  differentiated 

into  a  cartilaginous  cord  which  serves  to  strengthen  the  jaw.     To  this 

band  or  cord  the  name  of  the 
Fig.  298. 


discoverer, 
given.     It 


MeckeVs  Cartilage  from  Human  F-mbryo  of  Forty  to 
Foity-two  days,  and  before  the  appeaiance  of  the 
maxilla  y  bone  (mugnitied  ten  diameters):  A,  en- 
largement of  cartilage  near  its  union  with  the  neck 
of  ma  leus;  D,  union  with  cartiage  of  opposite  side; 
M,  head  of  malleus ;  N.  handle  of  malleus :  IC,  carti- 
lage of  tlie  incus;  i,  cartilage  of  the  stapes;  O,  car- 
tilage 01  the  OS  lenticulare  The  outlines  of  a  jaw 
have  been  added  to  the  figure  to  show  the  relative 
position  occupied  by  the  cartilag  in  the  jaw.  (After 
INIagitot  and  Kobin,"liean's  translation.) 


Meckel,  has  been 
is  formed  in  two 
parts  arising  from  the  mallei 
of  either  side,  which  unite,  as 
do  the  lateral  processes  of  the 
jaw,  at  the  symphysis  mentis. 
The  cartilaginous  matrices  of 
the  bones  of  the  ear  become 
directly  ossified,  as  does  the 
Meckelian  cartilage  of  the  jaw. 
The  former  undergo  ossification 
about  the  third  month. 

Regarding  Meckel's  cartilage 
very  little  has  been  written,  and 
I  deem  the  reason  to  lie  in  the 
fact  that  very  little  study  has 
been  given  to  the  subject  of  maxillary  ossification.  Foster  and  Balfour, 
speaking  of  the  development  of  the  mandibular  arch  of  the  chick,  say: 
"  In  the  inferior  maxillary  process  two  developments  of  cartilage  take 
place — a  proximal  and  a  distal.  The  proximal  cartilage  is  situated  at 
the  side  of  the  periotic  capsule,  but  is  not  united  with  it.     It  is  known  as 

the  quadrate,  and  in  the  early  stage  is 
merely  a  small  knob  of  cartilage.  The 
quadrate  cartilage  ossifies  as  the  quad- 
rate bone,  and  supplies  the  permanent 
articulation  for  the  lower  jaw.  The 
distal  rod  is  called  Meckel's  cartilage  ; 
it  soon  becomes  covered  by  investing 
(membranes)  bones,  which  form  the 
mandible,  and  its  proximal  end  ossi- 
fies as  the  articulare.'" 

Regarding  its  development,  Foster 
and  Balfi)ur  simj^ly  quote  from  Par- 
ker's account  of  the  pig:  ''In  a  some- 
what later  stage  (Fig.  299)  the  upper 
end  of  tlie  mandilmlar  bar,  without  be- 
coming segmented  from  the  ventral  jiart,  becomes  distinctly  swollen,  and 
clearly  corresponds  to  the  quadrate  region  of  other  types.  .  The  ventral 


Embryo  Pig  an  inch  a"d  a  third  long ;  side 
view  of  MandilMilar  and  1 1  void  .Aichcs 
(Parker):  iri,  tongue;  ink,  Meckelian  carti- 
lage; ml.  body  of  malleus;  mh,  manubri- 
uni  or  handle  of  the  malleus;  /'//,  tegmcii 
tympani ;  '.  incus;  .«',  stapes  The  rest  of 
the  letters  refer  to  the  hyoid  arch. 


GENERAL  ACCOUNT  OF  EMBRYONIC  DEVELOPMENT.       553 


part  of  the  bar  constitutes  IMeckel's  cartilage  (ink).  In  the  course  of 
further  development  the  Meckelian  part  of  the  mandibular  arch  becomes 
enveloped  in  a  superficial  ossification  forming  the  dentarv.  Its  upper 
end,  adjoining  the  quadrate  region,  becomes  calcified,  and  then  absorbed, 
and  its  lower,  with  the  exception  of  the  extreme,  is  ossified  and  subse- 
quently incorporated  in  the  dentarv."  Tomes  says  :  "  About  the  fortieth 
day  a  centre  of  ossification  appears  in  the  mandibular  process,  whicli, 
spreading  rapidly,  soon  forms  a  slight  osseous  jaw  outside  Meckel's  car- 
tilage, which  is  not,  however,  in  any  way  implicated  in  it,  and  very  soon 
begins  to  waste  away ;  so  that  by  the  end  of  the  sixth  month  it  has  dis- 
appeared. That  end  of  it  alone  which  extends  up  to  the  tympanum 
does  not  waste  away,  but  becomes  ossified  into  the  malleus.  There  are, 
however,  observers  who  hold  that  in  some  animals,  at  all  events,  Meckel's 
cartilage  plays  a  more  active  part  in  the  ossification  of  the  jaws."  Dean 
agrees  with  the  authors  above  quoted  on  all  essential  points. 

The  disappearance  of  Meckel's  cartilage  is  accomplished  by  calcifica- 
tion, and  afterward  by  ossification.  The  development  of  bone  in  the 
jaw  begins  in  the  embryonic  connective  tissue  surrounding  Meckel's 
cartilage ;  the  latter,  occupymg  the  central  portion  of  the  jaw,  is  sur- 


2210. 


Meckel's  Cartilage,  from  jaw  of  t-wo-and-a-half  months'  human  foetus  undergoing  ossification  :  n,  nor- 
mal cartilage-cells;  <;  enlarged  cells  containing  calcitic  material ;  db,db,  developing  bone  ;  cl,  con- 
nective tissue  (X  '2r)0). 

rounded  by  the  connective  tissue  of  the  mesoblastic  layer,  which  in  turn 
is  covered  externally  by  that  of  the  epiblast. 

Development  of  bone  in  the  inferior  maxilla  begins  in  the  mesoblastic 
layer  prior  to  the  differentiation  of  the  periosteum,  about  the  fortieth 
day.  As  the  forming  bands  of  bone  thicken  they  encroach  upon 
Meckel's  cartilage,  which  is  also  undergoing  calcification.     Under  the 


554  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

influence  of  the  osteoblasts  the  cartilage  is  broken  down  and  becomes 
ossified  and  incorporated  into  the  substance  of  the  maxilla.  These 
changes  are  very  plainly  sho\vn  in  the  accompanying  cut,  from  a  photo- 
micrograpli  (Fig.  300). 

Ossification  of  Meckel's  cartilage  differs  from  that  known  as  intercar- 
til((gi)iou.s;  in  the  latter  case  there  is  rapid  proliferation  of  the  cartilage- 
cells,  the  cartilaginous  head  (femur)  increasing  in  size  in  proportion  to 
the  encroachment  of  the  ossification  zone.  This  does  not  occur  in  ossi- 
fication of  Meckel's  cartilage.  There  is  no  increase  of  cartilage-cells, 
except  at  the  points  of  articulation,  where  true  intercartilaginous  ossi- 
fication occurs.  In  the  body  of  the  jaw  tlie  cartilage  simply  becomes 
calcified,  and  afterward  ossifi(Kl  and  incorporated  into  the  substance  of 
the  maxilla,  as  before  stated.  It  entirely  disappears  before  the  fifth 
month — not  by  icasfing  away,  but  by  ossification.  This  change  begins, 
as  we  have  seen,  at  two  and  a  half  months  ;  at  three  months  it  is  almost 
complete,  and  at  four  months,  in  nearly  every  case  which  I  have  exam- 
ined, no  trace  of  the  cartilage  remains.  In  the  pig  it  persists  much 
longer,  and  is  unaffected  by  ossific  processes  in  embryos  ten  centimeters 
in  length. 

Development  of  the  Blastoderm. 

In  the  unincubated  chicken  egg  the  blastoderm  is  composed  of  two 
layers — the  epiblast  and  the  hypoblast.  There  is  little  or  no  change 
observable  until  after  the  eighth  hour  of  incubation,  but  between  this 
and  the  twelfth  hour  marked  changes  occur.  Cross-sections  of  the 
chick  at  this  time  will  show  a  decided  proliferation  of  the  epiblastic 

Fig   301. 


-ep 


Transverse  Section  through  a  Blastoderm  of  Chick,  about  the  eightli  hour  after  incubation  (after  Bal- 
four); the  section  passes  througli  the  middle  of  the  primitive  streak:  juis,  primitive  streak; 
ep,  epiblast:  hy,  hypoblast;  yk,  yolk  of  the  germinal  wall. 

layer  in  the  region  of  the  primitive  streak.  The  epiblast,  previous  to 
this  time,  is  fi)rmed  of  a  single  layer  of  cells  somewhat  oval  in  shape, 
i\\\i\  to  the  lateral  pressure  of  fellow-cells. 

The  hy]iol)last  consists  of  a  single  layer  of  cells,  which  lie  parallel 
witii  the  surface  of  the  blastoderm,  while  the  epiblastic  layer  stands, 
palisade-like,  upon  the  surface.  Between  the  flat  layer  of  the  hypoblast 
and  the  proliferated  cells  of  the  epiblast,  are  seen  a  few  scattering  cells 
which  appear  to  have  arisen  from  the  hypoblast,  but  the  greater  part 
of  the  thickening  is  from  the  epiblast. 

There  is  little  or  no  change  appreciable  in  the  histological  appearance 
of  the  blastoderm  until  about  the  eighteenth  or  twentieth  hour,  when  the 


DEVELOrMENT  OF  THE  BLASTODERM. 


555 


epiblast — now  composed  of  one  or  more  layers  of  cells— ^is  seen  to  have 
separated  from  the  mass  of  proliferated  cells  which  lie  beneath  it.  It 
is  at  this  juncture  that  the  viesoblast  may  be  said  to  have  assumed  a 
separate  entity. 

The  mesoblast  is  composed,  as  we  have  seen,  of  cells  derived  from 
both  hypoblast  and  epiblast,  but  chiefly  from  the  latter.  About  the 
twentieth  hour,  if  the  cells  of  the  mesoblast  are  examined  with  a  high 
power  (Zeiss,  ^^  oil  im.),  it  will  be  seen  that  they  are  stellate  in  form. 
They  take  the  stain  similarly  to  the  cells  of  the  epiblast,  and  it  is  only 
in  carefully-prepared  specimens — studied  with  high  powers — that  we  are 
able  to  detect  any  difference.  They  lie  in  a  bed  of  protoplasm,  and  it 
is  from  this  fluid — with  which  they  are  constantly  bathed — that  they 
derive  their  nourishment.  They  are  simply  nucleated  structures,  each 
containing  numerous  granular  particles.  They  are  the  bioplasts  of  Beale, 
the  nuclei  of  the  future  cells  of  the  connective-tissue  group.  They  have 
no  cell-body,  and  consequently  no  cell-limit  or  wall.  As  they  advance 
in  age  they  gradually  accumulate  around  themselves  formed  material, 
probably  the  undigested  or  unassimilated  portion  of  the  surrounding 
protoplasm.  They  thus  assume  distinctive  and  characteristic  forms. 
Their  processes  gradually  become  thicker  and  more  pronounced,  so  as 
to  be  visible  even  with  low  powers.     The  changes  in  the  cells  can  now 

Fro.  302. 


Porcine  Embryo  {'2J  cm.  X  250) :  c.t,  embryonic  connective  tissue  of  mesoblast. 


be  seen  in  the  lower  jaw  of  a  fcjetal  pig  two  and  a  half  centimeters  in 
length  (Fig.  302). 

In  the  development  of  the  oral  cavity  and  associate  parts  we  do  not 
have  to  do  with  the  hypoblastic  layer  of  the  blastoderm,  so  we  M'ill 
hereafter  confine  ourselves  to  the  head  of  the  embryo. 

The  epiblast  in  an  embryo  pig  1  cm.  in  length  is  composed  of  one  or 
more  layers  of  nuclei  or  bioplasts  lying  in  a  bed  of  protoplasm.  With 
low  powers  they  appear  in  no  manner  different  from  the  underlying 
mesoblastic  cells,  except  that  the  nuclei  are  closer  together ;  and  in 
sections  stained  with  hfemotoxylon  and  eosin  assume  a  darker  hue  than 
those  of  the  mesoblast.  The  epiblast  now  constitutes  the  "  infant " 
layer  of  the  epithelium,  being  the  deepest  layer  of  the  rete  Malpighii. 


556 


DENTAL  EMBRYOLOGY  AXD  HISTOLOGY. 


It  surrounds  the  lower  jaw,  forming  a  lining  for  the  mouth  and  an  outer 
coat  for  the  jaw, 

Tlie  jaw  is  a  process  which  has  budded  off  from  the  main  body  of 
the  blastoderm,  and  is  composed  of  a  layer  of  mesodermic  tissue  sur- 


FiG.  303. 


c(,  coiiiiectivt;  tissue  ol"  uiesoblast ;  t-y;,  ejiiblast   single  laj'pr  of  cells).    The  epiblast  is  separated  from 

the  mesoblast  mechanically. 

rounded  bv  a  yesicle  or  sheath  of  the  e])iblast  (Fig.  303).  Here,  then, 
we  have  an  excellent  opportunity  to  study  the  several  tissues  A^'hich  arise 
from  these  two  layers  of  the  blastoderm,  as  far  as  the  microscopical  ap- 
pearances are  concerned.  A  1  cm.  pig  embryo  prc-^cnts  about  the  same 
stage  of  develojiment  macroscopically  as  found  in  a  human  embryo  of 
four  weeks.  Histologically,  it  may  be  comjiared  with  a  chick  of  from 
twenty-four  to  thirty-six  hours  or  a  rabbit  embryo  of  twelve  days. 


Products  op  the  Epiblast  and  Mesoblast. 

Let  us  first  consider  some  of  the  products  of  the  epiblastic  layer,  or, 
as  we  shall  hereafter  call  it,  the  epithelUd  layer.  These  are  nails,  hairs, 
glands,  and  the  oiamcl  organ. 

Development  of  Kails. — The  nails  are  appendages  of  the  ejiidermis, 
and  are  developed  })y  an  accretion  and  hornification  of  the  cells  which 
constitute  the  epithelial  layer.  Desquamation  does  not  occur,  but  the 
cells  coalesce,  and,  liccoming  glued  together,  form  the  nails.  The  nails 
can  be  re.solved  into  their  cellular  elements  by  the  use  of  dilute  nitric 
acid. 

In  nails  we  distinguish  three  portion,-; — the  body,  nail-groove,  and 
nail-bed.  The  nail  arises  from  the  nail-bed  by  a  hornification  of  the 
ejiithelium  of  that  portion;  it  increases  in  thickness  by  the  addition  of 
cells  from  the  under  side,  the  nail  being  thickest  at  its  free  border.     It 


PRODUCTS  OF  THE  EP IB  LA  ST  AND  MESO  BLAST.  557 

is  attached  along  its  lateral  borders  to  the  nail-grooves,  Avhieh  consist 
of  folds  in  the  skin.  The  nail  merges  by  almost  insensible  gradations 
from  the  corneous  layer  of  the  skin  in  its  posterior  portion  into  the 
hornified  nail.  The  sides  of  the  nail  are  not  soft,  and  do  not  pass 
gradually  from  the  corneous  layer  of  the  skin,  but  are  completely 
hornified  down  to  their  attachment  to  the  skin  in  the  lateral  grooves. 

The  nail  is  developed  in  the  hmnla — as  the  nail-bed  is  sometimes 
called — from  a  matrix  of  the  epithelial  cells  constituting  the  vete  Mal- 
pighii,  which,  thickening,  prevents  the  blood-vessels  of  the  corium  from 
showing  so  plainly  as  in  the  body,  and  accounts  for  the  lighter  color  of 
that  portion  of  the  nail.  Between  the  nail  and  the  corium  are  seen  the 
infant  cells  of  the  Malpighian  layer,  constituting  only  a  single  layer 
near  the  free  margin,  but  gradually  becoming  thicker  toward  the  poste- 
rior part  of  the  nail-body.  The  corium,  which  underlies  the  nail,  and 
is  situated  between  it  and  the  bone,  does  not  diifer  essentially  from 
the  corium  of  other  portions  of  the  skin.  The  papillae  are  somewhat 
longer,  and  are  inclined  slightly  forward  by  the  outward  growth  of  the 
nail,  which  is  firmly  attached  to  the  corium,  and  through  it  to  the  peri- 
osteum of  the  bone.  The  vascular  system  differs  in  no  manner  frcjni 
that  of  the  other  parts  of  the  corium  ;  the  capillary  vessels  end  in  ca})il- 
lary  loops  which  supply  nourishment  to  the  Malpighian  layer.  This 
layer  gradually  becomes  considerably  thickened,  and,  folding  upon  itself, 
forms  a  shalloM^  pocket  or  groove  which  will  in  time  be  occupied  by  the 
nail-root.  This  infolding  is  not  unlike  that  formed  for  the  glands,  hair, 
and  enamel  organ. 

The  cells  which  have  been  pushed  up  from  the  nail-bed  have  assumed 
a  peculiar  translucent  appearance,  and  do  not  take  the  stain  freely. 
They  are  becoming  hornified  by  desiccation  and  deposition  into  the  cell- 
body  of  a  greater  proportion  of  carbon  and  sulphur,  both  of  which  are 
generallv  found  in  the  epidermis.  As  a  consequence  of  desiccation,  the 
cells  which  constitute  the  body  of  the  nail  lose  their  nuclei  and  become 
condensed  into  a  compact  tissue  or  structure,  for  the  examination  of 
which  it  is  necessary  to  resort  to  the  use  of  strong  alkalies,  which  resolve 
the  nail  into  its  cellular  elements. 

In  the  developing  nail  the  line  of  division  between  the  epiderra 
coverino;  the  end  of  the  finger  and  the  free  border  of  the  nail  is 
plainly  marked  by  a  condensed  layer  of  cells,  which  does  not  partake 
of  the  nature  of  either  tissue,  but  which  lies,  as  it  were,  on  the  border- 
land between  the  two.  This  layer  will  form  the  attachment  of  the  nail 
at  its  free  margin. 

The  lengthening  of  the  nail  corresponds  with  the  gro-s^iih  of  the  fin- 
ger, being  from  the  posterior  portion  outward.  The  nail  is  somewhat 
thicker  at  the  free  border  than  it  is  nearer  its  origin. 

No  sweat  or  sebaceous  glands  are  found  underneath  the  nail,  which 
perhaps  accounts  for  the  change  of  the  epidermis  at  that  point  into  the 
nail  by  the  process  of  desiccation. 

Hairs,  glands,  and  the  enamel  organ  are  formed  by  an  ingrowth  of 
the  Malpighian  layer  into  the  mesodermic  portion  underneath.  Just 
why  the  rapid  multiplication  of  epithelial  cells  should  result  in  one 
place  in  the  formation  of  nails  or  horns,  while  in  another  part  their 


558 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 


increase  results  in  an  ingrowth  which  forms  hairs,  glands,  etc.,  is  a 
question  which  has  puzzled  the  brains  of  thoughtful  men  since  anything 
has  been  known  of  the  histology  of  tissues.  The  only  answer  that  can 
be  made  is  that  in  so  doing  the  cells  are  obeying  a  vital  poicer  which 
cannot  be  explained  from  a  knowledge  of  their  microscopical  character 
or  chemical  composition,  or  from  a  knowledge  of  the  ultimate  sub- 
stances into  which  they  may  be  resolved,  but  which  endows  each  cell 
with  a  distinct  individuality.  That  such  is  the  case  no  one  can  doubt 
who  has  for  himself  studied  the  development  of  tissues.  If  such  is  not 
the  case,  why  is  it  that  the  cells  of  the  mesoblast — which  in  the  first 
instance  arise  almost  altogether  from  the  epiblast — form  one  line  of 
tissues,  while  the  parent  epiblast  forms  another  entirely  different  ?  So 
far  as  we  can  make  out  in  the  early  stage  of  the  differentiation  of  the 
mesoblast  from  the  epiblast,  there  is  no  histological  difference  between 
the  two ;  but  they  have  each  separate  offices  to  perform,  and  unless 
interfered  with  by  lack  of  material  (cell-pabulum)  they  go  on  growing 
and  forming  until  they  have  produced  very  different  tissues.  From  the 
time  of  the  separation  of  the  mesoblast  from  the  epiblast,  histological 
differences  are  presented  M'hicli  become  more  and  more  marked  at  each 
succeeding  stage,  until  at  last  the  products  of  their  life-work  show  the 
widest  divero-ence. 

Development  of  Hairs. — The  process  of  the  development  of  hairs  is 
somewhat  more  complex  than  that  of  nails,  but  is  of  a  similar  nature. 

Fig.  304. 


A,  Hair-nidiment  from  an  Embryo  of  Six  Weeks:  a.  horny,  and  h,  mucous  or  >ralpighian  laver  of 

cuticle:  ',  basenient-niemhrane:  m,  cells,  some  of  which  are  assuming  au  oblong  figure, 'which 
chiefly  form  the  future  hair. 

B,  Hair-rudimei't,  with  the  Young  Hair  formed,  but  not  yet  risen  through  the  cuticle:  a,  hornv, 

6,  .Malpishian,  layer  ol  epidermis;  r,  outer,  </,  inner,  root  sheath:  p,  hair-knob;  f.  stem,  and  g', 
point,  of  the  hair;  A,  hair-papilla;  »,  «,  commencing  sebaceous  follicles. 

C,  Hair-follicle,  with  hair  just  protruded. 

Instead  of  being  developed,  like  the  nails,  upon  the  surface,  they  are 
developed  inside  a  pouch  or  sac,  through  the  mouths  of  Avhich  thev 
push  their  way  to  the  surface.     The  fii'st  appearance  of  the  development 


PRODUCTS  OF  THE  EPIBLAST  AND   MESOBLAST. 


559 


of  hairs  is  seen  in  the  pig  3  cm.  in  length  or  in  hnmun  fetuses  between 
the  third  and  fourth  months.     The  infant  cells  of  the  rete  Malpighu 
Fig.  305. 


Hair-follicle  in  Longitudinal  Section:  (/.mouth 
of  follicle;  0,  neck;  .,  bulb;  <l,  ^  dermic  coat 
^,  outer  root-sheath:  ;/,  inner  root-sheatli  /-, 
hair;  /;,  its  medulla;  /,  hair-knob;  m,  adipose 
tissue;  n,  hair-musde ;  o,  papilla  of  skin:  p, 
papilla  or  hair;  6-.  vete  mucosura  continuous 
with  outer  root-sheath;  fp,  horny  layer;  I,  seba- 
ceous gland. 

appear  to  thicken  at  many  points  ;  this 
dip  into  the  underlying  corium.     The 


Commencing  Replacement  of  Old 
by  New  Hair  (Toldt) :  ",  outer 
root-sheath  ;  b,  dermic  coat  of  fol- 
licle';  f,  down  growth  of  epithe- 
lium to  form  new  hair-follicle;  p, 
papilla  of  new  hair  commencing; 
./,  root  of  old  hair;  t,  duct  of  seba- 
ceous gland. 

thickening  proceeds  until  they 
cellular  activity  does  not  lessen 


560  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

until  the  sac  has  reached  the  typal  limit  of  its  growth.  The  sac  is  filled 
with  cells  which  have  been  pushed  off  from  the  infant  layer.  The  sur- 
rounding connective  tissue  has  now  become  somewhat  condensed,  and 
constitutes  the  outer  root-sheath.  The  continued  development  of  the 
cells  at  the  deepest  portion  of  the  sac  causes  it  to  expand  and  become 
bulbous ;  this  appearance  gives  rise  to  the  term  hair-bulb. 

From  this  time  onward  the  effort  of  Nature,  as  expressed  in  ingrowth, 
ceases,  and  her  energy  is  directed  toward  the  surface.  The  cells  which 
are  pushed  off  from  the  infant  layer  become  condensed  in  the  central 
portion  of  the  sac — not  into  a  solid  shaft,  but  into  the  cortical  portion 
of  the  hair  surrounding  the  medullary  cavity.  The  hair-bulb  rests  upon 
a  papilla,  y\'\\ich  is  developed  from  the  corium,  and  which  invaginates 
the  deepest  portion  of  the  hair-bulb,  so  that  the  latter  covers  the  sides 
of  the  papilla  in  much  the  same  manner  as  though  a  bell  had  been  let 
down  over  it ;  this  union  serves  to  form  the  attachment  of  the  base  of 
the  hair. 

The  connective-tissue  papillse  have  no  special  signification,  but  come 
and  go  as  the  hairs  are  destroyed  and  new  hairs  develop.  They  are  not 
a  special  product  of  foetal  life,  but  are  developed  all  through  life  as  new^ 
hairs  are  formed,  for  hairs  are  short-lived,  and  are  constantly  being  cast 
off',  and  new  ones  formed  in  their  places.  "NMien  the  hair-bulb  atrophies, 
a  new  bulb  is  sent  down  from  the  remaining  portion  of  the  hair-follicle 
(Fig.  306) ;  this  in  turn  becomes  invaginated  by  a  new  papilla ;  a  new 
liair  is  formed,  which  by  its  upward  growth  pushes  the  old  hair  out. 
Wiien  the  entire  epithelial  portion  of  the  follicle  atrophies,  there  cannot 
arise  a  new  bulb,  and  consequently  the  process  of  future  development 
ceases.  The  hair  papillae  contain  loops  of  capillary  vessels.  The  depth 
to  which  the  follicle  penetrates  into  the  subcutaneous  tissue  is  in  propor- 
tion to  the  size  and  length  of  the  hair,  as  is  also  the  thickness  of  the 
root-sheath.  Larger  hairs  are  set  more  deeply  and  firmly  in  the  under- 
Iving  tissue  than  smaller  ones.  Whether  the  size  of  the  hair  governs 
the  depth  and  firmness  of  its  attachment,  or  the  depth  and  firmness  the 
size  of  the  hair,  I  leave  to  the  reader  to  settle  for  himself  Probably 
Nature  knew  from  the  beginning  just  how  to  build  each  part  so  as  to 
have  it  biest  subserve  the  purpose  for  which  she  intended  it.  Questions 
of  this  kind  are  continually  arising  in  the  mind  of  the  student  in 
Embrvology,  and  especially  is  this  true  in  our  study  of  the  products 
of  the  epiblastic  layer. 

Dci-rlojtnicnt  of  Glands — Sebaceous  Glands. — These  are  a  differentia- 
tion from  the  same  infolding  of  the  epithelial  layer  as  the  hair-follicle, 
and  develop  sinndtaneously  with  it.  In  early  foetal  life  the  sebaceous 
oland  is  much  larger  and  more  prominent  than  the  hair-follicle — so  much 
so  that  the  hair-fi)llicle  is  a])])arently  situated  in  the  mouth  of  the  gland. 
Sflmceous  glands  belong  to  tlie  racemous  type  (like  a  buncli  of  grapes). 
TJK'V  are  developed  l)y  an  infolding  of  the  epithelial  layer,  which 
becomes  involuted,  forming  several  ])ockets  which  open  into  one  com- 
mon duct.  This  duct  finds  outlet  into  the  sheath  of  the  hair-follicle  or 
upon  the  surface  of  the  skin.  The  outer  wall  of  the  gland  is  composed 
of  a  connective-tissue  envelope  formed  from  the  slightly  condensed  sur- 
rounding connective  tissue  of  the  corium.    Inside  this  is  situated  a  layer 


PRODUCTS  OF  THE  EPIBLAST  AND  MESOBLAST. 


561 


of  small  polyhedral  granular  cells  containing  oval  nuclei ;  this  is  the 
continuation  of  the  infant  layer  of  rete  Malpighii.  Very  frequently 
these  cells  are  seen  to  contain  droplets  of  oil.  Their  office  is  to  secrete 
the  oil  which  serves  to  lubricate  the  hair  and  skin.     Inside  this  layer, 


Fig.  307. 


Sebaceous  Gland  and  Hair:  1,  hair-follicle;  2,  simple  gland;  0,  4,  5,  compound  glands. 

and  occupying  the  cavity  of  the  gland,  are  seen  cells  which  have  been 
pushed  off  from  the  outer  layer,  and  which  become  larger  as  they  near 
the  central  portion  of  the  gland.  The  older  cells  pass  through  varying 
stages  of  fatty  degeneration  until  they  are  forced  from  the  mouth  of 
the  gland  as  sebum,  a  substance  holding  in  suspension  minute  oil-glob- 
ule-^.  The  sebaceous  glands  rest  upon  the  erector  papillre  muscles, 
and  are  moved  as  the  hairs  move.  No  doubt  the  action  of  these 
muscles  materially  aids  the  ejection  of  the  contents  of  the  glands ; 
vigorous  brushing  of  the  hair  tends  to  increase  the  flow  of  this  oily 
secretion. 

Siveat- Glands. — The  other  glands  developed  from  the  epithelium  are 
the  tubular  sweat-glands.  Their  development  does  not  differ  materially 
from  that  of  the  sebaceous  glands,  except  that  instead  of  assuming  a  race- 
mous  form  they  curl  or  coil  upon  themselves  at  their  deepest  extremity, 
in  a  very  peculiar  manner,  presenting  the  appearance  of  a  ball  (Fig.  308). 

Vol.  I.— 36 


562 


DENTAL  EMBRYOLOGY  AXD  HISTOLOGY. 


The  epithelial  cells  found  in  sweat-glands  are  polyhedral  or  cuboidal  in 
form.  Their  office,  implied  in  their  name,  is  too  well  known  to  need 
further  explanation. 


Fig.  308. 


^ert  ca  Section  of  the  Skin  of  the  Thumb,  partly  diagrammatic:  o,  stratum  cor>,eum,  traversed  bv 
ducts  of  t\\o  glands;  h,  rete  niucosum,  with  j.roloiigations  extending  between  papilla  beneath; 
between  n  and  /,  is  seen  the  stratum  luci.lum  ;  r,  papillary  layer  of  corium.  Near  the  centre  of 
the  hgure  is  seen  a  i.ictile  corpuscle;  ,1,  reticular  layer  of  c'.rium  with  vascular  plexus  nucleated 
thrconn^ctil^'usMie   '"^'^'^P'*''^*''  '"'  ''""'* ''''  '«"'•  ««eat-glands ;  /,  fat-globules  iu  the  meshes  of 

Derelopmeni  of  the  Enamel  Organ. — The  development  of  this  organ 
differs  but  very  little  from  that  of  the  hair-follicle.  This  is  especially 
true  of  the  enamel  organ  of  the  permanent  molars,  the  cords  for  Avhich 
arise  directly  from  the  epithelial  layer  of  the  mucous  membrane  of  the 


PRODUCTS  OF  THE  EPIBLAST  AND  MESOBLAST. 


563 


mouth.  A  detailed  account  of  the  development  of  the  enamel  organ 
does  not  fall  within  the  province  of  this  section ;  we  will  therefore  con- 
fine ourselves  to  its  simplest  form  of  development  as  seen  in  the  sixth- 
year  molar.  The  cord  for  this  molar  is  said  by  some  to  arise  from  the 
distal  face  of  the  second-year  temporary  molar,  but  I  doubt  the  accuracy 
of  the  statement. 

At  the  point  where  the  cord  for  the  tooth  is  to  arise,  be  it  from  the 
hand  or  directly  from  the  surface  epithelium,  active  cell-multiplication 
is  seen.     The   layer  of  infant 

cells,  by  reason  of  this  cellu-  ^^«-  ^^^• 

lar  activity,  becomes  depressed 
into  the  substance  of  the  sub- 
epithelial tissue  in  the  form 
of  a  blind  pouch.  Fig.  309 — 
which  has  been  so  extensively 
copied  from  Frey's  Histology — 
was  evidently  taken  from  the 
posterior  portion  of  the  jaw, 
and  it  shows  quite  correctly  the 
changes  in  the  form  of  the  cord 
in  the  development  of  one  of 
the  permanent  molars.  I  will 
use  it  here  for  the  illustration 
of  the  point  in  hand. 

The  cells  of  the  infant  layer 
are  not  columnar,  as  shown  in 
the  cut,  but  oval  or  spheroidal 
(as  I  will  take  occasion  to 
show  when  we  come  to  the 
development  of  the  teeth  prop- 
er). This  cut  is  introduced  for 
the  purpose  of  calling  attention 
to  the  errors  of  many  who  have 
written  upon  this  subject. 

The  ingrowing  sac  elongates 
into  a  cord,  thu-;  sinking  more 
deeply  into  the  submucosse. 
(See  Fig.  309, 1 ,  d.)  The  great- 
e.•^t  cellular  activity  is  found  in 
the  deepest  portion  of  the  in- 
growing sac,  as  we  have  seen 
in  the  development  of  hairs 
and  glands.  The  cord  under  the  pressure  of  rapid  cell-multiplication 
becomes  bulbous.  In  turn,  this  bulbous  part  becomes  invaginated  by 
the  upward  growth  of  the  dentinal  papilla  (2,f) — at  first  slightly  (Fig. 
309,  2),  afterward  completely  (Fig.  309,  3).  Presently  it  is  severed 
from  the  epithelium  of  the  mouth  by  the  breaking  up  of  the  neck  of 
the  cord  :  at  the  same  time  there  springs  up  from  around  the  sides 
of  the  enamel  organ  a  connective-tissue  envelope  (3,  /;)  which  is  con- 
nected at  its  base  with  the  dentinal  papilla.     This  grows  up  and  around 


Three  Stages  in  Developing  Enamel-Organ  {^ramma- 
lian). 

1.  n,  dental  ridge ;  r,  infant  layer  of  cells,  here  wrongly 
figured  as  columnar;  il,  cord  for  permanent  molar 
(prohabl)')  as  it  arises  directly  from  the  epithelium 
of  mouth. 

2.  ^,  stellate  reticulum;  /,  dentinal  papilla;  o,  inner 
tunic.  • 

3.  A,  outer  tunic ;  i,  transverse  section  of  vessel ;  k, 
forming  bone. 


564 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 


the  enamel  organ,  enveloping  it  in  very  much  the  same  way  as  the 
hair-bulb  enwraps  the  papillae,  by  forming  a  bell-shaped  cover.  We 
have  now  a  fully-developed  dental  follicle,  the  connective-tissue  envelope 
corresponding  to  the  outer  root-sheath  of  the  hair-fbllicle.  The  layer 
of  epithelial  cells  which  lies  just  inside  the  connective-tissue  envelope 
is  a  continuation  of  the  infant  layer  of  the  rete  Malpighii,  and  the  cells 
have  not,  as  yet,  changed  their  shape,  being  more  or  less  oval,  tending 
somewhat  to  a  cylindrical  form.  They  are  mpst  emphatically  not 
columnar  or  prismatic,  as  has  been  so  often  stated  and  represented  in 
cuts  by  previous  authors.  That  they  do  become  so  later  no  one  can 
doubt,  but  not  until  they  are  ditferentiated  into  a  special  cell  for  a 
special  oflftce ;    and  that  is  the  secretion  of  the  enamel. 

Between  the  walls  of  the  invaginated  enamel  organ  the  older  cells, 
which  have  been  pushed  up  from  the  infant  layer  of  the  rete  Malpighii, 
are  assuming  a  stellate  shape  (Fig.  309,  2,  e),  and  we  find  the  spaces 
between  the  librils  filled  with  a  fluid  which  is  probably  rich  in  proteids. 

Let  us  now  turn  our  attention  to  the  connective-tissue  group,  the 
product  of  the  mesodermic  layer  of  the  blastoderm. 


Development  op  the  Connective-tissue  Group. 

As  before  stated,  connective  tissues  arise  from  the  mesoblastic  layer 
of  the  l)lastoderm.  For  convenience  of  study  we  Mill  consider — 1, 
embryonic  connective  cells  in  their  earliest  stages  of  development;  2, 
fibrillar  connective  tissue;  3,  plasma-cells;  4,  areolar  tissue;  5,  mucous 
tissue ;  0,  blood-corpuscles  and  vessels ;  7,  dentinal  papillae  and  odonto- 
blasts ;  8,  osteoblasts ;  9,  cement  organ. 

Embryovic  Comxedire  Tissue. — The  mesoblastic  layer  of  the  blasto- 
derm in  a  foetal  pig  1  cm.  in  length  is  composed  of  nucleated  bioplasmic 

Fig.  310. 


Porcine  Kmhryo  (2J  cm.  X  250) :  r/,  enil)ryonic  connective  tissue  of  niesoblast. 

bodies,  oval  or  round  in  form.  They  soon  begin  to  assume  a  fibrillated 
appearance,  sending  out  short  processes,  which  may  be  seen  in  the  chick 
at  tliirty  hours  and  in  the  pig  11  cm.  in  length  ;  in  a  pig  2^  cm.  the 
fil)rillated  nature  of  tlie  bioplasmic  bodies  is  more  marked  (F'ig.  310). 


DEVELOPMENT  OF  THE  CONNECTIVE-TISSUE  GROUP.      5G5 


The  processes  are  so  line  that  it  requires  very  high  amplification  to 
demonstrate  them.  The  intercellular  spaces,  filled  with  protoplasm,  are 
large  in  proportion  to  the  number  and  size  of"  the  cells.  As  devel- 
opment progresses  this  order  is  reversed,  and  the  cells  with  their  pro- 
cesses constitute  an  almost  solid  mass  of  tissue.  The  intercellular  /i6y//fa/' 
connective  tissue  is  formed  by  the  separation  of  the  protoplasm  into  very 
fine  fibres.  At  first  these  fibrils  are  few  in  number,  but  gradually 
increase  in  thickness  by  becoming  joined  together  into  bundles,  which 
anastomose  with  other  similar  bundles,  thus  forming  a  dense  network 
of  connecting  fibres.  The  longitudinal  striations  seen  upon  the  bundles 
of  fibres  are  due  to  the  fact  before  stated,  that  these  bundles  are  made 
up  of  primary  elementary  fibrils,  which  by  special  methods  of  technique 
or  staining  may  be  demonstrated.  Variations  in  the  size  of  the  bun- 
dles are  dependent  upon  the  number  of  fibrils  contained  in  them.  They 
are  held  together  by  a  semifluid  cement  substance,  which,  according  to 
Klein,  partakes  of  the  character  of  globulin. 

Fibrous  connective  tissue  forms  the  sheaths  of  muscles,  which  it 
binds  into  bands,  and  is  continuous  at  their  termini  as  tendons,  by 
which  they  are  attached  to  the  osseous  system.  It  also  forms  the  tissue 
of  the  periosteum,  pericementum,  and  the  perichondrium;  it  spreads 
out  into  membranes  and  lines  all  the  serous  cavities ;  forms  the  tissue 
of  the  dermal  and  subdermal  layers;  and  is,  indeed,  an  important  factor 
in  the  formation  of  nearly  all  the  organs  of  the  body.     Very  generally 


Deposition  of  Fat  in  Connective-tissue  Cells  :  /,  a  cell  with  a  few  isolated  fat-droplets  in  its  proto- 
plasin  ;  /',  a  cell  with  a  single  large  and  several  minute  drops ;  /",  fusion  of  two  large  di'ops ;  rj, 
granular  or  plasma  cell,  not  yet  exhibiting  any  fat-deposition;  c  t,  flat  connective-tissue  corpus- 
cle ;  c,  e,  network  of  capillaries. 

distributed  through  the  connective  tissue  are  round  cells,  called  plasma- 
cells.  These  are,  in  all  probability,  migrated  white  blood-corpuscles, 
and  have  been  previously  considered. 

Development  of  Fat  or  Areolar  Tissue. — This  is  formed  by  a  process 
of  infiltration  into  the  substance  of  the  plasma-cells.  At  first  these 
droplets  are  very  small,  but  as  they  accumulate  they  gradually  coalesce 
and  unite  to  form  larger  drops.  By  the  aggregation  and  fusion  of  the 
fat  droplets  the  cell-body  is  entirely  filled,  and  the  nucleus  is  crowded 
to  one  side  of  the  cell ;  a  thin  cell-wall  encloses  the  cell-contents,  and 


'm 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 


thus  we  have  ordinary  connective  tissue  developed  into  areolar  tissue. 
This,  as  we  have  seen  in  the  article  on  Anatomy,  forms  the  principal 
tissue  of  the  derm  and  many  other  portions  of  the  body. 

3Iucous  tis.sue  is  most  typically  shown  in  the  jelly  of  Wharton.  It 
belongs  normally  to  embryonal  life,  and  when  found  in  adult  tissues  is 
pathological  in  character,  and  is  then  called  myxomatous  tissue.  It 
belongs  to  the  connective-tissue  group,  and  is  composed  of  branching 
stellate  cells  lying  in  an  undiiferentiated  protoplasmic  basis-substance. 

Fig.  312. 


Jelly  of  Wharton  :  r,  ramified  cells  intercommunicating  by  tiieir  branches ;  I,  a  row  of  lymph-cells  ; 
/,  fibres  developing  in  the  ground-substance. 

I  introduce  raucous  tissue  here  in  order  to  show  the  distinction 
between  it  and  the  stellate  reticulum  of  the  enamel  organ,  which  we  are 
soon  to  discuss.     Some  have  called  the  latter  myxomatous  tissue. 

Development  of  Bloocl-corjniscles  and  Vessels. — If  we  stain  a  section 
thi'ough  the  mesodermic  layer  of  a  foetal  pig  1  cm.  in  length  very  deeply 
with  hfcmotoxylon,  and  afterward  with  eosin,  it  will  be  seen  that  some  of 
the  cells  are  dark  purple  and  others  bright  red.  In  form  they  are  simi- 
lar, and  it  is  only  by  the  differentiating  action  of  the  stain  that  we  are 
able  to  demonstrate  any  difference  between  them.  In  parts  of  the  section 
these  red  cells  are  indiscriminately  distributed  ;  in  other  portions,  how- 
ever, they  will  be  seen  to  have  arranged  themselves  in  rouleaux  ;  these  are 
the  newly-developed  blood-corpuscles.  The  embryonic  connective-tiseue 
cells  of  the  mesoblast  arrange  themselves  around  the  rows  of  blood-cor- 
puscles, and,  becoming  fil)rillated,  form  the  walls  of  the  capillary  vessels. 

In  an  older  embryo,  2h  cm.  in  length,  the  formation  of  capillary 
vessels  1)V  a  process  of  Inidding  may  be  distinctly  seen  (Fig.  313). 
These  arise  in  solid  bands  of  protoplasm  which  appear  red  in  sections 
stained  with  hsemotoxylon  and  eosin.  The  bands  extend  and  form  a 
network  of  granular  ])rotoplasm.  The  same  process  of  development  of 
new  vessels  may  be  seen  in  granulation-tissue.  The  solid  buds  or  pro- 
cesses become  holloAved  out  by  vncuolation,  and  into  the  tubes  thus 
formed  the  circulation  extends.  The  surrounding  protoplasm  becomes 
liquefied,  and  forms  tho  pla.^ma  in  which  the  corpuscles  float.  The  walls 
are  formed,  as  before  described,  by  the  embryonal  connective-tissue  cells. 


DEVELOPMENT  OF  THE   CONNECTIVE-TISSUE  GROUP.      567 


Fig.  313. 


At  first  they  are  quite  tliin,  but  as  the  tissues  grow  older  muscular  tissue 
is  developed  and  the  walls  of  the  vessels  are  thickened. 

From  the  above  description  it  will  be  seen  that  I  hold  that  the  blood 
is  developed  in  its  first  formation  from  the  embryonic  connective  cells 
of  the  mesoderm.  This  theory 
is  also  advanced  by  Klein  and 
many  others  who  have  written 
upon  the  subject ;  all  very 
generally  agree  in  classifying 
blood-corpuscles  in  the  connec- 
tive group.  Balfour  holds  es- 
sentially the  same  views  in  re- 
gard to  them,  and  locates  their 
origin  in  the  mesoblastic  layer. 
He  considers  that  the  formation 
of  the  protoplasmic  network  or 
bands  precedes  the  formation  of 
true  blood-corpuscles,  and  says  : 
"  In  the  pellucid  area,  where 
the  formation  of  the  blood-ves- 
sels may  be  most  easily  observed, 
a  number  of  mesoblastic  cells  are 
seen  to  send  out  processes  (Fig. 
314).  These  processes  unite, 
and  by  their  union  a  protoplas- 
mic network  is  formed  contain- 
ing nuclei  at  the  points  from 
which  the  processes  started. 
The  nuclei — which,  as  a  rule,  are  much  elongated  and  contain  large  oval 
nucleoli — increase  very  rapidly  by  division,  and  thus  form  groups  of 
nuclei  at  the,  so  to  speak,  nodal  points  of  the  network.  Several  nuclei 
may  also  be  seen  here  and  there  in  the  processes  themselves.  The  net- 
work being  completed,  these  groups  by  continued  division  of  the  nuclei 
increase  rapidly  in  size ;  the  protoplasm  around  them  acquires  a  red  color, 
and  the  whole  mass  breaks  up  into  blood-corpuscles  (Fig.  314,  b.  c).  The 
protoplasm  on  the  outside  of  each  group,  as  well  as  that  of  the  uniting 
processes,  remains  granular,  and  together  with  the  nuclei  in  it  forms  the 
walls  of  the  blood-vessels.  A  plasma  is  secreted  by  the  walls,  and  in 
this  the  blood-corpuscles  float  freely.  Each  nodal  point  is  thus  trans- 
formed into  a  more  or  less  rounded  mass  of  blood-corpuscles  floating  in 
plasma,  but  enveloped  by  a  layer  of  nucleated  protoplasm,  the  several 
groups  being  united  by  strands  of  nucleated  protoplasm.  These  uniting 
strands  rapidly  increase  in  thickness ;  new  processes  are  also  continually 
being  formed ;  and  thus  the  network  is  kept  close  and  thickset,  while 
the  area  is  increasing  in  size.  By  changes  similar  to  those  which  took 
place  in  the  nodal  points  blood-corpuscles  make  their  appearance  in  the 
processes  also,  the  central  portions  of  which  become  at  the  same  time 
liquefied.  By  the  continued  widening  of  the  connecting  processes  and 
solution  of  their  central  portions,  accompanied  by  a  corresponding 
increase  in  the  enveloping  nucleated  cells,   the  original   protoplasmic 


Porcine  Embryo  (2^4  cm.  X  250):  hi.  v.,  developing 
blood-vessel,  breaking  up  of  solid  baud  into  blood- 
corpuscles;  c/,  embryonal  connective  tissue. 


568 


DE^^TAL  EMBRYOLOGY  AND  HISTOLOGY. 


^.  /*=>  ^ 


network  is  converted  into  a  system  of  communicating  tubes,  the  canals 

of  which  contain  blood-corpuscles  and  plasma,  and  the  walls  of  Mhich 

are  formed  of  flattened  nucleated  cells. 

"  The  blood-corpuscles  pass  freely  from  the  nodal  points  into  the  hollow 

processes,  and  thus  the  network  of  protoplasm  becomes  a  net\york  of 

blood-vessels,  the  nuclei  of  the 
Fici.  314.  corpuscles   and  of  the  walls  of 

which  have  been,  by  separate 
paths  of  development,  derived 
fr(jm  the  nuclei  of  the  original 
j)rotoplasm.  The  formation  of 
the  corpuscles  does  not  proceed 
with  equal  rapidity  or  to  the 
same  extent  in  all  parts  of  the 
J^?^-  blastoderm.  By  far  the  greater 
part  are  formed  in  the  vascular 
area,  but  some  arise  in  the  pel- 
lucid area,  especially  in  the  hin- 
der part.  In  the  front  of  the 
pellucid  area  the  processes  are 
longer  and  the  network  accord- 
ingly more  open  ;  the  corpuscles 
also  are  both  later  in  appear- 
ing  and    less    numerous    when 

Surface  View,  from  below,  of  a  small  portion  of  the  lormetl. 

postirior  end   of  the  pellucid  area  of  a   thirty-six  Assumino-     fhc     trutll     of     the 

hours'   chick    (to   illustrate    the  formation   ol    the  ^S^UmiUg     lilt  ^  ^^"^^V       "^     ,    '^ 

Mood-capillaries  and   blood-vessels,   magnitied    vm  abovC  aCCOUUt,  it  IS  CVldcnt    that 

diameters):  7(.  <■.,  blood  corpuscles  at  a  nodal  point,  ^,       ,  ,        n                i        !•  xl             11 

already  beginning  to  acquire  a  red  color:  they  are  tllC   Ulood-VeSSClS  01    tllC  VOllv-SaC 

enclosed  in  a  layer  of  protoplasm   in  the  outermost  o  ,  i       ,.],  •    1,  .1 ,,  ,,  „^.  „„•    „  ."l^  m-,„f.pc 

part  of  which   are   found  nuclei,  a.    These  nuclei  Ol  lUe  CUlClv  GO  1101  ariSe  dS  SpdCCh 

subsequently  become  ^he  'uiciei  of  the  cei>s  lorni-       channels  between  the  adjacent 

ing  the  walls  of  the  vessels.     1  he  nodal  points  are  J 

unitedbvprotoplasmieprocesses;-.^^)-.,  also  contain-     cclls    01    the    niCSoblaSt,     DUt    are 
iiig  nuclei  with  large  nucleoli  (Ji).  i      ii  i  .     •        .1 

*  hollowed  out  in  tlie  communi- 

cating protoplasmic  substance  of  the  cells  themselves.  The  larger  ves- 
sels of  the  trunk,  however,  are  probably  formed  as  spaces  between  the 
cells,  much  as  in  the  case  of  the  heart. 

Tliere  yet  remain  to  be  considered  in  this  connection  the  dentinal 
pai)ill«e,  cement  organ,  odontoblasts,  osteoblasts,  and  cementoblasts. 

Devi'inid  J^ipiUa. — This  im])ortant  organ  is  developed  from  the 
embryonic  connective  tissue  of  the  mcsoblast  under  the  influence  of  the 
in'^-rowing  enamel  organ.  We  have  seen  in  our  study  of  developing 
hair  that  ])apilla^  are  developed  wherever  and  whenever  a  hair-bulb  is 
found  growing  into  the  connective  tissue,  whether  in  embryonic  or 
adult  life,  and  that  u])on  this  process  depends  the  reproduction  of  hair 
that  has  fallen  out.  Now,  I  consider  the  dentinal  pa])illfe  to  be  a  sim- 
ilar differentiatidii  of  the  ordinary  connective  tissue.  They  originate  at 
any  period  in  life,  from  the  development  of  the  first- formed  temporary 
teeth  to  that  of  the  wisdom  tooth  or  third  molar  of  the  permanent  set. 
In  the  li'dit  of  our  study  of  the  analogous  formation  of  the  hair-papillse, 
I  do  not  think  it  rational  to  believe  that  there  is  b,  papilkiry  layer,  sheet 
of  denthial  t'mue,  or  semilunar  area. 


DEVELOPMEST  OF  THE  CONNECTIVE-TISSUE  GROUP.      569 

No  difference  can  be  demonstrated  histologically  between  the  cells  of 
the  papillae  and  the  snrrounding  embryonic  connective-tissue  cells  of  the 
jaw.  Again,  it  is  not  to  be  presumed  that  this  dentinal  sheet  i)ersists 
until  all  the  dentinal  papillae  for  the  permanent  teeth  are  formed  ;  on 
the  contrary,  when  the  time  for  the  development  of  such  papilla  arrives, 
they  are  formed  from  the  ordinary  connective  tissue  found  in  contact  with 
the  cord  of  the  enamel  organ,  and  at  any  point  or  depth  to  Mhich  it 
reaches. 

The  cord  does  not  penetrate  the  mesoblastic  layer  searching  for  a 
papilla  already  formed  or  for  a  dentinal  sheet,  but,  like  the  solid 
ingrowth  which  forms  the  hair,  it  has  the  power  to  superintend  the 
ditiereutiation  of  a  papilla  for  itself.  The  enamel  organ  is  a  specialized 
tissue  which  superintends  tlie  formation  of  the  papilla  and  shapes  the 
pulp,  and  consequently  the  tooth  ;  in  a  word,  it  is  the  tirst  essential 
element  in  tooth-formation,  the  papilla  occupying  a  secondary  position. 

The  first  indication  of  the  development  of  the  pa])ill?e  varies  so  much 
in  the  sev^eral  teeth,  even  in  the  same  jaw,  that  no  set  rule  can  be  laid 
down.  It  is  safe  to  say,  however,  that  when  the  ingrowing  cords 
become  bulbous  the  time  is  ripe  for  their  appearance. 

The  papilla  is  first  seen  as  a  condensation  of  the  connective  tissue 
outside  and  in  juxtaposition  with  the  deepest  point  of  the  bulbous  cord. 
By  its  growth  in  a  direction  opposite  to  the  enamel  organ  of  the  tooth 
it  causes  this  organ  to  invaginate  itself,  after  which  there  is  differen- 
tiated from  the  surrounding  connective  tissue,  on  all  sides  of  the  bell- 
shaped  enamel  organ,  a  follicular  wall  which  is  connected  with  the 
papilla  at  its  base.  This  is  the  cement  organ,  in  connection  with  which 
cementoblasts  are  foUnd  underlying  this  fibrous  connective-tissue  layer, 
the  future  pericementum. 

Cementoblasts  are  analogous  to  osteoblasts ;  in  fact,  they  are  osteo- 
blasts which  have  received  the  additional  name  of  cementoblasts.  Per- 
sonally, I  would  prefer  to  call  them  by  their  original  name  but  for  the 
fact  that  we  have  adopted  the  name  cement  for  the  osseous  covering  of 
the  roots  of  teeth. 

Osteoblasts  are  specialized  cells  belonging  to  the  connective-tissue 
group,  and  the  probable  nature  of  their  origin  will  be  discussed  in  the 
section  on  Ossification. 

Upon  the  surface  of  the  dentinal  papilla,  at  a  period  which  precedes 
the  formation  of  dentine,  a  layer  of  cells  may  be  seen  ;  these  are  termed 
odontoblasts.  They  are  developed  from  the  ordinary  connective-tissue 
cells  of  the  papilla.  Their  differentiation  can  be  studied  by  following 
the  side  of  the  papilla  from  its  base  to  its  apex  in  a  specimen  which 
shows  the  beginning  of  the  process  of  dentinification. 

At  the  base  they  are  generally  spheroidal  or  oval  in  form,  but  higher 
up  on  the  sides  of  the  papilla  they  are  somewhat  cylindrical,  while  at 
the  apex  they  are  columnar.  They  are  sometimes  connected  with  the 
tissue  of  the  papilla  by  slender  processes. 

On  the  side  of  the  forming  dentine  they  have  one  or  more  processes 
called  dentinal  fibrils,  which  penetrate  the  forming  dentine  and  superin- 
tend its  arrangement  into  tubules,  the  centre  of  which  they  occupy  as 
the  organic  part  of  the  dentine.     In  some  instances  these  fibrils  pene- 


570  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

trate  the  intercellular  spaces  of  the  cementoblastic  layer,  and  dentine  is 
formed  around  the  terminal  fibrils,  causing  an  interdigitation  of  the 
dentinal  tubules  and  the  enamel-prisms.  This  interpenetration  precedes 
the  process  of  calcification  of  the  enamel. 

This  now  brings  us  to  the  consideration  of  the  subject  of  calcification, 
which  rightly  precedes  the  study  of  both  amelification  and  ossification. 

Calcification. 

"  Calcification  is  the  process  of  change  into  a  stony  substance  contain- 
ing much  lime,  as  in  the  formation  of  the  teeth  "  (R,  Owen).  In  the 
light  of  the  present  status  of  scientific  investigation  I  would  change  the 
above  definition  as  follows :  Calcification  is  that  process  by  which  (organic) 
tissues  become  hardened  by  deposition  of  salts  of  calcium  in  their  inter- 
cellular substance,  as  exemplified  in  the  formation  of  bones  and  teeth. 

The  intercellular  substance  found  in  organic  tissues  is  fluid,  and  into 
this  fluid  minute  particles  of  lime  salts,  in  such  fine  subdivision  as  not 
to  be  demonstrated  by  even  the  highest  powers  of  the  microscope,  are 
deposited  in  regular  systems  after  the  several  forms  of  calcified  tissues. 
This  arrangement  is  superintended  by  specialized  cells  for  each  particular 
structure — osteoblasts  for  bone,  odontoblasts  for  dentine,  etc.  These  cells 
secrete  lime  salts  and  deposit  them  in  the  intercellular  substance. 

All  cells  lie  embedded  in,  or  are  bathed  by,  a  fluid  which  is  more  or 
less  gelatinous  in  consistency.  It  is  from  this  surrounding  medium  that 
the  cells  derive  the  supply  of  nom-ishment  necessary  for  the  performance 
of  their  functions.  Cells  are  capable  of  cellular  activity  in  proportion 
to  the  amount  of  cell-pabulum  this  fluid  contains.  I  do  not  say  that 
cells  are  active  according  to  the  amount  of  food-supply  present,  but  that 
they  are  capable  of  putting  on  cellular  activity  just  in  proportion  to  the 
amount  of  cell-food  at  hand,  and  in  this  way  are  stimulated  to  increased 
functional  activity.  Bricks  cannot  be  made  without  straw,  neither  can 
tissues  present  increased  functional  powers  without  plenty  of  food  with 
which  to  nourish  themselves.  The  presence  of  an  intercellular  substance 
is  of  essential  importance  in  the  develoimient  of  tissues.  In  embryonic 
life  the  quantity  of  cell-pabulum  is  very  marked.  It  is  at  this  period 
that  calcification  begins  in  two  forms — ossification  and  amelification; 
the  first  under  the  superintendency  of  the  connective-tissue  group  of  cells, 
and  the  second  a  product  of  the  epithelium. 

Connective  tissue  is  develojied  from  the  mesoblast,  while  the  epithe- 
lium is  produced  from  the  ejiiblast.  In  our  former  studies  we  found  a 
wide  difference  between  the  tissues  of  the  two  layers,  and  we  shall  find 
a  yet  wider  difference  between  their  ]iroducts. 

Under  the  calcified  products  of  the  connective-tissue  group  we  w^ill 
consider  bone,  cement,  and  dentine ;  under  the  calcified  products  of 
epithelial  tissues,  enamel,  shells,  etc. 

The  essential  difference  between  the  two  depends  npon  the  matrix, 
and  the  manner  in  whicii  the  lime  salts  are  deposited,  rather  than  upon 
the  character  of  the  cells  Avhich  govern  the  deposition.  The  general 
appearance  of  cells  is  dependent,  to  a  very  considerable  extent,  on  the 
matrix  in  which  they  lie,  yet  an  epithelial  cell,  while  presenting  varia- 


CALCIFICATION.  571 

tions,  is  nevertheless  always  epithelial  in  its  nature,  and  so  are  its  prod- 
ucts. The  same  is  true  in  regard  to  the  connective-tissue  group  :  an 
interchange  between  the  two  tissues  is  not  known  in  all  the  domain  of 
normal  or  pathological  histology,  neither  can  this  interchange  occur 
between  the  products  of  the  two  tissues.  Those  who  hold  that  the 
enamel  is  a  differentiation  of  a  dentinal  basis-substance  have  not  com- 
prehended the  subject  in  all  its  bearings.  Enamel  is  no  more  modified 
bone  than  is  the  shell  of  the  mollusk. 

Enamel  and  shells  are  analogous  structures,  and  are  secreted  by  the 
epithelium  upon,  and  not  in,  the  substance  of  tissues.  The  shell  of  the 
snail  is  secreted  upon  its  surface,  and  the  lime  salts  form  a  semi-crystal- 
lized mass.  Enamel  is  secreted  by  the  ameloblasts  upon  the  already 
formed  layer  of  dentine,  there  being  no  basis-substance  between  the 
layer  of  ameloblasts  and  the  formed  layer  of  dentine,  and,  as  in  the 
ease  of  the  shell,  the  lime  salts  crystallize — not,  howev^er,  into  true 
crystals.  Shells  and  enamel  are  identical  except  in  their  mineral  con- 
stituents. Enamel  is  nothing  more  or  less  than  a  coat  of  mail,  and  as 
such  best  serves  the  processes  of  nature. 

As  we  have  seen  in  our  study  of  developing  epithelium,  there  is  little 
or  no  intercellular  substance  above  tlie  infant  layer  of  cells.  In  the 
development  of  nails  the  hornification  occurs,  not  in  the  infant  layer, 
but  in  the  older  layer,  or  "  stratum  granulosum"  of  other  writers.  So 
in  the  deposit  of  enamel  the  lime  salts  are  secreted  (shed  out)  by  the 
cells  of  the  infant  layer — not  in  the  infant  layer,  where  the  greatest 
amount  of  intercellular  substance  is  found,  but  upon  the  xnider  sur- 
face of  the  infant  layer — upon  an  already  formed  layer  of  dentine. 
These  cells  have  become  altered  in  form  and  specially  endowed  with 
functional  power.  This  point  "will  be  considered  in  presenting  the 
subject  of  the  development  of  the  ameloblasts. 

We  have  seen,  when  treating  of  the  development  of  connective  tissue, 
that  the  proportion  of  intercellular  substance  largely  preponderates  over 
the  cells  themselves.  Into  this  intercellular  substance  the  calcified 
products  of  the  connective-tissue  group  are  deposited. 

Connective  tissues  are  divided  into  three  great  classes:  (1)  fibrous 
connective  tissue ;  (2)  cartilage ;  and  (3)  bone,  in  which  claijs  dentine  is 
included.  Each  of  these  is  subdivided  into  several  varieties,  as  Mill 
appear  farther  on,  but  in  all  instances  the  ground  substa7ice,  matrix,  or 
intercellular  substance  is  to  be  distinguished  from  the  cells  themselves. 

In  the  fibrous  connective  tissue  the  matrix  yields  gelatin,  and  the  cells 
are  called  connective-tissue  corpuscles.  In  cartilage  the  ground  substance 
yields  chondrin,  and  the  cells  are  called  cartilage-cells.  In  the  third 
group  the  ground  substance  contains  inorganic  lime  salts,  and  the 
cells  are  termed  hone-celh. 

"  The  matrix  of  osseous  substance  is  a  dense  fibrous  connective  tissue 
— i.  e.  a  substance  yielding  gelatin  on  boiling.  The  cement  substance 
between  the  fibrils  is  petrified,  owing  to  a  deposit  of  insoluble  lime  salts, 
chiefly  carbonates  and  phosphates.  These  can  be  dissolved  out  by  strong 
acids  (as  hydrochloric),  and  thereby  converted  into  soluble  salts.  Thus 
the  organic  matrix  (Fig.  315)  of  osseous  substance,  called  ossein,  may  be 
obtained  as  a  soft,  flexible  material  easily  cut "  (Klein). 


572  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

The  ossein  mentioned  above  is  the  calco-globulin  of  Mr.  Rainey.     It 
is  evident  that  the  basis-substance  left  after  decalcifying  bone  has  changed 

its  nature,  and  no  longer  presents  the 
characteristics  of  the  intercellular  sub- 
stance in  which  the  lime  salts  were  de- 
posited. 

The  intercellular  substance  is  com- 
posed of  protoplasm.  In  life  this  con- 
tains, besides  the  albuminoids,  a  living 
principle  which  permits  it  to  modify  its 
Ibrm  and  perform  functions.  Just  M'hat 
this  principle  is  we  have  never,  by  chem- 
istry, been  able  to  determine,  for  by  the 

Appeuiuceot  MitiiY  lelt  iitei  He  a  citi-  i,cp\,f  flip  rp-nrpnt  whioli  WP  pmnlov  to 
citionb\H(l  Osseous, L imcii e  oblong  "^'^^  'J^  ^'■^^  iLdgcni  wiucn  w e  employ  lO 
br  uched  I  one  1  icun  t  and  tauaiicuii    demonstrate  its  molccular  constituency 

between  tueui.  ,  ,         ,.     .  .       .    ,  N 

we  destroy  the  livnig  prniciple,  and 
have  left  only  the  material  substance  which  held  the  active  principle  in 
bounds.  Chemical  analysis  shows  protoplasm  to  be  composed  of  pro- 
teids,  in  which  are  held  in  suspension  carbohydrates  and  fats.  These 
substances  are  undoubtedly  formed  from  protoplasm  by  the  action  of 
the  living  matter  of  the  cell.  We  also  find  in  different  parts  of  the 
body  several  varieties  of  substances  derived  from  the  above-mentioned 
constituents  of  protoplasm — gelatin,  mucin,  etc. 

Under  the  direction  of  the  vital  principle  found  in  living  protoplasm 
— viz.  cells — the  lime  salts  are  deposited  in  forms  peculiar  to  each 
tissue.  Lime  salts,  however,  may  crystallize  trifhouf  the  body,  but  the 
form  of  the  structure  in  the  body  depends  upon  the  superintendency  of 
specialized  cells.  Tubular  bone  or  dentine  is  deposited  by  odontoblasts, 
and  calcospherules  of  bone  by  osteoblasts.  These  cells  do  not  exert 
any  other  influence  upon  the  depositing  structure  than  that  of  shaping 
it  accordmg  to  certain  prescribed  and  prearranged  forms.  They  are,  in 
fact,  but  the  moulds  which  shape  the  accumulating  mass.  Where  lime 
salts  are  deposited  in  albumen  or  any  other  gelatinous  material  there 
appears  no  definite  form  other  than  that  naturally  assumed  by  the 
particular  lime  salt  when  undergoing  crystallization. 

Renal  calculi  are  in  all  probability  formed  by  the  deposition  of  lime 
salt  in  a  matrix  of  mucus,  for  similar  calculi  can  be  formed  artificially 
outside  the  body.  "  The  chemical  sid)stances  to  be  employed  in  the  pro- 
duction of  the  artificial  calculi,"  says  Mr.  Rainey,  "■  are  a  soluble  com- 
pound of  lime  and  carbonate  of  potash  or  soda  dissolved  in  separate 
portions  of  water,  and  some  viscid  vegetable  or  animal  substance,  such 
as  gum  or  albumen,  mixed  with  each  of  these  solutions.  The  mechani- 
cal conditions  required  to  act  in  conjunction  with  the  chemical  means  are 
the  presence  of  such  a  quantity  of  the  viscid  material  in  each  solution  as 
will  be  sufficient  to  make  two  solutions,  when  mixed  together,  of  about 
tlu!  same  density  as  that  of  the  nascent  carbonate  of  lime,  and  a  state  of 
perfect  rest  in  the  fluid  in  which  the  decomposition  is  going  on,  so  that 
the  newly-formed  com])ound  may  be  interfered  with  as  little  as  possible 
in  its  subsidence  to  the  sides  and  bottom  of  the  vessel.  This  will 
require  two  or  three  weeks  or  longei",  according  to  the  size  and  com- 


CALCIFICATION.  573 

pleteness  of  the  calculi.  But  I  have  not  found  that  they  increase  at 
all  after  six  weeks." 

Mr.  Rainey  has  by  many  and  thoroughly  scientific  tests  proven  the 
analogy  between  his  artificial  calculi  and  those  formed  in  the  body. 
The  lime  salts  are  deposited  in  both  cases  in  a  gelatinous  matrix,  but 
without  the  forming  influence  of  the  specialized  cells  which  we  find  in 
true  calcification.  The  difference  between  crystallization  outside  of  the 
body  and  crystallization  within  it  is  due  to  the  action  of  the  specially- 
endowed  cells  which  superintend  the  deposition  of  the  lime  salts. 

The  lime  salts  which  are  deposited  in  the  intercellular  substance  enter 
into  some  chemical  combination  with  the  protoplasm  which  composes 
this  intercellular  substance,  the  nature  of  which  is  not  known  ;  but  it 
is  not  due  to  any  special  action  of  the  living  protoplasm,  as  such,  for 
we  find  the  same  apparent  characteristics  shown  where  lime  salts  are 
thrown  down  in  albumen  or  mucilage.  The  product  thus  obtained  is 
insoluble  in  acids  :  a  portion  or  all  of  the  lime  salts  will  be  given  up, 
but  the  matrix  will  remain. 

On  this  subject  INIr.  Tomes  has  written  as  follows :  "  The  insoluble 
salts  of  lime  are  altered  in  their  behavior  by  association  Avith  organic 
compounds — a  fact  which  was  first  ]>ointed  out  by  Rainey  and  has 
been  more  recently  worked  out  by  Professor  Hasting  and  Dr.  Ord. 
If  a  soluble  salt  of  lime  be  slowly  mixed  with  another  solution 
capable  of  precipitating  the  lime,  the  resultant  lime  salt  will  go  down 
as  an  amorphous  powder,  or,  luider  some  circumstances,  in  minute 
crystals.  But  in  the  presence  of  gelatin,  albumen,  and  many  other 
organic  compounds  the  form  and  physical  character  of  the  lime  salts 
are  materially  altered,  and  in  the  place  of  an  amorphous  powder  there 
are  found  various  curious  but  definite  forms  quite  unlike  the  character 
of  crystals  produced  without  the  intervention  of  the  organic  substance. 
Mr.  Rainey  found  that  if  calcium  carbonate  be  slowly  formed  in  a  thick 
solution  of  mucilage  of  albumen,  the  resultant  salt  is  in  the  form  of 
globules,  laminated  in  structure,  so  that  the  globules  may  be  likened  to 
tiny  onions,  these  globules,  when  in  contact,  becoming  agglomerated 
into  a  single  laminated  mass,  it  ajipearing  as  if  the  laminse  in  immediate 
apposition  blended  with  one  another.  Globular  masses,  at  one  time  of 
mulberry-like  form,  lose  the  individuality  of  their  constituent  smaller 
globules,  and  become  smoothed  down  into  a  single  mass  ;  and  Mr. 
Rainey  suggests  as  an  explanation  of  the  laminated  structure  that  the 
smaller  masses  have  accumulated  in  concentric  layers  which  have  sub- 
sequently coalesced ;  and  in  the  substitution  of  the  globular  for  the 
amorphous  or  crystalline  form  in  the  salt  of  lime  when  in  contact  with 
various  organic  substances  Mr.  Rainey  claimed  to  find  the  clue  for  the 
explanation  of  the  development  of  shells,  teeth,  and  bone.  At  this 
point  Professor  Hasting  took  up  the  investigation,  and  found  that  other 
salts  of  lime  would  behave  in  a  similar  manner,  and  that  by  modifying 
the  condition  of  the  experiment  very  various  forms  might  be  produced. 
But  the  most  important  addition  to  our  knowledge  made  by  Professor 
Hasting  lay  in  the  very  peculiar  constitution  of  the  '  calcos])herites,'  by 
which  name  he  designated  the  globular  forms  seen  and  described  by 
Rainey.     That  these  are  built  up  of  concentric  lamina9  like  an  onion 


574  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

has  already  been  mentioned,  and  Mr.  Rainey  was  aware  that  albumen 
actually  entered  into  the  composition  of  the  globule,  since  it  retained 
its  form  even  after  the  application  of  acid.  But  Professor  Hasting  has 
shown  that  the  albumen  left  behind  after  treatment  of  a  calcospherite 
with  acid  is  no  longer  ordinary  albumen  :  it  is  profoundly  modified, 
and  has  become  exceedingly  resistant  to  the  action  of  acids,  alkalies, 
and  boiling  water,  and  in  fact  resembles  chitine,  the  substance  of  which 
the  hard  skin  of  insects  consists,  rather  than  any  other  body.  For  this 
modified  albumen  he  proposes  the  name  of '  calcoglobulin,'  as  it  appears 
that  the  lime  is  held  in  some  sort  of  chemical  combination,  for  the  last 
traces  of  lime  are  retained  very  obstinately  when  calcoglobulin  is  sub- 
mitted to  the  action  of  acids.  The  '■  calcospherite,'  then,  has  a  true 
matrix  of  calcoglobulin,  which  is  capable  of  retaining  its  form  and 
structure  after  the  removal  of  the  great  bulk  of  the  lime.  Now,  it  is 
a  very  suggestive  fact  that  in  the  investigation  of  calcification  Ave  con- 
stantly meet  with  structures  remarkable  for  this  indestructibility  ;  for 
example,  if  we  destroy  the  dentine  by  the  action  of  very  strong  acids  or 
by  variously-contrived  processes  of  decalcification,  putrefaction,  etc., 
there  remains  behind  a  tangled  mass  of  tubes,  the  '  dentinal  sheaths '  of 
Neumann,  which  are  really  the  immediate  walls  of  the  dentinal  tubes. 
Or  if  bone  be  disintegrated  by  certain  methods,  there  remain  behind 
large  tubes  found  to  be  the  linings  of  the  Haversian  canals  (Kolliker), 
and  small  rounded  bodies  recognizable  as  isolated  lacunte  ;  and  in  the 
culicula  dentis  Ave  have  another  excellent  example  of  this  peculiarly 
indestructible  tissue.  In  point  of  fact,  as  will  be  better  seen  after  devel- 
opment of  the  dental  tissue  has  been  more  fully  described,  on  the  border- 
land of  calcification,  between  the  completed,  fully-calcified  tissue  and  the 
formative  matrix,  as  yet  unimpregnated  with  lime,  there  very  constantly 
exists  a  stratum  of  tissue  which  in  its  physical  and  chemical  properties 
very  much  resembles  calcoglobulin." 

It  should  also  be  noted  that  globular,  spherical  forms  are  constantly 
to  be  seen  at  the  edges  of  the  thin  cap  of  forming  dentine,  and  may 
be  also  traced  in  and  around  the  interglobular  sj^aces.  Moreover, 
isolated  spherules  of  lime  salt  have  been  described  by  Messrs.  Robin 
and  INIagitot  as  occurring  abundantly  in  young  pulps  of  human  teeth, 
as  well  as  those  in  Herbivora,  where  their  presence  was  noted  by  Henle. 
This  brings  us  to  the  consideration  of  the  first  division  of  calcified 
products — viz.  bone. 

Ossification. 

By  ofiftifionfinn  we  mean  the  deposition,  under  the  superintcndency 
of  the  osteoblasts,  of  the  salts  of  calcium  into  the  intercellular  proto- 
plasmic basis-substance. 

Bone  is  simply  an  aggregation  of  calcospherules.  These  are  at  first 
thrown  out  or  secreted  as  a  thin  covering  around  the  osteoblasts.  The 
specialized  coll,  at  the  time  when  it  assumes  the  office  of  bone-builder, 
is  at  its  highest  state  of  development  as  regards  functional  activity,  and 
has  also  attained  its  greatest  magnitude.  From  the  formation  of  the 
first  layer  of  bone  the  cells  begin  to  decrease  in  size,  and  they  continue 


OSSIFICATION.  5/5 

to  lessen  until  the  typal  demands  of  each  spherule  are  reached,  when  the 
process  ceases.  The  wall  of  the  calcospherule  is  thickened  at  the  expense 
of  the  size  of  the  osteoblast  itself;  so  that  the  bone-cell — which  is  really 
the  encased  osteoblast — is  perceptibly  smaller  than  the  original  osteoblast. 

Osteoblasts  are  round  or  oval  bodies  varying  considerably  in  diameter. 
They  are  not  fibrillated,  and  in  this  respect  correspond  to  plasma-cells. 
They  lie  in  actual  contact  with  one  another,  and  as  ossification  proceeds 
the  points  of  contact  draw  out  into  fine  fibres.  Salts  of  calcium  are 
deposited  in  the  protoplasm  which  bathes  the  osteoblasts  and  have  their 
location  in  the  meshes  of  these  fibres. 

In  intermembranous  ossification  of  the  skull-cap  and  subperiosteal 
development  of  bone  the  osteoblasts -are  arranged  in  layers  in  the  sub- 
stance of  the  fibrous  membranes  or  underneath  them,  and  the  deposit 
of  lime  is  along  the  fibres,  giving  them  an  opaque,  granular  appearance. 
The  deposition  begins  on  one  side  of  the  line  of  osteoblasts,  and  pre- 
sents as  many  indentations  as  there  are  osteoblasts  in  line. 

The  crescentic  nature  of  the  first  part  of  the  layer  secreted  by  the 
osteoblasts  is  plainly  shown  when  they  (the  osteoblasts)  are  displaced  or 
where  thev  are  considerably  shrunken.  As  the  process  of  secretion 
proceeds  the  osteoblast  becomes  enclosed  in  a  thin  spherule  of  formed 
material,  designated  by  Mr.  Rainey  as  mlcoglobulln.  This  shell  of 
bone  is  pierced  here  and  there  by  the  fibres  of  the  osteoblast  which  are 
left^  as  the  osteoblast  shrinks.  The  deposition  of  bone  is  really  in  the 
meshes  of  these  fibres. 

The  body  of  the  cell  is  spheroidal,  hence  the  deposition  assumes  a 
spheroidal  form ;  accordingly,  we  denominate  it  a  calcosphende. 

As  the  process  of  secretion  goes  on  depositing  from  the  circumfer- 
ence toward  the  centre  the  fine  processes  before  mentioned  continue  to 
be  united  with  the  osteoblasts.  Their  terminal  fibrillre  anastomose  with 
those  of  other  osteoblasts,  and  these  again  with  others ;  those  which  lie 
nearest  the  capillary  vessels  connect  with  them,  thereby  receiving  nour- 
ishment, which  they  in  turn  give  to  the  outer  layer  of  bone-cells. 
The  office  of  these  processes,  then,  is  to  supply  the  nutrient  matter 
needed  to  support  life  in  the  bone-cells. 

Bone-cells  are  nothing  more  or  less  than  encapsuled  osteoblasts  which 
are  occupying  the  homes  which  they  have  builded  themselves.  The 
cavities  which  they  occupy  are  the  lacunce  of  the  old  writers ;  the  canals 
in  which  their  processes  lie  are  the  canalicuU,  and  the  capillary  vessels 
the  Haversian  system.  These  lacunae  and  their  canaliculi,  together  with 
the  Haversian  canals,  are  occupied  in  living  bone  by  the  above-described 
organic  element. 

If  we  dry  a  portion  of  the  shaft  of  a  long  bone — by  which  process 
we  destroy  the  organic  element — and  afterward  saw  oif  small  sections 
and  o-rind  them  quite  thin,  then  mount  them  in  hard  balsam  so  that 
the  spaces  will  not  become  penetrated  by  the  balsam,  but  remain  filled 
with  air,  we  may  observe  the  following  arrangement :  larger  or 
smaller  canals  (Haversian),  around  which  are  arranged,  concentrically, 
oval  spaces  (lacunae),  from  which  radiate  numerous  fine  canals  (canal- 
iculi), w^iich  connect  with  other  similar  canals,  and  these  in  turn  with 
the  Haversian  canals. 


57G 


DENTAL   EMBRYOLOGY  AND  HISTOLOGY. 


Now,  if  we  had  taken  a  portion  of  the  same  bone,  when  fresh,  and 
placed  it  in  dikite  picric  acid  and  decalcified  it,  afterward  cutting  thin 
sections  and  staining  them  with  picrocarmine,  we  should  not  have  seen 
the  cavities  which  we  observed  in  the  section  of  dried  bone ;  for  while 
by  the  process  of  drying  we  destroyed  the  contents  of  the  cavities,  by 
the  use  of  the  picric  acid  we  preserved  their  contents. 

In  lacunae  we  find  bone-cells  ;  in  canaliculi,  processes  of  bone-cells ; 
in  Haversian  canals,  capillary  vessels. 

By  studying  sections  prepared  according  to  the  methods  above  de- 
scribed, we  are  able  to  understand  the  real  formation  of  bone.  It  is 
needless  to  remark  that  our  present  knowledge  of  bone-formation  is  the 
result  of  the  accumulated  research  and  careful  observation  of  scientists 
for  many  generations. 

The  general  misuse  of  the  terms  lacunce,  canaliculi,  and  Haversian 
canals  attests  the  need  of  a  more  thorough  understanding  of  the  pro- 
cess of  bone-formation.  A  brief  recapitulation  of  the  more  important 
points  may  make  the  subject  clearer  to  the  reader. 

The  osteoblasts  do  not  become  calcified,  but  remain  as  the  life-occu- 
pants of  the  calcospherules,  and  by  reason  of  such  occupancy  make  it 
possible  for  us  to  produce,  by  drying,  the  cavities  known  as  lacunse. 
Calcification  is  a  process  of  secretion  around,  and  not  in,  the  cell.  The 
mollusk  secretes  upon,  and  not  in,  its  body,  and  the  secreted  portion  of 
its  shell  does  not  contain  organic  tissue.  The  only  living  matter 
found  therein  is  the  body  of  the  mollusk,  which  we  can  extract  and  yet 

Fig.  316. 


%,:mix% 


-•-*vi  -MWX/ 


m 


-.^  "\> 


Transverse  Section  of  Compact  Tissue  (of  Humerus).  (Magnified  about  l.iO  diameters )  Three  of 
the  Haversian  canals  are  seen,  with  their  concentric  rings;  also  the  lacunte,  with  the  canaliculi 
pxtendinp;  from  them  across  the  direction  of  the  laniellre.  The  Haversian  apertures  had  become 
filled  with  air  and  dfbris  in  Rrindinj,' down  tlic  section,  and  therefore  appear  bhick  in  the  figure, 
wliich  represents  the  object  as  viewed  with  transmitted  light. 

leave  the  shell  as  perfect  a  shell  as  before  the  death  of  its  occupant. 
We  do  not  think  of  attributing  to  the  ."^hell  the  possibility  even  of  such 
a  thing  as  an   inflammatory  process,  for  the  reason  that  the  shell  is 


OSSIFICATION. 


577 


Fig.  317. 


composed  of  material  unsusceptible  of  any  change  except  that  of  disin- 
tegration. The  mollusk  may  add  to  its  shell  internally,  but  it  nuist 
necessarily  be  at  the  expense  of  the  size  of  its  own  body.  And  so  it  is 
with  the  osteoblasts:  they  are  arranged  in  close  proximity — so  close 
that  the  first  secreted  calcospherule  jt)ins  that  of  a  neighboring  sj)he- 
rule,  and  by  this  juxtaposition  and  coalescence  solid  bone  is  formed. 

Fracture  of  the  shell  may  also  be  repaired  by  the  same  cells  .which 
in  the  first  place  secreted  the  shell. 

The  area  of  tissue  supplied  by  a  capillary  vessel  at  the  beginning  of 
the  process  of  calcification  marks  the  limit  of  the  Haversian  system. 
The  osteoblasts  are  arranged  around  the 
outer  portion  of  this  area,  antl  the  first- 
formed  layer  of  calcospherules  consti- 
tutes the  periphery  of  the  Haversian 
system  ;  the  next-formed  layer  of  sphe- 
rules lies  inside  the  first-formed  layer, 
thereby  lessening  the  space  occupied  by 
the  capillary  vessels ;  the  third  layer  is 
still  inside  the  second ;  and  so  on  centrip- 
etally,  until  the  several  layers  almost 
entirely  fill  the  space  (Fig.  316).  The 
remaining  space  is  occupied  by  the  vas- 
cular antl  lymphatic  system,  and  no  less 
an  authority  than  »Schaefer  claims  the 
presence  of  nerves  (Fig.  317). 

In  the  centripetal  manner  of  develo})- 
ment  I  see  a  wise  design  on  the  part  of 
Nature  to  limit  the  space  occupied  by  the 
calcospherules  and  mark  the  outline  of 
the  Haversian  system.  This  centrijietal 
arrangement  lessens  the  calil)re  of  the 
vessels,  but  yet  allows  them  abundant 
capacity  to  carry  sufficient  cell-pabulum  to  keep  alive  the  enclosed 
organic  tissue. 

Thus  is  cellular  activity  made  self-limiting  and  a  beautiful  and  sym- 
metrical object  conformed  to  its  purpose  brought  into  being.  Were  the 
j)rocess  of  bone-formation  centrifugal,  we  should  be  more  likely  to  find 
abnormalities  and  distortions. 

This  brings  us  to  the  consideration  of  the  several  forms  in  which 
bone  is  developed.  We  have  seen  how  the  calcospherules  are  built  and 
bv  their  aggregation  made  into  compact  bony  tissues,  and  it  now  remains 
to  discuss  the  several  different  forms  they  assume  under  the  government 
of  pre-existing  tissues  which  modify  their  arrangement. 

Nearly  every  author  gives  a  different  interpretation  of  the  existing 
classifications.  Upon  tjiose  known  as  intracartilaginous  and  subperi- 
osteal they  generally  agree,  but  there  seems  to  be  considerable  difficulty 
in  harmonizing  their  views  upon  the  third  class — viz.  intramembranous. 
This,  as  I  shall  try  to  show,  grows  out  of  the  fact  that  this  classification 
is  made  to  cover  too  nuich  ground. 

Dr.  T.  Mitchel  Prudden  describes  this  form  of  ossification  as  occur- 
VoL.  I.— 37 


Section  of  a  Haversian  Canal,  showinR 
its  contents  (highly  magnified) :  n,  small 
arterial  capillary  vessel ;  v,  large  ven- 
ous capillary;  ».,  pale  nerve-flbi'es  cut 
acioss;  /,  cleft-like  lymphatic  vessel: 
one  of  the  cells  forming  its  wall  com- 
municates by  fine  branches  with  the 
branches  of  a  bone-corpuscle.  The  sub- 
stance in  which  the  vessels  run  is  con- 
nective tissue  with  ramified  cells ;  its 
finely  granular  appearance  is  probably 
due  to  the  cross-section  of  fine  fibrils. 
The  caiiMl  is  surrounded  by  several  con- 
centric lamellie. 


578 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 


Fig.  318. 


ring  "  in  the  substance  of  pre-existing  fibrillar  connective-tissue  mem- 
branes," and  cites  the  skull-cap  as  a  typical  example.  He  classifies 
subperiosteal  development  separately. 

l)r.  Carjjenter  says :  "  The  intermembranous  fijrm  of  ossification  prin- 
cipally occurs  in  the  flat  bones  of  the  head,  and  is  also  the  mode  by 
which  long  bones  increase  in  girth."  It  will  be  seen  from  the  above 
that  Dr.  Carpenter  considers  intermembranous  and  subperiosteal  forma- 
tions of  bone  under  one  head. 

Klein  recognizes  two  classes — enchondral  and  periosteal,  or  inter- 
membranous— and  says  :  "All  the  bones  of  the  limbs  and  of  the  verte- 
bral cohunn,  the  sternum  and  the  ribs,  and  the  bones  forming  the  base 
of  the  skull,  are  preformed  in  the  early  embryo  as  solid  hyaline  carti- 
lage covered  with  a  membrane  identical  in  structure  and  function  with 
the  periosteum,  which   at  a  later  period   it   becomes.     The  tegmental 

bones  of  the  skull,  the  l)ones 
of  the  face,  with  the  lower  jaw, 
except  the  angle,  are  not  pre- 
formed at  all.  Only  a  mem- 
brane identical  with  the  future 
periosteum  is  present,  and  un- 
derneath and  from  this  bone  is 
gradually  deposited."  Under 
the  division  intermembranous 
he  further  says  :  "  All  bones  not 
preformed  in  the  embryo  as 
cartilage  are  developed  directly 
from  the  periosteum  in  the 
manner  of  periosteal  bone  just 
described." 

The  accompanying  cut  is 
here  reproduced  as  the  only 
one  pul)lished — at  least,  so  far 
as  I  am  aware — that  has  any 
reference  to  maxillary  ossifica- 
tion. It  is  evidently  taken 
from  a  quite  mature  foetus,  as 
osteoclasts  are  figured,  and  they 
do  not  make  theii"  appearance  in  the  jaws  until  very  near  birth,  at  which 
time  a  jieriosteum  has  been  difierentiated  and  subperiosteal  bone-forma- 
tion is  in  active  progress  ;  this  is  also  the  case  in  all  the  bones  of  the 
body,  the  maxillje  being  no  exception  to  the  rule. 

Dr.  Shakespeare,^  in  speaking  of  intramembranous  development  of 
bone,  says  :  "  The  intermembranous  formation  of  bone  is  analogous  to 
the  development  of  bone  from  the  periosteum.  For  instance,  the  bones 
of  the  cranium  have  their  origin  in  a  fibrous  membrane  which  soon  })re- 
sents  a  division  into  two  layers  similar  l)()th  in  structure  and  function  to 
the  outer  and  iimer  layers  of  the  periosteum." 

Schaefer^  makes  only  two  divisions — intercartilaginous  and  intermem- 
branous.    He  says :  "  Sometimes  the  bone  is  preceded  by  cartilage, 
'  Allen's -l?»o<om2/.  '  ^  See  Schaefer's /f/s/o/or/?/. 


A  Small  >rass  of  Bone-substance  in  the  Periosteum  of 
Lower  Jaw  of  a  Human  Fa'tus:  a,  osteogenetic  lay- 
er of  periosteum  ;  //,  multinucleated  giaut-cells,  niy- 
eloplexes.  The  one  in  the  niicldle  (jf  the  ujtper  mar- 
gin is  an  osteoclast,  whereas  I  he  smaller  one  to  the 
left  upper  corner  appears  concerned  in  the  forma- 
tion of  hone.  Above  (e)  the  osteoblast-cells  become 
surrounded  by  osseous  substance,  and  thus  become 
converted  into  bone  cells. 


OSSIFICATION. 


579 


Fig.  319. 


Usteoblasts  Irom  the  Parietal  Bone  of  a  Human 
Embryo  thirteen  weeks  old:  «,  bony  septa,  with 
the  cells  of  the  lacunte,  or  bone-corpuscles:  6, 
layers  of  osteoblasts;  c,  the  latter  in  transition 
to  bone-corpuscles  (very  high  power). 


which  first  of  all  becomes  calcified,  and  thi.s  is  invaded,  and  for  the 
most  part  removed,  bv  an  embryonic  tissue  which  deposits  bony  matter 
in  the  interior  of  the  cartilage,  whilst  at  the  same  time  lavers  of  bone 
are  being  formed  outside,  under- 
neath the  periosteum.  This  is  in- 
fercartilaginous  or  enchondral  ossi- 
fication. Sometimes  the  bone  is 
not  preceded  by  cartilage,  and  then 
the  only  process  which  occurs  is  one 
corresponding  to  subperio.'^teal  ossi- 
fication of  the  former  variety.  The 
ossification  is  then  known  as  intra- 
memhrcmous."  From  the  above  it 
is  .seen  that  this  author  makes  in- 
tramembranous  and  subpcrio.steal 
bone-formation  analogous  except 
as  regards  position. 

Gray  makes  two  main  divis- 
ion.s — intracartilaginous  and  in- 
tramembranous — and  places  sub- 
periosteal as  a  subdivision  of  the  second.  As  an  example  of  the 
first,  he  cites  the  "  long  bones  ;"  of  the  second,  the  "  cranial  bones  " — 
viz.  the  occipital  as  far  as  it  enters  into  the  formation  of  the  vault 
of  the  skull,  the  parietal  and  frontal  bones,  the  squamous  portion  of 
the  temporal  with  the  tympanic  ring,  the  Wormian  bones,  the  nasal, 
lachrymal,  malar,  palate,  upper  and  lower  maxillary,  and  vomer ;  also, 
apparently,  the  internal  pterygoid  and  the  sphenoidal  turbinated 
bones.  "  The  intramembranous  o.ssification,"  he  further  .'savs  when 
discussing  that  division,  "  is  that  by  which  the  bones  of  the  vortex 
of  the  skull  are  entirely  formed.  In  the  bones  which  are  so  devel- 
oped no  cartilaginous  mould  precedes  the  appearance  of  the  bone-tis.sue. 
The  process,  though  pointed  out  originally  by  Dr.  Nesbitt  in  the  vear 
178(>,  was  fir,st  accurately  described  by  Dr.  Sharpey,  and  it  does  not 
appear  that  subsequent  observers  have  been  able  to  add  anvthing  essen- 
tial to  his  description.  This  is  substantially  as  follows  :  In  the  mem- 
brane, which  occupies  the  place  of  the  future  bone  a  little  network  of 
bony  spiculse  is  at  first  noticed,  radiating  from  the  point  of  ossification. 
When  these  rays  of  growing  bone  are  examined  by  the  microscope, 
there  is  found  a  network  of  fine  clean  fibres  (osteogenetic  fibres),  which 
become  dark  and  granular  from  calcification,  and  as  thev  calcify  thev 
are  found  to  enclo.se  in  their  interior  large  granular  corpuscles,  or  osteo- 
blasts. These  corpuscles  at  first  lie  upon  the  o.steogenetic  fibres,  so  that 
the  corpuscles  must  be  removed  by  bru.shing  the  specimen  with  a  hair 
pencil  in  order  to  render  the  fibres  clear,  but  they  graduallv  sink  into 
the  areolae  developed  among  the  fibres.  The  areolae  appear  to  be  the 
rudiments  of  the  lacunae,  the  pa,ssages  between  the  fibres  form  the 
canaliculi,  and  the  osteoblasts  are  the  rudiments  of  the  bone-cells." 
This,  with  slight  modification,  is  a  very  good  description  of  intramem- 
branous ossification  as  .'^een  in  the  parietal  bones  of  the  skull-cap,  but 
does  not  an.swer  for  the  maxillae,  as  we  will  see  later  on. 


580 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 


Fig.  320. 


From  the  above  quotations  I  think  I  am  justified  in  saying  that 
all  agree  regarding  the  manner  and  method  of  intracartilaginous  and 
subperiosteal  bone-formation,  and  intramembranous  also,  in  so  far  as 
it  refers  to  the  parietal  Umes ;  but,  judging  from  the  paucity  of  illus- 
trations and  literature  treating  directly  upon  the  formation  of  the 
remainder  of  the  group  not  preformed  in  cartilage,  I  conclude  that 
there  has  been  less  investigation  of  this  than  of  kindred  subjects. 

From  my  own  studies  in  bone-formation,  I  am  convinced  that  we 
need  all  the  classifications  made  by  previous  writers,  and  that  still 
another  is  essential  to  a  clear  understanding  of  ossified  products,  I 
shall  therefore  make  a  fourth  class,  which  I  term  intcj:stiti(d.  In  our 
future  study  of  bone,  then,  we  shall  have  to  consider  four  ways  in  which 
it  may  be  developed :  I.  In  the  substance  of  the  embryonal  connective 
tissue  of  such  bones  as  are  not  preformed  in  cartilage ;  found  in  maxil- 
lary ossification  :  interditicd  (my  own  classification).  II.  In  pre-existing 
membranes,  as  in  the  skull-caj)  :  intramembranous.  III.  Underneath 
the  periosteum,  as  in  the  cortical  portion  of  long  bones  :  subperiosfeal. 
IV.  In  pre-existing  cartilage,  as  in  the  head  of  the  fenuir :  intracarti- 
laginous. 

I.  Interstitial  Formation  of  Bone. — I  introduce  this  term  for  the  ear- 
liest development  of  bone,  believing  that  it  is  needed.  The  term  intra- 
membranous, while  applying  to  the  manner  of  development  in  the 
parietal   and   some    others  of  the    flat    bones,   does    not  apply  to  the 

maxillae  and  bones  of  that  class. 
I  am  more  convinced  of  the  ne- 
cessity of  such  a  division  of  the 
intramembranous  group  than  of 
the  need  of  making  a  distinction 
between  the  latter  and  subperios- 
teal bone-formation.  At  best,  in- 
tramembranous ossification  occu- 
pies only  a  transitory  stage,  and 
gradually  passes  into  subperiosteal 
by  the  ditferentiation  of  the  peri- 
osteum ;  and  I  think  a  careful  con- 
sideration of  the  subject  will  so 
convince  the  reader. 

In  the  microscopic  investigation 
of  early  embryonic  life  (pig  2|-  cm., 
and  human  2  mo. ;  see  cut)  cells  are 
seen  grou])ed  together  here  and 
there  in  the  central  portions  of 
both  the  inferior  and  the  superior 
maxillfe,  which  have  taken  the 
stain  in  such  a  manner  as  to  call 
attention  to  their  apjicarance ;  in 
other  words,  they  have  been  differ- 
entiated by  the  staining  process.  ITnder  low  ))()wers  thev  do  not  difler 
in  f  )rm  iVoin  the  suridunding  cells,  but  under  high  amplification  they 
show  no  processes  as  do  the  ordinary  connective-tissue  cells  even  at 


Inferior  Maxilla  rortiiic  iMiibryo  {2]4  cm.  X 
210):  o,  osteoblasts  t;'"oui)e(l  together,  siirrouiid- 
ed  by  embryonal  connective  tissue,  cl. 


OSSIFICA  TIOX.  581 

this  age.  They  differ  in  more  than  mere  appearance,  however,  as  is 
evidenced  by  their  different  chemical  action  when  .subjected  to  the  stain- 
ing process,  when  they  take  on  a  darker  shade  than  other  cells. 

tStainiuf/  is  not  tiiKjeiiu/ ;  it  is  a  chemical  reaction  exerted  by  the 
separate  tissues  upon  certain  dyes,  by  reason  of  which  we  obtain  differ- 
ent colors  in  sections  which  contain  one  or  more  tissues  or  cells  which 
have  different  chemical  reactions,  as  in  the  case  in  hand.  The  darker- 
stained  cells  are  osteoblasts  {bone-builders)  (Fig.  321).     They  are  found 

Fig.  321. 


Porciue  Embryo  {n  cm.  long  X  2.50) :  a,  osteoblasts  situated  at  the  ends  of  the  lamellse  of  bone;  (^6, 
developing  lamella  of  bone  containing  bone-cells;  cl,  cl,  embryonal  connective  tissue. 

near  the  central  portion  of  the  jaw,  which,  though  composed  of  the 
mesoblast,  is  surrounded  by  the  epiblastic  layer.  .There  is  as  yet  no 
indication  of  a  condensation  of  the  connective  tissue  into  a  membrane 
such  as  we  find  when  ossification  fir.st  commences  in  the  skull-cap.  A 
few  osteoblasts — independent  of  the  influence  of  either  membrane  or 
periosteum — arrange  themselves  in  groups  here  and  there.  These 
groups  are  the  points  of  os.sification  (Fig.  320,  o),  and  from  them  the 
process  extends  as  the  jaAv  develops. 

At  fir.st  these  specialized  cells  are  grouped  together  in  a  double  layer, 
but  later  they  mav  be  seen  at  the  termini  of  the  trabeculfe — which  are 
already  in  a  somewhat  advanced  stage  of  calcification — where  they 
appear  to  be  a  continuation  of  the  process  of  bone-formation  (Fig.  321, 
o) ;  or,  to  use  a  simple  illu.stration,  they  are  the  fully-equipped  work- 
men (the  osteoblasts)  waiting  for  material  (lime  salt.s)  with  which  to 
begin  the  work  of  bone-building. 

Under  the  superintendency  of  the  osteoblasts,  a  crescentic  layer  of  true 
bone  is  deposited  upon  the  side  of  the  osteoblast  in  appo.^ition  with  a 
similar  crescentic  laver  formed  by  an  osteol)last  located  on  the  opposite 
side  of  the  line.     The   sides  of  each    crescent  join   similar   crescents 


582 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 


Fig.  322. 


C.SD 


formed  by  fellow-workmen  on  either  side.  As  deposition  progresses 
the  osteoblast  beeomes  encircled  by  a  shell  of  lime.  As  the  trabecula 
widens  by  enclosing  the  osteoblasts  which  lie  upon  its  sides  new  layers 
of  osteoblasts  are  found  arranging  themselves  on  the  walls,  which  in 
turn  become  enclosed  in  a  layer  of  bone.  Thus,  by  the  accumulation 
of  successive  layers  of  calcospherules,  the  broadening  of  the  bands  of 
bone-tissue  is  accomplished.  As  the  osteoblasts  build  themselves  into 
the  wall  their  places  are  taken  by  fresh  recruits.  AVhen  each  osteoblast, 
by  seci'cting  its  calcospherule,  completes  its  life-work  as  a  bone- 
builder,  it  becomes  a  bone-ail,  and  from  that  time  on  occupies  the 
house  it  has  builded.    (See  Fig.  322.) 

The  maxillary  bones,  including  the  alveolar  processes,  are  thus  pre- 
formed in  provisional  bone.     The  fo'tal  jaw  is  as  truly  the  antetype  of 

the  mature  jaw  as  the  fcetal 
head  of  the  femur,  wliich  is 
preformed  in  cartilage,  is  the 
j)attern  or  matrix-former  of 
the  mature  femur.  This  is 
so  even  in  the  very  early 
stages  of  its  development. 
The  alveolar  walls  surround 
the  microscopic  follicle  and 
present  the  same  ragged  ap- 
pearance when  the  overly- 
ing mucous  membrane  is  re- 
moved that  we  see  later  in 
mature  tissue.  The  maxil- 
lary bones  cannot  be  said  to 
have  any  special  poinU  of 
ossification,  as  do  other 
bones :  development  is  gen- 
eral. The  fact  that  the  al- 
veolar processes  have  not  theii"  analogue  in  form  in  any  other  portion 
of  the  body,  strongly  |)oints  to  the  correctness  of  my  views  regarding 
their  special   manner  of  development. 

The  first-form(>d  bone  is  removed  by  internal  resorption,  which  is 
concomitant  with  the  external  growth  by  regular  methods,  which  we 
sliall   now  describe. 

After  the  formation  of  the  pcriosti'um  two  other  classes  of  bone- 
development  occur — viz.  iiiir<nii('iiihf(iiioi(.s  and  .sKhjx'rioKfcaL  The  essen- 
tial point  of  ditference  between  the  two  is  found  in  the  location  of  the 
embryonal  j^lates  of  i)one.  Itdramembranous  development,  as  such  per 
fie,  belongs  entirely  to  fetal  life,  and  is  found  in  its  most  typical  form  in 
the  development  of  the  skull-caj) ;  here  it  has  reference  only  to  the  first- 
formed  i)one,  wliich  wc  have  befijre  said  is  provisional  in  character,  the 
growth  which  takes  place  after  birth  being  subjx'riosteal  in  its  nature. 
And  so  it  is  in  regard  to  i)ifersfif!(i/  development  :  the  cortical  substance 
of  the  mature  jaw  is  developed  underneath  the  periosteum.  Indeed,  we 
may  say  that  all  bone-fi)rmation  is  provisional  until  such  time  as  the 
bones  have  nearly  reached  the  typal  demands  of  nature,  for  of  those 


Human  Foetus,  2  months  (y  250) :  o,  ostef)t)lasts  (the  dark 
lines  which  come  to  the  edge  of  the  fi^'uie  at  h  represent 
l)an<ls  of  forming  l)one  i ;  r.  x/i.,  calcospherule  surrounding 
an  osleolilast ;  ct,  embryonal  connective  tissue. 


OSSIFICATION. 


583 


first  developed  not  a  trace  will  remain  in  the  fully-formed  bone.  The 
space  occupied  by  bone  in  the  foetal  jaw  will  be  nerve-canal  in  the 
mature  jaw  ;  of  the  later  products  of  calcification — say  after  birth — at 
least  some  will  be  found  in  the  fully-formed  jaw. 

In  placing  the  division-line  between  provisional  and  permanent  bone- 
formation  at  birth  I  do  not  wish  to  lay  down  any  arbitrary  rule.  I 
simply  desire  to  illustrate  as  clearly  as  I  am  able  to  do  so  my  meaning, 
and  impart  to  the  mind  of  the  reader  some  tangible  point  from  which 
to  reason.  Regarding  bone  developed  prior  to  birth,  I  think  it  is  per- 
fectly safe  to  say  that  not  a  trace  will  be  found  in  mature  bone.  In 
making  this  statement  I  do  not  lose  sight  of  the  fact  that  adult  tissues 
are  continually  being  reprodu(;ed.  I  speak  only  of  the  form,  not  of  the 
integral  constituents  of  the  formed  material.  Xevertheless,  if  there  is 
any  stability  in  tissues,  it  .surely  will  be  found  in  the  inorganic  formed 
material  of  bones. 

II.  IntrcuneinhrdnoHs  Formation  of  Bone. — We  \yill  now  consider  the 
second  division  of  our  classification — viz.  intrainenibra)Lom  development 
of  bone.  Prior  to  the  apj)earance  of  the  first  layers  of  bone  (pig  4  cm.) 
there  is  seen  a  condensation  of  the  connective  tissue  innnediately  under- 
neath the  epithelial  layer.  There  has  not  as  yet  been  any  attempt  on 
the  part  of  nature  to  differentiate  what  may  properly  be  termed  skin. 
The  epiljlast  is  composed  of  only  one  or  two  layers  of  epithelial  cells. 
The  condensed  layer  underneath  is  the  first  trace  of  the  future  peri- 

FiG.  323. 


Part  of  the  Growing  Edge  of  the  Developing  Parietid  l^one  of  a  Foetal  Cat  (1^  inch  long):  .sp,  bony 
spicules,  with  some  of  the  osteoblasts  embedded  in  them,  producing  the  lacunae;  o/,  osteogenic 
fibres  prolonging  the  spicules,  with  osteoblasts  (out)  between  them  and  applied  to  them. 

osteum.     There  is  as  yet    no    indication   of  perio.steum    in  the  jaws. 
Nature  hastens  ossification  in   the  skull-caj)    in    order  to  protect  the 


584 


DENTAL   EMBRYOLOGY  AND  HISTOLOGY 


delicate  tissues    of  the  brain-substance,   which  is  being   ditFerentiated 
even  at  this  early  period. 

If  a  piece  of  the  skull-cap  of  a  ftetal  cat  (Fig.  323),  one  and  a  half 
inches  in  length,  which  lias  been  hardened,  be  cut  out  and  divided  into 
its  several  layers,  and  examined  with  the  microscope,  thin  plates  of  bone 
will  be  seen;  these  can  be  rubbed  with  a  stiff  brush  until  they  are  thin 
enough  to  be  examined  by  high  powers.  If  the  })lates  have  l)een  pre- 
viously stained,  a  very  nice  specimen  can  thus  be  obtained.  But  for  the 
best  understanding  of  the  manner  of  development  we  take  the  parietal 
bone — say  of  a  five  months  old  human  foetus — and  decalcify  it  and  cut 
sections;  upon  examination,  lamellae,  or  plates  of  lione,  will  appear  in 
the  now  well-defined  fibrous  periosteum.  These  eml)ryonal  jilates  are 
situated   in  the  substance  of  the  periosteum   in   such  a  manner  as  to 

Fig.  324. 


m'^'-^(^^ 


Transverse  Section  of  a  Bone  (ulna).  (Magnified  20  diameters.)  The  openings  of  the  Haversi.in 
canals  are  .seen  encircled  by  concentric  lamellae.  Other  lamelke  run  parallel  with  the  surface, 
forming  the  cortical  layer. 

form  connecting  cavities  which  locate  blood-vessels  and  marrow -ti.-;sue. 
The  deposition  of  lime  salts  is  controlled  l)y  the  osteoblasts,  as  in  inter- 
stitial bone-formation.  These  lamellae  of  provisional  bone  are  so 
located  as  to  divide  the  fibrous  layer  into  two  sejiarate  layers :  from  the 
onter,  periosteum  is  formed  ;  and  from  the  inner,  the  (ha-a  mater  probably 
arises.  That  the.'^e  ])lates  of  bone  are  only  temporary  is  evidenced  even 
at  this  time,  for  side  by  side  with  the  osteol)lasts  are  found  o.steoclasts 
(bone-de.stroyers),  the  two  proces.-^es  going  hand  in  hand.  The  wall  is 
being  taken  down  as  fast  as  it  is  built  and  carried  farther  out,  so  as  to 
give  more  space  for  the  rapidly-growing  brain. 


OSSIFICATION. 


585 


III.  tSub-periosteal  Bone-fon nation. — As  the  name  implies,  this  form 
of  development  takes  place  underneath  the  periosteum,  and  is,  of  neces- 
sity, a  later  product  tlian  interstitial  development.  We  have  seen  that 
repair  of  bone  after  caries  is  generally  due  to  this  mode  of  growth. 

The  vascular  supply  for  the  nourishment  of  bones  is  largely  located 
in  the  periosteum.  Small  branches  of  the  larger  trunks  of  vessels, 
which  are  found  in  tlie  periosteum,  penetrate  the  cortical  portion  and 
form  anastomosing  loops  with  other  branches  which  are  found  in  the 
marrow-cavity.  It  is  thus  that  Haversian  canals  are  formed  at  right 
angles  to  the  surface  of  the  bone,  and  are  seen  to  radiate  toM'ard  the 

Fig.  325. 


Section  of  Phalangeal  Bone  of  Human  Fcetus,  5  months  (magnified  about  7o  diameters) :  o-,  the  cartilage- 
cells  iu  the  centre,  midway  between  the  epiphyses,  are  enlarfjed  and  separated  from  one  another 
by  a  dark-looking  calcified  matrix  ;  im,  layer  of  bone  deposited  underneath  the  periosteum  ;  «, 
layer  of  osteoblasts  by  which  the  layer  has  been  formed.  Some  ol  the  osteoblasts  are  already 
embedded  in  the  new  bone  as  bone-cells  in  the  lacuna.  The  cartilage-cells  are  becoming  enlarged 
and  flattened,  and  are  arranged  in  rows  above  and  below  the  calcified  centre.  At  the  ends  of  the 
cartilage  the  cells  are  small,  and  the  groups  are  irregularly  arranged  ;  the  cartilaginous  heads  are 
surrounded  by  perichondrium. 

centre   like  the  .spokes  of  a  wheel,  following  no  regular   cour.se,  but 

winding  here  and  there,  sometimes  crossing  and  recrossing  one  anotiier. 

In  the  shaft  of  a  lono:  bone  the  Haversian  svstems  follow  the  line  of 


586 


DENTAL   EMBRYoLOdY  AND   HISTOLOGY 


the  axis  of  tlu"  bone,  tlie  invgular  arraugciiu'iit    beiiit;-  must  gciuTally 
fouiul   near  the  ends  of  the  bone. 

Subperiosteal   bone-formation  does  not  begin  evenly  alono-  the  suriaee 


Fig.  326. 


Longitudinal  Section  through  the  Upper 
lliilf  of  the  necalcific'd  numerus  of  a 
Fdtal  Shet'i),  -'^  seen  under  a  niagnify- 
iiij;  iKiWcriif  about  :il)  dianifters  :  ;c,  tlie 
pari  (if  tlie  shall  which  was  jiriuiarily 
ussilifd  in  cartihige;  wliat  remains  of 
tile  piiiuary  bone  is  represented  a.s 
dark,  enveloped  by  the  clear  secondary 
deposit.  The  areohe  of  the  bone  are 
occupied  l)y  end)ryonic  marrow  with 
u.sleoblasts,  and  blood-vessels  variously 
cut,  represented  as  dark  lines.  One 
long  straight  vessel  (bv)  passes  in  ad- 
vance of  the  line  of  ossification  far 
into  the  cartilaginous  head;  nuist  of 
the  others  loop  round  close  to  the  car- 
tilage. At  one  or  two  places  in  the 
older  parts  t)f  the  hone  elongated  grouj)S 
of  cartilage-cells  (ci  may  still  be  seen, 
which  have  escaj)ed  absorption.  im, 
the  part  of  the  bone  that  has  been 
ossilicd  in  membrane — that  is  to  say,  in 
the  osteoblastic  tissue  under  the  peri- 
osteum. It  is  well  marked  otl'  iVoni 
tlie  central  jiortion,  and  is  bounded, 
perijiherally,  by  a  jagged  edge,  the  pro- 
jections of  which  are  indistinctly  seen 
to  be  prolonged  by  bunches  of  o.steo- 
genic  fibres.  A  row  of  osteoblasts 
covei's  the  su]H'rticial  layer  of  the  bone. 
The  subjieriosteal  layer  is  prolonged 
above  into  the  thickening  (/<),  which 
encroaches  u)ion  the  cartilage  of  the 
head  of  the  bone,  and  in  which  are 
seen,  amongst  numerous  osteoblasts 
and  a  few  blood-vessels,  tlie  straight 
longitudinal  osteogenic  fibres  (<</),  ami 
some  other  fibres  { pf)  cro.ssing  them, 
and  perhaps  representing  fibres  of 
Sharpey.  The  calcareous  salts  having 
been  removed  by  an  acid,  the  granular 
o.ssific  deposit  i)assing  up  between  the 
rows  of  cartilage-cells  is  not  seen  In 
this  specimen  ;  it  would  have  extended 
as  far  as  a  line  joining  the  marks  X  X. 
Observe  the  general  tendency  of  the 
osseous  trahecuUe  and  the  vascular 
channels  between  them  to  radiate  from 
the  original  centre  of  (issilication.  This 
is  found  to  prevail  more  or  less  in  all 
bones  when  tliey  are  fir^t  formed, 
although  the  direction  of  the  tiabecula; 
may  afterward  become  modified  in  re- 
lation with  varying  physiological  con- 
ditions, and  espi'cially  as  the  result  of 
pressure  in  ditlerent  directions. 


underneath  the  periosteum,  but  at  certain  points  which  are  governed  by 
tlie  location  of  a  cai)illary  blood -ves.sel.  At  fir.st  lamelLie  are  develo])ed 
at  riij;ht  anuies  to  the  jieriosteum  ;  the  first-formed  layer  is  pitted  and 
uneven,  but   as  the   jjroccss  extends  the  bone  becomes  more  compact, 


OSSIFICA  Tioy.  587 

until  a  smooth  .surface  is  formed.  From  this  time  on,  even  through 
the  process  of  resorption  and  rebuilding,  the  surface  is  nearly  always 
found  to  be  smooth.  Tlie  Haversian  systems  themselves  almost  entirely 
disappear  in  the  cortical  portion  of  long  bones,  the  tinal  deposition 
being  from  layers  of  osteoblasts  which  are  found  directly  under- 
neath the  periosteum.  Thus  a  dense  cortical  bone  is  formed  which 
gives  strength  to  the  bony  columns  (Fig.  324,  a). 

In  some  instances  the  penetrating  fibres  of  the  periosteum  are  found 
in  this  cortical  portion.  These  may  persist  for  a  longer  or  shorter  time 
as  such,  and  are  known  as  Sharpey's  fibres  (Fig.  7,  p.  41,  Sec.  on 
Anatomy).  A  similar  arrangement  is  seen  at  the  point  of  tendinous 
attachment  for  muscles. 

IV.  Intercartilaginous  Development  of  Bone. — As  early  as  the  fifth 
day  in  the  chick  and  in  1  cm.  foetal  pigs  certain  bones  are  found  preformed 
in  cartilage — viz.  tlie  bones  of  the  skeleton,  occipital,  sphenoid,  ethmoid, 
nasal,  etc.  It  will  be  found  that  these  cartilaginous  formations  bear  a 
very  close  resemblance  to  the  bones  which  will  replace  tiiem  ;  they  are 
the  matrix-formers  which  serve  as  the  antetypes  of  the  mature  tissues. 
This  is  shown  very  nicely  in  Fig.  325  ;  here  the  epiphyses  are  similar 
in  form  to  the  mature  articulating  heads  of  the  phalangeal  bone.  The 
cartilaginous  heads  are  only  separated  by  the  zone  of  ossification.  If 
tlie  section  had  been  made  through  the  same  phalanx,  before  develop- 
ment had  progressed  quite  so  flir,  the  heads  would  have  been  seen  to  be 
in  apposition. 

The  increase  in  length  of  the  bone  is  by  the  development  of  the  shaft:, 
the  heads  being  pushed  lengthwise  in  either  direction.  The  first  percep- 
tible change  is  seen  about  the  middle  of  the  })halanx.  The  cartilage- 
cells  are  enlarged  at  the  expense  of  the  intercellular  hyaline  basement- 
substance,  which  latter  is  becoming  finely  granular  in  appearance,  due 
to  infiltration  of  minute  granules  of  lime  salts.  This  change  in  the 
character  of  the  cartilage-cells  can  be  seen  extending  a  considerable  dis- 
tance from  the  borderland  of  calcification.  The  cells  have  arranged 
themselves  into  rows  on  a  line  with  the  axis  of  the  shaft,  gradually 
diminishing  in  size  from  the  enlarged  cells  in  the  ossification  zone,  to 
their  normal  size  as  found  in  the  unchanged  heads.  The  capillary 
blood-vessels  push  their  way  into  the  calcifying  cartilage,  or,  what  is 
more  probable,  the  penetration  of  the  capillaries  antedates  the  change 
in  the  cartilage.  This  arrangement  is  very  nicely  shown  at  bv  in  Fig. 
326,  where  a  blood-vessel  has  burrowed  its  way  into  the  very  centre 
of  the  cartilaginous  head. 

The  zone  of  calcification  which  has  been  figured  so  extensively  as 
occurring  in  the  central  portion  of  the  head,  and  which  some  authors 
claim  is  independent  of  the  action  of  the  blood-vessels,  I  have  proven 
— to  my  satisfaction,  at  least — to  be  none  other  than  a  zone  of  calcifica- 
tion located  around  the  terminal  loop  of  one  of  these  vessels. 

Sometimes  vessels  may  be  seen  to  enter  the  head  of  the  cartilage  from 
the  sides  as  well  as  from  the  marrow-cavity,  and  wherever  they  penetrate 
we  find  alterations  in  the  character  of  the  cartilage-cells.  These  changes 
are  chiefly  confined  to  the  arrangement  and  deposition  of  lime  salts  in 
the  basement  substance. 


588 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 


Prudden  says : '  "If  we  exaniint-  the  cartilage  at  a  considerable  distance 
from  the  line  of  ossification,  we  find  the  ordinary  appearance  of 
hvaline  cartilage  with  more  or  less  flattened  cells.  Approaching 
now  the  zone  of  ossification,  we    find  that    the    cells  are    larger,   are 


Fig.  327. 


Section  of  Part  of  one  of  the  Limb- 
bones  of  a  Foetal  Cat,  at  a  more  ad- 
vanced Stage  of  Ossification  than  is 
represented  in  Fig.  ;?2!i,  and  somewhat 
more  higlily  magnified.  The  calcifi- 
cation of  the  cartilage  matrix  has 
advanced  from  the  centre,  and  is  ex- 
tending between  the  groups  of  car- 
tilage-cells, which  are  arranged  in 
characteristic  rows.  The  subperiosteal 
bony  deposit  {im)  has  extended  imri 
passu  with  the  calcification  of  the 
cartilage  matrix.  The  cartilage-cells 
in  the  primary  areote  are  mostly 
slirunken  and  stellate;  in  some  cases 
they  have  dropped  out  of  the  space. 
At  //•  and  in  two  other  places  an  ir- 
ruption of  the  subperiosteal  tissue, 
composed  of  ramified  cells  with  osteo- 
blasts and  growing  bliKid-vessels,  Inis 
penetrated  the  subperiosteal  bony 
crust,  and  has  begun  to  excavate  the 
secondary  areolie  or  medullary  spaces ; 
;;,  fibrous  layer  of  the  periosteum;  o, 
layer  of  osteoblasts :  some  of  them  are 
embedded  in  the  os.seous  layer  as 
bone-corpuscles  in  lacuna;;  bl,  blood- 
vessels occupied  by  blood-corpuscles, 
rcyond  the  line  of  ossiflc  advance  the 
periosteum  may  be  noticed  to  be  dis- 
tinctly incurved.  This  incurvation 
is  gradually  moved  on,  the  cartilage 
expanding  behind  it  until  the  head 
of  the  bone  is  reached,  when  it  forms 
the  ])eriosleal  notch  (jr  groove  rejire- 
sented  in  the  preceding  figure. 


arranged  in  rows  or  gronps  of  frequently  four,  eight,  or  sixteen,  etc., 
the  intercellular  substance  being  less  in  amount,  corresjionding  to  the 
increase  in  size  and  numl)er  of  the  cells.  Farther  inward  we  find  the 
cells  still  more  plainly  arranged  in  rows,  very  large,  sometimes  globular 
or  fiattened  against  one  another,  and  the  basement-substance  reduced  to 
quite  thin  septa,  enclosing  spaces  in  which  the  rows  of  large  cartilage- 
cells  lie.  Then  comes  a  narrow  zone,  in  which  the  septa  of  the  base- 
ment-substance are  filled  with  fine  granules  of  lime  salts  :  calcification 
zone.  Here  the  cartilage-c-ells  have  assumed  a  peculiar  granular  cha- 
racter. Finally,  still  nearer  Me  find  that  the  lime  salts  have  disap- 
'  T.  M.  Prudden,  Normal  Hisiolocjy. 


OSSIFICATION. 


589 


From  Femur  of  Human  Fcetus  of  5  months  (X 
'250):  nc,  normal  cartilage;  cc,  calcified  carti- 
lage; lib,  the  dark  line  rt-preseuting  developing 
bone;  ?«/,  marrow  tissue. 


peared  from  the  septa,  and  that  the  spaces  which  contained  the  large 
granular  cartilage-cells  have  become  continuous  with  the  advancing  vas- 
cular, bone-walled  marrow-cavities,  above  described.     It  is  to  be  dis- 
tinctly understood  that  the  calcifi- 
cation zone  is  not  bone,  but  only  ^^^-  ^■^^■ 
calcified    cartilage,   the  true    bone 
being  first  fi_)rmed  after  this  lime 
has  disappeared,  on  the  surface  of 
the  septa  in  which  it  was  tempo- 
rarily deposited — for  what  purpose 
^ve  do  not  know."      (See  accom- 
panying figure,  328.) 

The  lengthening  of  the  shaft  pro- 
ceeds until  the  cartilaginous  head 
itself  becomes  ossified,  when  all 
further  extension  ceases  and  the 
bones  are  said  to  be  fully  devel- 
oped. This  time  varies  in  different 
bones  and  also  in  the  same  class  of 
bones. 

As  regards  the  origin  of  the  oste- 
oblasts in  the  first  instance  I  am 
pretty  fully  convinced  that  they  are 
the  ordinary  embryonic  connective- 
tissue  cells.  That  this  is  so  in  the  very  early  stages  such  as  we  have 
described  in  interstitial  development  (p.  580)  there  seems  to  be  no  room 
for  doubt.  The  close  intimacy  between  the  vascular  sujiply  and  ossifi- 
cation tends  to  confirm  the  o])inion  held  by  some,  that  they  are  modified 
white  blood-corpuscles.  For  my  part,  I  see  no  antagonism  between  the 
two  theories  above  mentioned.  I  think  it  can  be  quite  cleai'ly  demon- 
strated that  even  fixed  connective-tissue  cells'  are  only  modified  white 
blood-corpuscles  which  have  passed  through  several  gradations  governed 
by  location  and  environment,  appearing  (I.)  as  white  blood-corpuscles 
in  the  vessels;  (II.)  as  escaped  white  blood-corpuscles;  (III.)  plasma- 
cells  ;  (IV.)  fixed  connective-tissue  cells.  Ziegler  has  made  extensive 
studies  in  regard  to  the  changes  of  the  migrated  white  blood-corpuscles 
into  fixed  connective-tissue  cells  in  pathological  conditions  where  there 
is  set  up  a  process  of  progressive  metamorphosis,  and  says  that  without 
doubt  such  is  the  process  of  change. 

Osteoblasts  are  a  constant  concomitant  of  bone-formation.  Ossifica- 
tion is  a  process  which  is  under  the  superintendency  of  the  osteoblasts. 
We  have  seen  that  there  exists  an  intimate  relationship  between  the 
vascular  supply  and  calcification  which  precedes  ossification.  The 
breaking  down  of  the  cartilaginous  matrix  is,  without  doubt,  due  to  the 
modifying  influence  of  the  capillary  vessels.  The  hyaline  l)asement- 
substance  is  dissolved  and  the  cartilage-cells  are  liberated.  These  carti- 
lage-cells pass  into  the  form  of  fibrillated  connective-tissue  cells  from 
which  cartilage  is  originally  developed. 

The  point  I  desire  to  make  is  this — that  the  white  blood-cells  are  the 
common  basis  from  which  the  several  members  of  the  connective-tissue 


590  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

group  .'spring.  In  some  instances  osteoblasts  are  produced  from  con- 
net'tive-tissue  cells;  sometimes  they  have  their  origin  in  cartilage-cells; 
but  their  most  Irequent  and  persistent  source  is  found  in  the  white 
blood-corpuscles. 

Nature  always  uses  the  material  at  hand,  in  so  far  as  it  is  available. 
If  the  bone  is  being  deposited  by  intercartilaginous  ossification,  there  is 
no  necessity  that  the  cartilage-cells  should  be  destroyed  or  materially 
altered.  They  are,  no  doubt,  modified  and  endowed  with  special  func- 
tional powers ;  in  a  word,  they  become  osteoblasts.  And  such  use  of 
pre-existing  cells  may  occur  in  intramembranous  and  subperiosteal  bone- 
formation.  The  fixed  connective-tissue  cells  in  all  probability  act  as  cen- 
tres of  calcification.  In  interstitial  ossification  true  fibrous  connective 
tissue  has  not  as  yet  been  found  ;  it  is  embryonic  connective  tissue,  and 
the  cells  are  consequently  embryonic  connective-tissue  cells. 

There  is  very  little  difference,  except  as  regards  size,  between  the 
osteoblast  and  the  surrounding  connective-tissue  cells.  Thus  we  find 
that  bone  is  developed  in  truly  embryonic  tissue  as  well  as  in  older 
tissues ;  it  is  developed  in  cartilage  and  in  membranes ;  it  is  developed 
in  normal  and  in  pathological  conditions ;  and  yet  the  process  of  ossifi- 
cation is  ever  the  same,  although  the  location  or  arrangement  of  the 
deposition  may  vary  according  to  the  essential  differences  in  the  tissues 
in  which  bone  is  formed.  The  only  unvarying  element  that  is  found 
in  intimate  relation  with  all  these  tissues  is  the  migrated  white  blood- 
corpuscle  ;  and,  by  reason  of  its  close  relationship  with  the  process  of 
ossification,  it  seems  to  me  to  be  more  reasonable  to  infer  that  the  white 
blood-coi'puscle  becomes  modified  in  form  and  endowed  with  such  spe- 
cialized functional  power  as  to  be  able  to  superintend  the  development 
of  bone. 

Cementification. 

This  is  only  a  slightly-modified  form  of  Kubperiosteal  development  of 
bone.  In  mature  tissues  the  pulji,  covered  by  a  layer  of  dentine  vary- 
ing in  thickness,  acts  as  a  large  Haversian  canal,  around  which  the 
cement  is  dejiosited  in  concentric  layers,  the  whole  forming  a  large 
Haversian  system.  Sometimes  this  arrangement  is  modified,  and 
Haversian  canals  are  seen  running  at  right  angles  to  the  surface. 
AMien  this  does  occur,  cementification  differs  in  no  respect  from  sub- 
jx'riosteal   b()ne-formati(jn. 

I  have  cut  sections  from  the  roots  of  teeth  in  which  well-defined 
Haversian  canals  were  seen  to  enter  the  sides  of  the  roots,  and  I  have 
no  doubt  that  if  we  were  to  search  for  them  more  carefully  we  could 
often  find  them.  Quite  a  number  are  recorded  in  dental  literature 
under  the  name  of  mu/fipfe  foramina. 

Cementification  is  the  analogue  of  subperiosteal  formation  of  the 
cortical  substance  of  long  bones.  The  first  deposited  layer  of  cement 
is  permanent,  there  being  no  provisional  cement  to  be  afterward  broken 
down.  The  circumference  of  the  root  at  the  beginning  of  the  process 
of  the  de])ositi()n  of  cement  is  as  great  as  it  ever  attains.  The  increase 
in  thickness  of  the  dentine  is  from  the  periphery  toward  the  centre,  at 


DENTINIFICA  TION. 


591 


Fig. 


the  expense  of  the  size  of  the  pulp,  just  as  the  Haversian  systems  develop 
by  successive  layers  of  calcospherules  which  are  situated  inside  the  cir- 
cumferential layer.  The  thickening  of  the  cement  is  from  the  first  layer 
deposited  upon  the  dentine  externally,  thus  enlarging  the  circumference 
of  the  root.  The  limit  to  this  accretion 
is  found  in  the  fully-formed  alveolar  wall 
which  surrounds  the  root. 

When,  at  certain  points,  the  process 
extends  beyond  typal  limitations,  we  have 
a  pathological  condition,  and  malforma- 
tion results ;  in  later  years  the  cement 
may  become  thickened  (exostosis)  as  the 
result  of  constant  irritation. 

We  find  that  the  process  differs  in  no 
degree  from  the  first-formed  cement.  The 
pericementum  is  analogous  and  continuous 
with  the  periosteum.  It  is  a  cement  organ 
only  in  the  same  degree  that  the  periosteum 
is  a  bone  organ.  We  know  that  both  have 
the  special  function  of  superintending 
the  deposition  of  their  several  products 
after  injury  or  loss,  and  that,  stimulated 
by  irritation,  they  produce  pathological 
conditions  by  secondary  deposits.  They 
are  the  persistent  organs  under  the  direc- 
tion of  which  nature  repairs  injuries. 

The  individual  elements  which  form 
cement  are  the  osteoblasts,  or — if  it  is  de- 
sirable to  increase  the  number  of  terms  in 
connection  with  tooth-development — the 
ccmentob/a.sts.  C^alcospherules  of  lime  are 
formed  in  a  manner  similar  to  those  de- 
scribed in  connection  with  our  study  of 
ossification. 

A  single  layer  of  osteoblasts,  or  cemen- 
fohfriMx,  is  first  formed  around  the  per- 
iphery of  the  dentine  of  the  root.  By  a  process  identical  with  that 
of  subperiosteal  bone-formation,  the  cementoblasts  become  enclosed  in 
spherules  of  lime ;  successive  layers  appear,  each  in  turn  assuming  the 
characteristics  of  the  first-formed  layer,  till  finally,  by  their  aggregation, 
the  cement  is  thickened  to  the  typal  point.  A  section  of  cement  show- 
ing the  similarity  existing  between  it  and  bone  is  seen  in  the  accom- 
panying figure  (329,  1).  The  union  of  the  cement  and  the  dentine 
is  also  shown  very  nicely,  and  will  be  referred  to  farther  on,  when 
treating  of  that  subject. 


Section  of  Fang  parallel  to  the  Dentinal 
Tubules  f magnified  .'SOO  diameters):  1, 
cement,  with  large  bone-lacunse  and 
indications  of  lamella  ;  2,  granular  lay- 
er of  Purkinje  (interglobular  spaces;; 
o,  dentinal  tubules. 


Dentinification. 

Dentine  is  a  specialized  product  developed  by  specialized  cells.     In 
form  dentine  is  very  different  from  the  several  varieties  of  bone  hereto- 


592 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY 


fore  considered.  A\'e  have  already  studied — under  the  head  of  the  con- 
nective-tissue grou]) — the  development  of  the  special  cells  Mhich  super- 
intend its  formation — viz.  odontoblasts. 

Dentine  is  only  a  still  more  moditied  form  of  bone  than  cement.  If 
we  so  desired,  we  could  make  a  fifth  class  of  ossified  products  and  call 
it  tubular  ossification  ;  but  I  prefer  to  hold  to  the  existing  nomenclature, 
and  will  speak  of  the  process  as  dentinification. 

Ijike  cement,  the  iirst  layer  of  dentine  formed  is  a  jiennaiicnt  product. 
I  use  the  term  in  contradistinction  to  provisional  deposition  as  found  in 
the  study  of  ossification. 

Odontoblasts  are  a  modified  form  of  connective-tissue  cells.  They 
are  situated  upon  the  periphery  of  the  pulp,  and  send  out  rod-like  pro- 
cesses to  the  inner  side  of  the  enamel  organ  in  the  crown. 

Under  the  superintendency  of  the  odontoblasts  lime  salts  are  deposited 
around  these  rod-like  fibrils,  and  thus  form  tubular  dentine. 

In  our  studv  of  the  development  of  bone  we  found  that  canaliculi 
were  formed  by  the  deposition  of  lime  salts  around  the  fibrils  of  the 
osteoblasts  and  within  the  calcospherules.  Each  calcospherule  is  a 
separate  entity  composed  of  an  organic  bone-cell  with  radiating  pro- 
cesses around  which  inorganic  lime  salts  have  been  deposited  in  such  a 
manner  as  to  form  a  perfect  spherule.  The  dental  pulp  may  be  com- 
pared to  a  gigantic  osteoblast,  the  fibrils  of  the  odontoblasts  represent- 
ing the  fibrils  of  the  osteoblast.  The  dentine  covering  the  pulp 
corresponds  to  the  wall  of  the  calcospherules,  and  the  canals  of  the 
dentinal  tubvdi  to  the  canaliculi. 

The  de})osit  of  dentine  is  the  work  of  mature  cells  which  lie  upon  the 
surface  of"  the  dentinal  pulj),  being  arranged  in  a  single  row.     Dentine 

is  a  secretiim  of  lime  salts  under  the 
Fig.  330.  superintendency  of  the  odontoblasts 

— not  around  themselves,  as  in  the 
case  of  the  encapsuled  osteoblast, 
but  around  their  fibrils.  These 
being  rod-sha])e(l,  the  deposition 
naturally  assumes  a  tubular  fi>rm. 
The  fibrils  remain  as  the  persistent 
iji^'*'^LJt^Jf^^:^J',^3fv^^|f  organic    contents   of    the    dentinal 

^  -mi^B^^Allk-'*m'^-'<lL   ,  tu'buli,  just   as    the    fibres    of    the 

bone-cells  are  found  to  occujn'  the 
canaliculi.  The  thickening  of  the 
dentine  is  by  accretion  of  lime 
salts  in  such  a  manner  as  to 
lengthen  the  tubuli.  The  fibrils 
lengthen  as  the  dentine  thickens, 
and  the  odontoblasts  recede  before 
tlie  finning  dentine,  leaving  a  process  behind. 

Each  individual  (tdontoblast  does  not  become  encapsuled,  as  do  the 
osteol)lasts,  but  remains  free  upon  the  surface  of  the  j)ulp  all  through 
the  life  of  that  organ.  They  do,  however,  become  encapsuled,  in  the 
aggregate,  by  the  dentine  of  the  entire  tooth.  . 

As  we  have  before  said,  the  pulp,-  with  the  odontoblasts,  represents  a 


Part  of  Section  of  developing  Tootli  of  youii}; 
l!;it,  sliowinji  tiie  Mode  of  Iieposilion  (if  the 
Dentine  (liifihly  magnified):  n,  outer  layer  of 
fully-calcified  dentine;  li,  uncalcified  niatiix 
with  a  few  nodules  of  calcareous  matter;  <; 
(xlontoMasts  with  pruccsscs  extendiof^  into 
the  dentine;  </,  jiulp.  'flic  section  is  stained 
with  carmine,  which  ciijors  the  uncalcified 
matrix,  Init  not  the  calcified  part. 


DENTiyiFICA  TION.  593 

bone-cell ;  the  pulp-eavity,  a  lacuna ;  while  the  dentinal  fibrils  are 
analogous  to  the  processes  of  the  bone-cells.  The  canals  of  the 
dentinal  tubuli  represent  the  canaliculi  in  which  the  processes  or  fibrils 
are  situated. 

We  have  seen  that  the  thickening  of  the  wall  of  the  calcospherule  is 
at  the  expense  of  the  size  of  the  osteoblast,  and  to  a  certain  extent  this 
is  true  of  the  tooth.  But  it  must  be  remembered,  however,  that 
deposition  of  dentine  is  from  one  side  of  the  odontoblast,  and  not 
circumferentially,  as  is  the  case  in  ossification  (Fig.  330). 

Additions  to  the  thickness  of  bands  of  bone  are  produced  by  the 
addition  of  successive  layers  of  osteoblasts,  which  one  after  another 
become  enclosed  by  the  deposition  of  lime  salts.  The  thickening  of  the 
dentinal  wall  is  accomplished  by  a  single  layer  of  odontoblasts  which 
begin  the  process,  and  these  cells  persist  throughout  the  life  of  the 
pulp,  and  when  stimulated  by  the  irritation  of  invading  decay  have  the 
power  to  throw  out  a  secondary  layer  of  dentine,  which  acts  as  a  barrier 
against  the  enemy.  This  thickening  is  at  the  expense  of  the  cavity  of 
the  pulp,  and  consequently  of  that  of  the  size  of  the  organ  itself 

The  formation  of  the  dentine  of  the  root  is  also  somewhat  similar. 
The  circumference  of  the  outer  layer  of  the  dentine  of  the  root  is  as 
great  when  first  formed  as  it  ever  will  be.  The  thickening  of  the  Avail 
is  by  a  process  similar  to  that  seen  in  the  Haversian  systems,  which,  as 
we  know,  is  at  the  expense  of  the  contents  of  the  Haversian  canals. 

The  dentine  of  the  root  of  a  tooth  is  a  hollow  column  which  increases 
in  length  by  extension  and  in  thickness  by  internal  deposition  of  lime 
salts.  Under  the  superintendency  of  the  odontoblasts  new  layers  are 
being  continually  added  to  the  end  of  the  tube  until  the  necessary 
length  is  completed.  The  apical  foramen  is  the  open  end  of  the  cohmin. 
As  the  root  reaches  the  required  length  this  open  end  is  constricted 
by  internal  deposition,  and  finally  almost  closes,  until  we  see  it  as  it 
appears  in  the  ordinary  apical  foramen.  The  dentine  reaches  its  re- 
quired thickness  in  the  crown  first.  Sometimes  more  than  one  apical 
foramen  is  found  in  a  single  root.  This  is  due  to  a  division  of  the 
pulp  in  this  special  case,  and  the  phenomenon  is  governed  by  the 
same  law  that  regulates  the  development  of  the  separate  roots  of  the 
molar  teeth.  The  papilla  divides  into  several  parts,  which  indicate 
the  position  of  the  future  roots,  and  dentine  is  developed  around 
each  part  in  a  manner  exactly  similar  to  that  which  we  have  above 
described. 

In  the  development  of  the  dentine  of  the  crown  the  process  is  some- 
what modified.  In  shape  the  dentine  of  a  tooth  has  the  outward  appear- 
ance of  a  double  cone,  the  bases  uniting  at  the  cervical  ])ortion.  The 
papilla,  beginning  as  a  microscopic  object  lying  in  Avhat  is  afterward 
the  very  apex  of  the  pulp  at  the  cutting  edge  of  the  tooth,  commences 
the  deposition  of  the  dentine  directly  under  the  enamel  organ,  and  the 
tubules  are  developed  in  a  line  corresponding  to  the  axis  of  the  tooth. 
The  papilla  rapidly  widens  at  its  base,  throwing  out  odontoblasts  from 
its  side,  and  as  it  does  so  the  direction  of  the  tubules  gradually  changes, 
tending  more  and  more  to  a  position  at  right  angles  to  the  axis ;  which 
position  they  assume  at  the  neck  of  the  tooth.     The  pulp  has  its  great- 

VoL.  I.— 38 


594  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

est  diameter  at  the  cervical  portion  at  the  time  uhen  the  first  developed 
layer  of  dentine  is  formed  at  that  line.  From  this  time  forward  the 
thickening  of  the  wall  of  the  dentine  of  the  crown  can  be  truly  said  to 
be  at  the  expense  of  the  size  of  the  pulp. 

]\Iany  persons  have  been  deceived  by  mistaking  the  microscopic  organ 
for  the'  fully-developed,  or  macroscopic,  tooth.  At  eight  months  the 
crown  is  not  yet  fully  formed.  The  infolding  of  the  lower  portion  of 
the  enamel  organ  is  due  partly  to  the  shrinkage  of  the  very  delicate 
pulp-tissue  at  its  deepest  extremity  and  partly  to  the  fact  that  the  deep- 
est edge  of  the  enamel  organ  always  precedes  the  specialization  and  full 
development  of  the  pulp.  These  contracted  edges  will  in  time  be 
straightened  by  the  expansion  and  growth  of  the  pulp  at  that  point. 
In  order  to  become  convinced  that  this  appearance  is  not  the  exten- 
sion of  the  enamel  organ  below  the  cervical  portion  of  the  tooth,  as 
has  been  claimed  by  some  (thus  making  the  cement  organ  a  continua- 
tion of  the  enamel  organ),  it  is  only  necessary  to  measure  the  length 
of  the  enamel  organ  in  its  different  stages  of  development  and  com- 
pare these  Avith  the  length  of  a  fully-developed  enamel  cap. 

It  is  difficult  for  the  mind  to  picture  the  whole  of  an  object  from  a 
part,  and  it  is  still  harder  for  it  to  grasp  the  wide  distinction  existing 
between  microscopic  and  macroscopic  objects.  But  the  interpretation 
of  the  location  of  the  cervical  margin  of  a  developing  tooth,  which  at 
six  or  eight  months  has  become  a  macroscopic  object,  is  accomplished 
easily  enough.  This  can  be  done  with  an  ordinary  pocket-rule,  and 
does  not  require  any  of  the  refinements  of  microscopic  measurement. 

The  deposition  of  dentine  is  aroimd  the  fibrils  of  the  odontoblasts, 
which  latter  stand  nearly  at  right  angles  to  the  surface  of  the  dentine. 

Mature  dentine  is  a  solid  mass  of  calcified  tissue.  It  is  held  by  some 
that  it  is  composed  of  individual  tubes;  however  true  this  may  be  of 
forming  dentine,  it  cannot  be  said  of  mature  dentine.  In  the  process 
of  development  the  salts  of  calcium  are  deposited  around  the  fibrils  of 
the  odontoblasts,  and  in  a  certain  sense  dentinal  tubuli  may  be  said  to 
exist  at  that  time.  AVe  may  say  that  dentine  is  an  aggregation  of  tubes 
containing  fibrils,  but  in  the  process  of  aggregation  they  lose  their  iden- 
tity as  such,  becoming  cemented  together  into  a  solid  tissue. 

I  think,  however,  it  is  more  in  keeping  with  the  facts  in  the  case  to 
say  that  dentine  is  a  secretion  thrown  out  by  the  odontoblasts  in  the 
meshes  of  the  dentinal  fibrils.  The  deposition  is  in  the  protoplasm  which 
fills  the  interspaces  between  the  fibres.  By  the  deposition  of  lime  salts 
into  the  ])roto])lasmic  basis-substance  calcoglobulin  is  formed,  and  the 
dentine  tissue  becomes  a  homogeneous  mass  ])enetrated  by  many  par- 
allel canals  filled  with  the  persistent  dentinal  fibrils. 

Besides  the  parallel  canals  filled  with  the  dentinal  processes,  many 
lateral  canals  are  seen  branching  off  from  the  main  tubes  and  forming 
anastomoses  with  neighboring  canals.  It  must  not  be  lost  sight  of  for 
a  moment  that  the  appearances  seen  in  ground  sections  of  dentine  are 
produced  by  the  destruction  of  the  contents  of  the  dentinal  canals.  If 
we  hold  that  distinct  and  separate  dentinal  tubes  exist  in  mature  den- 
tine, then  we  must  consider  them  as  having  many  fine  branches,  in- 
creasing in  numbers  as  we  proceed  toward  the  periphery  of  the  dentine. 


AMELIFICA  TION. 


595 


This  is  not  consistent  with  our  ideas  of  the  character  of  a  tube.  No ; 
the  nature  of  dentine  is  very  like  that  of  mature  bone :  tliough  it 
assumes  a  different  form,  yet  it  is  developed  in  a  similar  manner,  and 
by  the  aggregation  and  agglomeration  of  its  individual  elements  a 
tissue   is    formed    which    we    class 

among    ossified    products.      Then,  l^ra.  .•> 

again,  the  occurrence  of  inten/lob- 
ular  spaces  in  dentine  militates 
against  the  tubular  theory.  These 
can  only  be  explained  by  admitting 
that  dentine  is  secreted  into  a  pro- 
toplasmic basis-substance.  "  Inter- 
globular spaces,"  so  called,  are 
composed  of  masses  of  calcoglobu- 
lin,  which  masses  have  not  become 
fully  calcified.  The  dentinal  fibrils 
pierce  them  and  are  continuous  upon 
either  side  (Fig.  331,  c) ;  while  they 
make  breaks  in  the  continuity  of 
the  dentine  tissue,  yet  they  do  not 
in  any  way  interfere  with  the  cha- 
racter or  form  of  the  dentinal  processes 
of  calcoglobulin,  see  p.  574.) 

In  conclusion,  the  fact  that  dentine  is  not  capable  of  being  broken  up 
into  tubes  is  in  my  mind  conclusive  evidence  against  the  theory  of  the 
existence  of  a  dentinal  sheath  per  se  as  the  wall  of  a  dentinal  tube. 
Dentine  is  an  osseous  tissue  permeated  by  numerous  anastomosing 
canals  which  in  life  locate  the  fibrils  of  the  odontoblasts. 


A  small  Portion  of  the  Dentine  with  Interglob- 
ular Spaees  (;i."iO  diameters):  c.  portion  of  in- 
cremental line  formed  by  the  interglobular 
spaces,  which  are  liere  filled  up  by  a  trans- 
parent material. 

(For  a  discussion  of  the  nature 


Amelification. 

The  late  Dr.  Carpenter,  who  gave  the  greater  part  of  his  life  to  the 
study  of  conchology,  and  who  has  perhajxs  done  more  than  any  other 
man  to  lighten  the  dark  places  of  tliis  subject,  says  :  "  The  structure  of 
the  outer  layer  of  the  common  Pinna  projects  beyond  the  inner,  and 
there  often  forms  laminae  sufficiently  thin  and  transparent  to  exhibit  its 
general  character  without  any  artificial  reduction.  If  a  small  portion 
of  such  a  lamina  be  examined  with  a  low  magnifving-power  bv  trans- 
mitted light,  each  of  its  surfaces  will  present  very  much  the  appearance 
of  a  honeycomb ;  whilst  its  broken  edge  exhibits  an  as])ect  which  is 
evidently  fibrous  to  the  eye,  but  which,  when  examined  under  the 
with  reflected  liffht,  resembles  that  of  an  assemblage  of 
This  outer  layer  is  thus  seen  to  be 
composed  of  a  vast  number  of  prisvis  having  a  tolerably  uniform  size 
and  usually  presenting  an  approach  to  the  hexagonal  shape.  These 
are  arranged  perpendicularly  (or  nearly  so)  to  the  surface  of  the 
lamina  of  the  shell ;  so  that  its  thickness  is  formed  by  their  length 
and  its  two  surfaces  by  their  extremities.  A  more  satisfactory  view 
of  these  prisms  is  obtained  by  grinding  down  a  lamina  until  it  pos- 
sesses a  high  degree  of  transparence,  the  prisms  being  then  seen  (Fig. 


microscope    „ ^...x   xv...v.^.^v^.   ^.g, 
segments  of  basaltic  columns. 


596 


DESTAL  EMBRYOLOGY  AND  HISTOLOGY. 


332)  to  be  themselves  composed  of  a  very  homogeneous  substance,  but 
to  be  separated  by  definite  and  strongly-marked  lines  of  division.  When 
such  a  lamina  is 'submitted  to  the  action  of  dilute  acid,  so  as  to  dissolve 
awav  the  carbonate  of  lime,  a  tolerably  firm  and  consistent  membrane 


Fig.  332. 


'J 


Section  of  Shell  oi  Finnn,  taken  transversely 
to  the  direction  of  its  prisms. 


Membranous  Basis  of  Shell  of  Pinna. 


is  left,  wliich  exhibits  the  prismatic  structure  just  as  perfectly  as  did  the 
original  shell  (Fig.  333),  its  hexagonal  division  bearing  a  strong  resem- 
blance to  the  walls  of  the  cells  of  the  pith  or  bark  of  a  plant."  The 
shell  of  the  Pinna  and  other  species  of  the  mollusk  family  is  a 
structure  analogous  to  enamel.  Both  are  calcified  products  of  the  epi- 
blast.  We  see  variations  in  the  form  of  the  products  of  the  connective- 
tissue  grou]) — as,  for  instance,  in  bone — and  we  also  find  variations  in 
calcified  epithelial  structures.  We  have  seen,  in  the  calcification  of 
bone,  that  cells  do  not  hcemnc  calcified,  but  simply  superintend  calcifica- 
tion ;  and  I  think  we  shall  be  able  to  show  that  the  same  rule  holds 
good  for  the  calcified  products  of  the  epiblast. 

As  we  have  already  said,  salts  of  calcium  enter  into  chemical  com- 
bination with  proteids,  and  thus  form  a  new  group  of  products  called  by 
j\Ir.  Rainey  c((fcor/Iohu/in.  Tliis  modified  form  of  albumen  is  insoluble 
in  acids ;  therefi)re  wc  liave  an  organic  matrix  left  behind  after  decalci- 
fving  the  several  varieties  of  bone.  The  form  of  the  b(me  is  seen  in  the 
decalcified  material.  This  .<ame  matrix  is  found  in  the  prismatic  layers 
of  sliells,  but  not  in  enamel.  There  must,  then,  be  some  reason  for  its 
existence  in  the  one  case,  and  not  in  the  other. 

I  hold,  with  Drs.  Carpenter  and  Huxley,  that  all  calcified  products 
are  excreted,  and  that  there  is  not  an  actual  conversion  of  living  cells 
into  calcified  ti.-^sues.  In  some  instances  the  cells  become  encapsuled, 
l)ut  lime  salts  are  not  deposited  in  the  body  of  the  cell ;  in  other  words, 
calcification  by  conversion  cannot  be  demoui^trated.  In  the  formation 
of  bone  variations  occur  due  to  the  jiosition  and  matrix  in  which  the 
dc])osition  takes  j^lace ;  this  is  also  the  case  with  the  products  of  the 
epiblast.    The  shell  of  the  Pinna  is  excreted,  or  shed  xmt,  upon  the  sur- 


AMELIFICATION.  597 

face  ;  the  calcified  product  occupies  the  position  of  the  stratum  granulo- 
sum,  or  what  I  term  the  older  layer  of  cells.  Upon  the  surface  of  the 
prismatic  layer  we  find  a  layer  of  hornified  or  corneous  cells,  and,  under- 
neath the  calcified  tissue,  the  formative  layer — viz.  the  rete  ]Malpighii,  or 
in/ant  layer  of  cells. 

It  is  well  known  that  this  infant  layer,  or  rete  jNIalpighii,  consists 
of  nucleated  structures  which  lie  in  a  bed  of  protoplasm.  This  layer 
of  protoplasm  suiTounds  and  bathes  the  cells  of  the  older  layer  to  a 
certain  extent,  growing  less  and  less  in  (piantity  as  we  approach  the 
surface.  This  protoplasmic  substance  does  not  differ  in  character 
from  that  which  surrounds  the  cells  of  the  connective-tissue  grou]). 
So  far  as  we  know,  the  two  fluids  are  identical :  salts  of  calcium 
enter  into  chemical  combination  with  protoplasm  in  the  latter  case, 
and  why  not  in  the  former? 

The  first-formed  layer  of  the  shell  of  the  mollusk  lies  in  the  proto- 
plasm which  bathos  the  formative,  or  infant,  layer  of  cells  of  the  rete 
JNIalpighii.  These  cells  are  the  active  agents  in  its  deposit ;  they  have 
become  specialized  and  endowed  with  new  functional  power  that  they 
may  superintend  the  deposition  of  the  salts  of  calcium  \\hich  enter  into 
the  composition  of  the  shell.  Their  office  is  identical  with  that  of  the 
osteoblast. 

The  «dcium  salts  are  shed  out  from  the  ends  of  the  cell  as  from  the 
surface  of  a  membrane — which,  indeed,  they  form.  They  do  not 
become  individually  encapsuled,  as  do  the  osteoblasts,  but  the  body 
of  the  Pinna,  covered  externally  ^vith  epithelium  which  remains  as 
the  lining  membrane  of  the  shell,  becomes  enclosed  by  the  shell,  and 
thus  the  infant  layer  may  be  said  to  be  encapsuled. 

The  thickening  of  the  shell  is  at  the  expense  of  the  size  of  the  body 
of  the  Pinna,  just  as  the  thickening  of  the  wall  of  the  calcospherule  is 
at  the  expense  of  the  size  of  the  osteoblast.  If  we  decalcify  a  shell  and 
make  sections,  we  find  a  matrix  which  differs  only  in  form  from  that 
found  in  bone.  The  prismatic  layer  of  the  rete  Malpighii  has  laid 
down  the  calcified  products  in  the  form  of  prisms,  and  cross-sections 
of  the  decalcified  product  will  reveal  their  form  just  as  well  as  ground- 
sections.  Cross-sections  will  present  the  appearance  of  a  honeycomb 
from  which  the  honey  has  been  extracted  :  the  extracted  honey  com- 
pares to  the  salts  of  calcium,  which  before  decalcification  existed  as 
prisms,  and  occupied,  as  did  the  fluid  honey,  the  cells  of  the. comb. 

In  the  development  of  the  shell  the  protoplasm  shed  out  between  the 
prismatic  cells  of  the  infant  layer  is  lin\ited  in  quantity.  The  secreted 
salts  of  calcium  which  are  thrown  out  bi/  the  cells  enter  into  chemi- 
cal combination  with  the  peripheral  layer  of  protoplasm  and  form 
calcoglobulin,  which,  as  we  have  before  shown,  is  insoluljle  in  acids. 
The  sheath  which  surrounds  the  prism,  as  the  protoplasm  does  the 
prismatic  cell,  may  be  compared  to  the  wax  in  the  cell  of  the  honey- 
comb. Regarding  the  sheath,  and  the  material  which  enters  into  its 
structure.  Dr.   Carpenter  says : 

"  It  sometimes  happens  in  recent,  but  still  more  commonly  in  fossil, 
shells  that  the  decay  of  the  animal  membrane  leaves  the  contained  prisms 
without  any  connecting  medium.     As  they  are  then  quite  isolated,  they 


598 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY 


can  be  readily  detached  one  from  another,  and  each  may  be  seen  to  be 
marked  by  striations.  By  making  ground-sections  of  the  shell  per- 
pendicularly to  its  surface  we  obtain  a  view  of  the  prisms  cut  in  the 
direction  of  their  length  (Fig.  334),  and  they  are  frequently  seen  to  be 
marked  by  delicate  transverse  strise  closely  resembling  those  observ- 
able on  the  prisms  of  the  enamel  of  teeth,  to  which  this  kind  of  shell- 
structure  may  be  considered  as  bearing  a  very  close  resemblance  except 
as  rciiards  the  mineral izing;  ingredients.  If  a  similar  section  be  decalci- 
fied  by  dilute  acids,  the  membranous  residuum "  (the  interprismatic 
cement-substance,  which  by  its  insolubility  in  acids  shows  it  to  be  per- 
haps identical  with  ]Mr.  Rainey's  calcoglobulin)  "  will  exhibit  the  same 
resemblance  to  the  walls  of  the  prismatic  cells  viewed  longitudinally, 
and  will  be  seen  to  be  more  or  less  regularly  marked  by  the  transverse 
stria  just  alluded  to."     (See  Fig.  335.) 

Fig.  335. 


Fig.  334. 


Sectiim  of  Shell  of  Pinnn  in  the  direction  of 
its  prisms. 


Oblique  Section  of  Prismatic  Shell- 
substance. 


''  These  appearances  seem  best  accounted  for  by  supposing  that  each 
(})risni)  is  lengthened  by  successive  additions  at  its  base. 

"  This  '  })rismatic  '  arrangement  of  the  carbonate  of  lime  in  the  shells 
of  Pinna  and  its  allies  has  been  long  familiar  to  conchologists  and 
regarded  by  them  as  the  result  of  crystallization.  When  it  was  first 
more  minutely  invested  by  Mr.  Bowesbank  and  the  author,  and  was 
shown  to  be  connected  with  a  similar  arrangement  in  the  membranous 
residuum  left  after  the  decalcification  of  the  shell-substance  by  acid, 
microscopists  generally  agreed  to  regard  it  as  a  calcified  epidermis,  the 
long  prismatic  cells  being  sujiposed  to  be  formed  by  the  coalescence  of 
the  epidermic  cells  in  files  and  giving  their  shape  to  the  deposit  of  car- 
bonate of  lime  formed  witliin  them.  The  progress  of  inquiry,  however, 
has  led  to  an  important  modification  of  this  interpretation,  the  author 
being  now  disposed  to  agree  witii  Prof  Huxley  in  the  belief  that  the 
entire  thickness  of  the  shell  is  formed  as  an  excretion  from  the  surface 


AMELIFICATIOK  599 

of  the  epidermis,  and  that  the  horny  layer  which  in  ordinary  shells 
forms  this  external  envelope,  or  '  periosti'acum,'  being  here  thrown  out 
at  the  same  time  with  the  ealcifvino;  material,  is  converted  into  the  like- 
ness  of  cellular  membrane  by  the  pressure  of  the  prisms  that  are  formed 
by  crystallization  at  regular  distances  in  the  midst  of  it. 

"■  The  internal  layer  of  the  shells  of  the  Margaritacese  and  some  other 
families  has  a  '  nacreous,'  or  iridescent,  lustre  Avhich  depends  (as  Sir  D. 
Brewster  has  shown)  upon  the  striation  of  its  surface  with  a  series  of 
grooved  lines,  which  usually  run  nearly  parallel  to  each  other. 

"  As  these  lines  are  not  obliterated  by  any  amount  of  polishing,  it  is 
obvious  that  their  presence  depends  upon  something  peculiar  in  the 
texture  of  this  substance,  and  not  upon  any  mere  superficial  arrange- 
ment. But  when  the  nacre  is  treated  with  dilute  acid,  so  as  to  dissolv'e 
its  calcareous  portion,  no  such  repetition  of  membranous  layers  is  to  be 
found  ;  on  the  contrary,  if  the  piece  of  nacre  be  the  product  of  one  act 
of  shell-formation,  there  is  but  a  single  layer  of  membrane.  This 
layer,  however,  is  found  to  present  a  more  or  less  folded  or  plaited 
arrangement,  and  the  lineation  of  the  nacreous  surface  may  perhaps 
be  thus  accounted  for.  A  similar  arrangement  is  found  in  pearls, 
which  are  rounded  concretions  projecting  from  the  inner  surface  of 
the  shells  of  Avicula  and  possessing  a  nacreous  structure  correspond- 
ing to  that  of  '  mother-of-pearl.'  Such  concretions  are  found  in 
many  other  shells,  especially  the  fresh- water  mussels,  Unio  and  Ano- 
don,  but  these  are  usually  less  remarkable  for  their  pearly  lustre ; 
and  when  formed  at  the  edge  of  the  valve,  they  may  be  partly,  or 
even  entirely,  made  up  of  the  prismatic  substance  of  the  external 
layer,  and  may  be,  consequently,  altogether  destitute  of  the  pearlv 
character.  In  all  the  genera  of  the  Margaritacese  we  find  the  exter- 
nal layer  of  the  shell  prismatic  and  of  considerable  thickness,  the 
internal  layer  being  nacreous.  But  it  is  only  in  the  shells  of  a  few  fam- 
ilies of  bivalves  that  the  combination  of  organic  Avith  mineral  compo- 
nents is  seen  in  the  same  distinct  form,  and  these  families  are  for  the 
most  part  nearly  allied  to  Pinna.  In  the  Unionidse  (or  fresh-water 
mussels)  nearly  the  whole  thickness  of  the  shell  is  made  up  of  the  inter- 
nal, or  '  nacreous,'  layer ;  but  a  uniform  stratum  of  prismatic  substance 
is  always  found  between  the  nacre  and  the  periostracum,  really  consti- 
tuting the  inner  layer  of  the  latter,  the  outer  being  simply  horny." 

The  nacreous  layer  of  the  shell  is  found  upon  the  inner  side,  next  to 
the  formative  layer,  and,  being  polished,  protects  the  shell  against  the 
action  of  any  pathological  condition  which  may  occur  in  the  body  of 
the  mollusk.  The  cortical,  or  nacreous,  layer  of  enamel  is  also  found 
next  to  the  formative  layer.  They  are  both  the  last-formed  products 
of  the  formative  organ.  The  polished  surface  of  enamel  also  protects 
it  against  pathological  conditions  which  may  arise  in  the  surroundings 
of  the  tooth. 

As  we  have  seen,  the  shell  is  secreted  above  the  infant  layer  of  the 
rete  Malpighii.  By  referring  to  the  section  on  the  development  of  the 
ameloblasts  it  will  be  seen  that  the  bulbous  cord  iuA-aginates  itself,  and 
thus  forms  a  double  cap  for  the  dentinal  papilla.  By  this  invagination 
the  ends  of  the  cells,  which  were  external  in  the  bulbous  cord,  come  in 


600  DENTAL   EMBRYOLOGY  AND  HISTOLOGY. 

contact  with  the  outer  surface  of  the  papilla..  Now,  the  enamel  is 
deposited,  or  secreted,  from  these  lower,  or  deeper,  ends  of  the  amelo- 
blasts ;  the  prismatic  layer  found  in  shells,  on  the  other  hand,  is  secreted 
from  the  upper  ends  of  the  cells.  If  enamel  were  secreted  in  a  similar 
manner,  the  ameloblasts  would  be  situate<l  between  the  forming  enamel 
and  the  dentine  ;  which  is  not  the  case. 

The  mineralizing  constituents  of  enamel  vary  considerably  from  those 
of  shells.  The  amount  of  organic  material  found  in  shells  is  also  far 
greater  than  that  of  enamel. 

Whether  there  is  less  protoplasm  shed  out  from  the  under  side  of  the 
cells  than  from  the  upper,  and  whether  the  mineral  ingredients  M'hich 
go  to  form  enamel-prisms  do  not  enter  into  combination  with  the  pro- 
toplasm as  readily  as  do  those  of  shells  and  bone,  are  points  which 
I  am  not  able  to  prove.  It  is  certain,  however,  that  there  is  found 
in  enamel  only  a  very  small  per  cent,  of  fixed  material. 

I  use  the  tcvm  fixed  material  to  designate  protoplasm  which  has  passed 
into  a  state  where  it  requires  to  be  digested  by  and  through  the  action 
of  the  living  principle  which  is  found  in  the  non-fixed  material.  It  is 
the  "  formed  material  "  of  Beale,  and  in  this  particular  instance  it  is  also 
the  "  calcoglobulin  "  of  Mr.  Rainey. 

According  to  different  chemical  analyses,  the  amount  of  fixed  material 
found  in  enamel  varies  from  1  to  3  per  cent. ;  it  is  only  demonstrable 
by  chemical  analysis.  There  is  not  a  sufficient  quantity  of  this  mate- 
rial to  be  demonstrated  by  the  microscope,  as  no  trace  of  a  matrix  can 
be  seen  after  decalcification.  I  doubt  if  there  enters  into  the  formation 
of  enamel,  as  a  necessary  constituent  part,  the  least  trace  of  protoplasm 
or  organic  material.  It  would  be  very  difficult  indeed  to  obtain  a  por- 
tion of  enamel  for  chemical  analysis  which  would  not  contain  some 
^'organic  material,"  using  the  term  as  in  contradistinction  to  inorganic. 
I  nmch  prefer  the  use  of  fixed  or  formed  material,  for  I  think  it  has 
been  pretty  conclusively  shown  that  organic,  or  living,  matter  cannot 
enter  into  chemical  combination  with  inorganic  matter,  as  such,  except 
the  living  lose  its  living  principle  and  become  non-living  (fixed  or 
formed  material).  When  we  consider  the  fact  that  enamel, is  devel- 
oped in  and  surrounded  by  organic  matter,  that  it  frequently  encapsules 
a  greater  or  less  amount,  and  that  the  fibres  of  the  dentine  interdigitate 
with  the  enamel-prisms,  it  does  not  seem  at  all  strange  that  analysis 
should  show  from  1  to  3  per  cent,  of  "organic"  material  which  has 
passed  into  formed  material  :  a  contrary  result  would  be  the  more 
sur]irising. 

If  dilute  acids  are  allowed  to  act  upon  shells,  the  salts  of  calcium 
which  form  the  prisms  are  dissolved,  leaving  a  matrix  of  fixed  mate- 
rial (calcoglobulin).  The  intcrprismatic  or  fixed  material  is  insoluble 
in  acids ;  the  latter  only  serve  to  harden  and  preserve  the  former. 
This  intcrprismatic  cement-substance  surrounds  the  prisms  as  a  sheath, 
and  cross-sections  of  decalcified  shells  plainly  demonstrate  its  existence. 
(See  Fig.  333.) 

When  enamel  is  acted  upon  by  dilute  chromic  acid  for  a  short  time, 
the  inter])rismatic  cement-sul)stan('e-  is  dissolved  out  and  the  prisms  fall 
apart  and   remain   unchanged,   thus  demonstrating   that  the    material 


AMELIFICA  HON. 


601 


which  holds  the  prisms  together  is  more  freely  soluble  in  this  acid  than 
are  the  prisms  themselves,  being  just  the  reverse  of  what  we  have  seen 
in  decalcification  of  shells  by  dilute  acids.  Then,  again,  when,  through 
disintegration,  the  organic  material  of  shells  is  destroyed,  the  prisms  are 
released  and  tall  apart.  Sucli  an  occurrence  in  connection  with  enamel 
is  not  known. 

Regarding  the  striations  found  upon  the  enamel-prisms,  I  am  fully 
satisfied  that  they  are  caused  by  inequalities  upon  the  surface  of  the 
prisms.  I  submitted  this  question  to  Mr.  Christian  Febiger  of  Wil- 
mington, Delaware,  ^vho  is  perhaps  the  best  authority  in  this  country 
upon  Diatomacere.  It  is  well  known  that  in  the  study  of  diatoms  the 
very  greatest  nicety  of  judgment  is  necessary  in  order  to  diftereutiate 
between  such  points  as  the  one  in  hand,  and  the  opinion  of  an  expert 
microscopist  like  Mr.  Febiger  should  have  a  very  considerable  weight. 
He  said,  without  hesitancy,  after  studying  a  ground-section  of  enamel  in 
which  the  markings  showed  quite  plainly,  that  they  were  ware-lines, 
due,  not  to  striations  or  interlacing  fibres,  but  to  inequalities  upon  the 
surface  of  the  section.  The  section  examined  had  been  placed  for  a 
very  short  time  in  a  dilute  solution  of  muriatic  acid  and  then  washed 
and  mounted  in  glycerin.  By  this  method  the  markings  show  better 
than  by  any  other  I  have  used.     The  accompanying  figure  shows  this 

Fig.  336. 


Enamel -Prisms  (350  diameters) :  A,  fragments  nnd  single  tibres  of  the  enamel  isolated  bj- the  actici 
of  hydrochloric  acid;  1!,  surface  of  a  small  fragment  of  enamel,  showing  the  hexagonal  ends  of 
the  fibres. 

appearance  very  accurately.  INIr.  Tomes  has  advanced  substantially  the 
same  opinion  ;  he  says  : 

"  In  perfectly  healthy  human  enamel  the  fibrillar  arrangement  is  not 
so  very  strongly  marked ;  the  prisms  are  solid,  are  apparently  in  abso- 
lute contact  with  one  another,  without  intervening  substance. 

"  But  Bodecker,  basing  his  conclusions  upon  the  examination  of  thin 
sections  stained  with  chloride  of  gold,  holds  that  enamel  is  built  up  of 
columns  of  calcified  substance  between  which  minute  spaces  exist. 
These  are  filled  by  a  material  which  takes  stain  deeply  and  is  probably 
analogous  to  the  cement-substance  of  epithelial  formations.     As  seen  in 


G02  DESTAL  EMBBYOLOGY  AND  HISTOLOGY. 

sections  it  p;ives  off  exceeding  fine  thorns,  which  apparently  pierce  the 
prisms  at  riglit  angles  to  their  length  ;  so  that  it  forms  a  close  network 
very  intimately  mixed  up  with  the  calcified  portion  of  the  enamel. 

''  It  is  not  of  uniform  thickness,  but  is  beaded,  and  Bodecker  attributes 
to  it  a  role  of  far  greater  importance  than  that  of  a  mere  cementing  sub- 
stance, for  he  regards  it  as  being  an  active  protoplasmic  network  which 
renders  the  enamel  much  more  *  alive '  than  it  has  liitherto  been  con- 
sidered to  be.  He  believes  it  to  become  continuous  with  the  soft  con- 
tents of  the  dentinal  tubes  through  the  medium  of  large  masses  of 
protoplasmic  matter  found  at  the  margins  of  the  enamel  and  dentine. 

"  But  although  there  are  various  reasons  for  suspecting  that  enamel  is 
not  completely  out  of  the  pale  of  nutrition  from  the  moment  that  a 
tooth  is  cut,  yet  further  observations  are  needed  before  the  activity  and 
importance  of  the  cement-substance  demonstrated  by  Bodecker  can  be 
held  to  be  fully  established.  Klein  remarks  that  'the  enamel-cells, 
like  all  epithelial  cells,  being  separated  from  one  another  by  a  homo- 
geneous interstitial  substance,  it  is  clear  that  the  remains  of  this  sub- 
stance must  occur  also  between  the  enamel-prisms ;  in  the  enamel  of  a 
developing  tooth  the  interstitial  substance  is  larger  in  amount  than  in 
the  fully-formed  organ.  It  is  improbable  that  nucleated  ])rotoj)lasmic 
masses  are  contained  in  the  interstitial  substance  of  the  enamel  of  a 
fully-formed  tooth,  as  is  maintained  quite  recently  by  Bodecker.' " 

The  first-formed  layer  of  enamel  is  deposited  in  more  or  less  proto- 
plasm. This  is  proven  by  the  fact  that  we  can  decalcify  immature  or 
developing  enamel  u])  to  a  certain  thickness,  and  yet  have  a  matrix  left. 
This  layer  becomes  more  fully  impregnated  with  lime  salts,  and  the 
later  deposition,  which  adds  to  the  length  of  the  enamel-prisms,  seems 
to  be  laid  down  without  any  matricial  substance. 

This  first-formed  layer  constitutes  the  zone  in  which  the  dentinal 
fibres  interdigitate  with  the  enamel-prisms. 

That  points  or  spaces  occur  in  enamel — the  analogue  of  the  inter- 
globular spaces  found  in  dentine — I  fully  believe ;  but  such  spaces  are 
filled  with  calcoglobulin,  and  not  with  living  protoplasm.  Any  such 
deviation  is  pathological,  as  it  is  in  dentine. 

AVhere  these  sj^aces  occur  upon  the  surface  of  the  enamel,  or  so  near 
the  surface  that  the  thin  layer  can  be  easily  broken  through,  they  give 
rise  to  the  pitted  or  grooved  points  found  in  erupted  teeth.  The  fixed 
material  is  dissolved  out  by  soluble  ferments  produced  by  the  organic 
tissue  surrounding  the  erujiting  tooth.  This  fixed  material  is  not  solu- 
ble in  the  ordinary  acids  of  the  mouth,  and  only  disintegrates  through 
the  action  of  soluble  ferments  and  putrefactive  processes.  Regarding 
the  character  of  these  fluids  I  refer  to  Dr.  Black's  article  u^jon  the 
Pathology  of  f'aries. 

A^ariations  in  the  hardness  of  enamel  are  due  to  several  conditions, 
some  normal,  others  pathological.  Xormal  variations  are  found  in  dif- 
ferent temperaments  and  in  different  s])ecies.  The  enamel  on  the  teeth 
of  rodents  is  much  harder  than  that  found  upon  the  teeth  of  carnivorous 
animals.  Such  variations  are  illustrations  of  the  law  of  "adaptation  to 
enviromnont,"  upon  which  so  much  stress  is  laid  bv  some  writers.  This 
I  admit,  but  claim  that  the  adaptative  power  existed  from  the  beginning. 


AMELIFICATION. 


603 


Fi0.  3:J7. 


Section  of  Hinge-tooth  of  3Iyo-arenaria. 


These  variations  are  seen  in  shells,  and  from  the  analogy  fonnd  in 
their  development  I  have  no  hesitancy  in  saying  that  variations  in  den- 
sity of  enamel  are  dependent  npon  the  same  conditions.  Dr.  Carpenter, 
speaking  of  the  varying  degrees  of  density  fonnd  in  shells,  says : 

"  This  [increased]  hardness  appears  to  depend  upon  the  mineral 
arrangement  of  carbonate  of  lime ;  for,  whilst  in  the  prismatic  and 
ordinary  nacreous  layers  this  has  the  crys- 
talline condition  of  calcite,  it  can  be  shown 
in  the  hard  shell  of  the  Pholas  to  have  the 
arrangement  of  arragonite,  the  difference 
between  the  two  being  evidenced  by  polar- 
ized light.  A  very  curious  appearance  is 
presented  by  a  section  of  a  large  hinge- 
tooth  of  Myo-arenaria  (Fig.  337),  on 
which  the  carbonate  of  lime  seems  to  be 
deposited  in  nodules  that  possess  a  crys- 
talline structure  resembling  that  of  the 
mineral  termed  laavellght.  Approaches  to 
this  curious  arrangement  are  seen  in  many 
other  shells." 

Variations  in  hardness  of  enamel  may 
arise,  as  we  have  already  indicated,  by 
reason  of  pathological  conditions  resulting  from  interglobular  spaces, 
which  sometimes  occur  in  enamel.  The  points  are,  without  doubt, 
analogous  to  such  spaces  found  in  dentine.  I  am  even  willing  to 
acknowledge  that  a  condition  corresponding  to  that  found  in  shells 
may  also  be  found  in  enamel — that  is,  an  interprismatic  matrix  can  be 
formed ;  but  if  it  should  occur,  it  would  be  pathological  in  character. 
I  have  ground  many  sections  of  teeth  and  examined  many  ground  by 
others,  but  have  yet  to  see  the  first  specimen  of  an  interprismatic 
matrix.  That  there  is  the  least  trace  of  organic  interprismatic  sub- 
stance to  be  demonsti'ated  in  normal  enamel  I  have  veiy  serious  doubts, 
and  think  the  action  of  dilute  acids  upon  fully-calcified  enamel  substan- 
tiates the  doubt. 

Let  us  study  such  action. 

A  ground-section  of  mature  enamel  should  be  placed  uj  on  a  slide 
and  a  cover-glass  cemented  on,  leaving  a  small  opening  on  two  sides. 
If  a  "l^th  of  1  per  cent,  solution  of  chromic  acid  be  allowed  to  run  under 
the  cover  by  capillary  attraction  and  then  removed  from  the  other  side 
by  blotting-paper,  we  can  study  the  action  of  the  acid  upon  the  stage 
of  the  microscope  with  high  powers. 

But  before  we  begin  the  study  of  the  action  of  chromic  acid  on  enamel 
let  us  see  how  it  acts  upon  organic  tissues.  It  is  considered  one  of  the  best 
preservative  fluids  we  have,  and  enters  into  the  famous  Midler's  fluid, 
which  is  noted  for  its  quality  of  preserving  nerve-tissue.  Now,  if  there 
is  any  organic  substance  in  enamel,  we  shall  be  able  to  preserve  it  in  good 
form  and  note  the  result.  The  interprismatic  substance  is  first  attacked 
by  the  acid  and  the  prisms  are  liberated  ;  chromate  of  calcium  crystals 
are  formed  in  great  numbers.  If  there  existed  an  organic  interpris- 
matic cement-substance,  the  action  of  this  dilute  solution  of  chromic  acid 


604  DESTAL   EMBRYOLOGY  AND  HISTOLOGY. 

would  tend  to  preserve  it,  and  the  prisms  would  be  held  together  more 
firmlv  than  before.  After  the  acid  has  been  allowed  to  act  fifteen  min- 
utes It  is  displaced  by  distilled  water  and  pressure  made  upon  the  coyer- 
glass,  when  the  prisms  fall  apart.  They  may  now  be  easily  examined 
even  with  very  high  po\\ers. 

If  we  substitute  a  solution  of  HCl  (nuuiatic  acid)  for  the  chromic- 
acid  solution,  and  of  similar  strength,  we  know  that  the  organic  tissues 
will  be  destroyed  by  its  action.  If  there  is  any  organic  tissue  cementing 
the  prisms  together,  we  should  certainly  be  able  to  demonstrate  it  here ; 
for  the  organic  substance  would  be  dissolved  out  and  the  prisms  lib- 
erated. But  is  such  the  case  ?  Far  from  it.  The  acid  acts  upon  the 
enamel  evenly  as  regards  its  penetration  from  the  free  margin  ;  it  dis- 
solves the  perij>hcral  portion  a  little  faster  than  it  does  the  body  of  the 
prism,  so  that  they  present  a  someM  hat  dentated  border  along  the  exter- 
nal, or  outer,  surface  of  the  enamel ;  but  the  whole  mass  gradually  melts 
away  before  the  action  of  the  acid,  not  leaving  the  least  trace  of  organic, 
or  fixed,  material  behind,  as  in  the  decalcification  of  bone  where  the 
same  acid  is  used.  The  fixed  material,  or  calcoglobulin,  as  we  have 
seen,  is  insoluble  in  acids;  hence,  if  enamel  Avere  calcified — as  is  bone — 
by  deposition  in  the  albuminous  intercellular  substance,  we  should  by 
both  of  the  above  methods  have  the  matrix  remaining  after  decalcifica- 
tion. 

In  my  experiments  I  have  taken  every  precaution  against  failure.  I 
have  embedded  ground-sections  of  teeth  fresh  from  the  mouth  in  cel- 
loidin  and  fixed  them  upon  a  slide,  taking  care  to  cut  the  outlines  of  the 
teeth  upon  the  reverse  side  of  the  slide  with  a  diamond.  After  observ- 
ing these  precautions,  I  allowed  a  |^  of  1  per  cent,  solution  to  flow  under 
the  cover-glass,  and  noted  the  result  by  placing  the  slide  upon  the  stage 
of  the  microscope  ;  but  I  have  never  been  able  to  see  any  reticular  sub- 
stance after  decalcification.  I  have  also  stained  sections  without  being 
able  to  demonstrate  any  matrix.  Such  a  basis-substance  could  not  by 
any  means  have  been  lost  or  destroyed  ;  the  celloidin  served  as  a  ])erfect 
embedding  mass,  and  was  not  acted  upon  by  the  acids  in  the  least 
degree,  neither  did  it  hinder  the  process  of  staining ;  for  it  is  well 
known  to  be  more  permeable  to  stains  than  tissue  itself. 

I  took  all  these  precautions  because  my  observations  regarding  the 
action  of  acids  upon  enamel  are  not  in  accord  v>ith  those  held  by  C 
Tomes  and  others,  and  I  consider  this  a  very  essential  point  to  estab- 
lish accurately.  IMr.  Tomes  does  not  state  whether  his  experiments 
were  made  upon  mature  or  developing  enamel,  but  from  the  cuts  he 
furnishes  one  would  infer  that  his  studies  were  made  upon  mature 
tissues,  as  it  is  not  possible  to  demonstrate  isolated  prisms — especially 
striated  prisms — until  calcification  is  completed,  or  nearly  so. 

Then,  again,  ]\Ir.  Tomes  speaks  of  the  above-mentioned  cut  as  fol- 
lows:' "The  accompanying  figure,  taken  from  enamel  softened  by 
prolonged  maceration  in  a  1  per  cent,  solution  of  chromic  acid,  shows 
this  well,"  etc.  There  is  a  mistake  somewhere.  Either  Mr.  Tomes's 
1  per  cent,  solution  of  chromic  acid  is  a  great  deal  weaker  than  the  one 
I  use,  or  else  English  teeth  decalcif\-  more  slowly  than  American  teeth  ; 

'  Tonies's  Dental  Anatomy,  p.  51. 


A  MEL  IFICA  TION.  GO  5 

for  I  have  found  that  the  action  of  a  1-per-eent.  solution  of  chromic 
acid,  even  when  not  prolonged,  results  in  complete  decalcification  and 
removal  of  the  entire  enamel-covering  of  a  tooth.  Again,  ]Mr.  Tomes 
says  :  '^  If  dilute  hydrochloric  acid  l)e  applied  to  a  section  of  enamel, 
the  axial  parts  of  the  fibres  (prisms)  are  first  attacked,  and  are  dissolved 
away ;  so  that  if  the  section  be  transverse  a  fenestrated  mass  remains." 
I  think  this  phenomenon  is  capable  of  an  opposite  interpretation.  If 
we  carefully  study  sections  of  enamel  ground  in  the  direction  of  the  axis 
of  the  prisms  which  have  been  exposed  to  the  action  of  a  very  dilute 
solution  (of  HCl),  we  find  that  the  edge  is  dentated,  and  that  the  light 
lines  which  mark  the  sides  of  the  prisms  end  in  the  bottom  of  the  inden- 
tations, thus  clearly  demonstrating  that  the  action  of  the  acid  is  slightly 
more  rapid  upon  the  peripheral  than  upon  the  axial  portion  of  the 
prism. 

The  next  statement  made  by  Mr.  Tomes  I  can  fully  substantiate.  It 
is  as  follows  :  "  During  the  formation  of  enamel  the  hardening  salts  are 
deposited  first  in  [aronnd)  the  periphery  of  the  enamel-cells  ;  so  that  the 
youngest  layer  of  enamel  is  full  of  holes,  each  one  of  which  corresponds 
to  the  centre  of  a  fibre  (prism)."  This  I  have  observed  as  a  constantly- 
occurring  phenomenon,  and  consider  it  as  thoroughly  substantiating  my 
position  that  the  enamel-cell,  or  ameloblast,  superintends  the  deposition 
of  the  enamel-prism,  and  does  not  become  directly  calcified,  as  is  held 
by  ]Mr.  Tomes. 

I  look  upon  enamel  as  nothing  more  or  less  than  a  coat  of  mail  sup- 
plied by  Nature  to  protect  the  dentine  and  subserve  the  processes  of 
mastication.  The  presence  of  any  considerable  organic  material  in  the 
enamel  would  be  directly  against  the  proper  fulfilment  of  its  office. 
Nature,  when  left  to  herself,  develops  a  beautiful  and  symmetrical 
object  perfectly  capable  of  subserving  its  purpose,  and  any  deviation 
from  this- standard  is  classed  under  the  head  of  pathological  conditions. 
The  fluids  of  the  mouth  are  ?iorw«%  alkaline  or  neutral,  and  against  the 
action  of  such  conditions  of  the  saliva  the  constituent  parts  of  enamel 
are  proof.  The  enamel  is  not  proof,  however,  against  the  action  of 
acids  ;    neither,  indeed,  was  it  intended  to  be. 

The  cross-striations  found  upon  enamel-prisms  as  well  as  upon  the 
prisms  of  shells  indicate  the  manner  of  their  develojiment — i.  e.  by 
addition  in  length.  This  also  accounts  for  the  layers  of  pigment  some- 
times seen  in  these  structures.  They  follow  the  course  of  the  striated 
lines,  and  are  undoubtedly  laid  down  at  varying  times  in  the  course  of 
the  formation  of  the  prisms.  The  pigment  seen  in  enamel  is  deposited  by 
the  ameloblasts.  Experiments  have  been  made  of  feeding  young  guinea- 
pigs  upon  madder,  then  allowing  some  time  to  elapse,  after  which  the 
madder  diet  is  resumed.  When  killed  and  tlie  tissues  studied,  the  mad- 
der dye  was  found  to  be  deposited  in  bands  or  layers  in  the  bone  which 
was  developed  while  the  experiment  was  being  carried  on.  The  bands 
of  unstained  bone  lying  between  the  layers  which  had  l:)een  colored  by 
the  dve  represented  the  period  whicli  had  elapsed  between  the  different 
experiments.  It  was  found  that  the  width  of  the  bands  was  entirely 
under  the  control  of  the  experimenter,  thus  conclusively  proving  that 
the  pigmentation  was  from  within,  and  that  it  was  secreted  by  the  bone- 


606  DENTAL  EMBRYOLOGY  AXD  HISTOLOGY. 

cells.  I  have  no  doubt  that  if  the  enamel  had  been  examined  it  Mould 
have  shown  a  similar  arrangement. 

The  amount  of  pigment  found  in  enamel  varies  very  considerably  in 
different  animals,  and  generally  bears  a  close  relation  to  the  density  of 
the  enamel ;  but  whether  it  has  any  influence  upon  the  hardness  or  not 
I  am  unable  to  say.  Those  teeth  Mhich  have  the  greatest  amount  of 
pigment  have  the  most  compact  formation,  and  rice  versa.  Pigmenta- 
tion after  eruption  comes  from  without  and  may  be  due  to  various 
causes  :  the  use  of  tobacco  is  the  most  probable  source  of  external  pig- 
mentation. The  interprismatic  cement-substance  becomes  dissolved  by 
the  acids  of  the  mouth  to  a  greater  or  less  depth,  and  the  pigment 
lodges  in  the  spaces  so  formed,  also  coating  the  surface. 

This  pigmentation  must  not  be  confounded  with  the  change  in  the 
color  of  the  enamel  which  results  from  death  of  the  pulp.  In  a  vast 
majority  of  cases  the  enamel  in  human  teeth,  by  reason  of  its  translucency, 
transmits  the  varying  changes  in  the  color  of  the  dentine.  That  there 
is  no  pigmentation  of  enamel  itself  in  these  cases  may  be  proved  by  cut- 
ting out  the  underlying  dentine  and  filling  with  chloride  of  zinc  or  some 
other  white  filling.  Indeed,  this  mode  of  "  mechanical  bleaching  "  has 
come  into  almost  general  practice. 

This  naturally  brings  us  to  the  consideration  of  the  dense  polished 
outer  coat  of  enamel. 

This  layer  shows  a  distinct  characteristic  variation  from  the  prismatic 
layer  underneath.  It  is  the  outer  capping  of  the  prisms,  and  furnishes 
a  polished  surface  for  the  coat  of  mail  which  is  best  adapted  for  its 
office.  Smooth,  polished  surfaces  are  known  to  resist  the  eroding  action 
of  acids  longer  than  rough  surfaces.  The  character  and  shape  of  the 
ameloblasts  change  before  this  layer  is  formed.  From  a  membrane 
comj)osed  of  prismatic  cells,  they  now  assume  a  horizontal  direction. 
I  have  studied  these  changes  in  the  form  and  direction  of  the  axis  of 
the  ameloblasts  in  sections  of  incisor  teeth  of  rodents,  where  it  was 
very  plainly  shown.  Enamel  is  here  being  continuously  formed  on  the 
labial  side,  at  the  base  of  the  tooth,  to  supply  loss  by  attrition.  All 
the  stages  of  calcification,  as  well  as  the  changes  which  occur  in  the 
ameloblasts,  are  plainly  demonstrated  in  one  tooth.  Below  a  certain 
point  the  enamel-prisms  are  yet  unfinished,  and  here  the  ameloblasts 
are  seen  to  be  prismatic  in  form ;  toward  the  surface  they  gradually 
shorten  and  widen  until  near  the  margin  of  the  gum,  when  thev  change 
from  a  position  at  right  angles  with  the  axis  of  the  tooth  to  a  longitu- 
dinal direction,  Mrs,  Emily  Whitman  also  noted  these  changes  in 
studying  the  development  of  the  teeth  in  the  ray  and  rabbit.  Mrs. 
Whitman  says :  "" 

"  The  cuticula  of  the  mammalian  tooth  has  several  times  been  found 
to  have  the  same  structure,  and  it  has  been  possible,  in  transverse  and 
longitudinal  sections,  to  trace  the  gradual  transition  of  the  enamel-cells 
into  a  perfectly  homogeneous  membrane  (Fig.  338),  the  cylindrical  cells 
growing  shcM'ter  as  they  approach  the  croAvn  of  the  tooth,  until,  instead 
of  being  columnar,  they  are  almost  square,  and  finally  flattened,  and 
at  last  the  outlines  of  the  cells  quite  disappear,  and  there  is  left  a 
perfectly  homogeneous  membrane. 


A  MELIFICA  TION. 


607 


"  These  clianges  are  not  easy  to  follow ;  in  many  preparations  it  is 
impossible  to  make  anything  out,  and  the  drawings  have  been  made 
from  most  fortunate  preparations  selected  from  some  thousands  of 
sections  prepared  in  various  ways. 

"  The  cuticula  dentis,  then,  is  formed  by  the  metamorphosis  of  more 
or  less  of  the  enamel-cells,  and  this  metamorphosis  may  begin  before 

Fig.  338. 


-)4 


^# 


J 


5\\1i 


Can.-t 


St-R- 


A  portion  of  a  Longitudinal  Vertical  Section  of  the  Upper  Small  lucisor  of  a  Rabbit:  em,  1,  2,  3,  4,  "i, 
are  cells  of  the  enamel-membrane  drawn  at  intervals,  showing  their  gradual  change  as  they 
approach  the  crown  of  the  tooth,  until,  on  its  exposed  portion,  they  form  :i  homogeneous  mem- 
brane.    Obj.  F.  Zeiss. 

any  calcification  of  the  underlying  dental  tissues.  In  this  stage  it  has 
been  frequently  taken  for  the  '  newly-formed  layer  of  enamel,'  for  the 
'basement-membrane,'   and   for  the   '  fir,st-formed    layer  of  dentine.'" 

It  is  evident  that  if  the  prisms  dejjend  upon  the  shape  of  the  amelo- 
blasts  for  their  form  the  lime  salts  laid  down  from  this  altered  mem- 
brane would  differ  materially  from  the  secretion  from  the  ends  of  the 
prismatic  ameloblasts,  and  so  we  find  it. 

The  analogy  between  the  internal  layer  of  the  Pinna,  which  we  have 
before  studied,  and  the  outer  layer  of  enamel,  is  complete.  Each 
individual  prism  of  enamel  is  the  work  of  a  single  aiueloblast ;  the 


608 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 


outer   layer   of  enamel,   however,   is  secreted   by   the   cuticula   dentis 
before  the  tooth  erupts. 

The  origin  and  office  of  Nasrayth's  membrane,  or  cuticula  dentis, 
has  been  a  matter  of  very  considerable  speculation.  I  am  fully  con- 
vinced, from  a  study  of  the  teeth  of  rodents,  that  this  mem]>rane  arises 
by  a  metamorphosis  of  the  ameloblastic  layer  as  described  by  Mrs.  Whit- 
man, and  I  farther  believe  that  the  change  in  the  character  of  this  mem- 
brane is  of  prime  importance  in  the  development  of  enamel.  We  have 
seen  that  the  enamel-prisms  derive  their  form  from  the  prismatic  amelo- 
blasts.  This  being  the  case,  the  ameloblastic  layer,  as  such,  could  not 
complete  the  calcification  of  the  cortical  layer  of  enamel.  This  layer  is 
deposited  underneath  the  cuticula  dentis,  and  in  its  deposition  the  life- 
work  of  this  membrane  is  com])leted ;  for  it  cannot  be  shown  to  have 
any  other  essential  signification.  In  a  newly-erupted  tooth  the  enamel 
may  be  divided  into  tliree  layers — the  internal,  or  prismatic  ;  the  corti- 
cal, or  nacreous;  and  the  organic  layer,  or  cuticula  dentis. 


Diagrammatic  Section  of  Eraniel  and  Dentine:  '7,  dentine;  e7;i,  enamel  prisms;  ?i/,  nacreous  layer ; 

(7,  cuticula  dentis. 

In  the  nacreous,  or  cortical,  layer  we  have  a  structure  analogous  in 
formation  and  character  to  the  internal,  or  nacreous,  layer  found  in 
shells.  The  latter  has  been  conclusively  demonstrated  by  Dr.  Car- 
penter to  be  secreted  by  the  altered  layer  of  cells  which  produced  the 
older  prismatic  layer.  The  cuticula  dentis  corresponds  to  the  mem- 
brane described  by  Dr.  Carpenter  as  found  in  connection  with  the 
nacreous  layer  of  shells. 

Variations  in  density  in  the  enamel  of  the  teeth  of  different  individ- 
uals are  due  to  several  causes.  The  first  essential  diflFerence  lies  in  the 
proportionate  amounts  of  phosphate  and  carbonate  of  calcium.  Enamel 
in  which  there  is  more  than  a  minimum  amount  of  calcium  carbonate 
will  be  softer  than  enamel  which  contains  less — the  deficiency  being 
sup])licd  by  phospliate  of  calcium — and  vice  versd,  as  will  be  seen  from 
the  following  table,  made  by  Von  Bibra  : 

Adult  Adult 

man.         woman. 

Calpinm  phosphate  and  fluoride 89.82  81.83 

Calcium  carbonnte 437  g  gg 

Masncsiiini  pliosphatc 1.34  2.55 

Otlier  salts 88  .97 

Cartilage 3.39  5.97 

Fat  . 20  a  trace. 

Organic 3.59  5.97 

Inorganic 96.41  94.03 

It  will  be  seen  l)y  the  above  table  that  the  essential  point  of  difference 
between  the  enamel  of  man  and  woman  lies  in  the  contained  amount 


AMELIFICATION.  609 

of  carbonate  and  phosphate  of  calcium.  It  is  a  well-known  fact  that, 
as  a  rule,  the  teeth  of  women  are  softer  than  those  of  men ;  this,  I  think, 
is  accounted  for  by  the  greater  per  cent,  of  carbonate  salts  of  calcium, 
being  4.37  in  man  and  8.88  in  woman.  There  is  also  found  more 
"  organic,"  or  fixed,  material  in  the  teeth  of  woman  than  in  man — 5.97 
in  the  former,  as  against  3.59  in  the  latter.  We  have  already  seen  that 
in  that  degree  in  which  enamel  contains  fixed,  or  organic,  material  is  it 
incapable  of  performing  its  office  and  resisting  the  action  of  the  fiuids 
of  the  mouth. 

Dr.  Miller  of  Berlin  has  very  conclusively  shown  that  the  products 
of  fermentation  have  the  power  of  digesting  the  fixed  material  found  in 
dentine ;  they  therefore  would  act  upon  any  similar  material  found  in 
enamel.  But,  as  I  have  said  before,  any  considerable  amount  of  fixed, 
or  organic,  material  in  enamel  is  pathological,  and  enamel  that  contains 
such  material  will  be  found  to  decay  very  early  in  life. 

The  newly-erupted  tooth  hardens  by  desiccation  after  it  makes  its 
appearance.  The  saliva  found  in  a  child's  mouth  is  neutral  or,  more 
generally,  alkaline.  The  latter  condition  probably  extracts  water  from 
the  enamel.  The  teeth  are  constantly  exposed  to  currents  of  air,  which 
certainly  extract  water.  This  is  fully  demonstrated  by  the  checkhu/  of 
the  enamel  in  the  mouths  of  persons  who  habitually  breathe  through  the 
mouth.  The  fact  that  the  enamel  of  teeth  which  have  been  extracted 
for  some  time  becomes  so  hard  that  it  will  turn  the  edges  of  our  best 
burrs  proves  the  correctness  of  my  assertion,  that  enamel  hardens  by 
desiccation. 

A  crystallized  substance  of  the  character  which  we  are  studying 
cannot  become  denser  than  it  is  except  by  giving  up  a  portion  of  its 
water  of  crystallization.  Crystallized  bodies  vary  in  density,  but  the 
variation  is  due  to  the  different  forms  of  crystallization  of  the  several 
ingredients  which  go  to  make  up  the  body.  When  crystals  give  up  a 
part  of  their  water  of  crystal ization  they  become  exceedingly  brittle. 
Now,  enamel  is  not  a  pure  crystallized  product,  but,  nevertheless, 
evinces  this  same  property  to  a  considerable  extent ;  you  can  chip  the 
thin  edge  of  the  enamel  in  the  artificially  dried  tooth  very  easily  by 
slight  pressure  of  the  thumb-nail.  I  know  of  no  law  by  which  a 
crystal  once  formed  can  become  denser  except  l)y  the  one  already 
named — viz.  that  of  desiccation.  I  know  it  is  a  popular  idea  among 
dentists  that  enamel  varies  in  hardness  at  different  times,  but  I  have 
never  seen  a  case  where  I  was  fully  convinced  that  enamel  once  softened 
by  the  acids  of  the  mouth  ever  became  harder,  except,  it  might  be,  by 
tlesiccation.  I  have  seen  children's  teeth  which  were  quite  soft  when 
erupted  become  harder  in  finie,  and  by  the  use  of  tooth-powders ;  but 
whether  it  M^as  the  powder  or  the  time — which  latter  allowed  of  desic- 
cation— is  an  open  question.  I  am  in  favor  of  crediting  the  latter 
with  accomplishing  the  benefit.  I  have  been  in  the  habit  of  using 
powder  dry,  and  so  advising  my  patients.  I  have  no  doubt  that,  so 
used,  it  will  extract  water  from  the  enamel  and  hasten  the  hardening 
process. 

The  enamel  of  teeth  which  have  given  up  a  portion  of  their  water 
of  crystallization  do  not  resorb  it  and  return  to  their  former  condition. 
Vol.  L— 39. 


610  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

When  it  has  become  checked  by  constant  breathing  through  the  mouth, 
it  always  remains  chocked.  Then,  again,  I  have  no  doubt  that  teeth 
the  enamel  of  which  has  softened — during  pregnancy,  for  instance 
— may  appear  to  harden  ;  but  in  such  cases  the  softening  has  been 
superficial,  and  this  thin  layer,  by  the  processes  of  attrition,  becomes 
worn  away,  and  the  underlying  layer  of  enamel,  which  has  not  been 
alfected,  becomes  polished  and  cannot  be  told  from  the  outer  layer  by 
ord  i  nary  obser  vat  ion . 

Finally,  then,  enamel  is  the  product  of  an  organ  which  in  the  erup- 
tion of  the  tooth  ceases  to  exist,  and  which,  if  it  does  remain,  is  lifted 
by  the  eruption  beyond  the  source  of  nutrient  supply  and  cannot  there- 
after exercise  any  influence  over  the  physical  condition  of  the  enamel. 
The  many  varieties  of  calcified  tissues  are  due  to  the  variations  in  the 
form  and  nature  of  the  matrices  and  the  conditions  and  positions  in 
which  the  lime  salts  are  laid  down.  They  are  not  dependent  upon  any 
variation  or  special  vital  function  exerted  upon  the  crystallizing  prod- 
ucts, but  are  due  to  the  form  of  crystallization  and  the  special  salts  of 
calcium  which  enter  into  their  formation.  I  do  not  think  that  the 
theory  ad\'anced  that  secondary  changes  do  occur  in  enamel  by  recrys- 
tallizatiou  can  be  demonstrated. 

Development  of  the  Teeth. 

It  is  with  the  feeling  that  no  easy  task  lies  before  me  that  I  enter 
upon  this  section.  Frey  has  well  said  that  tooth-development  is  the 
most  difficult  subject  that  embryologists  are  called  upon  to  demonstrate. 
The  study  of  developing  hair  and  glands  is  comparatively  simple,  and 
cah'ified  products  ahjue  do  not  seem  intricate ;  but  when  w'e  approach 
the  consideration  of  both  these  conditions  in  one  structure,  we  seem  to 
stand  before  an  unfathomable  mystery.  It  is  only  as  we  approach  the 
problem  from  the  standpoint  of  general  histology  that  we  get  anything 
like  a  full  and  true  interj^retation  of  the  phenomena  of  tooth-devel- 
opment. A  microscopic  examination  of  the  intimate  tissue  concerned 
in  tooth-devel()j)ment  led  to  the  discovery  that  the  teeth  are  developed 
in  the  mucous  membrane ;  that,  instead  of  standing  in  close  relation  to 
the  bony  skeleton  of  the  body,  they  are  a  part  of  its  outer,  or  dermal, 
system  ;  that  they  are  developed  in  a  similar  manner  to  hair,  nails,  glands, 
etc.,  by  a  jirocess  of  involution.  Besides  conducting  us  to  new  truths 
concerning  the  natnre  and  constitution  of  the  teeth,  the  microscope  has 
shown  us  how  to  apply  this  knowledge  in  a  better  system  of  hygienic 
rules  which  aim  at  rendering  their  decay  less  rapid,  their  life  more . 
vigorous,  and  their  loss  less  frequent. 

All  who  wish  successfully  to  prosecute  pathological  in(piiries  regard- 
ing decay  of  the  teeth  will  do  well  to  acquaint  themselves  not  only  with 
the  histological  character  of  the  teeth  of  the  human  subject,  but  with 
that  of  some  of  the  lower  animals. 

I  have  comjmred  tooth-development  in  the  human  with  that  found 
in  embryo  pigs,  calves,  and  lambs,  and  find  that  the  porcine  embryo 
varies  very  little  from  the  human,  l^ig  embryos  are  so  easily  obtained, 
and  in  any  size  desired,  that  I  am  confident  that  they  will  come  to  be 


THE  EMBRYONAL  MUCOUS  MEMBRANE  OF  THE  MOUTH.      611 

almost  universally  used  to  demonstrate  the  subject  under  consideration. 
I  furnish  them  to  my  classes,  and  allow  them  to  harden  and  cut  them 
at  will. 

The  very  early  stages  of  development  have  been  the  ones  over  which 
so  much  misunderstandmg  has  arisen,  and  these  differences  of  opinion 
have  largely  resulted  from  a  study  of  poor  specimens.  By  obtaining 
good  specimens  from  porcine  embryos  these  difficulties  can  be  obviated. 

The  late  advance  in  our  knowledge  of  this  subject  is  due  to  new 
technique  in  methods  of  staining  and  section-cutting,  especially  the 
introduction  of  celloidin,  by  means  of  which  we  have  been  able  to  obtain 
sections  of  human  teeth  that  had  progressed  even  as  far  as  the  eighth 
month,  and  teeth  of  other  animals  of  corresponding  age,  without  disturb- 
ing the  relationship  of  the  parts. 

Before  the  introduction  of  celloidin  into  our  technique  it  was  not 
possible  to  obtain  sections  of  jaws  with  teeth  in  situ  Avithout  more  or 
less  mutilation,  especially  if  calcification  had  proceeded  to  any  consid- 
erable extent ;  by  its  aid  I  have  been  able  to  preserve  a  serial  line 
of  slides  without  break  or  tear  in  the  sections  employed.  And, 
further,  the  illustrations  made  by  the  new  process  of  photolithograph- 
ing  have  enabled  me  to  eliminate  the  much-tabooed  "  personal  equa- 
tion" which  accompanies  wood-cuts.  Whatever  may  be  said  against 
photomicrography  in  its  delineation  of  cell-structure,  surely  no  excep- 
tion can  be  taken  to  it  as  a  delineator  of  the  outliaies  of  organs  .  or 
structures  like  the  developing  tooth.  It  gives  an  accurate  picture, 
upon  whose  exact  amplification  we  can  rely. 

I  have  taken  my  illustrations  from  serial  lines  of  porcine  embryos, 
referring  to  the  corresponding  ages  in  the  human  foetus  as  I  proceed, 
believing  that  it  is  better  to  describe  those  specimens  which  are  best  pre- 
served and  of  which  I  have  been  able  to  make  good  photomicrographs 
than  to  use  human  foetuses  less  perfectly  preserved. 

The  Embryonal  Mucous  Membrane  op  the  Mouth. 

There  exists  a  great  lack  of  agreement  among  writers  on  dental 
embryology  regarding  terms  and  descriptions  of  the  mucous  mem- 
brane of  the  mouth  during  the  evolution  of  the  teeth.  It  must  be 
rememl)ered  at  the  outset  that  the  membrane  itself  is  in  a  formative 
state  and  presents  different  aspects  in  the  several  stages.  The  most 
marked  changes  are  seen  in  the  epithelial  layer.  This  is  analogous 
and  continuous  with  the  skin  covering  the  body,  as  I  have  taken 
occasion  to  show  in  presenting  the  development  of  the  oral  cavity. 
There  is,  however,  one  point  of  difference  between  the  two,  due  to  the 
widely  different  conditions  in  Avhich  they  are  located.  The  external 
covering  of  the  body  is  constantly  subject  to  the  drying  action  of  the 
atmosphere,  which  produces  the  corneous  layer.  The  sweat-glands,  to 
a  greater  or  less  extent,  keep  the  skin  moist,  but  not  sufficiently  so 
'to  prevent  desiccation.  The  oral  mucous  membrane  is  at  all  times 
bathed  by  the  saliva,  which  prevents  it  from  assuming  the  corneous 
appearance  seen  in  the  outer  covering  of  the  body.  The  same  may 
be  said  of  the  rectum  and  vagina :  were  the  conditions  of  the  mem- 


612 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 


braiies  the  same  as  those  of  the  skin,  \ve  would  find  an  analogous 
condition  in  the  oldest  layer  of  cells.  As  proof  of  the  latter  state- 
ment I  cite  the  following  case,  to  which  my  attention  was  called  some 
time  ago — a  chronic  case  of  procidentia  of  over  two  years'  standing ; 


Enibi-yoiiu:  Mucous  Membrane. 

Mature  Mucous  Membrane. 

Skin. 

6 

3 

s 

s 
o 

s 

IS 

1 

Older  layer. 

Oldest  layer. 

Corneous  layer. 

Older  layer. 

Older  layer. 
Infant  layer. 

lufant  layer. 

Infant  layer. 

Basement-membrane. 

Embryonal  connective 
tis.siie. 

Papillary  layer  of  mem- 
bran  a  mucosEe. 

Papillary  layer  of 
dermis. 

Sub-mucosse. 

Subdermis. 

'.  above  diagram  shows  a  comparison  between  the  developing  nuicons  membrane,  mature  mucous 
memlirane,  and  skin.     Between  the  epidermis  and  dermis  lies  the  division-line  commonly  called 


the  mucous  membrane  of  the  vagina  was  turned  completely  inside  out, 
and  for  that  length  of  time  had  been  exposed  to  the  external  atmosphere. 
The  most  careful  examination,  except  for  the  absence  of  hairs,  could 
not  elicit  any  difference   between  that  which  was   formerly  the  lining 

Fig.  340. 


Porcine  Kmbryo  (1 


■  cm.  in  length, 


;  2.'>0):  (■/,  connective  tissue  of  mesoblast;  ep,  epiblast,  formed  of 
one  layer  of  cells. 


membrane  of  the  vagina  and  the  skin  covering  any  other  portion  of 
the  body.  Here  we  have  a  positive  demonstration  that  the  difference 
between  the  mucous  membrane  of  the  vagina  and  the  skin  is  one  of 
environment,  and  not  a  pliysiological  difference,  and  does  not  neces- 
sitate a  different  classification.     If  the  terms  which    appeared  first  in 


THE  EMBRYONAL   MUCOUS  MEMBRANE  OF  THE  MOUTH.      613 


Dean's  translation  of  Legro's  and  Magitot's  Denial  Follicle — viz. 
infant,  older,  and  oldest  layers — come  to  be  adopted,  it  \\\\\  very  con- 
siderably simplify  our  terminology  and  materially  assist  the  student 
to  a  comprehension  of  the  subject.  The  table  on  p.  612  will 
help  to  disabuse  these  terms  of  their  intricacies,  and  to  show  a  com- 
parison between  the  developing  mucous  membrane  as  seen  at  the  com- 
mencement of  the  formation  of  the  band,  the  mature  nuicous  membrane, 
and  the  skin. 

The  develo])ing  muc-ous  membrane,  as  shown  by  the  following  serial 
studies  from  photomicrogi-aphs,  will  exhibit  very  plainly  the  changes 
which  it  undergoes.  The  hrst  one  (Fig.  340),  taken  from  a  porcine 
embryo  1 — cm.  in  length,  shows  the  epithelial  layer  to  consist  of  a 
single  layer  of  cells.  Considerable  space  is  seen  between  the  cells, 
which  consist  simply  of  nuclei  lying  in  a  bed  of  protoplasm ;  they 
are  oval,  with  their  longest  axis  placed  longitudinally  and  parallel 
with  the  basement-membrane. 

The  next  one  in  the  series  (pig  \\  cm.)  indicates  that  rapid  cell- 
multiplication  is  proceeding.  The  nuicous  membrane  has  thickened, 
and   is   now   formed  of  several 

layers  of  spheroidal    cells — not  ^'^-  '^^^• 

arranged  in  strata,  but  pre- 
senting an  irregular  adjust- 
ment, in  some  instances  several 
cells  deep.  These  cells  have 
not  differentiated  any  cell-body 
or  wall,  but,  like  those  before 
seen,  are  still  located  in  a  bed  of 
protoplasm.  This  constitutes 
the  infant,  or  deepest,  layer  of 
the  rete  Malpighii. 

In  the  next  specimen  (j)orcine 
embryo  2^  cm.  in  length)  in  the 
region  of  the  band  the  epithelial 
layer  is  perceptibly  thickened, 
and  in  such  a  manner  as  to 
depress  the  underlying  tissue 
and  fill  the  groove  thus  made. 
This  figure  is  presented  here  to  show  that  at  the  very  inception  of  the 
formative  process  there  is  no  appearance  of  columnar  cells  in  the  deep- 
est layer  of  the  rete  Malpighii,  as  has  been  so  extensively  stated  by 
other  authors.  The  character  of  the  cells  of  the  infant  layer  has  not 
changed ;  there  has  sim])ly  been  an  aggregation  of  nuclei  along  the  line 
of  the  forming  band,  which  is  the  result  of  sucli  accumulation. 

In  the  next  of  our  series  (pig  3  cm.)  a  noticeable  change  is  seen  :  cell- 
multiplication  is  rapidly  progressing  and  the  mucous  membrane  is  con- 
siderably thickened.  The  infant  layer  is  as  well  marked  as  before  ;  the 
cells  are  of  a  similar  character,  nuclei  lying  in  a  bed  of  protoplasm,  j^er- 
haps  a  little  more  closely  packed,  thus  giving  the  infant  layer  a  darker 
appearance.  This  is  now  made  more  noticeable  by  the  fact  that  above 
the  infant  layer  a  second  layer  of  cells  is  seen,  forming  an  older  layer, 


Porcine  Embryo  (U  cm.  X  250):  fp,  epithelium,  in- 
fant layer ;  cl,  embryonal  connective  tissue  with 
large  intercellular  interspaces. 


614 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 


the  cells  of  which,  in  being  pushed  up  from  the  infant  layer,  have  car- 
ried a  certain  amount  of  protoplasm  with  them,  surrounding  each  cell. 
A  marked  diti'erence  is  seen  between  this  protoplasm,  which  surrounds 
the  nuclei  of  the  older  layer,  and  that  surrounding  the  nuclei  of  the 
infant  layer.  In  the  latter  case,  with  hsemotoxylon  and  eosin,  it  stains 
very  readily  and  darkly,  while  in  the  former  it  appears  as  an  un- 
stained mass  surrounding  the  nucleus.  The  nucleus  is  the  germinal 
matter,  while  the  unstained  mass  surrounding  it  is  the  formed  material 
(Beale).  The  nucleus  and  the  formed  material  constitute  what  is  com- 
monly known  as  a  cell. 

These  cells  are  surrounded  by  a  certain  quantity  of  protoplasm,  which 
stains  darkly,  as  does  the  intercellular  protoplasm  in  the  infant  layer, 
and  forms  the  lines  which  appear  in  the  older  layer  in  Fig.  343.  The 
quantity  of  intercellular  material  decreases  as  we  proceed  toward  the 

Fig.  342. 


Porcine  F.nibryo  (il  cm.  X  IM)-  h.  rogion  of  l)and  ;  t'p,  epitheliiiin,  infant  layer;  f/,  embryonal  con- 
nective tissue.  The  space  between  the  two  layers  was  produced  by"  tearing  the  specimen 
intentionally. 

surface,  and  the  quantity  of  formed  material  increases  ;  so  that  the  cells 
grow  larger.  This  surrounding  formed  material  of  the  cell-body  is,  in 
all  })robability,  the  uudigested  or  unassimilated  ]>rotO])lasm  from  which 
the  germirud  matter,  or  micleus,  draws  its  nourishment. 

As  we  ]iroceed  iu  our  examination  of  older  embryos  we  find  the  cells 
losing  their  well-defined  outlines,  until  they  assume  the  appearance 
seen  in  Fig.  272,  taken  from  a  scra])ing  of  the  tongue  in  an  adult 
human  mouth.  They  constitute  the  oldest  layer,  are  farthest  removed 
from  the  source  of  mitrition,  and  c()rres])ond  to  the  corneous  layer  of 
the  skin. 

For  a  description  of  the  epithelium  of  the  skin  I  cannot  do  better 
tiian  make  several   quotations  : 

''The  epithelium  constitutes  the  superficial  layer  of  the  skin.  Tn 
the  adult  tissue  the  epithelium  is  composed  of  tM'o  layers  of  cells — a 


THE  EMBRYONAL  MUCOUS  MEMBRANE  OF  THE  MOUTH.      615 

younger,  which  lies  at  the  deepest  portion,  and  an  older,  at  the  surface 
— the  '  outer  or  horny  layer,  consisting  of  very  thin,  transparent,  tough, 
scale-like  cells,  which  present,  for  the  most  part,  no  nuclei  and  are 
packed  closely  together ;  and  the  inner  layer,  the  so-called  mucous  or 
Malpighian  layer,  consisting  of  larger  and  smaller  nucleated  cells  of 
varying  shape  and  character.  In  the  deeper  portion,  adjoining  the 
corium,  the  cells  are  more  or  less  cylindrical ;  above  this  they  are  sphe- 
roidal or  polyhedral  or  elongated ;  still  nearer  the  surface  they  become 
flattened,  and  finally  merge  into  the  thin  cells  of  the  horny  layer.  In 
the  middle  zone  the  cells  present  a  peculiar  jagged  outline,  looking  as 
if  they  were  bordered  by  short,  delicate  spines,  by  which  the  cells 
appear  dovetailed  together.  These  spined  cells — called  prickle  cells — 
are  very  characteristic  of  this  part  of  the  epidermis,  and  are  also  found 

Fig.  343. 


Vertical  Section   Mucous  Membrane  of  Mouth  \'  cm.  porcine   embryo  X  2.10) :    o/,  older   layer    of 
cells;  //,  infant  layer  of  cells;  ct,  connective  tissue  of  mesoblast. 

in  certain  other  parts  of  the  body  where  stratified  epithelium  occurs,  as 
in  the  vagina,  raucous  membrane  of  the  mouth,  etc' "  (Pruddcn). 

Then  again : 

''  The  mucous  membrane  [of  the  mouth]  and  the  skin  are  ana- 
tomically analogous  and  continuous  structures.  The  first  clothes  the 
internal  and  the  other  the  external  surface,  and  the  description  of  the 
one  will,  wdth  slight  modifications,  apply  to  the  other.  In  a  general 
sense,  they  are  composed  of  two  strata,  or  layers — the  dermis  and  the 
epidermis  ;  yet,  for  convenience  of  description  rather  than  for  any  other 
reason,  thev  have  been  variously  subdivided.  The  external  stratum,  the 
epidermis,  composed  entirely  of  epithelial  cells,  has  been  described  as 
consisting  of  two  layers,  the  external  being  termed  the  corneous  and  the 


616  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

internal  the  INIalpighian.  The  '  scarf-skin  '  raised  on  tlie  external  sur- 
face of  the  skin  by  a  l)lister  and  the  pellicle  detached  from  the  palate 
bv  hot  drinks  represent  the  corneous  layer  of  the  epidermis.  By  some 
authors  this  is  called  the  '  true  epidermis/  and  by  some  the  '  cuticle,' 
This  layer  is  composed  of  the  old  epithelial  cells  which  have  ceased  to 
perform  any  of  the  vital  functions.  The  subjacent  layer,  formed  of 
living  epithelial  cells  which  vary  in  form  and  size,  is  denominated 
(among:  many  terms)  the  '  stratum  Malpighii '  "  (Dean's  Dental  FoUicle). 
These  descriptions  apply  to  adult  tissues.  Let  us  turn  uom^  to  the 
consideration  of  embryonal  tissues,  for  it  is  with  the  latter  that  we  have 
to  deal  in  the  study  of  the  development  of  the  teeth. 

Dental  Ridge. 

I  will  first  consider  a  section  from  the  jaw  of  a  porcine  embryo  1^ 
cm.  (Fig.  341 )  in  length  ;  this  compares  in  age  with  a  human  fcetus  of 
four  weeks.  In  the  epiblastic  layer  which  covers  the  gums  is  seen  the 
first  indication  of  that  cellular  activity  which  later  will  result  in  the 
evolution  of  the  teeth.  By  comparing  the  epithelial  covering  of  the 
gums  we  shall  see  that  it  is  composed  of  two  or  more  layers  of  oval 
cells  which  present  evidences  of  active  cell-multiplication,  while  the 
same  membrane  upon  the  outer  portion  of  the  body  is  yet  composed 
of  only  one  layer  of  cells.  The  thickening  of  the  epithelial  cov- 
ering of  the  gums  is  at  first  general,  and  results  in  the  formation  of 
a  thick  layer.  The  next  change  is  not  so  much  evidenced  upon  the 
surface  as  it  is  in  vertical  sections  of  the  jaws.  The  same  cellular 
activity  which  resulted  in  a  general  thickening  of  the  epithelial  cover- 
ing of  the  gums  now  becomes  centred  along  a  line  which  marks  the 
crest  of  the  gums  and  locates  the  line  to  be  occupied  by  the  future  arch 
of  teeth.  The  multiplication  of  cells  is  found  to  be  in  the  infant  layer 
of  the  rete  jSIalpighii,  or  that  layer  which  lies  nearest  the  supply  of 
cell-jiabulum  that  is  furnished  by  the  vessels  located  in  the  subepithe- 
lial tissue.  No  vascular  supply  has  ever  been  demonstrated  in  the 
cpithelia  pro])er. 

Rapid  cell-nudtiplication  along  the  line  just  described  results  in  a 
thickening  of  the  o/der  layer  of  cells,  giving  rise  to  a  slight  ridge 
higher  in  some  embryos  than  in  others.  This  ridge  has  been  des- 
ignated by  K()lliker,  Waldeyer,  and  Kallman  as  the  Kieferwall,  or 
maxillary  rampart. 

Concomitant  with  the  formation  of  the  ridge,  the  proliferation  of  the 
cells  of  the  infant  layer  causes  a  depression  of  the  subejMthelial  layer 
lying  inmiediately  underneath.  Were  we  to  lift  up  this  thickened 
e])ith('lial  layer,  it  would  leave  behind  a  groove  in  the  underlying 
tissue  ;  but  let  it  be  remembered  that  in  lifting  the  ridge  or  rampart  of 
e])ithelial  cells  we  have  made  the  groove.  It  is  never  a  ditch  or  groove 
per  se,  but,  when  found,  is  always  an  artificial  product  which  can  be 
made  at  Avill.  As  cell-nmltiplication  advances  this  groove  deepens, 
taking  a  direction  toward  the  centre  of  the  arch. 

To  this  groove  filled  with  epithelial  cells'  "  Legro  and  Magitot  have 
'  Dean's  translation,  Legro  and  Magitot. 


DENTAL  RIDGE. 


617 


given  the  name  bourrelet,  which  means  a  rounded  pad  or  cushion. 
This  structure  was  for  a  long  time  supposed  to  be  cartilaginous  in  its 
nature,  and  hence  called  cartilago  dentalis,  until  Raschkow  discovered 
its  epithelial  character.  M.  Guillot  (1859)  named  it  the  odontogenio 
part,  or  the  generating  part,  of  the  teeth." 

The  term  band,  which  has  been  so  universally  adopted,  while  not 
expressing  the  exact  nature  of  the  thickened  layer  of  cells,  yet  when 
modified  by  the  adjective  epifhe/kd  as  nearly  expresses  the  principal 
characteristics  as  any  other ;  and  for  lack  of  a  better  term  we  will  use 
it  hereafter. 

From  the  condition  seen  in  a  vertical  section  through  the  jaw  of  a  2^ 
cm.  porcine  embryo,  which  compares  with  the  human  at  from  the  forty- 
fifth  to  the  sixtieth  day,  as  seen 
in  the  accompanying  photomi- 
crogra])h  (Fig.  344),  the  epithe- 
lial band  rapidly  deepens  by 
cell-proliferation  at  the  deepest 
point.  The  centre  of  the  lower 
jaw  is  occupied  by  Meckel's 
cartilage,  and  the  axis  of  the 
band  assumes  a  direction  which 
would  cause  it  to  pass  between 
the  cartilage  and  the  inner  side  O'^i-!:^'''^^!!**®^:!/,- 
of  the  jaw.  Were  such  lines  %iMlMl^5fi^'!f ''?  ^ 
continued  in  the  same  direction  \^:0^^^^$^4^::<^:7^  "" 
from  several  points  of  the  band, 
thev  would  converge  to  a  ffiven 
centre. 

In  vertical  transverse  sections 
the  band  assumes  a  plough- 
share shape  with  the  mould- 
board  side  directed  toward  the 
inner  side  of  the  jaw.  This  is  shown  very  nicelv  in  Fig.  345,  taken 
from  a  porcine  embryo  21  cm.  in  length,  M'hich  compares  with  a  liuman 
foetus  of  two  and  one-half  months.  The  convex  surface  of  the  band  is 
toward  the  outer  side  of  the  ja^v.  This  peculiar  curve  is  almost  univer- 
sally seen,  and  constitutes  one  of  the  most  characteristic  and  persistent 
features  of  the  band.  The  walls  of  the  band  are  composed  of  the  i)if(iiit 
layer  of  cells,  while  its  centre  is  filled  with  the  o/der  cells,  which  have 
l)een  pushed  off  from  the  sides  as  new  cells  Iiave  been  developed  in  the 
infant  layer.  Note  the  fact — so  plainly  shown — that  the  deepest  layer  of 
the  rete  Malpighii  (infant  layer)  is  not  composed  of  columnar  cells,  but 
of  oval  nuclei  surrounded  by  a  mass  of  protoplasm,  which  does  not  as 
yet  present  any  indication  of  separating  into  cell-body  for  each  individ- 
ual cell.  AVhen  the  nuclei  are  pushed  up  from  this  bed  of  protoplasm, 
a  certain  amount  of  it  accumulates  around  each  nucleus  and  becomes  the 
cell-body,  on  the  surface  of  which  a  cell-membrane  soon  becomes  visible. 
We  have  then  a  ditch  or  groove  in  the  subepithelial  tissue  filled  to  over- 
flowing with  epithelial  cells  which  by  reason  of  their  growth  have  formed 
the  groove  in  which  they  lie. 


Porcine  Embryo  f2i^  cm.  X  fiO).  inferior  maxilla: 
B,  first  stage  in  the  formation  of  hand;  fp,  epithe- 
lium ;  cf,  embryonal  connective  tissue. 


618 


DENTAL   EMBRYOLOGY  AND   HISTOLOGY. 


The  band  as  seen  in  its  inception  is  broad  (Fio-.  344),  but  as  devel- 
opment progresses  and  it  sinks  deeper  into  the  jaw  it  becomes  narrower, 
as  seen  in  Fig.  345.     The  band  is  deepest  at  the  anterior  portion  of  the 


Fig.  345. 


Vertical  Section  Band  Porcine  Embryo  (21  cm.  X  250) :  e)i,  epithelium  with  infant  layer  (U) ;  b,  band  ; 

c/,  connective  tissue. 

jaw,  gradually  growing  shallower  until  it  flattens  out  into  the  epithelial 
covering  of  the  gums.  The  sections  here  shown  are  taken  from  the 
region  of  the  premolars  in  the  pig — first  or  second  molars  in  the  human 
embryo.  The  band  in  the  region  of  the  incisors  is  considerably  deeper 
than  at  the  }>oint  where  the  section  from  which  this  figure  was  made  w'as 
cut.     Po.steriorly  it  grows  shallower,  until  It  finally  disappears. 

Cellular  activity  increases  rather  than  diminishes  as  age  advances ; 
this  activity  evinces  itself  in  that  part  of  the  band  which  is  located 
deepest  in  the  tissues.  The  rapid  multiplication  of  cells  at  this  point 
causes  the  deepest  edge  of  the  band  to  become  expanded,  and  as  this 
band  sinks  farther  into  the  substance  of  the  jaw  this  expanded  por- 
tion becomes  indented  its  entire  length  through  the  resistance  offered 
by  the  underlying  tissues.  Thus  a  sheet,  or  lamina,  is  given  off  from 
the  inner  side  of  the  band. 

There  are  two  ways  of  demon.strating  the  formation  of  the  lamina — 
one  by  vertical  transvcr.<e  sections  of  the  jaw,  when  at  this  age  every 
section  cut  will  show  tlu;  band  as  a  W-shaped  infolding  of  the  infant 
layer ;  whereas  the  ])revious  figure  (345),  representing  an  earlier 
stage  in  development,  will  show  it  to  be  V-shaped.  Imagine  a  V- 
shaped  procc.«!s  by  reason  of  multi])lication  of  its  contents  becoming  U- 
shajicd,  and  aftci'ward,  by  indentation  of  the  base  of  the  process,  becom- 
ing W-.sha])('d,  and  you  have  a  fair  illustration  of  the  change  whicli  the 
infi)lding  epithelium  assumes.  (S(>e  Fig.  340,  .showing  the  W-shajied 
band  ;  b  represents  the  outer  base  of  the  W,  and  is  situated  on  the  outer 
side  of  the  jaw  and  corresponds  to  the  original  V-shaped  band-process ; 


DENTAL  RIDGE. 


619 


I  is  located  on  the  inner  side  of  the  jaw,  and  is  the  internal  sheet  or 
lamina  which  has  arisen  from  b,  as  if  a  second  V  had  been  added  to  the 
side  of  the  first,  thus  forming  the  W-shaped  process.  These  two  pro- 
cesses are  termed  the  band  and  lamina.  The  latter  is  only  a  process  of 
the  former.) 

If  we  cut  longitudinal  transverse  sections  of  both  sides  of  the  infe- 
rior maxilla,  we  first  obtain  sections  of  the  mucous  membrane ;  later 
we  get  sections  horseshoe-shaped  in  form,  the  outer  and  inner  edges  of 
which  will  show  a  layer  of  epithelium,  the  bulk  of  the  section  being 
made  up  of  embryonal  connective  tisue.  Located  equidistant  from 
either  side  we  will  see  a  band  of  epithelial  cells  which  extends  entirely 
around  the  arch  of  the  horseshoe-shaped  section.     Now,  if  such  a  sec- 

FiG.  346. 


Porcine  Embryo  (3  cm.  X  250) :  ep,  epithelium  with  infant  layer  at  ii;  ct,  connective  tissue;  6,  band; 

I,  lamina. 


tion  be  made  of  the  jaw  of  a  3  cm.  pig,  we  will  find  that  for  a  certain 
distance  from  the  surface  our  sections  will  apj^ear  as  above  described  ; 
but  as  soon  as  we  reach  the  deepest  part  of  the  ingrowing  epithelial 
proces.ses  we  will  find  two  (2)  bands  of  epithelial  cells  in.stead  of  one, 
thus  showing  that  we  have  cut  across  the  W-sha]ied  processes  known  as 
the  band  and  lamina.  Bet\veen  the  two  bands  the  space  is  occupied  by 
embryonal  connective  tissue  similar  to  that  formed  upon  either  side  of 
the  bands,  and  forming  the  boundary  of  the  section.  We  will  find,  as 
before,  on  both  outer  and  inner  side,  epithelium.  (See  Fig.  347,  repre- 
senting a  section  from  one-half  of  such  a  horseshoe-shaped  section.) 

As  we  have  seen,  cellular  activity  is  evidenced  in  the  deepest  portion 
of  the  ingrowing  processes.  The  lamina  forms  no  exception.  While 
cell-proliferation  apparently  seems  to  come  to  a  stand  in  the  band,  rapid 


620 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 


cell-multiplication  still  proceeds  in  the  lamina,  ^vhich  extends  deepei 
into  the  substance  of  the  jaw. 


Fig.  347. 


Longitudinal  Transverse  Section    Inferior  ^laxilla  (^  cm.  porcine  embryo  X  40):   b,  band,  solid  a( 
anterior  portion,  but  divided  posteridrly  into  band  and  lamina. 

As  this  change  is  being  accomplished  the  band  becomes  somewhat 
shallower  and  in  some  instances  disappears,  the  more  rapid  growth  of 
the  lamina  apparently  causing  the  straightening  of  the  outer  base  of  the 
W,  known  as  the  bund  ])roper.  When  we  consider  that  the  lamina  is 
only  an  offshoot  from  the  side  of  the  band,  it  is  very  easy  to  understand 
how  the  transferrence  of  development  from  one  side  of  the  band  to  the 
other  would  give  rise  to  the  disappearance  of  the  original  process. 

Development  so  far  has  been  general  in  character.  The  band  and 
lamina  have  a  common  office,  and  that  is  to  give  origin  and  direction  to 
the  cords  for  tlie  temporary  teeth.  Individualization  now  begins.  The 
intei'ual  development  of  cells  continues  with  unabated  energy,  express- 
ing itself,  not  in  the  extension  of  the  sheet,  or  lamina,  Init  at  regular 
intervals  which  correspond  to  the  ]iositions  to  be  occupied  by  the  tem- 
porary teeth.  Here  small  buds  make  their  appearance,  and  soon  extend 
into  slender  cords,  each  cord  developing  in  time  into  the  enamel  organ 
of  a  temporary  tooth  (Fig.  348). 

The  length  of  the  cord  varies  in  different  mammals,  those  in 
human  and  porcine  embryos  being  quite  short,  while  in  tlie  foetal 
calf  and  lamb  it  attains  considerable  length.  The  cords  for  the  per- 
manent teeth  are  of  necessity  longer  than  those  for  the  temporary  set, 


DENTAL  RIDGE. 


621 


having  to  descend  beyond  and  beneath  tlie  latter.     The  cord  is  com- 
posed of  a  solid  ingrowth  of  the  cells  which  constitute  the  lamina  from 


Fig.  348. 


Longitudinal  Transver.se  Section  of  both  sides  of  the  Inferior  Maxilla  (8  cm.  porcine  embryo  X  25) : 
6,  band ;  c,  cords  for  temporary  central  incisors ;  ct,  connective  tissue,  surrounded  on  its  outer 
circumference  by  a  thick  epiblastic  layer. 

which  the  cords  arise.  The  lamina,  as  we  have  seen,  arose  from  the 
band,  and  this  in  turn  from  the  oral  epithelium.  The  deepest  layer  of 
tiie  latter,  the  infant  layer,  consti- 
tutes the  outer  layer  of  the  cord.  ' 
It  is  composed  of  oval  or  spherical 
cells  similar  to  those  described  in 
studying  the  develojiment  of  hair 
and  glands.  These  cells  have  been 
very  extensively  spoken  of  as  col- 
umnar. They  sometimes  assume  a 
cylindrical  shape  when  the  layer  is 
only  one  cell  deep ;  but  if  more 
than  one  layer  exist,  then  they  are 
universally  oval  or  spherical.  The 
formation  of  the  cord  is  very  nicely 
shown  in  Fig.  349. 

The  cells  seen  at  c  are  the  older 
cells  which  have  been  pushed  off 
from  the  infant  layer  {d\  which 
forms  the  outer  tunic  of  the  cord. 
The  cords  at  first  stood  at  riglit 
angles  to  the  inner  side  of  the  band, 
having  an  axis  similar  to  the  direction  of  the  plane  of  the  lamina  of  which 


Vertical  Section  through  Band  from  .Taw  of  Por- 
cine Embryo  (.3J  cm.  X  60):  ey<,  epithelium  ;  ft, 
band ;  c,  cord  ;  cl,  connective  tissue. 


622 


DENTAL   EMBRYOLOGY  AND  LIISTOLOGY. 


they  are  an  extension.    They  radiate  to  a  common  centre,  and  lines  drawn 
through  their  several  axes  would  intei'sect  each  other  in  the  centre  of 


Fig.  35U. 


Same  as  349,  only  more  highly  tuagnifled:  6,  band  ;  c,  cord;  di;  dental  ridge  ;  ep,  epithelium  :  cl,  con- 
nective tissue. 

ba.se  of  the  tongue,  and  are  the  lines  referred  to  when  speaking  of  the 
direction  assumed  by  the  plane  of  the  band  in  the  first  instance. 

The  cord  soon  turns  sharply  upon  itself  and  dips  more  or  less  deeply 
downward  into  the  substance  of  the  jaw.  Internal  proliferation  of 
cells  results  in  the  formation  of  a  bulbous  extremity,  which  I  have 
designated  the  bulbous  cord.  With  these  changes  the  cord  is  seen  to  be 
becoming  more  deeply  embedded  in  the  substance  of  the  jaw  and  curves 
in  more  and  more  toward  the  plane  of  the  band,  thus  assuming  a  sickle 
shape.  (See  Fig.  351.)  The  cord  now  very  much  resembles  a  Mattson 
syringe  with  a  short  nozzle.  The  neck  of  the  cord,  which  forms  the 
connecting-link  between  the  bulbous  part  and  the  band,  does  not  keep 
pace  with  the  deepest  extremity  in  growth,  assuming  more  and  more  the 
character  of  a  neck,  and  is  very  rightly  named  the  neck  of  the  enamel 
organ. 

A  horizontal  transver.se  section  made  of  the  jaw  at  this  stage  of  devel- 
opment will  show  a  vertical  ti'ansverse  section  of  the  cord  lying  beside 
a  longitudinal  section  of  the  band. 

Studying  sections  from  the  jaw  of  a  3|-  cm.  pig,  we  notice  that  the  cord 
has  become  ])ear-shapcd,  and  the  section  presents  the  appearance  of  a  stir- 
rup. The  flattening  at  the  deepest  portion  is  caused  by  contact  with  a  new 
element — viz.  the  dentmal  papi(/a,  which  now  pre.sents  a  new  feature 
for  our  consideration. 

The  papilla  which  will  constitute  the  future  pulp  of  the  tooth  is,  as 


DENTAL  RIDGE. 

Fig.  351. 


623 


Vertical  Section  through  Rami  and  Cord  of  3*  cm.  Porcine  Embryo  X  60:  ep,  epithelium  with  infatii 
layer  (//):  ft, band;  r,  pear-shaped  cord;  Jy>,  dental  papilla ;  c/,  connective  tissue.  In  this  cut  the 
walls  of  the  cord  are  shown  very  plainly  to  be  a  continuation  of  the  infant  layer  of  the  epithelium. 

Fig.  352. 


cot 


Vertical  Transverse  Section  through  .Taw  of  Porcine  Embryo  (5^  cm.  X  60) :  N.  of  c,  neck  of  cord  for 
enamel  organ;  ep,  epithelium;  il,  infant  layer;  ft,  band;  o/,  outer  tunic;  it,  inner  tunic;  ct.  con- 
nective tissue ;  <//),  dental  papilla;  c.  d,  condensed  connective  tissue  forming  follicular  wall  and 
continuous  with  the  periosteum. 

we  have  before  said,  developed  from  the  subepithelial  connective  tissue 
of  the  jaw.  Its  s^rowth  is  upward,  or  gumwanl,  while  the  growth  of 
the  cord  has  been  downward  into  the  substance  of  the  jaw.     The  com- 


624 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 


Fig.  353. 


bination  of  these  two  elements  into  one  organ  seems  to  fnlfil  the  same 
olhee  as  does  fructification  in  the  egg.  New  life  is  at  once  infused  into 
the  tissue,  and  very  rapid  and  material  changes  now  occur.  The  process 
of  invagination  sets  in,  by  which  the  two  tunics  are  formed. 

A  ready  illustration  of  the  process  of  invagination  of  the  bulbous  cord 
is  made  by  taking  in  one  hand  a  syringe  with  an  egg-shaped  bulb,  the 

tube  beinp;  attached  to  the  small  end. 
Hold  the  tube  between  the  first  and 
second  fingers,  the  bulb  lying  in  the 
hand ;  with  the  end  of  the  thumb  of 
the  same  hand  press  the  large  end  of 
the  bulb  until  it  comes  in  contact 
with  the  small  end.  By  this  process 
the  larp;er  end  of  the  bulb  is  iuvaffi- 
nated  in  the  upper,  and  that  is  what  is 
meant  when  we  speak  of  the  invagi- 
nated  cord.  The  cord  invaginates 
itself  in  a  manner  similar  to  intes- 
tinal invagination.  In  this  perfect 
illustration  of  the  manner  in  which 
the  two  tunics  are  formed,  your  thumb 
represents  the  dentinal  papilla  filling 
the  concave  space  in  the  enamel  organ, 
and  the  tube  represents  the  neck  of 
the  cord  which  still  connects  the  enamel  organ  to  the  epithelial  layer  of 
the  mouth. 

Similar  invaginative  processes  occur  in  the  formation  of  the  hair-bulb 
and  the  glomeruli  of  the  kidney. 

As  invagination  jirogresses  the  older  layer  of  cells,  which  occu]>y  the 
intersjiace  between  the  walls  of  the  invaginating  canal,  are  seen  to  be 
undergoing  a  marked  change.  The  account  given  by  I^egro  and  Magitot 
is  so  complete,  and  so  conforms  to  my  views  upon  the  subject,  that  I  can- 
not do  better  than  incorporate  it  into  my  manuscript.     They  say  : 

"  If  we  now  examine  the  composition  of  the  enamel  organ  [at  the 
period  of  development  re^iresented  in  Fig.  354],  say  about  the  fifteenth 
week  of  the  human  embryo,  we  find  that  the  ])rimitive  elements  (polyg- 
onal cells,  which  occupy  its  central  portion,  and  the  [prismatic?]  cor- 
tical layer)  have  undergone  notable  modifications.  We  discover,  in 
fact,  that  the  middle  region  of  this  organ  is  occupied  by  some  elements 
of  a  lunr  form  essentially  differing  in  appearance  from  that  of  the  orig- 
inal cells.  These  are  stellate  bodieH,  composed  of  a  central  nucleus  sur- 
rounded by  a  trans])arent  or  finely-granulated  mass,  which  ramifies  and 
iuosculates  with  the  neighboring  elements.  These  star-shaped  bodies 
o('cu])y  at  first  only  the  centre  of  the  enamel  organ,  those  near  the  per- 
iphery preserving  their  original  polygonal  form,  but  becoming  stellate 
in  proportion  as  the  dimensions  of  the  organ  increase.  It  will  be 
noticed,  however,  that  the  anastomosing  processes  are  always  much 
longer  and  more  ramified  as  the  cells  are  situated  nearer  to  the  central 
portion,  while  in  the  vicinity  of  the  peri])hery  it  is  somewhat  difficult 
to  distinguish  these  processes,  as  they  are  here  only  rudimentary.     The 


DENTAL  RIDGE.  625 

elements  thus  described  are  immersed  in  a  translucid  amorphous  mass 
coagulable  in  acids  and  having  the  consistence  and  appearance  of  the 
white  of  an  egg.  These  starred  bodies — or  stellate  cells,  as  they  are 
usually  termed — are  formed  directly  at  the  expense  of  the  polygonal 
elements  composing  the  internal  mass  of  the  enamel  organ.  The  pro- 
cess is  as  follows  :  The  substance  mentioned  above  interposes  itself 
little  by  little  between  these  originally  small  polyhedral  cells,  and  thus 
their  walls  lose  their  mutual  contact  except  at  certain  points  where  they 
still  cohere.  As  a  direct  result  of  this  phenomenon  the  primitive  polyg- 
onal cells  exhibit  a  number  of  depressions  extending  from  their  exterior 
surface  toward  the  centre,  giving  them  their  stellate  appearance.  From 
this  transformation  the  primitive  cells  would  become  entirely  insulated 
by  the  intervention  of  this  new  mucous  formation  were  it  not  for  these 
connecting  processes,  which  give  to  this  organ,  as  a  whole,  its  peculiar 
reticulated  appearance  and  to  each  cell  its  stellate  form.  It  is  a  remark- 
able fact  that  no  line  of  juncture  can  be  discovered  where  these  cells 
are  connected  with  each  other,  the  various  reagents  failing  to  disclose 
the  least  trace  of  it,  so  effectually  have  these  parts  been  cemented 
together.  According  to  this  theory,  the  stellate  arrangement  of  the 
'  pulp '  of  the  enamel  organ  (the  intimate  composition  of  which  we  do 
not  propose  to  describe  in  this  memoir)  results  from  a  mmple  viodifica- 
tion  of  the  form  of  the  primitive  polygonal  cells — a  change  which  they 
have  undergone  passively,  as  it  were.  These  elements  of  the  enamel 
organ,  notwithstanding  their  stellate  form,  must  be  regarded,  therefore, 
as  absohiteli/  epithelial  in  their  nature.  The  mechanism  of  this  trans- 
formation, however,  differs  materially  from  that  given  by  Kolliker,  and 
after  him  bv  several  other  anatomists,  who  contend  that  these  prim- 
itive cells  might  take  this  stellate  form  spontaneously.  Our  opinion, 
however,  is  in  conformity  with  that  of  Walcleyer,  who  was  the  first  to 
properly  examine  and  describe  this  phenomenon,  though  Huxley  at  a 
much  earlier  day  had  advanced  the  idea  (hypothetically,  it  is  true)  that 
the  enamel  organ  had  an  epithelial  origin ;  but  he  did  not  indicate 
the  mode  whereby  the  transformation  of  its  elements  was  affected." 

The  stratum  intermedium  of  Hanover  consists  of  those  cells  which 
lie  nearest  the  infant  layer  of  tlie  inner  tunic.  They  have  not  become 
stellate,  as  have  the  cells  found  nearer  the  central  portion  of  the  enamel 
organ.  They  are  younger  than  are  the  stellate  cells.  They  have  no 
particular  signification  other  than  that  which  we  assigned  to  them"  when 
discussing  the  formation  of  the  cuticula  dentis.  Nearer  the  central  por- 
tion of  the  enamel  organ  a  more  marked  reticulation  is  seen  in  most 
specimens. 

The  vacuoled  appearance  of  the  interior  of  the  enamel  organs  begins 
in  the  central  portion  in  the  oldest  layer  of  cells  ;  the  cells  which  lie 
nearest  the  infant  layer  are  the  last  to  become  affected.  The  change 
does  not  occur  uniformly,  but  in  places  here  and  there.  This  is  shown 
very  nicely  in  the  accompanying  figure  (354).  The  part  from  which 
the  cut  was  taken  comprises  that  portion,  including  the  inner  tunic  and 
the  overlving  cells,  situated  immediately  above  the  apex  of  the  dentinal 
papilla.  The  infant  cells  of  the  inner  tunic  are  of  the  character  before 
described,  no  attempt  having  as  yet  been  made  upon  the  part  of  Nature 

Vol.  I.— 40. 


626 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 


to  differentiate  the  ameloblastic  layer.  Although  these  cells  occupy  the 
position  where  the  first  formation  of  enamel  will  make  its  appearance, 
the  older  layer  {of),  in  the  central  part  of  the  figure,  remains  unchanged, 
the  process  of  infiltration  having  not  as  yet  begun.  But  on  either  side 
of  these  unaltered  cells,  at  .sv,  sr,  the  stellate  cells  are  very  plainly 
shown.  Between  the  stellate  cells  larger  and  smaller  spaces  occur. 
This  stellate  appearance  is  largely  due  to  post-mortem  changes.  The 
actual  spaces  which  occur  between  the  stellate  cells  are  chiefly  the  result 
of  shrinkage.  If  an  osmic-acid  solution  (1  per  cent.)  and  alcohol,  equal 
parts,  be  injected  underneath  the  mucous  membrane  covering  the  jaws 
of  an  8  or  10  cm.  pig  while  the  embryo  is  yet  warm,  and  then  immersed 
in  a  similar  solution  to  harden,  the  post-mortem  changes  in  the  cells 
will  be  to  a  greater  or  less  extent  arrested.  If  we  lift  the  mucous 
membrane  from  its  bed  after  the  tissue  is  sufliciently  hardened,  the 
enamel  organs  will  adhere  and  bring  up  with  them  their  papillae.     The 


Inner  Tunic  Enamel  Organ  Porcine  Embryo  (6  cm.  X  250) :    i/,  inner  tunic;    o/,  older  layer;   sr,sr, 

stellate  reticulum. 

enamel  organ  is  thus  isolated  from  all  surrounding  calcified  tissue,  and 
we  are  able,  after  embedding,  to  make  sections  without  waiting  for  the 
bone  of  the  jaw  to  be  decalcified,  decalcification  necessitating  the  use  of 
acids  which  will  cause  more  or  less  change  in  the  soft  cells  in  the  interior 
of  the  enamel  organ.  Tlie  fibrillated  condition  of  the  stellate  cells  seen 
in  specimens  hardened  in  JMiiller's  fluid,  chromic  acid,  etc.  is  demon- 
strated, by  the  osmic-acid  method,  to  be  in  reality  a  broad  mesh.  The 
reticular  appearance  seen  in  the  chromic-acid  preparations  results  from 
post-m()rt(!m  shrinkage  in  the  older  cells  which  fill  the  interior  of  the 
enamel  organ.  I  fully  believe  that  if  we  could  examine  these  cells  at 
once,  before  any  shrinkage  occurs,  we  should  be  able  to  prove  the  fact 
that  in  life  they  are  not  stellate,  but  large  polygonal  cells.  I  am  led  to 
this  inference  by  the  above-noted  experiments^  the  better  methods  of 
technique  showing  a  less  fibrillated  appearance  than  do  other  methods 
Avhich  allow  more  shrinkage. 

Sections  of  isolated  enamel  organs  might  be  obtained  by  the  freezing 
method  were  it  not  for  their  minute  size  ;  if  this  could  be  done  without 
the  use  of  any  hardening  fluids,  better  studies  could  be  made.     It  is  to 


DENTAL  RIDGE.  627 

be  remembered  that  the  cells  which  occupy  the  central  portion  of  the 
enamel  organ  are  the  older  cells  which  have  been  pushed  off'  from  the 
sides  by  the  development  of  the  infant  layer,  which  constitutes  the 
walls  of  the  organ.  The  central  mass  of  cells  are  thus  enclosed  in 
a  sac  as  are  the  cells  of  sebaceous  glands.  The  latter,  under  this  con- 
dition, pass  through  a  retrograde  process  and  become,  through  fatty 
degeneration,  the  oily  material  secreted  by  the  glands.  The  cells  of  the 
enamel  organ  become  infiltrated  by  fluid  instead  of  fat ;  this  fluid  is 
freely  soluble  in  the  fluids  whicii  are  used  to  harden  the  tissues.  The 
cells  undergo  a  sort  of  retrograde  process  due  to  the  abnormal  confine- 
ment between  the  tunics  of  the  enamel  organ,  but  not  the  same  as  that 
found  in  the  glands  above  referred  to.  The  shrinkage  due  to  the  giv- 
ing up  of  this  water  results  in  the  stellate  form  they  assume  after  death. 
In  the  meshes  of  the  stellate  cells  prepared  by  the  osmic-acid  method  are 
seen  numerous  minute  granular  bodies  which  have  a  high  refractive 
power ;  if  a  few  drops  of  dilute  nitric  acid  be  put  on  the  slide  near  the 
edge  of  the  cover-glass  and  allowed  to  run  under  by  cai^illary  attraction, 
these  granular  bodies  will  disappear,  and  at  the  same  time  large  numbers 
of  bubbles  will  accumulate  and  force  themselves  out  from  under  the  cover- 
glass.  In  this  experiment  Ave  have  a  positive  demonstration  of  the  ])res- 
ence  of  carbonate  of  lime  in  the  meshes  of  the  stellate  cells  of  the  fully- 
<leveloped  enamel  organ  previous  to  the  beginning  of  the  process  of 
calcification  of  the  enamel.  These  granules  of  lime  do  not  appear  in 
sufficient  quantity  to  result  in  completely-calcified  tissue,  but  are  held 
in  a  state  of  suspension  ;  as  the  meshes  of  the  stellate  reticulum  shrink 
the  graimles  of  lime  are  brought  nearer  together,  and  by  approximation 
stiffen  the  tissue.  The  presence  of  a  non-shrinkable  material  in  the 
meshes  of  the  stellate  cells  of  the  enamel  organ  accounts  for  the  different 
results,  as  regards  shrinkage,  in  the  preparation  of  tissues. 

Previous  to  the  beginning  of  development  of  the  enamel  we  find  little 
or  no  shrinkage  of  tlie  enamel  organ  during  the  hardening  and  decalci- 
fying processes,  provided  the  hardening  is  accomplished  first.  It  is  only 
after  the  stellate  cells  have  given  up  a  ])ortion  of  their  lime  salts,  either 
by  forming  enamel  or  by  being  decalcified  l>efore  hardening,  that  any 
considerable  shrinkage  occurs.  The  shrinkage  in  the  first  instance  is 
localized  in  that  portion  nearest  the  forming  enamel ;  in  the  latter  it  is 
general.  The  shrinkage  on  the  part  of  the  enamel  organ,  in  any  case, 
is  more  apparent  than  real,  the  space  formed  by  the  separation  of  the 
enamel  from  the  ameloblasts  being  largely  due  to  the  greater  shrinkage 
of  the  dental  pulp,  which  draws  the  formed  dentine  and  enamel  down 
from  the  sides  of  the  cone-sha])ed  enamel  organ.  If  the  stellate  reticu- 
lum is,  as  has  been  stated,  very  rich  in  albumen,  and  does  not  contain 
calcific  material  in  large  quantities,  there  would  be  a  very  great  shrink- 
age in  preparation,  due  to  the  rapid  taking  up  of  its  water  by  the  acids 
used  in  decalcifving,  which  is  not  the  case  previous  to  the  commencement 
of  the  formation  of  the  enamel.  But  after  calcification  has  begun  and 
the  stellate  reticulum  has  given  up  a  portion  of  its  lime  salts,  then  more 
or  less  shrinkage  is  noticed  ;  or  if  decalcification  is  first  accomplished 
by  hydrochloric  acid,  which  has  no  hardening  property,  and  the  tissue 
is   afterward  hardened  in  alcohol,  we    notice  the  same  phenomenon, 


628  DESTAL  EMBRYOLOGY  AND  HISTOLOGY. 

which  is  due  to  the  same  cause — viz.  the  giving  up  of  its  lime  salts 
previous  to  the  coagulation  of  the  albumen  in  the  substance  of  the 
tissue.  Thus,  I  see  in  the  stellate  reticulum  an  essential  agent  in  the 
process  of  the  formation  of  the  enamel,  and  not  a  mere  occupier  of  the 
space  to  be  taken  by  the  formed  enamel,  as  some  would  have  us  believe. 

It  is  more.  In  the  first  place,  it  is  the  storehouse,  so  to  speak,  of  the 
calcific  material  from  which  the  first-formed  layer  of  enamel  is  derived. , 
Then,  again,  there  is  a  very  great  difference  in  form  between  the  enamel 
organs  of  the  centrals,  cuspids,  and  molars  in  the  sauie  mouth  ;  and 
that  this  difference  exists  among  the  several  classes  of  teeth,  none  will 
dispute.  From  this  I  hold  that  the  enamel  organ  is  the  matrix-former : 
as  the  foetal  femur  is  to  the  mature  femur,  so  is  the  enamel  organ  to  the 
fully-developed  tooth.  They  are  the  matrices  that  govern  the  form  of 
the  fully-developed  tissue — at  least,  in  -a  general  Avay  in  each  can  be 
seen  the  type  of  the  resulting  product.  The  concave  face  of  the  enamel 
organ  gives  form  to  the  future  tooth  in  the  Carnivora  by  the  dentine 
forming  against  the  inner  ends  of  the  ameloblasts.  Sometimes  the  fibrils 
of  the  odontoblasts  penetrate  between  the  ameloblasts,  and  we  have  as  a 
result  an  interlacing  of  the  dentinal  fibrils  and  the  enamel-prisms.  This 
interlacing  of  the  fibrils  of  the  odontoblasts  with  the  ameloblasts  mil- 
itates against  the  theory  of  a  limiting  membrane  existing  between  them. 
That  this  occurs  before  the  process  of  calcification  begins  I  have  no 
doubt,  although  I  have  not  been  able  to  demonstrate  it.  The  forcing 
of  the  soft  fibrils  of  the  odontoblasts  between  the  calcified  enamel-prisms 
is  impossible.  I  have  a  pathological  section  from  a  human  incisor, 
taken  from  the  superior  maxilla  of  a  man  who  when  he  was  four  years 
of  age  was  kicked  in  the  mouth  by  a  horse  and  seriously  injured. 
When  his  permanent  incisors  erupted,  they  had  furrows  on  their  labial 
and  lingual  faces,  showing  faulty  develojmient  ;  into  these  furroM'S 
horns  of  dentine  projected  fully  one-half  the  thickness  of  the  enamel. 
The  fissure  in  the  enamel  probably  resulted  from  a  displacement  of  the 
ameloblasts  at  the  time  of  the  accident.  Into  the  fissure  thus  formed 
the  filn'ils  of  the  odontoblasts  ])rojected,  thus  showing  the  tendency  of 
the  odontoblasts  to  send  out  their  fibrils  until  they  meet  an  obstruction. 
In  normal  develo])ment  this  obstruction  is  formed  by  the  inner  layer  of 
the  enamel  organ. 

Much  discussion  has  arisen  regarding  the  nature  of  the  unioti  occur- 
ring between  the  papilla  and  the  enamel  organ ;  there  exists  no  intimate 
connection  between  the  two  surfiices  other  than  that  of  perfect  adapta- 
tion to  each  other.  A'^essels  or  nerves  have  never  been  demonstrated 
to  ])ass  from  one  to  the  other.  The  relation  is  analogous  to  that  sus- 
tained by  the  e])ithelium  and  dermal  layers  of  the  mucous  membrane 
of  the  oral  cavity,  from  which  they  have  their  origin.  As  there  is  no 
direct  union  between  the  two  organs,  enamel  and  dentine,  so  is  there  no 
fiiu'h  union  between  their  products.  The  enamel  cap  can  be  very  easily 
lifted  from  off  tlie  dentine  cone,  especially  from  an  extracted  tooth 
which  has  been  allowed  to  dry.  The  enamel  and  dentine  separate  very 
readily  at  their  line  of  union  in  teeth  in  sifii  when  it  becomes  necessary 
to  remove  the  enamel  cap  for  the  ap})lication  of  bands  for  crowning 
roots,  thus  demonstrating  the  lack  of  positive  union  between  the  two. 


DENTAL  RIDGE. 


629 


Sections  from  the  jaw  of  a  6  cm.  jjig  show  the  process  of  invagination 
farther  advanced.  The  papilla,  which  originated  as  a  microscoi)ieal 
point,  rapidly  increases  in  size.    It  is  made  up  of  embryonal  connective- 


FiG.  355. 

nof  C. 


c.c.-t.. 


Ctr 


J> 


aw- 


:^i^^^S 


aiu- 


-sr 


Vertical  Transverse  Section  of  .Taw  of  Porcine  Embryo  (fi  cm.  X  60):  ep,  epithelium,  with  infant 
layer  (if) ;  /-,  band  ;  ?i  of  c,  neck  of  cord ;  c/,  connective  tissue  ;  c.  ct.,  follicular  wall ;  p,  periosteum ; 
aic,  alveolar  wall ;  o/,  outer  tunic;  ili)  dental  papilla,  with  (sp)  space  between  it  and  inner  tunic 
(it) ;  db,  developing  bone  of  jaw. 

tissue  cells  similar  to  those  found  in  other  parts  of  the  bodv.  It  is 
richly  supplied  with  capillary  vessels,  but  I  have  never  been  able  to 
demonstrate  any  nerve  fibres  in  the  formative  stages  of  the  dentinal 
organ 

Many  changes  are  now  seen  to  be  occurring  in  the  jaw ;  here  aj^pears 
the  first  attempt  upon  the  part  of  Nature  to  differentiate  a  periosteum. 
The  boundary  of  the  jaws  is  very  clearly  marked  by  the  condensation 
of  the  fibrous  connective  tissue  at  j^J^  (Fig.  356).  Outside  of  this  mem- 
branous layer  the  muscular  plates  are  seen  in  a  formative  state,  and 
external  to  the  muscular  layer  is  seen  the  dermal  tissue,  covered 
by  the  epidermis.  Inside  the  periosteum  is  seen  the  forming  bone 
of  the  jaw  (db,  db).  It  is  independent  of  the  periosteum  and  Meck- 
el's cartilage.  It  is  Y-shaped,  with  the  top  of  the  Y  toward  the 
mucous  membrane  of  the  mouth.  In  tlie  open,  or  upper,  part  of  the 
forming  bone  the  forming  enamel  organs  are  located  at  eo,  ro.  The  jjosi- 
tion  occupied  by  ]\Ieckel's  cartilage  is  peculiar  in  the  pig,  and  differs 
materially  from  that  in  the  human  embryo.  This  is  owing  to  the  dif- 
ferent form  of  the  t\^•o  arches.     The  human  is  horseshoe  in  shape,  and 


630 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 


the  cartilage  occupies  the  central  portion  of  the  arch ;  the  arch  in  the 
porcine  embryo  is  V-shaped,  the  base  of  the  V  corresponding  to  the 
anterior  portion  of  the  mouth.  The  two  sides  of  the  inferior  maxilla 
come  in  contact  at  a  considerable  distance  from  the  front  of  the  mouth 
and  at  the  point  of  union  of  the  two  sides  of  the  jaw.  JNIeckel's  car- 
tilage, which  in  the  posterior  portion  occupies  the  central  part  of  the 
jaw,  as  it  does  in  the  human  throughout,  is  seen  to  converge  toward 
the  inner  side  of  the  jaw  and  locate  in  apposition  with  its  fellow  of  the 
ojiposite  side.  At  the  anterior  portion  of  the  jaw  this  union  is  complete, 
but  as  we  proceed  posteriorly  the  sides  gradually  separate,  until,  in  the  re- 
gion of  the  molars,  they  are  entirely  separated.  Where  a  section  is  made 
across  both  sides  of  the  inferior  maxilla  this  divergence  between  the 
two  sides  of  Meckel's  cartilage  forms  an  accurate  guide  to  the  location 

Fig.  356. 


"i-ric 


Vertical  Transverse  Section  of  Jaw  of  Porcine  Embryo,  showing  differentiation  of  Periosteum  (."^  cm. 
X  ''■">)  ■  P)i  periosteum  of  eitlier  jaw ;  c.  ct.,  follicular  wall,  appearing  as  a  continuation  of  the  peri- 
osteum ;  b,  band;  eo,  enamel  organs  for  premolars;  vp,  epithelium;  db,  developing  bone;  mc, 
Meckel's  cartilage. 

of  the  section,  whether  it  is  a  central,  cuspid,  premolar,  or  molar.  After 
the  development  of  the  papilla  this  determination  can  be  made  by  the 
form  of  the  ])apilla,  whether  it  be  uni-  ov  multicuspid. 

The  direction  assumed  by  the  papilla  is  somewhat  across  the  axis  t)f 
the  enamel  organ  ;  and  if  it  be  a  cuspid,  the  form  of  the  papilla  is  more 
conical  than  that  of  a  central  incisor,  which  is  more  or  less  wedge-shaped. 

Springing  from  the  base  of  the  papilla  is  seen,  in  the  section,  two 
processes  which  are  connected  with  the  jKipilla.  These  are  sections  of  a 
circular  process  wliich  arises  all  around  the  base  of  the  papilla,  and, 
extending  up  and  around  the  outer  part  of  the  enamel  organ,  envelops 
it  as  an  outer  tunic.  This  connective-ti.S'^ue  envelope  does  not  in  reality 
arise  from  the  base  of  the  pulp,  but  is  formed  by  a  condensation  of  the 
fibrous  connective  tissue  in  which  the  enamel  organ  lies.     Its  connec- 


DENTAL  RIDGE.  631 

tion  with  the  papilla  is  accounted  for  in  that  the  papilla  itself  arises 
from  the  same  connective  tissue.  This  diiferentiation  of  the  connective- 
tissue  envelope  is  accomplished  contemporaneously  with  the  formation 
of  the  periosteum,  and  is  seen  at  c.  ct.  (Fig.  357). 

The  exact  office  of  this  connective-tissue  envelope  is  not  known.  I 
hold  that  it  eventually  forms  the  pencementuvi,  and  as  such  becomes 
the  cement  organ,  pp  marks  the  periosteum  for  the  jaw  ;  c.  cL,  the  peri- 
cementum for  the  root  of  the  tooth,  developed  at  the  same  time  from 
the  same  embryoplastic  elements,  and  later  analogous  and  contin- 
uous structures.  The  products  of  the  two  membranes  are  very 
similar,  cement  being  only  a  slightly  modiiied  form  of  cortical  bone ; 
which  latter,  as  we  have  seen,  is  formed  by  subperiosteal  develop- 
ment, and  the  former  by  subpericemental  ossification.  I  consider  the 
effort  to  differentiate  between  the  two  membranes  as  too  fine  a  dis- 
tinction to  be  substantiated.  That  some  slight  difference  can  be  found 
no  one  doubts,  but  it  arises  from  the  fact  that  the  pericementum  lies 
between  two  bony  walls,  while  the  periosteum  has  bone  only  on  one 
side  and  soft  tissues  on  the  other.  I  consider  it  a  case  of  adaptation 
to  environment. 

Sections  from  jaw  of  a  7  cm.  pig  show  the  process  of  condensation  of 
the  follicular  wall  more  markedly.  The  developing  germ  now  has  the 
appearance  of  being  surrounded  by  an  outer  envelope,  excepting  at  the 
upper  portion,  where  it  yet  remains  connected  with  the  mucous  mem- 
brane by  the  neck  of  the  enamel  organ.  The  stellate  arrangement  of 
the  internal,  or  older,  cells  of  the  enamel  organ  is  quite  well  marked. 
The  alveolar  wall  is  well  developed  and  extends  far  up  the  sides  of 
the  follicle.  The  body  of  the  bone  of  the  jaw  is  becoming  denser,  and 
the  developing  enamel  organ  more  nearly  fills  the  temporary  alveolus. 
The  position  occupied  by  the  dentinal  papilla  is  still  markedly  on  one 
side  of  the  axis  of  the  enamel  organ. 

Sections  from  the  jaw  of  an  8  cm.  porcine  embryo  show  the  process 
of  invagination  almost  complete.  The  concave  surface  of  the  cup- 
shaped  enamel  organ  is  filled  with  the  dentinal  papilla,  or  pulp.  The 
development  of  the  alveolar  wall  has  progressed  considerably.  The  size 
of  the  follicle  has  materially  augmented.  The  mucous  membrane  of  the 
mouth  has  increased  in  thickness.  The  neck  of  the  enamel  organ  is 
shortened  and  evidences  of  cellular  activity  are  seen  in  the  inner  tunic, 
over  the  apex  of  the  papilla.  The  stellate  reticulum  is  well  developed 
all  through  the  central  portion  of  the  enamel  organ.  The  sides  of  the 
alveolus  now  come  in  close  contact  with  the  sides  of  the  follicle,  the 
fibrous  connective  tissue  of  the  follicular  wall  uniting  and  blending 
with  the  periosteum  of  the  alveolar  wall.  The  cells  of  the  inner  tunic 
are  oval,  there  having  as  yet  been  no  attempt  u]:>on  the  part  of  Nature 
to  differentiate  ameloblasts.  Between  this  and  the  next  size  (10  cm.) 
this  change  occurs,  but,  as  their  development  can  be  demonstrated  upon 
the  sides  of  the  specimen  even  after  the  process  of  amelification  has  pro- 
gressed to  a  considerable  extent,  we  will  proceed  at  once  to  the  study  of 
a  section  from  a  10  cm.  porcine  embryo  which  has  been  injected. 

I  think  this  is  by  fiir  the  finest  specimen  I  have  prepared  ;  it  shows 
the  beginning  of  the  process  of  calcification  at  the  apex  of  the  papilla. 


632 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 


But  before  proceeding  to  discuss  that  phase  of  tooth-development  let  us 
take  into  consideration  the  other  changes  which  the  folli(;le  and  sur- 
roundings have  undergone.  In  the  first  place,  note  the  very  consider- 
able increase  in  size.     The  lens  with  which  the  photomicrograph  from 


Fig.  357. 


Vertical  Transverse  Section  of  .Taw  of  Porcine  Embryo  (S  cm.  X  00):  ep,  epithelium,  with  {U)  infant 
layer;  uof  c,  neck  of  cord;  c/,  connective  tissue;  c.rt.,  follicular  wall;  p,  periosteum;  rf^>,  dental 
papilla ;  ot,  outer  tnnic  ;  i/,  inner  tunic ;  m;  stellate  reticulum  ;  dh,  developing  bone. 

whi(!h  this  illustration  was  made  was  the  same  used  for  photographing 
all  the  others  of  the  series ;  I  purposely  used  the  same  amplification  for 
this  serial  line,  so  as  to  show  the  comparative  increase  in  size  as  well  as 
the  histological  changes  M'hich  occur. 

It  will  be  noticed  that  the  alveolar  wall  has  noticeably  increased  in 
height,  presenting  itself  a  little  above  the  apex  of  the  follicle.  This 
appearance  is,  however,  somewhat  deceptive,  for  we  must  take  into  con- 
sideration another  point,  and  that  is  the  disappearance  of  the  stellate 
reticulum  over  the  ajiex  of  tlie  developing  tooth,  which  markedly 
decreases  the  height  of  the  enamel  organ  at  that  point ;  it  also 
gives  the  follicle  tlie  ap})earance  of  having  settled  deeper  into  the  sub- 
stance of  the  jaw.  The  breaking  up  of  the  enamel  organ,  as  such,  over 
the  apex  of  the  forming  tooth  is  a  constant  accompaniment  of  the 
beginning  of  calcification.  The  enamel  organ  now  presents,  in  section, 
the  appearance  of  a  pair  of  saddle-bags  hanging  over  either  side  of  the 
dental  papilla,  or  pulp.     The  inner  and  outer  tunics  are  separated  by  a 


DENTAL  RIDGE. 


633 


well-developed  stellate  reticulum.  This  specimen  was  well  injected, 
and  the  vascular  supply  is  nicely  shown,  both  in  the  pulp  and  in  the 
follicular  wall.  At  the  apex  of  the  tooth  the  capillaries  come  in  direct 
contact  with  the  outer  ends  of  the  ameloblasts;  this  is  made  possible 


Fig.  358. 


,1.  -V,  ■(>'  'j«''.        .  «<•  ;;„  .    I   J,,    /l,|il  I • r-— rn f—  

M«i  «  . '  " ef  «/» ^s<t* ,  .\  *  > ,«.;.«-:  " '  ■    r  ■=   777'  '^ 


-tuk.ep, 
B 


Vertical  Transverse  Section  of  Jaw  of  Porcine  Kmbryo,  injected  (10  cm.  X  60):  ep,  epithelium,  vith 
(//)  infant  layer ;  a.  layer  of  ameloblasts ;  o,  layer  of  odontoblasts ;  cp,  cord  for  permanent  tooth  ; 
0/,  outer  tunic;  it,  inner  tunic;  sr,  stellate  reticulum;  ivh.ep.,  whorls  of  epithelium  formed  from 
outer  tunic  and  stellate  reticulum  ;  rf,  dentine ;  dp,  dentinal  pulp ;  v,  blood-vessels  of  pulp ;  ct,  con- 
nective tissue ;  c.  ct.,  follicular  wall ;  p,  periosteum  ;  up,  space. 

by  the  breaking  up  of  the  outer  tunic  and  the  disappearance  of  the 
stellate  reticulum.  The  entire  thickness  of  the  mucous  membrane  is 
not  shown  in  this  figure,  the  field  of  the  lens  not  being  large  enough  to 
include  it  all.     Over  the  apex  of  the  developing  tooth  masses  of  epithe- 


634  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

lial  cells — remnants  of  the  outer  tunic  and  the  stellate  reticulum — are 
seen,  and  are  marked  xch.  ep.  They  have  been  called  whorls  of  epithe- 
lium because  of  their  tendency  to  gather  into  nests  resembling  somewhat 
the  nests  seen  in  epithelioma.  The  space  between  the  apex  of  the  devel- 
oping tooth  and  the  overlying  epithelium  is  more  or  less  filled  with 
these  whorls  of  epithelial  cells  and  the  buddings  which  have  arisen  from 
the  sides  of  the  temporary  cord.  The  space  (.s^^)  seen  between  the  layer 
of  ameloblasts  and  the  forming  tooth-structure  is  the  result  of  shrink- 
age, which  occurred  as  a  post-mortem  change.  The  intimate  relationship 
between  the  follicular  wall  and  the  periosteum  is  well  exhibited  in  this 
figure. 

We  have  now  shown  the  three  organs  which  will  superintend  the 
calcification  of  the  tooth  :  the  layer  of  ameloblasts — that  is,  a  portion 
of  the  ameloblastic  layer,  as  seen  at  a ;  the  odontoblastic  layer,  situated 
over  the  apex  of  the  pulp,  at  o ;  and  the  follicular  wall,  at  c.  ct,  which 
will  form  the  osteogenetic  layer  for  the  development  of  the  cement. 

With  this  brief  summary,  we  will  now  take  up  the  consideration  of 
the  manner  in  which  the  cords  for  the  permanent  teeth  arise,  and  after- 
ward return  to  the  study  of  the  special  manner  in  which  calcification 
occurs. 

Development  of  the  Cord  for  the  Permanent  Teeth. 

What  I  have  thus  far  said  has  reference  to  the  twenty  temporary 
teeth.  The  permanent  teeth  which  will  displace  these  arise  from  an 
epithelial  cord  which  has  its  origin  from  the  cord  of  a  corresponding 
temporary  tooth.  This  statement  holds  good  for  the  centrals,  laterals, 
bicuspids,  and — in  some  instances — for  the  sixth-year  molars.  When 
the  sixth-year  molar  does  not  derive  its  cord  directly  from  the  mucous 
membrane  of  the  mouth,  it  arises  from  the  distal  face  of  the  second-year 
temporary  molars.  As  a  rule,  however,  the  cords  for  the  permanent  mo- 
lars arise  directly  from  the  epithelium  of  the  mouth.  It  is  held  by  some 
that  the  cords  tor  the  twelve  permanent  molars  arise  from  the  lamina 
at  the  same  time  as  the  cords  for  the  temporary  teeth,  but  lie  dormant 
until  the  time  comes  for  their  special  development ;  others  hold  that 
the  cords  spring  from  the  debris  of  the  tem])orary  cords.  I  do  not 
think  that  either  jiosition  can  be  substantiated,  for,  as  I  have  previously 
shown,  the  band  flattens  out  posteriorly  into  the  mucous  membrane  of 
the  jaw  at  about  the  position  to  be  occupied  by  the  sixth-year  molars. 
I  do  not  look  upon  the  band  as  an  essential  element  in  tooth-develop- 
ment except  as  it  serves  to  direct  the  line  of  the  dental  arch.  It  is  to 
be  remembered  that  at  the  time  when  the  formative  process  for  the  tem- 
porary teeth  begins  there  has  been  no  effort  upon  the  ])art  of  Nature  to 
establish  the  boundary  of  the  jaws.  The  muscular  plates  have  not  as 
yet  been  differentiated,  and  the  jaws  are  simply  solid  buds  from  the 
body  of  the  mesoblast,  and  are  surrounded  by  the  epiblastic  layer. 
Such  being  the  case,  the  band  acts  as  the  guide  to  the  proper  location 
of  the  temporary  teeth.  But,  the  jaws  having  been  formed,  the  twelve 
permanent  teeth  naturally  take  a  proper  location. 

Concomitant  with  the  origin  of  the  cords  for  the  permanent  teeth. 


DEVELOPMENT  OF  CORD  FOB  PERMANENT  TEETH.        635 


the  temporary  cords  present  certain  buddings  which  gather  themselves 
into  whorls  of  epithelial  cells ;  to  these  have  been  attributed  the  origin 
of  supernumerary  teeth.  I  have  no  opinion  to  advance  in  the  matter, 
never  having  seen  any  developing  enamel  organs  in  such  position  as  to 
connect  this  supposed  source  with  these  abnormalities.  The  cord  for  the 
permanent  teeth  arises,  as  a  rule,  from  the  lingual  aspect  of  the  tempo- 
rary follicle  or  the  cord  for  the  same.  With  the  severance  of  the  tempo- 
rary enamel  organ  from  its  cord,  the  cord  for  the  permanent  enamel  organ 
appears  as  a  continuation  of  the  former,  and  passes  down  upon  the 
lingual  aspect  of  the  temporary  tooth.  This  is  shown  in  the  preced- 
ing figure  (358).     The  direct  continuation  of  the  temporary  cord  into 

Fig.  359. 


Vertical  Transverse  Section  0  cm.  Bovine  Embryo  (^C  -oO) :  ep,  ei)ithelium ;  il,  infant  layer ;  cp,  cord  of 
permanent  tooth,  still  united  at  c  with  outer  tunic  (o/)  of  temporary  tooth;  it,  inner  tunic;  nl, 
older  layer  of  cells,  known  as  stratum  intermedium;  </;>,  dental  papilla;  </,  dentine;  sr,  stellate 
reticulum. 

the  permanent  is  nicely  shown  in  the  accompanying  cut  from  a  9  cm, 
bovine  embryo,  where  the  connection  is  not  yet  entirely  severed  between 
the  cord  and  the  temporary  tooth-follicle. 

The  time  for  the  origin  of  the  cord  for  the  permanent  teeth  varies 
considerably.  In  the  human  embryo  the  cord  for  the  jiermanent  cen- 
tral incisor  first  makes  its  appearance  about  the  fifth  month.  In  the 
porcine  and  bovine  embryos  the  cords  for  the  permanent  central  incisors 
arise  when  the  fcetus  has  attained  about  8  cm.  in  length.  Those  of  the 
premolars  in  porcine  embryos  arise  as  we  have  seen  in  the  1 0  cm.  fcetus 
(Fig,  358).  The  length  of  the  cords  for  the  permanent  teeth  varies 
noticeably  in  different  sjiecies  and  in  different  teeth  of  the  same  species. 
The  course  of  the  cords  for  the  permanent  teeth  also  assumes  a  more 
spiral  direction  than  do  the  cords  for  the  temporary  teeth.  I  have 
never  been  able  to  satisfy  myself  as  to  the  special  signification,  if  any, 


636 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 


that  these  convokitions  may  have.  They  may  arise  from  unequal  cellu- 
lar activity  at  different  points  ;  at  any  rate,  they  are  well-known  charac- 
teristics of  the  cords  for  the  permanent  Mdiich  distinguish  them  from 
the  cords  for  the  temporary  teeth.  The  cord  passes  down  upon  the  lin- 
gual aspect  of  the  temporary  tooth  and  follows  the  same  changes  which 


Fig.  360. 


a.w_ 


Section  of  .Taw  Eight  :\ronths  Hunian  Foetus,  showing  Vertical  Transverse  Section  of  Central  Incisor, 
(injected:  X  4()):  el,  onaniel;  d,  dentine;  (//<, dental  papilla  or  i)ulp;  air,  alveoliir  wall ;  ep,  enamel 
organ  permanent  tooth  ;  er,  entrance  to  vessels  ;  it,  nerve. 

we  have  noted  in  the  cord  for  the  tem])orary  tooth.  It  becomes  bulbous 
at  its  deepest  extremity  ;  then  it  becomes  invaginated  by  contact  Avith 
tlie  dental  ]>npilla,  after  which  it  settles  deeper  into  the  substance  of  the 
jaw,  and  is  finally  scj)arated  from  the  mucous  membrane  of  the  mouth. 
(See  Fig.  "^m,  cp.)     It  gradually  becomes  deeper  seated,  until  it  comes 


DEVELOPMENT  OF  CORD  FOR  PERMANENT  TEETH.       637 

to  occupy  a  position  directly  underneath  the  temporary  tot)th  and  is 
very  nicely  shown  in  Fig.  361,  representing  a  temporary  molar  from 
jaw  ot  rabbit,  ihe  multicuspid  nature  of  the  enamel  organ  for  the 
molar  teeth  is  here  plainly  sho\yn. 


Fig.  361. 


CL^ir. 


-cct 


reiuporary  Molar  (Rabbit),  with  permanent  developing  underneath;  the  enamel  has  been  removed 
by  acid  111  decalcifying  process:  rf,  dentine;  o,  odontoblasts;  ,nr  alveolar  wall  <V  dent  dm.h) 
of  |umTi4Sf°         Pe"nanent  molar;  rf^>^,  dental  papilla  from  permanent  mol'ar;  .^,  m'argin 

The  changes  which  occur  in  the  enamel  organ  have  been  considered 
under  the  head  of  the  formation  of  the  stellate  reticulum  and  develop- 
ment of  the  ameloblasts.  The  latter  we  noticed  briefly  under  the  prod- 
ucts of  the  epiblastic  layer.  .We  will  now  enter  into  the  study  with 
more  detail.     The  accompanying  figure  is  the  same  as  that  presented 


638 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 


on  p.  633.  and  is  here  introduced  to   serve  as  a  guide  to  the  higher- 
power  studies  which  are  to  follow.     The  circles  drawn  at  a,b,c,d  rep- 


aiu- 


ST. 


dp^=wm 


aiu- 


Vertical  Section  Jaw  Porcine  Embryo  (10  cm.  X  ^t)  :  circles  a,  h,  c,  d,  indicate  positions  from  which 
figures  are  taken  :  cp,  cord,  permanent :  tiic,  alveolar  wall ;  dp,  dental  papilla,  or  stellate  reticulum  ; 
11,  nerve;  t', vessels;  inc,  Meckel's  cartilage. 

resent  the  positions  from  which  Figs,  343,  363,  365,  366,  were  taken. 
The  first  of  these  we  presented  when  considering  the  development  of  the 
mucous  membrane  of  the  mouth,  on  p.  615. 

The  line  il  marks  the  infant  layer  of  cells.  This  line  also  consti- 
tutes the  outer  and  inner  tunic  of  the  enamel  organ.  The  cells  which 
fill  the  interspace  correspond  to  those  in  this  cut  marked  ol.  Now,  thor- 
oughly to  a})preciate  the  relative  positions  of  the  two  tunics  it  is  neces- 
sary to  remember  that  the  enamel  organ  is  formed  by  an  infolding  and 
involution  of  the  infant  layer  of  the  epithelium,  and  as  such  it  is  com- 
posed "lip  to  a  certain  time  of  elements  of  a  like  nature  with  the  infant 
layer  of  the  mouth,  from  which  it  arises.  After  a  time,  however,  the 
character  of  the  cells  undergoes  certain  changes,  which  we  will  describe 
later  on. 

AVe  took  occasion  to  say,  when  considering  a  section  from  a  por- 
cine embryo  8  cm.  (sie  Fig.  357)  in  length,  that  the  two  tunics,  both 
outer  and  inner,  gave  no  indication  of  the  appearance  of  the  amelo- 
blasts,  but  that  they  still  presented  the  same  features  seen  in  the  infant 
layer  of  the  mucous  membrane  of  the  mouth.  Up  to  this  time  the  outer 
and  inner  tunics  have  presented  the  same  features.  They  have  both 
been  composed  of  oval  nuclei  lying  in  beds  or  sheets  of  protojilasm 
which  constituted  the  walls,  inner  and  outer,  of  the  enamel  organ. 

Tlie  first  change  noted  is  seen  over  the  apex  of  the  jiapilla.  The  pro- 
toplasm begins  to  break  up  into  (columns,  which  stand  at  right  angles 
to  the  sides  of  the  papilla ;    each   column   contains  a  nucleus.     The 


DEVELOPMENT  OF  CORD  FOR  PERMANENT  TEETH.       639 


shapes  of  the  cells  are  not  unlike  those  previously  deseril>ed  in  study- 
ing the  sweat-glands.  They  are  columnar  or  basaltic  in  character,  and 
are,  as  may  be  inferred,  specialized  cells  for  a  special  purpose. 

The  several  stages  through  which  the  infant  layer  which  composes 
the  inner  tunic  passes  may  be  studied  in  the  one  specimen  in  hand.  We 
have  seen  the  character  of  the  cells  which  form  the  infant  layer  of  the 
mucous  membrane  of  the  mouth,  also  the  inner  tunic  of  the  enamel 
organ  of  the  8  cm.  pig.    By  referring  to  Fig.  362,  taken  from  the  side  of 

Fig.  363. 


Vertical  Transverse  Section  Central  Incisor  Porcine  Embryo  10  cm.;  free  border  enamel  organ  seen 
in  circle  ft,  Fig.  3B0  (X  250):  (//;,  dental  papilla;  ^r,  stellate  reticulum;  o/,  outer  tunic;  it,  inner 
tunic;  sp,  space;  c.  cl.,  condensed  connecti.ve  tissue  of  follicular  wall. 

the  enamel  organ  (circle  b),  it  will  be  seen  that  no  change  has  occurred. 
There  has  been  no  effort  upon  the  part  of  Nature  to  develop  amelo- 
blasts,  but  as  we  proceed  higher  up  the  sides  of  the  papilla  we  see  at 
circle  c  that  the  formation  of  columnar  cells  has  begun  ;  and  wlien  we 
reach  the  apex  circle  d,  well-marked  columnar  cells  are  seen.  Now,  thor- 
oughly to  understand  the  reason  why  we  do  not  find  columnar  cells  at 
b,  we  must  remember  that  calcification  begins  at  the  apex,  and  not  upon 
the  sides,  of  the  papilla.  The  lower  borders  of  the  enamel  organ  are 
growing  and  extending  deeper  and  deeper  into  the  substance  of  the 
jaw.  This  rapid  development  of  cells  continues  until  the  sides  of  the 
enamel  organ  have  attained  their  typal  length,  when  growth  ceases  and 
the  cells  of  the  inner  tunic  become  converted  into  true  columnar  cells, 
the  development  of  which  has  proceeded  from  the  apex  of  the  pa])illa 
along  the  sides  toward  the  free  border  of  the  enamel  organ.  So,  if  we 
reverse  the  order  of  our  study,  we  shall  be  able  to  follow  the  several 
stages  of  developing  ameloblasts.  But,  as  it  will  be  more  convenient  to 
study  the  formation  of  ameloblasts  and  odontoblasts  together,  we  will  do 
so,  first  premising  that  the  ameloblasts  are  a  product  of  the  epiblastic 


640 


DENTAL  EMBRYOLOGY  A  XL)  HISTOLOGY. 


layer  and  arise  from  the  inner  tunic,  and  that  the  odontoblasts  belong 
to  the  connective-tissue  group  and  are  derived  from  the  dentinal  papilla, 
or  pulp.     By  referring  to  Fig.  364,  taken  from  the  position  marked 


s>;  stellate  reticulum  :  i/,  inner  tunic  ;  o,  odoiitobl'astio  layer. 

bv  a  point  opposite  the  line  sr  (Fig.  362),  and  magnified  500  diameters, 
it  will  be  seen  that  the  ameloblasts  and  odontoblasts  have  not  as  yet 
made  their  appearance.  This  is  below  the  point  where  calcification  has 
reached.  Proceeding  up  the  sides  to  the  lowest  point  where  the  for- 
mation of  dentine  appears — marked  by  circle  c,  and  more  highly  mag- 
nified in  Fig.  3(35 — we  see  the  first  appearance  of  odontoblasts  (o) ;  they 
present  themselves  as  elongated  cells  with  fine  processes  extending  into 
the  homogeneous,  calcareous  mass.  On  the  outer  side  of  this  line  of 
forming  dentine  the  layer  of  ameloblasts  is  plainly  seen ;  the  amelo- 
blasts are  columnar  in  form,  wnth  the  nucleus  of  each  situated  at  its 
outer  end.  Still  outside  of  the  ameloblastic  layer  is  plainly  seen  the 
flattened  laver  of  older  cells  which  are  always  observed  lying  upon  the 
laver  of  ameloblasts ;  they  are  the  cells  which  have  not  become  stellate 
— the  stratum  intermedium.  Outside  of  these,  and  situated  Ijetween 
the  two  tunics,  is  the  stellate  reticulum,  which,  with  the  outer  tunic, 
is  rapidly  passing  through  a  retrograde  process  by  which  it  loses  its 
identity. 

The  development  of  dentine  always  precedes  the  formation  of  enamel. 
The  disappearance  of  the  outer  tunic  occurs  about  the  same  time  as  the 
beginning  of  tlie  calcification  of  the  first  layer  of  enamel,  the  salts  of 
calcium  which  are  stored  up  in  the  meshes  of  the  stellate  reticulum 
only  sufficing  to  furnisli  material  for  the  very  first  formed  layer  of 
enamel.  With  the  disappearance  of  the  outer  tunic  and  the  stellate 
reticulum,  as  such,  the  ameloblasts  come  in  direct  communication  with 


DEVELOPMENT  OF  CORD  FOR  PERMANENT  TEETH.       641 

the  rich  plexus  of  capillary  vessels,  the  latter  furnishing  the  lime  salts 
for  the  completion  of  the  calcification  of  the  enamel.  By  referring 
to  Fig.  366,  taken  from  circle  d,  it  will  be  seen  that  a  slight  layer  of 
enamel  has  been  formed  which  has  the  appearance  of  a  honeycombed 
layer.  Between  this  layer  of  enamel  and  the  layer  of  amelol^lasts  a 
space  is  noticed   which   was   caused   by  shrinkage  in  the  process   of 

Fig.  365. 


Circle  c,  Fig.  3G0  (X230):  dp,  dental  papilla;  o,  odontoblasts;  d,  dentine;  sp,  space;  a,  ameloblasts ; 

sr,  stellate  reticulum. 


hardening.  Into  this  space  projects  a  fibrillated  margin  of  the  amelo- 
blastic layer  known  as  Tomes's  processes,  of  which  we  will  speak  later. 
There  exists  considerable  confusion  regarding  the  outer  tunic  of  the 
enamel,  organ.  The  most  erroneous  statement  concerning  it  was  pub- 
lished by  Waldeyer,  who  says  :  "  As  far  as  the  external  epithelium 
reaches,  the  adjoining  connective  tissue  exhibits  its  tolerably  regularly- 
formed  vascular  papillse,  which  project  into  the  epithelium  and  cor- 
respond to  the  papillae  found  in  the  remaining  portion  of  the  oral 
mucous  membrane."  He  also  presents  a  cut  which  does  not  represent 
the  true  condition  of  the  enamel  organ  at  this  stage  of  development, 
either  in  the  human  or  porcine  foetus.  He  neglects,  however,  to  state 
the  age  or  length  of  the  foetus — two  essential  points  to  be  considered  in 
presenting  illustrations.  This  cut  has  been  extensively  copied,  and 
those  who  have  used  it  have  also  neglected  to  locate  it.  Now,  the 
outer  tunic  does  not  present  indentations  in  its  surface  until  it  begins  to 
break  up;  it  is  smooth  and  even,  like  the  inner- tunic,  until  the  time 
comes  for  its  disappearance.  The  history  of  its  retrogression  can  be 
followed  as  carefully  as  can  the  progression  of  the  inner  tunic.  If  we 
examine  Fig.  363,  taken  from  circle  h  of  Fig.  362,  we  shall  be  able  to 

Vol.  I.— 41 


642 


DENTAL  EMBRYOLOGY  AND  HISTOLOGY 


Fig.  366. 


note  tlie  difference  in  the  two  tnnies  at  the  free  margin  of  the  enamel 
organ.  In  yonnger  specimens  there  is  no  apparent  difference  between 
the  two,  but  it  must  now  be  remembered  that  calcification  has  com- 
menced at  the  apex  of  the  tooth,  and  that  material  changes  will  now 
occur  in  the  inner  tunic ;  these  have  been  noticed.  The  character  of  the 
enamel  organ  as  such  is  rapidly  changing  ;  it  has  served  its  purpose, 
and  from  now  on,  upon  the  apex  of  the  papillae,  it  will  disappear,  and 
this  change  will  gradually  proceed  down  the  sides  of  the  papillae  until 
the  typal  demands  of  the  enamel  cap  are  reached. 

There  is,  however,  a  marked  difference  between  the  inner  and  the 
outer  tunic  at  this  stage.  The  inner  tunic  gives  evidences  of  rapid  cell- 
proliferation  and  consists  of  many 
nuclei,  forming  a  thick  layer ;  on 
the  other  hand,  the  outer  tunic  con- 
sists of  a  single  layer  of  cells.  This 
is  very  happily  shown  in  the  figure 
by  the  shrinkage  which  has  occurred 
just  above  the  free  margin,  allow- 
ing the  outer  tunic  to  stand  out  in 
relief.  This  same  character  of  the 
outer  tunic,  as  compared  with  the 
inner  tunic,  is  seen  at  circle  c.  At 
circle  d  (Fig.  366)  the  outer  tunic 
and  the  cells  of  the  stellate  reticu- 
lum have  settled  down  upon  the  layer 
of  ameloblasts,  sometimes  arranging 
themselves  in  whorls,  seen  at  7vh.  ep. 
(Fig.  358).  Just  what  their  signifi- 
cation is  I  am  unable  to  state  pos- 
itively, but  from  my  studies  in  com- 
parative embryology  I  am  led  to 
believe  that  they  supply  the  places 
made  by  the  increase  in  the  circum- 
ference of  the  enamel,  and  account 
for  the  short  prisms  seen  in  ground- 
sections  of  enamel. 

In  the  development  of  teeth,  Avhere 
the  enamel  is  to  form  a  coat  of  mail 
on  the  crown  of  the  tooth — viz.  the 
Carnivora — the  line  of  ameloblasts 
that  is  first  formed  does  not  repre- 
sent the  same  number  of  ameloblasts 
that  will  finally  complete  the  process  of  calcification.  The  outer  cir- 
cumference of  the  developed  enamel  is  many  times  larger  than  that 
of  the  first  calcified  layer.  If  this  represented  a  straight  line,  as  the 
enamel  on  the  rodent's  tooth  does,  then  the  space  would  be  made  at  one 
end  of  the  line ;  but  here  it  is  in  the  form  of  the  greater  part  of  a  circle. 
The  expansion  occurs  at  all  parts,  and  the  cell-supply  from  which  the 
amelol)lasts  are  developed  is  found  lying  in  close  proximity  to  the 
ameloblasts.     Along  the  side  of  the  enamel   orsran  which  forms  the 


dn 


Vertical  Section  tliroiifch  .Spex  of  Central  In- 
cisor 10  cm.  Porcine  Embryo  (X  500) :  c.  c/., con- 
nective tissue  of  follicular  wall ;  /V,  flat  layer 
of  stratum  intermedium;  o,  ameloblasts :  Tp, 
Tomes  processes  into  space;  '■/,  enamel;  </, 
dentirie;  o,  odontoblasts;  dp,  dental  papilla. 


DEVELOPMENT  OF  CORD  FOR  PERMANENT  TEETH.       643 

straightest  line  fewer  cells  are  found  than  on  the  upper  arc  of  the  cir- 
cle, where  the  expansion  is  greatest. 

In  the  rodents  we  do  not  see  the  same  thickness  of  cells  outside  the 
ameloblastic  layer  as  we  find  in  the  Carniv^ora.  Previous  to  the  forma- 
tion of  the  ameloblasts  in  the  rodent's  tooth  the  inner  tunic  is  made  up 
of  three  or  four  cells,  arranged  as  before  described,  on  the  outer  boun- 
dary of  which  an  equally  thick  layer  of  spheroidal  cells  appears,  being 
also  densely  packed.  Outside  of  these  is  the  fibrous  connective-tissue 
envelope. 

This  dense  layer  of  spheroidal  cells  grows  thinner  toward  the  cut- 
ting edge,  until  at  the  point  wliere  the  prismatic  ameloblasts  are  fully 
formed  it  disappears,  and  we  find  the  fibrous  connective-tissue  layer 
with  its  numerous  capillaries  in  apposition  Avith  the  ends  of  the  amelo- 
blasts. The  office  of  the  spheroidal  cells  in  this  instance  is  to  develop 
ameloblasts  to  supply  the  places  of  those  which  were  carried  up  with  the 
growing  tooth,  enamel  being  developed  only  on  the  labial  face,  which 
represents  almost  a  straight  line.  The  extension  of  the  line  of  amelo- 
blasts is  from  the  first-formed  enamel-prism  nearest  the  base  of  the 
tooth,  and  here  we  find  located  the  supply  which  replaces  such  exten- 
sion. 

The  persistence  of  the  enamel  organ  at  the  base  of  the  continuously- 
growing  rodent's  tooth  has  to  my  mind  a  peculiar  signification  :  it  is  the 
forerunner  of  calcification.  The  same  thing  is  seen  upon  the  sides  of  the 
developing  tooth  in  the  Carnivora  and  Herbivora,  after  the  commence- 
ment of  the  calcification  of  the  enamel,  but  it  disappears  with  the  com- 
pletion of  the  enamel  cap  in  length.  The  final  calcification  in  thickness 
is  accomplished  after  the  atrophy  of  the  enamel  organ  has  occurred.  It 
is  absolutely  essential  that  the  capillary  vessels  should  come  in  contact 
with  the  enamel-cells  before  the  process  of  calcification  can  be  completed. 
In  the  human  fretus  this  atrophy  occurs  at  the  apex  about  the  fifth 
month,  when  only  a  very  thin  layer  of  enamel  has  been  formed. 

In  the  injected  specimens  which  I  have  made  and  studied  I  have 
never  been  able  to  demonstrate  any  vessels  in  the  internal  portion  of 
the  enamel  organ.  I  consider,  from  the  experiments  with  the  osmic- 
acid  preparations  of  enamel  organs,  that  the  lime  salts  which  go  to 
form  the  first  layer  of  enamel  are  supplied  by  the  enamel  organ  itself. 

The  quantity,  however,  as  I  have  before  stated,  is  not  sufficient  to 
complete  the  process  of  calcification  ;  l^ut  that  a  certain  proportion  is  fur- 
nished by  the  enamel  organ  I  have  no  (loul:)t.  I  have  never  been  able 
to  demonstrate  any  capillary  vessels  in  the  stratum  intermedium.  The 
nourishment  of  the  inner  tunic  comes  from  the  vessels  of  the  pulp  until 
such  time  as  it  is  cut  off  from  them  by  the  development  of  the  layer  of 
dentine  which  separates  them  most  effectually  from  that  source  of.' 
supply. 

The  enamel  organ  is  not  a  secreting  organ  except  in  so  fiir  as  it 
furnishes  the  lime  salts  for  the  calcification  of  the  first- formed  layer  of 
enamel,  because  its  disappearance  as  an  enamel  organ  quickly  follows 
the  formation  of  this  first  layer.  This  being  the  case,  the  supply  of 
salts  of  calcium  must  of  necessity  be  derived  from  another  source. 

As  regards  the  development  of  the  enamel,  there  are  many  theories. 


644  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

Some  hold  that  the  enamel  is  a  differentiation  of  a  dentinal  basis,  but 
the  fact  that  calcification  of  both  dentine  and  enamel,  beginning  at  the 
same  line,  progresses  in  opposite  directions,  makes  that  ground  unten- 
able. Others  hold  that  the  enamel  results  from  the  calcification  of  the 
enamel-cells  themselves.  From  a  casual  examination  this  does  appear 
to  be  so  ;  but  if  such  were  the  case,  then  at  the  beginning  of  calcification 
the  enamel-cells  would  correspond  in  length  to  the  length  of  the  devel- 
oped enamel-prisms,  and  the  decrease  in  the  length  of  the  enamel-cells 
would  be  commensurate  with  the  increase  in  the  thickness  of  the  enamel, 
or  the  enamel-cells  would  extend  on  themselves  as  calcifiation  progresses ; 
which  phenomenon  has  not  been  established.  It  is  asserted  that  the 
multiplication  of  the  ameloblasts  in  the  direction  of  their  length  is 
from  the  cells  of  the  stratum  intermedium  as  rapidly  as  calcification 
occurs  at  their  free  ends — that  is,  the  calcification  of  the  cell-body  at 
one  end  and  the  building  up  at  the  other  are  made  a  consequent 
necessity.  If  the  ameloblasts  are  directly  calcified,  it  is  the  only  place 
in  normal  development  of  tissue  where  calcification  of  cell-body  does 
occur.  In  the  development  of  bone  the  osteoblasts  do  not  become  cal- 
cified, but  the  lime  salts  are  de})osited  around  the  spherical  osteoblasts 
in  the  form  of  spherules,  increasing  in  thickness  from  within  outward ; 
and,  thus  approaching  one  another,  they  coalesce.  The  osteoblasts  per- 
sist as  the  organic  contents  of  the  lacunae.  The  connection  of  one 
lacuna  with  neighboring  lacunae  forms  the  canaliculi,  and  the  capillary 
blood-vessels  around  which  the  osteoblasts  are  arranged  become  the 
Haversian  canals. 

In  the  calcification  of  dentine,  as  we  have  seen,  the  odontoblasts  do 
not  become  directly  calcified,  but  send  out  rod-shaped  fibrils,  around 
which  tubular  dentine  is  formed  ;  so  also  in  the  enamel  we  have  the 
prismatic  ameloblasts  superintending  the  deposit  of  prismatic  enamel. 

If  a  newly-formed  la^^er  of  enamel  which  lies  on  the  dentine  in  a  thin 
plate  be  torn  off  from  a  thick  section  of  tooth  and  mounted,  the  outer 
surface  will  be  seen  to  be  pitted — that  is,  provided  you  have  succeeded 
in  getting  the  enamel  in  just  the  right  stage  of  calcification.  The 
periphery  of  the  pits  corresponds  to  that  of  the  ameloblasts.  The 
ameloblasts,  during  the  formation  of  enamel,  seem  to  be  impregnated 
with  lime  salts  and  break  with  a  clean  fracture  at  almost  any  point 
— sometimes  near  the  newly-formed  enamel,  and  sometimes  at  a  point 
just  inside  the  nucleus. 

C  S.  Tomes  noticed  the  fact  of  the  probable  impregnation  at  the  end 
nearest  the  forming  enamel,  and  cited  it  as  proof  of  the  actual  conver- 
sion of  the  ameloblasts  into  enamel-prisms.  The  impregnation  of  both 
ends  of  the  cells  is  accounted  for  in  the  fact  that  they  are  carrying  lime 
salts  to  the  forming  enamel.  The  pits  in  the  newly-formed  enamel  are 
the  central  portion  of  the  prisms,  from  which  the  still  uncalcified  exu- 
dation has  been  drawn  by  the  ameloblasts  when  they  were  separated 
from  it. 

This  semi-calcified  material,  which  adheres  to  the  ameloblasts,  gives 
the  appearance  of  a  fibril  or  prolongation  of  the  cells  themselves.  These 
fibrils — which  have  been  called  Tomes's  processes — I  consider  as  thus 
being  mechanically  made ;  for  they  do  not  always  appear,  but  depend 


DEVELOPMENT  OF  CORD  FOR  PERMANENT  TEETH.        645 

upon  a  certain  condition  of  the  calcific  material.  They  do  not  occur 
persistently,  as  do  the  fibrillse  of  the  odontoblasts.  I  have,  under  favor- 
able circumstances,  succeeded  in  demonstrating  them  in  sections  of  pigs' 
teeth,  where  they  showed  very  plainly  indeed,  being  nearly  or  quite  as 
lono;  as  the  ameloblasts  themselves  and  several  times  lono;er  than  the 
enamel  was  thick.  As  a  rule,  however,  the  ameloblasts  separate  from 
the  forming  enamel  so  as  to  leave  a  comparatively  smooth  line  or  plate 
— that  is,  provided  the  sections  have  been  sufficiently  thin,  so  as  not  to 
show  a  ragged  edge  from  the  overlapping  of  the  cells  themselves.  I 
have  never  been  able  to  demonsti'ate  processes  that  would  lead  me  to 
infer  the  least  analogy  between  them  and  the  fibrillte  of  the  odonto- 
blasts. That  the  enamel  organ  exists  in  the  commencement  of  the 
development  of  the  teeth  is  now  generally  admitted.  There  are  certain 
classes  of  teetli,  however,  that  do  not  possess  enamel,  and  in  which, 
although  there  is  an  enamel  organ  developed,  the  stellate  reticulum 
fails  to  appear.  In  all  cases  where  there  is  to  be  a  deposit  of  enamel 
we  find  a  stellate  reticulum  fully  developed,  and  my  observation  leads 
me  to  believe  that  the  calcification  of  the  enamel-matrix  is  due  to  the  cal- 
cific material  stored  in  the  meshes  of  the  stellate  cells  of  the  enamel  organ. 

The  subject  of  calcification  has  already  been  considered,  and  will  be 
referred  to  here  only  in  a  general  manner.  After  the  temporary  teeth 
are  developed  and  have  served  their  purpose,  they  are  then  removed  by 
resorption  of  their  roots  and  their  places  taken  by  the  permanent  set. 
The  process  of  resorption  is  physiological,  and  is  accomplished  through 
the  agency  of  giant-cells.  This  part  of  the  subject  has  been  considered 
quite  fully  under  the  head  of  Physiological  Action  of  Cells,  in  the  ojjen- 
ing  chapter.  The  comparative  stages  of  decalcification  of  the  temporary 
and  calcification  of  the  permanent  teeth  have  been  so  well  delineated  by 
Prof.  Pierce  in  his  chart  in  the  Dental  Cosmos  (August,  1884)  that  I 
cannot  do  better  than  reproduce  it  here  (see  p.  647),  together  with  the 
explanatory  text  accompanying  the  same : 

"  In  the  microscopical  examination  of  dense  animal  tissues,  or  such 
tissues  as  are  impregnated  with  the  salts  of  lime,  it  becomes  evident 
that  they,  like  vegetable  structures,  have  periods  of  growth  and  of  rest, 
Avhich  are  illustrated  by  concentric  layers  or  zonal  shades,  and  that, 
while  these  conditions  are  normal,  they  are  both  modified  and  intensified 
by  the  genius  presiding  over  the  function  of  nutrition.  Unfortunately, 
however,  in  dating  the  progressive  solidification  of  tissues,  we  can  with 
a  degree  of  certainty  mark  the  beginning  and  the  end  only,  the  inter- 
mediate lines  merely  approximating  the  conditions  Mdiich  we  attempt  to 
illustrate ;  yet  they  are  near  enough  to  exactness  to  give  a  comprehen- 
sive idea  of  the  condition  of  the  average  tooth  at  a  certain  age,  and  in  so 
doing  they  serve  as  an  important  guide  in  the  performance  of  many 
necessary  dental  operations  (Fig.  1). 

"  From  the  tabular  statement  or  chart  to  which  we  have  alluded 
above  we  see  that  by  the  seventh  week  of  intrauterine  life,  and  when 
the  embryo  is  less  than  one  and  a  quarter  inches  in  length,  preparation 
is  made  for  the  development  of  the  enamel-germ  or  matrix,  followed  in 
the  ninth  week  by  the  dentine-germ,  these  germs  continuing  in  or 
througli  their  progressive  stages  until  the  seventeenth  week,  when  we 


646  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

find  in  the  incisors  and  cuspids  the  border-line  between  the  enamel- 
and  dentine-germs  receiving  depositions  of  the  salts  of  lime ;  or,  to 
speak  more  correctly,  we  see  the  formation  of  the  odontoblast-cells 
and  their  conversion  into  dentine  and  the  ends  of  the  enamel-cells 
into  enamel  by  the  formation  and  calcification  of  the  ameloblasts.  By 
the  end  of  the  nineteenth  week  the  same  developmental  process  has 
reached  the  molars,  and  from  this  period  until  the  fortieth  week,  or 
time  of  birth,  the  growth  of  the  tooth-germs  and  their  calcification  pro- 
gress simultaneously.  At  birth  the  calcification  of  the  crowns  of  the 
eight  incisors  is  quite  complete ;  the  four  cuspids  and  four  first  molars 
are  fully  two-thirds  calcified,  and  the  four  temporary  second  molars 
have  their  crowns  for  half  their  length  solidified  by  the  same  process. 
At  the  end  of  the  following  three  months  the  infant  enters  into  the 
critical  period  of  its  life,  and  from  a  glance  at  the  condition  of  the 
twenty  deciduous  teeth  and  their  progressive  developmental  changes  it 
is  fair  to  assume  that  this  condition  has  not  a  little  to  do  with  the  vari- 
ous abnormal  systemic  lesions  or  disturbances  to  which  the  child  is 
liable  at  this  age.  In  close  proximity  to  the  sharp  and  irregular  edges 
of  the  calcifying  extremity  of  each  partial  or  complete  tooth-crown  lies 
the  vascular  papilla — the  primitive  tooth-pul}) — and  any  want  of  corre- 
spondence betAN'een  the  absorption  of  the  overlying  gum  at  the  coronal 
extremity  and  the  deposition  of  solid  matter  at  the  calcifying  or  papil- 
lary extremity  must  produce,  by  this  retarding  influence,  an  irritation 
limited  in  its  extent  by  the  number  of  teeth  advancing,  the  duration 
of  the  cause,  and  the  ramifications  of  the  trifacial  or  fifth  pair  of  nerves 
and  the  extent  of  the  sympathetic  disturbances  to  which  they  are  liable. 
The  necessity  for  operation  when  the  irritation  becomes  pathological  is 
so  unmistakable  that  it  seems  hardly  necessary  to  remind  you  of  the 
great  advantage  to  be  gained  from  the  free  use  of  the  lance  as  soon  as 
this  condition  becomes  apparent. 

"  Another  point  worthy  of  recognition  is  the  period  at  which  the  cal- 
cification of  the  apical  ends  of  the  roots  of  all  the  teeth  is  completed. 
Not  infrequently  these  deciduous  teeth,  before  eruption  is  complete, 
have  become  a  prey  to  rapid  molecular  decomposition  through  the 
agency  of  dental  caries.  Pulps  are  sometimes  exposed  while  yet  the 
root  is  not  completed  in  its  growth.  The  impropriety  of  resorting  to 
the  ordinary  method  of  pulp-devitalization  is,  under  such  circumstances, 
very  apj>arent.  When  we  consider  the  time  of  calcification,  it  is  not  a 
matter  of  surjirise  that  the  crowns  of  the  deciduous  teeth  are  much  less 
frequently  subject  to  maH'ormations  and  defects  arising  from  deficiency 
in  tlie  (juantity  and  quality  of  enamel  and  dentine  than  those  of  the 
permanent  set.  The  crowns  of  these  teeth  are  largely  provided  for  in 
embryonic  life,  and  unless  the  mother  during  gestation  is  in  markedly 
poor  health,  so  that  the  function  of  nutrition  is  but  imperfectly  per- 
formed, the  foetus  invariably  escapes  the  necessary  consequences  of  im- 
perfect nutrition,  which  is  so  conmion  after  birth  ;  yet  if  during  this 
im]K)rtant  period  to  the  embryo  there  should  be  a  ])rolonged  attack  of 
ill-health  and  systemic  depression,  the  crowns  of  the  deciduous  teeth 
would  give  its  history  by  deficiency  in  the  quantity  and  quality  of 
enamel  and  dentine. 


DEVELOPMENT  OF  CORD  FOB  PERMANENT  TEETH.        647 


648  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

"  We  come  now  to  the  permanent  teeth,  the  calcification  of  whicli  is 
illustrated  by  Fig.  2.  By  again  referring  to  the  tabular  statement  above 
mentioned  we  see  that  as  early  as  the  fifteenth  week  of  embryonic  life 
preparation  is  made  for  the  development  of  the  four  first  permanent 
molars,  and  following  close  upon  these,  in  the  sixteenth  week,  is  the 
inflection  giving  rise  to  the  enamel  organ  for  the  twenty  anterior  per- 
manent— the  successors  to  the  twenty  deciduous — teeth,  and  from  this 
period  until  the  birth  of  the  infant  the  germs  for  twenty-four  of  the 
permanent  teeth  are  ])assing  through  their  several  progressive  stages 
preparatory  to  receiving  the  salts  of  lime.  At  birth,  then,  the  child 
has  not  only  the  twenty  deciduous  teeth  largely  advanced  toward  calci- 
fication, but  has  germs  of  twenty-four  permanent  teeth,  in  twelve  of 
which  calcification  commences  the  first  year.  The  germ  of  the  second 
permanent  molar  makes  its  appearance  the  third  month,  and  that  of  the 
third  molar  the  third  year,  after  birth. 

"  The  permanent  teeth,  unlike  the  deciduous,  are  during  the  periods 
of  calcification  constantly  subjected  to  the  influence  of  morbid  systemic 
conditions,  and  any  abnormal  nutritional  condition,  of  but  a  few  days' 
duration,  if  occurring  during  the  period  of  coronal  calcification,  is  sure 
to  make  an  impression  upon  the  crowns  of  the  teeth,  which  are  at  the 
time  undergoing  this  process,  markings  or  defects  being  located  at  the 
point  of  calcification  and  limited  in  extent  or  modified  by  the  severity 
and  duration  of  the  abnormality  or  lesions.  The  principal  object  or 
advantage  of  Fig;.  2  will  be  to  determine  the  age  of  the  child  when 
the  systemic  conditions  existed  which  caused  the  faults  or  imperfec- 
tions in  the  development  of  the  teeth.  If  serious  nutritional  disturb- 
ances have  occurred  prio?  to  the  termination  of  the  tenth  year,  some 
one  or  more  of  the  permanent  teeth  must  in  all  probability  have  recorded 
it.  Another  service  which  this  illustration  will  render  will  be  in  deter- 
mining the  condition  of  the  apical  end  of  the  root  or  roots  in  any  given 
tooth,  when  beginning  treatment,  from  pulp-exposure  arising  either 
from  caries  or  fracture,  and  also  from  partial  or  complete  dislodgment 
by  accident.  This  knowledge  will  in  many  instances  aid  the  operator 
in  forming  his  judgment  as  to  the  best  methods  to  be  pursued  for  the 
relief  of  his  patient. 

"As  represented  by  the  first  and  second  lines  in  the  diagram,  we  see 
that  the  four  first  permanent  molars  and  the  eight  incisors  have  prior  to 
the  termination  of  the  first  year  all  received  a  portion  of  their  lime  salts, 
and  before  the  termination  of  the  third  year  twenty-four  of  the  thirty- 
two  teeth  are  in  this  jirocess  of  development.  The  fifth  year  the  second 
permanent  molars  and  the  eighth  year  the  third  molars  or  wisdom  teeth 
commence  cak^ification.  With  the  permanent  set  it  is  rarely  that  the 
patient  suffers  from  the  effects  of  interrupted  dentition,  as  is  so  fre- 
quently prominent  in  first  dentition  ;  yet  at  times  both  the  cuspids  and 
bicuspids  are  so  retarded  in  their  eruption  by  the  persistence  of  their 
deciduous  predecessors,  or  by  a  small  and  contracted  condition  of  the 
maxillary  bones,  that  serious  trouble  results;  also,  from  induration  of 
the  gums  or  non-absorption  of  the  anterior  portion  of  the  ramus  or 
tuberosity,  either  the  first,  second,  or  third  molar  may  be  the  cause  of 
much  local  inflammation  and  a  febrile  systemic  condition,  and  especially 


DEVELOPMENT  OF  COED  FOB  PERMANENT  TEETH.        649 

is  this  invariably  the  result  of  an  impacted  tliircl  molar.  The  fact  that 
the  third  molars  are  developed  during  the  period  of  childhood  and 
youth  and  while  the  system  is  liable  to  frequent  conditions  which  impair 
nutrition  is  probably  one  potent  reason  for  their  frequent  lack  of  useful- 
ness and  durability. 

"  The  decalcification  or  absorption  of  the  roots  of  the  deciduous  teeth 
is  illustrated  as  far  as  practicable  by  Fig.  3,  and  in  this  eifort  your 
essayist  has  found  it  extremely  difficult  to  do  more  than  approximate 
the  time  at  which  this  interesting  and  somewhat  obscure  physiological 
process  is  carried  on.  The  avei-age  period  at  M'liich  it  commences  Mill 
be  sufficient  to  indicate  the  time  when  much  care  will  be  necessary  in 
the  application  of  the  arsenical  paste  for  the  devitalization  of  the  pulp, 
and  in  the  subsequent  treatment  of  the  pulp-chamber  and  root-canal. 
This  process,  usually  commencing  in  the  incisors  before  the  close  of  the 
fourth  year,  progresses  gradually,  when  normally  accomplished,  from 
the  extreme  end  of  the  root  toward  the  crown  for  about  three  years, 
and  usually  releases  this  deciduous  crown  between  the  seventh  and 
eighth  years,  the  central  incisor  being  some  months  in  advance  of  the 
lateral.  The  absorption  of  the  roots  of  the  first  deciduous  molars  may 
be  placed  a  year  later  than  that  of  the  lateral  incisors,  commencing 
about  the  middle  or  close  of  the  sixth  year  and  terminating  with  the 
removal  of  the  first  deciduous  molars,  about  the  tenth  year,  the  second 
molars  following  usually  some  months  or  a  year  later.  The  cuspids — 
invariably  the  last  of  the  deciduous  teeth  to  be  shed — have  their  period 
of  absorption  from  the  eighth  to  the  twelfth  year.  AVhile  these  periods 
would  correspond  with  the  absorption  and  removal  of  the  teeth  in  the 
average  mouth,  so  variable  are  they  in  different  families  that  many 
would  be  widely  different  from  the  above  figures. 

"I  have  just  spoken  of  this  absorptive  process  as  being  physiological 
and  somewhat  obscure.     It  certainly  is  both,  and,  in  contradistinction 

to  the  evolution  of  the  tooth,  may  be  termed  its  dissolution 

What  induces  this  molecular  dissolution  it  is  difficult  to  state,  though 
the  several  conditions  which  are  always  present  are  readily  recognized  ; 
but  the  part  they  play  is  so  obscure  that  it  is  not  readily  ascertained. 
The  manner  of  its  commencement  when  successful — always  at  the  end 
of  the  root — and  the  presence  of  a  vascular  papilla  in  close  proximity 
to  the  absorbing  surface  are,  with  the  retention  of  pulp-vitality,  three 
essential  accompaniments,  and  the  absence  of  any  one  of  them  would 
militate  against  the  completion  of  the  process. 

"  The  statement  that  the  presence  and  pressure  of  the  permanent 
tooth  are  essential  cannot  be  sustained,  for  frequently  the  decalcification 
of  the  deciduous  tooth  is  successfully  accomplished  in  the  absence  of  its 
successor ;  and  again,  how  often  do  we  find  the  permanent  tooth  im- 
pacted against  or  within  the  bifurcated  roots  of  the  deciduous  molar,  or 
pressing  down  by  the  side  of  its  single-rooted  predecessor,  both  being 
more  or  less  displaced  by  the  persistence  of  the  deciduous  tooth  without 
absorption  !  That  the  organ  has  served  its  purpose,  and  that  the  nour- 
ishment which  had  previously  been  appropriated  by  it  is  diverted  or 
relegated  to  its  successor,  is  probably  the  most  plausible  explanation  we 
can  give  of  this  interesting  physiological  process. 


650  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

"  This  demonstration  of  dissolution  and  evolution  is  not  alone  con- 
fined to  the  teeth.  The  ramus  of  the  inferior  maxillary  gives  evidence 
of  a  similar  phenomenon  by  absorption  from  its  anterior  border,  with 
corresponding  growth  of  its  interstitial  tissue,  giving  development  and 
prominence  to  its  posterior  line.  There  are  also  bone-cased  cavities  and 
canals,  increasing  in  diameter  and  capacity  by  absorption  from  within 
and  addition  to  the  surrounding  walls.  These,  we  conclude,  are  the 
results  of  similar  physiological  efforts.  Roots  which  have  long  been 
bathed  in  pus  from  the  establishment  of  chronic  alveolar  abscesses  fre- 
quently display  a  worm-eaten  appearance.  This,  though  representing 
dissolution,  is  a  chemical  and  pathological  process  depending,  we  sur- 
mise, entirely  upon  the  acrid  condition  of  the  pus,  and  is  not  in  any 
case  to  be  mistaken  for  the  physiological  process  which  we  have  above 
described. 

"  In  recording  the  periods  of  calcification  of  the  deciduous  and  perma- 
nent teeth  it  should  be  noted  that  in  many  instances  a  want  of  corre- 
spondence between  their  calcification  and  eruption  exists.  By  jjrema- 
ture  removal  of  the  gum  the  crown  is  frequently  exposed  while  yet 
there  is  no  root-calcification,  as  instanced  in  deciduous  incisors  when 
erupted  at  birth,  their  crowns  only  being  calcified,  which  is  the  normal 
condition  of  these  teeth  at  this  age.  Again,  not  infrequently  the  persis- 
tence of  the  deciduous  cuspids  and  molars  as  well  as  of  the  indurated 
gum  over  an  advancing  permanent  molar  causes  delay  in  the  eruption 
of  the  permanent  teeth  until  after  the  calcification  of  their  roots  is  com- 
pleted. These  instances  illustrate  that  in  one  case  eruption  takes  place 
without  the  development  of  the  root,  and  in  the  other  we  have  complete 
develo])ment  of  both  crown  and  root  without  eruption. 

"  In  presenting  to  you  to-day  the  periods  of  calcification  as  repre- 
sented by  Fig.  2,  I  am  not  unmindful  that  Dr.  G.  V.  Black,  of  Jack- 
sonville, 111.,  had  previously  published  in  the  Proceedings  of  the 
Illinois  State  Dental  Society  a  series  of  diagrams  representing  the 
same  physiological  process.  The  results  of  his  researches  so  nearly 
correspond  with  those  of  mine  that  I  have  been  encouraged  to  present 
them  with  others  representing  the  calcification  and  decalcification  of 
the  deciduous  teeth." 

The  comparative  stages  of  calcification  of  the  temporary  and  perma- 
nent teeth  are  also  nicely  shown  in  Fig.  368,  taken  from  a  jaw  of  child 
seven  years  of  age.  (This  specimen  is  one  of  a  series  belonging  to  Prof. 
T.  C.  Stellwagcn.)  The  eruption  of  the  permanent  incisors  and  sixth- 
year  molars  has  been  accomjilished.  The  lateral  incisor  crown  and  a 
portion  of  the  root  are  formed.  The  root  of  the  temporary  lateral  is 
partially  resorbed.  The  ci'OAvns  of  the  cuspids,  first  and  second  bicus- 
pids, and  the  twelve-year  molars  are  well  advanced  in  the  process  of 
calcification.  The  roots  of  the  central  incisors  are  not,  however,  fully 
formed,  but  the  apical  foramen  still  remain  largely  open.  The  roots 
are  exposed  l)y  removing  the  bony  covering ;  sufficient  is  left  at  mf  to 
mark  the  mental  foramen.  The  cancellated  nature  of  the  alveolar  wall 
is  such  that  the  greatest  mobility  is  afforded  the  erupting  tooth.  The 
pressure  of  the  li})s  externally  prevents  the  arch  protruding ;  tliis  is 
opposed  by  the  outward  pressure  of  the  tongue,  so  that  no  uneasiness 


COMPARATIVE  CHRONOLOGY  OF  DENTAL  FOLLICLE.       651 

should  be  felt  by  the  practitioner,  provided  the  teeth  under  his  care  were 
erupting  the  upper  external  to  the  lower. 

Fig.  368. 


Drawing  from  Prepiired  Supciinen  from  Prof.  Stellwagen's  Cabinet:  n,  permanent  central  incisor; 
6,  erupting  permanent  lateral  incisor;  c,  developing  permanent  cuspid;  Ihi,  first  temporary 
molar;  2m,  second  temporary  molar;  ntf,  mental  foramen.  The  other  letters  plainly  indicate 
their  adaptation. 


Comparative  Chronology  op  the  Dental  Follicle. 

In  sections  from  the  jaws  of  the  common  snake  which  are  supplied 
with  successional  teeth,  all  the  stages  of  tooth-develo})ment  may  be 
observed  in  the  same  section,  from  the  first  infolding  of  the  mucous 
membrane  through  the  invaginative  process  to  complete  calcification. 
The  same  may  be  seen  in  sections  from  the  jaw  of  the  dogfish.  In  the 
human  foetus  the  first  indication  of  tooth-formation  is  seen  about  the 
forty-fifth  day,  and  consists  in  the  formation  of  the  epithelial  band. 
There  is  as  yet  no  indication  of  points  of  ossification ;  ISIeckel's  car- 
tilage marks  the  central  portion  of  the  inferior  maxilla.  Between  this 
age  and  two  months  the  evolution  of  the  lamina  and  cords  for  the  tem- 
porary is  accompli,shed.  The  cords  for  the  central  incisors  are  bulbous, 
while  those  for  the  other  teeth  show  varying  stages  of  development, 
those  for  the  molars  being  less  fully  developed  than  are  those  for  the 
incisors.  Ossification  is  seen  in  both  jaws  alike.  This  is  also  true  in 
regard  to  the  development  of  the  dental  follicles  for  the  temporary 
teeth,  which  occurs  simultaneously  in  both  jaws  for  the  same  teeth.  At 
three  months  the  enamel  for  the  incisor  teeth  is  nearly  developed,  the 
process  of  invagination  having  attained  considerable  progress.  Tlie  cen- 
tral portion  of  the  enamel  organ  gives  indication  of  formation  of  the 
stellate  reticulum.  The  forming  bone  has  become  a  distinctive  feature 
of  the  jaws  and  stands  out  in  bold  relief  in  sections  stained  with  hsemo- 


G52  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

toxylon  and  eosin.  There  is  no  noticeable  difference  between  the  i\\o 
tunics.     The  follicular  wall  is  plainly  seen. 

At  the  fourth  month  the  inner  tunic  at  the  apex  of  the  papilla  gives 
evidence  of  the  development  of  the  ameloblasts.  The  surface  of  the 
papilla  at  the  apex  also  is  covered  by  columnar  cells,  the  odontoblastic 
layer.  The  central  portion  of  the  enamel  organ  is  distinctly  stellate. 
The  stratum  intermedium,  lying  upon  the  outer  surface  of  tlie  amelo- 
blasts, is  also  well  marked.  The  follicular  wall  is  well  developed  and 
almost  surrounds  the  enamel  organ,  which  is  still  connected  to  the 
mucous  membrane  of  the  mouth  by  its  neck.  The  cord  for  the  perma- 
nent tooth  may  be  seen  in  some  instances  coming  off  from  the  side  of 
the  enamel  organ  or  from  the  neck  of  the  enamel  organ.  In  other  cases 
the  cords  for  the  permanent  do  not  make  their  appearance  until  a  later 
period.  I  have  not  been  able  either  by  measurement  or  by  other  signs 
to  establish  any  definite  time  for  the  origin  of  the  cords  of  the  perma- 
nent teeth. 

Between  the  fourth  and  fifth  month  for  the  central  incisors  is  accom- 
plished the  separation  of  the  enamel  organ  from  the  nmcous  membrane 
of  the  mouth  by  the  severance  of  the  cord  and  the  complete  encapsula- 
tion of  the  enamel  organ  by  the  follicular  wall. 

At  the  fifth  month  the  process  of  calcification  of  both  enamel  and 
dentine  has  considerably  advanced  for  the  incisors.  The  cuspids  also 
show  a  thin  enamel  cap.  The  first  and  second  molars  give  evidence  of 
the  multicuspid  arrangement.  The  cord  for  the  sixth-year  molar  is 
also  seen.  The  bone  of  the  jaw  is  largely  developed,  Meckel's  cartilage 
has  disappeared  by  ossification,  and  the  alveolar  walls  are  well  formed 
and  extend  high  up  on  the  sides  of  the  dental  follicles. 

At  the  eighth  month,  as  seen  in  Fig.  360,  calcification  has  progressed 
to  a  considerable  extent.  The  enamel  organ  for  the  permanent  central 
incisor  is  well  developed  and  somewhat  invaginated,  and  occupies  a 
position  upon  the  lingual  face  of  the  temporary  tooth. 

"  On  examining  sections  taken  from  the  jaws  of  subjects  two  or  three 
months  after  birth  we  discover  in  the  region  occupied  by  the  follicle  of 
the  first  permanent  molar  a  process  or  prolongation,  cylindrical  in  form, 
emanating  from  the  epithelial  cord  of  the  latter  f^ollicle,  and  which 
takes  a  horizontal  and  backward  direction,  terminating  in  a  bulbous 
extremity.  This  prolongation  is  the  commencement  of  the  follicle  of 
the  second  permanent  molar.  Thus  we  fix  the  date  of  the  origin  of 
this  follicle  at  the  third  month  after  birth.  At  about  the  third  year  of 
infancy  the  epithelial  bourgeon  that  represents  the  enamel  organ  of  the 
third  molar  originates  from  the  cord  of  the  preceding  tooth — that  is,  the 
second  permanent  molar.  According  to  the  numerous  observations  we 
have  made,  this  date  may  be  regarded  as  very  nearly  accurate,  though 
the  difficulties  of  which  we  have  already  s]>oken  have  prevented  us 
from  following  out  the  successive  phases  of  evolution  in  a  very  rigid 
manner.  Yet  that  a  little  cap  of  dentine  is  visible  in  this  follicle  about 
the  twelfth  year  is  true  beyond  a  doubt."  ^ 

Bovine  and  porcine  embryos  show  the  same  development  for  the  same 
lengths,  although  there  is  a  very  considerable  difference  in  the  sizes  of 
'  Dean's  trans.  Lecrro  and  Mao;itot. 


COMPARATIVE  CHRONOLOGY  OF  DENTAL  FOLLICLE.      653 

the  foetuses  at  birth.  Evokition  of  their  dental  follicles  seems  to  begin 
about  the  same  time. 

At  1-|-  cm.  in  the  porcine  embryo  there  is  no  indication  of  the  forma- 
tion of  the  band.  The  same  holds  good  for  the  bovine  embryos.  The 
mucous  membrane  of  the  mouth  of  each  is  thicker  than  the  external 
epithelium. 

At  2|-  cm.  the  band  is  distinctly  marked  and  the  cells  are  heaped  up 
over  the  line  of  the  infolding  epithelium. 

At  3  cm.  the  lamina  has  made  its  appearance,  and  shortly  afterward 
the  buds  for  the  cords  of  the  temporary  teeth  are  seen. 

At  4  cm.  the  process  of  invagination  begins,  which  marks  the  appear- 
ance of  the  dentinal  papillae;  these  arise  from  the  embryonal  connective- 
tissue  elements  into  which  the  enamel  organ  by  its  growth  is  projected. 

At  5  cm.  the  differentiation  of  the  follicular  wall  has  begun  from  the 
surrounding  embryonal  connective  tissue.  In  its  origin  and  character 
it  is  analogous  with  the  tissue  of  the  papilla,  but  seems  to  be  condensed 
into  a  membrane,  and  in  this  differs  from  the  pulp-tissue. 

At  6,  7,  and  8  cm.  invagination  is  seen  to  be  progressing,  until  at  the 
last-named  measurement  it  is  complete.  The  formation  of  the  stellate 
reticulum  has  also  been  accomplished.  The  bone  of  the  jaw,  which  first 
made  its  appearance  at  3  cm.,  has  now  well-defined  alveoli,  and  the 
bodies  of  the  maxilla?  are  vrell  developed. 

At  9  cm.  the  dentine  cap  is  plainly  visible,  and  the  cords  for  the  per- 
manent teeth  are  seen  springing  off  from  the  lingual  face  of  either  the 
enamel  organ  of  the  temporary  tooth  or  from  the  cord  of  the  same. 

At  10  cm.  the  enamel  organ  over  the  apex  of  the  papilla  has  disap- 
peared. The  enamel  presents  itself  as  a  thin  layer  lying  upon  a  cap  of 
dentine  of  considerable  thickness.  The  cord  for  the  ])ermanent  tooth 
extends  down  upon  the  side  of  the  follicle,  having  separated  from  the 
temporary  follicle,  which  is  now  fully  enclosed  by  the  fibrous  con- 
nective-tissue follicular  wall,  the  future  cement  organ. 

^ye  might  multiply  words  in  further  description  ;  suffice  it  to  say 
that  at  birth  the  crowns  of  the  central  incisors  are  fidly  formed,  and 
very  soon  after  erupt.  My  studies  in  ovine  embryos  have  been  confined 
to  some  half  dozen  at  birth ;  the  crowns  in  these  cases  were  fully  calci- 
fied and  offered  excellent  example^s  for  the  study  of  Nasmyth's  mem- 
brane, which  has  the  character  of  a  structureless  membrane  covering 
the  enamel,  and  which  is  easily  made  discernible  by  the  use  of  dilute 
acids. 

Sections  through  the  face  of  a  foetal  puppy,  the  facial  bones  of  which 
very  nearly  com])are  with  those  of  the  human  foetus,  make  good  studies. 

I  have  never  had  the  pleasure  of  examining  equine  foetuses,  and  fhall 
take  the  liberty  of  quoting  from  Legro  and  Magitot,  taken  from  Dean's 
translation  : 

"Our  observations  have  been  made  upon  equine  embryos  of  different 
ages.  From  these  we  have  determined  certain  facts  in  relation  to  the 
various  phases  of  follicular  evolution.  For  the  first  three  embryos  we 
are  indebted  to  the  courtesy  of  M.  Raynal,  of  the  veterinary  school  at 
Alfort.  In  the  youngest  of  these  (14  weeks)  the  enamel  organs  of  the 
central  nippers  (incisors)  are  already  formed  and  the  bulb  has  made  its 


654  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

appearance.  For  the  lateral  nippers  the  enamel  organ  is  jnst  beginning 
to  show  itself.  These  facts  indicate  that  the  evolution  of  the  follicles 
of  these  teeth  in  man  and  other  mammals  appears  to  be  synchronous. 
For  the  molars  it  is  found  that  at  this  same  epoch  the  bulb  has  appeared 
for  all  the  follicles  of  the  first  dentition,  as  have  also  the  first  traces  of 
the  follicular  wall.  In  a  second  embryo  (of  27  weeks)  the  follicles  of 
the  central  incisors  are  closed,  while  those  of  the  first  lateral  incisors 
are  just  beginning  to  exhibit  the  bulbs,  and  those  of  the  second  lateral 
incisors  only  the  enamel  organ.  These  facts,  as  we  see,  additionally 
confirm  the  unequal  development  of  the  diiferent  incisors  in  this  animal. 
In  the  molars  the  facts  are  analogous ;  the  follicle  of  the  first  temporary 
molar  is  closed  at  this  date,  while  the  enamel  organ  of  the  second  has 
only  just  made  its  appearance,  and  no  trace  of  that  of  the  third  molar  is 
yet  visible.  It  is  at  this  period,  also,  that  the  first  indication  of  the 
enamel  organ  appears  for  the  first  permanent  molar.  In  a  third 
embryo,  measuring  255  millimeters  [10  inches],  corresponding  to  about 
28  T  weeks,  the  follicles  of  the  permanent  incisors  are  closed  and  com- 
plete ;  the  enamel  organ  is  well  developed.  The  ameloblasts  of  the 
interior  bed  are  very  large,  and  the  external  epithelial  layer  has  already 
disappeared,  but  no  trace  of  dentine  yet  appears. 

"  The  follicles  of  the  permanent  incisors  have  arrived  at  the  period 
when  the  enamel  organ  already  caps  the  bulb,  which  is  just  appearing, 
but  is  not  yet  constricted  at  its  base.  For  the  temporary  molars  the 
follicles  are  about  equally  developed.  They  are  closed  and  well  formed, 
but  without  any  appearance  of  the  dentine  cap.  The  organ  of  coronal 
cement  is  already  beginning  to  manifest  itself.  From  the  fragments  of 
the  ruptured  epithelial  cord  numerous  buddings  have  been  produced. 

"  From  the  fourth  (an  equine  foetus  of  31 J  weeks),  owing  to  a  very 
prolonged  maceration  in  alcohol,  we  were  prevented  from  deriving  much 
advantage.  We  were  only  able  to  determine  that  the  temporary  follicles 
were  fully  developed  and  provided  with  caps  of  dentine  of  considerable 
thickness.  Some  fragments  of  the  epithelial  cord  (long  since  broken, 
without  doubt)  were  still  remaining.  The  organ  of  coronal  cement  was 
fully  developed. 

"  We  will  conclude  these  chronological  considerations  with  a  few 
notes  relative  to  the  rodents.  In  an  embryonal  guinea-pig  of  2  cm. 
[4  incli]  in  total  length,  Avhich  appeared  to  correspond  to  about  the 
middle  period  of  gestation,  the  follicle  was  at  the  stage  when  the  enamel 
organ,  in  form  of  a  hood,  covers  the  bulb ;  there  was  no  follicular  wajl 
or  dentine  cap  apparent. 

''In  another  embryo  of  the  same  species  of  4  cm.  [H  inches]  in 
length,  the  temporary  follicles  were  formed,  aud  their  stages  of  devel- 
opment were  nearly  the  same.  They  were  provided  with  a  dentine  cap 
covered  with  a  thin  layer  of  enamel.  In  the  rabbit  we  discover  that  at 
birth  the  incisors  have  effected  their  eruption,  the  molars  still  enclosed, 
but  already  capped  with  thick  layers  of  dentine  and  enamel.  Beneath 
the  temporary  molars  we  observe  the  presence  of  tiie  pennanent  follicles, 
already  ]>rovided  with  a  thin  but  distinctly  manifest  layer  of  dentine." 

The  Dental  Papilla,  or  Pulp. — The  dental  pulp  first  makes  its 
•appearance   as  a   slightly  condensed   area  of  tissue   in  juxtaposition 


NERVES  OF  THE  PULP.  655 

to  the  lowest  portion  of  the  developing  enamel  organ.  Its  diiferentia- 
tion  seems  to  be  controlled  by  the  enamel  organ.  It  is  composed  at 
this  early  stage  of  embryoplastic  connective-tissne  cells,  and  differs  in  no 
manner,  as  regards  its  constituent  elements,  from  the  surrounding  tissue. 
In  stained  specimens  it  presents  a  somewhat  darker  color,  due  to  the 
condensation  of  the  cells  which  compose  it.  As  we  consider  it  in  the 
further  stages  of  development  there  is  presented  no  characteristic  which 
may  not  be  seen  in  the  surrounding -embryonal  connective  tissue.  Blood- 
vessels early  show  themselves  and  form  numerous  anastomosing  loops, 
which  give  the  papilla  a  highly  vascular  nature.  The  first  indication 
of  the  ofiice  of  the  papilla,  or  pulp,  as  the  formative  organ  of  the  den- 
tine of  the  tooth,  is  seen  in  the  human  foetus  of  four  months  and  the 
porcine  embryo  8  or  9  cm.  in  length.  There  is  developed  a  layer  of 
cells  upon  the  apical  surface  of  the  papilla ;  these  cells  are  termed  odon- 
toblasts. At  first  they  are  oval  in  form  and  differ  very  little  from  the 
ordinary  connective-tissue  cells  Mhich  make  up  the  princij^al  portion  of 
the  papilla.  The  cells  of  this  outer  layer — mcmhrana  cboris,  as  it  has 
been  termed — gradually  become  elongated  and  send  out  processes  which 
connect  them  with  each  other  and  with  the  cells  of  the  pulp,  and  also 
extend  outward  toward  the  inner  tunic  of  the  enamel  organ.  These 
latter  processes  are  called  the  dentinal  fibrils.  The  odontoblasts  become 
columnar  in  shape  as  the  time  nears  for  the  commencement  of  their 
AYork  as  dentine-builders.  As  calcification  progresses  from  the  apex  of 
the  papilla  new  odontoblasts  are  developed  on  the  sides  of  the  papilla, 
until  the  membrana  eboris  forms  an  outer  "Covering  to  the  papilla,  and 
finally  the  fully-developed  pulp.  After  the  dentine  is  completely  cal- 
cified the  odontoblasts  again  change  their  form  into  oval  cells,  and  con- 
tinue to  exist  as  such  throughout  the  life  of  the  pulp.  When  stimulated 
l)y  irritation,  whether  from  caries  or  by  thermal  changes  brought  about 
by  loss  of  tooth-structure,  by  attrition,  or  abrasion,  the  odontoblasts 
again  assume  their  old  functional  activity  and  develop  secondary 
dentine. 

While  these  changes  have  been  going  on  in  the  formative  outer  layer 
of  the  pulp  the  embryonal  connective-tissue  cells  are  developed  into 
ordinary  connective-tissue  cells. 

Between  these  fixed  connective-tissue  cells  may  be  seen  the  ordinary 
plasma-cells  noticed  throughout  the  connective-tissue  system,  the  pnlp 
being  no  exception  to  the  rule. 

Nerves  of  the  Pulp. 

The  nerves  of  the  pulp  are  many  and  consist  of  medullated  and  non- 
medu Hated  fibres,  which  enter  the  pulp  through  the  apical  foramen  in 
various-sized  bundles.  Passing  forward,  they  break  up  into  smaller 
branches  and  form  a  rich  plexus  underneath  the  odontoblastic  layer. 
Regarding  their  termination  many  speculative  theories  have  been  ad- 
vanced, but  little  or  no  definite  knowledge  has  been  presented.  Some 
assert  that  the  finer  fibres  pass  between  the  odontoblasts  and  either  unite 
with  the  dentinal  fibrils  or  pass  with  them  into  the  dentinal  tubuli. 
Others  assert  that  the  non-medullated  fibres  become  united  with  the 


656.  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

stellate  layer  of  cells,  which  may  be  seen  lying  underneath  and  con- 
nected with  the  odontoblastic  layers. 

I  am  unable  to  make  any  statement  regarding  the  termination  of  the 
nerves  of  the  pulp.  I  am  very  skeptical  regarding  their  having  any 
direct  connection  with  the  fibrils  of  the  odontoblasts,  and  have  never 
been  able  to  demonstrate  any  such  relationship.  Tlien,  again,  as  no 
nerves  can  be  demonstrated  until  after  calcification  has  progressed  to 
a  very  considerable  extent,  the  proof  is  conclusive  that  they  are  not  an 
essential  element  to  the  process.  I  am  more  inclined  to  the  view  held 
by  Magitot — that  the  terminal  fibrils  unite  with  the  odontoblasts,  and 
that  sensation  is  thus  transmitted  by  the  dentinal  fibrils  to  the  terminal 
branches  of  the  nerves.  As  there  exists  a  very  considerable  degree  of 
ignorance  regarding  the  termination  of  nerves  in  other  parts  of  the 
body  where  the  conditions  are  favorable  for  their  demonstration,  I  do 
not  think  it  strange  that  we  should  be  unable  to  state  authoritatively 
just  how  they  terminate  in  the  pulp,  seeing  that  the  technique  for  their 
demonstration  in  that  organ  is  so  difficult. 

The  calcification  of  the  crown  being  completed  and  the  time  for  erup- 
tion having  arrived,  the  process  of  eruption  begins  as  the  tooth  makes 
its  appearance  above  the  gum.  The  root  is  gradually  developed;  the 
jaw  is  also  growing  rapidly  and  gives  a  firmer  setting  for  the  erupting 
tooth.  The  attachment  of  the  tooth  to  the  jaw  is  fibrous  in  character 
and  surrounds  the  root  as  a  membrane,  being  united  to  the  root  on  one 
side  by  many  fine  prolongations,  which  penetrate  and  anastomose  with 
the  processes  of  the  bone-cells  which  occupy  the  lacunae  of  the  cemen- 
tum.  A  similar  attachment  exists  with  the  alveolar  wall  upon  the 
outer  periphery.  The  development  of  the  cement,  as  we  have  seen 
when  discussing  that  subject,  is  accomplished  in  a  manner  identical  with 
subperiosteal  formation  of  bone.  The  formative  membrane  remains  as 
the  pericementum  and  persistent  cement  organ.  The  deposits  of  sec- 
ondary cement  known  as  exostoses  are  due  to  this  membrane.  The  pro- 
cess of  calcification  is  not  always  a  continuous,  harmonious  effi^rt  upon 
the  part  of  Nature,  but  is  subject  to  many  interruptions  ;  these  leave 
their  indications  upon  the  cement,  enamel,  and  dentine.  Interglobular 
spaces  are  seen  in  both  dentine  and  enamel.  These  ^ve  have  discussed 
to  a  considerable  extent.  The  pits  seen  upon  the  surface  of  the  enamel 
are  no  doubt,  in  some  instances,  caused  by  these  spaces.  The  serrations 
seen  upon  the  edges  of  newly-erupted  teeth — so  long  known  as  ''  Hutch- 
inson teeth" — have  now  pretty  generally  come  to  be  attributed  not  alto- 
gether to  congenital  syphilis,  but  to  lack  of  nourishment  or  inherited 
conditions  which  may  be  other  than  sy]>hilitic. 

Besides  the  markings  seen  upon  the  individual  prisms,  there  are  other 
lines  which  run  transversely  across  the  prisms.  These  have  been  called 
the  "broken  strise  of  Retzius."  The  lines  of  stratification  have  a  more 
or  less  decided  brownish  tint,  but  just  what  gives  rise  to  the  appearance 
I  am  unable  to  conjecture.  It  is  held  by  some  to  be  the  result  of  an 
arrest  in  the  process  of  calcification,  each  line  marking  such  a  period; 
others  hold  that  it  is  due  to  the  varying  character  of  food  taken  by  the 
mother  during  gestation,  some  being  rich  in  lime  salts  of  one  kind, 
while  another  salt  predominates  in  another  kind  of  food.     If  this  is  the 


^'ERVES  OF  THE  PULP. 


657 


case,  then  the  same  statement  will  hold  true  regarding  the  action  of 
food-stuffs  upon  the  teeth  of  the  second  dentition.  The  lines  of  strati- 
fication that  lie  nearest  the  dentine  are  longest  and  form  a  complete 
arch.  Those  that  lie  nearer  the  surface  do  not  form  an  arch,  but  "  run 
out "  on  the  sides  of  the  tooth,  growing  shorter  as  the  surface  near  the 
neck  of  the  tooth  is  reached.     Those  nearest  the  dentine  conform  more 


Fig.  369. 


Vertical  Section  of  a  Tooth  in  situ  Clo  diameters) :  c  is  placed  in  the  pulp-cavitv,  opposite  the  cervix 
or  neck  of  the  tooth  ;  the  part  above  is  the  crown,  tliat  below  is  tlio  root  (fang).  1,  enamel  with 
radial  and  concentric  markings;  2,  dentine  with  tubules  and  incremental  lines ;' 8,  cement  or 
crusta  petrosa,  with  bone-corpuscles ;  4,  dental  periosteum ;  5,  bone  of  lower  jaw. 

or  less  in  direction  to  the  surface  of  the  dentine,  but  the  lines  seen  near 
the  neck  stand  at  an  acute  angle  to  the  surface  of  the  dentine. 

These  lines  are  also  seen  in  the  dentine  and  bear  an  almost  parallel 
relation  to  the  surface,  although,  as  a  rule,  the  brownish  color  is  very 
generally  absent. 

The  pigmentation  of  enamel  of  many  of  the  rodent  family,  as  we  have 

Vol.  I.— 42 


658  DENTAL  EMBRYOLOGY  AND  HISTOLOGY. 

observed,  is  normally  so,  and  may  be  said  to  bear  a  close  relationsliip  to 
the  density  of  the  teeth,  those  hardest  being  most  deeply  pigmented,  and 
vice  versa.  This  ride  holds  good  in  human  teeth  as  well,  I  am  inclined 
to  the  opinion  that  chemical  constituents  of  the  enamel  have  much  to  do 
with  its  color.  The  darker  teeth  are  much  more  resistive  to  caries  than 
are  the  softer  varieties. 

In  the  accompanying  figure  we  have  combined  in  one  section  all  the 
])roducts  of  calcification  we  have  been  considering — viz.  bone  of  ja^v, 
cementum,  dentine,  and  enamel. 


PART  IV. 

GENERAL  AND  DENTAL  PATHOLOGY. 


GENERAL  PATHOLOGY. 

DENTAL  CARIES. 

PATHOLOGY  OF  THE  DENTAL  PULP. 

DISEASES    OF   THE    DENTAL   PULP,    AND    THEIR 
TREATMENT. 

DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 

ABRASION  AND   EROSION   OP   THE  TEETH. 


GENERAL  PATHOLOGY 

By  G.  V.  BLACK,  M.  D.,  D.D.S. 


Introduction. 

Health  is  a  standard  condition  of  the  body  in  which  all  of  its 
functions  are  regularly  and  normally  performed.  Any  marked  devi- 
ation from  this  is  disease,  no  matter  what  the  deviation  may  be.  It  is 
impossible  to  frame  a  strict  definition  of  this  standard  of  health,  for  the 
reason  that  it  may  vary  within  certain  but  rather  wide  limits.  It  is  not 
the  same  in  all  individuals,  nor  always  the  same  even  in  the  same 
person.  The  various  functions  may,  at  different  times  or  in  different 
individuals,  vary  quite  perceptibly  in  their  degree  of  activity  consid- 
ered as  a  whole,  so  that  some  persons  are  habitually  more  robust  than 
others.  Again,  among  the  individual  functions  some  may  be  relatively 
less  active  than  others  without  an  impairment  of  health  that  can  prop- 
erly be  considered  a  diseased  condition.  Some  functions  may  be  more 
active,  others  less  so,  and  yet  the  departure  from  the  normal  equilibrium 
of  functional  activity  may  not  be  such  as  to  impair  so  seriously  the 
equable  relation  and  mutual  dependence  of  the  various  functions  as  to 
justify  us  in  considering  the  individual  unsound  in  health.  A  person 
may  be  fairly  healthy  and  not  be  in  the  highest  degree  of  health. 

In  disease  there  is  a  deviation  in  the  performance  of  some  one  of 
the  functions  of  the  economy  so  marked  that  the  individual  is  readily 
conscious  of  discomfort,  or  such  morbid  processes  are  in  operation  as 
will  l)ring  about  a  condition  of  disability  by  their  continued  action. 
In  the  great  majority  of  diseased  conditions  the  patient  is  at  once  made 
conscious  by  his  sensations  that  something  is  wrong.  He  becomes 
aware  of  a  departure  from  the  normal  state  by  a  feeling  of  discomfort 
either  general  or  local.  There  are,  however,  some  forms  of  disease  so 
insidious  in  their  approach  that  the  patient  may  not  become  conscious 
of  their  presence  until  very  serious  mischief  has  been  done.  There- 
fore the  feelings  of  the  person,  while  they  are  Usually  a  safe  guide 
as  to  the  condition  of  the  health,  are  not  to  be  regarded  as  infallible. 

A  disease  is  an  assemblage  of  morbid  phenomena  that  have  so  often 
been  noticed  to  occur  contemporaneously  or  to  follow  each  other  in  a 
certain  order  as  to  enable  those  skilled  in  their  study  to  recognize  them 
as  marking  a  special  form  of  deviation  from  health.  In  the  study 
of  these  assemblages  of  symptoms,  the  groupings  of  which  mark  the 
different  diseases  known  to  us,  it  has  long  been  noted  that  certain  patho- 
logical states  are  common  to  various  individual  diseases.  Of  these  the 
most  constant  are  changes  in  the  circulation  of  the  blood  and  in  the 

661 


6(32  GENERAL   PATHOLOGY. 

blood  itself,  or  in  the  relation  of  the  blood  to  the  tissues.  Some  of  these 
changes  may  occur  without  other  morbid  symptoms  preceding  them — 
i.  c.  may  be  primary ;  or  they  may  be  dei^endent  on  changes  that  have 
preceded  them — /,  e.  may  be  secondary ;  others  are  always  secondary. 
In  the  study  of  individual  diseases  it  is  found  to  be  cumbersome  to 
enter  into  a  detailed  description  of  all  these  accompanying  phenomena. 
A  separate  description  of  them  is  most  convenient,  and  at  the  same 
time  far  more  satisfactory,  for  in  this  manner  we  may  save  much  repe- 
tition and  avoid  confusion.  If  the  processes  of  inflammation  be  under- 
stood, it  is  much  easier  to  describe  the  formation  of  an  alveolar  abscess, 
for  in  that  case  the  description  will  not  necessarily  include  a  detailed 
account  of  the  inflammatory  process,  but  may  be  confined  to  the  causes, 
peculiar  characteristics,  and  results  of  the  process  in  that  particular  situa- 
tion. As  this  is  true  here,  it  is  also  true  in  the  various  other  situations 
in  which  local  inflammations  may  occur  ;  and  what  is  true  of  inflamma- 
tion applies  also  to  many  other  morbid  phenomena.  For  these  reasons 
I  purpose  describing  under  the  above  caption  various  morbid  conditions 
that  are  common  to  many  diseases,  especially  those  of  the  blood  and  of 
its  circulation. 

The  Pulse. 

The  pulse  is  produced  by  the  action  of  the  heart.  This  organ  acts  as 
a  pump,  taking  the  blood  from  the  great  veins  and  driving  it  into  the 
arteries.  With  each  contraction  of  the  Iieart  a  considerable  quantity  of 
blood  is  projected  forcibly  into  the  aorta,  and  through  this  it  is  distrib- 
uted to  the  entire  arterial  system.  The  arteries  are  so  many  elastic 
tubes,  and  the  volume  of  blood  in  passing  causes  a  sudden  expansion 
of  their  walls  at  each  impulse,  which  may  be  distinctly  felt  on  placing 
the  finger  over  any  artery  that  lies  near  the  surface.  In  the  very  super- 
ficial arteries  tlie  impulse  may,  in  many  instances,  be  seen.  This 
movement-  is  known  as  "  the  pulse."  As  the  pulse  is  caused  by  the 
action  of  the  heart,  it  becomes  an  index  to  the  condition  of  that  organ. 
If  the  heart  be  strong  and  vigorous,  we  will  find  a  strong  pulse ;  if 
weak,  the  ])nlse  \vill  be  correspondingly  so.  Tliis  result  is  modified  by 
the  condition  of  the  arteries.  The  arteries  are  not  simply  elastic  tubes, 
but  contain  within  their  walls  a  circular  coat  of  smooth  muscular  fibres 
by  which  their  calibre  may  be  diminished  or  increased,  this  action  being 
governed  by  the  vaso-motor  system  of  nerves ;  which  influence  is  con- 
tinually modifying  the  pulse  in  various  ways. 

The  importance  of  an  accurate  knowledge  of  the  pulse  becomes  mani- 
fest when  we  consider  that  most  diseases  kill  by  arresting  the  action  of 
the  heart.  In  all  cases  of  accident  the  condition  of  the  pulse  will  give 
a  more  certain  indication  as  to  the  immediate  danger  of  the  sufferer 
than  an  examination  of  the  local  injury  sustained,  for  the  reason  that 
it  affords  an  index  to  the  condition  of  the  nervous  system,  and  tells  the 
surgeon  at  once  whether  or  not  the  patient  has  suffered  anv  considerable 
depression  of  vital  power  in  cons-equence  of  the  injury.  In  disease  the 
])ulse  is  sure  to  give  the  signal  of  danger  promptly  and  afford  an  early 
indication  for  treatment.     It  is  true  that  in  manv  instances  the  nervous 


THE  PULSE.  663 

system  gives  way  first,  as  is  shown  by  muttering  delirium  and  sleepless- 
ness ;  but  in  these  cases  the  anxiety  of  the  physician  arises  more  from 
the  effect  these  conditions  will  ultimately  have  on  the  circulation  than 
from  danger  as  manifested  directly  through  the  nervous  system.  This 
delirium  and  inability  to  rest  exhaust  the  patient,  and  at  last  the  heart 
by  its  feeble  pulsations  signals  the  approach  of  fatal  debility.  In  case 
of  typhoid  fever  the  delirium  may  be  marked  and  long  continued,  yet 
so  long  as  the  action  of  the  heart  remains  good,  as  indicated  by  the  cha- 
racter of  the  pulse,  fair  hopes  may  be  entertained  that  the  patient  will 
recover.  It  is  the  final  effect  of  disease  on  the  heart  that  destroys  life ; 
therefore  it  is  hardly  possible  to  overestimate  the  importance  of  an  inti- 
mate knowledge  of  the  varying  qualities  of  the  pulse  and  the  indica- 
tions they  give  of  the  effects  of  disease  on  the  powers  of  life. 

In  the  study  of  the  varying  phases  of  the  pulse  we  should  recognize 
three  principal  divisions  of  the  subject — namely,  1st,  frequency ;  2d, 
quality ;  3d,  intermittence. 

Frequency  of  the  pulse  relates  solely  to  the  succession  of  the  pulsa- 
tions. These  may  succeed  each  other  with  varying  rapidity,  giving  a 
frequent  or  infrequent  pulse. 

Under  the  term  quality  we  consider  the  character  of  the  individual 
pulsations.  This  division  of  the  subject  is  at  once  the  most  important 
and  the  most  difficult.  Quality  is  rarely  dependent  upon  frequency  or 
infrequency,  but  these  conditions  are  usually  dependent  upon  quality. 
We  may  express  the  principal  qualities  of  the  pulse  as  follows :  The 
individual  pulsations  may  be  strong  or  weak,  hard  or  soft,  large  or  small, 
quick  or  slow  (or  short  or  long),  compressible  or  incompressible,  regular 
or  irregular,  dicrotous. 

Intermittence  is  the  failure  of  an  occasional  pulsation.  This  may 
occur  very  regularly,  or  it  may  be  irregular  in  its  occurrence.  ]More 
frequently  it  is  the  failure  of  every  third  or  fourth  beat  or  pulsation. 

ExAMiXATiox  OF  THE  PuLSE. — The  pulse  may  be  examined  in  any 
artery  that  lies  near  enough  the  surface  to  be  easily  felt  by  the  finger.  The 
radial  artery  at  the  wrist  is,  however,  the  one  generally  used,  because 
it  is  the  most  convenient.  Any  other  artery  may  be  selected  if  from 
any  cause  the  use  of  this  one  should  be  inconvenient.  If  the  examina- 
tion is  only  for  the  determination  of  the  frequency  of  the  pulse,  any 
position  in  which  the  pulsations  can  be  distinctly  felt  will  answer  the 
purpose ;  but  for  determining  the  qualities  of  the  pulse  much  more  care 
is  required.  In  making  this  examination  the  wrist  of  the  patient  should 
usually  be  taken  between  the  thumb  and  fingers  in  such  a  way  that  the 
ends  of  three  fingers  may  be  placed  easily  on  the  artery.  The  position 
should  never  be  strained  or  uncomfortable  either  to  the  patient  or  the 
physician.  The  wrist  of  the  patient  should  be  straight  or  a  little 
extended,  but  it  should  not  be  flexed,  for  in  that  case  the  artery  is 
placed  in  a  bad  position  for  examination.  In  simply  counting  the  pulse 
one  finger  is  all  that  is  required.  In  determining  the  qualities  of  the 
pulse  one  finger  should  first  be  pressed  very  lightly  on  the  artery,  and 
afterward  more  firmly,  and  the  pressure  varied  from  time  to  time 
until  all  of  the  finer  qualities  are  ascertained.  In  determining  the 
compressibility  of  the  pulse  all  three  fingers  should  be  used,  bringing 


664  GENERAL  PATHOLOGY. 

them  to  bear  one  after  the  other  until  the  degree  of  compressibility 
is  ascertained.  Of  this  I  will  presently  speak  more  definitely.  The 
matter  of  the  examination  of  the  pulse  demands  much  careful  and  patient 
study  from  those  ^Yho  would  become  proficient  in  the  determination  of 
its  qualities  and  in  the  interpretation  of  its  meanings.  There  are  vari- 
ous circumstances  that  modify  the  normal  pulse,  some  of  which  will  be 
mentioned  hereafter.  It  must  always  be  remembered  that  the  pulse  at 
the  wrist  varies  very  much  in  volume  in  different  individuals,  on  account 
of  differences  in  the  size  of  the  artery,  so  that  mere  volume  has  not  so 
much  significance  at  a  first  examination.  Also,  the  radial  arteries  of 
the  two  sides  often  differ  in  size  very  materially,  so  that  one  may  serve 
to  correct  the  other.  In  any  case  in  which  the  examination  of  the  radial 
])ulse  leaves  the  condition  of  the  circulation  in  doubt,  other  arteries 
should  be  consulted  for  the  more  perfect  correction  of  the  readings. 
In  the  administration  of  anaesthetics  it  is  very  convenient  to  take  the 
pulse  from  the  temporal  artery. 

Frequency  of  the  Pul8I-:. — In  health  the  frequency  of  the  pulse 
presents  wide  variations.  Some  persons  in  seemingly  good  health  have 
habitually  a  pulse  of  100  beats  in  the  minute,  while  in  others  it  may 
fall  as  low  as  50.  These  extremes  of  variation  are,  however,  very  rare. 
The  greater  number  of  persons  will  be  found  to  have  a  pulse-rate  of 
from  60  to  85  beats  in  the  minute.  Anything  above  85  may  be 
regarded  as  an  abnormally  frequent  pulse  in  the  adult.  On  the  other 
hand,  anvthing  below  60  may  be  regarded  as  abnormally  infrequent. 
In  children  the  pulse  is  more  frequent  than  in  adults.  The  following 
statement  will  give  a  suflficientlv  clear  idea  of  this  : 

The  infant  at  birth Pulse-rate  140 

The  child  at  five  years "         J  00 

The  child  at  tert  years "  90 

The  pulse  of  children  is,  of  course,  subject  to  variations  similar  to  those 
of  the  adult.  In  women  the  pulse  is  a  little  more  frequent  than  in  men, 
the  excess  averaging  about  nine  beats  in  the  minute.  Position  also 
affects  the  pulse-rate ;  it  is  a  little  more  frequent  in  the  standing  than 
in  the  recumbent  posture.  In  sleep  the  pulse  usually  falls  about  ten 
beats  in  the  minute. 

There  are  many  causes  of  frequency  of  the  puke,  such  as  severe 
exercise,  emotional  or  mental  excitement,  hysteria,  diseases  of  the  heart, 
debility,  fever,  reflex  irritation,  etc. 

Usually,  it  is  not  difficult  to  determine  the  cause  of  frequency  of  the 
pulse.  Frequency  produced  by  violent  exercise,  emotion,  or  mental 
excitement  passes  away  very  soon  after  the  cessation  of  the  cause. 
Therefore,  examinations  made  at  intervals  will,  if  the  patient  be  kept 
under  observation,  soon  clear  up  this  point.  Nervous  patients  usually 
present  an  acceleration  of  the  pulse  when  first  approached  by  the  phy- 
sician, especially  if  he  be  a  stranger ;  and  for  this  reason  the  pulse 
should  be  again  taken  after  some  time  has  elapsed. 

In  hysteria  there  is  sometimes  a  pulse  very  frequent  and  continuous ; 
the  rate  may  be  as  high  as  150  beats  in  the  minute.  In  patients  that 
present  themselves  for  dental  operations  this  cause  of  frequency  will 


THE  PULSE.  665 

sometimes  give  rise  to  some  difficulty  in  diagnosis.  A  little  observa- 
tion of  these  cases  will,  however,  almost  always  set  the  operator  right. 
When  grave  illness  occurs  the  hysteria  usually  disappears  spontane- 
ously. 

In  fevers  the  pulse  is  generally  accelerated  in  proportion  to  the  rise 
of  the  temperature.  This  is  not  uniform,  however.  In  a  few  instances 
I  have  noted  a  very  high  temperature  associated  with  an  infrequent 
pulse,  but  this  is  evidently  rare.  From  what  has  been  said  in  regard 
to  the  variations  of  the  pulse  in  health,  it  will  be  seen  that  there  is  no 
absolute  pulse-temperature  ratio.  Any  rule  that  may  be  given  is  sub- 
ject to  considerable  variations.  In  general  it  may  be  stated  that  there 
will  be  an  increased  frequency  of  eight  beats  of  the  pulse  to  each  degree 
of  rise  in  the  temperature.  The  same  causes  accelerate  the  pulse  more 
in  children  than  in  adults,  and  the  ratio  also  varies  somewhat  in  differ- 
ent fevers.  Thus,  with  a  given  temperature  the  pulse  is  more  frequent 
in  scarlet  than  in  typhoid  fever.  A  pulse  which  has  a  greater  rapidity 
than  the  temperature  explains  indicates  debility  of  the  heart,  unless  it 
be  dependent  upon  mental  excitement,  hysteria,  or  organic  cardiac  dis- 
ease. It  may  be  stated  as  a  law  of  the  action  of  the  heart  that  what  it 
lacks  in  power  it  endeavors  to  make  up  in  frequency.  A  jjulse  that 
day  by  day  becomes  more  frequent,  the  temperature  remaining  the  same, 
shows  progressive  prostration.  A  pulse  of  130  occurring  in  fever  is 
serious,  a  pulse  of  140  to  150  shows  great  danger,  and  a  patient  with  a 
pulse-rate  of  160  will  almost  certainly  die. 

Inflammations  of  the  heart  and  its  membranes  are  exceptions  to  this 
rule,  for  in  these  a  very  frequent  pulse  is  of  less  serious  import.  In  such 
cases  we  may  find  a  pretty  severe  pericarditis  with  extensive  eifusion 
into  the  pericardial  sac,  with  perhaps  but  little  rise  of  the  temper- 
ature, and  a  pulse  of  140  to  150  per  minute,  and  very  bad  in  quality,, 
without  very  great  danger  to  life.  Here  the  state  of  the  pulse  is  the 
direct  result  of  the  condition  of  the  heart  itself,  and  does  not  reflect  the 
condition  of  the  vital  powers,  as  it  does  when  it  is  secondarih^  aifected 
through  the  general  prostration  of  the  nervous  system.  In  these  forms 
of  heart  lesion,  especially  in  endocarditis,  the  muscular  substance  of  the 
organ  is  also  inflamed,  which  disturbs  its  action,  or  its  motions  may  be 
interfered  with  by  the  exuded  fluid  in  the  cavity  of  the  pericardium. 
With  this  embarrassment  the  circulation  becomes  very  poor,  and  from 
the  want  of  oxygenation  of  the  blood  the  patient  may  show  consider- 
able blueness  of  the  skin  ;  the  breathing  too  may  be  proportionately 
hurried ;  yet  clinical  observation  shows  that  very  few  die  directly  from 
this  cause,  it  being  rather  a  remote  cause  of  death  through  injury  to 
the  valves  of  the  heart  or  through  a  resultant  fatty  degeneration..  Of 
valvular  lesions  I  will  speak  again. 

Qualities  of  the  Pulse. — Under  this  head  it  is  my  purpose' to 
inquire  especially  into  the  character  of  the  individual  pulsations.  These 
depend  upon  the  condition  of  the  heart  and  arteries  jointly.  If  the  heart 
is  weak,  it  cannot  give  strong  pulsations,  and,  other  things  being  equal, 
the  pulsations  will  be  lacking  in  volume  and  tone.  The  condition  of 
the  arteries,  however,  may  modify  this  in  several  ways,  so  that  various 
characters  will  be  produced.     As  has  been  said,  the  calibres  of  the  arte- 


(?66  GENERAL  PATHOLOGY. 

ries  are  directly  affected  by  the  vaso-motor  system  of  nerves.  This  pro- 
duces what  is  known  as  variations  in  "arterial  tension."  In  the  condi- 
tion of  health  the  blood  may  be  said  to  be  grasped  by  the  muscular  coats 
of  the  arteries  with  a  certain  degree  of  force.  Therefore  the  blood  is 
constantly  subjected  to  a  considerable  degree  of  pressure,  which  is 
plainly  indicated  by  the  "  spirting  "  Mhen  an  artery  is  severed.  Bleed- 
ing lessens  the  volume  of  the  blood  directly,  yet  it  requires  a  consider- 
able reduction  in  the  volume  to  very  materially  reduce  the  arterial  pres- 
sure. So  too,  conversely,  the  volume  of  the  blood  may  be  doubled  by 
the  process  of  transfusion  before  the  arterial  tension  is  materially 
increased.  This  equality  of  the  arterial  tension  is  maintained  directly 
by  the  nervous  system  acting  upon  the  muscular  coats  of  the  arteries, 
through  which  these  vessels  are  contracted  or  expanded  to  accommodate 
the  changing  volume  of  the  blood.  This  tension  in  disease  is  subject  to 
very  wide  alterations,  and,  in  the  main,  these  alterations  reflect  the  con- 
dition of  the  nervous  system.  It  is  this  coincidence  of  conditions  that 
gives  to  the  qualities  of  the  pulse  their  importance.  In  disease  strength 
of  the  heart  and  tension  of  the  arterial  system  do  not  always  coincide. 
The  source  of  their  enervation  is  different.  The  heart  receives  its 
supply  from  the  great  sympathetic  and  from  ganglia  situated  within 
itself,  but  principally  from  the  pneumogastric,  while  the  vaso-motor 
nerves  seem  to  arise  from  the  spinal  cord.  Hence,  while  in  many 
respects  the  condition  of  the  heart  and  arteries  may  coincide,  they  do 
not  do  so  of  necessity. 

^1  compressible  jmlse  is  produced  by  relaxation  of  arterial  tension. 
This  condition  permits  the  blood  to  flow  through  the  arterial  system 
and  into  the  capillaries  with  less  restraint,  and,  if  the  heart  is  strong, 
produces  a  large  soft  pulse  that  may  be  readily  compressed.  In  this  con- 
dition of  the  arteries  a  weak  heart  will  produce  a  correspondingly  small 
and  quick  pulse.  The  compressibility  of  the  pulse  is  ascertained  by 
placing  t^vo  or  more  fingers  on  the  artery  and  exerting  more  or  less 
firm  pressure  until  the  pulsation  is  no  longer  felt  under  the  finger  near- 
est the  distal  (or  terminal)  end  of  the  vessel.  The  degree  of  pres- 
sure required  to  do  this  determines  the  compressibility.  If  this  is  not 
accomplished  with  a  reasonable  pressure,  the  pulse  is  said  to  be  incom- 
pressible and  marks  a  strong  heart  with  a  fairly  high  arterial  tension, 
and  indicates  a  good  condition  of  the  system.  If  this  incompressibility 
is  extreme,  as  is  often  the  case  in  the  beginning  of  fevers,  sedatives  are 
called  for,  and  especially  so  if  the  pulse  is  very  frequent.  In  the  reverse 
case,  if  the  pulse  be  easily  compressible,  quick,  and  very  frequent,  it 
marks  a  condition  of  general  prostration,  and  calls  for  stinmlants,  espe- 
cially cardiac  stimulants,  such  as  digitalis.  It  will  be  noted  here  that 
these  differences  are  based  on  the  qualities  of  the  pulse  independent  of 
its  frequency.  Yet  it  is  a  clinical  fact  that  a  full  strong  pulse  never 
becomes  so  frequent  as  the  small  quick  pulse,  which  is  the  indication  of 
dangerous  prostration. 

A  relaxed  condition  of  the  arterioles  with  a  heart  of  only  moderate 
strength  will  give  a  full  round  pulse  that,  if  not  closely  observed,  might 
readily  be  mistaken  for  a  strong  heart-beat.  The  ease  with  wliich  it 
may  be  compressed  ^ill  at  once  correct  the  error  and  set  the  physician 


THE  PULSE.  667 

right  as  to  the  actual  condition  of  lii.s  patient.  In  the  rehixed  condition 
of  the  arteries  their  walls  present  but  little  resistance  to  expansion  by 
the  blood-wave,  and  a  \'ery  feeble  contraction  of  the  heart  is  sufficient 
to  produce  a  tolerable  dilatation  of  the  artery,  and  the  blood  passes  into 
the  capillaries — which  are  probably  also  dilated — so  easily  that  it  pro- 
duces very  little  resistance  to  compression.  On  the  other  hand,  in  high 
tension  of  the  arterial  system  the  artery  is  sometimes  found  to  be  so 
tense  and  hard  that  it  is  easily  felt  by  the  finger  even  in  diastole  of  the 
heart,  and  may  be  traced  for  a  considerable  distance  up  the  arm,  feeling 
much  like  another  tendon  Ivina;  amona;  the  tendons  of  the  wrist.  In 
such  cases,  even  thougli  the  heart  may  have  a  fair  degree  of  strength,  the 
pulse-beat  is  small,  hard,  and  long — small,  because  the  heart,  though  of 
good  strength,  is  unable  to  produce  much  expansion  of  the  tense,  hard 
walls  of  the  artery ;  it  is  hard  for  the  same  reason ;  and  it  is  long  be- 
cause the  blood  cannot  pass  otherwise  than  slowly  into  the  capillaries 
on  account  of  the  diminished  calibre  of  the  arterioles.  This  marks  a 
condition  of  nervous  irritation,  and  usually,  when  it  is  extreme,  an  exalt- 
ation of  sensibility.  When  these  conditions  are  present  in  connection 
with  a  w^eakened  condition  of  the  heart,  we  will  find  a  small,  frecpient, 
and  shot-like  pulse,  and  as  the  decline  of  the  patient  progresses  and 
the  tension  begins  to  give  way  the  pulse  becomes  quick  and  thready. 

The  sphygmograph  is  an  instrument  for  recording  the  pulse-waves, 
and  much  aid  is  obtained  from  it  in  the  study  of  the  varieties  presented 
by  them.  This  instrument  will,  however,  only  give  us  the  form  of 
the  pulse-wave.  It  is  not  to  be  depended  upon  for  information  as  to 
the  strength  of  the  pulsations,  for  this  is  not  always  shown  by  the 
height  of  the  pulse- wave,  as  has  already  been  sufficiently  indicated ; 
and  even  if  this  were  not  the  case,  it  is  so  difficult  to  apply  the  instru- 
ment to  the  artery  with  equal  regularity  that  there  is  much  uncertainty 
in  its  use.  The  pictures  of  the  jiulse  made  by  this  instrument  are,  hoM'- 
ever,  of  the  greatest  benefit  in  gaining  an  accurate  knowledge  of  the  con- 
ditions of  the  circulation  ;  they  point  out  at  once  the  differences  between 
high  and  low  arterial  tension,  and  the  study  of  them  leads  the  observer 
to  a  better  judgment  of  these  conditions  by  the  use  of  the  finger.  For 
this  reason  I  introduce  some  tracings  representing  some  of  the  prin- 
cipal varieties  of  pulsations.     (See  Fig.  370.) 

In  most  diseases,  both  acute  and  chronic,  failure  of  the  circulation  is 
very  generally  accompanied  by  evident  signs  of  general  prostration  and 
failure  of  the  powers  of  life.  Yet  by  watchfulness  this  may  be  first 
discovered  in  the  pulse ;  and  it  is  not  infrequently  the  case  that  this 
sign  is  present  for  some  time  before  others  manifest  themselves.  A 
patient  with  fever  may  not  show  any  special  evidences  of  weakness ; 
the  temperature  may  not  be  very  high  ;  he  may  take  food  fairly  Avell ; 
turn  in  bed  with  seeming  ease,  and  the  voice  may  be  strong ;  but  if  the 
pulse  is  frequent  and  easily  compressible,  the  patient  is  liable  to  sink  at 
any  time,  and,  in  fact,  is  in  a  dangerous  condition.  It  must  always  be 
remembered  that  there  are  occasional  individual  peculiarities  which 
render  the  pulse  especially  sensitive,  so  that  a  little  fever  may  accelerate 
it  greatly  without  indicating  danger.  Such  peculiarities  can  be  learned 
only  by  acquaintance  with  the  individual  patients. 


668 


GENERAL  PATHOLOGY. 


The  following  conditions  nsually  give  rise  to  high  arterial  tension : 
Affections  of  the  nervous  system ;  the  rigor  of  fevers ;  Bright's  disease 
of  the  kidneys  ;  lead-poisoning  ;  gout ;  degeneration  of  the  vessels. 

It  may  be  useful  to  add  here  some  account  of  the  changes  that  may 
be  expected  in  the  pulse  during  the  progress  of  an  ordinary  acute  ill- 


FiG.  370. 


(p)  Picrotous. 
Sphygmographic  Tracings  illustrating  Different  Characters  of  the  Pulse. 

ness.  These  present,  of  course,  great  variations  in  different  cases,  yet 
there  are  certain  changes  that  follow  in  succession  so  often  that  they 
may  be  said  to  form  a  sort  of  general  rule.  In  case  a  person  of  robust 
constitution  be  attacked  "svith  acute  fever,  the  pulse  will  differ  in  the 
separate  stages  of  the  progress  of  the  affection.  During  the  chill  the 
arteries  contract — /.  c.  high  arterial  tension  occurs — and  the  pulse  is 
frequent,  small,  hard,  long,  and  incompressible  (Fig.  370,  d).  During 
the  continuance  of  this  condition  the  temperature  of  the  patient  rises 
rapidly.  With  the  disappearance  of  the  chill  it  will  be  found  that  the 
pulse  has  changed  in  character  in  one  particular :  the  arterial  tension 
has  relaxed.  The  pulse  now  becomes  large,  and  is  much  softer,  but  it 
is  still  strong  and  incompressible,  for  the  heart  is  yet  vigorous,  and  is 
perhaps  ex<'ited  to  unusual  activity,  giving  a  "  full  bounding  pulse" 
(Fig.  370, />).  This  is  a  condition  in  Avhicli  sedatives  are  of  advantage, 
especially  if  this  character  of  pulse  be  very  marked.    As  the  fever  con- 


THE  PULSE.  669 

timies  for  days,  and  perhaps  for  weeks,  oscillations  "will  occur  in  the 
qualities  of  the  pulse,  especially  if  there  is  a  disposition  to  recurring 
chill.  But  without  this  there  will  be  oscillations  both  in  the  streng-th 
of  the  contractions  of  the  heart  and  the  tension  of  the  arteries ;  but  in 
the  long'  run  both  these  will  be  found  to  be  gradually  losing  ground  ; 
the  pulse  becomes  both  smaller  and  softer,  and  the  individual  beats  are 
comparatively  short  (Fig.  370,  c).  Gradually  the  pulse  becomes  very 
compressible,  indicating  extreme  exhaustion  of  the  nervous  mechanism. 

In  case  there  is  a  chsappearance  of  the  fever,  an  enlargement  of  the 
pulse-beat  indicates  safety  for  the  patient ;  provided  always  that  this 
enlargement  is  from  increased  strength  of  the  heart,  and  not  from 
increased  relaxation  of  the  arteries.  This  is  determined  by  the  com- 
parative compressibility  of  the  pulse.  Increased  arterial  relaxation  is 
usual  at  the  time  of  the  subsidence  of  a  protracted  fever,  but  if  the  pulse 
shows  a  fair  increase  in  volume  at  the  same  time,  all  is  well.  If,  how- 
ever, the  volume  of  the  pulse  fails  to  increase  with  the  arterial  relaxation, 
fatal  prostration  is  indicated  and  arterial  stimulants  are  urgently  called 
for.  If  the  case  approaches  a  fatal  termination,  the  pulse  becomes  very 
small,  quick,  frequent,  and  generally  thready.  In  case  of  recovery  the 
pulse  gradually  reassumes  its  former  vigor  with  the  returning  strength 
of  the  patient. 

Irregularities  of  the  Pulse. — The  normal  pulse  is  perfectly 
regular  in  its  rhythm ;  that  is  to  say,  the  contractions  of  the  heart  fol- 
low each  other  in  very  exact  time,  one  beat  occupying  just  as  much 
time  in  its  performance  as  another.  In  disease  this  regular  rhythm  is 
sometimes  disturbed,  in  such  a  way  that  some  contractions  of  the  heart 
occupy  more  time  in  their  performance  than  others,  so  that  a  long  pul- 
sation may  be  followed  by  a  short  one.  In  this  way  the  normal  rhythm 
is  lost  and  the  beating  of  the  heart  becomes  irregular.  In  all  such  cases 
the  force  of  the  heart-beats  is  as  irregular  as  the  time.  A  strong  pul- 
sation will  follow  a  weak  one.  These  variations  from  the  normal  are 
known  as  the  Irregular  puhe  (Fig.  370,/).  This  must  be  sharply  dis- 
tinguished from  the  intermittent  pulse.  In  this  the  regularity  of  the 
heart-beat  is  maintained,  but  occasionally  a  beat  fails.  The  irregular 
pulse  is  of  far  more  significance  than  the  intermittent.  It  is  most  fre- 
quently seen  associated  with  disease  of  the  mitral  valve,  though  it  occurs 
sometimes  in  great  prostration  of  the  heart  in  the  later  stages  of  fevers 
that  terminate  fatally.  This  pulse  is  said  to  be  diagnostic  of  mitral 
disease,  but  it  must  be  remembered  that  it  is  not  always  present  in  this 
aifection,  there  being  many  cases  of  extensive  mitral  lesion  accompanied 
with  a  perfectly  regular  pulse ;  yet  when  irregularity  occurs  without 
other  symptoms  being  present  to  account  for  it,  this  disorder  is  at  least 
suggested.  Irregularity  is  also  frequently  present  in  fatty  degeneration 
of  the  heart.  This  pulse  is  occasionally  seen,  too,  in  connection  with 
disorders  of  the  nervous  system,  and  is  often  a  valuable  diagnostic  sign 
in  meningitis,  both  in  the  acute  and  tubercular  forms.  Except  in 
aifections  of  the  membranes  of  the  brain,  an  irregular  pulse  is  very 
rare  in  children,  even  in  the  same  disorders  in  Avhich  it  is  seen  in 
adults.  Irregularity  is  usually  cured,  or  at  least  greatly  benefited,  by 
the  use  of  heart-stimulants. 


670  GENERAL  PATHOLOGY. 

DiCROTiSM. — Dierotism  results  from  diminished  arterial  tension,  and 
is  the  exaggeration  of  the  normal  impulse  or  shock  seemingly  given  to 
the  blood-wave  by  the  closure  of  the  aortic  valves.  Vie\ving  the  heart 
as  a  pump,  and  following  its  motions,  we  will  easily  gain  an  under- 
standing of  this  secondary  Avave  which  the  sphygmograph  shows  us  is 
present  in  all  forms  of  the  pulse,  and  which  may  be  seen  in  all  the 
charts  on  page  668.  When  the  ventricle  is  filled  the  heart  contracts 
forcibly  and  the  blood  is  driven  into  the  aorta.  Then  there  comes  the 
expansion  of  the  ventricle  from  which  the  bl(.)od  has  just  been  ex])elled, 
and  the  tend<?ncy  is  for  the  blood  to  return  into  the  heart.  As  a  matter 
of  fact,  a  portion  of  the  blood  now  contained  in  the  elastic  artery  does, 
with  the  cessation  of  the  impulse,  return  toward  the  heart ;  and  in  this 
act  the  aortic  valves  are  caught  and  forcibly  closed,  causing  a  sudden 
arrest  of  the  returning  volume  of  blood  at  a  time  when  the  artery  is  in 
active  contraction  upon  it.  These  two  forces,  acting  together  at  a  time 
when  there  is  a  marked  relaxation  of  the  arterial  system,  cause  a  second 
expansion  of  the  principal  blood-wave,  which  necessarily  occurs  during 
its  subsidence,  as  is  seen  in  the  charts.  It  is  probably  only  in  great 
arterial  relaxation  that  marked  dierotism  can  occur,  and  it  is  usually 
associated  with  weakness  of  the  heart  as  well.  In  some  instances  this 
second  l)lood-wave  is  almost  as  high  as  that  of  the  true  pulsation,  and 
may  be  plainly  recognized  with  the  finger,  so  that  one  not  accustomed 
to  pulse-examinations  might  mistake  its  significance  and  count  the  beats 
as  double  their  real  frequency.  This  form  of  pulse,  however,  is  very 
rare,  although  it  is  occasionally  met  with  in  fevers. 

Intermittent  Pulse. — AVhen  the  rhythm  of  the  pulse  is  regular, 
with  the  exception  that  an  occasional  beat  fails,  it  is  said  to  be  an  infer- 
mittent  pulse.  The  omissions  of  the  beat  may  take  ])lace  frequently  or  a 
considerable  interval  may  occur  between  them  (Fig.  370,  e).  They  may 
happen  regularly  after  every  second  or  third  beat,  or  even  after  longer 
periods  ;  sometimes  they  are  entirely  irregular  in  their  occurrence. 
Intermittence  differs  entirely  from  irregularity  of  ])ulse,  and  is  of  much 
less  serious  import.  In  some  persons  intermittence  of  the  pulse  is  a 
constitutional  peculiarity,  lifelong  in  duration  and  unattended  by  evil 
consequences ;  more  frequently  it  does  not  a]>pear  until  midtlle  life ;  in 
other  cases  its  occurrence  is  only  occasional,  the  attacks  being  induced 
by  the  use  of  certain  articles  of  food  or  by  certain  extraneous  conditions. 
Many  j^ersons  who  have  a  pulse  occasionally  intermittent  are  made  very 
imcomfortable  by  it,  but  perhaps  the  greater  number  are  unconscious  of 
the  condition.  It  seems  in  no  way  to  endanger  life,  and  the  sphygmo- 
gra])h  shows  that  in  many  cases  the  ap])arently  omitted  beat  is  really  a 
very  feeble  ])ulsation  not  sufficiently  pronounced  to  be  felt  by  the  finger. 

The  Puese  in  I^esions  of  the  Heart. — The  importance  which  the 
subject  of  lesions  of  the  heart  has  for  the  specialist,  and  jiarticidarly  for 
those  who  administer  anaesthetics,  is  such  that  I  do  not  like  to  ])ass  the 
sul)ject  without  notice,  although  anything  like  a  sufficient  treatment  of  the 
variations  of  the  pulse  in  these  conditions  would  be  beyond  the  scope  of 
this  article.  There  is  not  much  doubt  that  the  failure  on  the  part  of 
dentists  to  detect  these  conditions  contributes  to  the  number  of  fatalities 
that  are  continually  occurring  in  that  special  field  of  practice.     A  close 


VARIATIOyS  IX  THE  BLOOD,   AND  IN  ITS  DISTRIBUTION.      671 

study  of  the  pulse  is  one  of  the  best  safeguards  against  these  calamitous 
results.  But  a  short  time  since  a  person  presented  herself  to  me  asking 
that  an  ansesthetic  be  administered  for  the  extraction  of  a  tooth.  Exam- 
ination of  the  pulse  at  once  revealed  insufficiency  of  the  aortic  valves, 
and  on  inquiry  it  was  learned  that  the  patient  had  gone  outside  of  her 
personal  acquaintance  for  the  express  purpose  of  obtaining  an  anaesthetic 
which  had  been  denied  her  at  home.  A  few  weeks  later  she  suddenly- 
died. 

In  aortic  regurgitation  from  any  considerable  insufficiency  of  the 
valves  the  pulse  is  quite  characteristic.  The  blood  flows  back  into  the 
heart  during  diastole,  instead  of  being  caught  and  held  by  the  aortic 
valves,  and  the  arteries  become  quickly  collapsed  or  much  more  empty 
of  blood  than  in  other  conditions.  This  gives  a  pulse  of  great  arterial 
relaxation  with  a  marked  exaggeration  in  certain  directions.  The  rise 
of  the  blood-wave  may  be  the  same  as  in  the  ordinary  pulse,  but  when 
the  height  is  reached  it  falls  suddenly,  almost  as  if  the  artery  had  col- 
lapsed. This  characteristic  presents  various  degrees  as  the  aortic  insuf- 
ficiency is  more  or  less  extensive.  In  extreme  cases  the  pulse  seems  to 
give  the  fingers  a  quick,  sharp,  shot-like  blow,  and  disappears  as  sud- 
denly as  it  came.  These  phenomena  are  intensified  by  raising  the  w'rist 
high  above  the  patient's  head,  so  that  gravitation  will  assist  in  empty- 
ing the  artery. 

In  aoitic  regurgitation  the  pulse  is  often  visible  in  certain  of  the 
superficial  arteries,  but  this  also  occurs  in  arterial  degeneration  and 
in  very  high  arterial  tension,  especially  if  persistent  tor  some  time. 
Markedly  visible  pulsations  in  the  neck  should  always  lead  to  further 
examination  for  the  cause.  In  high  tension  the  artery  remains  com- 
paratively hard  and  firm  during  diastole  of  the  heart,  while  in  aortic 
regurgitation  it  collapses  suddenly.  In  the  former  condition  the  pulse- 
beat  is  long,  and  in  the  latter  it  is  short  or  quick.  In  degeneration  of 
the  arteries  the  vessels  become  tortuous,  and  remain  distinctly  hard  after 
all  the  blood  has  been  pressed  out  of  them ;  and  if  degeneration  is 
extensive,  calcareous  plates  are  frequently  found  in  the  arterial  walls. 

The  pulse-beats  in  aortic  obstrucfion,  so  long  as  the  heart  is  otherwise 
perfect,  are  long,  small,  and  infrequent.  The  reasons  for  this  are 
explained  by  the  fact  of  the  increased  difficulty  of  the  transit  of  the 
blood  through  the  narrowed  orifice.  This  makes  the  rise  of  the  blood- 
wave  peculiarly  slow.  Hence  the  peculiar  characters  of  the  pulse.  If 
this  condition  is  accompanied  by  other  lesions,  the  pulse  wall,  of  course, 
be  modified. 

Mitral  disease  has  already  been  noticed. 

Variations  in  the  Blood,  and  in  its  Distribution. 

Before  entering  upon  the  study  of  the  variations  that  occur  in  the 
amount,  quality,  and  distribution  of  the  blood,  it  seems  well  to  refresh 
the  mind  of  the  reader  as  to  certain  points  in  the  physiology  of  the  cir- 
culation. While  studying  the  pulse  we  learned  that  the  arterial  system 
is  under  the  control  of  the  vaso-motor  system  of  nerves  in  such  a  way 
as  to  give  high  and  low  arterial  tension.    This  system  of  nerves  is  capa- 


G72  GENERAL  PATHOLOGY. 

bie  of  changing  the  condition  of  the  circulation  of  the  blood  in  various 
other  ways,  and  of  accommodating  a  greater  or  less  amount  of  blood  in 
the  vessels,  either  as  a  whole  or  in  individual  parts  of  the  circulatory 
system ;  that  is  to  say,  the  vaso-motor  system  does  not  necessarily  act 
as  a  unit,  operating  at  once  on  the  whole  vascular  system,  expanding 
or  dilating  it  as  a  whole,  but  it  may  and  does  act  locally  as  well,  pro- 
ducing variations  in  the  supply  of  blood  to  the  different  parts  of  the 
organism.  Many  of  these  local  variations  are  of  a  purely  physiological 
nature,  such  as  occur  in  the  glands  during  their  quiescent  and  their 
active  states.  As  an  instance  of  this  action  I  may  refer  to  the  well- 
demonstrated  fact  that  the  supply  of  blood  to  the  salivary  glands  may 
be  greatly  increased,  even  by  the  sight  of  desirable  food  :  the  glands 
become  turgid,  and  the  outpouring  of  the  saliva  is  at  once  begun  or 
greatly  increased.  Every  dentist  is  also  well  acquainted  with  the 
marked  excitement  of  the  salivary  glands  during  the  performance  of 
painful  operations  within  the  mouth.  These  are  examples  of  reflex 
actions  of  the  nervous  system  by  which  impressions  received  by  sensory 
nerves  produce  local  variations  in  the  circulation  by  being  reflected 
through  the  vaso-motors,  and  may  be  regarded  as  the  type  of  the  reflex 
phenomena  of  the  vaso-motor  system  wherever  they  occur.  Dilatations 
and  contractions  of  the  vascular  system  occur  in  response  to  irritation  of,  or 
impressions  made  upon,  sensory  nerves.  The  impression  received  by  the 
sensory  nerve  passes  along  the  course  of  the  afferent  nerve  to  the  cen- 
tral ganglion,  and  from  thence  is  reflected  back  through  the  efferent 
nerve  as  a  motor  impulse.  This  statement  holds  good  in  both  normal 
and  abnormal  conditions.  In  the  mechanism  of  the  nutritive  functions 
impressions  are  probably  received  by  nerves  not  sensory  in  the  ordinary 
sense  or  in  the  sense  that  the  impresssions  they  convey  are  perceived 
by  the  mind  in  any  way.  The  result,  however,  is  precisely  the  same  in 
tlie  one  case  as  in  the  other.  My  meaning  here  may  be  illustrated  by 
the  results  of  the  ligation  of  the  arteries.  When  an  artery  conveying 
the  blood  to  a  certain  part  is  ligated  the  immediate  result  is  to  lessen 
the  blood-supply  to  that  part,  even  though  it  is  supplied  by  several 
other  arteries.  Within  a  very  short  time  there  is  a  dilatation  of  the 
other  vessels  leading  to  the  part,  so  that  the  blood-supply  becomes 
normal.  This  will  always  occur  if  the  necessary  quantity  of  blood 
can  be  supplied  by  a  reasonable  expansion  of  these  vessels.  How  does 
this  occur?  It  is  not  from  the  injury  sustained  and  by  reflection  through 
the  sensory  nerves,  for  an  injury  otherwise  similar,  but  not  diminishing 
the  blood-supply,  would  not  produce  a  similar  effect.  Then  the  effect 
must  be  produced  by  other  nerves  that  take  cognizance  of  the  nutritive 
])rocesses  and  reflect  the  needs  of  the  tissues  for  the  nutritive  fluid.  In 
this  manner  the  blood-supply  to  the  several  parts  of  tlie  body  is  regu- 
lated in  accordance  with  the  needs  of  each,  and  is  continually  under- 
going change,  especially  in  the  glandular  organs  that  are  periodical 
in  their  activity.  These  changes  may  be  seen  also  in  any  of  the  tis- 
sues that  may  be  subjected  to  microscojjic  examination  in  tlie  living 
state.  The  small  arteries  do  not  remain  uniformly  of  the  same  diam- 
eter, but  are  seen  to  contract  and  expand  more  or  less  continuously,  now 
admitting  more,  now  less,  blood  to  the  part.     It  would  seem,  then,  that 


VARIATIONS  IN  THE  BLOOD,   AND  IN  ITS  DISTRIBUTION.      673 

the  needs  of  each  individual  tissue  are  thus  reflected  through  the  vaso- 
motor nerves  in  such  a  manner  that  tliere  is  a  corresponding  movement 
of  the  muscular  fibres  of  the  arteries  regulating  the  blood-supply  in 
every  part  of  the  body,  and  that  the  nerves  thus  acting  play  the  part 
of  sensory  nerves  in  the  reflex  phenomena  in  the  fact  that  they  convey 
afferent  impulses  that  are  in  turn  converted  into  efferent  motor  impulses. 
This  is  in  accord  with  the  general  physiojogical  law  that  sensory  inipres- 
sions  or  impulses  travel  from  the  distal  to  the  central  (afferent),  and  all 
motor  impulses  travel  from  the  central  to  the  distal  (efferent).  In  the 
normal  healthy  organism  the  harmony  of  these  relations  is  preserved. 
In  disease  this  harmony  is  often  seriously  disturbed,  and  it  is  my  pur- 
pose to  notice  some  of  these  disturbances  presently. 

Pursuing  the  study  of  this  system  of  nerves,  it  is  definitely  ascertained 
that  paralysis  of  the  vaso-motor  nerves  produces  arterial  relaxation. 
If  the  nerves  distributed  to  any  part  are  severed — as,  for  instance, 
those  supplying  the  hinder  leg  of  an  animal — all  of  the  arteries  of 
that  member  dilate  and  the  leg  becomes  surcharged  with  blood.  This 
seems  to  show  that  it  is  the  office  of  this  system  of  nerves  to  hold,  by 
means  of  the  circular  muscular  fibres  of  the  blood-vessels,  a  certain 
grasp  or  pressure  on  the  blood  they  contain,  and  that  the  maintenance 
of  this  pressure — or  tone,  as  it  is  sometimes  called — is  necessary  to  the 
proper  performance  of  the  functions  of  the  circulation.  The  greatest 
proportionate  amount  of  muscular  fibre  is  in  the  smallest  arteries,  and 
it  is  these  that  undergo  the  greatest  change  in  calibre.  In  this  way  the 
blood  is  not  only  more  firmly  grasped,  but  its  outflow  from  the  arteries 
into  the  capillaries  is  regulated. 

Experiment  shows  that  after  the  vaso-motor  nerves  of  a  part  have 
been  severed  and  the  vessels  have  lost  their  tone,  this  will  in  time  be 
recovered,  the  nerves  in  the  mean  time  remaining  asunder.  From, 
this  experimental  fact  it  is  inferred  that  there  are  ganglia  in  the  walls, 
of  the  blood-vessels  themselves  that  are  capable  of  maintaining  the  tone 
of  the  circulation  in  the  absence  of  the  central  force  or  influence,  but 
that  under  all  ordinary  conditions  these  minor  ganglia  are  dominated! 
and  controlled  by  the  one  central  power  which  unifies  the  whole  system, 
and  renders  it  complete.  This  is,  in  brief,  a  recital  of  the  mechanism 
of  the  vaso-motor  influence,  and  its  office  in  the  control  of  the  circula- 
tion as  at  present  understood.  A  more  detailed  discussion  of  it,  while 
very  desirable,  is  beyond  the  limit  of  this  article. 

Plethora. — The  term  plethora  is  used  to  designate  a  condition  in 
which  the  total  quantity  of  the  blood  is  too  great.  The  term  general 
hypercemia  is  also  used  in  the  same  sense.  This  condition  will  occur 
when  from  any  cause  the  blood-forming  organs  are  unduly  active,  and 
is  indicated  by  habitual  over-fulness  of  the  capillaries  as  shown  in 
undue  redness  of  the  skin  and  turgescence  of  the  venous  circulation, 
especially  that  of  the  abdominal  region  known  as  the  portal  svstem. 
AVe  may  also  have  another  condition  closely  akin  to  this,  in  which  the 
bulk  of  the  blood  is  not  notably  increased,  but  in  which  the  propor- 
tion of  the  red  corpuscles  is  greater  than  normal.  The  fluid  portions 
of  the  blood  are  probably  subject  to  greater  fluctuations  than  are  its 
solid  constituents ;  and  within  reasonable  bounds  this  is  of  compara- 

VoL.  I.— 43 


674  .  GENERAL  PATHOLOGY. 

lively  little  importance.  The  energies  of  the  body,  and  especially  its 
nutritive  powers,  upon  which  these  energies  depend,  are  closely  con- 
nected with  the  corpuscular  elements  of  the  blood,  especially  the  red 
corpuscles.  Their  importance  is  shown  by  the  fact  that  animals  bled 
nearly  to  death  may  be  resuscitated  by  the  injection  of  these  corpuscles 
in  serum.  From  what  is  known  of  their  physiological  relations,  it 
might  be  inferred  that  the  eifect  of  an  excessive  quantity  of  blood  with 
the  full  proportion  of  red  corpuscles,  or  of  a  superabundance  of  the  red 
corpuscles  without  an  excess  of  fluid,  would  produce  over-activity  of  the 
circulation  and  a  disposition  to  undue  excitation  of  the  organs  of  the 
body.  Such  effects,  in  fact,  constitute  the  phenomena  of  the  condition  of 
plethora.  The  power  of  the  heart's  action  is  increased ;  sensibility  and 
muscular  irritability  are  augmented  ;  some  rise  in  the  temperature  may 
be  noted ;  the  brain  is  more  prone  to  excitement ;  and  the  whole  body 
takes  on  a  full  and  rotund  outline.  Pain  in  the  head  is  liable  to  be 
produced  by  excitement  or  by  stimulants,  on  account  of  the  unusual 
power  of  the  circulation ;  and  this  condition  is  thought  to  involve  a 
liability  to  cerebral  congestion.  Febrile  attacks  are  rendered  more 
intense,  and  acute  inflammations  are  more  readily  excited.  It  is 
important  to  discriminate  between  plethora  and  other  morbid  con- 
ditions. In  pregnancy  the  fluid  elements  of  the  blood  are  often  nuich 
increased  without  a  true  plethora.  In  this  case  there  is  not  an  abnor- 
mal increase  of  the  red  blood-globules,  and  other  signs  of  the  state  of 
plethora  are  wanting.  Abnormal  fulness  of  the  blood-vessels  from 
some  impediment  to  the  returning  veins  might  sometimes  be  mistaken 
for  this  condition. 

A  tendency  to  plethora  may  be  inherited,  or  it  may  be  acquired  by 
over-feeding  on  rich  foods,  wines,  etc.,  connected  with  diminished 
expenditure  of  blood-constituents  in  the  nutrition  of  the  body.  This 
is  directly  favored  by  sedentary  habits,  the  digestive  and  assimilative 
functions  remaining  active. 

Experiments  in  the  transfusion  of  blood  in  animals  give  us  some  idea 
of  the  extent  to  which  the  volume  of  the  blood  maybe  increased.  AVorm 
Mueller  injected  the  defibrinated  blood  of  dogs  into  other  dogs,  and  by 
careful  experiment  found  that  the  normal  amount  of  blood  might  be 
increased  one-half  or  three- fourths  without  materially  endangering  the 
health  of  the  animal,  and  double  the  normal  quantity  would  be  borne 
without  much  apparent  inconvenience.  If,  however,  the  quantity  was 
increased  much  beyond  this,  perturbations  of  the  circulation  occurred, 
and  the  animal  died  within  a  day  or  two.  It  appears  from  these 
experiments  that  the  excess  of  blood  injected  is  quickly  disposed  of — 
that  within  three  or  four  days  there  is  only  an  excess  of  the  globules, 
and  at  the  end  of  two  weeks  these  also  have  disappeared.  From  the 
results  of  these  experiments  it  may  be  concluded  that  there  is  some 
mechanism  in  the  body  having  the  power  of  regulating  the  amount 
of  the  l^lood,  but  as  to  what  this  mechanism  may  be  there  is  as  yet 
no  definite  knowledge. 

Local  Hyper/E.mia,  or  Congestion. — Local  hyperfemia  consists  in 
the  presence  of  an  undue  amount  of  blood  in  a  particular  part.  Tavo  vari- 
eties, differing  in  mode  of  origin  and  in  character,  are  recognized :  these  are 


VABTATIONS  IN  THE  BLOOD,   AND  IN  ITS  DISTRIBUTION.     675 

known  as  act  ice  and  passive,  or  arterial  and  venous  hyper?emia  or  con- 
gestion. It  is  essential  that  the  distinction  between  these  forms  be  well 
understood,  for  they  arise  under  different  circumstances  and  are  of  widely 
diiferent  significance.  Local  hypersemia,  when  active,  is  dependent  on  the 
condition  of  the  arteries,  and  when  passive  on  the  condition  of  the  veins. 
In  the  active  variety  the  arterioles  of  the  affected  region  are  actively 
dilated,  admitting  to  the  part  an  unusual  amount  of  blood  ;  this  flows 
unobstructed  through  the  capillaries  to  the  veins,  and  there  is,  conse- 
quently, an  increased  amount  of  blood  passing  through  the  aifected  area, 
the  blood  being;  therefore  more  highlv  arterial  than  normal.  In  the 
passive  or  venous  variety  these  conditions  are  exactly  reversed.  There 
is  some  obstruction  to  the  passage  of  the  blood  by  the  veins  aivay  from 
the  part ;  and  the  actual  amount  of  blood  passing  through  it  is  dimin- 
ished, the  blood  itself  being  more  highly  venous  than  normal.  In 
active  hyperceniia  there  is  not  an  unusual  retention  of  the  blood  in  the 
part,  but  rather  the  reverse ;  while  in  the  passive  variety  there  is  an 
unusual  retention  of  the  blood  in  the  part.  These  are  the  essential 
points  of  diflerence  in  the  two  forms  of  hypertemia. 

Active  local  hypercemia  is  constantly  occurring  in  the  organism  as  a 
physiological  process  in  all  those  glandular  organs  that  have  normal 
periods  of  activity  and  (juiescence.  This  happens  with  most  of  the 
secretory  organs.  The  salivary  glands  are  hypersemic  while  actively 
secreting  during  the  process  of  eating.  The  glands  of  the  stomach  con- 
tain more  blood,  and  much  more  is  passing  through  their  vessels,  dur- 
ing the  process  of  digestion  than  in  the  periods  of  rest.  This  is  called 
for  by  the  increased  amount  of  work  to  be  accomplished  at  these  times, 
and  serves  as  an  illustration  of  the  perfect  and  delicate  wofking  of  the 
mechanism  of  the  nutritive  processes.  Tliis  is  not  confined  to  the  glan- 
dular structures,  but  extends  to  the  other  tissues  as  well.  A  muscle 
receives  more  blood  in  its  periods  of  active  work  than  in  its  periods  of 
rest.  Any  perversion  or  undue  and  hurtful  activity  of  any  of  these 
processes  constitutes  a  pathological  hyperaemia,  and  the  natural  inference 
would  be  that  an  organism  so  adjusted,  and  seemingly  so  liable  to  over- 
strain upon  its  individual  parts,  would  be  very  prone  to  this  kind  of 
perversion  of  functional  activity.  Clinical  experience  shows,  however, 
that  this  kind  of  difficulty  is  not  so  common  as  might  be  expected ;  yet 
its  occurrence  is  of  sufficient  frequency  to  afford  numerous  examples. 
The  pulp  of  a  tooth  in  the  normal  condition  transmits  but  one  sensa- 
tion, that  of  pain,  excited  by  heat  or  cold ;  at  each  such  excitation  there 
is  a  transient  dilatation  of  its  arterioles.  If  this  form  of  excitation 
be  frequently  repeated  for  a  considerable  period,  a  condition  of  patho- 
logical hypersemia  will  be  induced,  during  the  continuance  of  which 
the  least  possible  thermal  change  will  produce  excruciating  pain. 
This  may  be  considered  an  exaltation  of  a  perfectly  normal  function 
to  such  a  degree  that  it  becomes  a  pathological  condition.  Some- 
thing of  the  same  nature  is  seen  in  the  glandular  system.  The 
stomach  is  often  teased  into  a  state  of  physiological  hypereemia  by 
the  ingestion  of  improper  food,  and  the  brain  may  take  on  a  similar 
condition  from  repeated  mental  excitement.  These  are  types  of  hyper- 
semia  that  are  liable  to  be  followed  by  the  inflammatory  process,  and 


676  GENERAL  PATHOLOGY. 

their    further   discussion    will    be   taken    up  in   connection  with   that 
subject. 

It  is  to  direct  experimentation  through  vivisection  that  we  are  in- 
debted for  our  knowledge  of  the  phenomena  of  hypersemia  in  its  simple 
and  uncomplicated  forms,  and  indeed  for  what  knowledge  we  possess  of 
the  vaso-motor  system  of  nerves.     There  are  no  anatomical  differences 
existing  in  the  nervous  system  by  which  we  can  know  a  motor  from  a 
sensory  nerve.     By  means  of  vivisection,  then,  the  vaso-motor  nerves 
are  found  to  emanate  from  the  spinal  cord  with  the  posterior  or  sensory 
roots  of  the  spinal  nerves,  and  pass  to  the  sympathetic  system  by  way 
of  the  rami  covimunicantcs.     Ai'ter  passing  some  distance,  up  or  down 
as  the  case  may  be,  with  this  system,  they  again  join  the  spinal  nerves 
in   communicating  branches,  and  pass  to  the  extremities  in  company 
v/ith  the  motor  and  sensory  nerves  of  these  parts.     When  hyper^emia 
is  produced  directly  by  severing  the  vaso-motor  nerves,  it  presents  the 
following  phenomena :  The  parts  become  somewhat  swollen  and  red- 
dened by  the  entrance  of  a  greater  amount  of  blood  into  them,  and  at 
the  same  time  the  temperature  is  markedly  elevated.     The  elevation  of 
temperature,  however,  in  the  most  intense  hyperaemia  that  can  be  pro- 
duced never  quite  reaches  that  of  the  central  portions  of  the  body ; 
indeed,  it  may  be  accounted  for  in  all  cases  by  the  increased  amount  of 
warm  blood  passing  through  the  circulatory  apparatus.     This  process, 
when   excited   in   this  way — i  c.  by  interference  with  the  vaso-motor 
nerves — never  leads  to  inflammation.     It  seem-s  to  have  relation  solely 
to  the  state  of  the  blood-vessels,  which  are  simply  widely  dilated,  ad- 
mitting a  larger  quantity  of  blood.     If  the  induced  hypersemia  be  of 
large  extent  the  immediate  effect  is  to  reduce  the  general  blood-pressure; 
but  this  is  cjuickly  regained,  unless  there  are  other  reasons  for  depres- 
sion.    The  blood-pressure  seems  to  have  little  to  do  with  the  state  of 
hyperpemia,  for  it  is  no  greater  in  the  hypersemic  part  than  elsewhere. 
Indeed,  it  may  be  actually  less,  for  the  reason  that  the  blood  is  less 
hindered  in  its  passage  to  the  venous  system,  there  seeming  to  be  an 
expansion  of  the  capillaries  as  well.     Owing  to  the  increased  diffused 
redness  this  is  well  seen  in  any  parts  that  are  sufficiently  transparent. 
We  can  now  understand  why  we  have  a  collateral  hypersemia  after 
the    ligation    of  an   artery.     If  the  carotid  artery  be  tied,  the  corre- 
sponding vessel  of  the  opposite  side  becomes  expanded.     This  is  not  to 
be  explained  by  increase  of  the  blood-pressure  caused  by  the  stoppage 
of  the  flow  through  tlie  artery  ligated,  for  such  increase  of  pressure 
would  be  either  general  or  in  the  arteries  most  directly  connected  with 
the  ligated  branch.     This  is  not  the  case.     The  expanded  artery  is  the 
one  that  can  most  directly  su})j)ly  the  territory  deprived  of  blood  by 
the  ligation.     This  is  a  reflex  phenomenon,  taking  place  through  the 
action  of  the  vaso-motor  nerves  in  response  to  the  needs  of  certain  tis- 
sues for  blood.     This  is  the  type  of  the  reflex  phenomena  of  the  vaso- 
motor nerves  in  all  cases  of  this  character.      Increased  quantities  of 
blood  are,  through  these  reflex  actions,  called  to  special  parts  or  terri- 
tories of  the  circulation  under  a  great  variety  of  circumstances  of  which 
some  have  already  been  indicated.     If  the  hands  are  smartly  struck 
together  a  few  times,  a  reponse  in  the  form  of  increased  redness  will  be 


VARIATIONS  IN  THE  BLOOD,   AND  IN  ITS  DISTRIBUTION.     677 

received,  a  local  hyperemia  having  been  called  forth.  This  simple 
experiment  will  serve  to  illustrate  a  principle  which  seems  of  import- 
ance in  the  study  of  the  subject,  and  constitutes  the  basis  of  a  division 
of  the  local  hyperemias  into  two  classes.  It  has  already  been  suffi- 
ciently explained  that  simple  hypersemia,  or  local  dilatation  of  the  vas- 
cular svstem  throusjh  reflex  action,  never  g-ives  rise  to  inflammation.  It 
is  evident,  however,  that  in  the  experiment  just  related  a  continuance  or 
increased  severity  of  the  cause  might  beget  the  inflammatory  process. 
This  is  true  of  very  many  of  the  causes  of  local  hypersemia,  and  many 
of  them  are  actually  followed  by  inflammation ;  therefore  they  may  be 
designated  as  hypercemian  of  irritation.  In  this  case  the  inflammation 
is  not  in  consequence  of  the  hypersemia,  for  we  have  seen  that  inflam- 
mation does  not  necessarily  follow  the  most  extended  dilatation  of  the 
vessels  in  complete  paralysis  of  the  vaso-motor  nerves  :  the  inflamma- 
tion is  the  result  of  tissue  injury. 

Increase  of  blood-pressure  is  not  often  local,  and  even  if  it  were  it 
could  not  ordinarily  j)roduce  hyperemia.  The  vessels  of  the  general 
system  cannot  be  dilated  to  any  considerable  degree  by  this  cause.  In 
the  lungs,  however,  the  case  is  different.  Here  the  object  is  the  aeration 
of  the  blood,  and  the  vessels  are  so  arranged  in  the  walls  of  the  air- 
vesicles  that  the  blood  is  spread  out  in  very  thin  sheets.  These  capil- 
lary sheets  are  not  composed  of  simple  round  anastomosing  ca])illary 
twigs,  as  in  the  other  parts  of  the  body,  but  in  the  normal  condition  of 
expansion  of  the  lung  they  are  distinctly  flattened.  This  renders  them 
easily  distensible  by  increase  of  pressure.^  Therefore  we  are  liable  to 
active  congestion  of  these  organs  in  consequence  of  sudden  increase  of 
the  blood-pressure  from  any  cause. 

Passit^e  hypercemia  occurs  whenever  there  is  obstruction  to  the 
flow  of  blood  away  from  the  j)art  by  the  veins.  In  this  case  the  cap- 
illary system  of  the  region  becomes  overfilled  with  blood,  which,  on 
account  of  retention  or  unusually  slow  movement,  becomes  highly 
venous  in  character.  This  is  also  called  passive  congeMion,  venous 
hypercemia ,  or  congestion.  This  state  is  seen  in  connection  with  debil- 
ity or  enfeeblement  of  the  heart.  In  the  normal  state  of  the  circula- 
tion the  blood  is  urged  forward  with  sufficient  power  to  cause  it  to 
ascend  from  dependent  parts  against  gravity  without  perceptible  hin- 
drance ;  but  if  the  heart,  which  is  the  principal  motive-power  of  tlie 
circulation,  becomes  weakened  or  disabled  in  its  valves,  the  blood  fails 
to  return  promptly  by  the  veins,  and  stagnation  is  the  result.  The 
effect  is  the  same  if  the  veins  be  so  obstructed  that  there  is  only  a 
partial  return  of  the  blood  from  a  part,  the  circulation  being  otherwise 
good.  The  congestion,  except  in  the  lungs,  is  probably  in  no  case 
materially  increased  by  arterial  pressure,  as  was  formerly  supposed. 
TJie  dilatation  of  the  capillaries  is  a  reflex  phenomenon  occurring  in 
response  to  the  needs  of  the  tissues  for  arterial  blood.  Every  individual 
living  cell  in  the  organism  must  have  access  to  free  oxygen,  must  absorb 
oxygen  and  exhale  carbonic  acid — must  breathe  in  order  to  maintain  its 

'  See  monograph,  "The  Circulation  of  the  Blood  in  the  Air-vesicles  of  the  Lungs," 
bv  G.  V.  Black,  D.  D.  S.,  St.  Louis  Med.  and  Surg.  Journal,  and  3Iissouri  Dental  Journal^ 
1878. 


678  GENERAL  PATHOLOGY. 

vitality.  This  is  just  as  true  of  the  individual  elements  of  the  organ- 
ism as  of  the  organism  as  a  whole.  We  have  already  seen  that  it  is  the 
office  of  the  vaso-motor  system  of  nerves  to  regulate  the  supply  of  blood 
to  the  individual  parts  of  the  organism,  and  with  this,  of  course,  the 
supply  of  oxygen  which  the  blood  conveys.  The  dilatation  of  the 
vessels  is,  under  these  circumstances,  a  gasp  for  breath.  In  this  thought 
we  have  the  key  to  the  otherwise  singular  phenomena  of  the  so-called 
passive  congestions.  These  congestions  occur  on  interference  with  the 
circulation,  whether  the  arterial  pressure  is  high  or  low,  wdiether  the 
power  that  drives  the  blood  be  great  or  small.  It  occurs  if  the  veins 
be  obstructed  before  a  powerful  current  of  blood  driven  by  a  vigorous 
heart,  or  in  the  presence  of  a  feeble  current  driven  by  a  heart  too  weak 
to  compel  the  return  of  the  blood  against  the  attraction  of  gravitation. 

This  kind  of  hypersemia  may  occur  under  a  great  variety  of  circum- 
stances, and  is  common  to  a  great  variety  of  diseases.  It  is  seen  first  in 
the  dependent  portions  of  the  body  in  all  the  forms  of  valvular  disease 
of  the  heart  when  they  have  made  such  progress  as  to  interfere  mate- 
rially with  the  propulsion  of  the  blood.  It  is  prone  to  occur  in  diseases 
of  the  kidneys,  and  is  an  element  in  all  dropsical  disorders.  It  is  lia- 
ble to  occur  in  the  later  periods  of  any  of  the  continued  fevers  that 
cause  great  enfeeblement.  It  is  seen  in  ansemia  and  great  nervous 
exhaustion  ;  indeed,  in  any  condition  of  great  reduction  of  the  vital 
powers.  It  occurs  also  from  pressure  on  the  veins  preventing  the  return 
of  the  blood.  This  is  often  seen  in  the  pregnant  female  from  the  pres- 
sure of  the  uterus  on  the  veins.  In  persons  not  very  strong  it  may  occur 
in  the  feet  from  long  standing,  as  is  not  uiifrequently  noted  among  den- 
tists who  stand  much  at  the  chair.  It  may  be  produced  by  tumors  that 
compress  or  otherwise  obstruct  the  veins — in  short,  by  anything  what- 
ever that  obstructs  the  free  passage  of  the  blood  back  to  the  heart. 

The  results  of  paKsive  hypercrmia  are  somewhat  complex.  In  case  of 
the  obstruction  of  a  vein  the  amount  of  hypersemia  will  obviously 
depend  on  the  number  of  anastomosing  branches  in  the  neighborhood. 
If  these  be  sufficient,  the  blood  will  be  conveyed  by  these  channels,  and 
no  hyperemia  will  result.  But  in  case  these  are  not  present  in  sufficient 
number  to  convey  the  blood,  then  the  retained  blood  becomes  more  than 
usually  venous  in  character  ;  and  in  proportion  as  this  takes  place  the 
vessels  of  the  ]xirt  are  dilated,  relaxed,  admitting  more  and  more  blood 
to  the  part.  The  degree  of  this  engorgement  will  depend  directly  on 
the  amount  of  obstruction,  and  may  vary  from  a  slight  fulness  of  the 
vessels  to  complete  stagnation  and  the  complete  fiUing  of  the  tissue  vyith 
hloofl.  In  case  there  is  only  a  moderate  slowing  of  the  blood-current, 
the  tissue  will  contain  more  blood  than  the  normal  quantity,  but  the 
hiost  obvious  sign  will  be  the  escape  of  an  undue  proportion  of  the 
blood-serum  from  the  vessels  into  the  tissues,  especially  the  cellular, 
areolar,  or  connective  tissues  of  the  pan,  forming  what  is  known  as 
ce.dema.  When  this  escape  of  the  fluid  parts  of  the  blood  is  not  consid- 
erable, it  is  taken  u]>  by  the  lymjihatic  vessels  of  the  part  and  conveyed 
back  into  the  blood  ;  but  if  there  is  more  than  these  vessels  can  dis]iose 
of  in  this  way,  then  the  part  becomes  swollen  and  oedematous.  This 
swelling  is  characteristic  in  that  it  has  a  doughy  feel  under  the  finger, 


VARTATIO^^S  IN  THE  BLOOD,  AND  IN  ITS  DISTRIBUTION.     679 


blood-globules 


and  remains  deeply  pitted  for  some  time  after  the  removal  of  the  pres- 
sure. If  now  the  obstruction  is  removed,  the  blood-current  is  soon 
re-established  and  the  oedema  disappears.  The  occurrence  of  these 
phenomena  is  the  same  when  the  obstruction  is  the  result  of  any 
other  cause,  as  great  debility. 

Dlapedesis  of  the  red  hlood-globides  occurs  when  the  stagnation  is 
more   considerable.     This   is   the   passage  of  the   red 
through    the    walls    of   the 

blood-vessels    into   the    tis-  ^^^-  3^2. 

sues.  This  occurs  mainly, 
if  not  entirely,  in  the  capil- 
laries without  the  rupture 
of  their  walls.  There  seems 
to  be  some  difference  of 
opinion  as  to  whether  the 
blood-globules  pass  through  ^^'^'  ^^l. 

the  endothelial  plates  of 
which  these  walls  are 
formed,  or  pass  out  between 
them  at  points,  called  sto- 
mata,  where  several  of  these 
plates  join,  as  shown  in  the 
diagram  (Fig.  372).  The 
fact  of  the  escape  of  the 
red  onlobules  is  well  shown 
in  passive  hypersemia  arti- 
ficially produced  by  ligating 
the  veins  in  the  tongue  of 
the  frog.  After  a  consider- 
able amount  of  red  blood 
has  escaped  into  the  tissues 
by  this  process,  if  the  cause 
is  removed  complete  recovery  takes  place  and  the  arteries  seem  to  have 
suffered  no  injury ;  the  hemorrhage  ceases  at  once.  Arnold  supposed 
that  the  so-called  stomata  at  the  corners  of  the  endothelial  plates  were 
enlarged,  as  shown  in  tlie  figure ;  but  this  idea  seems  now  to  have  been 
given  up  in  favor  of  the  doctrine  that  the  globules  pass  through  the 
tissue  without  leaving  any  sign. 

The  nutritive  power  of  the  tissues  becomes  much  weakened  in  passive 
hypersemia  if  long  continued.  This  gives  rise  to  the  sloughing  of  parts 
that  bear  the  pressure  of  the  body,  and  the  formation  of  what  are  called 
bed-sores,  these  being  prone  to  occur  in  great  debility  caused  by  long- 
continued  fever  or  by  other  protracted  illnesses  that  notably  weaken 
the  circulation. 

Gangrene  may  occur  in  case  of  extreme  passive  hypememia  with 
intense  oedema.  In  this  case  the  aeration  of  the  tissues  fails  so  com- 
pletely that  they  die  en  masse.  In  this  way  in  a  case  of  Bright's 
disease  of  the  kidneys  I  have  seen  a  whole  limb  become  gangre- 
nous. 

Thrombosis. 


Normal   Capillary,  with  Capillaries  after  Passive  Ilyper- 

endotheliiun    mapped  semia  :  apertures  between  the 

out  liy  tieatment  with  cells  greatly  enlarged — the  so- 

nitrate  of  silver.  called  stomata  (Arnold). 


-A  thrombus  is  a  blood-clot  that  forms,  under  a  vari- 


G80  GENERAL  PATHOLOGY. 

ety  of  circumstances,  in  the  vessels  while  tlie  blood  is  actively  circulat- 
ing. The  clot  which  closes  the  divided  end  of  an  artery  and  that  which 
forms  after  the  ligation  of  an  artery  are  also  called  thrombi.  These 
varieties  of  thrombi  differ  quite  remarkably  in  character.  In  order 
that  we  may  appreciate  these  differences  it  is  necessary  that  we  study 
their  mode  of  formation.  The  coagulation  of  the  blood  has  been  very 
closely  studied  (Zahn),  both  theoretically  and  in  its  clinical  aspect.  And 
the  conditions  under  which  the  blood  will  coagulate  seem  to  have  been 
pretty  clearly  made  out.  In  order  that  a  clot  may  form  three  agents 
are  essential — fibrin  ferment,  fibrinogen,  and  paraglobulin  (kSchmidt). 
In  the  presence  of  the  fibrin  ferment  the  two  latter  substances  unite  to 
form  fibrin,  which  is  the  essential  factor  in  the  formation  of  the  clot. 
The  paraglobulin  and  the  ferment  substance  are  found  to  reside  in  the 
white  blood-globules,  and  the  fibrinogen  exists  in  a  state  of  solution  in 
the  blood-plasma.  In  order  that  a  blood-clot  may  form,  it  is  necessary 
that  white  blood-globules  be  disintegrated  and  the  ferment  substance 
and  paraglobulin  set  free.  Therefore  as  long  as  the  white  corpuscles 
are  circulating  and  remain  alive  the  blood  will  continue  fluid.  In  order 
to  maintain  the  life  of  the  ^^liite  blood-corpuscles  it  is  necessary  that 
they  should  not  be  exposed  to  contact  with  dead  matter  nor  with  in- 
flamed or  injured  tissue.  It  has  been  demonstrated  by  experiment 
(Lister)  that  the  blood  may  be  kept  fluid  in  the  still  condition  for  a  long 
time  if  it  is  in  contact  with  living  tissue.  If  within  the  living  body  an 
artery  is  carefully  ligaied  (so  as  not  to  injure  its  internal  coat)  at  two 
j)oints  in  such  a  manner  as  to  include  a  portion  filled  with  blood,  this 
will  remain  fluid  for  twelve  or  fifteen  days.  If  the  section  thus  ligated 
be  cut  out,  the  blood  will,  under  favorable  circumstances,  remain  fluid 
for  several  days.  These  experiments  show  clearly  that  the  coagulation 
of  blood  is  not  on  account  of  the  arrest  of  motion,  as  was  once  sup- 
posed. When  we  examine  critically  all  the  conditions  under  which  the 
coagulation  of  the  blood  takes  place,  it  will  be  found  that  the  cardinal 
points  are  these :  Contact  with  dead  matter,  such  as  the  walls  of  the 
vessel  in  which  it  is  drawn  or  any  inanimate  object — (the  more  rough 
and  uneven  the  surface  of  contact  the  quicker  will  be  the  coagulation), 
contact  with  chrnu/ed  living  tissue,  whether  this  change  be  the  result  of 
inflammation  or  injury,  such  as  cutting,  bruising,  or  tearing  the  flesh. 
Under  any  of  these  circumstances  some  of  the  white  globides  of  the 
blood  become  so  far  disintegrated  as  to  give  up  the  paraglobulin  and 
fibrin  ferment,  and  in  the  presence  of  the  latter  the  former  at  once  unites 
with  the  fibrinogen  of  the  blood-plasma  for  the  formation  of  the  semi- 
solid fibres  of  fibrin  by  which  the  blood  is  held  together  in  a  gelatinous 
mass. 

In  hemorrhage  occurring  from  the  division  of  an  artery  the  closure 
of  the  severed  extremity  by  thrombus  is  favored  by  the  flow  of  the 
blood  over  the  injured  tissue,  and  the  greater  the  amount  of  injured 
tissue  with  which  the  blood  may  come  in  contact  in  proportion  to  the 
calibre  of  the  vessel,  the  quicker  it  will  be  closed.  Therefore,  an  artery 
severed  by  a  blunt  instrument  that  causes  much  bruising  of  the  tissues 
is  much  nioi'e  readily  closed  l)v  the  clotting  of  the  blood  than  if  severed 
by  a  very  sharp  instrument.    Nature  has  also  provided  means  of  increas- 


VABIATIOyS  IN  THE  BLOOD,  AND  IN  ITS  DISTRIBUTION.     681 


Natural  H»nio.stabis.  The  divided 
ends  of  the  artery  ((/)  retract 
witiiin  the  sheath  {</),  and  by 
contractiug  diminish  the  calibie 
of  the  canal.  IShjod  coagulates  in 
the  sheath  (a)  around  tlie  orifice 
of  the  divided  vessel,  and  in  the 
artery  itself  {h)  up  to  the  first 
branch  (c);  and  lastly,  plastic 
lymph  is  poured  out  from  the 
divided  coats  of  the  vessel,  and 
by  its  organization  the  perma- 
nent closure  takes  place  (Jones). 


iiig  tlie  contact  of  the  escaping  blood  with  the  injured  ti.ssue.  When  an 
artery  is  severed,  the  inner  coat  contracts 
within  the  outer  walls — /.  c.  becomes  the 
shorter — and  is  pulled  backward  into  the  outer 
wall  of  the  vessel,  and  at  the  same  time  the 
cut  end  is  narrowed  (Fig.  373).  In  this  way 
the  flowing  blood  is  brought  into  contact  with 
the  greatest  possible  surface  of  injured  tissue. 
The  formation  of  the  thrombus  is  begun  by 
the  adhesion  of  the  wliite  blood-globules  to 
the  injured  surface.  These  adhere  one  after 
another,  and  are  held  fast  by  the  formation 
of  a  little  fibrin  ;  others  adhere,  and  more 
fibrin  is  formed  until  the  end  of  the  vessel  is 
completely  filled.  In  this  process  the  red 
globules  take  no  part,  and  if  the  thrombus 
is  very  slowly  formed,  very  few  of  them 
will  be  included  in  the  clot,  and  it  will  be 
white  or  gray  in  color.  In  this  position, 
however,  a  thrombus  is  usually  red  from  the 
entanglement  of  red  globules.  After  the  ar- 
tery is  closed  the  coagulation  of  the  blood  in 
the  artery  proceeds  until  the  first  lateral 
branch  is  reached.  This  in  time  becomes  organized,  or  rather  is 
absorbed,  and  its  place  filled  with  new  tissue,  and  the  vessel  is  per- 
manently closed  (Figs.  374  and  375). 

In  the  ligation  of  arteries  the  blood  is  caused  to  clot  by  injury  to  the 
internal  coat.  In  this  case  the  thrombus  is  always  red,  for  it  contains 
all  the  blood-constituents.  If  the  clot  should  not,  before  the  ligature 
comes  away,  become  sufficiently  firm  to  resist  the  blood-pressure,  sec- 
ondary hemorrhage  will  occur. 

Thrombi  form  in  the  blood-vessels  under  various  circumstances.  This 
may  be  well  studied  in  the  mesentery  of  the  frog.  When  this  is  ex- 
posed for  microscopic  study,  a  vessel  of  some  size  may  be  in  some  way 
injured — by  pricking  with  a  needle  or  placing  some  irritant  in  contact 
with  it — and  the  progress  of  the  building  of  the  thrombus  watched. 
As  the  blood  passes  over  the  injured  point  a  few  white  globules  adhere 
to  it.  Upon  these  others  are  slowly  deposited  in  successive  layers,  and 
the  little  himp  is  seen  to  grow  larger  and  larger  as  the  successi\'e  layers 
are  deposited.  This  may  continue  steadily  until  tlie  vessel  is  completely 
occluded  and  the  pa.ssage  of  the  blood  stopped  ;  or  after  a  little  clump 
is  formed  it  may  be  detached  by  some  movement  or  by  the  force  of  the 
jjassing  blood-current  and  float  away.  A  second  clump  will  then  be 
deposited  in  the  same  manner  as  the  first.  During  the  growth  of  these 
the  outline  of  the  white  blood-globules  is  usually  lost.  They  seem,  as 
the  rule,  to  become  fused  with  the  forming  fibrin  into  one  mass,  though 
sometimes  a  few  continue  to  show  their  outlines.  It  does  not  seem  that 
the  destruction  of  very  many  white  blood-globules  is  necessary  to  pro- 
duce a  considerable  clot.  The  liberated  material  acts  as  a  ferment,  and 
according  to  the  law  of  the  action  of  ferments  a  very  little  may  produce 


682 


GENERA  L  FA  THOL  0  G  Y. 


a  great  result  by  causing  changes  in  other  substances  without  itself 
entering  into  the  combination. 

Thrombi  formed  in  the  manner  just  stated  are  always  white  or  nearly 
so.  This  is  always  the  case  when  they  are  formed  slowly  in  the  blood- 
stream, from  the  fact  that  very  few  red  blood-globules  or  none  become 
entangled  in  the  forming  mass.  This  circumstance  enables  the  pathol- 
ogist to  determine  whether  or  not  a  given  blood-clot  has  been  formed 

Fig.  375. 


Fig.  374. 


Longitudinal  Section  of  the  I.igatiired  Kiid 
of  the  (rural  Artery  of  a  Dog,  fifty  days 
after  the  application  of  the  ligature,  show- 
ing the  newly-formed  vessels  in  the  throm- 
bus and  their  communications  with  the 
vasa  vasorum  :  7//,  thrombus;  J/,  muscular 
coat ;  Z,  external  coat  (X  20,  O.  Weber). 


A  Thrombus,  ten  days  old,  after 
moditied  ligation.  Longitudinal 
cut.  Low  power.  Afier  ligature 
at  A,  the  artery  was  seized  and 
compressed  at  B  between  the 
arms  of  a  pair  of  forceps,  a,  ad- 
ventitia ;  r»,  media ;  c,  cellular 
tissue ;  p,  cellular  formation  at 
bottom  of  clot,  non-organized, 
and  apparently  not  larger  than 
such  an  accumulation  usually  is 
at  five  days ;  it  consists  mainly  of 
cells  similar  to  white  blood-cor- 
puscles; only  a  few  epithelioid 
cells  are  .scattered  through  it, 
and  no  granulations  springing 
from  it  penetnite  the  crevices 
of  the  laminated  clot  (d)  imme- 
diately above ;  at  p', ;»"  there  is 
an  ingrowth  of  the  intima  and 
inner  layers  of  the  media.  At  L, 
above  the  point  of  compression, 
a  blood-clot  like  that  at  il  rested, 
but  handling  caused  its  disjjlace- 
ment. 


])v  gradual  growth  on  account  of  some  injury,  inflammatory  or  other- 
wise, to  the  vessels,  or  from  stagnation  of  the  blood.  This  character  of 
clot  can  be  closely  imitated  artificially  by  rapidly  whipj^ing  freshly- 
drawn  blood  with  a  bundle  of  small  twigs,  to  which  the  forming  fibrin 
will  adhere,  leaving  the  red  globules  in  the  blood-scrum.  By  working 
quickly  and  carefully  the  clot  adhering  to  the  twigs  will  be  nearly 
white,  and  all  the  fibrin  can  in  this  way  be  taken  from  the  blood.  This 
is  the  mode  of  preparing  defibrinated  blood  ior  transfusion. 

But  one  cause  is  known  for  the  formation  of  thrombi  in  the  living 
vessels,  and  this  is  some  actual  injury  to  their  walls.  This  injury  may 
be  effected  in  a  multitude  of  ways.  On  account  of  pressure  or  extreme 
weakness  of  the  heart  the  blood  may  stagnate  in  the  vessels  luitil  the 
endothelium  becomes  seriously  impaired.     Arteritis  may  affect  them,  or, 


VARIATIONS  IN  THE  BLOOD,  AND  IN  ITS  DISTRIBUTION.      683 

in  fact,  any  of  the  diseases  to  which  the  arteries  are  liable.  It  may 
result  directly  from  injury  in  wounds,  pricking  with  sharp  instruments 
as  the  result  of  accident  or  in  using  the  hypodermic  needle,  etc. 

Thrombi  often  form  in  the  debilitated  heart.  This  is  supposed  to 
occur  when  the  cavities  of  the  heart  are  not  completely  emptied  of  blood 
at  each  contraction.  Under  such  circumstances  a  portion  of  blood  will 
remain  in  the  apex  of  the  ventricle  and  stagnate,  or  it  may  lodge 
behind  the  valves  or  in  other  nooks.  The  clotting,  once  begun,  may 
continue  until  the  motions  of  the  heart  are  so  interfered  with  as  to  cause 
death.  A  diseased  and  roughened  condition  of  the  valves  of  the  heart 
is  another  cause  of  thrombus. 

The  organization  of  thrombi  will  be  considered  under  the  head  of 
Processes  of  Repair. 

Embolism. — Embolism  is  usually  a  result  of  thrombosis.  A  part  or 
the  whole  of  a  thrombus  becomes  detached  from  its  place  of  formation 
and  floats  away  with  the  blood-stream.  If  this  be  in  the  arteries,  it 
must  pass  into  a  smaller  artery,  and  finally  it  will  come  to  a  point 
where  the  calibre  of  the  vessel  is  too  narrow  to  allow  it  to  pass,  and  the 
plugging  of  the  artery  and  the  stoppage  of  the  flow  of  blood  through  it 
are  the  result.  An  embolus  is,  however,  not  necessarily  a  detached 
thrombus.  It  may  be  any  conceivable  thing  that  can  gain  entrance  to 
the  vessels  and  travel  with  the  blood,  as  detached  bits  of  tumor,  chalky 
deposits  from  the  valves,  oil-globules,  or  air  that  may  have  gained 
entrance  to  the  vessels,  or  other  foreign  substance.  If  we  know  Avhere 
an  embolus  starts,  we  can  have  some  idea  where  it  will  lodge.  If  it  be 
in  an  artery,  it  is  likely  to  follow  the  most  direct  line  until  a  point  is 
found  too  small  for  it  to  pass ;  if  it  is  in  the  portal  system,  it  must 
lodge  in  the  liver ;  if  it  is  in  the  veins,  it  must  lodge  in  the  lungs  after 
passing  the  heart ;  if  it  is  in  the  heart,  it  may  go  to  any  part  of  the 
general  system,  but  the  manner  in  which  the  carotids  are  given  oif  from 
the  arch  of  the  aorta  frequently  causes  emboli  to  be  sent  to  the  brain. 

The  results  of  einbollsiii  vary  greatly  with  the  position  of  the  lodg- 
ment of  the  embolus.  In  case  there  are  many  arteries  with  free  anasto- 
moses, the  circulation  is  restored  almost  at  once,  and  no  harm  results, 
for  it  is  only  the  capillary  circulation  that  is  important  to  the  tissues. 
The  most  that  can  occur  in  this  case  will  be  the  formation  of  an  abscess, 
and  this  is  not  likely  to  result  unless  the  embolus  contains  septic  mate- 
rial. Generally  the  embolic  clot  becomes  organized,  or,  more  strictly, 
is  partially  absorbed,  and  this  part  of  the  artery  is  reduced  to  a  solid 

Hemorrharjic  infarction  results  from  embolism  of  arteries  that  have 
no  anastomosing  connections.  These  are  sometimes  called  end-arteries. 
This  arrangement  of  the  arteries  occurs  in  several  of  the  organs  of  the 
body,  as  the  brain,  the  kidneys,  the  lungs,  the  spleen,  the  pulps  of  the 
single-rooted  teeth,  and  in  various  other  positions.  Infarction  is  very 
important  on  account  of  the  serious,  and  often  fatal,  damage  clone  to 
important  organs.  Such  arteries  supply  blood  to  a  definite  piece  of 
tissue,  and  when  this  supply  is  cut  off*  by  an  embolus  death  of  that  tis- 
sue is  the  inevitable  consequence.  The  lateral  branches  of  the  principal 
arteries  of  the  tongue  of  the  frog  are  without  anastomosing  branches, 


684  GENERAL  PATHOLOGY. 

and  Cohnheim  has  employed  them  to  study  this  subject  experimentally 
(Fig.  376).      He  introduced  little  pellets  of  blackened  wax  into  the 


Diagram  of  the  conditions  following  Embolism  of  an  End-artery.  In  the  figure  to  the  left  the  state 
oC  antt'uiia  altei  the  eiiiboliMii  is  shown  ;  in  the  other  tigiire  the  regurgitant  current  from  the  vein 
is  indicated  (after  Cohnheim). 

division  of  the  aorta  that  communicates  with  the  tongue,  and  succeeded 
in  obstructing  these  particular  arteries.  When  thus  obstructed  the  effect 
was  to  stop  the  luovement  of  the  blood  in  the  area  supplied  by  the 
branch  in  arteries,  capillaries,  and  veins.  This  state  did  not  remain 
long,  for  soon  there  was  observed  a  backward  movement  of  the  blood 
through  the  vein  into  the  capillaries  of  the  district,  which  went  on 
slowly  until  these  were  distended  with  blood.  But  the  movement  did 
not  cease  with  the  wide  distension  of  the  vessels,  for  soon  a  remarkable 
phenomenon  became  apparent — the  rapid  diapedesis  of  the  red  globules 
of  the  blood  into  the  ti.ssues.  This  went  on  until  the  whole  area  was 
completely  engorged  with  blood.  How  can  this  be  explained?  It 
is  said  that  the  diapedesis  is  occasioned  by  the  impairment  of  the 
capillary  walls  from  deprivation  of  arterial  blood,  but  we  have  already 
seen,  while  studying  active  hypersemia,  that  diapedesis  also  occurs  from 
the  ob.struction  of  the  veins,  and  that  if  the  obstruction  be  removed 
within  a  reasonable  time,  the  capillary  walls  prove  not  to  be  impaired. 
It  seems  to  me  clear  that  this  is  not  the  true  explanation  of  this  phe- 
nomenon. Neither  are  the  vessels  expanded  by  the  pressure  of  the 
blood,  for,  as  we  have  seen,  the  blood-pressure  is  reduced  to  the  lowest 
possible  standard  by  the  clo.-^ure  of  the  artery.  The  expansion  of  the 
vessels  in  this,  as  in  other  instances  that  I  have  heretofore  noticed,  is  to 
be  explained  from  the  standpoint  of  physiology  rather  than  from  that 
of  dynamics.  These  tissues  are  deprived  of  aerated  blood,  and  the 
expansion  of  the  vessels  is  a  reflex  phenomenon  denoting  an  effort  to 
supply  this  need.  The  needs  of  the  tissues  are  supplied,  normally,  by 
the  absorption  of  certain  constituents  of  the  blood  ;  and  here  we  find 
this  so  exaggeratc<l  that  the  \rhoh  blood  is  absorbed  in  the  effort  to  obtain 
aeration.  Tiierefore,  the  tissues  of  the  region  become  completely 
engorged  with  blood,  which,'  as  the  impairment  of  tissue  proceeds, 
coagulates,  and  the  coagulum  encloses  the  tissue  in  its  meshes.  That 
there  occurs  final  deterioration  of  the  endothelium  of  the  vessels  is  a 
matter  of  course,  but  this  is  not  the  cause  of  the  diapedesis,  but  a  result 
of  deprivation  of  aerated  blood. 


VARIATIONS  IN  THE  BLOOD,   AND   IN  ITS  DISTRIBUTION.      68o 


Fig.  37 


An  infarct  will  have  the  forni  of  the  bit  of  tissne  supplied  by  the 
artery  plugged  by  the  embolus,  and  is  usually  cone-shaped,  with  the 
apex  at  the  point  Avhere  the  embolus  has  lodged 
and  the  base  at  the  surface  of  the  organ  in 
which  it  has  occurred  (Fig.  377).  In  recent 
infarcts  the  appearance  is  that  of  a  blood-clot 
in  the  tissues.  In  time  this  shrinks  and  the 
fluid  portions  disappear  by  absorption.  Sur- 
rounding it  there  is  a  zone  of  hypeneniic  tissue, 
and  usually  some  projection  of  young  granula- 
tion-cells into  its  mass.  Under  favorable  cir- 
cumstances the  whole  infarct  will  be  absorbed 
and  its  place  supplied  by  fibrous  tissue,  as  is 
generally  the  case  in  the  spleen.  But  very 
often  the  infarct  becomes  of  a  pale-yellow  or 
whitish  color,  from  the  loss  of  the  coloring 
matter  of  the  blood,  and  finally  undergoes  fatty 
degeneration,  and  is  absorbed  or  remains  as  a 
kind  of  cyst.  The  position  of  the  infarction 
has  to  do  with  the  evils  connected  with  it.  In 
the  brain  the  infarct  is  more  prone  to  softening 
than  in  other  regions,  apparently  on  account  of 
the  very  small  amount  of  the  connective-tissue  element,  and  its  presence 
there  is  of  much  graver  moment,  owing  to  the  importance  of  the  tissue 
destroyed 


Diagram  of  a  nemorihnf;ic  In- 
farct:  a,  artery  obliterateJ  by 
aneinbolus(f);'i;,vein  filled  with 
a  second  iry  thrombus  {(/i);  1, 
centre  of  infarct  which  is  he- 
coniiiig  disintegrated  ;  2,  area 
of  extravasation  ;  o.areaof  col- 
lateral hyperseniia  (O.  Weber). 


depending 
cause  the 
involved. 


In  other  positions  the  injury  is  less  serious,  the  degree 
on  the  amount  of  tissue  included.  In  the  retina  it  may 
loss  of  sight;  in  the  kidney,  the  loss  of  the  gland-tissue 
If  the  embolus  lodge  in  the  artery  of  a  tooth-pulp  at  the 
apical  foramen,  the  pulp  will  be  lost ;  and,  as  in  this  position  the  fluids 
are  not  readily  absorbed,  alveolar  abscess  is  sooner  or  later  likely  to 
occur.  It  must  be  remembered  that  the  plugging  of  such  minute 
arteries  as  this  may  be  by  oil-globules. 

He:morrhage.^ — Hemorrhage  may  occur  in  two  distinct  forms — by 
rupture  of  the  vessels  and  by  diapedesis.  The  blood  may  pass  outside 
of  the  body,  may  escape  into  the  cavities  of  the  body,  or  it  may  make 
})lace  for  itself  in  the  tissues  by  forcing  them  asunder,  or  it  may  infil- 
trate the  tissues.  Hemorrhage  by  rupture  may  occur  from  any  of  the 
vessels,  great  or  small ;.  that  by  diapedesis  occurs  only  in  the  capillaries. 
The  latter  has  already  been  considered  in  some  of  its  phases.  Hemor- 
rhage tVom  rupture  is  generally  traumatic  in  origin,  as  in  wounds  made 
by  cutting  or  tearing  the  flesh.  It  may  also  occur  from  sloughing  or 
by  the  perforation  of  the  vessels  by  ulceration.  Disease  of  the  vessel 
may  so  weaken  the  walls  that  they  give  way  to  the  blood-pressure,  as  in 
aneurism,  atheroma,  etc.  There  are  some  persons  whose  blood-vessels 
are  so  constituted  that  they  are  unusually  easy  of  rupture.  This  is 
called  the  hemorrhagic  diathesis.  It  is  sometimes  inherited.  Aside 
from  these  causes  there  are  some  diseases,  as  scurvy,  the  anremias,  and 
the  septic  fevers,  in  which  a  disposition  to  hemorrhage  is  induced  either 
by  alterations  of  the  constitution  of  the  blood  or  of  the  tissues.  In  some 
of  the  diseases  named,  and  also  in   purpura  hemorrhagica,  blood  is 


686 


GENERAL  PA THOLOG Y. 


extravasatecl  in  small  spots  of  tissue-ecchymoses — often  freely  distrib- 
uted over  the  body.  It  is  probable  that  in  some  of  these  cases  the  bleed- 
ing is  by  diapedesis. 

Hemorrhage  is  stopped  naturally  by  the  coagulation  of  the  blood. 
This  was  described  under  the  head  of  Thrombosis  (p.  679).  In  some 
conditions  of  the  blood  there  seems  to  be  a  partial  failure  of  coagulation, 
and  in  this  case  the  stoppage  of  the  bleeding  becomes  more  difficult. 
This  is  often  noticed  in  the  hemorrhagic  diathesis,  and  occurs  in  persons 
who  little  by  little  have  lost  a  large  amount  of  blood,  until  they  have 
become  ansemic.  It  is  also  seen  in  the  spontaneous  anseniias  and  in 
exhaustion  from  fevers.  Under  ordinary  circumstances  the  loss  of 
blood,  by  reducing  the  power  of  the  circulation,  assists  in  the  arrest  of 
hemorrhage,  but  this  occurs  only  before  the  blood  has  become  changed 
by  the  loss  of  a  large  proportion  of  its  red  blood-globules ;  these  are 
always  lost  in  greater  proportion  than  the  other  constituents  of  the 
blood,  and  are  not  replaced  with  the  same  facility.  This  accounts  for 
the  change  in  the  constitution  of  the  blood  in  repeated  hemorrhages.  In 
all  of  these  cases  the  eflPort  should  be  to  restore  the  normal  condition  of 
the  blood  by  appropriate  treatment.  This  applies  to  bleeding  by  dia- 
pedesis as  well. 

The  absorption  of  blood  that  has  escaped  into  the  tissues  is  a  matter 
of  much  interest,  and  presents  some  singular  phenomena.  When  the 
fluid  portions  of  the  blood  alone  escape,  forming  oedema,  the  serum  is, 
if  not  in  too  great  quantity,  disposed  of  by  the  lymphatic  vessels. 
Some  of  the  corpuscular  elements  may  also  be  carried  off  in  the  same 
way  ;  but  where  a  considerable  number  of  the  red  globules  are  distrib- 
uted in  the  tissues  they  cannot  be  so  removed,  and  are  disposed  of, 
many  of  them  at  least,  by  the  wandering  cells.  These  cells  accomjilish 
this  by  taking  them  into  themselves  as  the  amoeba  takes  its  food.  Once 
within  the  wandering  cells,  they  soon  disappear  (Fig.  378).  It  is  not 
Fig.  378. 


Cells  containinK  Blood-corpuscles  from 
the  neighborhood  of  a  lleinorrhage: 
a,  with  fresh  corpuscles ;  b,  with  dark 
granules  from  disintegration  of  red 
corpuscles. 


Fig.  379. 


t    C3 

Crystals  of  Hsematoidin  from  an  Old  Hemorrhage  in 
the  Urain  :  their  color  is  reddish-brown  (X  35li). 


unusual  to  see  several  red  globules  within  one  wandering  cell,  as  shown 
in  the  figure.  It  is  of  course  impossible  that  the  nuiltitude  of  red  globules 
in  large  extravasations  should  be  disposed  of  in  this  way.  These  lose  their 
fluid  portions  by  absorption,  and  the  globules  remain.  Their  coloring 
matter  is  slowly  dissolved  out,  and  often  stains  the  tissues  of  the  neigh- 


VARIATIONS  IN  THE  BLOOD,   AND  IN  ITS  DISTRIBUTION.      687 


borhood.     This  staining  is  of  various  colors,  according  to  the  concen- 
tration of  the  coloring  matter,  from  a  blue-black  to  a  light-yellow  tinge. 
The  dissolved  coloring  matter  is  finally  all  absorbed,  and  the  tissues 

pi-Gsent  their  usual  apiiearance.  ^ 

V  r  •  1       1  1         i  Fig.  380, 

In  case  of  considerable  extrav- 
asations forming  clots  the  col- 
oring matter  is  often  deposited 
in  the  crystalline  form  (Figs. 
379  and  380).  I  have  obtained 
some  beautiful  crystallizations 
by  the  section  of  clots  occurring 
a  short  time  before  death,  and 
also  from  uterine  clots.  (See 
Fig.  381.) 

Anaemia. — The  term  ancemia 
in  its  strict  sense  means  tcithoid 
blood,  but  it  is  used  to  designate 
those  conditions  in  which  the 
blood    is  deficient  in   quantity 

or  in  quality.  Deficiency  in  crystals  of  Hfemiu,  prepared  artificially  by  addinsr 
quantity  may  result  directly  glaclal  acetic  acid  to  a  drop  of  blood,  heating  and 
1  -^  •'  1     •         I  evaporating  to  dryness  ( X  ■ioO). 

from   hemorrhage,  and  is  then 

called  acute  traumatic  anaemia.  Otherwise  than  in  this  M^ay  a  true 
deficiency  in  the  quantity  of  the  blood,  without  other  deviations  from 
the  normal  standard,  is  rarely  seen.     By  active  hemorrhage  the  arte- 

FiG.  381. 


Crystals  of  Heematoidin  from  a  Uteiine  Blood-clot.    The  crystals  have  been  somewhat  broken  in  the 
cutting  of  the  section  (Blacl^,  X  40). 

rial  tension  is  rapidly  reduced,  and  general  debility  is  induced  in 
proportion  to  the  loss  of  blood.  The  bulk  of  the  blood,  however,  is 
quickly  made  up  by  the  absorption  of  the  fluids  from  the  alimentary 


688 


GENERA L  PA  TIIOL 00 Y. 


canal  and  the  tissues  into  the  circulation,  and  the  normal  tension  is 
thus  restored.  Besides  this,  a  notable  loss  of  blood  may  occur,  and 
the  tension  be  kept  up  by  the  contraction  of  the  arterial  walls  under 
the  influence  of  the  vaso-motor  nerves.  In  these  two  ways  the  arte- 
rial system  accommodates  itself  to  a  considerable  loss  of  blood  with- 
out the  occurrence  of  notable  anremia  ;  and  it  is  only  by  the  loss  of 
large  quantities  of  blood  tliat  serious  damage  to  the  vital  powers  re- 
sults. In  case  the  loss  of  blood  occurs  repeatedly,  a  qualitative  dam- 
age to  that  fluid  results  without  notably  diminishing  its  bulk,  for  the 
])lasma  is  replaced  much  more  readily  than  the  corpuscular  elements. 
The  white  blood-globules  move  slowly  along  the  walls  of  the  vessels, 
and  are  much  inclined  to  cling  to  them,  and  are  not  lost  in  hemorrhage 
in  the  Same  proportion  as  the  red  globules,  which  usually  occupy  the 
central  portion  of  the  blood-stream.  Now,  the  red  globules  when  lost 
are  regenerated  very  slowly  ;  therefore,  when  hemorrhages  occur  fre- 
quently the  eifect  on  the  quality  of  the  blood,  if  the  loss  is  considerable 
in  the  aggregate,  may  become  serious.  This  constitutes  what  is  known 
as  hydrccmia,  or  Avatery  blood.  The  nutritive  value  of  the  blood 
depends  on  the  proportion  of  its  red  globules,  and  if  these  are  deficient 
a  condition  of  debility  results,  no  matter  what  the  bulk  of  the  circulat- 
ing fluid. 

SDontaneous  ancvmia  is  a  term  used  to  designate  a  condition  of  defi- 
ciency of  the  red  corpuscles  occurring  without  any  direct  loss  of  blood. 
The  normal  pro])ortion  of  the  red  globules  to  the  whole  blood  is  esti- 
mated at  about  13  per  cent.  In  spontaneous  anaemia  it  may  sink  as 
low  as  6  or  even  4  per  cent.  In  this  condition  there  is  always  a 
notable  reduction  of  the  vital  powers,  and  such  patients  usually  exhibit 
marked  debility.  This  condition  may  be  induced  by  a  great  variety 
of  circumstances,  such  as  exhaustion  from  overwork  of  any  kind,  and 
especially  by  continuous  mental  application.  It  is  also  induced  by  a 
variety  of  forms  of  chronic  illness  and  by  protracted  fevers. 

Essential  or  pernicious  ancemia  may  come  on  without  any  perceivable 
connection  with  other  ailment  of  any  kind,  and  is  prone  to  a  fatal  ter- 
mination. Its  characteristic  is  a  marked 
reduction  in  the  number  of  red  cor- 
puscles. Some  authorities  describe  a 
red  globule  inferior  in  size  to  the  nor- 
mal red  one  as  characteristic  of  this 
disease  (Fig.  382).  So  far  as  I  am 
able  to  determine,  it  seems  probable 
that  this  is  not  an  abnormal  form  of 
red  globule,  but  a  white  globule  that 
has  become  stained  with  the  coloring 
matter  of  the  red.  Cornil  and  Ran- 
vier  state  that  they  have  not  been  able 
to  find  these  abnormal  corpuscles,  but 
find  that  "  many  white  corpuscles, 
especially  the  largest,  contain  veiy 
small  amber-colored  spherical  granules  grouped  around  the  nuclei. 
This  can  be  explained  by  the/:lestruction  of  the  red  corpuscles,  particles 


Blood    in   Pernicious    Anaemia:    tiie   larger 

bodies  are  the  normal  red  corpuscles ;  the 

smaller  are  the  round,  more  deeply  colored 

.     ones   usually   found— so-called  niicrocytes 

(Kichhorst). 


VABIATIOXS  IN  THE  BLOOD,  AND  IN  ITS  DISTRIBUTION.      689 

of  which  have  been  absorbed  by  the  M'hite  corpuscles."  It  is  known 
that  in  heakh  there  is  a  continuous  consumption  of  the  red  corpus- 
cles of  the  blood,  and  it  is  probable  that  the  essential  phenomenon 
of  this  disease  is  an  exaggeration  of  this  function,  and  that  the  con- 
sumption exceeds  the  powers  of  regeneration.  This  consumption  is 
supposed  to  take  place  in  the  liver,  but  it  is  also  known  that  under 
certain  circumstances  the  red  globules  are  destroyed  by  the  white,  and 
that  these  may  become  temporarily  stained.  This  leads  to  the  supposi- 
tion that  these  corpuscles  may  be  of  that  character.  The  place  of  the 
formation  of  the  red  blood-corpusclfs  is  not  certainly  known.  This 
function  has  been  attributed  to  the  spleen,  to  the  lymphatic  glands,  and 
to  the  marrow  of  the  bones.  The  bone- 
marrow  seems  to  have  been  found  in  a  Fig.  383. 
diseased  state  in  many  cases  of  anaemia, 
and  under  these  circumstances  cells  very 
like  the  red  blood-globules  have  been  dis- 
covered (Fig.  383). 

Chlorosis  is  a  form  of  anaemia  seen  in 
females  at  or  about  the  age  of  puberty. 
It  is  supposed  to  be  due  to  a  deficiency 

ill  the  formation  of  the  red  blood-corpus-  ^^^.^  ^^^  ,j^^^,ii^  „,  b^^^  .^  p^^. 
cles,  and  is  verv  amenable  to  treatment        nicious  Ancemia:  «,  uucieated  red 

•  ,1,1  ", .  /.  .  -fTT'.i      ,1  •  corpuscles;  c,  a  red  corpuscle  with 

M'ltll  the  preparation   Ot    iron.        With    this  grauular  nucleus;  />,  large  nucleated 

condition  there  is  often  associated  some  'iow  "jToo)!' ^"''' ""''' ^'''''* 
deficiency  in  the  vascular  system,  such  as 

narrowness  of  the  aorta  or  some  of  the  important  blood-vessels.  Con- 
trary to  what  is  usually  seen  in  the  other  forms  of  anaemia,  the  body 
seems  well  nourished  in  chlorosis,  but  there  is  the  same  defect  in  the 
proportion  of  the  red  blood-globules.  The  flesh,  however,  is  usually 
soft  and  flabby,  and  a  disposition  to  oedema  is  manifest  in  the  extrem- 
ities. Chlorotic  patients  are  more  than  usually  liable  to  nervous 
disorders. 

In  all  these  forms  of  anaemia  the  diminution  of  the  coloring  matter 
of  the  blood  appears  to  be  the  prime  factor,  and  cases  of  marked  cha- 
racter now  and  then  occur  in  which  this  deficiency  is  very  marked, 
while  the  number  of  the  corpuscles  remains  normal  or  nearly  so.  The 
bulk  of  the  blood  is  not  necessarily  diminished,  but  may  be  more  watery 
than  normal,  and  may  not  clot  so  readily.  This  often  gives  rise  to 
difficulty  in  controlling  hemorrhage.  Secondary  changes  in  the  tissues, 
especially  in  the  form  of  fatty  degenerations,  may  occur  in  any  of  the 
forms  of  anaemia  from  the  imperfect  nutrition  of  the  tissues.  Inflam- 
matory processes  are  languidly  performed,  and  are  more  prone  to  run  a 
chronic  course.  The  treatment  of  alveolar  abscess,  diseased  pulps  of 
teeth,  or  any  of  the  inflammatory  diseases  of  the  mouth  or  other  parts 
is  rendered  more  uncertain  and  difficult. 

Local  ancemia  is  the  diminution  of  the  blood  of  a  part.  It  is  prob- 
able that  this  occurs  in  various  organs  as  a  feature  of  the  neuroses  or 
as  perversions  of  innervation.  There  seems  to  be  such  a  thing  as  a 
tonic  spasm  of  the  arteries  of  a  part  or  organ,  during  the  continuance 
of  which  the  amount  of  blood  admitted  to  it  is  materially  lessened. 

Vol.  l.—U 


690  GENERAL  PATHOLOGY. 

Some  neuralo-ic  aifections  are  thouoht  to  be  of  this  character.  Anaemia 
m  all  of  its  forms  is  especially  liable  to  give  rise  to,  and,  seemingly, 
not  unfrequently  constitutes  the  basis  of,  the  more  obstinate  forms  of 
neuralgic  affections. 


Inflammation. 

The  classic  signs  of  inflammation  are  redness,  heat,  pain,  and  swelling. 
These  describe  -with  sufficient  accuracy  the  more  obvious  superficial 
characteristics  ordinarily  presented  by  the  inflammatory  process,  but 
convey  very  little  idea  of  the  changes  that  are  in  progress.  These 
processes  have  for  the  most  part  been  learned  in  comparatively  recent 
times  by  direct  microscopic  observation  of  inflammations  artificially 
produced  for  this  special  purpose.  In  the  study  of  this  process  sharply 
divergent  views  have  been  developed  by  certain  prominent  pathologists,  - 
each  of  whom  has  his  followers ;  so  that  the  student  in  his  first  attempts 
to  follow  the  explanations  given  in  the  different  works  that  have  recently 
appeared  is  very  liable  to  find  himself  in  a  confused  labyrinth  of  con- 
flicting detail,  from  which  he  will  emerge  with  anything  but  clearly- 
formed  views  of  the  phenomena.  For  this  reason  I  think  it  best  occa- 
sionally, in  the  course  of  my  descriptions  of  these  processes,  to  make 
brief  citations  of  these  differences  as  I  understand  them,  with  the  view 
of  assisting  younger  readers  in  clearing  up  this  seeming  confusion. 
Otherwise  than  this  I  shall  adhere  to  the  plan  I  have  thus  tar  followed 
of  making  but  few  references  to  the  opinions  of  others. 

For  the  microscopic  study  of  the  phenomena  of  inflammation  any  of 
the  membranes  that  are  sufficiently  thin  and  transparent  to  be  readily 
observed  during  the  life  of  the  animal  may  be  employed,  as  the  web  of 
the  frog's  foot,  the  frog's  tongue,  the  omentum,  or  the  mesentery. 
When  such  a  membrane  is  prepared  for  examination  and  placed  on 
the  stage  of  the  microscope,  an  irritant  is  applied  and  the  subsequent 
changes  observed.  The  changes  induced  in  this  process  may  also  be 
studied  by  the  more  ordinary  plans  of  microscopic  research. 

When  the  tongue,  mesentery,  or  web  of  the  foot  of  the  frog  is  brought 
under  observation,  the  blood  in  the  vessels  is  seen  to  be  circulating  in 
the  normal  manner.  Upon  the  application  of  an  irritant  the  first  nota- 
ble change  is  a  contraction  of  the  vessels.  This  is  so  slight,  and  endures 
for  so  short  a  time,  that  some  obsei'vers  have  even  denied  its  occurrence. 
Very  soon  the  vessels  begin  to  dilate,  and  the  flow  of  the  blood  through 
the  part  is  notably  increased.  The  streams  are  larger  and  the  blood 
flows  more  swiftly.  This  is  now,  to  all  appearance,  a  simple  hyper- 
remia,  the  hypencniia  of  irritation,  that  invariably  precedes  the  ap]iear- 
ance  of  inflammation.  After  this  has  persisted  for  a  time  it  will  be 
noticed  that  the  blood-streams  are  slowing  their  movement.  Where 
before  the  individual  corpuscles  could  with  difliculty  be  made  out  on 
account  of  their  rapid  movement,  they  are  now  readily  distinguishable. 
The  red  globules  for  the  most  part  occupy  the  centre  of  the  current, 
while  the  Avhite  are  seen  to  be  creeping  along  the  margins,  stopping  and 
clinging  to  the  vessel's  M'all,  then  letting  go  and  moving  on,  to  stop  and 
cling  fast  again.     This  is  repeated  continuously  by  the  white  globules 


INFLAMiVA  TION. 


691 


ihat  are  seen  passing  the  field  of  view.  Finally,  some  are  seen  to 
become  more  decidedly  adherent  to  the  wall,  as  if  fused  with  it,  and 
others  to  be  likewise  adherent  in  the  neighborhood.  As  this  progresses 
they  begin  to  be  piled  the  one  on  the  other ;  and  all  this  time  the  blood- 
current  is  becoming  slower  and  slower.  Some  of  the  white  globules 
that  have  seemed  to  hold  fast  are  seen  to  loosen,  and  after  swaying  for 
a  time  float  away  with  the  current.  In  all  this  movement  it  will  be 
noticed  that  the  globules  appear  to  be  developing  an  adhesiveness  that 
they  did  not  manifest  at  the  beginning  of  the  observation.  Those  that 
gradually  break  away  and  move  off  from  the  focus  of  the  irritation — 
Avhich  now  can  only  be  seen  in  this  disposition  to  stickiness — seem  to 
lose  this  property  as  they  recede  from  the  field.  This  will  give  the 
impression  that  it  is  the  vesseVs  wall  in  which  this  stickiness  is  devel- 
oped, and  not  in  the  blood-globule.  In  the  focus  of  this  action  the  adhe- 
sion of  the  white  o-lobules  will  o-q  on  until  the  entire  inner  wall  of  the 
vessel  is  completely  covered  as  with  a  pavement,  and  they  may  be  piled 
one  upon  the  other.  This  adhesion  of  the  globules  is  the  first  step  in 
the  process  that  can  be  considered  as  significant  of  inflammation.  It 
may  indeed  be  inferred  that  the  hypereemia  is  that  of  irritation,  and  will 
lead  to  inflammation ;  but  there  is  nothing  in  the  microscopic  appear- 
ance of  the  tissues  or  of  the  blood  in  the  vessels  by  which  the  diflerence 
can  be  noted  until  the  adhesion  of  the  white  globules  has  become  man- 
ifest. With  the  adhesion  of  the  white  globules,  as  it  advances,  there  is 
also  seen  a  disposition  to  the  adhesion  of  the  red.  These  at  first  occu- 
pied the  centre  of  the  blood-streams,  but  as  the  adhesion  of  the  white 
globules  progresses  the  channels  become  narrowed,  the  motion  of  the 

Fig.  384. 


Fig.  385. 


y.^'%r.^       J^h^         ^0^    ^^ 


Fig.  3S4. — A  Capillary  of  the  iMesentery  of  a  Frog  nine  hours  inflamed,  showing  detachment  of  an 
endothelial  cell,  which  is  finally  carried  off  by  the  blood-current  (high-power) :  e,  capillary  walls; 
/,  white  blood-corpuscles  or  leucocytes  external  to  the  walls;  /,  capillary  endothelia,  granular  and 
swollen  with  projecting  liellies;  ff,  cells  of  adventitia,  also  swollen  and  granular;  o,  (/,  /,  colorless 
corpuscles  ailherent  to  the  walls;  d  is  rather  firmly  bound  to  the  wall  by  means  of  a  bud  pene- 
trating the  latter ;  /,  a  corpuscle  adherent  to  the  point  of  union  of  two  adjacent  endothelial  cells; 
a,  a  white  corpuscle  adhering  tightly  to  the  upper  end  of  an  endothelial  cell,  b,  which  is  partly 
pried  out  from  its  bed  by  the  action  of  the  red  discs.  The  arrow  indicates  the  direction  of  the 
current  (Shakespeare). 

Fig.  .385.— a  White  Blood-corpuscle,  or  Leucocyte,  from  human  blood,  showing  amceboid  movement 
(Klein). 


blood  is  slow,  and  the  red  globules  turn  aside  also  and  begin  to  adhere 
to  the  walls  with  the  white.    In  this  way  the  channels  are  progressively 


692 


GENERAL  PATHOLOGY. 


filled  up  with  the  mass  of  globules,  and  the  motion  of  the  blood  is  finally 
stopped  altogether.     This  is  the  condition  of  stasis  (Fig.  384), 

Before  this  point  has  been  reached  another  phenomenon  will  have 
become  manifest — the  cUapedesis  of  the  tchite  blood-globules  from  the 
vessels  into  the  surrounding  tissues.  Under  favorable  circumstances 
some  of  the  adherent  globules  will  be  seen  to  have  sent  a  prolongation 
through  the  wall  of  the  vessel  (Fig.  384,  d),  and  gradually  the  whole 
of  the  globule  follows  it,  and  is  on  the  other  side  among  the  tissues. 
Here  its  amoeboid  movements  become  more  apparent,  and  it  is  seen  to 
move  among  the  tissues  surrounding  it  (Fig.  385).'  This  diapedesis 
now  goes  on  rapidly,  a  few  red  globules  mingling  Avith  the  white,  until 
the  Avhole  of  the  tissue  is  thickly  studded  with  them,  especially  in  the 
neighborhood  of  the  vessels.  In  the  mean  time,  the  fluid  con.'^tituents 
of  the  blood  have  also  escaped  from  the  vessels  to  so  great  an  extent 
that  the  tissue  has  become  swollen  and  clouded  to  such  a  degree  that 
the  further  following  of  the  phenomena  is  seriously  interfered  with,  so 
that  the  changes  that  finally  occur  in  the  tissue  itself  cannot  be  followed 

Fig.  386. 


v^S^^;^^^- 


%\^ 


\ 


Inflamcrl  TTuman  Onientiini.  The  plietioniena  of  inflammation  are  seen  in  the  veins  and  capillaries, 
the  condition  hcinst  normal  at  the  artery  (r),  where  ft  represents  endothelium  covering  the  tra- 
bccula  (a).  In  the  vein  (il)  there  am  many  white  corpuscles  along  the  wall :  some  of  these  are  emi- 
grating (e) ;  /,  desquamated  endothelium  ;  ff,  extravasated  red  corpuscles  (Ziegler). 

with  the  accuracy  that  scientific  precision  demands.     Fig.  386  gives  an 
idea  of  the  appearances  presented  in  inflammation  of  the  omentum. 
We  may  now  review  the  processes  we  have  thus  far  observed,  with 

'  On  account  of  the  var.iety  of  positions  in  whicli  this  cell  is  seen,  and  its  peculiar 
chanp;es  of  form,  it  has  Iteen  designated  by  a  variety  of  names.  In  tiie  blood  it  is 
called  the  white  blood-corpuscle  or  leucocyte;  in  the  tissues  outside  of  the  blood- 
vessels it  is  variously  designated  as  the  leucocyte,  amceboid  cell,  or  wandering  cell. 
These  terms  therefore  api)ly  to  the  san:e  cell-forms. 


INFLAMMATION.  693' 

the  view  of  a  better  understanding  of  their  meaning.  The  hyperpemia 
is  undoubtedly  of  the  same  nature  as  hyperseniia  in  general,  and  in 
itself  presents  no  phenomenon  other  than  that  of  the  most  simple  dilata- 
tion of  the  blood-vessels.  As  we  have  seen  (p.  692),  this  process  does 
not  lead  to  inflammation,  yet  here  we  find  it  forming  a  part  of  the 
inflammatory  condition.  This  happens  from  the  tact  that  in  this  case 
there  is  an  additional  element  not  present  in  simple  local  hyperemia. 
This  additional  element  is  tissue  injury.  The  hypersemia  can  be  in  no 
way  the  cause  of  the  inflammation,  but  the  same  causes  that  produce 
inflammation  induce  hyperaemia  as  one  of  its  phenomena.  This  hyper- 
emia may  be  induced  by  a  tissue  injury  so  slight  that  no  characteristic 
inflammation  results ;  for  it  must  be  understood  that  this  process  may 
begin  to  decline  and  go  on  to  the  resumption  of  the  normal  condition  at 
any  stage  whatsoever.  Therefore  this  is  called  the  hypercemia  of  irrita- 
tion. In  severe  inflammation  this  hypersemia  is  much  diffused  in  the 
neighborhood,  as  seen  in  the  diffusion  of  the  redness  and  heat.  It  gives 
rise  to  oedema  and  swelling  in  the  neighboring  parts,  without  the  accom- 
panying inflammatory  process,  which  in  all  of  the  phlegmonous  varieties 
is  confined  to  a  certain  area  called  the  focus. 

The  elevation  of  the  temperature,  so  far  as  this  is  capable  of  being 
determined  by  experiment,  is  due  to  the  hypersemia.  The  increase  of 
heat  is  carried  to  the  part  by  the  greater  influx  of  warm  blood ;  there- 
fore it  never  rises  higher  than  that  of  the  internal  parts,  no  matter  how 
intense  the  inflammation.  Cohnheim  caused  an  intense  inflammation  in 
one  fore  leg  of  a  dog  by  scalding,  and  hypersemia  in  the  other  by  divid- 
ing the  vaso-motor  nerves,  and  examined  the  blood  returning  from  each. 
That  from  the  hypersemic  limb  was  found  to  be  slightly  the  warmer. 
The  mass  of  experimentation  in  this  direction  confirms  this  observation. 
This  seems  to  completely  refute  the  doctrine  that  the  increase  of  heat  in 
inflammation  is  ciiused  by  the  more  active  metamorphosis  of  tissue 
through  increased  oxidation.  It  is  now  certain  that  if  increased  heat 
is  thus  developed,  it  is  to  so  slight  an  extent  as  not  to  be  appreciable  by 
the  ordinary  means  of  experimentation. 

The  swelling  is  caused  by  three  separate  factors  :  the  dilatation  (^f  the 
arteries,  capillaries,  and  veins ;  the  hypersemic  exudation ;  and  the  in- 
flammatory exudation.  The  blood-vessels,  especially  the  capillaries, 
become  widely  expanded ;  and  in  most  of  the  tissues  these  are  so 
numerous  that  this  dilatation  in  itself  must  cause  a  considerable  increase 
in  the  dimensions  of  the  part.  The  swelling  is,  however,  manifestly 
produced  chiefly  by  the  exudates,  and  Avill  be  great  or  small  as  these 
are  abundant  or  scanty.  If  the  hypersemia  is  intense  and  widely  dif- 
fused, it  will  produce  a  corresponding  amount  of  oedema  in  the  neigh- 
borhood. This,  in  many  of  the  varieties  of  inflammation,  is  sharply 
differentiated  from  the  inflammatory  focus,  showing  itself  in  the  readi- 
ness with  which  it  is  pitted  by  pressure  of  the  finger.  The  swell- 
ing in  the  part  inflamed,  on  the  contrary,  becomes  hard  and  resistant. 
This  difference  is  owing  to  the  different  character  of  the  exudates  in 
these  localities.  The  qualities  of  these  will  be  considered  under  the 
head  of  Exudates. 

The  pain  in  inflammation  is  supposed  to  be  caused  partly  by  the 


694  GENERAL  PATHOLOGY. 

injury  to  the  tissues  and  nerves  of  the  part  which  has  produced  the  in- 
flammation, and  partly  by  the  compression  and  stretching  of  the  nerves 
by  the  swelling.  The  fact  that  inflammations  occurring  in  the  same  parts 
under  diflerent  circumstances  difl'er  very  remarkably  in  this  respect 
seems  to  show  that  the  cause  has  much  to  do  with  the  production  of 
pain.  This  is  illustrated  by  comparison  of  the  pain  produced  by  a  plas- 
ter of  mustard-seed  with  that  caused  by  a  plaster  of  cantharides.  In 
many  cases  the  amount  of  pain  is  not  in  proportion  to  the  intensity  of 
the  inflammation ;  in  others  it  is  excessive.  As  a  rule,  inflammations 
occurring  in  the  firmer  tissues  are  more  painful  than  those  occur- 
ring in  parts  that  are  less  dense.  The  individual  tissues  vary  much 
as  to  the  intensity  of  the  pain  induced.  Our  knowledge  of  the  modus 
operandi  of  the  production  of  pain  is  so  limited  that  not  much  can  be 
gained  by  the  consideration  of  the  subject. 

The  exudates  are  derived  mostly  from  the  blood.  These  are  the  ser- 
ous, the  fibrinous,  and  the  corpuscular.  The  serous  exudate  is  poured 
out  from  the  dilated  blood-vessels  in  the  neighborhood  of  the  inflam- 
matory focus — in  the  region  of  hypersemia.  It  is  not  peculiar  to  inflam- 
mation, but  occurs  in  all  the  forms  of  hyperemia.  It  is  a  thin,  watery 
fluid,  diflering  slightly  from  the  plasma  of  the  blood.  It  is  but  slightly 
coagulable,  and  does  not  coagulute  in  the  tissues.  It,  however,  seems 
always  to  contain  some  fibriuogenous  matter  in  addition  to  dissolved 
albumen. 

The  fbrinous  exudate  is  peculiar  to  inflammation.  It  contains  in 
solution  a  large  amount  of  fibrinogen.  This  amount  seems  not  to  be 
constant,  but  varies  widely  in  different  cases.  It  is  always  exuded  from 
the  blood-vessels  in  the  fluid  state  and  coagulates  in  the  tissues.  It  is 
this  that  causes  the  first  clinical  diflerences  between  hypersemia  and 
inflammation ;  the  exudate  of  hyper£emia  remains  fluid  in  the  tissues, 
and  is  therefore  easily  displaced  by  pressure  of  the  flnger,  while  the 
exudate  of  inflammation  coagulates  in  the  tissues,  and  is  not  easily  dis- 
placed by  the  finger,  but  forms  a  firm  and  resistant  swelling.  This 
exudate  seems  also  to  have  more  of  the  j)roperties  of  glue  than  is  found 
in  the  blood-clot,  and  it  serves  to  bind  the  lips  of  a  wound  together  wdth 
considerable  firmness.  Most  pathologists  seem  to  regard  the  coagula- 
tion of  this  exudate  as  taking  place  in  the  same  manner  as  that  I  have 
descril)ed  for  coagulation  of  the  blood  (]).  680) ;  but  there  is  reason  to 
suppose  that  the  origin  of  the  fibrin  ferment  is  diflerent.  Instead  of  this 
being  furnished  entirely  by  tlie  destruction  of  the  white  blood-globules, 
it  may,  and  probably  is,  furnished  principally  by  the  inflamed  tissue. 
It  has  been  suggested  by  Dcnys  de  Commercy  and  Alexander  Schmidt 
that  this  coagulation  is  eflected  by  a  substance  furnished  by  the  tissues 
in  a  state  of  inflanunation,  called  by  the  latter  fihrino-plastin.  It  is 
stated  by  Cornil  and  llanvier  that  "  under  the  influence  of  an  intense 
inflannnatory  congestion  the  fil)rin()us  matter  escapes  from  the  vessels 
and  coagulates  by  uniting  with  the  fibrino-plastic  substance  derived 
from  the  cells.  The  coagulation  takes  place  suddenly  and  in  successive 
layers,  the  exudate  in  contact  with  the  tissues  alone  coagulating."  The 
amount  of  this  exudate  is  in  many  instances  very  large,  and  very  thick 
lavers  are  sometimes  found  lining  the  serous  cavities  when  their  walls 


INFLAMMATION.  695 

are  inflamed  (Fig.  387).  Within  the  tissues  this  exudate  has  but  a 
limited  duration.  It  soon  disintegrates  and  disappears.  It  first  breaks 
up  into  fine  granules,  and  finally  be- 
comes completely  liquefied. 

The  ivhite  blood-covpusdes  are  ex- 
uded (by  diapedesis)  with  the  fibrin- 
ous exudate,  and  they  always  accom- 
pany it  in  the  tissues.  Their  mo- 
tions are  probably  not  interfered  ^— 
with  to  any  considerable  extent  by 
the  coagulation.  I  have  remarked 
that  the  movements  of  the  white 
blood-globules  increased  greatly 
after  their  exit  from  the  vessels. 
This  seems  to  be  kept  up  so  far 
as  they  have  been  traced.  They  are 
uot  alwavs  confined  to  the  tissues 

ii      .              i*     •           1      J.              1         •    J.        1  Iris  inflamed  after  injury  by  a  piece  of  iron 

that    are  living,   but  wander   into  al-  thrust  into  the  eyebalho,  pigment;  fi.circu- 

mn^t    nnvfliino-    tlmf    pnmpc    in    tlipir  lar  tibres;  c,  radiating  fibres  ;(/,  inflammatory 

mObt    anyining    mat    comes    in    tneir  exudate  composed  of  coagulated  lymph  and 

WaV.         Blood-clot      is      invaded     by  leucocytes.     Leucocytes  are  seen  also  in  the 

,     •                 ,      ,            ,                    _oii     1         -^1  tissue  (X  350,  Black). 

them,  and  tliey  become  filled  with 

the  red  globules.  (See  Fig.  387.)  If  milk  is  injected,  they  take  up  the 
milk-globules  and  become  filled  with  them.  If  an  insoluble  coloring 
matter,  in  fine  powder  be  injected,  the  particles  of  this  also  are  taken 
up ;  and  much  use  has  been  made  of  this  by  pathologists  in  tracing 
the  wanderings  of  the.se  little  bodies.  If  a  frog  be  injected  wuth  finely 
granular  vermilion,  and  then  the  cornea  of  another  animal,  as  the  rab- 
bit, is  removed  and  buried  in  the  tissues  of  the  frog,  and  left  for  tAvo  or 
three  days,  it  will  be  found  on  examination  that  the  leucocytes  of  the 
frog  have  wandered  into  the  fragment  of  cornea  in  great  numbers, 
carrying  with  them  the  vermilion  as  a  mark  of  their  identity.  If  the 
swimming-bladder  of  a  fish  be  filled  with  water  which  has  been  so 
impregnated  with  common  salt  as  to  be  of  the  same  density  as  the 
blood,  and  then  buried  in  the  tissues  of  an  animal  until  inflammation 
is  established  about  it,  these  bodies  will  be  found  in  the  water,  they 
having  penetrated  the  bladder  membrane.  Nothing  but  actual  solids 
seems  to  hinder  their  wanderings,  and  wherever  they  go  they  are  con- 
tinually picking  up  any  little  particles  they  may  meet  in  their  way 
which  do  not  belong  in  the  tissues  or  have  become  useless  there. 

Tissue-changes  in  infamniation  have  been  the  subject  of  the  most  per- 
sistent inquiry  on  the  part  of  experimental  pathologists  within  the  last 
decade,  and  have  given  rise  to  much  controversy.  It  will  be  remem- 
bered that  when  we  terminated  the  study  of  inflammation  by  aid  of  the 
microscope  (p.  692)  the  tissue  had  become  so  clouded  by  the  inflamma- 
tory exudates  that  further  observation  of  the  changes  going  on  was 
impracticable.  This  fact  has  confined  this  mode  of  the  study  of  the 
subject  to  the  onset  of  the  inflammatory  process.  No  plan  has  as  yet 
been  devised  by  which  the  further  changes  which  may  occur  in  the 
tissue-cells  of  the  part  can  be  accurately  observed  during  the  life  of  the 
animal ;  thus  efforts  for  the  further  accurate  following  of  these  processes 


696  GENERAL  PATHOLOGY. 

are  siibjeet  to  the  greatest  disadvantage.  There  have  been  many  and 
various  attempts  to  overcome  this  difficuhy,  and  after  following  out 
with  some  care  all  of  the  more  feasible  of  these,  success  has  been  but 
partial.  This  is  also  illustrated  by  the  differences  of  opinion  that  exist 
as  to  the  actual  occurrences.  Difference  of  opinion  as  to  the  explana- 
tion of  the  meaning  of  phenomena  does  not  argue  faulty  observation,  but 
when  our  best  observers  differ  diametrically  in  regard  to  what  actually 
occurs,  the  morphological  changes,  we  must  suppose  that  the  observa- 
tions are  either  so  difficult  that  they  are  liable  to  be  inaccurate,  or  that 
the  morphological  changes  are  inconstant,  or  at  least  differ  under  cir- 
cumstances so  nearly  the  same  that  observers  have  failed  to  note  the 
divergence.  HoMever  this  may  be,  the  part  the  tissues  play  in  the 
process  of  inflammation  is  not  yet  so  accurately  known  that  the  best 
observers  are  able  to  harmonize  their  findings.  In  some  cases  the  differ- 
ences of  opinion  seem  to  result  from  modes  of  expression  and  in  the 
explanation  of  phenomena  rather  than  in  differences  of  observed  phe- 
nomena. Other  disagreements  occur  from  the  use  of  different  modes 
of  observation.  I  will  note  the  principal  points  of  divergence  as  I 
proceed. 

In  the  prosecution  of  this  inquiry  the  effort  has  been  to  follow  up  the 
tissue-changes  in  those  non-vascular  structures  deriving  their  nutriment 
from  blood-vessels  that  lay  at  a  consideraljle  distance.  This  is  done 
with  the  view  of  separating  as  perfectly  as  possible  the  phenomena  due 
to  tissue-change  from  those  that  are  due  to  infiltration  from  the  vascular 
system.  For  this  purpose  the  cornea  and  the  cartilages  have  usually 
been  selected.  The  healthy  eye  of  the  frog  or  other  animal  may  be 
used.  A  puncture  is  made,  and  the  serum  from  the  anterior  chamber 
is  collected  in  a  suitable  receptacle.  A  piece  of  the  cornea  is  now 
excised  and  immersed  in  the  liquid  with  the  membrane  of  Descemet 
U])])ermost,  and  the  little  chamber  so  closed  as  to  prevent  evaporation, 
with  the  view  of  preventing  changes  in  the  density  of  the  liquid.  Pre- 
pared in  this  way,  the  tissue  will  retain  its  vitality  for  a  considerable 
time,  and  give  the  best  opportunity  possible  for  the  study  of  the  normal 
structure.  So  long  as  the  life  of  the  tissue  remains  perfect,  no  structure 
whatever  can  be  made  out ;  every  part  is  perfectly  transparent ;  but  as 
the  tissue  begins  to  die  its  form-elements  come  into  view  one  after 
another — first,  the  epithelium,  then  usually  some  leucocytes  just 
beneath,  and  finally  the  cornea-corpuscles  with  their  branching  pro- 
cesses. This  observation  is  first  made  to  familiarize  the  observer  with 
the  normal  appearances.  Then  the  observations  on  the  inflamed  cornea 
are  made  in  precisely  the  same  manner  for  the  study  of  the  changes 
that  may  have  occurred.  This  is  Professor  von  Recklinghausen's 
method,  and  with  slight  variations  has  been  adopted  by  nearly  all 
who  have  made  this  class  of  observations.  Now  the  cornea  of  the 
living  animal  is  irritated  in  some  definite  way,  and  after  the  lapse  of 
a  certain  time,  which  varies  in  duration  in  different  observations,  it  is 
treated  in  the  same  way  and  the  tissue-changes  studied.  In  these 
studies  improvements  have  been  made  from  time  to  time,  the  most 
notable  of  which  is  that  by  Pi-of  Strieker,  of  the  continuous  irriga- 
tion of  the  tissues  under  examination,  with  the  serum  of  the  animal 


IN  FLA  MM  A  TION. 


697 


Fig 


from  which  they  were  taken,  this   keeping  them   for  a  longer  time 
alive. 

For  a  description  of  the  changes  which  occur  in  the  tissues  of  the 
cornea  when  studied  in  this  way  I  cannot  do  better  than  to  make  some 
quotations  from  the  admirable  article  of  J.  Burdon  Sanderson  m  Holmes's 
Hystem  of  Surgery : 

"  If  a  cornea  which  has  been  irritated  a  quarter  of  an  hour  before  by 
the  application  of  a  point  of  caustic  to  its  surface  is  examined  in  the 
same  way  (as  described  above),  the  conjunctival  epithelial  layer  can  at 
once  be  distinguished,  along  with  a  few  leucocytes,  underneath  and 
among  the  epithelial  elements.  If  an  hour  or  two  has  elapsed,  the 
proper  cornea-corpuscles  are  visible  as  dark  stellate  or  spindle-shaped 
spots  on  a  transparent  ground.  Of  these,  some  are  homogeneous,  and 
can  be  distinguished  from  the  surrounding  substance  by  a  slight  differ- 
ence of  shade.  In  others,  which  are  finely  granular,  the  processes  or 
rays  are  subject  to  slight  variations  of  contour.  These  amoeboid  move- 
ments of  the  rays,  although  very  sluggish  as  compared  with  young  pro- 
toplasm in  general,  are  rendered  much  more  active  by  subjecting  the 
preparation  to  a  stream  of  blood-serum."  .  .  .  .  "  lu  the  cornea  excised 
three  hours  after  irritation  some  of  the  corpuscles  exhibit  no  change, 
excepting  that  their  outlines  are  more  strongly  marked ;  in  others  there 
seem  to  be,  in  addition  to  the  irregular  nucleus  above  referred  to,  one  or 

more  spheroidal  bodies  which  are  im- 
bedded in  some  other  ])art  of  the  cor- 
puscle (Fig.  388).  This  appearance 
affords  the  earliest  sign  that  the  pro- 
cess which  has  hitherto  been  called 
'proliferation'  is  beginning;  that  is  to 
say,  that  the  mode  of  life  of  the  proto- 
plasmic mass  is  changing  from  the  nor- 
mal quiescent  state  which  fits  it  to  take 
part  in  a  permanent  tissue  to  the  state 
of  reproductive  or  germinating  activity 
— that  new  bodies  are  being  formed  in 
the  body  of  the  parent  mass,  to  A\hich 
such  terms  as  'germs'  or  'offspring' 
are  applicable.  A  part  of  the  original 
livino;  substance  of  the  element  begins 
a  new  life,  much  more  active  than  it 
before  possessed,  and  a  new  organic 
development.  Since  the  introduction 
of  the  method  of  observing  structural  changes  in  living  tissues,  pathol- 
ogists have  learned  that  it  is  a  constant  characteristic  of  the  change  we 
are  considering  that  the  rejuvenescent  part  or  substance  acquires  the 
property  of  contractility ;  in  other  words,  that  all  protoplasm  when 
assuming  new  life  and  beginning  new  organic  development  is  endowed 
with  the  faculty  of  amoeboid  movement. 

"  Between  the  fifth  and  twelfth  hours  after  irritation  the  cornea- 
corpuscles  become  more  distinct  and  granular,  while  tlieir  ]>rocesses 
become  thicker  and  shorter,  until  at  length  many  of  them  lose  altogether 


Cornea  of  the  Frog,  excised  three  hours 
after  irritation  (Sanderson). 


698  GENERAL  PATHOLOGY. 

their  characteristic  stellate  or  caudate  outline  and  are  converted  into  irreg- 
ular clumps.     If  the  cornea  is  exam- 
ined in  this  stage  after  treatment  with Fig.  389. 

chloride  of  gold,   it  is   seen  that  in  ^W. 
those   parts   in  which  the   structural  p  "^ 
changes  are  most  advanced  the   nor-  B 
mal  character  of  the  tissue  is  entirely  Br 
lost  (Fig.  389).     The  beautiful   net- B 
work  produced  by  the  interlacing  of  Wf: 
the    normal   corpuscles    is    no    longer  k 
visible ;  in  place  of  it  the  field  is  scat-  ^ 
tered  over  with   clumps  of  irregular  ^ 
form,  in  some  of  which  the  caudse  are  F 
represented  by  rounded  knobs,  while  m 
in  others  the  outlines  are  almost  sphe-  |r 
roidal.      Most  of  these  bodies  are  so  t^ 

crrnnnlir  tlint  tlipir  r-nntpnts!   r-nnnnf  Iip    Altered    Corpuscles  of   the  Cornea,  excised 
gidiuuar  inai  ineu^  COnrenih   Cannoi  Oe        gj^jj^t  jjo^j.^  after  irritation  (Sanderson). 

distinguished,  but  in  others  the  newly- 
formed  germs  are  plainly  visible.     The  number  of  these  germs  varies 
according  to  the  stage  of  irritation,  so  that  in  the  same  cornea  clumps 
containing  a  numerous  offspring  may  be  seen  in  one  part,  while  in  others 
the  germination  is  only  beginning  (Figs.  390,  391). 

"  That  the  interpretation  suggested  by  these  appearances  is  the  true 
one,  that  the  clumps  containing  numerous  round  corpuscles  are  nearly 

Fig.  390.  Fig.  391. 


Cornea,  sixteen   hours  after  irritation:   anioe-        Cornea,  ahout  twenty-four  hours  after  the  iiiser- 
lioid    luasses    containing    numerous    newly-  tion    of  a   fine    ligature:     masses    containing 

formed   elements   (Sanderson).  young   elements   in   the   neighborhood  of   the 

thread  (.Sanderson). 

of  the  nature  of  mother-cells,  the  observer  can  best  assure  himself  by 
returning  to  the  method  of  examination  first  described  ;  that  is  to  say, 
by  placing  the  inflamed  tissue  under  the  microscope  alive,  at  the  same 
time  stimulating  the  elements  in  question  to  increased  amoeboid  move- 
ment by  irrigation  with  serum.  It  is  tiien  seen  that  the  germs  chano-e 
their  relative  ])osition  Avith  tlie  movements  of  the  mass  of  protoplasm  in 
whicii  they  are  enclosed,  just   in  tlie  same  way  as  the  granules  and 


INFLA  HLVA  TION.  699 

ingesta  do  in  the  body  of  an  amoeba,  rolling  one  over  another  in  such 
a  manner  as  Avould  not  be  possible  if  they  were  not  really  contained  in 
the  mass." 

It  is  on  observations  of  the  same  nature  as  those  so  well  described 
in  these  paragraphs  that  Prof.  Strieker  has  founded  his  doctrine  of 
inflammation,  which  he  expresses  in  these  words  (I  quote  from  his 
article  in  the  Lifernational  Encyclopcedia  of  Surgery).  He  considers 
the  essential  phenomena  to  consist  of  "  metamorphosis  of  tissue ;  return 
to  the  eitihryonie  condition;  division  into  amoeboid  cells  of  the  masses 
which  have  become  movable ;  hence  the  destruction  cind  the  suppuration." 
This  constitutes  the  basis  of  the  doctrine  of  inflammation  as  taught  by 
Strieker  and  otliers  who  have  confirmed  his  observations.  Cornil  and 
Ranvier  {Manucd  of  Pathological  Histology,  1880)  express  the  same 
idea  in  the  following  words :  "  The  process  evolves  in  the  following 
order  :  hyjjertrophy  of  the  nucleus  ;  increase,  then  division,  of  the  jiroto- 
plasin ;  destrudion  of  the  envelojjing  membrane  of  the  cell ;  destruction 
of  the  fibrous  or  of  the  fundamental  substance  ;  production  of  fundamen- 
tal tissue;  formcdion  of  new  vessels."  According  to  this  doctrine,  the 
tissues  in  inflammation  are  stimulated  to  greater  activity  in  that  amoe- 
boid cells  are  formed  by  the  division  of  the  original  cells  of  the  part, 
and  the  cells  thus  formed  may,  in  the  height  of  the  inflammatory  pro- 
cess, become  pus-corpuscles  through  a  lowering  of  their  vitality,  as  in 
the  formation  of  abscess  on  pus-yielding  surfaces  or  mingled  in  the 
tissues  (purulent  infiltration)  ;  and  in  that  when  the  height  of  the  pro- 
cess has  passed  such  cells  as  have  not  been  too  much  reduced  in  vitality 
enter  into  the  process  of  repair.  The  diapedesis  and  wandering  of  the 
leucocytes  are  noted,  but  they  are  assigned  a  subordinate  place  in  the 
formation  of  pus  and  the  building  of  tissue  in  the  reparative  process. 
Tlie  leucocytes  are  intermingled,  but  the  principal  part,  both  in  the 
formation  of  pus  and  the  rebuilding,  is  done  by  the  cells  newly  formed 
by  the  breaking  up  of  the  old  protoplasmic  masses. 

This  doctrine  is  directly  controverted  byCohnheim  and  his  colaborers, 
who  contend  that  all  pus  is  formed  directly  from  the  diapedesis  and 
collect  ion  of  the  leucocytes  from  the  blood,  and  that  all  tissue  repair  is 
accomplished  by  the  development  of  these  cells.  These  pathologists 
regard  the  tissues  as  taking  no  part  whatever  in  the  process — that  they 
are  passive,  or  if  they  undergo  any  change  it  is  always  retrograde, 
wdiich  if  continued  results,in  the  death  of  the  cells;  in  which  condition 
they  mingle  with  the  pus  without  forming  a  characteristic  element,  but 
in  form  of  minute  bits  or  shreds  of  dead  tissue  if  not  completely  dis- 
solved. Cohnheim  particularly  has  repeated  Strieker's  observations  in 
the  most  painstaking  way  without  being  able  to  discover  the  tissue- 
changes  described,  and  upon  this  negative  evidence  reaffirms  his  doc- 
trine that  the  tissues  remain  passive.  On  the  contrary,  it  is  claimed 
that  Cohnheim  has,  in  repeating  Strieker's  experiments,  so  varied  them 
that  they  have  been  rendered  ineffective.  However  this  may  be,  there 
still  remains  a  disagreement  on  this  point,  Strieker  asserting  the  activity 
of  the  tissues  in  the  inflammatory  process,  and  Cohnheim  as  positively 
asserting  that  they  are  passive. 

Touching  the  theory  of  inflammation  held  by  Cohnheim,  it  seems 


700  GENERAL  PATHOLOGY. 

that  his  attention  has  been  arrested  principally  by  the  changes  that 
occur  in  the  vessel's  wall.  These  changes  become  obvious  in  various 
ways,  and  constitute,  in  the  microscopic  study  of  the  subject,  the  most 
prominent  factors.  As  we  have  seen  in  the  microscopic  study,  the  first 
sign  which  is  characteristic  is  the  development  of  an  adhesive  quality 
by  the  vessel's  wall,  which  causes  the  passing  blood-globules  to  linger, 
and  finally  to  adhere.  This  change  increases  until  the  passage  of  the 
globules  is  arrested  and  stasis  induced.  Then  we  have  an  increased 
permeability  of  the  wall  of  the  vessel ;  its  fluid  contents  pass  through 
in  greater  quantity  than  normal,  and  in  addition  to  this  the  white  glob- 
ules pass  through  the  wall  in  abnormal  numbers.  These  processes  have 
been  studied  in  the  most  painstaking  way  by  the  best  experimental 
pathologists,  and  I  think  most  observers  will  agree  with  Ziegler  Avhen 
he  says  that  "  the  alterations  in  the  vessel  which  take  place  in  inflam- 
mation cannot  be  histolooicallv  demonstrated,"  These  chano;es  are 
not  of  a  morphological  character,  at  least  until  very  great  progress  has 
been  made,  but  relate  solely  to  the  physiological  condition  of  the  tissue 
composing  the  vessel's  wall.  This  condition  Cohnheim  su})poses  to  be 
that  of  paralysis  produced  directly  or  indirectly  by  the  exciting  cause 
of  the  inflammation.  The  vessels  are  widely  expanded,  and  remain  so 
during  the  continuance  of  the  process.  The  adjacent  tissues  are  also 
regarded  as  paralyzed;  and  in  this  condition  take  no  part  ^^•hatever  in 
the  processes  that  are  going  forward.  This  narrows  the  inflannnatory 
process  to  a  very  few  factors  :  injury  to  the  tissues,  and  especially  to  the 
vessel's  wall,  by  any  form  of  irritation  ;  paralysis  of  the  tissues,  and 
especially  of  the  vessel's  wall,  as  a  result  of  this  injury  ;  increased  per- 
meability of  the  vessel's  wall  to  both  the  fluid  and  the  globular  elements 
of  the  blood,  which  permits  their  escape  into  or  among  the  elements  of 
the  tissue ;  the  tissues  while  in  the  state  of  paralysis  become  crowded 
wath  these  elements  to  an  abnormal  degree ;  under  these  adverse  con- 
ditions the  tissue-changes  that  occur  are  in  the  direction  of  their  death 
and  destruction  ;  pus  is  formed  by  the  aggregation  of  leucocytes,  which 
come  originally  from  the  blood  by  diapedesis  through  the  walls  of  the 
vessels,  mingled  Avith  the  results  of  the  disintegration  and  liquefaction 
of  tissue  that  may  be  destroyed.  Briefly  stated,  these  constitute  the 
phenomena  of  inflannnation,  as  held  by  Cohnheim  and  his  followers. 
The  changes  in  the  tissue-cells,  a  description  of  which  I  have  quoted 
from  the  admirable  article  of  Burdon-Sanderson,  are  denied ;  and  it  is 
claimed  that  all  ])ns-corpuscles  originate  from  the  white  blood-corpus- 
cles, and  that  all  the  tissue  of  repair  is  also  derived  from  the  same 
source  through  the  development  of  these  same  white  blood-cells. 

TJie  exciting  cause  of  wfariunation  /.s  tis.s'ue  iiijiiry.  It  is  obvious  that 
this  may  occur  in  a  multitude  of  forms.  It  may  result  directly  from  a 
wound,  and  this  may  vary  from  the  slightest  ]irick  of  a  thorn  to  the 
crushing  of  a  limb.  It  may  occur  from  a  chemical  irritant,  such  as  the 
caustics,  or  irritating  medicaments,  either  animal  or  vegetable,  as  the 
Spanish  fly  or  mustard.  It  may  occur  from  the  action  of  irritants 
that  are  carried  to  the  spot  by  the  blood  itself,  as  is  seen  in  in- 
flammation of  the  gingiva?  by  mercury  or  the  inflammation  of  the 
neck  of  the   bladder  by  cantharides.     It  may  also  be  caused  by  the 


INFLA  MM  A  TION. 


701 


presence  of  micro-organisms  that  may  gain  access  to,  and  are  able  to 
develop  in,  the  tissues,  as  in  the  case  of  the  Bacillus  anthracis  and  many 
other  microscopic  forms  that  have  been  made  known  by  recent  experi- 
mental study.  These  varying  causes  of  inflammation  give  rise  to  various 
outward  expressions  of  the  phenomena.  Some  inflammations  are  con- 
centrated within  a  very  small  area,  while  others  are  diff'use  or  are  spread 
over  a  comparatively  large  area.  Some  aflect  a  certain  tissue  only,  while 
others  may  affect  several  varieties  of  tissue  at  the  same  time.  Some 
inflammations  are  prone  to  pass  on  to  the  production  of  pus,  as  is  the 
apical  pericementitis,'  while  others  are  prone  to  terminate  in  resolution 
without  the  formation  of  pus,  as  in  erysipelas.  If  the  cause  acts  con- 
tinuously the  inflammation  will  become  chronic ;  in  case  the  action  of 
the  cause  is  but  momentary,  the  induced  inflammation  will  generally 
terminate  after  an  acute  stage  of  short  duration.  These  variations  as  to 
cause,  coupled  with  individual  idiosyncrasies  and  various  conditions  of 
body,  give  rise  to  the  different  forms  of  the  affection. 

Abscess  is  the  result  of  a  severe  but  circumscribed  inflammation  which 
causes  the  destruction  of  a  certain  area  of  tissue ;  or  leucocytes  may  col- 
lect in  large  numbers  at  the  centre  of  the  focus  of  the  inflammatory 
process,  and,  being  reduced  to  a  very  low  state  of  vitality,  become  aggre- 
gated together  and  cause  a  separation  of  the  tissues,  thus  forming  a  jnis- 
cavity.  The  differences  of  opinion  as  to  the  origin  of  these  cells  has 
been  mentioned,  and  need  not  be  further  discussed  at  present ;  for, 
whether  they  arise  in  the  one  way  or  the  other,  they  become  pus-cor- 
puscles when  reduced  to  a  certain  state  of  vitality  or  when  they  com- 
mingle with  the  contents  of  a  pus-chamber  (Figs.  392,  393).     Tissue  is 


Fig.  392. 


Fig.  393. 


Pus-cells:    a,  from  a  granulating   wound;   ft,        Pus  corpuscles :   1,n,h.  in  water;  c,  (7,  e,  after  the 
from  an  abscess  of  cellular  tissue;   c,  the  action  of  acetic  acid;  2,  divisiou  of  nuclei  (Vir- 

same  treated  with  dilute  acetic  acid ;  d,  from  chow). 

a  bone  fistula  (necrosis);  e,  migrating  cells 
(Rindfleisch). 

usually  destroyed  in  the  focus  of  an  intense  inflammation,  and,  becoming 
dissolved  or  forming  small  gangrenous  masses,  mingles  with  the  fluid 
and  corpuscular  exudates  to  swell  the  volume  of  pus.  While  this  is  in 
progress  in  the  focus  of  the  inflammation  the  exudation  of  coagulable 
lymph  is  filling  the  surrounding  tissues,  and  in  this  way  the  abscess 
is,  as  it  were,  walled  in.  The  abscess  may  continue  to  enlarge  by  a 
continuous  destruction  of  its  immediate  walls.  This  destruction  is, 
however,  usually  greatest  in  the  direction  of  the  least  resistance,  which 
brings  the  pus  nearer  the  surface,  favoring  its  discharge.  In  this 
event,  if  there  is  no  continuous  cause  of  tissue  injury  keeping  up  the 
^  Inflammation  at  the  apex  of  the  I'oot  of  a  tooth  after  the  death  of  the  pulp. 


702  GENERAL  PATHOLOGY. 

inflammatory  process,  the  walls  of  the  abscess-cavity  begin  to  be  built 
up  by  granulations,  and  healing  is  accomplished  in  the  same  manner  as 
in  any  other  breach  of  continuity. 

An  idccr'^  is  a  condition  attended  by  a  progressive  destruction  of 
tissue,  accompanied  with  the  formation  of  pus  or  ichor  in  some  of  its 
forms,  and  which  is  confined  to  the  surface  of  the  body  or  to  natural 
cavities,  as  the  mucous  surfaces.  In  this  condition  there  is  often  a 
cause  that  continues  to  act  and  keeps  up  the  discharge  indefinitely; 
otherwise  the  ulcer  heals  after  the  first  destruction  of  tissue  and  the 
formation  of  pus.  The  process  is  in  no  wise  different  in  its  modus 
operandi  from  that  taking  place  in  abscess,  except  that  of  location,  the 
one  being  within  the  tissues,  the  other  on  the  surface.  The  word  tdcer 
carries  with  it,  however,  the  idea  of  chronicity  connected  with  progres- 
sive waste  or  destruction  of  tissue. 

In  case  of  abscess  or  ulceration  Strieker  accounts  for  the  destruction 
of  tissue  at  the  focus  of  the  inflammation  on  the  theory  of  the  conver- 
sion of  the  fixed  cells  into  amoeboid  cells,  which  finally  are  converted 
into  pus-cells.  Hence  the  disapi)carance  of  tissue  and  the  formation 
of  the  cavity.  After  the  intensity  of  the  inflammatory  process  has 
passed  the  same  amoeboid  cells  Avhicli  have  been  converted  into  pus-cells 
begin  to  develop,  and  finally  form  the  tissue  of  repair.  According  to 
Cohnhcim,  all  this  is  the  work  of  the  exuded  white  blood-corpuscles. 

An  inflammation  may  begin  to  abate  at  any  stage  of  the  process. 
"  The  repair  of  the  damaged  vessel-wall  is  brought  about  by  the  vis 
medicatrix  of  the  blood  itself"  (Ziegler).  If,  when  the  injurious  influ- 
ence has  ceased,  the  blood  brings  to  the  injured  vessel  the  material 
required  for  restoring  it  to  its  normal  state,  the  inflammatory  disturb- 
ance comes  to  an  end,  the  exudation  ceases,  and  the  process  of  healing 
is  begun.  In  the  earlier  stages  of  the  process  this  consists  in  the 
restoration  of  the  walls  of  the  vessels  to  their  normal  state  of  compara- 
tive impenetrability,  and  the  removal  of  the  exudates  by  the  lymphatics 
and  blood-vessels.  If  a  small  amount  of  tissue  has  been  injured,  it  is 
reproduced,  the  muscle-cell  producing  new  muscle,  periosteum  produ- 
cing new  bone,  and  so  on  (Ziegler). 

This  manner  of  reproduction  is,  however,  confined  to  very  small 

'  There  seems  to  be  considerable  confusion  in  the  use  of  this  word.  Many  make  no 
difference  between  the  processes  of  ulceration  and  suppuration,  while  others  distinguish 
sharply  between  them.  Loomis  {Principles  cuid  Praclice  of  Medicine]  regards  suppu- 
ration and  ulceration  as  the  same  processes,  except  that  that  M'hicli  forms  a  cavity,  a 
pocket  within  the  tissues,  is  an  abscess,  and  that  which  is  limited  to  tlie  surface  is  an 
ulcer. 

Sir  .James  Paget  says:  "Ulceration  is  that  part  or  effect  of  an  inflammatory  process 
in  which  the  materials  or  inflamed  tissues,  liquefied  or  degenerate,  are  cast  oli'  in  solu- 
tion or  very  minute  ]iarticles  from  the  free  surfaces,  or,  more  rarely,  are  absorbed  from 
the  suriVice  of  tlie  body"  (Hobnes'fi  Sysiem  nf  Surgery).  In  this  article  beholds  dis- 
tinctly tlie  doctrine  (if  I  understand  him  aright)  tiiat  laudable  pus  is  not  foi'med  in 
ulceration.  It  nuist  be  ichor  or  something  lower  than  laudable  pus;  and  as  "the  ulcer 
tends  to  heal  its  discharge  becomes  more  like  laudable  jius." 

W.  H.  Van  Buren  {International  Eiiryclojicedia  of  Surgery)  regards  that  process  of 
destruction  of  tissue  by  which  the  contents  of  an  abscess  make  their  way  to  the  surface 
as  ulceration,  and  says :  "  Under  all  possible  circumstances  this  molecular  death  is  the 
essential  feature  of  the  i)rocess  which  we  call  ulceration." 

Billrotii  (Surgical  Patholoyy)  says:  "An  ulcer  is  a  wounded  surface  which  shows  no 
tendency  to  lieal." 


INFLAMMATION.  703 

araounts  of  tissue.  If  any  considerable  masses  are  to  be  re-formed,  it  is 
accomplished  by  a  process  entirely  different.  In  the  explanation  of  this 
process  there  is  again  encountered  a  divergence  of  views  among  pathol- 
ogists, which,  however,  has  its  foundation  in  the  differences  of  opinion 
already  explained.  It  amounts  to  simply  this  :  Is  the  regeneration  of 
the  lost  parts  accomplished  by  the  return  of  the  normal  fixed  cells  to 
the  embryonal  form,  the  amoeboid  state,  and  the  redevelopment  of  these, 
or  is  it  accomplished  by  the  development  of  the  leucocytes  into  con- 
nective-tissue cells  ?  I  need  not  again  enter  this  field  of  controversy, 
as  all  agree  that  the  new  tissue  formed  in  the  healing  of  wounds  is  by 
the  development  of  the  amoeboid  cells,  which  according  to  the  one 
theory  are  produced  from  the  fixed  cells,  and  according  to  the  other 
from  the  leucocytes.  The  new  tissue  formed  is  called  granulation- 
tissue,  inflammatory  new  formation,  scar-tissue,  tissue  of  repair,  etc. 
The  formation  of  this  tissue  takes  place  in  this  wise :  If  the  surfaces 
of  a  wound  be  examined  twenty-four  hours  alter  it  is  inflicted,  they 
will  be  found  intensely  red  and  more  or  less  swollen.  The  tissue- 
elements  are  still  distinguishable,  but  have  become  somewhat  blurred. 
On  the  second  or  third  day  the  original  tissue  is  hidden  from  view, 
being  covered  with  a  more  or  less  copious  secretion,  which  at  first  is 
inclined  to  dry,  if  not  too  abundant,  into  a  semi-gelatinous  film,  which, 
as  the  secretion  becomes  better  established,  changes  to  a  creamy  con- 
sistence and  assumes  a  yellowish  hue.  This  is  composed  of  coagulable 
albuminous  matter  mixed  with  numerous  corpuscular  elements.  The 
latter  are  amoeboid  cells  that  have  sunk  so  low  in  the  scale  of  vitality 
as  to  be  incapable  of  further  development,  and  have  become  pus-corjjus- 
cles.  Here  and  there  over  the  surface  of  the  wound,  if  it  is  doing  well, 
will  be  seen  little  red  prominences.  These  are  granulations,  which  are 
composed  almost  entirely  of  the  same  amoeboid  cells,  which  have  taken 
on  a  redevelopment  and  are  destined  to  form  the  new  tissue  for  the 
filling  of  the  wound.  Thus  the  pus  and  the  newly-formed  tissue  are 
developed  from  the  same  class  of  cell-forms ;  the  one  sinks  so  low  in 
the  scale  of  life  that  it  cannot  recuperate,  and  the  other,  being  more 
favorably  placed,  lives  and  grows.  These  cells  result  from  the  inflam- 
mation set  in  action  by  the  injury  to  the  tissues  in  the  production  of 
the  wound,  through  which  the  adjacent  tissue  becomes  infiltrated  with 
leucocytes,  and  probably  others  are  developed  by  changes  in  the  fixed 
cells  as  well,  and  both  go  to  the  formation  of  either  pus  or  granulations 
as  they  may  be  more  or  less  favorably  placed.  It  would  seem  that  the 
so-called  leucocyte  is  the  proper  reparative  cell  of  the  connective  tissues 
belonging  to  them  and  having  its  home  among  them.  The  name  of 
white  blood-corpuscle  is  a  misnomer.  The  wandering  of  the  cell  by 
way  of  the  blood-streams  is  perfectly  natural  and  normal.  These  cells 
wander  through  the  tissues  at  will,  and  are  found  everywhere,  in  all  of 
the  tissues  and  in  the  blood.  They  are  most  probably  a  product  of  the 
connective-tissue  group,  and  in  their  development  always  form  connective 
tissue.  I  therefore  regard  each  of  the  views,  although  they  seem  to  stand 
over  against  each  other,  as  substantially  correct,  but  only  representing  a 
part  of  the  phenomena  of  the  inflammatory  process.  The  combination  of 
the  two  is  necessary  to  the  complete  explanation  of  the  cycle  of  events. 


704 


GENERAL  PATHOLOGY. 


"Wherever  there  is  trouble  in  the  tissue  the  leucocytes  are  congregated, 
they  being  attracted  by  the  changes  that  take  place  in  the  fluids  of  the 
part.  Thus  the  stickiness  of  the  vessel's  wall  brought  about  by  changes 
in  the  cells  under  the  influence  of  an  irritant  arrests  those  that  are  in 
the  circulation,  and  others  are  promptly  formed  by  the  changes  in  the 
cells  of  the  injured  tissue. 

We  may  now  pursue  the  development  of  these  cells  in  the  forma- 
tion of  the  granulations  and  subsequently  of  the  tissue  of  repair.  The 
whole  life-history  of  these  cells  has  not  yet  been  made  out,  but 
much  in  regard  to  their  growth  is  known.  The  brilliant  experiments 
of  Ziegler  will  illustrate  the  subject  best.  This  experimenter  placed 
together  bits  of  glass,  one  of  which  was  a  cover-glass  used  in  micro- 
scopic observations,  so  as  to  leave  a  space  of  a  very  small  fraction  of  a 
line  between  them,  and  these  he  buried  in  the  flesh  of  a  living  animal. 
The  presence  of  this,  together  with  the  injury  caused  in  placing  it, 
produced  sulficient  inflammatory  action  to  bring  a  number  of  wan- 
dering cells  to  the  spot.  These  crept  in  between  the  bits  of  glass, 
and  developed  there.  And  as  these  were  so  close  together,  the  cells 
were  necessarily  in  a  single  layer,  which  placed  them  well  for  micro- 
scopic study.  These  bits  of  glass  were  removed  from  day  to  day 
and  the  development  of  the  cells  studied.     Fig.  394  is  an  illustration 


Granulation-cells:  a  and  Oj,  leucocytes;  h.  h,  various  formative  cells;  c,  formative  cell  with  two 
nuclei;  e^,  with  many  nuclei;  rf,  f/,  rf,  formative  cells  developing  connective  tissue;  e,  complete 
connective  tissue  (X  500,  picrocarmine  preparation,  Ziegler). 

of  these,  showing  the  progressive  changes  of  form  of  the  individual 
cells  in  the  formation  of  tissue,  a  is  the  form  of  the  cell  when  it  first 
takes  its  place  as  a  granulation-cell ;  a,  shows  the  same  cell  as  degener- 
ated into  a  pus-cell ;  6  shows  various  forms  assumed  by  the  cells  in  the 
course  of  their  development  into  tissue.  In  watching  these  from  day  to 
day  it  is  found  that  certain  of  the  cells,  presumably  the  weaker,  disap- 
pear ;  and  Ziegler  supposes  that  they  are  devoured  by  the  stronger  or 


INFLAMMA  TION. 


705 


that  tlieir  substance  goes  to  feed  them.  In  other  instances  several  cells 
seeni  to  flow  together  and  form  one  with  many  nuclei,  as  seen  at  c,  Cj,  the 
so-called  giant-cells.  Within  my  personal  observation  this  form  of  cell 
has  occurred  mostly  in  connection  with  secondary  neoplasms.  They 
would  probably  occur  in  connection  with  Ziegler's  glass  slips,  but  I 
doubt  their  general  presence  in  healthy  granulations.  It  will  be  seen  by 
studying  the  illustration  how  the  cells  increase  in  volume  and  put  out 
long  slender  processes.  By  the  interlacing  of  these  with  similar  pro- 
cesses from  the  neighboring  cells  they  become  very  firmly  united  into 
tissue.  But  this  is  not  all.  At  d  the  cells  are  shown  still  further 
developed,  and  in  the  forms  to  the  right  in  connection  with  this  letter 
it  will  be  noticed  that  the  granular  area  of  the  cell  has  diminished  and 
is  connected  with  a  finely  fibrous  substance,  which  is  also  seen  at  e,  which 
represents  the  developed  tissue.  This  fibrous  material  is  a  connecting 
substance  which  finally  forms  the  bulk  of  the  reparative  tissue,  the 
original  cell  remaining  as  a  delicate  spindle-cell. 

If  a  wound  be  watched  from  day  to  day,  it  will  be  seen  how  it  is  pro- 


ao9'; 


section  through  the  border  of  a  Healiiif;  Surface  of  Granulations  :  n,  secretion  of  pus  •  ft  granulation- 
tissue,  with  capilhiry  loops,  whose  walls  consist  of  a  longitudinal  layer  of  cells  decre  I'sing  in  thick- 
ness from  within  outward;  c,  begiiniingof  the  cicatricial  formation  in  the  deep  layers  (spindle- 
cell  tissue) ;  (/.cicatricial  tissue;  ^  complete  epithelial  covering;  the  central  layer  of  cells  consists 
ot  serrated  cells;  y,  young  epithelial  cells;  g,  zone  of  ditlerentiation  (x  30U,  Itiiidfleisch). 

gressively  filled  up  by  the  growth  of  the  granulations.  The  cells  are 
piled  the  one  on  the  other  in  the  form  of  little  clumps  which  may  be 
seen  with  the  naked  eye,  and  it  is  these  that  have  given  the  name  of 

Vol.  I.— Jo 


706 


GENERAL  PATHOLOGY. 


"  granulations."  This  seems  to  require  that  new  cells  be  continually 
approaching  the  surface  and  taking  their  place  at  the  very  outer  surface 
of  the  granulations.  In  the  microscopic  study  of  granulation-tissue  it 
is  found  that  the  cells  actually  do  this ;  that  is,  the  y<jung  cells  are  on 
the  surface  (Fig.  395) ;  but  what  portion  of  them  wander  to  this  posi- 
tion from  the  tissues  beneath  or  by  way  of  the  blood-vessels,  and  what 
portion  are  developed  in  mtu  by  multiplication,  is  still  an  open  question. 
Great  multitudes  of  the  cells  are  separated  from  the  surface  as  pus-cells, 
and  in  this  May  are  lost. 

When,  in  the  growth  of  the  granulations,  two  opposite  sides  approxi- 
mate, and  finally  touch  each  other,  the  cells  coalesce  in  the  same  man- 
ner as  the  cells  that  are  piled  the  one  on  the  other,  and  thus  union  is 
established  and  the  opposing  walls  of  the  wound  are  united.  It  there- 
fore follows  that  if  the  o])posing  surfaces  of  a  wound  are  placed  in  per- 
fect approximation,  the  first  cells  that  take  their  places  at  the  surface 
unite  the  wound,  and  the  time  required  and  the  expenditure  of  vital 
energy  are  reduced  to  the  minimum.  In  what  is  known. as  healing  by 
first  intention  the  wound  is  sealed  by  the  plastic  exudate  which  I  have 
described  as  first  covering  the  surface  of  the  open  wound  as  a  semi-gelat- 
inous film.  This  holds  the  adjacent  walls  together,  and  the  cells  that 
perform  the  true  reparative  process  find  within  this  gelatinous  substance 
the  best  possible  conditions  for  their  development,  so  that  in  this  posi- 
tion none  are  lost  in  the  form  of  pus-cells. 

The  development  of  blood-vessels  keeps  even  pace  with  the  formation 
of  the  granulations,  so  that  every  little  granule  or  clump  of  cells  has  its 
vascular  loop  which  carries  the  nutritive  fluid  directly  to  it.  The  vas- 
cular network  of  vessels  that  forms  in  granulation-tissue  is  exceedingly 
rich  and  intricate.     Some  idea  of  this  is  shown  in  Fig.  396.    The  man- 


FiG.  39G. 


New  Formation  of  Rlood-vcssels  in  a  Oranulatinfj  AVound  (after  Arnold). 

ner  of  the  formation  of  these  vessels  is  jirobably  the  same  in  all  tissue 
that  is  in  the  process  of  development,  whether  it  be  in  the  original 
growth  or  in  the  tissue  of  repair.  This  is  by  a  process  of  budding  from 
the  blood-vessels  already  formed.  It  always  takes  its  rise  from  the 
capillary  loops,  the  bud  from  one  always  joining  with  one  from  a  neigh- 


IXFLAMlLi  TION. 


707 


Fig.  397. 


boring  loop,  as  shown  in  Fig.  395.  These  loops  are  formed  as  solid 
processes,  and  hollowed  out  afterward  by  the  removal  of  the  central 
substance  of  the  cells.  This  process  of  the  formation  of  ducts  takes 
place  in  the  same  manner  in  the  vegetable  Idngdom,  and  is  easily 
observed,  especially  in  the  sprouting  of  seeds.  If  a  number  of  grains 
of  corn  be  planted  in  damp  earth  under  suitable  conditions  for  germi- 
nation, and  every  twelve  hours  sections  for  microscopic  examination  be 
made  of  two  of  these  (one  cut  lengthwise  and  the  other  cross^vise  of  the 
germ),  the  process  of  the  formation  of  the  ducts,  which  are  hollowed  out 
in  the  same  manner  as  the 
blood-vessels  in  animals,  may 
be  followed  with  the  greatest 
accuracy.  In  Fig.  397,  at  «, 
I  have  represented  a  vow  of 
large  cells  as  they  appear  in 
the  germ  of  the  grain  twelve 
hours  after  planting,  and  at 
b  the  cross-section  is  shown. 
These  grow  in  length,  and 
their  number  is  increased  by 
fission.  After  a  certain  time 
their  growth  seems  to  cease; 
they  begin  to  lose  the  central 
part  of  their  substance  and 
are  rapidly  converted  into 
tubes,  the  walls  of  the  cells 
alone  remaining,  which  are 
joined  together  end  to  end. 
At  c  and  d  of  the  figure  these 
are  shown  as  they  appear  on 
the  fifth  day.  This  seems  to 
conform  very  perfectly  to  the 
manner  of  formation  of  the 
first  blood-vessels  in  the  de- 
velopment of  the  foetus,  and  is  much  easier  of  accurate  study. 

In  the  animal,  after  the  formation  of  vessels  is  once  begun,  all 
new  vessels  are  formed  from  buds  given  off  from  cells  of  the  existing 
vessels;  These,  though  they  unite  A\'ith  similar  buds,  seem  to  be  per- 
fectly fused  together  as  a  single  cell.  After  the  hollowing  out  is  accom- 
plished, however,  the  formed  vessel  presents  the  usual  appearance  of 
epithelial  plates  joined  together  for  the  formation  of  its  walls. 

Granulation-tissue  during  its  formation  is  very  soft  and  friable.  The 
capillary  loops  come  so  near  the  surface,  and  their  walls  are  so  thin, 
that  the  slightest  touch  is  likely  to  cause  hemorrhage,  and  the  tissue 
contains  much  fluid.  As  it  grows  older  and  the  cells  begin  to  assume 
the  spindle  shape  and  form  the  fibrous  connecting  substance,  it  becomes 
much  drier  and  firmer.  Many  of  the  capillary  loops  that  were  formed 
during  the  growth  of  the  granulalions  are  obliterated  and  the  tissue 
shrinks,  drawing  the  surfaces  of  the  wounds  together,  usually  in  such  a 
way  as  to  diminish  its  surfaces  and  lessen  the  remaining  scar.     This 


Formation  of  the  Ducts  in  the  Sprouting  of  a  Grain  of 
Corn,  in  sections  cut  twelve  hours  aftir  planting.  A 
series  of  large  solid  cells  are  seen  placed  end  to  end,  as 
at  11.  b  is  a  cross-section  of  the  same,  showing  the  cell 
to  be  finely  granular,  and  staining  brings  the  nucleus 
into  view.  It  is  shown  surrounded  by  the  neighboring 
cells,  c  shows  the  same  cell  converted  into  a  tube  by 
hollowing  out.  Fifth  day:  </,  the  duct  on  the  iil'th  day, 
showing  the  elongated  cells  hollowed  out,  forming 
a  tube,  the  walls  of  which  show  "  duct-uiarkiugs " 
(Black). 


GENERA  L  PA  THOL  0  G  Y. 


tendency  to  shrinkage,  while  in  the  main  beneficial,  sometimes  produces 
disastrous  results.  This  is  seen  most  prominently  in  case  of  burns  or 
other  injuries  involving  a  large  extent  of  surface,  in  which  the  shrink- 
age of  the  cicatrix  often  produces  distortion.  This  shrinkage  continues 
for  a  considerable  time  after  the  complete  cicatrization  of  the  wound. 

The  reproduction  of  epithelium  is  always  by  proliferation  from  the 
existing  epithelial  cells  at  the  margin  of  the  wound  or  by  division  of 
young  cells.  In  normal  conditions  the  epithelial  cells  are  continually 
being  shed,  and  are  as  constantly  being  regenerated  by  the  multiplica- 
tion and  growth  of  cells  from  beneath.  These  cells  are  never  produced 
from  connective-tissue  cells,  but  always  from  the  epithelial  cell ;  hence 
in  the  healing  of  wounds  the  epidermis  that  finally  covers  in  the  gran- 
ulations is  projected  from  the  margins.  This  is  seen  in  the  form  of  a 
very  delicate  film  at  first  extending  a  little  way  inward  all  around  the 
wound.     Fig.  398  gives  the  microscopic  characters  of  such  a  film  froiu 

Fig.  398. 


Regeneration  of  Epithelium  in  Cornea  of  a  Rabbit-  i.  fibioub  tian^foiniation  of  nuelens;  fi,  partial 
separation  of  the  hbres  and  hour-fjlass  change  of  nucleus  in  the  process  ol  division:  c,  complete 
divi^sion  of  nucleus;  (/,  complete  division  of  cell  (Eberth). 

the  cornea  of  the  rabbit,  and  illustrates  the  process  of  division  of  the 
young  cells.  This  increases  from  day  to  day  in  width  until  all  of  the 
granulations  are  covered  in,  the  secretions  cease,  and  the  wound  is 
healed.  For  some  time,  however,  the  layer  of  epithelium  remains  very 
thin  and  soft.  By  degrees  this  becomes  thicker  and  denser,  until  in 
most  small  wounds  it  approac-hes  closely  the  characters  of  the  normal 
})arts,  but  in  large  wounds  it  usually  remains  permanently  much  thin- 
ner than  normal. 

Tranxphntfifion  of  epithelium  to  the  surface  of  granulations  is  prac- 
tised for  the  ])urpose  of  l)ringing  about  a  more  speedy  cicatrization  of 
the  wound.  This  little  operation  illustrates  an  important  point  in  the 
]ihvsiology  of  these  cells  which  determines  their  behavior  in  pathological 
conditions.     When  the  epithelium  is  completely  destroyed  over  a  con- 


INFLAMMATION. 


709 


siderable  surface,  as  by  a  burn,  no  epithelium  is  produced  on  that  sur- 
face except  as  it  is  projected  from  the  margins  \vhere  the  epithelium  is 
intact.  Now,  if  the  smallest  bits  of  the  epidermis  from  any  portion  of 
the  body  of  the  same  individual  or  of  another  be  clipped  off  and  laid 
on  the  granulations,  it  will  be  observed  that  within  a  few  days  a  film 
of  epithelium  will  spread  from  this  point.  By  placing  many  of  these 
it  is  possible  to  cause  a  large  wound  to  cicatrize  much  sooner  than  it 
would  otherwise  do.  In  this  way  the  peculiar  epidermis  of  the  white 
man  may  be  transplanted  to  the  negro,  producing  a  patch  of  white  skin, 
or  vice  versd.  This  shows  that  these  cells  have,  independent  of  the 
organism  to  which  they  belong,  a  life  and  individuality  of  their  own 
which  they  are  capable  of  carrying  into  strange  places  and  of  asserting 
among  strangers. 

The  organization  of  blood-cfot,  so  called,  is  a  process  of  great  import- 
ance, not  only  as  a  matter  of  scientific  inquiry,  but  also  in  its  clinical 
bearings.  The  blood-clot  meets  the  surgeon  at  every  turn,  and  its  clin- 
ical importance  cannot  well  be  over-estimated.  If  he  ties  an  artery,  he 
depends  on  the  so-called  organization  of  the  blood-clot  that  forms  in 
its  interior  to  hold  against  the  blood-pressure  after  the  ligature  has 
sloughed  out  or  has  been  absorbed.     If  a  blood-clot  forms  in  a  wound 


Fig.  399. 


Fig.  400. 


MhhSk 


Fig.  399.— Absorption  of  Blood-clot.  Section  through  the  margin  of  a  clot  formed  among  the  tissues  by 
extravasation,  showing  the  growth  of  granulations  by  which  it  is  removed:  o,  n,  portions  of  clot ; 
b.  b,  original  tissue;  c,  c,  granulations  springini:  from  the  original  tissue  and  projecting  into  the 
clot;  d,  <1,  wandering  cells  or  leucocytes  that  seem  to  have  taken  red  blood-discs  into  their  inte- 
rior.    (Section  cut  in  gum  arable  and  stained  with  ha.'matoxylin  ;  X  350,  Black. 1 

Fig.  4U0.— Absorption  of  Blood-clot.  Section  through  the  margin  of  a  blood-clot  formed  by  extravasation 
in  the  tissues,  showing  the  growth  of  the  granulations  by  which  it  is  removed:  a,  poriion  of  clot, 
showing  fibrinous  reticulum  enclosing  the  blood-discs,  which  ;ire  much  shrunken,  and  occasional 
wandering  cells  interspersed;  h,  newly-formed  tissue  projecting  into  the  mass  in  the  form  of  pro- 
ces.ses.  which  are  covered  with  young  granulation-ceds,  c.  c.  The  granulations  are  in  intimate 
relation  with  the  clot.    (Section  cut  in  gum  arable  and  stained  with  hematoxylin  ;  X  350,  Black.) 

after  it  has  been  closed,  what  is  its  significance?  how  is  it  disposed  of? 
and  what  is  its  effect  on  the  healing  of  the  wound  ?     These  questions 


710 


GENERA  L  PA  THOL  0  G  Y. 


■will   now  admit  of  answer,  thanks  to  the  experimental  study  of  recent 
years. 

AVhen  a  blood-clot  has  formed  from  any  cause  in  the  midst  of  tissues 
of  fair  functional  activity,  a^\•ay  from  contact  with  the  air,  and  there- 
fore safe  from  contamination  from  without,  it  causes  a  slight  inflamma- 
tory process  to  be  developed  in  its  immediate  neighborhood.  This 
brings  to  the  spot  numbers  of  the  amoeboid  cells,  which  actively  attack 
the  clot  in  all  its  parts,  but  especially  its  margins.  In  addition  to  the 
cells  that  wander  free  into  the  clot,  granulations  spring  out  into  it  from 
all  sides,  and  as  they  grow  the  clot  disappears  to  give  them  room  (Figs. 
399  and  400).  The  clot  is  digested,  dissolved,  and  removed.  Thus  the 
connective-tissue  forming  cells  grow  into  the  substance  of  the  clot  as  they 
grow  into  the  meshes  of  the  sponge  in  the  sponge  graft,  and  the  clot  is 
removed  by  solution  in  the  same  manner  as  the  sponge.  In  this  manner 
very  large  clots  are  many  times  removed,  leaving  in  their  stead  a  quan- 
tity of  newly-formed  tissue  that  is  of  no  value.  In  time  this  also  shrinks 
aM'ay  partly  and  is  partly  absorbed,  so  that  in  the  end  but  little  remains 
to  show  that  there  has  been  a  clot  in  the  lo(;ality.  The  clot  itself  has  no 
power  of  organization  any  more  than  the  sponge  in  the  sponge  graft, 
but  as  the  sponge  it  acts  as  a  stimulant  to  the  growth  of  the  granula- 
tions by  which  it  is  removed.  It  is  possible  also  that  in  some  positions 
the  blood-clot  may,  as  the  sponge  graft,  act  as  a  ladder  on  tchich  granu- 
lations may  climb,  and  in  this  manner  assist  in  the  formation  of  tissue 
for  the  filling  out  of  lost  parts ;  but  in  this  respect  it  is  much  inferior 
even  to  the  sponge  in  the  character  of  the  new  tissue  produced,  which 
is  usually  of  a  very  loose  texture  and  shrinks  together  to  an  extreme 
degree  (Fig.  401). 

Fig.  401. 


<  k 


From  the  Cross-section  of  an  Arterial  Thrombus  of  Three  iSIonths:  /,  luraina  of  vessels  in  the  throm- 
bus, X,  X,  X  (X  300,  Riudfleisch). 

In  order  that  the  granulations  shall  grow  in  blood-clot  it  must  remain 
a.septic.  Therefore  it  usually  hapjiens  that  clots  which  are  exposed  to 
the  air  are  decompo.sed,  and  constitute  a  much  greater  hindrance  to  the 
healing  ]iroccss  than  in  subcutaneous  wounds.  It  has  been  shown  by 
Ijister  that  blood-clots  do  not  decompose  as  readily  as  mo.st  other  sub- 
stances ;  yet  clinical  ex]x'ricnco  demonstrates  that  in  very  many  cases 
their  decomposition  seriously  interferes  with  the  process  of  granulation 
by  becoming  the  foci  of  septic  ])rocesses.  If  the  clot  remains  aseptic, 
it  retards  the  jirocess  of  healing  by  the  time  required  to  fill  it  with 
granulations.     I  think  a  close  comparative  study  will  show  that  granu- 


FEVER.  711 

lations  form  less  rapidly  in  a  blood-clot  than  in  the  filling  of  an  open 
wound,  and  certainly  the  tissue  formed  is  usually  much  less  perfect. 
Formerly  it  was  held  that  the  substance  of  the  clot  became  itself  tis- 
sue. This  was  the  conclusion  arrived  at  by  O.Weber,  Budnoif,  and 
others,  but  recent  studies  have  shown  so  plainly  that  the  organization 
takes  place  in  the  manner  I  have  just  stated  that  it  is  accepted  by 
pathologists  generally. 

Fever. 

Fever  is  a  condition  of  tlie  general  system  characterized  by  elevation 
of  the  temperature  and  attended  with  increased  frequency  of  the  pulse. 
This  condition  has  no  known  anatomical  characters ;  at  least,  none  that 
seem  really  essential  to  the  condition  of  fever.  It  seems  to  consist  of  a 
disturbance  of  the  function  of  heat-production,  or  of  the  relations  that 
normally  exist  between  the  functions  of  heat-production  and  heat-dissi- 
pation. Fever  occurs  as  an  accompaniment  of  many  and  various  lesions ; 
and  so  common  is  this  that  it  is  expected  to  follow  any  lesion  of  con- 
siderable gravity,  and  in  such  cases  may  be  considered  as  symptomatic. 
Fever  occurs  also  as  the  forerunner  and  accompaniment  of  most  o^  the 
grave  inflammations,  such  as  pneumonitis  or  lung  fever,  inflammation 
of  Peyer's  patches  in  typhoid  fever,  and  various  other  forms  of  disease 
known  as  the  essential  fevers,  so  called  from  the  fact  that  the  condition 
of  fever  seems  to  be  the  prominent  factor  in  tlie  disease.  It  also  pre- 
cedes and  accompanies  the  inflammation  of  the  skin  or  eruption  in  the 
exanthems,  as  in  smallpox,  scarlet  fever,  measles,  etc.  Fever  usually 
occurs  after  the  infliction  of  wounds  or  surgical  procedures  which  pro- 
duce tissue  injury  of  any  conceivable  kind  in  which  much  tissue  is 
involved.  This  is  the  more  certain  of  occurrence  if  the  wound  is  open 
to  the  surface.  This  form  of  tlie  disorder  is  known  as  wound  fever  or 
surgical  fever.  Fever  is  also  liable  to  occur  without  any  appreciable 
lesion  of  any  known  kind  whatever  that  we  are  able  to  determine  by 
our  physical  senses,  either  as  a  forerunner,  accompaniment,  or  sequel. 
A  person  may  be  attacked  with  a  feeling  of  languor,  perhaps  have  some 
headache,  abnormal  dryness  of  the  nmcous  membranes,  some  thirst,  etc., 
and  a  thermometer  placed  under  the  tongue  may  show  a  rise  in  the 
bodily  temperature  of  from  three  to  five  degrees.  At  the  same  time  the 
pulse  may  rise  in  frequency  from  75  beats  in  the  minute  to  100  or  even 
120.  These  symptoms  may  continue  from  six  to  twenty-four  hours, 
and  then  subside  with  complete  restoration  to  health,  leaving  no  sign 
whatever  of  any  disease  connected  with  or  explaining  this  disturbance 
of  function. 

From  what  has  been  said  it  would  seem  evident  that  fever  does  not 
arise  from  any  one  specific  morbific  cause :  it  may,  and  evidently  does, 
arise  from  a  variety  of  causes.  As  throwing  light  on  this  point,  it 
might  be  useful  to  inquire  into  the  particular  tissue  prominently 
affected,  but  as  there  are  no  anatomical  lesions  yet  discovered  that 
are  essential  to  this  condition,  the  inquiry  must  be  directed  by  the  dis- 
turbance of  function.  This  leads  to  the  questioning  of  the  particular 
systems  that  make  up  the  community  of  systems  that  combine  to  form 


712  GENERAL  PATHOLOGY. 

the  sum  of  tlie  functional  activities.  In  this  inquiry  we  will  be  more 
or  less  troubled  by  uncertainties.  The  older  pathologists  seem  to  have 
regarded  the  nervous  system  as  the  one  specially  aliected,  but  recent 
investigations  point  to  the  blood  as  being  primarily  at  fault,  or  at  least 
indicate  that  fever  results  from  some  form  of  poison  that  has  gained 
access  to  the  blood  and  is  circulating  in  it.  Recent  experiments  demon- 
strate that  the  injection  of  pure  healthy  pus  into  the  veins  of  the  dog 
produces  fever  with  certainty  and  promptness,  and  that  the  fever  thus 
induced  runs  a  very  regular  course,  passing  away  in  two  days,  more  or 
less,  according  to  the  amount  of  pus  injected  (Senator).  In  this  case  it 
would  seem  that  fever  has  a  material  cause,  in  that  a  substance  is  in  the 
blood  that  in  some  way  interferes  with  the  proper  and  normal  func- 
tions so  as  to  increase  its  temperature.  This  increase  in  the  tempera- 
ture is  the  one  essential  factor.  Increased  frequency  of  the  pulse  is  a 
usual  accompaniment  of  fever,  but  is  not  invariably  i)resent,  and  may 
be  induced  by  various  causes  independent  of  fever.  AVe  may  and  do 
have  fever  without  increased  frequeufy^  of  the  pulse,  and  we  may  reduce 
the  frequency  of  the  pulse  during  the  existence  of  fever  without  mate- 
rially altering  the  temperature.  It  is  well  known  that  during  the  exist- 
ence, of  fever  the  pulse-rate  may,  by  the  administration  of  veratrum 
viride,  be  reduced  without  lowering  the  temperature  as  expressed  by 
the  thermometer.  I  recall  a  case  of  typhoid  fever  in  a  boy  of  twelve 
years,  m  ho  when  I  first  saw  him  had  a  pulse-rate  of  70  to  the  minute, 
and  at  the  same  time  a  body-temperature  of  107°  F.,  as  registered  by  a 
thermometer  in  the  axilla.  In  this  case  veratrum  viride  had  been  given. 
Occasionally,  even  where  no  heart  sedative  has  been  administered,  fever 
may  be  seen  without  a  frequent  pulse,  though  this  is  evidently  rare.  It 
is  not  very  uncommon,  however,  to  see  the  temperature  out  of  propor- 
tion to  the  frequency  of  the  pulse,  or  the  reverse.  A  high  pulse-rate, 
therefore,  while  an  accompaniment  that  is  almost  universal,  is  not  abso- 
lutely essential  to  the  condition  of  fever.  As  it  is  with  this,  so  it  is  with 
the  other  symptoms,  as  thirst,  loss  of  appetite,  the  sensation  of  heat  felt 
by  the  patient,  etc.  Any  of  these  may  be  wanting,  and  in  some  rare 
cases  all  of  them,  and  still  the  continued  elevation  of  the  temperature 
marks  the  condition  of  fever  as  being  present  notwithstanding.  Fever, 
then,  is  shown  to  l)e  present  l)y  the  existence  of  this  one  fact  of  high 
temperature,  and  tlie  other  conditions  that  usually  accompany  it  are 
due  to  this  increase  of  the  temperature — are  caused  by  the  fever — are 
products  and  not  essential  factors. 

Tlie  increase  of  heat  in  fever  is  not  in  any  sense  local.  Even  though 
the  febrile  movement  may  have  resulted  from  a  purely  local  inflamma- 
tion, the  rise  of  temperature  is  always  general  and  affects  all  parts  of 
the  body  alike.  Increased  locjil  heat  accompanying  local  inflammations 
must  not  be  confounded  with  fever.  In  fever  the  whole  blood  is 
warmer  than  normal,  and  this  increase  may  stop  at  five  or  eight  degrees 
above  the  normal,  or  in  severe  cases  it  may  pass  on  to  ten,  but  rarely 
above  this  limit.  The  organism  in  its  normal  condition  possesses  a  self- 
regulating  power  as  regards  its  temperature  which  under  the  varving 
circumstances  of  climate  and  seasons  preserves  the  blood  at  about  the 
same  degree  of  heat — viz.  98°  to  99°  F.     Therefore  when  it  is  observed 


FEVER.  713 

that  this  equable  temperature  is  disturbed,  and  that  an  elevation  is 
steadily  progressing  or  is  maintained  above  the  normal,  some  factor  has 
entered  into  the  economy  from  without,  or  has  been  produced  by  faulty 
chemico-vital  processes  within,  that  has  the  effect  of  unbalancing  the 
combined  functions  of  heat-production  and  heat-dissipation.  This  may 
occur  shortly  after  the  receipt  of  an  injury  or  the  rise  of  an  inflamma- 
tion or  of  a  complaint  of  languor,  or  seemingly  as  the  result  of  the  most 
varied  physical  disturbances. 

All  of  the  features  of  the  affection  are  arranged  around  this  one  cen- 
tral phenomenon.  The  patient  may  or  may  not  be  conscious  of  the 
increased  heat.  At  the  beginning  of  the  rise  of  his  temperature  he 
generally  complains  of  chilly  sensations.  What  is  known  as  a  chill  or 
rigor  is  coincident  with  a  rise  of  temperature  that  is  more  or  less  sudden 
or  rapid,  as  is  indicated  by  a  thermometer  under  the  tongue  or  in  the 
axilla.  The  sensations  of  the  patient  are  not  to  be  trusted,  for  while  he 
is  shivering  with  cold  his  temperature  may  rise  several  degrees.  After- 
ward flashes  of  heat  begin  to  alternate  with  the  sensation  of  cold,  and  as 
the  case  progresses  the  patient  becomes  ujipleasantly  conscious  of  the 
increased  heat  of  his  body.  In  the  onset  of  certain  forms  of  fever  the 
occurrence  of  chill  is  a  prominent  manifestation.  This  is  especially 
the  case  in  what  is  known  as  chills  and  fever ;  and  indeed  in  all  of  the 
types  of  malarial  fever  the  duration  and  severity  of  the  chill  are  espe- 
cially marked,  and  the  patient  may  be  shivering  with  cold  for  an  hour 
or  more,  during  which  time  he  is  unable  to  recognize  the  fact  that  he  is 
really  unusually  warm.  The  chill  seems  to  mark  a  sudden  rise  of  tem- 
perature, but  the  gravity  of  the  chill  is  not  always  in  proportion  to  the 
rapidity  of  the  increase  of  heat.  It  has  been  suggested  that  the  chill  is 
an  illusory  sensation  brought  about  by  the  change  in  the  temperature 
relation  of  the  body  and  the  surrounding  air ;  but  there  is  evidently 
some  other  factor  in  the  production  of  chill  that  is  not  yet  certainly 
made  out. 

In  other  than  the  malarial  fevers  there  is  much  difference  as  to  the 
production  of  chill.  Thus,  in  most  of  the  grave  inflammations  of  the 
internal  organs,  such  as  occur  in  pneumonitis  and  other  of  the  continued 
fevers  that  are  accompanied  with  distinct  and  severe  inflammations,  the 
occurrence  of  chill  at  the  onset  is  the  rule,  and  the  severity  of  the  chill 
usually  bears  some  proportion  to  the  severity  of  the  attack.  In  inflam- 
mations not  primarily  accompanied  with  fever  a  chill  is  very  likely  to 
mark  the  beginning  of  the  formation  of  pus  or  the  development  of  an 
abscess.  It  is  generally  not  very  severe,  and  the  fever  which  results 
usually  passes  away  with  the  more  complete  formation  of  the  abscess. 
This  seems  to  have  some  relation  to  the  particular  conditions  at  the  seat 
of  the  inflammatory  process,  in  that  the  fever  is  called  forth  in  the  early 
period  of  the  inflammation  or  of  the  formation  of  pus,  and  ceases  after 
the  effusion  of  plastic  lymph  has,  so  to  speak,  walled  in  the  inflannna- 
tory  products  by  the  closure  of  the  lymphatics,  by  which  absorption  into 
the  general  circulation  is  prevented  or  rendered  less  in  amount.  I  will 
speak  of  this  again. 

In  surgical  fever  (fever  following  shock  or  accompanying  the  devel- 
opment of  inflammation  in  a  wound)  the  chill  is  usually  absent  or  but 


714  GENERAL  PATHOLOGY. 

slightly  developed.  The  fever  in  this  case  comes  on  more  gradually, 
and  the  temperature  does  not  attain  so  high  a  degree.  If,  however,  the 
chill  shoukl  be  pronounced,  the  fever  which  follows  is  likely  to  be 
accompanied  Mith  graver  symptoms  than  the  fever  that  is  ushered  in 
Avithout  marked  chill. 

In  connection  with  the  increase  in  the  temperature  of  the  blood  in 
fever  other  evidences  are  presented,  showing  derangement  of  the  func- 
tions of  heat-production.  Tissues  are  being  destroyed  by  combustion 
or  oxidation  to  an  abnormal  degree  in  consequence  of  the  necessity  for 
material  sufficient  to  keep  up  the  increased  heat-jH'oduction.  It  appears 
from  the  recent  experimental  studies  of  Senator,  H.  C.  AVood,  and  others 
that  the  excretion  of  urea  is  doubled  or  tripled  as  a  result  of  the 
increased  destruction  of  all)uminous  material — blood-plasma,  blood- 
corjiuscles,  the  sarcose  elements  of  muscular  tissue,  etc.  Hence  the 
increase  in  the  salts  of  the  urine  and  the  increased  excretion  of  carbonic 
acid  which  are  also  noted.  At  the  same  time,  digestion  and  assimilation 
are  disordered,  appetite  is  wanting  or  is  seriously  impaired,  and  in  this 
way  the  usual  food-supply  for  renewing  the  waste  of  the  tissues  is 
greatly  diminished  or  cut  otf  entirely.  Hence  the  absorption  of  adipose 
tissue,  waste  of  the  muscles,  and  impairment  of  the  blood  ibllow  as 
results  of,  or  it  may  be  said  form  a  part  of  the  phenomena  of,  fever.  It 
thus  becomes  evident  that  the  abnoi'mal  production  of  heat  during  fever 
is  maintained  by  the  consumption  of  valuable  material  not  used  for  this 
purpose  in  a  state  of  health,  or  the  regeneration  of  which  is  prevented 
by  the  accompanying  conditions  of  impairment  of  the  functions  of  diges- 
tion and  assimilation.  With  this  view  fever  might  be  said  to  consist  of 
a  disorder  of  nutrition  made  manifest  in  increased  heat-production  and 
increased  tissue-waste. 

It  appears  from  the  exhaustive  experimental  research  of  Prof  H.  C 
Wood  that  the  temperature  of  the  body  is  no  certain  guide  to  the  extent 
of  the  abnormal  heat-production  that  maybe  in  progress  in  a  given  case 
of  fever,  for  another  factor  enters  into  the  disorder — namely,  disordered 
heat-dissipation.  It  therefore  follows  that  if  the  dissipation  of  heat  be 
interfered  with,  a  rise  of  the  temperature  of  the  body  may  occur  M'ithout 
over-heat-production,  and,  vice  vcrsd,  over-heat-production  may  be  pres- 
ent without  rise  of  bodily  temperature.  It  thus  appears  that  the  heat 
of  the  body  is  controlled  in  a  large  degree  by  the  orderly  jilay  that  nor- 
mally exists  l)etween  the  combined  functions  of  heat-production  and 
heat-dissij)ati()n,  and  that  the  occurrence  of  a  rise  of  temperature  may  be 
due  to  either  increased  heat-production  or  diminished  heat-dissipation. 
Touching  this  point  Prof.  Wood  formulates  the  following  proposition : 
"  Fever  is  a  complex  nutritive  disturbance,  in  which  there  is  excessive 
production  of  such  ])ortion  of  the  bodily  heat  as  is  derived  from  chem- 
ical movements  in  the  accunudatcd  material  of  the  organism,  the  over- 
])lus  being  sometimes  less,  sometimes  more,  than  the  loss  of  heat-pro- 
duction resulting  from  abstinence  from  food.  The  degree  of  bodily 
tem])erature  in  fever  depends,  in  greater  or  less  measure,  upon  a  dis- 
turbance in  tlie  natural  play  between  the  functions  of  heat-production 
and  heat-dissipation,  and  is  not  an  accurate  measure  of  the  intensity  of 
increased  chemical  movements  of  the  tissues." 


FEVER.  715 

The  cause  of  fever  is  in  some  degree  elucidated  by  the  experimental 
research  of  Senator,  ah-eady  aHuded  to.  This  experimenter  injected  fresh 
heahhv  pulse  into  the  subcutaneous  tissue  of  dogs,  and  found  that  it  reg- 
nlarlyproduced  a  state  of  fever.  Two  or  three  hours  after  the  pus  was 
injected  the  temperature  began  to  rise,  and  a  state  of  fever  was  inaugurated 
that  continued  two  or  three  days,  and  subsided  unless  the  injection  ^yas 
repeated.  This  and  similar  experiments  have  established  a  connection 
between  inflammation  and  fever  that  'svas  inferred  previous  to  the 
experimentation,  but  which  is  now  placed  on  a  more  certain  basis. 
The  relation  between  these  processes  has  been  observed  clinically  since 
the  inception  of  surgical  knowledge.  When  a  wound  of  considerable 
magnitude  is  inflicted,  clinical  experience  has  led  men  to  expect  the  rise 
of  fever  to  coincide  very  closely  with  the  rise  of  inflammation  in  the 
wound ;  and  it  has  beeii  noticed  especially  that  if  the  progress  of  the 
wound  was  flivorable,  this  fever  Mould  begin  to  subside  when  the 
inflammatory  process  had  reached  a  certain  point — /.  e.  when  the  secre- 
tions were  established,  as  the  process  has  been  denominated.  This  cor- 
responds very  closely  with  the  time  when  the  wound  is,  so  to  speak, 
walled  in  by  the  inflammatory  exudates  in  such  a  manner  as  to  prevent 
absorjition  of  the  materials  elaborated  by  the  inflammatory  process. 

If  the  fever  recurs  after  this  period  or  if  it  persists,  the  surgeon  is  led 
to  seek  some  other  cause  for  its  recurrence  or  persistence.  This  is  gen- 
erally found  to  be  some  change  in  the  condition  of  the  wound  or  in  the 
development  of  an  abscess  in  connection  with  some  foreign  substance 
overlooked — a  pocket  in  an  unexplored  nook  in  which  retained  pus  has 
begun  burrowing,  or  something  of  this  general  nature  that  has  caused  a 
fresh  inflammatory  movement ;  or  it  may  be  that  the  wound  as  a  w  hole 
has  taken  on  a  septic  condition.  When  no  such  causes  as  these  can  be 
found  in  connection  with  the  case,  the  surgeon  of  to-day  will  regard  the 
fever  as  arising  from  conditions  foreign  to  the  wound  itself. 

In  this  view  of  the  matter  we  must  suppose  that  some  material  has 
been  elaborated  in  connection  with  the  process  of  inflammation  which, 
when  taken  into  the  blood,  has  the  effect  of  disturbing  the  existing  nor- 
mal relations  between  heat-production  and  heat-dissipation  in  such  a 
way  as  to  give  rise  to  fever,  or  which  increases  heat-production.  This, 
as  we  have  seen,  has  been  the  direct  result  of  the  injection  of  the  fresh 
products  of  inflammation  into  healthy  animals ;  therefore  in  the  light 
of  the  clinical  history  of  wound  surgery,  and  the  connection  of  fever 
therewith  as  related  above,  we  cannot  escape  the  conviction  that  the 
fever  in  each  instance  has  a  material  cause  in  the  absorption  of  the  prod- 
ucts of  inflammation  directly  from  the  wound  into  the  circulation. 

In  pursuing  the  clinical  history  of  this  subject  farther  we  shall  find 
that  fever  is  also  produced  by  inflammations  independently  of  the 
formation  of  pus,  though  not  so  generally  perhaps ;  yet  the  number  of 
cases  in  which  the  fever  is  developed  before  the  beginning  of  pus-forma- 
tion is  really  very  large.  Then  the  cause  of  fever,  in  these  cases  at  least, 
is  not  necessarily  the  absorption  of  the  pus  itself,  but  of  the  products 
of  perverted  cell-action  which  precede  the  development  of  pus.  Some 
reference  to  these  products  have  been  made  in  the  study  of  the  process 
of  inflammation  as  relating  to  the  activity  of  the  tissues.     In  this  per- 


716  GENERAL  PATHOLOGY. 

version  of  cell-activity  under  the  influence  of,  or  as  a  result  of,  irrita- 
tion or  tissue  injury,  products  of  an  abnormal  character  seem  to  be 
formed  which,  when  carried  into  the  circulation  in  sufficient  quantity, 
serve  to  inaugurate  the  condition  of  fever.  On  the  basis  of  observations 
similar  to  those  cited  above  Dr.  Sanderson  speaks  of  the  "  infective  " 
power  of  the  products  of  ordinary  inflanuuation,  and  arrives  at  the  con- 
clusi<Mi  that  "  fever  is  the  product  of  a  lever-producing  cause  contained 
in  the  blo(xl  or  tissue-juices,  the  morbific  action  of  which  on  the  organ- 
ism is  antecedent  to  all  functional  disturbance  whatever ;"  and  speaks 
of  fever  as  "  from  first  to  last  a  disorder  of  protoplasm." 

It  is  not  necessary  to  suppose  that  all  fevers  result  from  the  products 
of  infiannnation  ;  indeed,  such  an  hypothesis  could  not  be  maintained 
upon  the  facts  at  present  in  our  possession,  for  many  cases  of  fever 
occur  M-hicli  are  in  no  way  related  to  inflammation,  so  far  as  physical 
examination  has  thus  far  developed.  This  seems  to  be  but  one  cause 
out  of  many.  It  seems  probable  that  there  are  other  forms  of  perverted 
cell-action,  not  yet  known  to  us,  which  take  place  in  the  economy 
and  are  capable  of  giving  rise  to  products  which  may  act  as  a  cause. 
Putridity  is  regarded  as  a  cause,  and  the  soluble  sepsin  of  Bergman, 
which  is  undoubtedly  the  waste  product  of  certain  micro-organisms, 
and  which  holds  a  close  relationship  to  the  alkaloids  of  the  higher 
plants,  has  been  demonstrated  experimentally  to  be  capable  of  produ- 
cing fever  \\hen  introduced  into  the  system.  Besides  this,  a  number 
of  micro-organisms  have  been  proved  to  stand  in  a  causative  relation  to 
fever,  and  other  causes  will  in  all  probability  be  identified  in  the  near 
future. 

The  supposition  so  widely  held  that  fever  has  its  origin  in  irritation, 
which  has  given  rise  to  the  terms  "irritative  fever,"  "^sympathetic 
fever,"  "  fever  from  constitutional  irritation,"  seems  not  to  be  main- 
tained. The  most  persistent  experimentation  with  that  end  in  view  has 
failed  (in  dogs)  to  produce  fever  by  the  irritation  of  peripheral  nerves. 
Dr.  I>illroth  has  made  these  experiments  in  various  ways,  as  by  forcible 
injectit)ns  of  air  into  the  subcutaneous  tissue,  by  exposing  nerve-trunks 
and  irritating  them  with  ammonia,  by  suspending  weights  to  nerve- 
trunks,  by  tearing  the  inner  coats  of  the  vessels,  by  injecting  powders 
into  the  blood  so  as  to  form  emboli,  by  rubbing  the  ears  with  croton 
oil,  etc.,  and  in  no  case  did  he  succeed  in  producing  immediate  fever. 
On  this  and  similar  experimentation  he  arrived  at  the  conclusion  that 
fever  always  has  a  material  cause.  Various  other  experiments  have 
been  made  with  this  end  in  view,  and  after  a  close  review  of  them  it 
seems  that  the  conclusions  of  Billroth  are  maintained.  This  idea  of 
irritative  fever  has  been  so  widely  held,  and  has  seemed  so  well  sus- 
tained by  clinical  observation,  that  it  is  displaced  with  difficulty ;  but, 
as  Prof.  Wood  sf)  ajitlv  says,  "as  our  knowlege  grows,  fevers  supposed 
to  be  due  to  peri])heral  irritations  are  shown,  one  by  one,  to  have  their 
origin  in  toxicmia." 

Still,  it  seems  hardly  possible  that  all  of  the  fugitive  fevers  that  we 
see,  many  of  them  enduring  only  for  a  few  hours  and  then  passing  away 
with  complete  restoration  of  health,  or  those  mild  febrile  reactions  of 
childhood  that   arise  seemingly   from   slight  intestinal   irritations,  the 


FEVER.  Ill 

fever  so  common  during  the  cutting  of  the  teeth  of  children,  and  the 
like,  all  come  from  an  actual  poisoning  of  the  blood.  However  this 
may  be,  it  is  now  very  certain  that  all  of  the  graver  forms  of  fever 
which  were  formerly  supposed  to  arise  from  irritation  are  due  to  a 
material  cause  circulating  in  the  blood. 

How  the  fever-producing  poisons  act  in  the  production  of  fever,  or 
upon  what  tissue,  cannot  now  be  certainly  affirmed.  It  does  not  seem 
probalile  that  their  action  is  on  the  general  protoplasm  of  the  body.  If 
this  were  the  case,  fever  would  often  be  expressed  locally,  for  it  is 
hardly  conceivable  that  in  all  cases  the  poison  could  be  so  perfectly  dis- 
tributed that  no  local  expressions  of  its  action  should  be  noticed.  Then 
it  must  act  on  the  blood  directly  or  on  the  nervous  system.  These  two 
form  systems  that  are  more  general  and  widereaching  in  their  bonds  of 
union  with  the  system  at  large  than  any  other.  The  nervous  phenom- 
ena of  fever  are  so  prominent  that  in  the  absence  of  exact  experimental 
evidence  we  would  naturally  look  to  it  as  the  system  most  prominently 
affected.  It  is  well  known  that  certain  poisons  affect  certain  portions 
of  the  brain  or  nervous  system  prominently  when  they  gain  access  to 
the  circulation  and  are  carried  to  the  particular  part  by  the  blood.  This 
is  seen  in  the  action  of  alcohol,  of  opium,  of  strychnia,  and  many  other 
drugs.  All  of  these  in  a  certain  sense  act  as  blood-poisons  ;  that  is  to 
say,  they  reach  the  tissue  upon  which  their  impression  is  made  through 
the  medium  of  the  blood.  It  seems  most  probable  that  the  fever-pro- 
ducing poisons  act  in  the  same  way.  Of  ordinary  malarial  fever  Prof. 
Wood  says :  "  The  chill,  the  fever,  and  the  sweating  in  their  regular 
sequence  and  their  periodical  occurrences  most  plainly  bear  evidence  to 
a  neurotic  origin."  The  same  author  calls  attention  also  to  the  well- 
known  fact  that  the  paroxysm  of  fever  may  be  replaced  with  a  par- 
oxysm of  neuralgia  "  and  various  local  vaso-motor  and  secretory  dis- 
turbances "  which  can  with  difficulty  be  conceived  as  being  induced 
otherwise  than  through  the  nervous  system. 

The  discussion  of  our  present  knowledge  of  a  probable  heat-centre, 
or  several  centres  acting  in  unison  in  a  state  of  health  for  the  control 
of  the  temperature  of  the  body,  in  its  relations  to  fever-production 
would  lead  me  beyond  the  space  alloted  to  this  article.  The  experi- 
mentation that  has  been  had,  especially  that  by  Prof.  Wood,  amounts 
almost  to  a  demonstration,  although  the  centre  is  not  precisely  located. 
The  complete  demonstration  of  such  a  centre,  and  of  its  powers  and 
capabilities,  will  add  greatly  to  our  knowledge  of  this  important  sub- 
ject. So  far,  it  has  been  definitely  determined  that  irritation  of  cer- 
tain portions  of  the  brain  affect  heat-production  and  heat-dissipation 
in  a  very  marked  degree ;  and  this  knowledge  seems  entirely  suf- 
ficient to  serve  as  the  basis  of  the  doctrine  set  forth  above.  On  this 
basis  Prof.  Wood  formulates  the  following :  "  Irritative  fever,  if  it 
exist,  is  produced  by  an  action  on  the  nervous  system.  Fever  occur- 
ring in  case  of  blood-poisoning  is  often,  and  probably  always,  the 
result  of  a  direct  or  indirect  action  of  the  poison  on  the  central  ner- 
vous system,  and  hence  is  a  neurosis." 

Results  of  Fever. — The  usual  tendency  of  fever  is  toward  self- 
limitation.      In  other  words,  the  tendency  is  toward  a  spontaneous 


718  GENERAL  PATHOLOGY. 

return  to  health  after  some  days — more  or  less  according  to  the  nature 
of  tlie  cause.  For  instance,  in  the  case  of  a  common  boil  of  moderate 
severity  we  should  expect  a  rather  mild  form  of  fever,  lasting  one 
or  two  days  and  then  passing  away.  In  inflammations  of  greater 
extent  a  greater  rise  of  temperature  and  continuing  for  a  longer  time 
would  be  expected.  In  cases  of  acute  alveolar  abscess  there  may 
be  a  temperature  of  104°  F.,  running  for  two  or  three  days.  This, 
however,  may  be  regarded  as  rather  unusual,  and  when  it  occurs  marks 
the  case  as  a  somewhat  grave  one,  with  the  j)robability  that  some  necrosis 
of  bone  about  the  root  of  the  affected  tot)th  will  occur.  This  necrosis 
is  not  caused  by  the  fever,  but  results  from  the  severity  of  the  inflam- 
mation causing  the  fever.  Therefore  the  severity  of  the  fever  is  some 
indication  as  to  the  severity  of  inflammations.  It  may  be  stated  that 
all  of  the  symptomatic  fevers  which  accompany  the  slighter  forms  of 
inflammation,  such  as  I  have  mentioned,  pass  away  spontaneously  within 
a  few  days.  In  the  continued  fevers  the  cause  is  more  persistent,  and 
evidently  remains  in  action  for  a  nuich  longer  time,  this  differing  much 
with  the  various  forms  of  these  aflections. 

If  fever  exceeds  a  certain  degree,  it  becomes  in  itself  dangerous  to 
life.  It  rarely  exceeds  107°  or  108°  F. ;  that  is  to  say,  this  intensity 
of  fever,  or  a  rise  of  the  temperature  of  the  blood  to  this  degree,  is 
usually  fatal  if  it  continues  many  hours.  Some  time  since  there  came 
under  my  observation  the  case  of  a  young  woman  from  whom  the 
ovaries  had  been  removed  for  the  cure  of  \iolent  and  persistent  hys- 
teria: the  temperature  began  to  rise  a  short  time  after  the  operation,  the 
increase  continuing  rapidly  and  steadily  in  spite  of  all  efforts  to  coun- 
teract it.  Within  ten  hours  it  had  passed  108°  F.,  and  in  another  hour 
the  patient  died,  with  the  thermometer  indicating  the  extreme  tempera- 
ture of  110°.  After  death  the  temperature  continued  to  rise  until  112° 
was  reached.  It  is  usual  for  cases  having  a  temperature  of  108°  or  over 
to  prove  rapidly  fatal,  although  some  instances  of  recovery  after  a  much 
higher  temperature  had  occurred  have  been  reported.  Therefore,  the 
upward  limit  of  fever  is  controlled  only  by  the  endurance  of  the  par- 
ticular ])atient.  There  is  usually  no  great  danger  from  fever  until  106° 
is  passed,  unless  the  high  temperature  be  long  maintained  ;  but  this 
temperature  is  not  to  be  endured  very  long  without  remission.  In  the 
continued  fevers,  in  M'hich  the  temperature  reaches  this  height,  there  are 
regular  remissions,  usually  corresponding  with  the  diurnal  fall  of  tem- 
perature in  health,  which  seem  to  relieve  the  patient  and  enable  him  to 
endure  the  very  high  temperature  of  the  evening. 

Persons  sometimes  succumb  to  a  much  lower  temperature,  though  this 
is  rather  unusual  unless  there  is  some  other  cause  of  death  co-operating. 
A  few  years  ago  I  had  under  observation  a  case  of  seemingly  mild  type 
of  typhoid  fever  in  which  the  patient  became  comatose,  and  died  on  the 
tenth  day,  the  fever  not  having  risen  above  103°  at  any  time.  Post- 
mortem examination  revealed  the  usual  lesion  of  this  stage  of  the  dis- 
ease, but  this  was  mild  in  degree.  Xo  cause  of  death  was  found  other 
than  the  fever. 

From  the  nature  of  fever  there  must  be  much  injury  to  the  tissues, 
especially  if  the  febrile  movement  is  intense  and  long  continued.     The 


SHOCK.  719 

injurv  to  the  nervous  structures  is  manifest  in  the  delirium  and  other 
perturbations  of  the  mental  faculties  that  so  generally  accompany  severe 
fevers.  In  severe  and  long-continued  attacks  the  muscles  are  especially 
affected  by  the  destruction  of  the  sarcose  element  of  the  fibres.  In  this 
way  portions  of  the  fibres  of  certain  muscles  are  occasionally  injured  to 
such  an  extent  as  to  cause  lameness  for  some  time  after  recovery.  The 
general  emaciation  has  been  spoken  of:  this  is  the  usual  result  of  fever ; 
all  of  the  tissues  suffer  \vaste,  but  the  fatty  tissues  are  perhaps  destroyed 
to  a  greater  extent  than  any  others. 

Shock. 

Shock  is  a  sudden  and  notable  depression  of  the  vital  powers  result- 
ing from  an  injury  more  or  less  grave,  or  from  an  impression  made  on 
the  nervous  system  through  the  medium  of  the  sensorium,  as  by  fright, 
sudden  and  overpowering  mental  emotion,  etc.  In  its  phenomena  it 
seems  to  consist  of  a  sudden  check  of  the  circulation  brought  about 
througli  the  agency  of  the  nervous  system  :  this  may  be  so  grave  as  to 
cause  instant  death,  or  may  result  in  prostration  more  or  less  prolonged, 
with  or  without  a  successful  reaction  following  it.  It  was  lonij  ago 
noted  that  death  sometimes  resulted  suddenly  after  injuries  that  left  no 
trace  of  their  destructive  effects  on  the  vital  organs,  and  that  many 
instances  in  which  death  was  less  immediate  could  not  be  explained  by 
the  visible  effects  of  the  injury  sustained.  It  frequently  occurs  that 
persons  who  have  sustained  some  injury  sink  into  a  state  of  prostration 
not  to  be  accounted  for  by  the  severity  of  the  hurt,  such  persons,  even 
though  apparently  moribund,  being  sometimes  within  a  day  or  two 
restored  to  their  usual  health  and  vigor.  These  cases  can  be  explained 
in  no  way  other  than  upon  the  supposition  that  the  nervous  system  had 
been  suddenly  overpowered.  Hence  the  term  shock.  Collapse  is  also 
used  in  the  same  sense. 

It  is  not  to  be  inferred  that  there  is  actually  no  tissue-change  in  these 
cases,  but  there  certainly  is  none  that  can  be  recognized  by  our  physical 
senses  through  either  macroscopic  or  microscopic  examination.  It  can- 
not be  supposed,  however,  that  such  grave  symptoms  can  occur  Ayithout 
some  molecular  disturbance  in  the  nerve-cells  which  for  the  time  renders 
them  incapable  of  the  proper  performance  of  their  functions. 

The  cause  of  shock  has  been  a  subject  of  much  inquiry,  especially 
among  surgeons,  who  are  continually  brought  in  contact  with  the 
graver  forms  of  this  condition.  The  general  nature  of  shock  remains 
the  same,  no  matter  whether  it  result  from  bodily  injury  or  mental 
impressions.  Diminished  energy  of  the  nervous  system,  resulting  in 
enfeeblement  of  the  circulation,  is  prominent  in  every  symptom,  and 
the  general  reduction  of  the  vital  powers  seems  to  depend  on  this  for 
its  inauguration  and  continuance.  The  injury  to  the  nervous  system  is 
especially  manifest  in  the  demeanor  of  the  sufferer,  and  this  is  expressed 
in  a  variety  of  ways.  In  one  case  a  person  Avho  has  received  a  serious 
injury  may  for  a  time  apparently  disregard  it ;  he  seems  not  to  suffer 
pain,  and  is  possessed  of  a  calmness  that  under  the  circumstances  is 
entirely  unnatural,  while  at  the  same  moment  the  surgeon  will  perhaps 


720  GESEEAL  PATHOLOGY. 

discover  a  marked  pallor,  soon  followed  by  coldness  of  the  skin.  The 
pulse  becomes  Meak,  small  in  volume,  and  passes  under  the  finger  with 
a  peculiarly  short  and  quick  stroke,  denoting  an  extreme  relaxation  of 
the  vascular  system.  The  failure  of  the  nervous  system  is  seen  in  other 
directions  as  well.  Questions  are  answered  slowly  and  hesitatingly,  as 
though  not  fairly  understood ;  the  tone  of  the  voice  is  changed,  and 
perhaps  markedly  enfeebled.  The  motions  of  the  patient  may  show 
extreme  weakness ;  sentences  give  place  to  monosyllables ;  and  the 
patient  may  sink  into  a  state  bordering  u^Jon  unconsciousness,  in 
which  he  takes  no  notice  of  what  is  going  on  around  him.  He  may 
recover  from  this  condition  speedily,  with  full  restoration  of  the  normal 
tone  and  vigor  of  the  nervous  system,  or  recovery  may  be  delayed 
indefinitely.  There  is,  however,  generally  a  reaction  within  one  or 
two  days. 

In  other  cases  all  of  the  more  profound  symptoms  of  shock  may 
occur  suddenly.  Coma,  or  even  death,  may  almost  immediately  follow 
the  receipt  of  a  comparatively  trifling  injury  or  from  mental  impressions 
that  in  other  persons,  and  perhaps  in  the  same  person  at  another  time, 
would  scarcely  be  noticed. 

Shock  differs  materially  from  syncope.  Emotion,  the  sight  of  a  wound, 
and  various  trifling  circumstances  may  cause  a  momentary  stoppage  of 
the  action  of  the  heart,  with  a  temporary  loss  of  consciousness,  and  not 
be  productive  of  shock.  The  production  of  shock  evidently  involves 
some  other  factor,  for  instead  of  a  temporary  arrest  of  function  there 
appears  to  be  a  real  injury  to  the  structure  upon  which  the  functioning 
poAver  depends  that  renders  immediate  recovery  impossible.  Time  must 
be  had  for  recovery  from  this  tissue  injury,  and  during  this  period  these 
functions  are  imperfectly  performed,  apparently  from  lack  of  power. 
The  symptoms  seem  to  point  to  the  failure  of  those  nerve-centres  that 
maintain  the  proper  tension  of  the  vascular  system.  Normally,  the 
walls  of  the  arteries  are  contracted  upon  the  blood  they  contain,  so  as 
to  keep  up  a  certain  degree  of  arterial  pressure,  this  being  to  a  lesser 
extent  complemented  by  the  veins.  In  shock  there  is  a  sudden  letting 
go  of  this  tension,  of  this  grasp  on  the  blood.  The  vascular  system  is 
relaxed  abnormally,  and  in  such  a  manner  as  to  interfere  with  the  cir- 
culation. At  the  same  time  there  is  a  relaxation  of  the  energies  of  the 
heart,  but  not  a  stoppage  as  in  syncope,  except  it  be  in  some  of  those 
grave  forms  that  result  in  almost  instant  death,  in  which  this  point  can- 
not Avell  be  studied  and  distinguished  from  other  symptoms.  The  rule 
is  that  the  heart  maintains  its  action,  but  in  a  very  feeble  way ;  and  it 
appears  to  have  been  shown  by  experiment  on  the  frog  that  even  Avhen 
the  heart  is  stop]")ed  it  may  be  induced  to  resume  its  action  by  supplying 
it  M'ith  blood.  Prof.  Goltz  of  Strasbourg  j^erformed  the  experiment  in 
this  way :  A  frog  was  suspended  in  a  vertical  position  with  the  legs 
hanging  down  and  the  heart  exposed.  After  a  few  moments'  delay,  to 
see  that  the  circulation  was  going  forward  normally,  the  animal  was 
struck  a  smart  blow  on  the  surface  of  the  abdomen.  The  heart  stopped 
its  contractions  at  once,  and  af^er  a  few  moments  began  again  feebly, 
but  it  was  clear  that  it  was  propelling  no  blood  into  the  aorta,  for  the 
upper  part  of  the  vena  cava  was  empty  and  no  blood  was  supplied  to 


SHOCK.  721 

tlie  heart.  The  effect  of  the  blow  seemed  to  have  paralyzed  those 
nerve-centres  which  control  the  tension  of  the  vascular  system,  causing 
sucli  a  dilatation  of  the  vessels  of  the  abdomen  particularly  that  the 
blood  did  not  fill  them,  and  the  heart  was  unable  to  proceed  normally 
for  Avant  of  the  usual  stimulus  of  a  proper  blood-supply.  When  the 
animal  was  laid  down,  so  that  gravitation  would  bring  the  blood  to  the 
heart,  the  normal  pulsations  were  resumed.  It  is  clear  that  the  animal 
could  not  have  recovered  had  it  remained  suspended,  for  without  the 
circulation,  which  under  the  circumstances  could  not  be  resumed,  the 
nerve-centres  could  not  recover  their  vigor.  But  with  this  the  tension 
was  soon  restored.  This  experiment  shows  that  an  animal — and  prob- 
ably a  man  as  well — may  bleed  to  death  without  the  loss  of  a  drop  of 
blood,  simply  by  the  dilatation  of  the  vessels  to  such  an  extent  that  they 
shall  not  be  filled  with  blood.  It  is  probable  that  the  great  vessels  of 
the  abdomen  when  utterly  relaxed  will  contain  the  whole  blood  of  the 
vascular  system,  and  in  this  condition  it  will  for  the  time  be  as  com- 
pletely lost  to  the  system  as  though  it  had  been  poured  out.  This  seems 
to  indicate  the  exact  manner  of  death  in  some  of  the  cases  of  shock 
already  alluded  to.  Savory  states  that  instant  death  may  occur  from 
a  blow  on  the  epigastrium  which,  though  severe,  leaves  no  detectable 
lesion ;  and  Mansel-Moullin  relates  a  case  of  sudden  death  from  shock 
caused  by  the  introduction  of  a  trocar  into  a  cyst  of  the  liver,  in  which 
the  tissue  injury  was  so  trifling  that  death  could  not  be  explained  except 
on  a  supposition  of  a  paralysis  of  the  vaso-motor  centres. 

These  facts  seem  to  show  plainly  the  nature  of  the  condition  which  is 
known  as  shock  or  collapse.  The  vaso-motor  nerves  are  for  the  time 
rendered  inoperative,  and  in  this  way  the  circulation  is  so  enfeebled, 
when  not  cut  off  entirely,  that  its  functions  are  imperfectly  performed, 
and  the  whole  svstem  suffers  in  consequence.  There  seems  to  be  a  pos- 
itive enfeeblement  of  the  heart  as  well,  probably  from  the  same  cause, 
for  in  those  cases  of  the  lesser  degrees  of  shock  the  effect  on  the  heart 
seems  to  be  the  prominent  factor,  at  least  the  most  marked  symptom.  Yet 
in  all  cases  the  character  of  tlie  pulse,  which  is  very  short  and  compres- 
sible, speaks  plainly  of  lack  of  arterial  tension.  The  heart  is  so  far 
independent  of  other  innervation  than  that  contained  within  its  own 
walls  that  it  is  capable  of  continuing  its  regular  rhythmical  actions  when 
all  other  sources  of  nerve-supply  are  cut  off.  The  great  nerve-centres 
may  be  removed  one  after  another  until  the  last  one  is  severed,  and  yet 
the  nerves  contained  in  its  own  walls  will  serve  the  purpose  of  continuing 
its  motions.  At  the  same  time,  it  is  so  connected  with  these  great  nerve- 
centres  that  the  irritation  of  one  of  its  connecting  branches  may  bring  it 
to  an  immediate  stop.  Not  only  this,  but  irritation  applied  to  a  per- 
ipheral nerve  may  produce  the  same  effect  through  reflex  action.  We^ 
have  also  learned  through  direct  experiment,  some  of  which  was  detailed 
while  treating  of  hyperemia,  that  the  blood-vessels,  veins  as  well  as 
arteries,  are  under  a  control  of  the  same  nature  and  are  affected  in 
the  same  way  by  similar  causes.  While  all  of  this  is  true,  and  the 
heart  may  be  stopped  by  these  reflex  impulses,  and  the  tone  of  the 
arteries  may  be  relaxed,  the  local  nerves  of  the  heart  will,  after  a  time, 
set  up  these  actions  anew  independently  of  other  nerve-influence.     It  is 

Vol.  I.— 46 


722  GENERAL  PATHOLOGY. 

not  shown  that  the  blood-vessels  will  recover  their  tone  so  readily  as 
the  heart,  but,  on  the  contrary,  experiment  and  clinical  observation 
combine  in  the  illustration  of  the  fact  that  their  enfeeblement  is  recov- 
ered from  with  much  greater  difficulty. 

The  molecular  disturbances  in  shock  should  not  be  passed  over  without 
notice.     All  function  is  directly  dependent  upon  remolecularizations  of 
matter,  or  at  least  molecular  motion  or  chemico-vital  changes  in  some 
form.     This  is  the  opinion  of  the  scientific  world  at  the  present  time. 
In  the  performance  of  labor  by  the  muscles  the  sarcose  material  of  the 
fibres  undergoes  molecular  changes  with  every  contraction,  and  these 
changes  result  in  the  formation  of  waste  products  which  are  eliminated. 
Therefore  if  these  changes  occur  with  such  rapidity  that  this  cannot  be 
resupplied   by  the  nutrient  functions  in  the  necessary  proportion,  the 
muscle  becomes  exhausted ;  rest  is  then  necessary  that  nutritive  repair 
may  bring  the  muscle  up  to  the  normal  standard  again.     That  which 
is  true  of  the  muscles  is  true  also  of  other  tissues.     If  in  any  case  a 
functioning  tissue  is  called  upon  for  an  extraordinary  expenditure  of 
energy,  exhaustion  occurs  very  quickly.     In  the  case  of  shock  the  ner- 
vous system  is  overcome,  and  fails  either  partially  or  altogether  in  the 
performance  of  certain  of  its  normal  functions,  such  as  that  of  main- 
taining the  usual  tension  of  tlie  circulating  system,  and  to  a  lesser 
degree,  perhaps,  that  of  cerebration  and  the  voluntary  motions.     This, 
however,  is  not  the  only  injury  that  occurs  in  shock.     Under  some  cir- 
cumstances the  life-force  as  it  exists  in  the  individual  cell  is  unable  to 
carry  forward  in  the  normal  manner  its  remolecularizations  of  matter 
in  the  processes  of  nutrition  and  denutrition,  and  the  changes  become 
abnormal,  resulting  in  the  formation  of  substances  unhealthful  in  quality 
or  quantity.     This  is  seen  in  fatty  degeneration.     The  tone  of  the  life- 
force  as  it  exists  in  the  individual  cells  is  lowered  to  such  a  degree  that 
the  matter  of  wliich  the  cell  is  composed,  instead  of  passing  regularly 
on  to  the  formation  of  waste  products  in  the  normal  manner,  falls  into 
the  molecular  groupings  of  oil.     This  oil  gathers  in  the  form  of  minute 
globules  in  the  midst  of  the  cell,  instead  of  passing  away  with  the 
normal  waste  products;  which   circumstance  permits  of  its  discovery 
by  means  of  microscopic  examination — a  thing  that  would  be  impossi- 
ble if  the  abnormal  substance  were  more  soluble.     Changes  of  a  similar 
nature  undoubtedly  occur  in  shock,  though  they  difter  in  the  character 
of  the  products.     Just  what  these  changes  are  is  unknown,  but  the 
evidence  that  they  occur  is  to  my  mind  conclusive.     It  has  long  been 
known  that  fright,  or  any  other  form  of  mental  impression  productive 
of  a  slight  degree  of  shock,  is  liable  so  to  change  the  milk  of  the 
nursing  woman  that  it  will  act  as  a  poison  to  the  child.     This  can  be 
explained  only  on  the  supposition  that  the  chemico-vital  changes — the 
remolecularizations  of  matter — which  take  place  in  the  formation  of  the 
waste  products,  and  in  the  elaboration  of  the  secretions  as  well,  have 
been  imperfectly,  or  at  least  improperly,  carried  on,  and  have  resulted 
in  the  formation  of  abnormal  molecular  groupings,  thus  giving  rise  to 
chemical  substances  that  prove  injurious. 

In  the  discussion  of  the  subject  of  fever  it  Avas  explained  that  it 
was  always  the  effect  of  a  material  cause.     One  of  the  most  common 


SHOCK.  723 

of  these  is  always  produced  in  the  peculiar  tissue-changes  that  are 
taking  place  in  the  process  of  inflammation,  and  we  find  fever  to 
result  in  case  the  inflammatory  movement  is  considerable.  All  forms 
of  shock  are  followed  during  the  stage  of  reaction  by  fever.  The  regu- 
larity of  the  occurrence  of  this  fever  leaves  us  no  room  to  doubt  that  it 
has  resulted  from  some  injury  to  the  tissues  which  has  rendered  the 
performance  of  the  chemico-vital  remolecularizations  both  difficult  and 
imperfect  in  their  results,  so  that  molecular  groupings  are  formed  that 
give  a  chemical  substance  capable  of  producing  fever.  There  is,  then, 
in  addition  to  the  paralysis  of  the  vaso-motor  nerve-centres,  or  as  a 
result  of  this,  an  injury  to  some  portion  of  the  tissues;  and  this  may 
be  the  nerve-tissue  through  which  the  chemico-vital  changes  are  ren- 
dered imperfect  or  abnormal. 

The  symjitoms  of  shock  vary  indefinitely  in  its  different  manifesta- 
tions, but  these  differences  are  more  of  degree  than  of  kind.  In  its 
extreme  forms  its  features  are  plainly  marked.  The  appearance  of 
the  patient  is  that  of  the  most  extreme  prostration.  There  is  pallor 
of  the  face  and  of  tlie  whole  surface  of  the  body ;  this  is  also  very 
apparent  in  the  mucous  membranes  where  they  are  exposed  to  view,  as 
in  the  lips  and  mouth.  The  surface  is  abnormally  cold,  and  is  covered 
with  moisture,  sometimes  like  great  drops  of  sweat,  cold  and  clammy 
in  character.  The  features  appear  pinched  and  dull,  the  eyelids  are 
drooped,  and  the  eye  itself  seems  to  have  lost  its  wonted  expression. 
The  debility  of  the  muscular  system  is  apparent  in  every  motion  if  the 
patient  attempts  to  move  at  all,  and  even  in  his  position  Mhen  he  is 
motionless.  The  respiratory  movements  are  usually  feeble  and  short; 
they  may  be  panting  and  irregular  or  gasping,  and  in  the  most  grave 
conditions  may  be  scarcely  perceptible.  The  pulse  is  generally  frequent, 
though  it  may  be  rather  infrequent,  and  occasionally  quite  irregular. 
It  is  always  very  weak,  and  passes  under  the  finger  with  a  short  quick 
stroke,  leaving  the  artery  soft  and  limp  between  the  heart-beats,  and  is 
Tery  compressible,  indicating  the  extreme  relaxation  of  the  arteries. 
The  temperature  is  always  more  or  less  reduced,  and  it  seems  that  the 
amount  of  the  reduction  is  some  indication  of  the  gravity  of  the  case, 
though  some  of  the  cases  with  very  low  temperature  recover  even  after 
a  temperature  of  93°  F.,  and  Wagstaffe  reports  a  case  that  recovered 
after  tlie  extreme  depression  of  91.5°  F.  had  been  reached.  The  mind 
is  generally  clear,  but  the  person  may  be  drowsy  and  bewildered  when 
aroused.  In  a  minority  of  cases  the  senses  are  unusually  acute — so 
much  so  that  the  patient  seems  continually  on  the  alert  and  bordering 
on  a  condition  of  excitement.  In  this  latter  condition  questions  may 
be  answered  in  a  quick,  jerky  manner,  but  more  generally  they  are 
answered  hesitatingly,  as  though  very  slowly  comprehended. 

These  symptoms  may  vary  in  degree  from  a  condition  in  which  death 
occurs  within  a  few  moments  or  a  few  hours  to  that  of  an  impairment 
of  the  functions  to  so  slight  a  degree  as  to  amount  to  nothing  more 
than  an  expression  of  weariness.  Every  conceivable  condition  between 
these  extremes  may  be  noticed.  In  the  medium  or  lighter  forms  of 
shock  there  is  often  seen  that  which  Travers  has  aptly  termed  "  prostra- 
tion with  excitement."     This  may  be  present  from  the  first,  or  it  may 


724  GENERAL  PATHOLOGY. 

become  apparent  during  the  following  reaction.  The  patient  may  seem 
perfectly  frantic  and  tortured  ^vith  the  most  terrible  forebodings,  in 
which  condition  no  question  will  be  answered  or  apparently  noticed.  I 
once  witnessed  a  case  of  this  kind  in  a  man  who  had  had  both  legs  crushed 
under  a  raihvav-car,  and  who  screamed  the  same  words  almost  contin- 
uously until  stopped  by  the  administration  of  an  ansesthetic  preparatory 
to  amputation.  In  this  condition  nothing  in  the  way  of  encouragement 
is  heeded,  no  form  of  advice  or  counsel  is  of  any  use,  though  there 
seems  no  lack  of  consciousness.  The  mind  is  too  completely  occupied 
with  the  terrors  of  the  situation  to  admit  any  other  mental  impression. 
In  all  of  this  the  condition  of  the  circulation  and  of  the  skill,  and  all 
of  the  other  symptoms  except  those  relating  to  the  condition  of  the 
mental  faculties,  are  the  same,  only  perhaps  less  in  degree,  as  in  cases 
of  profound  shock  with  stupor.  This,  like  all  of  the  other  conditions 
of  shock,  may  be  manifested  in  all  degrees  from  a  mere  watchfulness  to 
the  most  complete  delirium. 

The  liability  of  individuals  to  sJwck  seems  not  to  be  regulated  by  any 
known  laws.  One  person  dies  from  shock  under  apparently  the  same 
circumstances  under  Mdiich  another  escapes  it  entirely.  Nothing  definite 
can  be  stated  as  to  the  liability  of  this  or  that  individual  to  shock  under 
given  circumstances ;  yet  it  may  be  affirmed  that  as  a  general  rule  those 
whose  constitutions  have  been  broken  down  by  debauchery  are  more 
liable  to  shock  than  others.  Individual  idiosyncrasy  that  cannot  be 
determined  in  advance  seems  to  have  much  to  do  with  the  difference  of 
liability.  Taken  all  in  all,  it  may  be  said  that  the  liability  to  shock  is 
in  proportion  to  the  extent  of  the  injury.  Hence  grave  forms  of  shock 
are  oftenest  seen  in  connection  with  serious  injuries  and  extensive  sur- 
gical operations.  Extensive  burns,  scalds,  and  contusions,  crushing 
wounds  and  capital  surgical  operations,  are  most  often  attended  with 
grave  forms  of  shock.  The  danger  seems  to  be  greatest  in  case  of 
Avounds  of  the  trunk,  especially  of  the  abdomen,  and  decreases  as  the 
seat  of  injury  is  extended  along  the  extremities.  A  comparatively  large 
projiortion  of  cases  of  shock  have  been  observed  in  connection  with 
railway  accidents,  resulting  in  part,  perhaps,  from  sudden  suspension 
of  motion  or  from  being  thrown  violently  against  objects,  and  in  part 
from  fright.  IVIansel-Moullin  states  that  "  instances  of  severe  and  last- 
ing shock,  often  assuming  most  insidious  forms,  are  met  with  from  time 
to  time  in  cases  of  this  kind,  without  there  being  any  definite  bodily 
lesion,  and,  indeed,  are  often  tlie  more  severe  when  this  is  quite  absent 
and  there  is  no  other  explanation  than  the  general  mental  cause."  Some 
years  ago  I  observed  a  case  illustrative  of  this.  A  car,  when  at  full 
speed,  was  thrown  violently  down  an  embankment,  and  fell  on  its  side. 
One  of  the  passengers  fell  with  his  hands  through  a  window,  where 
they  M'cre  caught  between  the  car  and  the  ground  in  such  a  way  as  to 
hold  him  fast.  The  car  inunediately  took  fire  and  was  burning  rapidly 
when  he  was  rescued.  When  I  saw  him,  four  hours  after,  he  was  in  a 
state  of  profound  shock,  in  which  he  took  no  notice  whatever  of  what 
was  going  on  around  him.  Xo  bodily  injury  was  found  except  a  slight 
cut  on  one  cheek  made  by  glass.  Reaction  began  in  about  twenty-four 
hours,  and  he  made  a  good  recovery. 


SHOCK.  725 

Reaction  from  shock  varies  extremely  in  diiferent  cases.  Sometimes 
it  is  prompt,  and  the  usual  health  is  resumed  rapidly  and  perfectly.  In 
other  cases  it  is  tardy,  and  the  patient  lingers  along  for  days  and  weeks 
without  marked  improvement ;  and  it  is  noteworthy  that  this  is  as 
apt  to  be  the  result  in  the  lighter  as  in  the  graver  forms  of  shock. 
As  a  rule,  reaction  may  be  expected  to  begin  Avithin  one  or  two  days. 
During  the  reaction  the  temperature,  which  is  below  the  normal,  usu- 
ally rises  several  degrees ;  and  the  rule  is  that  there  is  marked  though 
not  very  intense  fever.  The  occurrence  of  this  in  a  mild  degree  is 
regarded  as  favorable,  and  when  it  occurs  promptly  the  patient  will 
usually  go  rapidly  on  to  complete  recovery.  If  it  is  delayed  and  not 
well  marked,  recovery  is  generally  slow  and  often  very  imperfect.  The 
principal  thing  to  be  done  is  to  give  the  patient  quiet  and  as  perfect  rest 
as  possible.  The  large  majority  of  surgeons  recommend  the  judicious 
use  of  stimulants,  especially  brandy,  for  the  purpose  of  favoring  reac- 
tion ;  but  a  few — notably  the  late  Dr.  J.  T.  Hodgen  of  St.  Louis — 
reject  this  treatment  as  bad  practice,  and  prefer  to  depend  on  complete 
rest.  The  mental  condition  is  of  importance.  The  mind  should  be  as 
much  at  rest  as  possible,  and  especially  should  sleep  be  had.  JNIost 
surgeons  agree  in  the  use  of  opium,  when  necessary,  to  procure  this. 
Among  other  stimulants,  strychnia,  belladonna,  and  digitalis  have  been 
used  with  advantage. 

Shock  resulting  from  dental  operaiions  seems  not  to  have  received  due 
consideration  in  past  years,  for  the  reason,  perhaps,  that  it  is  seldom 
seen  in  its  graver  forms.  It  should  not  be  forgotten,  however,  that  it 
is  liable  to  occur  at  any  time  with  all  of  its  attendant  dangers.  But  it  is 
the  lesser  and  more  insidious  forms  of  shock  that  are  most  to  be  feared 
as  a  result  of  dental  operations.  The  following  passage  from  ]Mr. 
Savory's  article  on  this  subject  in  Holmes's  System  of  Surgery  is  appli- 
cable here : 

"  Hitherto,  the  influence  of  shock  has  been  considered  only  in  its 
extreme  effects  when  directly  producing  a  state  of  collapse,  but  it  must 
be  a  very  narrow  view  of  the  subject  which  would  overlook  its  less 
severe  though  much  more  frequent  results.  It  may  operate  in  any 
degree,  and  produce  in  one  case,  as  has  already  been  seen,  instant  death, 
or  a  state  not  to  be  distinguished  from  it  for  a  time  even  by  the  most 
anxious  scrutiny;,  in  another  case  effects  so  trivial  that  the  symptoms 
pass  unnoticed  or  unheeded  by  a  superficial  observer. 

"  There  are  many  cases  on  record,  and  many  more  known  to  every 
surgeon,  of  death  from  this  cause,  less  sudden,  but  in  many  instances 
scarcely  less  inevitable.  In  some  cases  injuries  or  operations  compara- 
tively trivial  in  their  nature  induce  a  condition  of  otherwise  unaccount- 
able debility,  and  terminate  in  death  by  asthenia.  A  careful  inquiry 
into  the  history  of  such  cases  will  often  elicit  facts  which  enable  us  to 
reconcile  the  apparent  disproportion  of  cause  and  effect. 

"After  injuries  or  operations  sufficiently  severe  to  produce  a  serious 
impression  on  the  system,  yet  by  no  means  amounting  to  a  condition  of 
collapse,  reaction  is  sometimes  defective  and  unduly  delayed.  The 
patient  remains  depressed ;  there  is  no  heat  of  surface ;  the  pulse  is 
weak  and  perhaps  unsteady ;  he  does  not  sleep  soundly,  though  he  may 


726  GENERAL  PATHOLOGY. 

be  constantly  dozing ;  and  the  stomach  is  often  irritable.  In  a  word, 
there  is  an  absence  of  '  sympathetic  fever.' " 

In  these  paragraphs  we  tind  an  expression  of  conditions  that  not 
unfrequently  follow  as  a  result  of  dental  operations.  They  are  closely 
akin  to  what  is  known  as  nervous  exhaustion,  but  approach  closer  still 
to  the  condition  of  true  shock  in  its  lighter  manifestations.  These 
two  conditions  grade  into  each  other  in  such  a  way  that  no  exact 
line  can  be  drawn.  The  major  forms  of  shock  occur  suddenly  from 
some  impression  that  overpowers  the  nervous  system  at  a  single  stroke, 
producing  a  marked  dilatation  of  the  whole  vascular  system,  so  as  to 
leave  the  heart  without  a  due  supply  of  blood.  Nervous  exhaustion 
comes  on  very  slowly  from  some  cause  that  continues  to  act,  and  is  often 
very  insidious  in  its  approach.  It  occurs  oftenest,  perhaps,  from  too 
continuous  employment,  mental  strain,  or  any  continuous  condition  that 
overtaxes  the  nervous  enero-ies  for  a  considerable  time.  In  manv  cases 
the  minor  forms  of  shock  do  not  occur  so  suddenly  as  is  usually  the 
case  in  the  major  forms,  nor  so  slowly  as  in  nervous  exhaustion,  but  are 
usually  the  result  of  more  or  less  prolonged  pain,  nervous  irritation, 
mental  excitement,  or  some  form  of  extraordinary  effort.  On  this 
point  Mr.  Savory,  after  describing  the  more  immediate  results  of 
shock,  says :  "  But  the  effects  of  a  shock  to  the  system  are  not  always 
thus  limited  in  their  nature  and  duration.  Those  which  have  been 
described  may  be  termed  primary  or  direct,  but  sometimes  these  are 
succeeded  by  those  that  are  more  remote  and  secondary,  including  per- 
haps, after  a  shorter  or  longer  interval,  grave  mischief,  or  it  may  be 
even  death.  It  is  not  uncommon  to  have  various  forms  of  local  disease 
or  disturbance  of  the  general  health  referred  to  some  previous  shock 
which  the  system  has  sustained.  '  He  has  never  been  the  man  he  was 
since — '  is  a  familiar  allusion  to  a  case  of  this  kind  ;  and  after  making 
every  allowance  for  exaggeration  and  misinterpretation,  the  relation  of 
cause  and  effect  between  some  j)revious  shock  and  present  mischief  may 
often  be  clearly  and  unequivocally  established." 

Such  results  as  these  arc  liable  to  hajipen  occasionally  in  dental  prac- 
tice, and  the  lighter  manifestations  of  shock  are  of  frequent  occurrence. 
A  patient,  perhaps  a  lady,  presents  herself  at  the  time  of  her  appoint- 
ment to  have  several  fillings  inserted.  There  may  be  some  special 
reason  on  her  part  or  on  the  part  of  the  operator  for  a  long  sitting.  As 
the  operations  j^rogress  it  is  found  that  they  are  very  painful,  yet  the 
patient  is  anxious  to  have  them  done  with,  and  makes  an  heroic  effort  to 
bear  the  pain  so  that  their  accomplisliment  may  not  be  delayed.  Thus 
the  ojierations  go  forward  for  one,  two,  three,  and  it  may  be  four  hours 
continuously.  The  operator  may  even  be  encouraged  to  persist  by  the 
not  unusual  fact  that  the  patient  flinches  less  in  the  third  hour  than  in 
tlie  first ;  but  if  he  would  follow  up  the  pulse  from  hour  to  hour,  he 
would  find  certain  changes  taking  ])lacc.  It  will  have  lost  markedly 
in  tone  and  volume,  and  as  it  passes  under  the  finger  may  perhaps 
present  a  peculiar  thrill  that  was  not  ])resent  at  the  beginning  of  the 
operations.  Sometimes  it  will  be  more  frequent,  sometimes  less.  There 
is  also  a  ]ierceptible  change  in  the  character  of  the  motions  of  the 
patient.     They  may  be  quick,  with  a  slight  inclination  to  jerkiness,  or 


SHOCK.  727 

be  languid  and  unusually  slow.  The  face  is  pale,  and  the  thermometer 
shows  a  slight  reduction  of  the  temperature.  The  patient  is  finally  dis- 
charged, and  goes  her  way  without  any  very  decisive  sign  that  there  is 
anything  wrong ;  but  she  has  a  restless  night,  and  the  next  day  there  is 
slight  fever.  This  is  of  a  mild  type  perhaps,  and  occasions  no  great 
uneasiness,  or  it  may  be  more  severe  and  accompanied  with  a  feeling  of 
great  weariness.  In  the  more  ordinary  cases  this  passes  away  in  from 
three  to  five  days  with  complete  restoration  to  health,  but  occasionally 
the  patient  falls  into  a  state  of  nervous  exhaustion  from  which  she 
rallies  very  slowly. 

I  might  give  a  number  of  cases  coming  under  my  observation  illustra- 
tive of  this,  but  one  or  two  must  suffice.  One  of  the  most  notable  of 
these  was  observed  some  ten  years  ago.  A  young  lady  of  eighteen  came 
from  a  distance  by  appointment  to  have  carious  teeth  filled.  Upon  exam- 
ination it  was  found  that  there  were  two  exposed  pulps,  besides  other 
smaller  cavities.  Both  the  young  lady  and  her  parents  insisted  that  all 
should  be  done  that  day  if  it  was  possible,  it  being  necessary  that  they 
should  return  on  account  of  important  engagements :  the  lady  said  that 
she  had  no  fears  as  to  bearing  any  necessary  operation,  even  the  direct 
removal  of  the  exposed  pulps.  The  operations  were  proceeded  with, 
and  everything  was  borne  without  a  murmur.  My  patient  was  a  fine 
specimen  of  physical  development,  and  I  soon  found  that  she  prided 
herself  on  her  powers  of  endurance.  The  pulps  were,  at  her  urgent  re- 
quest that  there  should  be  no  delay,  removed  directly  with  the  broach, 
and  the  filling  proceeded  with.  After  three  hours  of  continuous  ope- 
rating the  patient  was  discharged  for  two  hours'  rest.  She  returned 
promptly,  but  something  in  her  appearance  arrested  my  attention  as  not 
being  just  right,  yet  in  answer  to  questions  she  said  she  felt  perfectly 
well,  only  a  little  tired.  The  operations  were  resumed,  and  all  went 
well  at  first,  but  after  an  hour,  the  latter  part  of  which  had  been  occu- 
pied in  the  excavation  of  a  very  sensitive  cavity,  I  found  that  the  pulse 
had  become  very  easily  compressible  and  other  evidences  of  shock  were 
becoming  very  apparent.  Gutta-percha  fillings  were  placed  in  the  cav- 
ities excavated  and  operations  suspended.  I  found  it  necessary  to  assist 
her  to  a  couch,  as  it  was  evident  that  she  was  unable  to  walk  steadily. 
After  two  hours  in  the  recumbent  posture  she  seemed  better,  and  was 
taken  to  the  train  by  her  parents,  and  went  home,  some  fifty  miles  by 
rail,  and  I  saw  her  no  more.  I  afterward  learned  from  her  mother  that 
her  condition  became  much  worse  en  route  home,  and  that  for  four  or 
five  days  she  was  in  "  a  stupid  condition,"  and  after  this  she  passed  into 
a  nervous  fever  which  continued  for  several  months.  Up  to  the  time  I 
last  heard  from  her,  four  years  after  the  incident,  she  had  been  more  or 
less  an  invalid. 

In  dental  practice  the  temptation  to  overtax  patients  who  are  so  situ- 
ated that  it  is  very  inconvenient  for  them  to  make  frequent  visits  is  very 
great,  and  great  care  should  be  exercised  to  avoid  evil  results.  The 
case  I  have  given  is  aii  extreme  one,  it  is  true,  but  many  cases  of  a  less 
grave  character  occur,  and  from  much  more  trivial  operations.  Only 
a  short  time  ago  I  placed  fillings  in  two  lower  molars  for  a  lady  of 
about  twenty-three,  at  the  time  in  rather  delicate  health,  though  she 


728  GENERAL  PATHOLOGY. 

considered  herself  fairly  well.  The  teeth  Avere  quite  sensitive,  but  there 
was  no  unusual  difficulty.  The  operation  was  followed  by  very  decided 
shock,  sufficient  to  confine  her  to  the  bed  for  several  days.  After  six 
weeks  the  operations  on  other  teeth  were  undertaken,  special  care  being 
exercised  ;  yet  after  an  operation  of  an  hour's  duration  there  was  decided 
prostration,  followed  the  next  day  by  fever  and  restlessness.  This  patient 
was  evidently  extraordinarily  susceptible  to  shock,  but  the  case  serves  to 
illustrate  the  necessity  for  due  care  in  the  performance  of  dental  opera- 
tions, and  especially  the  necessity  for  a  close  study  of  this  subject  by 
dentists  as  well  as  by  other  specialists  in  medicine. 


DENTAL  CARIES. 

By  G.  V.  BLACK,  M.  D.,  D.  D.  S. 


Introduction. 

Caries  of  the  Teeth  consists  of  a  chemical  disintegration  of 
the  elements  of  the  tooth,  molecule  by  molecule.  This  disintegration 
always  begins  on  the  surface  of  the  tooth,  usually  in  some  pit,  groove, 
or  other  irregularity,  at  the  point  of  contact  of  the  proximal  surfaces 
and  about  the  necks  of  the  teeth.  Such  places  are  protected  from  the 
friction  of  mastication  and  the  movements  of  the  lips  and  tongue,  thus 
favoring  the  lodgment  of  particles  of  food  until  fermentation  takes 
place,  this  resulting  in  the  formation  of  products  which  decompose  the 
constituents  of  the  tooth.  When  a  beginning  has  been  made,  the 
destructive  process  spreads  toward  the  interior  of  the  organ ;  and,  as 
the  dentine  is  more  readily  affected  than  the  enamel,  a  cavity  is  formed 
whose  interior  is  larger  than  its  orifice.  This  cavity  enlarges  very  grad- 
ually— so  slowly,  indeed,  that  usually,  if  examined  at  an  interval  of  a 
week  or  a  month,  no  progress  is  appreciable.  But  if  the  examination  be 
instituted  after  an  interval  of  two  or  three  months,  it  will  generally 
be  found  that  progress  is  very  decided.  Thus,  the  area  of  the  decay 
increases  steadily  until  the  crown  of  the  affected  tooth  is  destroyed. 
There  are,  however,  in  different  cases  great  variations  in  the  rapidity 
with  which  the  disease  advances.  As  caries  progresses,  the  enamel,  on 
account  of  its  greater  resistance  to  disintegration,  is  undermined  by  the 
solution  of  the  dentine  and  is  left  unsupported ;  the  enamel  itself,  how- 
ever, also  slowly  disintegrates  on  its  inner  surface,  and  finally  breaks 
away,  leaving  an  irregular  jagged  opening.  This  effect  is  extremely 
variable.  Sometimes  the  breaking  away  is  such  that  the  cavity  is 
widely  open  before  there  is  very  much  destruction  of  tooth-substance ; 
in  other  cases  a  larger  portion  of  the  dentine  may  be  destroyed,  while 
the  enamel  remains  almost  perfect. 

The  color  of  caries  varies  from  an  ashy  gray  or  white  to  a  bluish  or 
deep  black.  Every  shade  between  these  may  be  found.  Many  of  the 
intermediate  colors  have  something  of  a  yellowish  hue.  It  is  common 
for  the  decayed  mass  to  present  different  shades  of  color  in  different 
parts.  The  rule  is  that  the  outer  parts  are  darkest,  while  the  inner 
approach  more  nearly  the  color  of  the  tooth,  or  may  even  be  lighter 
in  shade.  Occasionally  other  colors  may  be  seen,  but  I  am  persuaded 
that  these  are  accidental  and  dependent  on  some  unusual  extraneous 
deposit.  Those  decays  that  present  in  the  greater  part  of  the  mass  the 
nearest  approach  to  the  color  of  the  tooth,  or  are  lighter  in  shade,  rep- 

729 


730  DENTAL  CARIES. 

resent  those  that  are  rapidly  progressive ;  while,  on  the  other  hand,  those 
that  present  a  deep-black  appearance  throughout  their  mass  are  making 
very  slow  progress  or  have  ceased  to  progress  at  all.  These  latter  have 
been  termed  stationary  decays. 

It  is  not  necessary  that  all  the  elements  of  the  tooth-substance  be 
disintegrated  to  constitute  caries.  In  most  cases  of  rapidly  progressive 
caries  there  is  remaining  in  the  softened  mass  a  sufficient  amount  of  the 
original  elements  to  preserve  the  histological  forms  of  the  dentine.  This 
serves  to  separate  caries  sharply  from  certain  other  accidents  and  diseases 
to  which  the  teeth  are  liable,  among  which  I  may  mention  mechanical 
abiasion,  spontaneous  or  chemical  abrasion,  and  the  absorptive  pro- 
cesses. In  these  the  constituents  of  the  dentine  are  removed  entire,  and 
in  the  first  two  the  surface  is  left  hard  and  firm,  while  in  the  latter  the 
softening  is  very  slight  indeed.  These  must  not  be  confomided  with 
caries.  They  will  not  be  considered  in  this  article  except  as  they  stand 
related  to  true  caries.  In  caries  the  elements  of  the  dentine  are  always 
removed  piecemeal,  producing  first  a  softened  mass,  which  afterward 
suifers  further  disintegration,  and  finally  falls  to  pieces,  forming  a 
cavity.  Therefore,  it  is  a  constant  condition  of  progressive  caries  that 
those  portions  of  the  decaying  mass  that  are  nearest  the  sound  dentine 
are  comparatively  little  softened,  and  upon  microscopic  section  present 
the  histological  forms  of  the  dentine  M'ith  but  little  change.  As  we 
recede  farther  from  the  junction  of  the  diseased  part  with  that  which 
remains  normal,  we  find  that  the  disintegration  is  progressive  until 
all  trace  of  the  original  form-elements  are  lost,  and  we  have  noth- 
ing remaining  but  debris  or  an  open  cavity. 

Caries  of  the  teeth  has  been  known  in  all  historic  ages  of  the  world, 
and  wherever  prehistoric  human  remains  have  been  discovered  traces 
of  this  disease  have  been  found.  It  seems  to  be,  and  to  have  been, 
universal  in  the  sense  of  affecting  all  nations  and  tribes  of  the  human 
race.  All  have  not  been  equally  affected,  but  no  race  of  men  seems  to 
have  escaped  its  ravages.  It  has  been  thought  that  the  savage  races 
were  not  so  much  afflicted  as  the  civilized,  but  my  own  study  of  the 
remains  of  ancient  peoples  will  not  bear  out  this  opinion.  This  research 
has,  however,  been  limited  within  comparatively  narrow  bounds — too 
narrow,  perhaps,  to  serve  as  the  basis  of  conclusions.  Unfortunately, 
the  literature  of  the  subject  furnishes  no  data  that  are  of  much  value 
in  this  direction,  l)ut  what  there  are  strongly  support  the  statements 
made  above.  Some  hasty  examinations  recenth'  made  of  the  condition 
of  prehistoric  skulls  found  in  a  number  of  the  principal  museums  show 
that  those  ])coples  were  subject  to  decay  of  the  teeth  to  as  great  an  ex- 
tent as  the  civilized  races  of  to-day.  It  is  possible  that  future  research 
upon  this  point  will  show  that  certain  races  which  have  lived  in  a  certain 
way  or  u)>on  certain  kinds  of  food  may  have  suffered  less  than  others 
which  have  lived  differently.  The  studies  I  have  been  able  to  make 
in  this  direction  indicate  that  the  races  of  men  who  have  eaten  largely 
of  acid  fruits  have  had  less  decay  of  the  teeth  than*  those  who  have 
been  debarr(>d  by  their  position  or  climate  from  the  use  of  such  articles 
of  food.  Generally,  those  tribes  that  have  subsisted  largely  on  flesh 
and  grain  have  suffered  more  from  caries  than  those  that  have  had  a 


ETIOLOGY  OF  CARIES.  731 

more  exclusively  vegetable  and  fruit  diet.  Our  knowledge  upon  this 
point  is,  however,  too  meagre  to  warrant  any  lengthy  discussion  of  it. 
Among  the  individuals  of  the  same  tribe  or  nation  there  are  observed 
the  greatest  differences  in  the  liability  to  caries  of  the  teeth.  Some  per- 
sons in  almost  every  community  escape  it  entirely,  while  others,  their 
neighbors,  subjected  seemingly  to  the  same  influences,  suffer  from  its 
ravages.  The  reasons  for  this  are  wholly  unknown.  The  persons  who 
escape  this  disease  are,  however,  comparatively  few.  There  is  no  dis- 
ease that  is  so  common  or  so  widespread  or  that  so  generally  afflicts 
the  human  family. 

Etiology  of  Caries. 

In  the  study  of  the  causes  of  disease  it  is  common  to  divide  them 
into  predisposing  and  exciting.  The  predisposing  causes  are  such  as 
render  the  individual  more  liable  to  attack,  but  are  not  in  themselves 
suflicient  to  usher  in  the  disease.  The  exciting  causes  are  such  as  are 
actually  responsible  for  its  inauguration.  It  is  the  custom  of  writers 
on  pathology  to  consider  the  predisposing  causes  of  the  particular  dis- 
ease under  consideration  first,  and  this  is  usually  the  most  natural 
order  of  presentation ;  but  in  the  present  case  there  seems  to  be  suf- 
cient  reason  for  reversing  this  order.  It  does  not  appear  that  the  pre- 
vious consideration  of  the  predisposing  causes  will  materially  contribute 
to  an  understanding  of  the  exciting  causes,  but  these  will  be  much  easier 
understood  after  the  exciting  causes  have  been  studied,  and  the  presenta- 
tion will  thus  be  simplified. 

It  seems  well,  however,  that  in  the  beginning  of  this  study  we  notice 
the  views  that  within  a  century  past  have  from  time  to  time  been  pre- 
sented, and  which  illustrate  the  growth  of  thought  as  observation  and 
experience  have  added  fact  after  fact  to  our  knowledge  of  the  subject. 
It  has  been  treated  of  by  very  ancient  writers,  but  the  works  of  Boudett 
and  Jourdain,  which  appeared  within  the  interval  from  1754  to  1766, 
seem  to  have  been  the  foundation  of  the  scientific  investigations  that 
were  undertaken  in  after-years,  and  mark  an  era  of  awakening  thought 
and  of  experimental  study.  Before  this  time  many  had  written,  and  in 
a  sense  had  written  well,  but  they  seem  to  have  recorded  such  thoughts 
as  came  to  them  from  what,  as  compared  with  the  authors  mentioned 
and  those  that  came  after  them,  may  be  considered  casual  observation. 
The  common  thought  of  the  medical  men  of  those  days  was  that  decay 
of  the  teeth  resulted  from  inflammation,  and  the  effort  was  to  account 
for  its  phenomena  on  tliat  hypotliesis.  John  Hunter,  who  was  a  very  close 
observer  and  a  careful  writer,  while  regarding  caries  of  the  teeth  as  result- 
ing from  inflammation,  much  in  the  same  manner  as  necrosis  of  the 
bones  or  mortification  of  the  soft  parts,  expresses  dissatisfaction  with 
this  idea,  deeming  it  insufficient  for  the  explanation  of  the  phenomena 
of  gradual  decomposition  wdth  the  formation  of  the  carious  cavities. 
He  does  not,  however,  offer  any  theory  on  this  point. ^ 

^  This  is  fairly  shown  in  the  following  extract  from  the  work  of  John  Hunter 
(Practical  Treatise  on  the  D('.sra.s^.?  of  the  Teeth,  and  the  Consequences  of  them,  1778): 
"  The  most  common  disease  to  which  the  teeth  are  exposed  is  such  a  decay  as  would 


732  DENTAL  CARIES. 

Mr.  Fox  in  LS06,  and  others  of  about  this  period,  were  much  more 
exact  in  their  descriptions  of  the  processes  of  caries.  It  was  regarded 
as  resulting  from  inflammation  of  the  lining  membrane  of  the  pulp- 
chamber  (membrana  eboris).  This,  in  case  it  was  severe,  was  regarded 
as  depriving  the  dentine  of  its  nutrition,  and,  it  was  sujiposed,  would 
occur  at  isolated  points  within  the  pulp-chamber,  as  in  inflammation  of 
the  periosteum  of  the  bones,  causing  the  death  of  certain  portions  of 
the  dentine,  Avhich  would  then  decompose  with  the  formation  of  the 
carious  cavities. 

Mr.  Bell  as  late  as  1829  still  regarded  caries  as  a  result  of  inflam- 
mation, but  gives  a  different  explanation  of  the  process.  He  assumes 
as  a  cause  an  inflammation  of  the  dentine  beginning  immediately  beneath 
the  enamel,  or,  in  other  words,  in  the  superficial  portions  of  the  dentine, 
resulting  in  the  death  of  the  part  inflamed.  This  dead  part  then  acts 
as  an  irritant,  causing  the  continuance  of  the  inflammation,  and  thus 
the  process  is  progressive  until  the  destruction  of  the  crown  of  the  tooth 
is  accomplished.     He  says  : 

"  It  (caries)  may  be  defined,  mortification  of  amj  jmrt  of  a  tooth, producing 
gradual  decomposition  of  its  substance.  The  latter  clause  of  the  definition 
is  not,  perhaps,  essential,  but  it  expresses  the  invariable  condition  of  the 
disease. 

"  The  true  proximate  cause  of  dental  gangrene  (caries)  is  inflammation, 
and  the  following  appears  to  be  the  manner  in  which  it  takes  place:  When, 
from,  cold  or  any  other  cause,  a  tooth  becomes  inflamed,  the  part  which  suf- 
fers the  most  severely  is  unable,  from  its  possessing  comparatively  but  a 
small  degree  of  vital  power,  to  recover  from  the  efiects  of  inflammation, 
and  mortification  of  the  part  is  the  consequence 

"  The  situation  in  which  gangrene  (caries)  invariably  makes  its  first 
appearance,  immediately  under  the  enamel,  upon  the  surface  of  the  bone, 
is,  I  think,  ex])]icaljle  only  with  the  view  I  have  taken  of  the  structure  of 
the  teeth  and  tlie  nature  of  this  disease.  As  the  vessels  and  nerves  which 
supply  the  bone  of  the  teeth  are  principally  derived  from  the  internal 
membrane,  it  is  natural  to  conclude  that  in  so  dense  a  structure  the  organ- 
ization would  be  less  perfect  in  those  parts  which  are  fiirthest  removed 
from  its  source,  and  that,  in  the  same  proportion,  they  would  be  less  cap- 
able of  resisting  the  progress  of  mortification 

"The  continued  and  invariable  progress  of  dental  gangrene  is  only  to  be 
accounted  for  by  following  up  the  same  reasoning.  When  a  portion  of 
any  of  the  other  bones  loses  its  vitality,  it  acts  as  an  extraneous  body,  pro- 
ducing irritation  in  the  surrounding  parts,  and  a  process  of  absorption  is 
set  up  in  a  line  of  living  bone  in  contact  with  it  in  order  to  effect  its  sepa- 
ration. A  similar  effort  ap])ears  to  me  to  be  made  in  gangrene  of  the  teeth, 
but  with  a  very  diffei'ent  result,  in  accordance  with  the  difference  in  the 

appear  to  deserve  the  name  of  mortification.  But  there  is  something  more;  for  tlie 
simple  death  of  the  part  would  produce  but  little  etiect,  as  we  find  that  teeth  are  not 
subject  to  jiutrefaction  after  death,  and  therefore  I  am  apt  to  suspect  that  during  life 
there  is  some  operation  going  on  that  produces  a  change  in  the  diseased  part.  It  almost 
always  begins  externally  in  the  small  part  of  the  body  of  the  tooth,  and  commonly 
appears  first  as  an  opa<pie  white  spot.  This  is  owing  to  the  enamel  losing  its  regular 
crystalline  texture  and  bcini;  reduced  to  a  state  of  powder,  from  the  attraction  of  cohe- 
sion being  destroyed,  which  i)roduces  similar  effects  to  those  of  powdered  crystal. 
When  this  has  crinnbled  away,  the  bony  part  of  the  tooth  is  exposed  (the  dentine); 
and  when  the  disease  has  attacked  this  part,  it  generally  appears  as  a  brown  speck." 


ETIOLOGY  OF  CARIES.  733 

structure  of  the  two  seats  of  the  disease.  When  a  portion  of  the  tooth  is 
killed  by  inflammation,  it  excites,  as  in  the  other  case,  an  increased  action  in 
the  vessels  of  the  surrounding  portion  of  bone;  but  that  very  action, which 
in  such  bones  as  possess  greater  vital  power  becomes  remedial  by  promot- 
ing the  removal  of  the  cause  of  irritation,  produces  in  the  present  case  the 
continued  extension  of  the  disease,  for  the  irritation  thus  excited,  instead 
of  effecting  the  removal  of  the  part  by  absorption,  as  in  other  necrosed 
l)ones,  at  once  destroys  its  vitality  and  renders  it  only  an  additional  por- 
tion of  dead  matter  to  that  which  had  already  existed.  This,  in  its  turn, 
becomes  an  extraneous  and  irritating  body  to  the  surrounding  bone,  in 
which  the  same  action  is  set  up  and  the  same  mortification  produced ;  and 
thus  portion  after  portion  is  successively  irritated  and  killed,  until  the 
Avhole  crown  of  the  tooth  is  destroyed." 

Dr.  Fitch  of  Philadelphia,  who  wrote  in  1829,  also  expresses  very 
similar  views,  and  in  the  second  edition  of  his  work,  published  in  1835, 
I  find  this  view  maintained  and  supported  by  citations  of  the  works  of 
Hunter,  Fox,  Koecker,  and  others. 

Koecker,  while  holding  opinions  almost  identical  with  those  of  Bell 
as  to  the  part  taken  by  inflammation  in  the  initiation  and  progress  of 
caries,  adds  a  new  thought.  After  a  full  and  careful  reading  of  his 
work,  I  should  interpret  his  meaning  to  be  about  this  :  Decay  is  a  two- 
fold process  :  the  first  of  these  is  inflammation  of  the  dentine,  resulting 
in  the  death  of  a  portion  of  the  inflamed  area ;  the  second  is  the  disin- 
tegration of  this  dead  or  mortified  part  by  chemical  agencies  or  putre- 
faction. ^Vhile  thus  recognizing  the  agency  of  chemical  processes  in  the 
production  of  the  cavity,  he  supposes  that  they  act  only  on  parts  which 
have  been  rendered  inert  by  a  preceding  inflammatory  process.  He 
says :  ^ 

"  One  great  cause  of  confusion  and  contradiction  pre-eminently  discover- 
able in  every  essay  treating  either  theoretically  or  practically  of  this  fatal 
malady  (caries)  of  the  teeth  is  the  surprising  manner  in  which  the  disease 
itself  has  been  confounded  with  its  efiects,  viz.  putrefaction,  or  the  living 
tooth  under  the  influence  of  the  disease,  and  the  dead  tooth  which  has  been 
destroyed  by  it — an  error  by  which  authors  have  been  led  aAvay  from  the 
subject  in  their  inquiries  and  observations,  and  have  been  induced  to  adopt 
and  to  advance  theories  and  practices  false  and  unnatural  in  their  fiicts 
and  principles,  as  well  as  dangerous  and  destructive  in  their  application. 

"  Caries  of  the  teeth  must  be  considered  as  similar  to  gangrene  in  other 
parts  of  the  system.  And  where  we  speak  of  caries  as  a  disease  we  mean 
that  diseased  action  in  the  bony  structure  of  the  living  tooth  produced  by 
the  chemical  irritation  of  its  dead  and  rotten  parts. 

"  Hence  it  is  indispensable  that  we  should  make  a  due  distinction 
between  caries  considered  as  a  disease  in  the  tooth  and  the  effect  of  that 
disease — viz.  mortification  and  putrefaction  of  its  whole  structure. 

"  Caries,  in  fact,  is  that  state  of  the  tooth  in  which  mortification  has 
taken  place  in  one  part  and  inflammation  in  the  part  contiguous  to  it,  the 
former  originally  produced  by  the  latter,  and  the  latter  continually  kept 
up  by  the  former." 

Nevertheless,  this  author,  in  common  with  his  contemporaries,  de- 
scribes two  forms  of  caries — one  beginning  on  the  surface  of  the  tooth, 

^  Principles  of  Dental  Surgery,  by  Leonard  Koecker,  M.  D.,  p.  111. 


734  DENTAL  CARIES. 

and  the  other  beginning  in  the  interior  of  tlie  tooth-structure,  internal 
caries.  This  latter  he  seems  to  have  regarded  as  analogous  to  abscess 
occurring  in  the  bone,  and  says : 

"  As  the  disease  is  more  actively  resisted  by  the  greater  vascularity,  and 
consequent  activity,  of  the  internal  structure  than  by  the  harder  and  less 
vital  external  parts  of  the  tooth,  it  never  proceeds  so  far  toward  the  cavity 
containinji;  the  nerves  as  to  render  this  membrane  altogether  unprotected 
by  the  bony  structure,  before  it  has  penetrated  through  the  external  osseous 
parts,  including  the  enamel,  and  has  thus  formed  a  natural  outlet  for  the 
bony  abscess." 

It  is  curious  how  long  and  how  continuously  this  old  error  of  regard- 
ing caries  as  having  its  beginnings  within  the  structure  of  the  dentine 
was  maintained — an  error  that,  seemingly,  should  have  been  corrected 
by  any  reasonably  close  observer.  Yet,  with  the  then  pre\-ailing  sup- 
position that  caries  was  the  result  of  inflammation,  there  seemed  to  be 
no  reason  why  it  should  not  as  readily  have  its  beginning  in  the  depths 
of  the  dentine  as  on  its  surface.  Koecker  makes  a  sharp  advance,  how- 
ever, ujion  the  observations  of  his  predecessors,  in  that  he  affirms 
decisively  that  caries  never  extends  inwardly  so  far  as  the  pulp  of  the 
tooth  without  having  first  appeared  on  the  surface  of  the  organ. 

It  will  be  noticed  that  these  views  coincide  with  the  theories  of  the 
causes  of  diseases  of  the  bones  in  general,  but  especially  those  resulting 
in  caries  or  necrosis.  Decay  of  the  teeth  was  regarded  as  a  sim- 
ilar affection,  but  it  was  assumed,  that,  on  account  of  their  inability  to 
repair  the  damages  to  their  structure,  the  dead  portion  decomposed  and 
a  cavity  was  formed.  The  causes  which  were  then  generally  regarded 
as  leading  to  this  inflammation  were  changes  of  temperature  and  other 
injurious  impressions  upon  the  surface  of  the  teeth.  It  was,  however, 
held  l)v  some  that  the  causes  might  be  wholly  internal,  and  that  decay 
might  l)egin  in  the  internal  parts  of  the  tooth  (Fox)  and  work  its  way 
outward,  not  appearing  on  the  surface  until  great  damage  had  already 
been  sustained.  This  opinion  followed  naturally  from  the  supposition 
that  decay  resulted  from  inflammation  beginning  in  the  membrana 
eboris.  In  the  bones  inflammation  of  the  periosteum  may  deprive 
the  part  beneath  of  nourishment  and  cause  its  necrosis ;  after  this 
manner,  inflammation  of  the  membrana  eboris  was  regarded  as  depriv- 
ing the  superimposed  dentine  of  its  nourishment,  causing  caries.  But 
the  supposition  most  generally  advocated  was  that  the  inflammation 
began  in  the  dentine,  just  beneath  the  enamel. 

About  1830  the  inflammatory  theory  was  attacked  by  a  very  large 
nundier  of  intelligent  dentists,  and  it  was  shown  that,  without  great 
modification,  it  was  untenable.  Harris  in  America,  Robertson  in  Eng- 
land, Regnard  in  France,  and  very  many  others,  presented  arguments 
against  it.  Among  the  most  potent  of  these  was  that  based  on  the  fact 
that  human  teeth  that  had  been  removed,  and  afterward  prepared  and 
mounted  as  substitutes,  artificial  teeth  made  from  ivory,  etc.,  were  as 
liable  to  decay  as  the  natural  organs.  As  such  materials  were  then 
much  used  for  these  purposes,  this  fact  was  very  generally  noted.  This 
decay,  which  was  in  all  respects  like  that  in  the  natural  organs  and  ran 


ETIOLOGY  OF  CARIES.  735 

a  similar  course,  could  not  have  been  caused  by  inflammation  or  by  any- 
vital  process  pertaining  to  the  tooth  itself.  Hence  the  cause  of  decay  must 
be  regarded  as  extraneous  to  the  teeth  and  acting  upon  them  from  without. 
Harris,  especially,  has  given  emphasis  to  another  form  of  argument  that 
deserves  mention  from  its  intrinsic  importance  in  educating  the  mind  to 
the  appreciation  of  the  fitness  of  any  proposed  remedy  for  a  given  dis- 
ease. At  the  time  the  inflammatory  theory  was  in  vogue  as  explaining 
the  nature  of  caries,  the  best  authorities,  although  recommending  the 
operation  of  filling  the  carious  cavities,  expected  only  temporary  relief 
from  it.  But  it  was  rapidly  becoming  the  custom  to  All  the  cavities 
for  the  purpose  of  curing  the  affection,  also  to  remove  superficial  decay 
with  the  file  for  a  similar  purpose.  In  the  hands  of  skilled  persons 
these  operations  were  becoming  very  effective.  It  is  evident  that  if 
the  decay  of  the  tooth  was  the  result  of  vital  forces  resident  within  its 
substance,  these  remedies  would  tend  to  increase  the  mischief  they 
were  designed  to  cure. 

In  1835,  Robertson  of  Birmingham,  England,  published  his  remark- 
able work,^  in  which  he  advanced  the  theory  that  caries  resulted  from 
chemical  disintegration  of  the  tooth-substance,  and  denied  the  agency 
of  inflammation.  This  destruction  was  accomplished,  he  contended, 
by  the  action  of  an  acid  which  was  generated  by  decomposition  of  ali- 
mentary particles  or  of  fluids  of  the  mouth  suffered  to  lodge  about  the 
teeth.  These  points  of  lodgment  were  shown  to  be  the  same  as  those 
in  which  caries  made  its  beginnings,  as  in  pits,  grooves,  and  crevices, 
also  between  the  teeth  or  about  the  margins  of  the  gums. 

Regnard  of  Paris  also  published  a  work  in  1838  in  which  he  defined 
caries  as  ^'destruction  of  the  teeth  by  decomposition.'''  This,  he  contended, 
was  accomplished  by  an  acid  generated  by  decompositions  taking  place 
in  the  very  spot  where  its  effects  were  shown. 

As  supporting  this  opinion,  Regnard  has  formulated  the  following  :^ 

"  1st.  Artificial  teeth  were  fastened  by  threads  of  silk.  These  threads, 
which  surrounded  the  neighboring  teeth,  became  impregnated  with  saliva 
and  covered  with  alimentary  particles,  and  soon  corrupted  them ;  they 
became  then  a  cause  of  caries  to  the  teeth.  This  is  so  true  that  the  limits 
of  the  caries  j^roceeding  from  this  cause  are  traced  by  the  limits  of  the 
thread  itself. 

"  2d.  For  sustaining  the  artificial  teeth  metallic  caps  are  made  to  envelop 
one  or  more  of  the  natural  teeth.  These  constantly  served  to  remove  the 
pain  produced  by  the  wearing  away  of  the  teeth.  These  caps  were  not 
made  with  so  much  precision  that  there  did  not  exist  any  space  between 
them  (and  the  teeth).  The  fluids  of  the  mouth,  the  alimentary  particles, 
soon  lodged  in  these  spaces ;  and  if  the  persons  who  wore  these  caps  were 
not  very  careful,  these  fluids  of  the  mouth,  these  alimentary  particles, 
decomposed  and  became  the  active  cause  of  caries  to  the  teeth.  I  have 
seen  molars  whose  crowns  were  entirely  destroyed  by  this  cause  in  the 
space  of  six,  five,  and  even  four,  months. 

"  3d.  Human  teeth  and  the  teeth  of  the  hippopotamus  were  used  for 
artificial  teeth.     These  teeth,  being  of  an  organic  nature,  are  capable  of 

^  A  Practical  Treatise  on  the  Human  Teeth,  f^hnwivc/  the  Cans^es  of  thnr  Defitrnclion  and 
the  Meana  of  their  Preservation,  by  William  Robertson,  Old  Square,  Birmingham. 
'Quoted  from  Desirabode,  Part  1st,  p.  169. 


736  DENTAL   CARIES. 

decomposing  in  the  mouth.     Then,  if  by  a  badly-arranged  economy  the  . 
persons  who  wore  them  still  preserved  them  when  they  were  in  a  state  of 
decomposition,  they  decayed  the  neighboring  teeth  which  are  in  immediate 
contact  Avith  them." 

Regnard  further  enforces  his  doctrine  by  the  following  considerations : 

"  If,  now,  I  devote  my  attention  to  the  different  parts  of  the  teeth  in 
which  decay  commences,  I  see  that  they  are  precisely  those  Avhere  the  ali- 
ments and  tiuids  of  the  mouth  stop  and  remain  snfficiently  long  to  decom- 
pose themselves.  It  is  in  the  necks  of  the  teeth,  in  the  interstices  of  these 
organs,  in  the  anfractuosities  of  the  large  molars,  in  these  pointed  holes 
that  we  observe  sometimes  upon  the  external  face  of  the  first  and  second 
large  inferior  molars  or  upon  atrophied  teeth.  If  we  reflect  precisely  upon 
the  mode  of  action  of  caries,  we  see  that  they  act  in  the  same  manner  as  an 
acid,  that  they  deprive  the  tooth  of  its  phosphate  of  lime,  and  upon  the 
point  where  it  exerts  itself  reduces  it  to  a  cartilaginous  substance.  Let 
us  see  if  we  can  find  in  the  decomposition  of  the  alimentary  particles  or 
buccal  humors  an  explanation  of  these  phenomena.  Now,  chemistry  teaches 
us  that  all  vegetable  or  animal  substances  in  a  state  of  decomposition  give 
birth  to  aeidiferous  products,  to  nitric  acid,  sulphuric  acid,  etc. — all  acids 
which  produce  the  same  effect  on  the  teeth," 

Regnard  advanced  arguments  that  were,  in  eifect,  identical  with  those 
of  Robertson.  These  views  were  immediately  antagonized  in  France  by 
M.  Desirabode.  While  this  author  did  not  deny  that  the  teeth  might 
be  injured  by  acids,  he  says  :  "  To  take  the  action  of  acids  upon  the 
teeth  as  the  cause  of  decay  in  as  absolute  a  sense  as  Regnard,  is,  accord- 
ing to  our  opinion,  an  error — a  great  error." 

In  opposition  to  the  theory  advanced  by  Regnard,  M.  Desirabode 
formulates  the  following  propositions :  ^ 

"  1st.  A  great  number  of  caries  commence  in  the  ivory,  which  is  often 
deeply  affected,  whilst  the  enamel  is  entire 

"  2d.  Many  teeth,  principally  the  last  large  molars,  come  from  their 
alveoli  deeply  decayed,  without,  consequently,  having  been  submitted  to  the 
action  of  any  kind  of  an  acid. 

"  3d.  If  it  was  always  and  solely  an  acid  which  affects  the  teeth,  this 
action  would  be  general ;  it  would  have  hut  one  point  of  decay ;  the  ivhole 
of  the  dental  system  would  certainly  be  decayed. 

*  "^      *  *  *  *  * 

"  oth.  Finally,  the  saliva  and  buccal  humors  are  not  as  frequently  acid 
as  Regnard  thought ;  we  have  often  found  alkalies  among  persons  who  had 
their  teeth  badly  decayed.  Our  researches  in  this  respect  accord  perfectly 
with  the  opinion  of  Dr.  Donni,who  expresses  himself  thus: 

"  *  The  alkalinity  of  the  saliva  has  been  avowed  long  since,  but  it  has 
been  proven  only — in  these  latter  years  particularly — by  the  experiments 
of  Tiedman  and  Gmelin.'  " 

In  regard  to  the  first  of  these  propositions  he  says : 

"  Caries,  according  to  our  knowledge,  as  we  have  already  said,  proceeds 
frequently  from  the  interior  to  the  exterior.  Smote  in  its  vitality  either 
by  an  act  of  nature  which  cannot  be  explained,  and  to  which  the  pulp  is 

'  Complete  Ftemems  of  the  Science  and  Art  nj  Dentistry,  by  j\[.  Desirabode,  Surgeon 
Dentist  to  the  King,  Part  1st,  p.  160. 


ETIOLOGY  OF  CARIES.  737 

not  always  a  stranger,  or  because  the  delicateness  of  its  tissue  was  not  able 
to  resist  the  agents  with  which  teeth  are  constantly  brought  in  contact,  the 
ivory  becomes  the  seat  of  a  change  which  affects  at  the  same  time  its  color 
and  the  force  of  cohesion  w^hich  unites  its  particles.  A  yellow  or  brown 
spot  manifests  itself  near  the  enamel,  Avhich  it  invades  by  degrees  until  it 
extends  upon  the  surface  of  the  crown.  This  envelope  loses  in  this  respect 
its  transparency,  a  natural  consequence  of  the  separation  of  the  elements 
which  constitute  it.  Whilst  the  interval  layer  of  ivory  which  unites  the 
enamel  with  the  subjacent  layers  is  not  destroyed,  the  spot  preserves  the 
color,  and  even  shining  aspect,  which  belongs  to  the  teeth ;  but  it  loses  this 
brilliancy  as  soon  as  the  connection  is  severed  which  binds  the  ivory  and 
enamel  together." 

He  then  proceeds  with  the  presentation  of  the  usual  arguments  in 
favor  of  the  old  hypothesis,  which  are  fairly  represented  in  the  above. 
It  is  easy  for  us  of  the  present  generation  to  see  that  these  arguments 
were  based  upon  erroneous  observations,  but  we  must  remember  that 
very  many  facts  that  are  thoroughly  established  to-day  were  then  either 
unknown  or  the  observations  leading  to  their  establishment  were 
accredited  by  comparatively  few  persons.  And  in  this  instance  the 
great  majority  of  dental  operators  asserted  that  decay  did  begin  in 
the  interior  of  the  dentine.  This  illustrates  some  of  the  difficulties  in 
the  way  of  advance  of  thought. 

It  must  be  remembered  that  at  the  time  these  works  were  written  the 
views  expressed  by  Robertson  and  Regnard  were  in  the  most  direct 
opposition  to  the  theory  generally  lield — namely,  that  caries  resulted  in 
some  way  from  inflammation  of  the  dentine ;  and,  as  might  be  expected, 
they  were  not  very  readily  accepted.  These  authors  denied  in  toto  the 
influence  of  inflammation  in  the  production  of  caries,  and  advanced 
what  has  since  been  known  as  the  chemical  theory — that  all  caries  of 
the  teeth  is  the  result  of  chemical  action  or  is  caused  by  the  operation 
of  a  corrosive  agent  acting  from  without.  This  entirely  precluded  the 
idea  that  decay  ever,  in  any  case,  had  its  beginning  in  the  internal  parts 
of  a  tooth,  and  the  accuracy  of  the  observations  that  led  to  that  belief 
was  boldly  questioned  and  denied.  Further,  the  origin  of  the  corrosive 
agent  was  accounted  for  on  the  hypothesis  (for  it  could  not  at  that  time 
have  been  said  to  be  proven)  that  it  was  produced  at  the  very  spot 
where  decay  began  by  the  lodgment  and  fermentation  of  particles  of 
food.  Each  of  these  authors  proceeds  to  examine  most  attentively  the 
particular  spots  at  which  each  of  the  several  teeth  are  most  liable  to  the 
beginnings  of  decay,  and  finds  that  it  never  occurs  on  clean  and  smooth 
surfaces,  but,  on  the  contrary,  the  attack  is  in  all  instances  made  at  such 
points  as  collect  and  retain  alimentary  particles,  as  in  the  interstices 
between  the  teeth,  in  pits  and  grooves  in  the  enamel,  or  at  such  points 
as,  from  any  cause  whatever,  retain  particles  until  fermentation  takes 
place ;  consequently,  they  claim  that  decay  is  caused  by  an  acid  produced 
by  the  fermentation  of  particles  of  food  at  the  spot  where  the  decay  com- 
mences. So  far  as  it  is  here  expressed,  I  believe  this  view^  of  the  etiology 
of  caries  to  be  strictly  correct,  and  that  the  facts  developed  during  the 
succeeding  years  tend  to  confirm  it. 

When  we  consider  the  fact  that  at  the  time  these  authors  wrote  the 

Vol.  .1.-47 


738  DENTAL  CARIES. 

best  of  liuman  thought  and  intelligence,  and  the  deductions  from  all 
observations  except  their  own,  were  diametrically  opposed  to  their  the- 
ory (a  theory  which  all  of  the  labor  of  the  years  intervening  up  to 
the  present  time  has  hardly  been  sufficient  to  demonstrate),  that  the  laws 
of  fermentation  were  very  little  understood,  and  that  they  had  not  the 
means  of  confirming  their  suppositions  by  direct  experiments  made 
either  by  themselves  or  by  others,  their  writings  seem  very  remark- 
able. 

AVhile  their  knowledge  w^as  limited  within  a  comparatively  narrow 
range,  and  their  work  as  a  whole  exhibits  less  of  learning  than  that  of 
many  of  their  contemporaries,  yet  they  perfectly  agree  on  this  point, 
and  evidently  arrived  at  the  true  conclusions  regarding  it  from  a  close 
analytical  study  of  the  phenomena  of  decay  as  they  observed  them. 

The  generally  erroneous  nature  of  the  thought  and  observation  of 
that  period  is  well  expressed  in  the  arguments  against  these  views  by 
Desirabode. 

The  bold  denial  by  these  men  that  caries  ever  had  its  beginning 
within  the  dentine,  as  its  truth  was  gradually  established,  had,  however, 
great  weight  in  confirming  the  chemical  hypothesis. 

It  is  exceedingly  curious  to  note  that  in  accepting  the  chemical 
theory  a  large  part  of  the  profession  either  misunderstood  or  lost 
sight  of  its  main  facts  as  related  by  the  authors  I  have  mentioned. 
Perhaps  the  most  prevalent  error,  and  one  that  has  been  most  persist- 
ently prominent,  is  that  contained  in  the  objection  that  was  imme- 
diately expressed  by  INI.  Desirabode — namely,  that  if  acids  caused 
decay,  they  would,  from  their  necessary  general  distribution  in  the 
mouth,  act  upon  all  parts  of  the  teeth,  instead  of  spending  their  force 
on  particular  points.  It  will  be  seen  at  once  that  the  idea  of  the  local- 
ized development  of  an  acid  by  fermentation  is  lost  sight  of  in  the 
expression  of  this  objection.  If  the  acid  enters  the  mouth  with  the 
fluids  as  they  are  secreted  by  the  glands,  or  with  the  food,  or  in  any 
manner  by  which  they  would  be  generally  distributed,  there  is  no  reason 
why  they  should  act  at  particular  points  only. 

On  the  other  hand,  much  confusion  has  arisen  through  the  supposi- 
tion that  caries  might  be  caused  by  acids  commingled  with  the  fluids 
of  the  mouth  or  introduced  from  without.  This  is  the  form  of  error 
that  has  been  most  persistently  present  in  the  writings  on  this  subject 
up  to  the  present  time.  I  may  say  that  the  acidity  or  alkalinity  of  the 
general  fluids  of  the  mouth  or  of  the  food  plays  but  a  small  part  in  the 
case,  ])rovided  these  reactions  be  not  in  such  degree  as  materially  to 
modify  the  act  of  fermentation  taking  place  in  the  out-of-the-way  points 
about  the  teetli.  The  teeth  may  decay  when  the  fluids  of  the  mouth 
are  habitually  acid  or  when  they  are  habitually  alkaline.  The  condition 
governing  the  beginning  and  progress  of  caries  is  neither  of  these,  but  is 
dependent  directly  on  the  lodgment  of  substances  at  particular  points 
and  their  fermentation  with  the  production  of  an  acid.  It  is  in  this 
manner  that  caries  has  its  beginnings,  and  its  progress  is  maintained  by 
the  continuance  of  this  act  of  fermentation. 

The  faijure  to  grasp  this  thought  in  its  full  meaning  was  perhaps 
quite  natural.     This  subject  of  fermentation  has  been  one  of  the  most 


ETIOLOGY  OF  CARIES.  739 

difficult  Avith  which  the  intelligence  of  man  has  had  to  grapple,  and  was 
evidently  not  understood  by  those  who  conceived  the  fermentation 
hypothesis  for  the  origin  of  caries.  It  was,  indeed,  known  that  many 
substances  give  rise  to  acids  of  various  kinds  during  the  process  of 
decomposition  by  fermentation  or  putrefaction,  but  what  was  the  modus 
operandi  was  an  open  question  that  was  debated  at  that  day  only  by 
the  most  astute  chemists.  The  molecular-motion  theory  of  fermenta- 
tion and  putrefaction  cannot  be  said  to  have  been  fully  developed  until 
1840,  when  Justus  Liebig  wrote  his  Chemistry  in  its  AppJication  to 
Af/riculture  and  Physiology  as  a  report  to  the  British  Association  for 
the  Advancement  of  Science.  The  subject  had,  indeed,  been  under  dis- 
cussion for  several  centuries  without  the  development  of  any  theory  for 
the  rational  explanation  of  the  observed  phenomena  upon  which  the 
learned  men  of  the  world  could  agree.  This  theory  had  been  imper- 
fectly shadowed  forth  for  many  years,  but  it  seemed  to  require  the 
genius  of  Liebig  to  systematize  and  place  it  before  the  world  of  thought 
in  tangible  form.  Yet  even  before  the  work  was  completed  an  antag- 
onist had  arisen  in  the  germ  theory  of  these  processes,  growing  out  of 
the  discovery  of  the  yeast-plant  by  Schwann  in  1838  ;  and  these  two 
rival  theories  have  struggled  with  each  other  for  the  mastery  almost  up 
to  the  present  time,  and  there  are  perhaps  many  who  will  assume  that 
the  struggle  is  still  going  on.  During  this  time  it  is  but  fair  to  say 
that  there  has  been  no  theory  of  fermentation  that  has  been  fully 
accepted.  The  full  explanation  of  caries  of  the  teeth  re(]uired  an 
acceptable  explanation  of  the  processes  of  fermentation,  and  the  learn- 
ing of  the  period  failed  to  afford  this.  For  this  reason  the  subject  has 
always  been  enveloped  in  a  degree  of  obscurity  that  has  rendered  all 
attempts  at  explanation  unsatisfactory. 

In  this  condition  of  the  minds  of  men  it  is  cjuite  natural  that  other 
modes  of  explanation  should  be  sought.  And  in  the  last  half  century 
almost  every  source  of  knowledge  has  been  questioned  with  the  hope 
of  obtaining  an  answer,  but  none  has  been  vouchsafed ;  for  after 
threading  the  labyrinth  of  the  theories  propounded — and  these  have 
been  many — the  questioner  has  again  turned  back  to  the  theory  of  fer- 
mentation with  all  its  mystery  and  uncertainty.  When  Ave  review  the 
literature  of  the  subject  we  find  that  since  the  time  of  Robertson 
and  Regnard  this  explanation  of  the  subject  has  never  been  entirely 
lost  sight  of.  It  must  be  confessed,  hoAvever,  that  it  has  often  been 
presented  in  so  confused  a  manner,  and  so  mixed  with  other  theories, 
that  its  best  friends  could  Avith  difficulty  recognize  that  a  A'estige  of  it 
remained. 

NoAv,  after  the  work  of  so  many  years  has  been  added  in  the  effort 
to  explain  the  nature  of  fermentation,  and  Avhen  the  labors  of  such  men 
as  ScliAA'ann,  Schroeder,  Lister,  Koch,  Klein,  and  Miller  haA^e  made  us 
acquainted  Avith  the  agency  of  micro-organisms  in  the  processes  of  fer- 
mentation and  putrefaction,  this  seems  to  be  regarded  as  another  of  the 
ncAv  theories  which  haA'e  sprung  to  the  front  demanding  a  hearing.  If 
any  ha\'e  this  thought,  I  wish  to  say  that  it  is  a  misconception.  It  is 
but  a  further  explanation  of  the  old  theory  as  propounded  by  Robertson 
and  Regnard — an  explanation  of  the  processes  of  the  fermentation  by 


740  DENTAL  CARIES. 

which  the  acid  spoken  of  by  them  is  produced — and  as  such  is  not  a 
theory  that  in  any  wise  supplants  or  displaces  that  hypothesis. 

Among  the  writings  that  have  ai)peared  since  the  works  of  Robert- 
son and  Kegnard  there  are  perhaps  none  that  have  deservedly  attracted 
more  attention  than  those  of  John  Tomes.  As  a  microscopist  and  his- 
tologist  this  author  probably  did  more  to  give  the  profession  correct  views 
of  the  structure  of  the  teeth  and  the  phenomena  presented  by  caries 
than  any  other  writer. 

As  a  contemporary  of  Robertson,  Mr.  Tomes  was  well  acquainted 
with  his  views ;  but  Ave  do  not  find  in  his  work  any  discussion  of  the 
theory  of  fermentation  as  applied  to  this  subject.  Mr.  Tomes  was  a 
microscopist,  and  as  such  depended  very  largely  on  the  teaching  of  that 
instrument  for  the  views  he  entertained,  and  his  writings  seem  to  indi- 
cate that  he  began  with  a  strong  bias  in  favor  of  the  theory  of  inflam- 
mation. Mr,  Robertson,  on  the  other  hand,  was  not  a  microscopist, 
and  seems  not  to  have  had  any  confidence  that  studies  made  by  the  aid 
of  that  instrument  would  be  of  any  assistance  in  the  explanation  of  the 
nature  of  caries.  Under  these  circumstances  it  is  not  surprising  that 
the  views  of  the  two  men  should  be  divergent. 

In  the  earlier  writings  of  Mr.  Tomes  we  find  views  expressed  that 
coincide  in  the  main  with  those  of  Koecker,  but  with  a  more  decided 
loaning  to  the  theory  of  the  action  of  acids  as  the  active  agents  in  the 
disintegration  of  parts  rendered  susceptible  to  their  operation  by  a  dis- 
eased action  going  on  within  the  dentine.  While  this  disease  of  the 
dentine  was  regarded  as  being  of  the  nature  of  inflammation,  Mr. 
Tomes  finds  by  his  microscopic  inquiries  that  the  phenomena  of  this 
process,  as  we  understand  them  in  its  occurrence  elsewhere  in  the  tissues, 
cannot  take  place  in  the  dentine.  Yet  he  concludes  by  saying,  in  eifect, 
that  these  phenomena  are  only  the  observed  result  of  disturbance  of  the 
vital  processes  which  are  beyond  the  reach  of  investigation.  The  den- 
tine is  evidently  endowed  with  vitality,  though  this  vitality  is  invested 
in  a  different  histological  form  from  that  of  other  tissues  of  the  body, 
rendering  it  imjwssible  that  the  same  phenomena  should  appear  on 
account  of  or  in  response  to  a  given  disturbance  of  this  vitality.  The 
dentine  cannot  become  hypersemic,  because  there  is  no  provision  for  the 
circulation  of  the  blood-globules  within  its  structure ;  the  entrance  of 
leucocytes  is  prevented  by  the  smallness  of  its  tubules ;  and  so  on  with 
all  of  the  usual  phenomena  of  the  process  known  as  inflammation ;  yet 
we  cannot,  on  account  of  these  differences  in  histological  form,  assert 
that  the  vitality  existing  in  the  dentine  may  not  be  disturbed  in  such  a 
manner  as  to  ])roduce  phenomena  which  will  be  peculiar  to  its  histologi- 
cal forms.  ]Mr.  Tomes  has  critically  examined  the  phenomena  of  caries, 
evidently  with  the  intent  to  discover  whether  there  were  presented  any 
conditions  indicating  a  disturbance  of  the  vitality  of  the  dentine.  In 
this  search  it  must  be  admitted  that  he  is  in  a  degree  successful,  for  he  has 
shown  what  every  cx]>ericnced  dental  surgeon  must  recognize  as  true — 
namely,  that  in  the  beginnings  of  caries  the  dentine  at  the  point  of  incip- 
ient disintegration  becomes  hypersensitive,  and  not  a  few  patients  com- 
plain when  the  parts  are  disturbed  by  the  contact  of  foreign  bodies. 
This  phenomenon  seems  to  be  a  sufficient  evidence  of  a  disturbance  of 


ETIOLOGY  OF  CARIES.  741 

vitality,  for  how  else  can  we  account  for  the  hyperesthesia  ?  As  the 
caries  advances  and  the  point  of  exposure  of  the  dentine  is  removed 
from  the  surface,  this  manifestation  of  pain  is  diminished  or  relieved, 
this  agreeing  precisely  with  similar  phenomena  manifested  in  injuries 
to  the  surface  of  the  body ;  for  it  is  well  known  that  the  skin  is  more 
sensitive  to  painful  impressions  than  the  parts  beneath. 

Again,  Mr.  Tomes  describes  what  he  terms  "  the  transparent  zone  " 
as  existing  between  the  dentine  affected  by  caries  and  that  which  has 
remained  perfectly  normal.  In  his  earlier  works  this  was  regarded  as 
being  caused  by  the  calcification  of  the  dentinal  fibrils,  and  as  such  was 
regarded  as  a  vital  act  of  resistance  to  the  advance  of  the  carious  pro- 
cess— an  act  by  which  the  fibrils  shut  themselves  in  from  an  external 
irritant,  and  attempted  to  build  a  barrier  against  further  disintegration. 

There  is  no  doubt  as  to  the  microscopic  appearances  described,  but  in 
his  earlier  works,  or  those  that  were  written  soon  after  the  discovery  of 
the  dental  fibrils,  this  author  seems  to  have  been  unfortunate  in  his 
interpretation  of  them ;  for  it  has  been  since  determined  that  instead  of 
being  an  act  of  vitality,"  by  which  a  barrier  is  placed  against  the  further 
progress  of  disintegration,  it  is,  in  fact,  only  the  earliest  stage  of  that 
process,  and  there  is  really  no  calcification  of  the  fibrils.  Mr.  Tomes 
corrects  this  error  in  the  recent  editions  of  his  work. 

From  these  studies  Mr.  Tomes  concluded  that  the  life-force  resident 
in  the  dentine  possesses  a  certain  power  of  resistance  to  injurious  im- 
pressions, and  that  this  resisting  power  must  be  overcome  by  some 
force  or  cause  before  disintegration  can  occur.  In  other  words,  the 
phenomena  of  caries  must  be  preceded  by  something  having  the  power 
of  destroying  the  life  of  the  part.  This  something  may  be  a  diseased 
state  of  the  dentine  similar  in  its  nature  to  inflammation  of  the  other 
tissues ;  but  for  this  idea  he  does  not  strenuously  contend,  for  he  sup- 
poses that  the  life  of  the  part  may  be  destroyed  by  the  same  agent  that 
effects  the  disintegration.     Mr.  Tomes  says  :  ^ 

"  In  speaking  of  the  predisposing  and  exciting  causes  of  caries,  allusion 
has  yet  to  be  made  to  those  agents  which  may  be  regarded  as  acting  in  the 
double  capacity  of  depriving  the  dentine  of  its  normal  powers  of  resistance 
and  of  producing  its  immediate  decomposition. 

"  In  considering  the  subject  from  this  point  of  view,  we  must  be  prepared 
to  admit  that  the  dentine  is  possessed  of  vitality,  and  that  vitality  must 
have  been  lost  before  the  tissues  undergo  decomposition.  If  we  take,  for 
example,  the  effect  produced  on  the  skin  by  the  application  of  caustic  pot- 
ash, the  immediate  result  is  the  destruction  of  vitality  in  the  part  with 
which  it  comes  in  contact,  and  its  secondary  effect  will  be  the  disorganiza- 
tion of  the  part  destroyed.  But  had  the  power  exerted  by  the  potash  been 
incapable  of  depriving  the  skin  of  vitality,  the  secondary  effect,  that  of  pro- 
ducing decomposition,  would  have  been  successfully  resisted.  In  the  case 
of  a  tooth  the  application  of  potash  would  not  produce  conclusive  results, 
but  the  use  of  a  mineral  acid  would  be  followed  by  consequences  similar  to 
those  mentioned  with  respect  to  the  skin.  The  vitality  of  the  part  would 
be  destroyed,  and  decomposition  would  succeed  the  loss  of  life. 

"  It  may  be  said  that  agents  of  this  character  are  not  applied  to  the 
teeth,  but  such  as  have  sufficient  power  to  destroy  are  applied ;  and  it  is 

^  System  of  Dental  Surgery,  p.  372,  3d  ed.,  1859. 


742  DENTAL  CARIES. 

by  taking  an  extreme  case  that  we  are  best  able  to  examine  the  mode  of 
action  and  the  ensuing  results. 

"  Litmus-paper  applied  within  the  cavity  of  a  carious  tooth  almost  inva- 
riably gives  strongly-marked  acid  reaction,  and  thus  furnishes  evidence  of 
the  existence  of  an  agent  capable,  if  unresisted  by  the  vitality  of  the  den- 
tine, of  depriving  that  tissue  of  its  earthy  constituents,  leaving  the  gelatin 
to  undergo  gradual  decomposition,  favored  by  the  heat  and  moisture  of  the 
mouth." 

JNIr.  Tomes,  tlierefore,  while  insistino;  on  the  presence  of  vital  phe- 
nomena in  the  })roduction  of  caries,  finally  admits  a  process  that  is 
almost  purely  chemical.  From  this  point  he  proceeds  to  examine  into 
the  condition  of  the  oral  fluids  with  the  view  of  finding  the  acids  that 
do  the  mischief.     He  says  : 

"  In  examining  the  circumstances  under  which  the  decomposition  of  the 
dentine  takes  place  and  under  which  it  is  resisted,  apart  from  the  influence 
of  vitality,  any  one  must  be  struck  with  the  power  that  is  exerted  by  the 
mere  form  of  the  surface  involved.  Supposing  the  disease  to  be  situated 
in  a  deep  Assure  or  upon  the  side  of  a  tooth  against  which  another  tooth  is 
placed,  the  decomposition  will  go  on  with  more  or  less  rapidity,  the  rate 
being  varied  in  accordance  with  the  condition  of  the  oral  fluids.  But  if 
the  cavity  be  superficial,  and  so  placed  that  it  is  subject  to  friction  during 
mastication,  the  progress  is  relatively  slow  ;  and  if  the  low  walls  of  such  a 
cavity  be  removed,  the  part  will  become  polished  by  the  act  of  mastication 
and  l)y  the  motions  of  the  tongue,  and  decomposition  will  be  completely 
arrested  quite  independently  of  any  ])ower  of  resistance  exercised  by  vital 
action.  Again,  let  a  tooth  be  placed  under  circumstances  the  opposite  of 
the  preceding.  For  example,  take  a  bicuspid  of  the  upper  jaw  the  distal 
surface  of  which  is  decayed,  and  remove  the  softened  dentine ;  then  let  dry 
cotton  wool  be  forced  between  the  defective  tooth  and  its  neighbor,  and 
renewed  only  once  in  three  or  four  days ;  at  the  end  of  a  fortnight  or  three 
weeks  it  will  be  found  that  the  surface  of  the  cavity,  which  Avas  left  hard 
and  dense  after  the  first  operation,  has  become  soft,  and  that  the  softening 
extends  to  a  considerable  depth.  Had  the  cotton,  prior  to  its  inti^oduction 
between  the  teeth,  been  dii:)ped  into  a  solution  of  resinous  gum,  such  as 
mastic,  the  surface  of  the  cavity  would  have  remained  unaltered,  owing  to 
the  exclusion  of  moisture.  But  where  .the  wool  only  is  used,  the  secretions 
of  the  mouth  are  not  only  not  excluded,  but  are  held  in  constant  apposition 
with  the  exposed  dentine  by  the  saturated  wool. 

"  Fxperiments  of  this  character  lead  to  the  conclusion  that  Avithin  the 
mouth  are  agents  present  which,  under  favoring  circumstances,  are  capable 
of  decomposing  the  dental  tissues,  and  the  source  of  these  agents  becomes 
the  next  question  which  naturally  suggests  itself." 

This  astute  writer  has  left  the  subject  of  the  influence  of  fermentation 
in  tlie  production  of  acids  untouched.  He  attentively  examined  the 
fluids  of  the  mouth  in  varying  conditions  of  the  system,  and  found  in 
them  acids,  which  he  concluded  must  be  sufficient  to  account  for  the  phe- 
nomena of  the  disintegration  of  the  dentine  in  the  form  of  caries.  That 
these  acids  are  fi)und  there  is  no  doubt.  Under  various  circumstances 
the  saliva  itself  becomes  acid,  and  from  my  own  examinations,  which 
have  been  somewhat  extended,  it  api)ears  that  it  is  usually  acid  (the 
mixed  fluid)  in  the  state  of  fasting ;  and  the  mucus  is  slightly  acid  in 


ETIOLOGY  OF  CARIES.  743 

the  greater  number  of  persons  I  have  examined ;  especially  is  this  so  if 
the  gums  about  the  necks  of  the  teeth  are  slightly  irritated.  Indeed, 
I  may  say  that  from  my  own  observations  I  have  conclusively  con- 
firmed Mr.  Tomes's  findings  as  to  the  frequency  of  acidity  of  the  fluids 
of  the  mouth.  But  this  does  not  constitute  a  satisfactory  explanation 
of  the  occurrence  of  caries.  Against  such  a  supposition  the  argument 
of  Desirabode,  quoted  in  a  note  elsewhere,  applies  with  its  full  force. 
If  we  succeed  in  accounting  for  the  production  of  decay  on  the  chemical 
hypothesis  at  all,  we  must  account  for  the  application  of  the  acid  to  the 
particular  point  where  that  decay  manifests  itself,  to  the  exclusion  of 
other  jmrts  of  the  denture ;  otherwise  we  must  fail.  Therefore,  acidity 
of  the  fluids  of  the  mouth  cannot  be  the  active  exciting  cause  of  caries, 
though  it  is  possible  that  this  condition  may  be  indirectly  instrumental 
as  a  predisposing  cause.  This  feature  of  the  subject  will  be  discussed 
on  another  page. 

There  is  no  doubt  that  the  writings  of  Mr.  Tomes  had  a  powerful 
effect  in  drawing  the  thought  of  tlie  profession  away  from  the  fermen- 
tation hypothesis  as  an  explanation  of  the  active  cause  of  caries  of  the 
teeth.  This,  however,  can  hardly  have  delayed  the  full  explanation  of 
the  phenomena,  for  before  the  processes  of  fermentation  and  putrefac- 
tion could  become  explainable  a  vast  deal  of  labor  in  other  directions 
was  necessary ;  and  this,  from  the  very  nature  of  the  case,  could  best 
be  done  by  others  than  those  actively  engaged  in  dental  practice. 

This  search  in  the  fluids  of  the  mouth  for  the  active  factor  in  the 
production  of  caries  did  not  begin,  however,  with  Mr.  Toines.  Amos 
^\^estcot,  for  the  purpose  of  ascertaining  what  effect  the  acids  supposed 
to  be  present  in  the  oral  fluids  would  exert  on  the  teeth,  had  already 
made  a  series  of  experiments,  in  which  he  found  that  they  were  decal- 
cified by  very  high  dilutions. 

These  experiments  were  published  in  the  third  volume  of  the  Ameri- 
can Journal  of  Dental  Science,  and  have  been  referred  to  by  many 
writers  since  that  time.  They  led  to  a  vast  number  of  analyses  of 
the  oral  fluids  in  all  conditions  of  health  and  disease,  and  almost 
unlimited  experimentation  in  decalcification  of  tlie  teeth  in  varied 
dilutions  and  compounds  of  the  various  known  acids,  an  intimate 
acquaintance  with  the  varying  conditions  of  the  oral  secretions  and 
the  effects  of  acids  on  dentine  being  thus  developed,  but  little  or  noth- 
ing being  accomplished  explaining  the  processes  of  caries  of  the  teeth, 
except  to  demonstrate  that  in  simple  solution  by  acids  certain  of  the 
phenomena  of  caries  are  absent. 

In  the  progress  of  this  study  the  most  diverse  views  have  from  time 
to  time  appeared,  and  the  formation  in  the  fluids  of  the  mouth  of  almost 
every  known  acid,  by  some  possible  changes  of  molecular  groupings,  has 
been  assumed. 

Some  few  have  been  satisfied  with  the  theory  of  fermentation,  as  was 
Goddard,  who  supposed  acetic  fermentation  to  be  the  prime  factor ;  ^ 
but  the  great  majority  of  writers  have  invoked  the  aid  of  vital  processes 
resident  in  the  tooth  itself  for  the  production  of  caries  or  for  limiting  its 
effects,  or  for  both ;  and,  altogether,  the  agency  of  vitality  in  this  process 

^  Goddard  on  the  Teeth,  1854. 


744  DENTAL  CARIES. 

has  been  most  thoroughly  studied,  seemingly  in  all  possible  aspects, 
but  -without  results.  At  the  present  time  the  only  influence  that  we 
can  attribute  to  vitality  is  that  it  has  some  power  to  limit  the  rapidity 
of  decay  in  the  otherwise  normal  tooth.  Teeth  that  have  lost  their 
pulps,  and  as  a  result  the  vitality  of  the  dentine,  decay  more  rapidly. 
The  great  number  of  pulpless  teeth  now  retained  in  the  mouth 
give  abundant  opportunity  for  observation  upon  this  point ;  but  it  is 
uncertain  whether  this  slower  progress  of  caries  in  the  living  tooth  is 
on  account  of  its  vitality  or  because  the  tubules  are  occupied  with  the 
dentinal  fibrils  in  such  a  way  as  to  prevent  by  their  bulk  that  more  rapid 
ingress  of  the  agent  of  solution  which  would  occur  were  the  tubules 
laid  open  by  the  loss  of  the  fibrils.  This  latter  thought  seems  to  be 
more  in  harmony  with  the  phenomena,  and  yet  it  must  be  admitted  that 
it  is  difficult  to  conceive  that  the  living  contents  of  the  tubules,  the  den- 
tinal fibrils,  should  be  powerless  and  incapable  of  exerting  any  influence 
when  their  vitality  is  directly  disturbed.  Yet,  after  all  the  study  that 
has  been  expended  on  this  point,  there  have  been  developed  no  evidences 
of  vital  resistance  on  the  part  of  the  dentine  itself,  other  than  hyperses- 
thesia,  capable  of  withstanding  adverse  criticism. 

The  principal  evidence  of  vitality  of  the  dentine,  however,  is  exhib- 
ited in  changes  that  occur  in  the  tissues  of  the  pulp  itself  on  account  of 
irritation  of  the  distal  ends  of  the  dentinal  fibrils  in  the  processes  of 
caries  and  of  the  abrasions.  These  are  fully  considered  in  the  article 
on  Pathology  of  the  Dental  Pulp,  and  need  not  be  referred  to  here, 
especially  as  they  do  not  relate  to  caries  further  than  that  they  are  one 
of  its  remote  consequences.  The  fact  that  these  morbid  effects  are  trans- 
ferred to  the  pulp  through  a  considerable  portion  of  dentine,  without 
visible  change  in  the  dentine  itself,  denotes  its  incapacity  for  the  exhibi- 
tion of  morbific  changes  through  vital  activity  or  the  agency  of  vital 
forces  resident  within  itself. 

A  few  observers  seem  to  have  abandoned  both  tli»e  chemical  and  the 
vital  theory,  and  have  sought  to  explain  the  results  by  other  means. 
Bridgcman,  in  an  essay  on  this  subject,*  attributes  caries  to  peculiar 
electrical  conditions  in  which  the  crown  of  the  tooth  becomes  the  pos- 
itive electrode,  and  the  tissues  in  which  the  tooth  is  invested  the  nega- 
tive. When  these  conditions  are  intensified  by  abnormal  qualities  of 
the  fluids  of  the  mouth,  the  crown  porticm  of  the  tooth  yields  up  its 
lime  salts,  setting  free  the  acids  with  which  they  were  combined  ;  and 
this  leads  to  molecular  disintegration  of  the  substance  of  the  dentine  in 
the  form  of  caries.  This  is  certainly  a  very  ingenious  theory,  but  is  at 
variance  with  so  many  facts  that  any  eff(>rt  to  maintain  it  must  be  futile. 
It  can  be  readily  understood,  however,  that  by  placing  different  metals 
in  the  teeth  as  fillings  the  saliva  may  act  as  an  excitant  and  a  battery 
be  produced.  From  these  artificial  conditions  I  have  seen  effects  that 
seemed  to  be  the  product  of  electrical  currents. 

Another  thought  has  been   advanced  to   account  for  caries  on  the 

hypothesis  of  vital  action.     In  this  it  is  supposed  that  on  account  of  a 

disturbance  of  vitality,  such  as  might  produce  inflammation  in  other 

parts  of  the  system,  the  imtrition — or,  more  properly,  the  vital  action — 

*  TninsactwiiH  Odontulogicul  Soc,  vol.  iii.  p.  369. 


ETIOLOGY  OF  CARIES.  745 

of  the  particular  part  is  disturbed  in  such  a  manner  that  an  additional 
molecule  of  acid  is  formed,  giving  rise  to  the  acid  superphosphate  of 
lime  or  the  withdrawal  of  a  molecule  of  lime,  which  is  replaced  by 
basic  water,  thus  changing  the  insoluble  neutral  phosphate  into  a  solu- 
ble acid  phosphate.  This  idea  seems  to  have  arisen  from  a  suggestion 
by  Mr.  Coleman  that  the  acidity  of  caries  was  probably  due  to  the 
formation  of  the  acid  phosphate  of  lime. 

Among  the  many  theories  that  have  appeared  from  time  to  time  to 
account  for  caries  by  the  introduction  or  development  of  particular  acids 
in  the  mouth,  there  are  several  that  deserve  mention  either  because  of 
the  high  estimation  in  which  they  have  been  held  by  large  numbers  of 
intelligent  practitioners,  or  for  their  intrinsic  importance,  or  for  the 
ingenuity  with  which  they  have  been  presented.  One  of  these,  espe- 
cially urged  by  Dr.  George  Watt,  and  which  may  be  termed  the  min- 
eral-acid theory,  has  in  America  exercised  considerable  influence.  I 
should,  however,  say  that,  while  Dr.  Watt  claims  that  these  acids  espe- 
cially are  the  cause  of  decay,  he  does  not  exclude  the  action  of  the 
organic  acids.  According  to  this  theory,  the  particular  acids  produc- 
tive of.  the  great  mass  of  caries  are  nitric,  sulphuric,  and  chloro- 
hydric.  These  give  rise  to  three  distinct  varieties  of  decay,  differing 
the  one  from  the  other  in  accordance  with  what  is  supposed  to  be  the 
peculiar  action  of  each  of  the  acids  in  question.  Nitric  acid  is  said  to 
produce  white  decay ;  sulphuric,  black  decay  ;  and  the  chlorohydric,  the 
intermediate  colors.  It  is  held  that  any  of  these  acids  may  be  formed 
in  the  mouth  or  may  be  introduced  into  that  cavity,  but  for  the  produc- 
tion of  caries  they  must  be  formed  at  the  exact  spot  at  which  they  act 
upon  the  tooth  by  some  form  of  decomposition  which  takes  place  in 
substances  that  may  fincl  lodgment  about  the  teeth.  This,  then,  is  in 
strict  accord  with  the  theory  of  Robertson,  and  amounts  to  an  effort  to 
explain  the  mode  of  procedure  by  which  the  acid  is  produced  and  to 
define  the  particular  acids. 

With  regard  to  nitric  acid,  Dr.  Watt  says  :  ^ 

"It  is  a  singular  fact  that  though  oxygen  and  nitrogen  manifest  but 
little  affinity  for  each  other,  yet  they  unite  in  various  proportions,  forming 
at  least  five  well-known  distinct  compounds.  It  appears,  however,  from  a 
variety  of  circumstances,  that  their  tendency  is  to  unite  in  the  proportions 
which  form  nitric  acid.  The  protoxyd  is  readily  decomposed,  and  yields 
nitrogen,  oxygen,  and  nitrous  acid.  The  binoxide,  if  brought  in  contact 
with  the  atmosphere,  takes  from  it  two  equivalents  of  oxygen,  and  also 
becomes  nitrous  acid,  or  NO4  (the  old  chemical  formulae  are  used  here). 
Hyponitrous  acid,  NO^,  on  admixture  witli  water  is  converted  into  nitric 
acid  and  binoxide  of  nitrogen ;  thus,  3NO3  =  NO5  +  2N0.2,  in  which  case 
the  latter  will  be  converted  into  nitric  acid.  It  follows  from  this  that  if 
oxygen,  and  nitrogen  unite  at  all  in  the  mouth,  let  the  proportions  be,  at 
the  first,  what  they  will,  nitric  acid  must  be  the  ultimate  result,  as  air  and 
moisture,  the  only  agents  necessary  in  the  transformation,  are  here  always 
present 

"  Nitrogen  is  emphatically  a  conservative  element,  and  manifests  but 
little  tendency  to  unite  with  anything,  and  especially  with  oxygen.     It  is 

^  Chemical  Essays,  p.  62. 


746  DENTAL  CARIES. 

probable,  therefore,  that  these  two  elements  unite  indirectly.  It  should  be 
borne  in  mind  that  organic  nitrogenous  bodies  contain  hydrogen  and 
oxygen  as  well  as  nitrogen.  Consequently,  by  their  decomposition,  these 
elements  are  liberated.  The  mutual  affinities  of  the  hydrogen  and  nitro- 
gen take  precedence,  and  the  result  is  the  formation  of  ammonia,  NH3. 
But  ammonia  exposed  to  the  action  of  oxygen  is  always  decomposed,  an 
oxide  of  nitrogen  being  formed,  and  of  course  nitric  acid  is  the  result. 

"  AVith  this  view  of  the  case,  and  from  the  fact  that  many  persons  per- 
mit the  buccal  mucus  as  well  as  particles  of  nitrogenous  food  to  remain 
around,  upon,  and  between  the  teeth  till  decompo^'ition  is  effected,  it  is  not 
surprising  that  the  white  variety  of  dental  caries  is  so  frequently  found." 

The  formation  of  other  acids  in  the  mouth  is  followed  out  by  a  sim- 
ilar mode  of  procedure.     For  instance,  this  author  says  : 

"  Albumen  is  a  constituent  of  mucus,  and  is  contained  in  many  articles 
of  food.  Sulphur,  if  not  a  constituent  of,  is  always  united  Avith,  albumen. 
Its  ordinary  presence  in  the  mouth  is  therefore  easily  explained.  Sulphur 
and  oxygen  unite  directly  under  various  circumstances,  as  in  the  combus- 
tion of  sulphur,  but  it  is  probable  that  the  union  here  is  effected  by  indirect 
means.  Hydrosulphuric  acid,  or  sulphuretted  hydrogen,  is  one  of  the  results 
of  putrefactive  decomposition  of  albuminous  substances.  The  breaths  of 
our  jnitients  often  bear  ample  testimony  to  its  presence  in  the  mouth.  Now, 
the  oxygen  of  the  atmosphere  rapidly  decomposes  this  acid  by  taking  its 
hydrogen  to  form  water.  The  sulphur  is  therefore  set  free,  and,  being  in 
the  nascent  state,  its  affinities  are  increased  in  energy,  and  it  also  unites 
Avith  oxygen,  forming  the  sulphurous  acid,  SO,,  which  in  the'  presence  of 
the  water  of  the  saliva  is  rapidly  converted  into  sulphuric  acid,  or  SO3" 

This  acid  is  regarded  as  acting  on  the  constituents  of  the  tooth  but 
very  feebly,  so  that  the  texture  of  the  dentine  is  not  entirely  broken  up, 
but  by  its  tendency  to  the  removal  of  the  elements  necessary  to  the  for- 
mation of  water,  for  which  it  has  a  very  powerful  affinity,  the  tooth- 
substance  is  carbonized,  giving  rise  to  very  black,  slowly  progressive 
decays. 

In  respect  to  the  formation  of  chlorohydric  acid  the  following  C[Uota- 
tion  will  be  sufficient : 

"  Though  in  its  normal  state  the  saliva  is  alkaline,  yet  in  a  great  variety 
of  abnormal  conditions  it  contains  one  or  more  free  acids,  and  the  chloro- 
hydric is  one  of  those  most  frequently  present.  It  often  originates,  no 
doubt,  in  tlie  decomposition  of  the  soluble  chlorides  contained  in  the  saliva 
and  mucus.  When  the  chlorine  of  these  is  liberated,  it  takes  hydrogen 
from  the  water  of  the  saliva,  and  this  acid  is  the  result  of  the  union." 

Tliis  acid,  in  the  degree  of  concentration  in  wliich  it  Mould  be  likely 
to  be  produced  in  tiie  mouth,  is  not  regarded  as  capable  of  dissolving 
the  animal  ])ortions  of  the  tooth.  It  is  therefore  supposed  to  remove 
the  lime  salts,  giving  rise  to  those  sofit,  pulpy  forms  of  caries  in  which 
there  is  a  large  mass  that  still  retains  its  histological  forms. 

In  his  essays  on  this  subject  this  author  lias  endeavored  to  keep  before 
his  readers  the  idea  that  the  acid  must  be  formed  at  the  very  spot  where 
its  effects  are  manifested  in  the  production  of  the  phenomena  of  caries, 
for  he  has  taken  ])ains  to  state  in  connection  with  the  consideration  of 


ETIOLOGY  OF  CARIES.  747 

each  of  these  acids  that  it  may  be  taken  into  the  mouth  Mith  the  food 
or  in  the  form  of  medicine,  and  that,  while  if  used  in  this  fashion  care- 
lessly it  might  injure  the  teeth,  it  could  not  thus  produce  the  phenomena 
of  caries,  evidently  for  the  reason  that  its  action  would  not  be  spent  on 
the  particular  parts  of  the  teeth,  to  the  exclusion  of  other  parts. 

The  views  entertained  of  the  formation  of  these  acids  in  the  mouth 
seem  not  to  rest  on  any  basis  of  experimental  study  of  which  we  have 
record,  but  rather  upon  a  supposed  likeness  of  the  varieties  of  caries  to 
the  observed  action  of  these  particular  acids.  Later  developments  show 
that  the  results  are  dependent  u}K)n  other  agents. 

The  views  just  given  have  been  much  more  prominent  in  America 
than  in  Europe.  It  seems  that  in  the  Old  World  the  tendency  has  been 
to  regard  the  organic  acids  as  those  more  likely  to  be  concerned  in  the 
production  of  caries.  Their  action  has  been  investigated  in  this  coun- 
try as  well,  but  the  most  elaborate  treatise  on  this  phase  of  the  subject 
has  been  written  by  Dr.  Magitot  of  Paris. 

After  a  very  elaborate  study  of  the  etiology  of  dental  caries  Dr. 
Magitot  says :  ^ 

"  The  preceding  considerations  tend  to  establish  that  dental  caries  results 
from  a  purely  chemical  alteration  of  the  enamel  and  ivory  of  the  teeth, 
either  by  the  products  of  acid  fermentation  developed  in  the  saliva  or  by 
active  agents  introduced  directly  into  the  mouth.  Now,  if  this  theory  be 
correct,  we  should  be  able  to  obtain  the  same  effects  by  subjecting  sound 
human  teeth  out  of  the  body  and  deprived  of  life  to  the  direct  action  of 
the  same  agents  which  produce  this  affection  in  the  economy.  This  is  in 
fact  possible,  and  we  shall  relate  and  develop  a  series  of  experiments  by 
which,  sometimes  in  the  mouth  and  under  the  ordinary  conditions  of  devel- 
opment of  natural  caries,  sometimes  in  liquids  artificially  prepared,  we  have 
produced  changes  identical  with  that  of  this  malady. 

"  Thus  will  be  demonstrated,  as  it  seems,  without  doubt,  the  true  nature 
of  dental  caries,  which  it  will  be  impossible  to  regard  henceforward  as  an 
affection  of  internal  and  organic  origin  or  a  vital  lesion  of  nutrition,  as  has 
been  generally  believed  up  to  this  time." 

Some  of  the  experiments  related  by  Dr.  Magitot  consist  in  a  syste- 
matic observation  of  human  teeth  prepared  and  mounted  on  natural  roots 
as  pivot  teeth.  After  some  years  of  wear  in  mouths  in  which  caries 
was  actively  progressive  in  the  remaining  natural  teeth,  tlie  substituted 
teeth  were  affected  with  caries  in  the  same  manner  as  the  natural  organs. 
The  cavities  were  of  the  same  form,  in  the  same  positions  in  which  caries 
is  seen  to  attack  the  natural  organs,  and  the  whole  appearance  of  the 
cavities  produced  showed  the  affection  to  be  precisely  similar.  There 
was  the  same  kind  of  progressive  softening  of  the  dentine,  and  the  con- 
tents of  the  cavities  had  the  same  acid  reaction  that  is  always  found 
to  exist  in  progressive  caries  of  natural  teeth. 

These  experiments  are  related  at  length,  and  are  considered  as  settling 
beyond  all  doubt  the  fact  that  caries  is  caused  by  an  agent  acting  from 
without,  and  is  independent  of  the  vitality  of  the  tooth  attacked.  Dr. 
Magitot,  however,  says:  "A  fundamental  distinction  must  be  observed. 

^  Treatise  on  Dental  Caries,  Experimental  and  Therapeutical  Investifjations,  by  Dr.  E. 
Magitot,  translated  by  Thomas  Chandler,  D.  M.  D.,  p.  121. 


748  DENTAL  CARIES. 

It  consists  iu  the  absence  of  all  phenomena  of  reaction  on  the  part  of 
the  tooth  and  the  absent  dental  pulp,  whilst  in  pathological  caries  the 
injured  organ  reacts  and  struggles  against  the  invasion  of  the  disease." 
This  resistance  is  regarded  as  sufficient  to  render  the  progress  of  the 
disease  slower,  and  even,  in  some  favorable  cases,  to  arrest  it  altogether. 

Another  series  of  experiments  was  undertaken  to  determine  the  effect 
on  the  teeth  out  of  the  mouth  of  solutions  of  different  substances.  Some 
of  these  were  fermentable,  others  not. 

Several  experiments  were  made  with  solutions  of  sugar.  Solutions 
were  made  with  one  part  of  sugar  to  three  parts  of  water,  and  in  this 
perfectly  sound  teeth  were  placed  under  two  conditions  :  1st.  They  Mere 
simply  laid  in  the  liquid  without  any  kind  of  protection  ;  2d.  The  teeth 
were  completely  protected  with  a  coating  of  wax  except  at  a  single  point 
on  the  enamel.  The  vessel  was  then  set  away  loosely  corked  and 
allowed  to  remain  two  years,  in  which  time  the  solutions  were,  of  course, 
allowed  to  undergo  the  process  of  fermentation.  At  the  end  of  the  two 
years  the  fluid  was  found  markedly  acid,  of  a  deep  reddish  color,  and 
covered  with  a  deep  mould.  The  teeth  not  protected  by  the  coating  of 
wax  were  completely  decalcified.  The  teeth  protected  with  wax  at  all 
but  one  point  were  also  decalcified,  but  at  the  point  of  exposure  there 
was  a  localized  cavity  having  all  the  characteristics  of  caries.  In 
another  experiment  identical  with  this,  except  that  a  little  animal  mat- 
ter was  added  to  hasten  the  process  of  fermentation,  the  result  was 
almost  exactly  similar.  In  the  third  experiment  a  few  drops  of  crea- 
sote  were  added,  to  prevent  fermentation.  This  seems  to  have  failed. 
The  fermentation  proceeded  with  results  similar  to  those  just  described. 
In  the  fourth  experiment  glucose  was  added  and  a  few  drops  of  creasote, 
to  prevent  fei»mentation,  and  the  teeth  were  placed  in  solution  as  before. 
In  this  instance  fermentation  was  successfully  prevented.  The  solution 
at  the  end  of  tM'o  years  remained  clear.  There  was  no  mould  and 
none  of  the  teeth  showed  any  alteration  whatever.  In  the  fifth  experi- 
ment teeth  arranged  in  the  same  way  were  placed  in  a  cold  saturated 
solution  of  sugar  of  milk.  No  fermentation  took  place,  and  there  w^as 
no  effect  produced  on  the  teeth.  In  the  sixth  experiment  a  one-to- 
three  solution  of  cane-sugar  in  distilled  water  was  brought  to  the 
boiling-point  and  hermetically  sealed  while  hot.  A  group  of  sound 
teeth  had  been  weighed  with  great  care  and  placed  in  the  flask  before 
heating  the  solution.  At  the  end  of  two  years  no  fermentation  had 
taken  place.  The  teeth  appeared  unchanged.  They  were  dried  and 
again  weighed,  and  it  was  found  that  they  had  undergone  no  loss  what- 
ever. A  seventh  experiment  with  glucose  under  identical  conditions 
with  tlie  last  showed  similar  results. 

The  experiments  with  sugar  seem  to  show  conclusively  that  as  sugar 
it  has  no  hurtful  influence  on  the  teeth,  but  when  fermentation  takes 
place  the  teeth  are  profoundly  affected.  In  each  of  the  cases  the  fermen- 
tation was  of  the  acid  character,  not  vinous,  and  the  acid  first  produced 
was  generally  acetic  or  lactic,  which  latter  acid  usually  passes  into  the 
butvric  fermentation,  and  finally  is  liable  to  change  into  other  forms  as 
the  different  fermentative  processes  succeed  each  other.  In  this  series  of 
experiments,  therefore,  the  teeth  were  in  turn  subjected  to  various  acids 


ETIOLOGY  OF  CARIES.  749 

without  any  knowledge  as  to  their  strength  or  the  duration  of  the  expos- 
ure to  any  particular  one ;  but  the  results  show  conclusively  what  we 
may  expect  from  the  fermentation  of  sugar  in  contact  with  the  teeth. 

In  another  series  of  experiments  the  white  of  an  egg  was  mixed 
with  water,  the  conditions  being  otherwise  the  same  as  in  the  experi- 
ments with  sugar.  At  the  end  of  two  years  the  results  were  very  sim- 
ilar. In  the  solutions  that  underwent  the  process  of  fermentation  the 
teeth  were  decalcified,  but  in  those  in  which  fermentation  did  not  take 
place  the  teeth  remained  perfect. 

Experiments  with  the  organic  acids  produced  the  following  results ; 
in  each  case  the  teeth  remained  in  the  solution  two  years : 

Lactic  acid,  1  to  1000,  but  slight  effect. 

Lactic  acid,  1  to  100,  teeth  decalcified. 

Butyric  acid,  1  to  1000,  teeth  partially  decalcified. 

Butyric  acid,  1  to  100,  teeth  completely  decalcified. 

Citric  acid,  1  to  1000,  teeth  partially  decalcified. 

Citric  acid,  1  to  100,  teeth  wholly  decalcified. 

Malic  acid,  1  to  1000,  enamel  chalky,  dentine  partially  decalcified. 

Malic  acid,  1  to  100,  teeth  decalcified. 

Cider,  teeth  decalcified. 

Acetic  acid,  1  to  1000,  teeth  not  affected. 

Acetic  acid,  1  to  100,  enamel  not  affected,  dentine  decalcified,  and  the 
roots  of  the  teeth  shrivelled. 

This  gives  a  fairly  good  idea  of  the  power  possessed  by  the  organic 
acids  to  decalcify  the  teeth.  It  must  be  remembered,  however,  that  in 
the  solution  of  1  to  100  the  decalcification,  though  complete  in  two 
years,  progresses  very  slowly,  so  that  a  momentary  exposure  of  a  tooth 
to  even  a  much  stronger  solution  would  be  productive  of  no'  appreciable 
injury. 

Dr.  Magitot  has  experimented  also  with  many  other  substances  whose 
action  seems  to  me  to  have  little  or  no  relation  to  the  etiology  of  caries. 
The  views  entertained  by  him,  however,  doubtless  led  him  to  attach  to 
them  an  importance  greater  than  I  can  give  them.     He  says  :^ 

"  It  is  perfectly  established  that  dental  caries  results  from  the  direct 
alteration  of  the  oi'gan  by  means  of  substances  which  originate  in  the  saliva 
or  are  accidentally  introduced — an  alteration  usually  preceded  and  favored 
by  certain  congenital  or  acquired  predispositions  of  structure  or  anatomical 
conformation 

"  Caries,  regarded  from  this  point  of  view,  consists,  then,  precisely  in  a 
simple  solution  of  the  calcareous  salts  of  the  dental  tissues  by  an  acid 
element  developed  or  brought  in  contact  with  them.  Such  is  the  rigor- 
ously logical  conclusion  which  seems  to  us  to  result  from  all  the  considera- 
tions and  experiments  just  stated." 

It  would  seem  that  this  author  places  substances  introduced  into  the 
oral  cavity  upon  the  same  plane  as  those  developed  in  contact  with  the 
teeth.  This  being  the  case,  he  has  experimented  with  the  acids  and 
substances  contained  in  food  or  condiments.  It  is  also  curious  to  note 
that  while  he  has  been  careful  as  to  the  fermentation  of  the  fluids  with 

1  Pp.  158-164. 


750  DENTAL   CARIES. 

which  he  has  experimented — and  in  a  large  number  of  them  fermenta- 
tion has  produced  the  acid  which  has  decalcified  the  teeth  experimented 
upon,  which  fact  he  particularly  notes — yet  he  nowhere  puts  prominently 
forward  the  thought  that  these  agents  are  formed  in  contact  with  the 
identical  points  at  which  caries  is  manifested.  It  is  true  that  fermenta- 
tion taking  place  within  the  mouth  is  many  times  alluded  to,  and  the 
agency  of  micro-organisms  in  the  process  is  also  admitted ;  still,  but 
slight  importance  is  attached  to  them. 
Continuino-,  Magitot  says  :^ 

"Other  secondary  phenomena  are  sometimes  produced  concurrently 
about  the  altered  parts,  and  have  by  various  observers  been  held  to  a  cer- 
tain degree  responsible.  It  is  thus  that  putrid  decompositions,  which  have 
especially  for  their  source  debris  of  animal  or  vegetable  substances  of  ali- 
mentation, have  been  invoked  ;  in  like  manner  the  cryptogams  and  vibrios, 
whose  formation  we  have  regarded  as  an  epiphenomenon  of  the  malady, 
have  been  considered  as  agents  of  the  alteration  by  Facinus,  thus  taking 
precedence  of  the  theories  of  Pasteur." 

It  seems  to  have  been  Dr.  Magitot's  thought  that  the  agents  that 
produce  caries  are  either  developed  in  the  fluids  of  the  mouth,  and 
evolved  with  them  as  they  are  secreted,  or  else  are  introduced  from 
without,  rather  than  formed  in  isolated  points  of  fermentation.  In  his 
search  for  these  agencies  all  the  varying  conditions  of  the  fluids  of  the 
mouth  in  health  and  disease  have  been  questioned.  That  in  such 
agencies  are  to  be  found  some  of  the  predisposing  causes  of  the  malady 
there  seems  no  reasonable  doubt ;  but  certainly,  after  all  the  fruitless 
search  of  the  last  half  century,  it  is  time  to  turn  our  attention  else- 
where. I  would  here  reiterate  the  proposition  that  if  the  cause  of 
caries  of  the  teeth  is  to  be  found  in  the  disintegration  of  their  structure 
by  an  acid  or  by  acids,  we  must  find  that  these  agents  are  produced  or 
applied  at  the  very  spot  where  the  caries  has  its  beginnings  or  is  making 
its  advances.  Otherwise  we  must  fail.  Caries  of  the  teeth  is,  as  a  mal- 
ady, strictly  localized,  and  is  not  the  product  of  any  agent  distributed 
generally  in  the  oral  fluids. 

There  are  many  other  authors,  such  as  Weld,  Salter,  Coleman,  Taft, 
and  others,  who  have  written  well  on  this  subject,  and  from  whom  we 
might  quote ;  but  in  doing  so  only  slight  shades  of  difference  in  the 
views  presented  would  be  obtained,  without  in  any  wise  affecting  the 
ti-end  of  thought  already  given ;  it  is,  therefore,  unnecessary  to  our 
present  purpose. 

Agency  of  Micro-organisms  in  Caries. 

In  the  jirevious  pages  considerations  have  been  presented  which  lead 
to  the  conclusion  that  caries  of  the  teeth  is  a  result  of  the  corrosive  action 
of  acids  developed  in  contact  with  them.  Certain  observations  of  the 
utmost  importance  in  the  further  explanation  of  these  processes  are  now 
to  be  noticed.  They  relate  to  the  agency  of  those  micro-organisms  con- 
cerned in  the  various  fermentative  processes  by  which  acids  are  produced. 

'  P.  164. 


AGENCY  OF  MICRO-ORGANISMS  IN  CARIES.  751 

From  time  to  time  durino;  the  discussion  of  the  relations  of  micro- 
organisms  to  the  process  of  lermentation  there  have  appeared  suggestions 
that  decay  of  the  teeth  might  be  a  result  of  the  action  of  microbes.  But 
the  first  extended  study  of  fungi  in  connection  with  this  process  was 
undertaken  by  Leber  and  Rottenstein,  who  published  an  account  of 
their  observations  in  1867.'  At  the  time  their  studies  were  made  plans 
for  the  separation  and  individual  study  of  those  micro-organisms  which 
appear  in  conne(;tion  with  the  carious  process  had  not  been  systematized. 
Hence  these  observers  seem  to  have  confounded  all  other  micro-organ- 
isms with  Leptothrix  buccalis.  By  treating  decayed  dentine  with  iodine 
and  acids  a  violet  color  of  the  granular  masses  filling  the  widened 
tubules  was  obtained,  and  the  conclusion  that  these  were  composed, 
in  part  at  least,  of  micro-organisms  was  announced — an  observation 
since  confirmed  by  the  use  of  the  improved  methods  of  staining  intro- 
duced by  Dr.  Koch.  So  complete  has  this  demonstration  been  that  in 
any  case  of  erosive  softening  of  tooth-structure  within  M'hich  micro- 
organisms cannot  be  demonstrated  by  well-known  processes  we  are 
justified  in  saying  that  such  a  softening  is  not  true  caries,  or  is  not  of 
the  nature  of  caries  as  it  is  found  in  the  human  mouth.  Leber  and  Rot- 
tenstein  do  not  regard  the  fungus  as  capable  of  penetrating  the  normal 
enamel  or  dentine,  but  suppose  that,  a  beginning  being  made  by  an  acid, 
it  enters,  and  by  its  growth  assists  in  the  destructive  process. 

The  following  extracts  define  the  views  of  these  authors  upon  this 
point  (pp.  68-97) : 

"  From  what  has  been  said,  it  results  that  two  principal  phenomena  man- 
ifest themselves  in  the  formation  of  dental  caries — viz.  the  action  of  acids, 
and  the  rapid  development  of  a  parasitic  plant,  the  Leptothrix  bucccdis."  .... 
"  It  seems  that  the  fungi  are  not  able  to  penetrate  an  enamel  of  normal  con- 
sistency. The  dentine  itself,  in  its  normal  condition  of  densitv,  offers  great 
difficulties  to  their  entrance,  and  we  are  not  yet  sure  that  the  leptothrix 
could  triumph  over  this  resistance."  .  .  .  .  "  We  cannot  decide  at  present  if 
the  leptothrix  is  able  to  penetrate  sound  dentine  when  from  any  circum- 
stance it  happens  to  be  denuded."  .  .  .  .  "  But  if  the  enamel  or  dentine 
become  less  resistant  at  any  point  through  the  action  of  acids,  or  if  at  the 
surfiice  of  the  dentine  a  loss  of  substance  has  occurred,  then  the  elements 
of  the  fungus  can  pass  into  the  interior  of  the  dental  tissues,  and  produce 
by  their  distension,  especially  of  the  dentine,  effects  of  softening  and  destruc- 
tion niuch  more  rapid  than  the  action  of  acids  alone  is  able  to  accomplish." 
.  .  .  .  "  The  participation  of  the  fungus  is  constant  in  the  production  of 
caries  which  has  reached  this  stage.  As  soon  as  a  loss  of  substance  can  be 
shown  there  is  found  the  presence  of  fungus,  so  that  the  question  whether 
or  no  acids  alone  could  produce  ravages  more  considerable  is  without 
importance." 

The  modus  operandi  by  M-hich  Leptothrix  buccalis  (or  other  micro- 
organisms) may  produce  softening  of  the  dentine  is  left  without  expla- 
nation. It  may  here  be  mentioned  that  in  the  very  beginning  of  this 
line  of  investigation  a  mistaken  idea  was  entei'tained,  which  has  been 
perpetuated  in  nearly  all  subsequent  writings  upon  the  subject — that  if 
micro-organisms  are  instrumental  in  the  production  of  decay  they  must 
^An  English  translation  appeared  in  1868. 


752  DENTAL   CARIES. 

first  enter  the  structure  of  the  tootli.  This  error  seems  dependent  upon 
a  faikire  (which  is  very  apparent)  fully  to  comprehend  the  theory  of  fer- 
mentation with  the  production  of  an  acid,  which  acid,  being  formed  in 
contact  with  a  particular  part  of  the  tooth,  acts  chemically  upon  its  sub- 
stance and  decomposes  it.  It  should  be  remembered  that  if  microbes  act 
at  all  in  this  process  it  is  through  their  agency  in  setting  up  fermentative 
changes,  during  the  progress  of  which  substances  are  chemically  altered 
in  such  a  way  as  to  create  an  acid  or  other  chemical  agent  capable  of  act- 
ing on  the  constituents  of  the  tooth  and  decomposing  them.  Therefore 
contact  with  the  tooth,  provided  this  contact  be  suiftciently  prolonged, 
is  all  that  is  required.  The  chemical  substance  provided  goes  before 
and  prepares  the  way  for  the  entrance  of  fermentative  agents.  This 
fact  being  kept  in  mind,  much  of  the  confusion  of  ideas  apparent  m  the 
earlier  discussions  of  this  question  will  be  prevented. 

The  work  of  Leber  and  Kottenstein  made  a  profound  impression  on 
the  dental  profession,  notwithstanding  the  fact  that  most  of  their  propo- 
sitions fell  from  lack  of  evidence.  The  subject  has  since  then  been 
taken  up  by  others,  improved  methods  have  been  devised,  and  our 
knowledge  has  been  greatly  increased.  In  this  work  Messrs.  Milles 
and  Underwood  of  London  have  taken  an  important  part.  Their  results 
were  communicated  at  the  meeting  of  the  World's  Medical  Congress  held 
in  London  in  1881.  These  gentlemen  had  the  use  of  the  improved  stain- 
ing methods  introduced  by  Dr.  Koch,  and  fully  verified  the  findings  of 
Leber  and  Rottenstein  as  to  the  presence  of  micro-organisms  in  the  tubules 
of  carious  dentine.  After  an  extended  series  of  flask  experiments,  they 
announce  the  conclusion  that  the  decalcification  of  the  teeth  in  decay  is 
accomplished  by  an  acid  secreted  by  the  organisms,  and  that  there  are 
other  phenomena  present,  such  as  the  widening  of  the  tubules  and  the 
discoloration  of  the  decayed  mass,  which  are  not  to  be  explained  by  the 
action  of  acids.  The  widening  of  the  tubules  is  regarded  as  being  the 
direct  work  of  the  micro-organisms,  which  consume  the  dentinal  fibrils 
and  the  decalcified  walls  of  the  tubules  (they  use  the  term  channels),  and 
in  this  way  finally  break  down  the  entire  mass. 

After  passing  over  the  vital  theory  of  caries  as  being  already  com- 
pletely disproved,  Milles  and  Underwood  say : 

"  With  regard  to  the  purely  chemical  theory,  we  cannot  accept  it  as 
wholly  satisfoctory,  for  the  following  reasons  : 

"  1.  Because  the  destruction  of  dentine  effected  by  the  action  of  acids 
alone  under  aseptic  conditions  does  not  resemble  caries  either  in  color  or  in 
consistency,  it  being  colorless  and  gelatinous,  the  process  uniforrply 
attacking  all  parts  of  the  surface. 

"  2.  Because  sections  of  dentine  so  destroyed  show  uniform  destruction 
of  the  matrix,  but  not  enlargement  of  the  channels  occupied  by  the  fibrils ; 
whereas  the  true  caries  first  attacks  the  soft  tissues — i.  e.  the  fibrils — and 
encroaches  from  that  point  d'appni  upon  the  surrounding  calcified  structure, 
thereby  producing  the  characteristic  enlargement  of  the  channels,  until  tAVO 
channels  break  into  one,  the  intervening  matrix  being  wholly  destroyed. 

"  3.  That,  although  artificial  caries  has  been  produced  exactly  resembling 
true  caries,  we  have  failed  to  discover  any  record  of  experiments  in  which 
this  has  been  the  case  when  septic  influences  were  excluded.     Two  experi- 


AGENCY  OF  MICRO-ORGANISMS  IN  CARIES.  753 

ments  have  indeed  been  recorded  in  which  the  teeth  were  protected  from 
septic  agencies,  in  one  by  the  addition  of  creasote,  in  the  other  by  hermetic 
sealing  of  the  flask  (see  Magitot's  experiments),  and  in  neither  of  these  did 
caries  occur.  We  assume,  therefore,  that  two  factors  haye  always  been  in 
operation:  (1)  the  action  of  acids,  and  (2)  the  action  of  germs.  Further, 
our  own  flasks  show  that  malic  and  butyric  acid,  with  saliya  in  a  meat 
infusion,  haye  not,  under  aseptic  conditions,  produced  caries. 

"  It  may  be  asked.  If  a  tooth  can  be  decalcified  by  acids  out  of  the  mouth, 
and  these  acids  are  constantly  in  action  in  the  mouth,  then  if  they  produce 
caries  why  can  they  not  produce  simple  decalcification  ?  To  this  it  may  be 
replied  that  acids  alone  do  not  destroy  a  liying  tissue — that  the  stomach  is 
not  digested  by  |ts  own  acids  until  it  has  been  remoyed  from  the  body. 

"  4.  Lastly,  we  would  ui"ge  that  when  caries  occurs  in  the  mouth  it  is 
always  under  circumstances  more  favorable  to  the  action  of  germs  than  to 
that  of  acids.  There  is  always,  first  of  all,  a  minute  pit  or  haven  where 
germs  can  rest  undisturbed  and  attack  the  tissue.  We  cannot,  upon  the 
purely  acid  hypothesis,  explain  why  the  same  acids  that  originally  caused  the 
decay,  gaining  access  through  some  minute  imperfection  of  the  armor  of 
enamel,  do  not  in  the  same  mouth  or  under  the  same  conditions  attack  the 
wounded  enamel  at  the  edges  of  a  filling.  The  germs  cannot  rest  there : 
they  are  constantly  washed  away  if  the  surface  is  fairly  smooth ;  but  the 
acids  literally  bathe  the  part  (during  the  intervals  between  the  acts  of  mas- 
tication, when  the  alkaline  parotid  and  submaxillary  saliva  neutralizes 
their  action). 

"This  theory — which,  for  the  sake  of  distinction,  may  be  called  'septic' 
— is  rather  an  amplification  of  the  chemical  theory  than  a  contradiction  of 
it.  Most  probably  the  work  of  decalcification  is  entirely  performed  by  the 
action  of  acids,  but  these  acids  are,  we  think,  secreted  by  the  germs  them- 
selves, and  the  organic  fibrils  upon  which  the  organisms  feed,  and  in  which 
they  multiply,  are  the  scene  of  the  manufacture  of  their  characteristic- 
acids,  which,  in  turn,  decalcify  the  matrix  and  discolor  the  whole  mass.. 

"  From  our  observations  on  cementum  to  which  caries  has  extended  we- 
conclude  that  the  process  is  very  similar :  the  bioplasmic  contents  of  the 
lacunDe  and  canaliculi  afford  board  and  lodging  for  the  organisms,  which 
multiply,  and,  when  sufficiently  numerous,  decalcify  the  surrounding  bone,, 
so  that  each  lacuna  loses  its  outline  and  extends  in  all  directions." 

In  regard  to  the  order  of  the  occurrence  of  tlie  phenomena  of  caries, 
and  the  relation  of  micro-organisms  thereto,  the  conclusions  of  these 
observers  were  an  advance  upon  anything  before  developed,  and,  con- 
sidering; the  fact  that  they  had  not  been  able  to  make  out  the  life-historv 
of  the  fungus,  its  physiological  processes,  by  any  manner  of  demon- 
stration, it  seems  quite  remarkable  that  they  should  have  approached 
so  nearly  to  accuracy  of  judgment.  They  did  not  make  the'  neces- 
sary separation  of  the  organisms  found,  nor  cultivations  for  the  study  of 
their  individual  characters  and  the  molecular  changes  or  remoleculariza- 
tions  of  matter  they  induce  when  in  contact  ^yith  different  substances. 

This,  thanks  to  Dr.  ]Miller,  has  been  done  in  case  of  some  of  the 
micro-organisms  of  the  mouth,  and  it  only  requires  a  continuance  of 
the  work  to  make  us  familiar  with  them  all.  It  must  be  remembered, 
however,  that  this  requires  a  vast  amount  of  labor  of  the  most  pains- 
taking character  as  well  as  a  thorough  training  in  this  kind  of  work. 
I  have  had  enough  experience  in  it  myself  to  form  some  judgment  in 
Vol.  I.— 48 


754  DENTAL   CARIES. 

the  matter,  and  it  seems  to  me  impossible  for  one  burdened  with  the 
cares  of  a  full,  or  even  a  light,  practice  successfully  to  carry  out  any 
considerable  series  of  these  observations  with  that  care  and  accuracy 
which  the  subject  demands.  The  chances  for  contaminations  and  mis- 
takes in  various  directions  are  so  great  as  to  require  one's  whole  thought 
for  their  successful  avoidance.  For  these  reasons  I  shall  not,  in  what 
I  have  to  say  on  this  particular  subject,  put  forward  my  own  observa- 
tions where  I  can  avail  myself  of  those  of  persons  whom  I  know  to 
have  been  better  situated  and  better  prepared  for  the  work,  and  whose 
skill  is  known  and  recognized.  I  would  say,  however,  that  it  is  by 
no  means  certain  that  one  who  has  busied  himself  principally  with 
original  research  of  this  character  is  best  calculated  to  construct  theories 
from  the  facts  derived  from  even  his  own  experiments. 

This  work  is  as  yet  in  its  infancy,  and,  though  enough  has  been 
accomplished  to  furnish  an  ample  basis  of  fact  for  the  formation  of 
well-grounded  theories  not  only  as  to  the  agency  of  micro-organisms, 
but  also  as  to  the  modes  of  their  action,  the  development  of  many  addi- 
tional facts  may  be  expected  in  the  near  future.  It  seems  unnecessary 
to  follow  all  who  have  written  on  this  point.  Nearly  all  who  have 
attempted  to  investigate  in  this  field  have  added  something  to  our  know- 
ledge of  it.  Even  in  those  cases  in  which  no  facts  of  enduring  value  have 
been  added  difficulties  have  been  illustrated  for  the  benefit  of  those  who 
followed.  But,  after  all,  the  most  important  part  of  the  w^ork  has  been 
done  by  those  in  no  wise  connected  with  the  dental  profession,  and  it  is 
to  them  we  must  go  for  a  knowledge  of  the  agency  of  micro-organisms 
in  the  decompositions  in  general,  and  the  work  in  our  particular  field 
must  be  guided  and  directed  by  the  information  thus  gained. 

Ever  since  the  discovery  of  the  yeast-plant  by  Schwann,  and  the 
establishment  of  the  fact  of  its  necessary  participation  in  the  act  of 
alcoholic  fermentation,  it  has  been  assumed  by  a  considerable  portion 
of  the  best  students  of  natural  phenomena  that  this  was  the  type  of 
all  fermentations  and  decompositions.  Indeed,  it  was  soon  shown  by 
Schwann  and  his  colaborers  that  sterilized  solutions  Avould  not  undergo 
decomposition,  fermentation,  or  putrefaction  Avhen  hermetically  sealed, 
nor  even  after  the  admission  of  air  purified  by  heat.  This,  hoAvever, 
was  not  considered  conclusive.  It  was  claimed  that  the  disposition  to 
decomposition  is  communicated  by  the  contact  of  substances  in  a  state 
of  molecular  motion,  by  which  their  elements  are  being  rearranged  in 
new  forms,  and  that  heat  will  stop  this  molecular  movement  and  destroy 
the  tendency  until  it  is  again  communicated  by  the  contact  of  this  kind 
of  influence.'  This,  it  was  asserted,  might  exist  in  the  gaseous  form 
and  be  freely  comnmnicated  by  means  of  the  air.  In  1854,  however, 
Schroeder  sterilized  fermentable  solutions  and  soups,  to  which  he  ad- 
mitted air  after  having  filtered  it  through  sterilized  cotton,  with  the 
idea  that  if  organic  germs  caused  decomposition  these  would  be  caught 
in  the  meshes  of  the  filter.  This  experiment  was  eminently  successful. 
Solutions  did  not  decompose,  though  the  air  was  admitted  without  heat 
or  other  cliange  than  removal  of  the  particles  floating  therein.  These 
particles  were  supposed  to  be — in  part,  at  least — organic  germs  wdiich 

'  See  Liebig's  Organic  Chemistry  in  Us  Application  to  Physiology  and  Agriculture. 


AGENCY  OF  MICRO-ORGANISMS  IN  CARIES.  755 

would  undergo  development  when  brought  in  contact  with  a  favor- 
able soil. 

After  this  came  the  brilliant  experiments  of  Pasteur  and  his  colabor- 
ers,  in  which  it  was  conclusively  proven  that  none  of  the  fermentations 
or  putrefactions  could  progress  without  the  presence  of  organic  germs, 
and  that  each  one  of  these  is  dependent  on  the  presence  of  a  special 
form  of  organism  peculiar  to  it,  and  to  none  other.  Following  close  on 
these  discoveries  came  their  application  in  surgery  by  Lister,  who  by 
the  use  of  appropriate  means  for  arresting  the  ingress  of  micro-organ- 
isms succeeded  in  preventing  decomposition  in  wounds.  These  results, 
most  of  which  have  been  accomplished  Avithin  my  own  lifetime  and 
memory,  have  had  the  effect  of  almost  completely  banishing  the  old 
molecular-motion  theory  of  Liebig  and  substituting  the  germ  theory  in 
its  stead. 

The  brilliant  results  of  this  series  of  observations  are  of  the  greatest 
importance  in  the  explanation  of  the  phenomena  under  consideration. 
For  this  reason  the  close  study  of  these  fermentative  processes  is  of  the 
utmost  importance  to  those  who  would  gain  the  most  accurate  under- 
standing of  caries  of  the  teeth. 

As  briefly  representing  the  results  of  these  investigations  we  may  form- 
ulate the  following  propositions : 

The  act  of  fermentation  comprises  the  physiological  processes  of  life 
— namely, 

1st.  The  formation  of  a  solv^ent  (which  is  usually  an  unorganized  fer- 
ment, peptonizing  agent,  or  diastase)  for  the  performance  of  the  act  of 
digestion,  or  the  preparation  of  food-material  for  absorption  and  assimi- 
lation. 

2d.  Assimilation  or  nutrition,  or  the  act  of  tissue-building. 

3d.  The  formation  of  waste  products,  the  act  of  denutrition,  or  the 
shedding  out  of  material  that  has  once  been  formed  into  protoplasm  or 
used  in  connection  with  the  process  of  tissue-building. 

4th.  The  capability  of  reproduction  in  a  definite  line  of  forms. 

The  performance  of  these  acts  is  the  condition  of  the  physical  existence 
of  life,  and  they  must  be  performed  by  every  form  of  life,  no  matter 
how  high  or  how  low  in  the  scale. 

As  illustrating  the  physiological  processes  of  fermentation,  it  is  well 
to  study  tiie  higher  plants  (not  disregarding  the  physiological  processes 
of  the  higher  animals),  for  the  reason  that  in  them  certain  processes  can 
be  better  made  out  than  in  the  microscopic  organisms.  For  this  pur- 
pose I  have  made  diligent  study  of  some  particular  plants  that  seemed 
to  giv^e  better  facilities  than  others.  Among  these  studies  the  sprouting 
of  the  grain  of  corn  presents  especial  facilities  for  observation  in  micro- 
scopic section.  It,  as  most  others,  is  composed  of  three  natural  divis- 
ions— the  germ,  the  perigerm,  and  the  starch  envelope.  The  germ  is 
the  embryo  plant ;  the  perigerm  (the  scutellum  of  botanists)  is  the  organ 
of  digestion  destined  to  serve  the  needs  of  the  germ  during  its  embrv- 
onic  development ;  the  starch  envelope  is  a  store  of  food  to  serve  the 
young  plant  until  such  time  as  it  shall  have  developed  the  organs  with 
which  it  will  be  enabled  to  gather  its  own  food. 

Under  the  influence  of  warmth  and  moisture  the  germ  is  quickened 


756  DENTAL   CARIES. 

into  activity,  and  at  the  same  time  the  perigerm  elaborates  a  substance 
which  is  knoNvn  as  a  sokible  or  unorganized  ferment,  the  office  of  which 
is  the  digestion  of  the  store  of  starch  with  wliich  it  is  surrounded.  This 
sokible  ferment,  diastase,  or  digestive  fluid,  comes  in  contact  M'ith  the 
starch-granules  and  converts  this  substance  into  glucose  and  levulose. 
This  is  exactly  similar,  physiologically,  to  the  formation  of  the  pep- 
tones by  the  gastric  juice  of  the  animal,  and  is  the  digestion  M'hich  fits 
the  food,  the  starch,  for  the  needs  of  the  developing  germ  of  the  corn. 
When  this  remolecularization  of  the  starch  is  thus  accomplished,  it  is 
taken  up  by  a  set  of  ducts  that  convey  it  to  the  germ.  This  set  of 
ducts  ramify  plentifully  through  the  mass  of  the  perigerm  and  form  a 
plexus  immediately  beneath  its  epithelium,  a  layer  of  columnar  cells 
separating  the  perigerm  from  the  starch  envelope.  By  the  careful 
use  of  sugar  tests  it  is  possible  to  follow  this  sugar  along  these  ducts  to 
the  germ,  and,  after  the  growth  of  the  germ  has  advanced  somewhat, 
into  the  ducts  of  the  growing  plant.  But  here  it  is  lost ;  another  kind 
of  remolecularization  has  taken  place,  by  which  it  is  converted  into  the 
tissues  of  the  growing  plant.  This  change  is  nutrition.  As  these  pro- 
cesses go  forward,  and  are  followed  by  the  preparation  of  sections  at  the 
expiration  of  each  twelve  hours  after  the  planting  of  the  grain,  it  will 
be  seen  that  the  starch-grains  that  lie  nearest  the  perigerm  have  disap- 
peared, and  that  the  meshes  in  which  they  lie  are  empty,  and  afterward 
those  that  lie  next,  and  so  they  continue  to  disappear  as  the  germ  grow^s, 
until  its  rootlet  has  struck  down  into  the  soil  and  the  leaflet  is  spread  to 
the  air.  The  organs  for  the  gathering  of  the  food  for  the  plant  have 
found  the  elements  from  w'hich  that  food  is  to  be  obtained,  and  the 
store  of  starch,  not  yet  quite  exhausted,  is  no  longer  needed. 

But  this  is  not  all.  If  the  grains  of  corn  are  planted  in  a  soil  the 
constituents  of  which  have  been  chemically  examined,  it  will  be  found 
that  during  the  process  of  germination  this  soil  has  received  acetic  acid. 
This  is  in  accord  with  the  laws  of  life  as  we  find  them  everywhere 
expressed  wherever  they  have  been  sufficiently  examined,  for  in  con- 
junction with  all  growth  we  find  the  formation  of  wast-e  products.  In 
this  case  the  waste  products  are  acetic  acid,  which  is  left  in  the  soil,  and 
carbon  dioxide,  that  is  given  off  to  the  air.  This,  as  we  shall  see  pres- 
ently, is  the  type  of  the  jjrocess  of  fermentation. 

Suppose  we  have  planted  the  seed  in  two  inches  of  damp  sand  placed 
upon  a  piece  of  polished  marble.  Growth  takes  place,  and  the  roots 
strike  down  through  the  loose  sand  and  soon  come  in  contact  with  the 
solid  stone.  They  are  unable  to  penetrate  this,  and,  instead,  they  spread 
out  upon  its  surface.  After  this  growth  has  continued  for  a  time,  if  the 
plants  and  sand  be  carefully  removed  from  the  polished  si  one,  it  Avill 
be  found  tliat  wherever  a  rootlet  has  come  in  contact  with  it,  it  has 
left  its  trace  in  the  form  of  a  removal  of  the  polish  ;  and  a  close  exam- 
ination of  this  shows  that  a  portion  of  the  solid  rock  has  been  dissolved 
and  removed,  leaving  the  imprint  of  every  rootlet  (Sachs).  The  roots 
have  been  doing  the  same  toward  the  stone  that  the  perigerm  did  toward 
the  store  of  starch.  They  have  been  preparing  the  food  for  the  nutri- 
tion of  the  growing  plant,  and  the  liardness,  the  apparent  insolubility, 
of  the  stone  has  not  been  a  sufficient  barrier  against  them.     They  have 


AGE2vCY  OF  3ITCR0-0R0ANISMS  IN  CARIES.  757 

furnished  the  means  of  dissolving  it  (Sachs  supposes  this  solvent  to  be 
carbon  dioxide),  and  have  appropriated  such  of  its  elements  as  were 
demanded  by  the  needs  of  the  plant.  This  is  an  illustration  of  the 
universal  law  that  all  living  things,  both  plant  and  animal,  must  digest 
and  prepare  food-material  for  assimilation.  In  the  physiological  sense 
it  is  not  essentially  different  from  the  digestion  which  takes  place  in  all 
the  higher  animals,  including  man.  In  the  higher  animals  this  is  a 
very  complex  process  performed  by  an  elaborate  jjhysical  mechanism. 
In  the  walls  of  the  stomach  a  special  tissue  is  developed,  the  office 
of  which  is  to  prepare  the  unorganized  ferment,  pepsin,  which,  with 
the  aid  of  other  substances  elaborated  by  similarly  specialized  organs, 
performs  the  office  of  digestion  for  the  whole  group  of  cellular  forms 
that  constitute  the  animal. 

In  the  seed  there  is  still  a  division  of  labor.  Here  we  find,  indeed, 
in  the  perigerm  an  organ  set  apart  for  the  accomplishment  of  the  act  of 
dio'estion  as  in  the  hioher  animals,  but  its  mechanism  is  so  different  and 
so  simplified  that  nothing  but  the  closest  study  of  its  functions  w'ill 
remind  the  student  of  the  analogy  that  exists  between  it  and  the  stomach 
of  the  animal.  In  the  plant  there  is  no  specialized  group  of  cells  for 
this  office,  but  the  performance  of  the  act  is  distributed  among  the  root- 
lets. Now,  when  we  follow  this  process  down  through  the  lowly  organ- 
isms, we  find  a  continuous  simplification  of  the  mechanism  for  the  per- 
formance of  this  function  until  all  trace  of  a  specialized  organ  is  lost. 

Shall  we  conclude  from  this  that  the  function  is  lost?  Is  it  not  more 
probable  that  as  we  descend  to  those  very  lowly  organisms  we  will  find  all 
of  these  functions  combined  in  the  single  cell  ?  If,  now,  we  turn  our  atten- 
tion to  the  plant  known  as  the  torula,  which  is  the  active  agent  in  alco- 
holic fermentation,  and  study  its  physiology,  we  find  the  following  fiicts  : 

"  When  pure  vinous  yeast  is  washed  with  distilled  water,  a  peculiar 
substance  is  found  dissolved  in  the  water.  This  is  yielded  continually 
during  the  life  of  the  plant.  Examinations  have  proven  this  substance 
to  be  an  unorganized  ferment  having  a  peculiar  effect  upon  sugar.  This 
has  been  examined  by  Berthelot,  Becamp,  and  others.  It  has  been  pre- 
cipitated and  obtained  in  the  form  of  a  powder  somewhat  similar  to  pep- 
sin, and  when  redissolved  has  been  found  to  retain  its  original  power 
over  cane-sugar.  This  action  is  to  split  up  the  sugar  into  tMO  sub- 
stances, called  glucose  and  levnlose 

"This  reaction  always  takes  place  as  the  primary  step  in  alcoholic 
fermentation,  and  is  the  primary  digestion  which  permits  the  appropri- 
ation of  the  food-material  by  the  yeast-plant.  This  is  entirely  analogous 
to  the  digestion  of  food  in  the  stomach  of  an  animal,  by  which  such  food 
is  received  in  the  blood,  to  be  conveyed  to  the  tissues  for  their  nutrition, 
and  is  the  same  as  the  digestion  of  starch  in  the  seed ;  but  it  is  accom- 
plished in  the  surrounding  media  instead  of  a  receptacle  provided  for 
the  pur]3ose. 

"  This  is  one  instance  of  a  type  of  digestion  which  I  believe  to  be 
universal  in  case  of  all  unicellular  animals  and  plants.  The  formation  of 
a  stomach  is  a  j^rovision  for  the  conservation  of  force,  but  it  in  no  way 
changes  the  modus  operandi  of  the  digestive  function."  ^ 

^  Formation  of  Poisons  by  Micro-organisms,  p.  84,  Black. 


758  DENTAL  CABIES. 

Here,  as  in  all  other  forms  of  life,  we  are  unable  to  follow  by  any 
form  of  experimentation  known  to  us  the  further  changes  that  take 
place.  In  the  seed  we  have  followed  the  digested  material  into  the 
ducts  of  the  growing  germ,  and  they  are  lost  in  what  we  suppose  to  be 
the  changes  of  nutrition.  In  the  animal  we  may  follow  the  digested 
material  into  the  blood,  and  again  it  is  lost  in  the  changes  of  the  nutri- 
tive process.  But  in  both  of  these  we  find  the  material  returned  again 
in  the  form  of  waste  products.  Now,  in  the  yeast-plant  we  have  also 
followed  the  changes  consequent  upon  the  digestive  process.  We  may 
also  watch  the  growth  of  the  plant  by  the  aid  of  the  microscope,  and  see 
the  young  buds  si)ring  forth,  and  follow  their  development  into  full- 
grown  cells.  AVe  have  no  reason  for  the  supposition  that  this  growth  is 
different  in  the  main  points  of  its  physiology  from  the  other  forms  of 
life  that  we  see  around  lis.  Then  the  further  changes  in  the  digested 
material  must  be  those  of  the  nutrition  of  the  plant  through  which  its 
growth  is  maintained,  and  in  harmony  with  all  other  forms  of  life  the 
material  must  be  returned  in  the  form  of  waste  products.  This  we  find 
in  the  form  of  alcohol  and  carbon  dioxide.  This,  then,  is  fermentation, 
and  forms  the  recognized  type  of  all  of  the  fermentations  known  to  us. 
In  all  that  have  yet  been  sufficiently  made  out,  in  which  the  life-pro- 
cesses have  been  successfully  followed,  the  essential  phenomena  have 
been  found  to  agree  substantially  with  those  here  detailed.  Among  the 
animal  forms  the  principal  waste  products  are  urea  and  carbon  dioxide. 
Among  the  vegetable  forms  the  waste  products  are  the  alkaloids,  the 
organic  acids,  and  carbon  dioxide.  In  the  torula,  which  is  the  agent 
of  alcoholic  fermentation,  the  waste  products  are  alcohol  and  carbon 
dioxide.  In  acetic  fermentation  the  waste  products  are  acetic  acid  and 
carbon  dioxide.  This  proves  to  be  the  law  of  fermentation  and  putre- 
faction so  far  as  they  have  yet  been  accurately  followed.' 

It  will  be  seen  that  these  propositions  cover  the  essential  factors  of 
all  life-processes,  and  link  together  the  proposed  three  kingdoms  (the 
mici'obe,  the  vegetable,  the  animal)  in  one  chain  of  functional  activities 
that  are  common  to  all  and  necessary  to  all.  That  fermentation  is  the 
result  of  the  life-processes  of  certain  forms  of  micro-organisms  may  now 
be  accepted  as  a  truism,  and  will  not  be  argued. 

There  are  certain  chemical  processes  which  in  their  results  closely 
imitate  the  fermentations.  These  are  still  called  fermentation,  but  they 
are  essentially  different  in  their  mode.  A  number  of  substances  which 
are  formed  naturally  by  true  processes  of  fermentation  can  be  formed 
artificially  by  chemical  processes. 

Wliat  is  called  fermentation  by  an  unorganized  ferment  is  but  the  first 
step  in  a  true  fermentation.  In  digestion  this  is  seen  in  the  conversion 
of  starch  into  sugar  by  the  ptyalin  of  the  saliva,  in  the  conversion  of 
flesh  into  peptone  by  pepsin,  in  the  conversion  of  cane-sugar  into  glucose 
and  Icvulose  by  the  unorganized  ferment  of  the  torula  or  vinous  yeast- 
plant.  All  of  these  are  agents  formed  in  the  life-processes  of  living 
organisms,  and  the  fact  that  they  may  l)e  separated  from  that  organism, 
precipitated,  and  dried,  and  will  j)erfi)rm  their  function  afterward  on 

^  I  have  devel()i)etl  tliese  laws  more  at  length  in  (he  little  work  Formation  nf  Poisons 
by  Jlicro-orf/unismn. 


AGEXCY  OF  MICRO-ORGANISMS  IN  CARTES.  759 

being  dissolved  in  water,  only  shows  their  wonderfnl  power.  They 
are  only  the  agents  of  digestion  separated  from  the  organisms  by 
which  they  were  formed.  The  boiling  temperature  renders  them 
inert. 

The  essential  physiological  processes  of  the  life  of  agents  of  fermenta- 
tion must  harmonize  with  those  which  characterize  life  in  general,  for 
while,  in  the  study  of  biology,  Ave  find  the  most  endless  variety  of  form, 
there  is  presented  only  one  plan  of  relation  to  the  material  world.  The 
physical  instruments  for  the  performance  of  these  acts  may  vary  indefi- 
nitely without  vitiating  the  act  itself.  Thus  a  description  of  a  process 
of  fermentation  of  any  particular  character  involves  the  physiological 
processes  of  the  organism  which  is  the  agent  of  that  fermentative  change. 
This  is  very  much  more  important  than  the  morpliology  of  that  particu- 
lar form  of  life.  As  the  agent  of  fermentative  changes,  we  are  princi- 
pally interested  in  its  behavior  toward  the  material  world  in  respect  to 
its  physiological  acts ;  or,  in  other  words,  we  should  inquire  into  the 
nature  of  its  digestive  agent  and  its  waste  products.  What  is  its  food, 
and  in  what  chemical  form  is  it  delivered  back  after  having  served  the 
purposes  of  the  organism  ?  These  are  its  essential  characteristics.  As 
a  micro-organism,  iia  form  may  be  confounded  with  others  even  by  the 
skilled  observer. 

It  is  this  feature  of  the  experimentation  and  observations  of  Dr. 
Miller  of  Berlin  that  gives  them  their  peculiar  value.  In  the  studies  of 
this  subject  in  its  relations  to  caries  of  the  teeth  antecedent  to  his,  many 
had  perliaps  seen  the  same  micro-organisms,  which  act  as  the  agents  of 
that  fermentation  by  which  tlie  acids  are  formed,  through  which  the 
dissolution  of  the  substance  of  the  tooth  in  caries  is  effected ;  but  no 
one  had  made  sufficient  study  of  their  physiology  to  know  anything  of 
their  remolecularizations  of  matter,  and  they  therefore  failed  to  learn 
their  essential  characteristics.  While  these  previous  studies  were  very 
important  in  that  they  served  to  show  the  difficulties  with  which  the 
observer  had  to  contend,  and  were  essential  to  the  formation  of  appro- 
priate plans  of  experiment,  they  are  now  of  little  use  in  the  further 
elucidation  of  tlie  process  of  caries.^ 

Dr.  Miller  began  his  observations  with  a  series  of  experiments  with 
saliva,  with  a  view  to  ascertaining  whether,  organic  germs  being  excluded, 
it  contains  anything  capable  of  setting  in  motion  such  a  process  of  change 
as  would  produce  an  acid  at  isolated  spots  where  it  or  food  might  be 
detained  about  the  teeth.  In  this  search  the  ordinary  phenomena  of 
the  conversion  of  starch  by  ptyalin  was  observed,  but  with  this  conver- 
sion the  process  terminated.  Sugar  was  formed,  but  no  acid  of  any 
kind.  This  agrees  perfectly  with  all  that  was  known  of  the  fermenta- 
tive powers  of  this  fluid ;  and  from  many  sources  we  have  learned  that 
the  further  decomposition  of  food -particles  lodging  about  the  teeth  must 
be  in  accord  with  the  decompositions  in  general — that  is  to  say,  it  must  be 

^  The  experiments  of  Dr.  Miller  of  Berlin,  Germany,  to  which  I  shall  have  frequent 
occasion  to  allude  in  what  follows,  were  published  in  the  Independent  Pracliiioner  of  p^eb- 
rnary,  March,  and  May,  1S84.  and  May  and  June,  1885;  and  I  deem  them  so  important 
that,  with  the  consent  of  Dr.  Miller,  and  through  the  courtesy  of  Dr.  Barrett,  editor  of 
the  above-named  journal,  they  are  reproduced  as  an  appendix  to  this  paper. 


760  DENTAL  CARIES. 

accomplished  by  the  life-processes  of  an  organic  ferment.  In  the  decom- 
position of  these  particles  as  they  from  time  to  time  are  presented  in  the 
mouth,  a  considerable  variety  of  fungi  are  to  be  found.  The  separation 
of  each  of  these  the  one  from  the  other,  and  the  study  of  their  physio- 
logical processes  separately  by  individual  cultivations,  would  be  a  great 
task,  and  was  not  at  first  undertaken.  In  the  previous  studies  of  this 
subject  it  had  been  sufficiently  determined  that  the  micro-organisms 
appearing  in  the  deeper  parts  of  the  mass  of  progressive  caries  were 
much  more  constant  in  their  characters  and  apparently  presented  fewer 
varieties.  This  being  the  case,  it  seemed  best  to  study  the  organisms 
found  there.  With  this  in  view,  culture-mediums^  were  infected  by 
fragments  of  softened  dentine  taken  from  the  deeper  portions  of  the 
carious  mass,  with  precautions  to  prevent  the  ingress  of  any  germs 
from  other  sources.  These  were  kept  in  an  incubating  apparatus  at  the 
temperature  of  the  blood.  The  usual  controls  (culture-mediums  pre- 
pared, but  not  infected)  were  placed  with  them.  Fermentation  took 
place  promptly  in  the  infected  tubes.  This  occurred  with  sufficient 
uniformity  to  demonstrate  conclusively  that  the  ferment  was  derived 
from  the  carious  dentine.  The  fermentation  was  constantly  accompanied 
by  acidification  of  the  culture-medium,  as  shown  by  the  use  of  litmus- 
paper.  Other  mediums  were  then  infected  by  transferring  to  them  a 
minute  portion  from  one  of  those  that  had  undergone  the  fermentative 
process.  These  new  cultures  promptly  underwent  the"  same  process. 
This  was  continued  for  a  sufficient  number  of  generations  to  show  con- 
clusively that  there  was  present  an  organic  ferment  capable  of  the  con- 
tinuous propagation  of  its  kind — a  poini  of  great  importance  in  this 
investigation.  This  much  being  determined,  the  question  of  the  capa- 
bility of  the  acid  generated  to  decompose  the  elements  of  the  tooth  with- 
out other  concentration  than  that  attained  in  the  culture  was  tried.  For 
this  purpose  fragments  of  fresh  and  sound  dentine  were  introduced  into 
the  cultures.  These  were  promptly  softened  by  the  solution  of  the 
lime  salts. 

Thus  was  found  a  ferment  within  the  carious  dentine  showing  itself 
capable  of  continuous  propagation  in  a  certain  line  ;  hence,  a  living  fer- 
ment. It  was  also  demonstrated  that  this  living  ferment  is  capable  of 
forming  an  acid  of  sufficient  concentration  to  decalcify  dentine.  In 
connection  with  these  cultures  there  constantly  appeared  a  micro-organ- 
ism in  appearance  the  same  as  that  so  constantly  present  within  the  cari- 
ous dentine.  As  this  remains  the  same  in  all  of  the  cultures,  it  is  per- 
fectly evident  that  it  is  the  organic  ferment  which  by  its  life-processes 
produces  the  results  stated. 

By  methods  which  seem  to  have  been  carried  out  with  due  care.  Dr. 
Miller  has  found,  isolated,  and  tested  the  unorganized  ferment  (soluble 
ferment)  or  digestive  fluid  of  this  organism.  This  he  found  to  have  an 
effect  upon  cane-sugar  identical  with  that  of  the  unorganized  ferment 
of  the  yeast-plant — /.  e.  it  converts  cane-sugar  into  levulose  and  glucose 
(dextrose).  This  action  is  similar  to  that  of  most  of  the  organisms 
subsisting  upon  the  sugars. 

The  acid  produced  has  also  been  subjected  to  analysis  by  the  same 

'  See  appendix  to  this  paper. 


AGENCY  OF  MICRO-ORGANISMS  IN  CARIES.  761 

experimenter,  and  found  to  be  lactic  acid,  the  waste  product  of  the 
organism.^ 

Thus  the  four  essentials  in  the  physiology  of  this  organism  have  been 
made  out — viz.  a  digestive  body,  assimilation  as  shown  by  growth,  a 
definite  waste  product  (lactic  acid),  and  the  capacity  for  reproduction  in 
a  definite  line  of  forms.  These  findings  sufficiently  demonstrate  the 
existence  of  a  living  ferment ;  and  as  this  ferment  was  in  all  instances 
obtained  directly  from  the  deeper  parts  of  carious  dentine,  and  the 
acid  produced  is  proven  to  be  sufficiently  active,  without  fm'ther  con- 
centration, to  decompose  the  elements  of  a  tooth,  the  evidence  seems 
sufficient  to  connect  it  with  this  process  as  the  cause. 

There  are,  however,  some  other  points  in  the  physiology  of  this 
organism,  some  of  which  have  been  determined;  very  important  in  rela- 
tion to  the  process  of  decay.  In  the  depths  of  a  carious  mass  the 
access  of  the  oxygen  of  the  air  is,  to  say  the  least,  very  precarious,  and 
it  becomes  important  to  know  whether  the  organism  is  capable  of  devel- 
opment when  excluded  from  free  oxygen.  It  would  seem,  from  a  review 
of  Dr.  Miller's  experiments,  that  it  is  practically  anaerobic,  as  its  devel- 
opment is  not  hindered  by  any  exclusion  from  the  air  that  he  was  able 
to  devise.  It  is  also  certain  that  the  presence  of  oxygen  is  not  espe- 
cially detrimental  to  its  growth  or  its  acid-generating  power,  as  it  pro- 
duced sufficient  acid  to  decalcify  dentine  when  enclosed  in  a  tube  corked 
with  cotton.  Therefore  the  organism  is  capable  of  development  and 
the  production  of  its  characteristic  acid  on  tJie  surface  of  a  tooth  upon 
which  it  may  find  a  lodgment,  or  in  the  innermost  depths  to  which  it 
may  penetrate  the  dentine.  In  its  relation  to  caries  this  is  a  very 
important  consideration ;  for  if  there  is  no  other  hindrance  to  its  devel- 
opment and  the  performance  of  the  functions  detailed,  caries  would  be 
practically  incurable  without  the  complete  removal  and  exclusion  of  the 
organism  from  the  carious  cavity.  As  it  might  proliferate  anew  and 
renew  the  fermentative  process,  the  leaving  of  a  single  germ  on  any 
part  of  tlie  walls  of  a  cavity  would  effectually  destroy  the  usefulness 
of  an  otherwise  most  perfect  stopping.  After  making  many  examina- 
tions of  decayed  dentine  and  the  organisms  found  in  it,  I  cannot  con- 
ceive that  in  all  of  the  carious  cavities  successfully  treated  by  the 
stopping  process  a  perfect  removal  can  have  been  effected  ;  some  explana- 
tion of  their  failure  to  proliferate  becomes  necessary. 

It  is  possible  that  this  explanation  will  be  found  in  a  failure  of  the 
food-supply  of  the  organism.  It  is  well  known  that  micro-organisms 
are  often  confined  to  certain  qualities  of  food,  as  is  the  case  with  other 

^  In  the  earlier  controversies  it  was  pointed  out  by  Justus  Liebia;  that  if  alc<iliol  was 
formed  as  an  effect  of  the  life  and  growth  of  the  yeast-plant,  as  claimed  by  Schwann, 
it  must  be  regarded  as  the  waste  product  of  that  organism.  In  the  discussions  of  recent 
years  this  point  has  not  had  the  prominence  given  it  that  it  deserves.  Indeed,  most 
writers  have  left  it  without  explanation.  At  the  same  time,  they  have  recognized  cer- 
tain facts  going  to  show  that  tliis  is  the  true  explanation  of  the  phenomena.  One  of 
the  Tnost  prominent  of  these  is  that  this  product,  when  it  exceeds  a  certain  amount,  is 
always  poisonous  to  the  organism  wliich  produces  it,  and  thus  checks  its  development. 
This  effect  is  in  ail  respects  similar  to  that  of  urea  upon  the  animal  in  case  of  failure 
of  excretion,  and  in  harmony  with  well-known  pliysiological  laws.  Dr.  Miller  in  his 
experiments  has  found  also  that  when  a  certain  amount  of  lactic  acid  has  been  formed 
the  growth  of  the  organism  is  retarded. 


762  DENTAL  CARIES. 

organized  beings,  and  Dr.  Miller's  findings  seem  to  demonstrate  with 
sufficient  clearness  that  the  different  forms  of  sugar  constitute  the  nat- 
ural food  of  the  plant,  those  not  directly  fermentable  being  promptly 
converted  by  the  unorganized  ferment  of  the  organism.  It  seems  also 
that  the  organism  is  capable  of  growing  in  beef-extracts  without  the 
presence  of  sugar,  but  with  such  a  complete  change  in  its  physiological 
operations  that  no  acid  is  produced.  This  singular  phenomenon  is 
vouched  for  by  Dr.  Miller.  In  my  own  experiments  on  this  point  the 
fungus  did  not  seem  to  grow  well,  but  there  was  generally,  after  some 
days,  a  slight  acidification,  though  nothing  comparable  to  that  in  the 
sugar  cultures.  The  great  difficulty  I  experienced  in  the  prevention  of 
contaminations  leads  me  to  place  more  confidence  in  Dr.  Miller's  exper- 
iments than  in  my  own,  yet  after  what  I  have  seen  I  cannot  regard  the 
organism  as  being  at  home  in  a  pure  beef-extract.  Then,  if  by  the  opera- 
tion of  filling  it  is  enclosed  in  such  a  manner  that  sugar  cannot  be  obtained, 
its  power  in  the  production  of  caries  is  at  an  end  as  soon  as  the  sugar 
enclosed  with  it  is  consumed. 

So  far  as  the  growth  of  the  organism  in  the  mouth  is  concerned,  the 
question  of  its  power  to  digest  starch  is  of  but  little  consequence,  for 
the  reason  that  this  substance  is  always  converted  into  a  fermentable 
sugar  by  the  j)tyalin  of  the  saliva.  Therefore,  if  any  of  the  forms  of 
sugar  or  starch  are  present  in  solution,  they  will  be  readily  absorbed  to 
almost  any  depth  by  carious  dentine.  Thus  the  organism  is  supplied 
with  the  proper  food  for  the  production  of  lactic  acid,  and  can  act  in 
the  production  of  caries.  There  are,  perhaps,  very  few  mouths  in 
which  this  form  of  food  is  not  supplied  in  sufficient  amount  for  its  needs, 
and  it  is  well  demonstrated  by  experiment  that  in  case  of  temporary 
deficiency  there  will  be  no  destruction  of  the  organism,  for  it  may  sub- 
sist— for  a  time,  at  least — without  this  aliment. 

This  series  of  facts  developed  by  direct  experiment  seems  sufficient  to 
demonstrate  the  correctness  of  the  suppositions  of  Robertson  and  Reg- 
nard.  They  fill  the  gap  left  by  them — viz.  the  demonstration  of  the 
process  of  fermentation  and  the  production  of  the  acid  by  which  the 
constituents  of  the  teeth  are  decomposed.  This  demonstration,  however, 
does  more  than  explain  the  development  of  the  acid  and  the  solution 
of  the  lime  salts  of  the  tooth.  Caries  ]>resents  phenomena  other  than 
these,  and  which  all  previous  theories  failed  to  account  for — notably  the 
widening  of  the  tubules  and  the  constant  appearance  of  micro-organisms 
within  them  ;  for  in  the  solution  of  teeth  by  acids  this  characteristic 
widening  of  the  tubuli  is  not  present.  In  natural  caries  the  tubuli  are 
constantly  found  packed  full  of  micro-organisms,  and  in  the  series  of 
experiments  alluded  to  it  has  been  demonstrated  that  these  organisms 
are  capable  of  liquefying  several  varieties  of  semisolid  culture-mediums, 
and  my  own  experiments  show  that  some  liquefaction  of  gelatin  occurs  in 
the  j)resence  of  a  very  small  amount  of  sugar.  In  addition  to  this,  it  is 
fairly  well  shown  that  the  organism  is  capable  of  living  on  pure  beef- 
extracts.  To  do  this  it  must  digest  them.  With  these  facts  in  view, 
the  widening  of  the  tubules  is  easily  accounted  for.  A  portion  of  the 
glue-giving  basis-substance,  after  having  been  robbed  of  its  lime  salts, 
is  dissolved.     It  is  probable  that  this  is  done  by  the  unorganized  fer- 


AGENCY  OF  MICRO-ORGANISMS  IN  CARIES.  763 

ment  of  the  organism,  and  that  the  results  of  this  digestion  are  appro- 
priated. Indeed,  the  known  facts  detailed  render  this  the  most  obvious 
explanation  of  the  phenomenon.  It  accounts  not  only  for  the  widening 
of  the  tubules,  but  for  the  final  complete  breaking  down  of  the  struc- 
ture of  the  dentine  with  the  formation  of  a  cavity.  It  is  not  necessary, 
however,  to  refer  the  final  disintegration  of  tooth-structure  to  the  action 
of  this  organism  alone ;  for  after  a  considerable  degree  of  softening  has 
occurred  it  is  probable  that  other  organisms,  so  plentiful  in  the  mouth, 
may  assist  in  the  process. 

Another  point  in  the  physiological  processes  of  living  beings  deserves 
notice  here.  It  is  an  established  law  that  the  waste  products  of  an 
organism  become  poisonous  to  that  organism  when  they  have  collected 
in  a  certain  quantity.  This  is  true  of  urea  in  the  animal,  it  is  true  of 
alcohol  in  the  vinous  fermentation,  and  Dr.  Miller  found  it  to  be  true 
of  the  organism  causing  caries.  When  lactic  acid  has  accumulated  in 
certain  amount  (this  amount  being  not  yet  definitely  determined),  the 
further  development  of  the  organisms  is  interfered  with.  Their  power 
to  go  on  producing  lactic  acid  in  the  depths  of  the  dentine  is  accounted 
for  by  the  formation  from  the  lime  salts  of  the  tooth  of  the  lactate  of 
lime,  which  does  not  interfere  with  the  further  development,  and,  in 
fact,  is  equivalent  to  a  removal  of  the  waste  product.  Ijong  before  the 
existence  of  a  special  organism  in  lactic  fermentation  was  known,  it  had 
been  found  that  by  adding  chalk  or  other  form  of  lime  the  fermentation 
could  be  continued  and  much  more  lactic  acid  produced.  Following  up 
these  facts,  Dr.  Miller  has  analyzed  carious  dentine  and  found  it  to 
contain  calcium  lactate. 

With  these  facts  before  us,  the  localization  of  caries  is  no  longer  an 
enigma.  It  is  clear  that  with  the  motions  of  mastication  and  of  the 
lips  and  tongue  these  organisms  will  not  be  allowed  to  grow  on  any 
parts  of  the  teeth  that  are  exposed  to  friction.  Hence  caries  never 
occurs  at  such  points.  But  they  may  grow  in  the  form  of  little  col- 
onies in  any  places  where  they  are  secluded  from  direct  washings  by  the 
saliva,  and  in  which  they  are  protected  from  displacement.  Such  pro- 
tected points  are  found  between  adjacent  teeth,  in  pits,  fissures,  or  any 
irregularities  of  form  that  will  give  them  lodgment.  These  points  give 
the  opportunity  for  fungi.  Direct  experiment  shows  that  they  ^vill  pro- 
duce acid  abundantly  within  twenty-four  hours  after  their  implanta- 
tion. If  in  any  such  place  this  acid  is  developed  in  contact  with  the 
tooth,  and  the  development  is  allowed  to  progress  without  interruption, 
the  effect  of  the  acid  will  be  to  decompose  the  enamel,  and  finally  to 
penetrate  it  and  form  a  place  of  lodgment  in  which  the  fungus  can  con- 
tinue its  development  without  being  subject  to  frequent  dis])lacements. 
Many  have  said  that  this  fungus  is  incapable  of  attacking  enamel. 
That  is  evidently  true.  The  fungus  has  no  power  of  attacking  any- 
thing or  growing  into  anything,  except  it  be  a  thing  that  offers  spaces 
filled  with  soft  tissue,  or  openings  into  which  it  may  grow  as  the  vine 
grows  through  the  spaces  in  a  lattice-work.  It  is  not  the  organism  that 
makes  the  attack,  but  the  products  of  the  organism,  the  lactic  acid. 
When  the  dentinal  tubules  are  once  exposed,  they  form  a  protection  to 
those  filaments  of  the  fungus  which  strike  into  them  in  the  process  of 


764  DENTAL  CARIES. 

growth,  and  development  occurs  in  that  direction.  Hence  the  continu- 
ous progress  of  caries  when  it  has  once  fairly  begun  in  the  dentine.  Then 
the  growth  will  continue  in  any  direction  in  which  space  is  oifered  for 
the  development  of  filaments.  In  this  way  the  tubules  become  packed 
full  of  the  organisms,  and  the  surrounding  dentine  is  always  decalcified 
in  advance  of  the  growth  of  the  fungus  by  the  lactic  acid  produced. 
That  this  is  the  true  explanation  of  the  etiology  of  dental  caries  there  is 
no  longer  a  reasonable  doubt.  There  is  nothing  presented  in  the  phe- 
nomena of  the  affection  of  which  this  does  not  afford  a  rational  explana- 
tion. That  there  are  difficulties  still  surrounding  some  phases  of  the 
occurrence  or  non-occurrence  of  the  affection  in  special  cases  and  under 
special  conditions  there  is  no  question.  These  will  be  discussed  on 
another  page. 

I  take  the  following  extract,  written  by  the  American  editor,  from 
Coleman's  Dental  Surgery  and  Pathology: 

"A  theory  has  been  advanced  that  these  parasites,  which  may  be  found 
in  mouths  where  the  teeth  are  perfectly  sound  and  without  any  unfilled 
cavities  of  decay,  have  lodged  in  the  carious  places  simply  as  locations 
where  they  are  partially  protected  from  dislodgment  by  the  breath,  drink, 
or  food,  as  fissured  rocks  will  support  vegetable  or  animal  life  in  the  crev- 
ices, while  the  smooth  surfaces,  exposed  to  the  winds  and  rains,  are  bare  of 
vegetation." 

So  far  as  plant-life  is  concerned  this  is  about  correct.  The  rootlets 
of  plants  can  no  more  obtain  a  hold  upon  the  rocks  in  such  positions  than 
the  fungus  of  caries  can  grow  on  the  exposed  parts  of  a  tooth.  But  where 
a  crevice  furnishes  a  place  for  the  lodgment  of  a  seed,  and  moisture 
retains  a  little  dust,  plants  are  found  to  grow,  and  their  rootlets  emit  a 
solvent  that  causes  the  solid  stones  to  yield  them  nourishment.  In  this 
wav  the  hard  rocks  are  caused  to  crumble.  I  have  already  explained 
how  it  is  that  the  rootlets  of  the  growing  plant  leave  their  imprint  on 
polished  stone.  It  is  well  known  that  old  tombstones  that  have  been 
allowed  to  become  moss-grown  first  lose  their  polish,  then  their  surface 
is  softened  and  crumbles  away.  The  lichens  leave  their  imprint  upon 
the  rocks  by  dissolving  and  appropriating  a  part  of  their  substance. 
So  it  is  with  plant-life  wherever  found.  The  relation  of  life  to  the 
material  world  is  such  that  many  of  its  forms  will  wrest  their  food 
from  even  the  solid  stones  by  aid  of  the  juices  formed  for  this  purpose. 
The  fungus  of  caries  destroys  the  teeth  in  a  similar  manner. 

Phenomena  of  Caries. 

The  phenomena  presented  by  caries  have  been  well  described  by 
Tomes  and  others  who  have  followed  him.  In  this  study  there  has 
not  been  much  disagreement  as  to  what  has  been  seen.  There  have, 
however,  been  sharp  disagreements  as  to  the  interpretation  of  the  phe- 
nomena observed.  The  more  important  of  these  points  of  difference 
have  now  been  for  the  most  part  harmonized,  and  the  controversy  need 
not  here  be  revived.  For  these  reasons  I  do  not  deem  it  desirable  that 
the  progressive  development  of  the  views  now  entertained  be  followed 


PHENOMENA   OF  CARIES.  765 

out.  It  will  be  sufficient  to  describe  these  changes  as  we  now  under- 
stand them,  with  but  occasional  references  to  the  views  of  those  who 
have  previously  written  upon  the  subject. 

Caries  is  not  known  to  begin  on  a  smooth,  clean  surface  of  a  tooth. 
It  may,  as  already  stated,  begin  in  any  position  in  which  lodgments  occur, 
whether  the  surface  be  even  or  not,  but  it  is  seen  much  oftener  to  occur 
upon  uneven  surfaces,  or  those  that  lie  in  contact  with  an  adjoining  tooth 
or  in  such  relation  to  it  as  to  protect  a  portion  of  the  surface  from  fric- 
tion, and  thus  favor  the  lodgment  of  particles  of  food.  Fissures  that  occur 
in  the  enamel  are  also  often  affected  w'ith  caries.  In  case  caries  begins  in 
a  fissure  of  the  enamel  of  a  tooth  after  it  has  fully  risen  above  the  gum 
(in  the  eruption  of  the  tooth),  the  first  obvious  sign  is  the  dark  color  of 
the  fissure.  This  change  of  color  may  be  very  decided  or  very  slight. 
The  amount  of  change  of  color  in  t]^e  fissure  itself  gives  no  indication 
of  the  amount  of  caries.  Indeed,  we  may  often  find  these  fissures  dis- 
colored when  there  is  no  caries  whatever.  Usually,  however,  trial  with 
an  instrument  will  show  an  exposure  of  the  dentine,  with  softening 
immediately  beneath  the  fissure.  Probably,  in  a  large  proportion  of 
these  cases,  the  enamel  in  the  deeper  parts  of  the  fissure  was  never  per- 
fect. Often  there  may  be  reasonable  doubt  as  to  whether  the  imper- 
fections seen  are  the  result  of  the  agent  productive  of  caries  or  of 
faulty  development.  I  will  therefore  describe  the  effects  seen  in  caries 
of  the  enamel  in  connection  with  the  appearances  presented  by  the  affec- 
tion in  other  positions. 

When  the  enamel  of  a  fissure  has  been  penetrated,  a  softening  of  the 
dentine  occurs  immediately  beneath.  If  the  tooth  is  very  nearly  normal 
in  its  structure,  this  softening  is  in  the  form  of  a  cone  with  its  apex 
toward  the  pulp  of  the  tooth  and  its  base  against  the  enamel  imme- 
diately surrounding  the  fissure.  If  the  fissure  is  of  some  considerable 
length,  it  may  modify  this  form  slightly.  It  is  readily  seen  from  the 
form  of  the  cavity  that  there  is  a  tendency  to  follow  the  dentinal  tubes, 
for  the  greatest  penetration  is  almost  uniformly  along  the  length  of 
those  tubes  terminating  immediately  beneath  the  fissure.  There  is  also 
seen  a  marked  disposition  to  extension  laterally.  When  I  analyze  my 
observations  closely  in  regard  to  this  lateral  extension,  I  find  it  to  be 
very  much  confined  to  the  immediate  region  of  the  junction  of  the  den- 
tine and  the  enamel.  If  now  the  structure  of  the  dentine  at  this  point 
is  closely  studied,  it  is  found  to  be  a  region  in  which  there  are  a  great 
number  of  anastomosing  loops  connecting  the  dentinal  tubes,  and  as  ncAV 
tubes  become  involved  penetration  takes  place  in  tlie  direction  of  their 
length.  These  facts  show  that  there  is  a  strong  tendency  to  penetration 
in  the  direction  of  the  natural  openings  in  the  dentinal  structure — a 
fact  that  has  been  remarked  by  most  of  those  who  have  studied  the 
subject,  es]>ecially  by  Tomes,  Leber,  and  Rottenstein.  The  penetration, 
however,  does  not  in  all  cases  seem  to  be  confined  to  these  directions, 
for  carious  cavities  are  found  of  the  most  various  shapes ;  and  the 
instances  in  which  penetration  has  been  transverse  to  the  direction  of 
the  tubules  are  not  few.  These  differences  have  been  especially  noted 
by  the  older  authors,  and  have  given  rise  to  the  terms  "  penetrating 
caries,"  "  spreading  caries,"  etc.     These  deviations  from  the  direction 


766 


DENTAL   CARIES. 


of  the  tubules  are  often,  if  not  always,  clue  to  faulty  formation  of  the 
dentine.  This  is  most  distinctly  demonstrable  in  the  case  of  what  is 
called  spreading  caries.  It  is  seen  oftener  in  the  first  molars  than  any 
other  teeth,  and  in  the  carious  points  having  their  beginnings  in  the 
fissures  of  the  grinding  surface.  In  these  cases,  if  the  carious  process 
has  not  already  progressed  so  far  as  to  have  destroyed  much  of  the 
crown,  it  will  at  once  be  seen  that  the  development  of  the  first-formed 
portion  of  the  crown  was  distinctly  faulty.  If  tlie  decay  has  proceeded 
so  far  as  to  destroy  the  evidence  of  this  in  the  particular  tooth,  it  may 
generally  be  demonstrated  by  the  examination  of  those  portions  of  the 
other  teeth  which  were  in  process  of  formation  at  the  same  time.  Thus, 
when  the  first  molars  are  affected,  the  surface  at  or  near  the  cutting 
edges  of  the  central  incisors  should  be  scrutinized.  In  these  cases  the 
decay  often  spreads  over  the  crown  of  the  tooth  superficially,  destroying 
the  entire  grinding  surface  without  penetrating  to  a  considerable  depth. 
Not  unfrequently  this  is  so  very  marked  that  the  caries  is  seen  to  extend 
under  the  enamel  over  the  margins  of  the  grinding  surface  in  such  a 
way  that  when  the  enamel  breaks  away  the  remaining  part  of  the  crown 
is  nearly  flat.  At  this  point  the  decay  may  cease,  as  the  parts  are 
smoothed  down  by  the  friction  of  mastication. 

If  in  a  case  of  this  kind  not  too  much  affected  by  the  destructive 
process  sections  are  prepared  for  microscopic  examination,  it  will  be 

found  that  in  the  dentine  there 
Fjg.  402.  ^j.g   numerous  imperfections  in 

the  form  of  interglobular  spaces, 
or  there  may  be  very  imperfect 
depositions  of  lime  salts,  pre- 
senting various  forms,  but  espe- 
cially are  they  often  seen  in  the 
form  of  a  granular  layer,  more 
or  less  thick,  just  beneath  the 
enamel.  Every  case  of  caries 
I  have  examined  presenting 
marked  deviations  from  the 
direction  of  penetration  which  I 
first  described  has  been  explain- 
able on  the  basis  of  faulty  forma- 
tion. Therefore  the  proposition 
seems  to  be  maintained  that 
caries  penetrates  dentine  mosth/ 
in  the  direction  of  its  ncdurcd 
openings.  The  fact  that  in 
many  cases  the  openings  are 
abnormal  and  due  to  faults 
of  development  does  not  affect  this  statement. 

The  penetration  transversely  to  the  dentinal  tubules  of  the  crown 
portion  of  the  tooth  in  normally-formed  dentine  is  usuallv  verv  slight 
indeed,  and  that  which  does  occur  is  probably  due  to  penetration  through 
the  very  fine  connecting  tubuli  which  pass  from  the  one  to  the  other. 
The  reasons  for  this  become  very  obvious  when  considered  in  connection 


Carious  Dentine,  stained  with  fiidhsin  to  show  micro- 
orcanisnis.  The  section  shows  the  condition  of  tlie 
tubules  as  filled  with  niicro-orRanisnis  alone  the  junc- 
tion of  the  dentine  with  the  enamel  at  n.  The  tubules 
are  very  much  enlarged.    (^'^  immersion  objective.) 


PHENOMENA   OF  CARIES.  767 

with  the  cause  of  caries  as  detailed  in  the  former  pages  of  this  paper. 
Tlie  fungi  which  effect  the  dissohition  of  the  elements  of  the  tooth  by 
the  formation  of  their  special  products  grow  into  the  natural  openings, 
and  are  confined  to  them  until  such  time  as  the  structure  falls  to  pieces. 
This  falling  to  pieces  does  not  occur  suddenly,  but  there  is  ordinarily  a 
more  or  less  considerable  thickness  of  affected  dentine  covering  that 
which  is  yet  normal.  In  this,  in  which  the  histological  elements  still 
retain  their  forms  nearly  perfect,  the  natural  openings  are  found  to  be 
crowded  with  the  fungus  up  to  within  a  short  distance  from  the  normal 
tissue.  There  is,  I  believe,  always  a  zone  of  partially  softened  dentine, 
free  from  the  fungus,  lying  next  to  that  which  remains  normal.  In  all 
the  lateral  branches  large  enough  to  admit  them,  the  fungus  granules  will 
be  found  in  single  file,  while  very  many  tubuli  are  seen  to  be  too  small 
to  permit  their  entrance.  Thus  a  reason  for  this  peculiarity  in  the  direc- 
tion of  penetration  is  furnished. 

If,  beginning  at  other  points  on  the  surface  of  the  tooth,  the  direction 
in  which  caries  penetrates  is  examined,  we  find  the  same  general  rule 
observed ;  and  if  the  structure  of  the  tissue  involved  is  known,  the 
direction  that  the  softening  will  take  may  be  readily  foreseen.  The 
deviations  from  the  normal  direction  of  the  natural  openings  of  the  tissue 
will  be  in  consequence  of  some  one  of  the  forms  of  abnormal  develop- 
ment ;  and  an  acquaintance  with  these  will  be,  in  the  main,  a  sufficient 
guide  in  determining  the  direction  probably  followed  by  the  carious  pro- 
cess in  those  instances  of  deviation  from  the  usual  course  which  are  occa- 
sionally met  with.  All  who  have  made  extensive  studies  of  faulty  devel- 
opment have  noted  the  frequency  of  a  granular  zone  just  beneath  the 
enamel,  especially  in  the  sides  of  the  crown  toward  the  neck  of  the 
tooth.  In  other  cases  there  is  a  distinct  enlargement  of  the  anastomos- 
ing loops  of  the  tubules  at  the  juncture  of  the  dentine  and  enamel. 
Again,  rings  of  interglobular  spaces  more  or  less  perfectly  encircling 
the  crown  occur  quite  often.  Many  of  these  are,  however,  broken  up 
into  irregular  clumps  or  isolated  patches.  It  will  readily  be  seen  that 
these  conditions  will  give  the  direction  of  penetration  great  variations 
and  result  in  cavities  of  irregular  forms.  Some  will  spread  widely  just 
beneath  the  enamel  and  produce  a  broad  shallow  cavity ;  possibly  this 
spreading  may  be  in  a  particular  direction,  which,  if  the  point  of  begin- 
ning is  on  the  side  of  the  crown,  is  likely  to  be  in  a  direction  leading 
arouiid  the  tooth. 

The  penetration  of  the  structure  in  the  line  of  the  tubules  leads  to 
the  exposure  of  the  pulp,  usually  before  great  spreading  has  occurred. 
Extended  examinations  show  that  in  any  considerable  number  of  cases 
in  teeth  of  the  best  development  exposure  of  the  pulp  will  occur  with 
the  least  destruction  of  tissue ;  that  is  to  say,  that  the  more  perfect  the 
development,  the  more  completely  the  penetration  is  confined  to  the 
direction  of  the  tubules. 

The  effects  of  the  softening  of  dentine  by  caries  are  different  from 
those  observed  in  softening  obtained  by  simple  solution  in  an  acid.  If 
a  section  of  dentine  is  subjected  to  the  action  of  a  mineral  acid,  the 
decalcification  of  its  Avhole  substance  occurs  ;  but  there  is  a  marked  dis- 
position to  the  isolation  of  the  individual  tubes  by  the  more  rapid  solu- 


768  DENTAL  CARIES. 

tion  of  tlie  intertubular  substance.  In  this  way,  by  careful  work,  the 
tubules  may  be  isolated  without  any  apparent  enlargement  of  their  inter- 
nal calibre.  The  appearances  are  distinctly  dilfei-ent  in  caries.  It  is 
true  that  there  is  seen  some  disposition  to  the  isolation  of  the  tubules, 
but  at  the  same  time  the  internal  calibre  is  distinctly  and  markedly 
enlarged  ;  and  this  enlargement  of  the  internal  diameter  is  often,  if  not 
most  generally,  such  as  to  destroy  the  walls  of  the  tubes  before  the  dis- 
solution of  the  intertubular  substance,  thus  merging  two  into  one,  three 
into  one,  etc.,  until  the  histological  structure  is  lost.  In  many  instances 
this  enlargement  is  seen  to  be  quite  regular,  but  in  the  greater  number 
of  cases  I  have  examined  there  has  been  a  disposition  to  irregular  swell- 
ings or  a  more  or  less  nodulated  appearance  of  the  individual  tubes. 
Among  the  ditferent  tubules  there  are  also  very  great  differences  noted. 
•Some  are  very  much  enlarged,  while  others  are  but  slightly  changed. 
In  all  of  these  a  proper  staining  with  an  aniline  dye  will  show  that  all 
available  space  within  the  swollen  tubules  is  occupied  by  micro-organ- 
isms. This  condition  of  enlargement  does  not  occur  until  the  tubules 
are  occupied  by  this  fungus.  As  has  been  before  remarked,  the  soften- 
ing precedes  the  growth  of  the  fungus,  but  the  enlargement  of  the 
tubules  does  not. 

Very  early  in  the  progress  of  the  softening  the  tubules  present  a 
very  peculiar  appearance,  in  that  the  intertubular  substance  becomes 
more  clearly  defined,  and  in  such  a  way  as  to  outline  the  tubular  walls. 
This  appearance  has  been  described  by  Tomes  as  similar  to  a  multitude 
of  tobacco-pipe  stems  in  cross-section.  The  effect  Avill  not  be  produced 
by  the  solution  of  dentine  in  an  acid,  but  is  peculiar  to  caries  as  it 
occurs  naturally  in  the  human  mouth.  In  stainings  made  with  chloride 
of  gold  of  sections  of  fresh  dentine  softened  to  a  certain  degree  with 
acids  this  appearance  may  be  greatly  exaggerated  by  the  staining  of 
the  walls  of  the  tubules  a  bright  red,  while  the  intertubular  substance 
remains  clear.  It  may  also  be  shown  in  other  ways  that  the  inter- 
tubular substance  is  different  in  some  degree  from  the  walls  of  the 
tubules ;  but  no  satisfactory  explanation  of  this  peculiar  appearance 
in  caries  has  yet  come  to  my  notice. 

The  penetration  of  enamel  is  distinctly  different  from  the  penetration 
of  dentine.  This  substance  has  not  the  natural  openings  that  are  cha- 
racteristic of  the  dentine,  and  therefore  does  not  present  the  same  oppor- 
tunities for  growth  of  the  fungus  within  its  structure.  It  has  been 
held  by  most  of  those  who  have  written  on  this  subject  that  the  fungus 
is  incapable  of  attacking  enamel.  If  by  the  term  '^  attack  "  is  meant  an 
invasion  or  growth  of  the  fungus  into  the  substance  of  the  enamel,  this 
view  is  correct.  No  signs  of  the  fungus  are  to  be  found  in  the  enamel 
until  after  it  has  become  so  far  disorganized  that  its  crystals  are  loosened 
and  begin  to  fall  apart.  Except  that  of  localization,  and  in  some  in- 
stances discoloration,  the  softening  of  the  enamel  in  the  first  stages  of 
caries  presents  no  other  phenomena  than  those  produced  on  that  sub- 
stance by  acid  action  out  of  the  mouth.  In  case  this  effect  is  rapid,  the 
^namel  is  seen  to  lose  its  transparency,  and  soon  its  crystals  or  prisms 
show  a  disposition  to  fall  apart  in  such  a  way  as  to  give  the  impression 


PHENOMENA   OF  CARIES.  769 

that  they  have  been  separated  the  one  from  the  other.'  This  disinte- 
grated material  is  easily  removed  from  the  surface  in  the  form  of  a  fine 
dust,  and  upon  microscopic  examination  is  found  to  be  composed  of 
short  lengths  of  the  enamel-prisms  or  rods.  It  seems  that  the  acid  has 
the  eifect  of  dissolving;  the  connecting  substance  which  unites  these 
prisms  or  rods  into  a  compact  mass,  and  that  the  rods  themselves  are 
dissolved  more  slowly.  Thus  the  enamel  first  becomes  porous,  and 
finally  some  of  the  rods  fall  away,  leaving  minute  openings  through  its 
substance  by  way  of  which  the  fungi  of  caries  are  admitted  to  the  den- 
tine beneath.  On  the  proximal  surfiices  of  the  teeth,  near  the  point  of 
contact,  a  portion  thus  softened  may  frequently  be  found  ;  this  may  be 
brushed  away  and  the  surface  again  polished,  and  show  no  opening 
exposing  the  dentine.  Other  such  cases  may  on  careful  investigation 
show  one  or  several  openings  of  minute  size  through  which  the  dentine 
is  exposed.  After  such  exposure  the  enamel  is  undermined  by  the  more 
rapid  softening  of  the  dentine,  which  extends  laterally  under  it.  In  this 
condition  the  enamel  is  more  or  less  dmntegrated  from  its  internal  siir- 
face.  This  disintegration  presents  precisely  the  same  characteristics  as 
that  occurring  on  the  outer  surface.^  In  this  way  the  enamel  is  grad- 
ually destroyed  through  its  entire  thickness,  or  more  often,  by  the  more 
rapid  disintegration  of  the  dentine  beneath,  is  weakened  and  left  unsup- 
ported, and  breaks  away,  leaving  the  opening  into  the  cavity  jagged 
-and  irregular.  In  many  instances  of  very  rapid  decay,  however,  espe- 
cially if  the  enamel  be  very  thick  and  strong,  the  carious  process  will 
extend  to  a  considerable  distance  under  it  laterally  before  breakage 
occurs ;  and  in  this  case  the  opening  may  be  so  small  that  the  cavity 
might  escape  detection  but  for  a  slight  discoloration  which  is  seen 
through  the  enamel. 

Discoloration  in  caries  presents  a  wide  i^ange  of  variation.  When  it 
occurs  in  the  fissures,  as  in  the  grinding  or  buccal  surfaces  of  the  molars, 
it  is  generally  accompanied  from  its  commencement  by  a  dark  color  of  the 
enamel  along  the  walls  of  the  fissure.  The  carious  dentine  beneath  may 
be  very  dark ;  it  may  also  be  white,  slightly  yellowish,  or  of  any  shade 
between  this  and  a  jet  black.  In  caries  commencing  in  the  proximal 
surfaces  of  the  teeth,  if  the  progress  in  tlie  enamel  be  very  slow  or  if 
the  process  of  softening  has  been  only  slight  and  then  has  ceased,  the 
surface  of  the  enamel  becomes  very  dark  to  a  point  as  deep  as  the  injury 
to  its  structure  extends.  In  many  cases,  however,  particularly  those  in 
which  the  progress  is  rapid,  the  surface  of  the  enamel  afi'ected  loses  its 
transparency,  but  remains  white,  or  it  may  be  even  whiter  than  normal. 
The  rule,  both  in  caries  of  enamel  and  in  that  of  dentine,  is  that  the  more 
rapid  the  progress  of  the  disease  the  lighter  the  resultant  color.     But  even 

'  As  representing  the  histological  elements  of  the  enamel,  the  words  prisms,  crystals, 
and  rods  have  been  used  in  a  like  sense  by  writers. 

'  J.  Tomes  has  described  the  solntion  of  the  enamel-rods  as  occnrring  first  in  the  cen- 
tral part  of  the  rod.  This  appearance  is  often  given  in  artificially-prepared  specimens 
in  which  a  section  has  been  momentarily  exposed  to  the  action  of  an  acid.  But  in  all 
of  my  experiments  in  which  sections  have  been  exposed  to  the  action  of  dilute  acids 
until  the  enamel-rods  have  fallen  apart,  it  has  seemed  clear  that  the  connecting  sub- 
stances were  primarily  dissolved,  thus  separating  the  rods.  I  have  uniformly  found 
this  true  of  carious  softening. 

Vol.  I.— 49 


770  DENTAL   CARIES. 

where  the  mass  of  the  carious  contents  of  a  cavity  are  light  colored' 
there  is  often  some  discoloration  about  its  margins.  When  the  opening 
into  the  cavity  is  hidden  on  the  proximate  sides  of  the  teeth  or  under 
cover  of  a  deep  fissure,  the  location  of  many  carious  areas  is  shown  by 
their  color  appearing  through  the  enamel. 

The  discoloration  of  the  carious  parts  does  not  seem  to  depend  in  any 
degree  on  the  carious  process.  It  appears  to  be  determined  by  the  set- 
tling of  coloring  matters  into  the  partly-decomposed  tissue.  These 
seem  to  be  derived  chiefly  from  the  dark  sulphurets  formed  in  the 
mouth  by  the  action  of  sulphuretted  hydrogen  upon  such  metallic  ele- 
ments as  may  be  present.  This  discoloration  is  easily  and  perfectly 
imitated  out  of  the  mouth  upon  teeth  that  have  been  acted  upon  to 
any  considerable  extent  by  acids.  To  accomplish  this,  place  them  in 
water  holding  a  small  quantity  of  sulphuretted  hydrogen  in  solution^ 
fill  the  vessel  full,  and  place  in  the  dark  to  prevent  decomposition  of 
the  solution  ;  and  the  tissues  of  the  teeth,  to  a  point  as  deep  as  that 
affected  by  the  acid,  will  gradually  assume  a  dark  color.  This  fact^ 
taken  together  with  the  other  fact — that  all  rapidly-progressive  cases  of 
caries  are  in  color  white  or  nearly  so,  especially  in  their  inner  parts — 
leads  to  the  supposition  that  the  discoloration  is  in  no  wise  dependent 
on  the  agent  that  produces  caries,  but  is  borrowed  from  without.  It 
should  be  mentioned  also  that  when  caries  has  ceased  or  become  station- 
ary all  of  the  injured  tissue  usually  assumes  a  dark  color  within  a  short 
time.  The  color  of  caries,  therefore,  affords  some  index  to  the  rate  of 
progress.  The  lighter  colors  pertain  to  the  more  rapidly  progressive 
cases,  and  the  very  dark  colors,  those  that  are  dark  through  the  sub- 
stance of  the  dentine,  to  cases  that  are  stationary.     The  fungus  is  dead. 

Predisposing  Causes  of  Caries. 

The  study  of  the  predisposing  causes  of  caries  presents  a  wide  range 
for  observation  and  speculation.  Certain  conditions  manifestly  predis- 
pose the  teeth  to  caries,  and  the  manner  of  their  effect  is  easy  of  explana- 
tion. Other  conditions  seem  to  predispose  to  caries,  while  the  manner 
in  whicli  they  act  to  that  end  is,  with  our  present  knowledge,  not 
demonstrable.  jNIany  conditions  heretofore  regarded  as  active  causes 
of  caries  nuist  now  be  viewed  as  predisposing  causes  only,  or  as  having-^ 
no  relation  to  the  affection. 

Faidty  formation  of  the  teeth  is  probably  one  of  the  most  effective  pre- 
disposing causes  of  caries.  Yet  in  a  more  strict  sense  it  cannot  be 
regarded  otherwise  than  as  a  condition  giving  opportnnity  for  the  dis- 
ease. These  fauUy  formations  may  be  divided  into  two  varieties  of 
deviation  from  the  normal — those  relating  to  form,  and  those  relating  to- 
structure,  the  latter  of  which,  so  far  as  they  relate  to  the  dentine,  have 
been  considered  in  connection  with  the  ])henomena  of  caries.  It  seems 
clear  that  an  acid  which  will  dissolve  the  lime  salts  of  the  teeth  will  do 
so  whether  the  fi)rmation  be  good  or  indifferent ;  for  this  faulty  forma- 
tion has  relation  not  to  the  molecular  or  chemical  composition  of  these 
salts,  but  to  the  jihysical  structui-e  of  the  part.  Density  makes  a 
great  difference  in  the  rapidity  of  the  solution,  on  the  same  principle 


PREDISPOSING   CAUSES  OF  CARIES.  771 

that  an  acid  capable  of  dissolving  or  decomposing  very  soft  and  porous 
chalk  will  also  decompose  chalk  of  the  most  solid  form.  The  latter 
will,  however  be  decomposed  much  more  slowly  than  the  former,  for 
the  reason  that  the  acid  can  act  only  on  the  surface,  while  if  the  acid 
permeates  the  structure  it  will  act  much  more  rapidly.  This  is  the 
principle  upon  which  the  more  rapid  decay  of  the  teeth  of  faulty  struc- 
ture must  be  explained.  We  may  add  to  this  the  fact  that  in  many 
cases  of  faulty  formation  there  is  not  so  much  of  the  lime  salts  to  be 
dissolved  as  in  the  denser  structures. 

On  this  principle  it  is  clear  that  if  in  any  case  the  structure  of  the 
enamel  is  imperfect  it  will  be  more  susceptible  to  injury  by  the  agents 
productive  of  caries  than  if  it  were  perfect,  and  will  be  penetrated 
where,  under  otherwise  similar  conditions,  a  perfect  enamel  would  not ; 
at  least,  the  time  required  to  effect  the  penetration  would  be  very  differ- 
ent in  the  two  cases.  The  cause  that  acts  on  the  one,  however,  will  act 
on  the  other  only  in  less  degree. 

Imperfections  of  the  enamel  of  the  teeth  are  liable  to  occur  in  any 
position.  It  has  generally  been  claimed  that  they  are  especially  liable 
to  occur  on  the  jjroximal  surfaces.  My  own  examinations  do  not  bear 
out  this  idea.  It  is  true  that  in  the  majority  of  cases  the  enamel  is 
somewhat  thinner  on  these  surfaces,  but  its  structure  seems  to  be  just  as 
good  as  elsewhere,  and  its  power  to  resist  the  corrosive  action  of  acids 
is  the  same,  except  that  its  thinness  allows  it  to  be  penetrated  more 
quickly. 

The  faults  in  enamel  which  chiefly  predispose  to  decay  of  the  teeth 
are  those  which  occur  in  the  form  of  pits  and  fissures.  These  combine 
faults  of  structure  with  faults  of  form.  They  occur  in  the  grinding 
surfaces,  and  less  frequently  in  the  buccal  surfaces  of  the  molars,  in  the 
grinding  surfaces  of  the  bicuspids,  and  in  the  palatine  surfaces  of  the 
incisors.  Teeth  of  the  best  form  and  structure  otherwise  seem  to  be 
most  liable  to  this  class  of  faults ;  especially  those  that  are  large  and 
the  cusps  of  which  are  very  prominent.  In  most  of  these  cases  it 
seems  that  the  growth  of  the  enamel  organ  has  not  quite  kept  pace  with 
the  growth  of  the  dentine,  or  that  there  has  been  a  want  of  correspond- 
ence between  the  two  in  such  a  way  that  the  last  of  the  ameloblasts  to 
be  calcified  are  pulled  slightly  apart,  a  fissure  resulting  as  a  consequence.^ 

'  I  have  carefully  followed  the  formation  of  this  class  of  faults  in  microscopic  sec- 
tions of  growing  human  teeth  during  their  entire  period  of  development,  and  noted 
especially  the  relations  of  the  formation  of  the  dentine  and  enamel  from  the  beginning 
to  the  end  of  the  calcification  of  the  crown.  There  seems  to  be  an  impression  that  the 
entire  crown  of  the  tooth  is  formed  before  the  calcification  begins.  This  is  an  error. 
The  formation  and  calcification  are  in  progress  at  the  same  moment,  but  as  soon  as  a 
part  is  calcified  it  ceases  to  change  its  form.  This  calcification  begins  on  the  summit 
of  the  cusps,  and  at  this  time  all  of  the  form  of  the  tooth  that  is  unchangeable  is  rep- 
resented in  those  points.  Tlie  remaining  parts  of  the  tooth  are  not  yet  formed.  Take, 
for  example,  a  bicuspid.  The  first  hard  tissue  is  the  points  of  the  cusps,  and  these  lie 
very  close  together,  but  do  not  touch.  As  growth  proceeds  they  move  farther  apart 
continuously  until  the  form  of  the  grinding  surface  of  the  tooth  is  completed.  Now, 
if  there  has  been  a  strong  growth  of  dentine,  and  the  enamel  is  built  thick  and  high 
on  the  cusps,  the  breadth  of  the  enamel-membrane  is  not  sufficient  to  dip  down  perfectly 
into  the  centre  of  the  depression,  and  its  cells  are  separated  at  the  central  point  in  such 
a  way  as  to  leave  a  gap  which  is  finally  represented  by  a  fissure.  The  princi])le  of  the 
formation  of  the  fissure  is  the  same  in  all  positions,  and  applies  to  the  formation  of  pits 


772  DENTAL   CARIES. 

This  is  occasionally  so  complete  that  a  portion  of  the  dentine  is  left 
uncovered  or  with  but  a  slight  thickness  of  very  imperfect  enamel. 
This  is  not  always  enamel  in  the  true  sense,  in  that  it  is  devoid  of 
enamel-rods.  It  is  probably  composed  of  the  same  matter  as  the  con- 
necting substance  between  the  enamel-rods,  which,  as  we  have  found,  is 
easier  of  solution  than  the  substance  of  the  rods  themselves.  This  ease 
of  solution,  however,  is  not  the  principal  condition  predisposing  to 
caries.  The  predisposition  is  found  principally  in  the  form — a  pit  or 
groove,  giving  opportunity  for  caries  by  serving  as  a  point  for  the 
retention  of  particles  of  food,  etc.,  until  the  process  of  fermentation  has 
created  an  acid  which  will  act  on  the  tissue.  When  it  is  once  implanted 
in  them,  these  pits  protect  the  fungus  from  dislodgment,  thus  favoring 
its  development,  and  little  by  little  the  enamel  is  dissolved  out  and 
admission  to  the  dentine  gained. 

The  manner  of  contact  of  the  proximal  surfaces  has  much  significance 
in  predisposing  the  teeth  to  decay.  Those  in  which  there  is  the  great- 
est amount  of  surface  not  self-cleansing  are,  other  things  being  equal, 
most  liable  to  caries.  Hence,  teeth  so  formed  that  the  proximal  surfaces 
are  at  all  points  very  nearly  in  contact,  yet  without  actually  touching,  are 
rendered  more  liable  to  caries,  provided  the  festoon  of  the  gum  does  not 
fill  the  space.  When  I  analyze  the  conditions  under  Avhich  caries  is 
most  liable  to  occur,  I  am  convinced  that  this  is  of  great  imjiortance, 
and  that  caries  generally  does  not  occur  while  this  space  is  filled  by  the 
gum  to  the  point  of  contact  of  the  adjacent  teeth.  Two  reasons  may 
be  given  for  this :  First,  the  festoon  of  the  gum  fills  the  space  and 
tends  to  prevent  lodgments  from  occurring ;  second,  the  secretion  given 
out  by  the  healthy  gum,  especially  that  coming  from  the  gingival  space, 
is  antiseptic  to  a  sufficient  degree  to  prevent  fermentation  of  very  slight 
amounts  of  matter  in  immediate  contact  with  it.  Therefore,  so  long  as 
the  gum  remains  healthy,  decay  does  not  begin  in  immediate  contact 
with  its  border.  The  breaking  down  of  this  septum  of  the  gum  by 
the  repeated  forcing  of  food  between  the  teeth  or  from  other  causes 
becomes  a  predisposing  cause  of  decay.  I  may  add  also  that,  without 
becoming  distinctly  unhealthy,  the  gum  sometimes  recedes  slightly  from 
between  the  teeth,  and  in  this  way  predisposes  the  teeth  to  caries  by 
giving  opportunity  for  its  beginnings,  in  that  a  receptacle  is  formed  for 
the  lodgment  of  particles  whicli  undergo  fermentation  in  contact  with 
the  t^eth.  Malpositions  of  the  teeth,  when  of  such  character  as  to  favor 
such  lodgments,  also  predispose  to  the  beginning  of  caries ;  and  in  these 
cases  it  is  often  shown  that  what  is  supposed  to  be  the  strongest  enamel 
will  be  penetrated  if  placed  in  such  position  that  lodgments  occur 
against  it. 

Hereditary  injlvences  are  very  powerful  predisjwsing  causes  of  decay 
of  the  teeth.  Tliis  has  been  recognized  by  all  who  have  examined  the 
subject.  Indeed,  this  influence  is  too  manifest  to  be  overlooked  by  any 
one  who  has  given  the  subject  close  attention.  It  seems  to  me,  however, 
that  it  has  in  tlic  ])ast  been  by  many  much  overrated,  though  it  must 

as  well.  It  seems  evident  that  the  ameloblasts  will  allow  of  some  spreading  without 
division  one  from  the  other,  but  this  tolerance  is  limited,  and  in  the  later  stages  of  cal- 
cification tlie  power  of  proliferation  is  reduced  to  the  lowest  point. 


PREDISPOSING   CAUSES   OF  CARIES.  773 

be  acknowledged  as  an  important  factor.  Two  separate  factors  enter 
int(j  the  law  of  heredity  in  its  relation  to  caries :  one  of  these  is  capable 
of  demonstration ;  the  other  must  for  the  present  be  regarded  as  an 
hypothesis.  The  first  is  all  told  in  the  transmission  of  form.  That 
peculiarities  of  form  are  transmissible  from  parent  to  child  is  of  course 
generally  held  to  be  a  truism,  and  requires  only  simple  mention.  As 
has  been  seen  in  the  previous  pages,  deviations  from  the  best  forms  of 
teeth  are  powerful  in  predisposing  to  caries.  This  element  of  heredity, 
great  as  it  is,  is  probably  not  the  greatest.  This  does  not  furnish  a 
reason  why  one  person  may  go  through  a  long  life  without  caries,  \y\\\\e 
much  the  greater  number  of  his  neighbors  suffer  from  its  effects.  There 
is  undoubtedly  something  in  the  constitution  of  the  fluids  of  the  mouth 
of  different  persons  rendering  them  favorable  or  unfavorable  to  the 
propagation  of  fermentation.  Differences  in  the  constitution  of  the 
saliva  of  different  individuals  are  sufficiently  manifest.  Some  persons 
have  saliva  which  is  exceedingly  viscid  or  emits  a  peculiar  odor,  and 
one  or  the  other  of  these  peculiarities  is  likely  to  be  present  in  other 
members  of  the  family.  This  is  also  true  of  other  fluids,  as  the  per- 
spiration. It  is  also  true  that  the  lower  animals  are  subject  to  diseases 
having  their  basis  in  the  growth  of  micro-organisms  to  which  men 
are  not  liable,  and  vice  versa.  Men  are  but  slightly  susceptible  to 
anthrax,  which  makes  such  havoc  among  sheep  and  cattle  in  some 
parts  of  Europe,  while  the  lower  animals  are  not  subject  to  measles, 
whooping  cough,  etc.  Again,  adults  are  usually  insusceptible  to 
many  diseases  which  prevail  among  children.  In  the  present  state  of 
our  knowledge  we  can  account  for  these  differences  only  on  the  sup- 
position that  there  are  variations  in  the  constitution  of  the  cellular  ele- 
ments or  fluids  which  render  them  in  the  one  case  unfavorable,  and  in 
the  other  favorable,  to  the  action  of  the  cause  of  disease.  It  is  only  on 
this  supposition  that  a  rational  explanation  can  at  present  be  founded. 
There  has  been  great  endeavor  to  explain  the  tendency  to  caries  upon 
the  basis  of  changes  in  the  nutrition  and  structure  of  the  teeth  them- 
selves. Certainly,  there  has  been  sufficient  study  of  this  point  to 
demonstrate  that  the  predisposition  is  not  explainable  on  this  basis. 
We  must  assume  that  in  some  cases  the  cause  of  caries  is  not  present  in 
the  mouth,  or,  if  present,  that  it  is  too  feeble  to  produce  active  results. 
There  is  not  a  sufficient  difference  in  the  structure  of  the  teeth  them- 
selves to  account  for  the  manifest  differences  seen  in  practice.  Indeed, 
the  strongest  and  best-formed  teeth  often  fall  a  prey  to  caries  and  are 
rapidly  destroyed,  while  in  other  cases  teeth  not  nearly  so  good  either 
in  form  or  structure  are  unaffected.  When  we  examine  the  cause  of 
caries  and  the  conditions  of  its  activity,  we  are  forced  to  the  supposition 
that  the  basis  of  these  differences  is  in  the  environment  of  that  cause, 
affecting  its  activity,  not  in  the  power  of  the  teeth  to  resist. 

This  holds  a  close  relation  to  heredity  as  manifested  in  other  diseases. 
Of  all  diseases  that  are  to-day  regarded  as  hereditary,  there  is  probably 
not  more  than  one  (syphilis)  directly  transmissible  from  parent  to  child. 
In  all  others  the  element  of  heredity  must  be  in  the  constitution  of  the 
cellular  elements  or  the  peculiar  character  of  the  fluids  that  in  some  way 
renders  the  subject  susceptible  to  the  particular  form  of  disease.     If  the 


774  DENTAL   CARIES. 

special  disease  has  as  its  basis  a  change  in  the  physiological  qualities  or 
activities  of  the  cellular  elements,  as  in  the  cancers,  there  is  something  in 
the  physiological  constitution  of  the  individual  rendering  the  cellular 
elements  peculiarly  liable  to  this  form  of  excitement.  If  the  particular 
disease  has  a  fermentation  as  its  basis,  the  fluids  of  the  individual  must 
furnish  a  favorable  soil  for  the  growth  of  the  fungus  of  that  fermenta- 
tion. Again,  persons  acquire  a  temporary  susceptibility  to  certain  dis- 
eases, not  from  a  condition  of  ill-health  that  is  in  any  way  manifest, 
but  apparently  through  some  minor  changes,  as  yet  impossible  of  anal- 
ysis, in  the  action  of  the  vital  forces  of  the  organism  or  constitution  of 
the  fluids.  If  we  can  trust  the  combined  observations  of  the  profession, 
changes  that  are  of  the  same  order  certainly  occur  in  the  predisposition 
to  caries.  Why  is  it  that  pregnant  women  become  temporarily  more 
susceptible  to  caries?  Certainly  not  from  any  change  in  the  structure 
of  the  teeth  themselves,  rendering  their  lime  salts  more  easy  of  solution 
by  an  acid.  Of  all  the  tissues  of  the  body,  the  teeth  are  least  prone  to 
structural  changes  consequent  upon  variations  in  nutrition,  and  there- 
fore are  least  liable  to  temporary  susceptibility  to  disease  on  that 
account. 

The  saliva  is  certainly  in  a  large  degree  antiseptic  in  its  qualities,  and 
opposes  the  process  of  fermentation,  notwithstanding  the  fact  that  fer- 
mentation, in  some  of  its  forms,  is  continually  in  progress  in  the  mouth. 
It  is  practically  impossible  to  protect  wounds  of  the  mouth  from  micro- 
organisms, yet  these  wounds  are  less  liable  to  sepsis  than  any  others  in 
the  organism  that  are  exposed  to  external  influences. 

It  is  possible  that  what  have  been  noted  as  the  antiseptic  qualities  of 
the  saliva  as  seen  in  its  relation  to  wounds  in  the  mouth  may  be  due 
to  the  continued  irrigation  of  the  surfaces  by  the  flow  of  fresh  saliva, 
Mdiich  washes  away  septic  organisms  or  their  products.  This  in  a  large 
degree  explains  the  occurrence  of  decay  in  protected  points  only,  and  fur- 
nishes a  reason  for  the  rare  occurrence  of  caries  in  the  lower  incisors. 

When  all  of  the  facts  known  to  us  are  considered,  the  most  plausible 
supposition  is  that  there  are  diflerences  in  the  saliva  that  in  some  cases 
render  it  an  unfavorable  soil  for  the  propagation  of  the  peculiar  fermen- 
tation found  to  be  the  cause  of  caries.  In  other  cases  it  becomes  a  very 
fav^orable  soil  for  the  growth  of  this  peculiar  fungus,  and  caries  is  cor- 
res])ondingly  active.  When  we  look  around  us  and  gather  together  the 
facts  at  our  command  in  regard  to  the  susceptil)ilities  of  those  forms  of 
life  which  we  know,  and  see  how  they  affect  each  other  in  ways  that  seem 
inscrutable,  these  suppositions,  while  losing  none  of  their  mystery,  are 
seen  to  be  in  harmony  with  those  forced  upon  us  in  other  fields  of 
observation. 

Morbid  Conditions  of  the  Fluids  of  the  Mouth. 

By  most  authors  who  in  tlie  ]iast  have  examined  the  "subject  morbid 
conditions  of  the  saliva  and  of  the  mucus  of  the  mouth  have  been  con- 
sidered as  among  the  active  causes  of  caries.  In  view  of  the  expla- 
nation given  in  the  previous  ]>ages,  this  becomes  impossible.  If  the 
causes  of  caries  have  been  correctly  detailed,  the  influences  favorable  to 


MOBBID   CONDITIONS  OF  THE  FLUIDS  OF  THE  MOUTH.   775 

<;aries  exerted  by  the  morbid  conditions  of  the  saliva  must  be  subordi- 
nate or  secondary,  in  that  they  furnish  a  better  soil  for  the  promotion 
of  fermentation  or  assist  in  decomposition  by  virtue  of  the  acid  they 
may  contain.  The  iirst  of  these  inflnences  has  been  considered  under 
the  head  of  Heredity.  That  the  fluids  of  the  mouth  often  contain  acids 
in  a  very  dilute  form,  but  sufficient  in  amount  to  be  readily  detected  by 
litmus-paper,  is  well  known  to  all  who  have  given  attention  to  the  sub- 
ject. This  acid,  whatever  its  origin,  is  distributed  generally  in  the 
fluids.  There  is  no  localization  demonstrable  by  our  present  modes  of 
research,  except  it  be  that  the  mucus  exuded  from  the  gum  in  a  state 
of  irritation  is  more  markedly  acid  than  the  other  fluids.  This  latter 
point,  as  it  affects  only  special  cases,  will  be  examined  later. 

Some  years  ago  very  extended  examinations  of  the  fluids  of  the 
mouth  were  made  with  reference  to  acidity  and  its  possible  connec- 
tion with  caries.  I  made  personal  tests  in  several  thousand  cases. 
These  gave  rather  complex  results,  but  in  the  main  seemed  to  demon- 
strate that  the  two  conditions  were  in  no  wise  connected  as  cause 
tind  effect.  So  decided  was  this  that,  while  I  went  into  the  series  of 
observations  with  a  conviction  that  Tomes,  Magitot,  and  others  were 
right  in  attributing  caries  to  this  cause,  I  retired  with  the  belief  that, 
whatever  be  the  cause  of  caries,  it  has  little  or  no  connection  with 
acid  saliva.  In  many  the  tendency  to  caries  was  not  in  any  degree 
related  to  the  degree  of  acidity  of  the  fluids  of  the  mouth.  In  an  article 
which  I  wrote  in  1880,  after  this  series  of  experiments,  these  sentences 
occur:  "Decay  of  the  teeth  is  certainly  a  specific  disease,  running  a 
specific  course,  and  evidently  arising  from  a  specific  cause,  but  this 
<^ause  is  not  as  yet  certainly  known."  .  .  .  .  "  While  there  is  no  decay 
without  the  presence  of  an  acid,  there  is  not  necessarily  decay  because 
of  the  presence  of  an  acid."  .  .  .  .  "  While  an  acid  is  not  only  always 
present,  but  is  probably  a  neeessity  to  the  inception  and  progress  of 
•decay,  there  may  be  an  agent  acting  in  conjunction  with  the  acid  that 
is  not  yet  known  or  recognized." 

Now,  after  the  demonstration  of  the  cause  of  caries  by  Dr.  Miller, 
which  represents  the  unknoicn  in  these  sentences,  ^ve  are  able  to  analyze 
the  probable  effects  of  morbid  conditions  of  the  fluids  of  the  mouth  more 
olosely  than  before,  especially  after  studying  the  microscopic  phenomena 
in  the  light  thrown  upon  them  by  the  demonstration  of  the  cause.  It 
is  now  perfectly  clear  that  acids  alone,  while  they  may  decalcify  the 
teeth,  cannot  produce  the  phenomena  of  caries.  Dr.  Mayr  has  well 
said:  "The  decay  under  consideration  is  so  specific  that  the  mere  action 
of  acids  is  not  sufficient  to  produce  it."^  The  occurrence  of  micro- 
organisms in,  and  the  widening  of  the  calibre  of,  the  tubules  is  a  prom- 
inent manifestation  without  which  the  presence  of  caries,  no  matter 
what  the  amount  of  softening,  may  confidently  be  denied.  This  has 
now  been  confirmed  by  so  many  observers  that  it  has  become  a  truism  ; 
and  after  the  studies  of  the  physiology  of  this  fungus  cited  in  the  pre- 
vious pages  we  have  no  need  to  go  to  the  fluids  of  the  mouth  to  find 
the  acid.  It  is  developed  in  situ.  Acids  that  are  commingled  with  the 
fluids  of  the  mouth,  whether  developed  therein  or  introduced  from  with- 

^  Independent  Practitioner,  1884,  p.  195. 


776  DENTAL   CARIES. 

out,  cannot  produce  caries.  There  is  no  reason  why  an  acid  commin- 
gled with  the  fluids  of  the  mouth  should  exert  a  localized  action  on  the 
teeth.  Their  action  Mould  be  general,  and  greatest  on  the  exposed  sur- 
faces. It  is  not  impossible  that  some  such  effect  is  produced — indeed, 
I  have  seen  evidence  that  such  is  the  case — but  this  does  not  seem  to- 
have  any  relation  to  the  localized  action  which  represents  the  inception 
of  caries. 

Acid  mucus  occurs  under  circumstances  that  seem  in  certain  cases  to 
connect  it  with  the  inception  of  caries.  These  are  those  forms  of  the  disease 
which  occur  near  the  margin  of  the  gum  in  connection  with  points  of 
irritation.  In  irritations  of  the  gum-tissue  there  often  arises  a  markedly 
acid  condition  of  the  mucus  exuded  at  that  spot.  This  has  been  espe- 
cially noted  by  Tomes  and  Magitot,  and  is  regarded  by  them  as  a  direct 
cause  of  decay  of  the  teeth.  I  cannot,  in  the  light  of  recent  develop- 
ments, regard  it  as  a  cause  of  caries  proper,  but  it  may  be  productive 
of  a  softening  of  the  tissue  at  that  point  or  an  actual  solution  of  the 
lime  salts,  which  will  give  ■the  opportunity  for  the  implantation  of  the 
agents  productive  of  fermentation  and  caries.  Certainly,  observation 
seems  to  connect  local  irritations  of  the  gingivse  with  a  certain  propor- 
tion of  that  form  t)f  caries  beginning  about  the  necks  of  the  teeth  ;  and 
it  is  sufficiently  demonstrated  that  under  these  circumstances  the  mucus 
is  markedly  acid.  It  should  be  noted,  however,  that  in  these  cases  the 
irritation  is  not  of  such  a  character  as  to  be  productive  of  pus.  All 
observation  shows  that  pus,  wherever  it  occurs,  is  directly  preventive 
of  caries.  If  under  any  circumstances  pus  is  continuously  discharged 
into  a  cavity  of  decay,  the  decay  ceases.  This  furnishes  a  reason 
why  roots  of  teeth  protruded  through  the  gum,  and  thus  exjjosed, 
so  seldom  decay.  There  is  generally  an  irritation  of  tissue  in  their 
neighborhood  sufficient  to  keep  them  more  or  less  bathed  in  pus.  This 
is  also  noted  in  case  of  roots  which  have  lost  their  crowns,  and  the  gum 
of  which  is  in  such  a  condition  as  to  keep  its  broken  end  bathed  in  pus ; 
also  in  som6  cases  in  which  chronic  alveolar  abscess  discharges  into  a 
cavity  through  the  pulp-canal.  This  affords  a  condition  of  environ- 
ment that  is  markedly  opposed  to  caries ;  and,  though  pus  is  dis- 
tinctly different  from  saliva,  it  is  still  an  evidence  of  the  possibility 
— we  may  say  the  probability — that  changes  in  the  constitution  of  the 
saliva  may  occur  that  will  render  it  unfavorable  to  the  propagation  of 
caries. 

There  is  another  form  of  acid  mucus  that  seems  to  be  distinctly  differ- 
ent from  that  ])roduced  by  irritation  of  the  gums,  in  that  no  irritation  is 
apparent  and  the  condition  is  more  or  less  permanent.  In  some  cases  it 
seems  to  be  hereditary.  It  may,  however,  be  acquired.  In  this  condi- 
tion the  mucus  seems  much  indisposed  to  mix  with  the  other  fluids  of 
the  mouth.  It  is  more  viscid  than  normal,  and  may  be  drawn  out  in 
long  threads  by  touching  tlie  finger  to  the  gums  and  withdrawing  it,  I 
have  seen  cases  in  wliich  these  threads  could  be  extended  to  the  arm's 
length  before  they  wovdd  break.  This  character  of  the  mucus  has  been 
noted  by  a  considerable  number  of  writers,  and  seems  to  have  been 
regarded  as  an  active  cause  of  caries.  It  certainly  appears  to  furnish  a 
condition  favorable  to  the  propagation  of  the  disease,  for  in  most  of  the 


MORBID   CONDITIONS  OF  THE  FLUIDS  OF  THE  3I0UTH.   777 

cases  that  have  come  under  my  observation  caries  has  existed,  and  has 
been  severe  and  usually  difficult  of  successful  treatment. 

Absorptive  prooesses  stand  in  such  close  relation,  clinically,  to  the 
production  of  acid  mucus  from  points  of  irritation,  and  the  results, 
when  slight,  are  so  similar,  that  it  is  difficult  to  discriminate  between 
them.  I  have  reference  here  to  absorptions  just  beneath  the  margin  of 
the  gum  or  at  the  point  of  union  of  the  soft  tissue  with  the  tooth,  con- 
sequent upon  some  slight  irritation.  This  is  a  factor  in  the  predispos- 
ing causes  of  caries  that  has  not  until  recently  had  recognition.^  This 
absorption  is  in  all  respects  similar  to  that  Avliich  occurs  at  the  roots  of 
teeth  which  have  been  transplanted,  and,  like  that,  is  dependent  on  a 
slight  irritation  of  tissue,  through  which  irritation  it  is  caused  to  tempo- 
rarily take  on  a  new  function — that  of  the  production  of  a  substance 
which  dissolves  the  hard  structures  with  which  it  is  in  contact,  making 
room  for  the  growth  of  its  own  granulations. 

The  phencjmena  of  absorption  may  be  studied  in  a  variety  of  positions 
and  circumstances.  Wherever  observed,  we  find  very  much  the  same 
conditions  in  the  tissue  involved.  This  is  true  whether  it  be  in  the 
removal  of  the  root  of  a  temporary  tooth,  removal  of  bone  in  change  of 
form  (physiological),  removal  of  the  roots  of  replanted  teeth,  burrowing 
into  pieces  of  ivory  that  have  been  thrust  into  the  flesh  for  the  purpose 
of  experiment  (Krause,  Koelliker,  Tomes),  removal  of  sponge  in  the 
sponge-graft,  or  the  absorpti(jn  of  the  surgeon's  animal-membrane  liga- 
tures (pathological).  In  all  cases  granulation-cells  or  leucocytes  are 
brought  in  contact  with  the  substance  to  be  removed,  under  the  influ- 
ence of  which  it  gradually  disappears.  (In  the  physiological  absorption 
of  bone  the  osteoblasts  have  been  regarded  as  performing  this  function.) 
Just  what  the  cellular  action  is  in  these  cases  is  not  at  the  ])resent  time 
positively  demonstrable.  But  that  the  substance  which  effects  the  solu- 
tion is  of  the  nature  of  an  unorganized  ferment  seems  almost  certain. 
Krause  suggests  that  it  contains  lactic  acid.  At  any  rate,  the  granula- 
tions invade  the  tissue  gradually,  and  room  is  made  for  thcm^Dy  its  dis- 
appearance. In  this  way  the  part  is  burrowed  out,  whether  it  be  bone, 
tooth-substance,  catgut,  or  sponge,  and  the  granulations  fill  the  space. 
In  all  cases  of  pathological  absorption  it  is  fairly  demonstrable  that  the 
action  is  in  response  to  an  irritation  or  excitement  of  a  mild  character 
of  the  cells  of  the  part  in  which  leucocytes  are  formed  or  called  and  pro- 
ceed to  the  building  of  granulations.  If  in  any  case  the  irritation  is  of 
such  intensity  that  pus  is  formed,  the  process  of  absorption  fails.  As 
the  ])art  of  the  tooth  acted  uj)on  rises  above  the  soft  tissues,  this  in  time 
becomes  dark  colored  ;  and  if  it  be  on  a  smooth,  self-cleaning  surface 
not  too  deej),  no  decay  results.  If,  however,  the  process  of  absorption 
has  produced  excavations  sufficiently  deep  to  afford  lodgments  and  thus 
give  the  opportunity  for  fermentation,  the  result  is  the  formation  of  a 
cavity  by  true  caries.  Then  these  absorptions  are  not  a  direct  cause  of 
decay,  nor  are  they  caries  in  themselves ;  but  they  give  the  opportunity 
for  the  implantation  of  true  caries,  and  are  therefore  a  predisposing 
cause. 

Prof.  W.  H.  Eames  of  St.  Louis  has  described  certain  effects  upon 
^  Formation  of  Poisons  by  Micro-orcjanisnis,  1884,  Black. 


778  DENTAL   CARIES. 

the  crowns  of  teeth  as  the  product  of  absorption  brought  about  by  tlie 
absorbent  organ,  so  called,  which  removes  the  root  of  the  temporary 
tooth  or  effects  the  liberation  of  the  permanent  tooth  in  the  process  of 
its  eruption  through  the  gums.^ 

Cervical  absorptions  (absorptions  at  the  necks  of  the  teeth)  are  gener- 
ally very  small  affairs  which  before  caries  results  are  liable  to  be  over- 
looked ;  indeed,  heretofore  they  have  been  altogether  unnoticed.  They 
occur  about  the  necks  of  the  teeth  after  the  age  of  maturity  or  late  in 
life.  As  the  irritation  proceeds  there  is  often  a  tendency  to  the  short- 
ening of  the  gingival  margin,  in  such  a  way  as  to  expose  more  of  the 
neck  of  the  tooth.  In  this  manner  the  injury  becomes  exposed,  and  caries 
is  implanted.  In  many  cases  the  irritation  causes  a  thickening  and 
eversion  of  the  gum  in  the  form  of  a  little  pocket;  caries  is  induced, 
and  proceeds  to  the  fo>"mation  of  a  cavity.  This  is  oftenest  seen  on 
the  buccal  surfaces. 

I  have  said  that  cervical  absorptions  are  generally  slight.  This,  how- 
ever, is  not  always  the  case.  I  have  in  my  possession  several  specimens 
in  which  they  are  very  large,  having  destroyed  a  large  part  of  the  crown 
of  the  tooth.  In  one  of  these,  a  lower  molar,  the  pulp-cavity  was  laid 
open.  The  granulation-tissue  which  filled  the  space  was  still  in  the 
cavity  formed,  and  came  away  with  it  when  it  was  extracted,  giving 
me  the  opportunity  for  a  close  inspection.  This,  however,  shoe's  no 
differences  from  the  absorptions  in  general.  In  another  lower  molar 
the  larger  part  of  the  crown  was  destroyed,  and  the  posterior  root 
separated  from  it  by  granulations  that  seemed  to  have  grown  in 
from  the  gum  at  the  posterior  border.  Cavities  formed  in  this  M'ay 
differ  from  those  formed  by  caries,  in  that  there  is  very  little  softened 
tissue ;  and  this  does  not  present  the  phenomena  of  caries,  but  those 
of  absorptions  of  the  roots  of  the  })ermanent  teeth. 

Clinically,  it  is  almost  impracticable  to  divide  these  effects  when  slight 
from  those  supposed  to  be  produced  by  acid  mucus.  There  is  a  similar 
irritation  of  the  gum,  and  the  general  appearances  are  very  closely  allied 
as  to  the  effects  upon  the  tooth-structure.  They  occur  at  very  nearly  the 
same  points  on  the  surfaces  of  the  teeth,  so  that  after  the  occurrence 
of  caries  the  one  cannot  with  certainty  be  told  from  the  other.  The 
results  of  acid  mucus,  however,  are  always  distinctly  below  (toward  the 
crown)  the  margin  of  the  gum,  while  cervical  absorption  is  always  at 
a  point  in  contact  with  the  gum  and  covered  by  it. 

Diseases  of  various  sorts  have  been  regarded  as  predisposing  to  caries 
of  the  teeth,  and  many  observations  tend  to  confirm  this  supposition. 
In  some  of  the  contiuued  fevers  there  is  an  acid  condition  of  the  scanty 
saliva  continuing  for  days  and  weeks  together ;  and  it  is  not  uncommon 
to  find  a  number  of  carious  cavities  making  their  a])pearance  a  short 
time  after  convalescence,  as  has  already  been  explained.  The  distribu- 
tion of  the  acid  saliva  is  general,  and  its  effects  should  be  seen,  if  at 
all,  on  the  tectli  generally,  not  localized.  A  more  probable  explana- 
tion of  these  ])hen()mena  is  to  be  found  in  the  fact  that  through  neglect 
for  so  long  a  ])eriod  to  remove  lodgments  fermentation  in  the  interstices 
about  the  teeth  has  been  allowed  to  go  on  unobstructed.     This  applies 

'  Transactions  of  lite  Illinois  Stale  Dental  Society,  1884. 


CLINICAL  HISTORY  OF  CARIES.  779 

to  all  forms  of  disease  that  interfere  ^vitli  the  usual  motions  of  the 
mouth  or  with  the  usual  care  of  the  teeth.  There  is  no  sufficient  evi- 
dence that  diseased  conditions  give  rise  to  changes  in  the  teeth  them- 
selves that  render  them  more  susceptible  to  caries. 

There  is,  however,  sufficient  proof  that  a  predisposition  to  caries  is 
often  acquii'ed  in  cases  Avhere  it  did  not  exist  in  early  life  or  is  not 
transmitted  as  a  hereditary  predisposition.  As  explained  in  connection 
with  the  subject  of  heredity,  the  supposition  that  some  change  in  the 
constitution  of  the  saliva  renders  it  a  more  favorable  soil  for  the  prop- 
agation of  fermentation  is  the  only  hypothesis  which,  with  our  present 
knowledge,  seems  tenable.  This  explanation  applies  to  variations  in  the 
constitution  of  the  fluids  brought  about  by  temporary  deviations  from 
health,  as  well  as  more  lasting  changes. 

Clinical  History  of  Caries. 

Under  this  caption  it  is  intended  to  study  caries  of  the  teeth  as  jt 
appears  clinically,  laying  aside  the  consideration  of  its  etiology  and 
microscopic  features  except  as  incidental  references. 

Caries  has  pretty  definitely  fixed  habits  as  to  its  points  of  beginning, 
and  one  of  its  most  notable  characteristics  is  that  it  never  attacks  a 
tooth  on  a  surface  that  is  smooth  and  is  constantly  kept  worn  and 
clean  by  the  attrition  of  mastication  or  the  friction  of  the  tongue, 
lips,  or  cheeks.     All  such  points  are  absolutely  exempt  from  attack. 

The  points  on  the  surface  of  the  teeth  at  which  caries  has  its  begin- 
nings may  conveniently  be  divided  into  four  classes,  according  to  the 
character  of  the  surface : 

Class  1st.  Pits  and  grooves  in  the  enamel ; 

Glass  2d.  Proximal  surfaces  ; 

Class  3d.  Smooth  surfaces  which  from  any  cause  are  habitually 
unclean ; 

Class  J/ih.  Necks  of  the  teeth,  at  or  near  the  junction  of  the  cemen- 
tuni  and  enamel. 

These  classes  of  caries  have  different  characters  peculiar  to  these  posi- 
tions, and  which  are  of  considerable  importance  in  a  clinical  sense. 

The  first  class  is,  in  a  large  majority  of  patients  presenting  themselves 
for  dental  operations,  the  earliest  to  make  its  appearance.  It  occurs  in 
the  pits  and  grooves  in  the  enamel  wherever  found — in  the  molars,  in 
the  corrugations  of  the  grinding  surface,  and  in  the  groove  or  pit  which 
is  often  present  in  the  buccal  surface ;  in  the  bicuspids,  in  the  groove  in 
the  grinding  surface  or  pits  that  often  occur  at  either  end  of  this  groove ; 
in  the  upper  incisors,  in  a  pit  or  groove  often  present  in  the  lingual  sur- 
face ;  in  any  pits,  grooves,  or  imperfections  resulting  from  faulty  forma- 
tions or  arrest  of  development  in  any  position  in  the  surface  oif  any  of 
the  teeth. 

The  occurrence  of  this  class  of  decays  is  dependent  principally  on  the 
opportunity  ^iven  for  fermentation  at  these  points  by  the  depth  of  the 
pits  and  grooves  in  the  several  teeth.  This  is  modified  by  the  individ- 
ual predisposition  to  caries.  In  the  child  this  latter  may  be  inferred 
after  having  learned  the  condition  of  the  teeth  of  the  parents.    If  caries 


780  DENTAL  CARIES. 

begins  early  in  these  positions,,  it  may  or  may  not  be  marked  by  a  dark 
color  of  the  pit  or  groove.  If,  however,  a  beginning  is  delayed  for  from 
five  to  ten  years  after  the  eruption  of  the  tooth,  a  dark  color  is  usually 
present.  The  enamel  in  this  position  is  very  thick  and  heavy,  and  the 
pit  or  groove  often  penetrates  it  more  or  less  completely  ;  so  that  caries 
apparently  does  not  begin  on  the  outside,  but  in  the  depths,  of  the  pit, 
from  which  it  spreads  under  the  strong  enamel  to  a  considerable  extent, 
and  often  penetrates  the  dentine  deeply  before  giving  any  sign,  especially 
in  children  where  the  dark  color  is  not  present  as  a  warning.  This  is 
often  shown  by  an  ashy-gray  color  seen  through  the  enamel.  In  older 
patients  this  color  is  more  generally  dark. 

This  type  of  caries  often  appears  very  soon  after  the  eruption  of  the 
tooth  ;  the  first  to  appear  in  the  permanent  teeth  are  usually  in  the  first 
molars.  These  cavities  occur  in  about  25  per  cent,  of  first  molars,  or 
an  average  of  one  to  every  patient  m^io  applies  for  dental  operations. 

(My  charts,  which  are  presented  on  pp.  782-785,  are  constructed  from 
my  records  of  fillings,  and  teeth  extracted  are  not  taken  into  account. 
This  in  some  degree  vitiates  the  result.  First  molars  are  extracted  in 
larger  proportions  than  other  teeth ;  therefore  the  numbers  given  in  the 
text  are  probably  too  low.) 

In  the  main,  there  is  a  considerable  degree  of  correspondence  as  to 
time  in  the  beginnings  of  caries  in  the  pits  of  the  several  teeth,  pro- 
vided these  pits  are  about  equal  in  depth  and  form  ;  so  that  in  the  reten- 
tion of  foreign  matter  they  will  be  about  equal.  For  instance,  if  decay 
0(!curs  in  the  first  molar  at  eight  years,  or  two  years  after  its  eruption, 
decay  may  be  expected  in  the  pits  of  the  second  molar  about  fourteen, 
the  corresponding  period  in  the  age  of  the  tooth  or  time  after  its  erup- 
tion. It  will  be  seen  that  if  the  conditions  are  the  same  the  same  time 
will  be  required  to  produce  a  cavity,  and  observation  shows  that  in  the 
majority  of  cases  this  is  true  clinically.  The  second  molars,  however, 
show  only  about  15  per  cent,  of  decays  in  the  pits,  or  only  a  little  more 
than  half  as  many  as  the  first  molars.  This  is  probably  due  to  the  fact 
that  the  pits  are  generally  not  so  deep.  This  is  also  true  of  the  bicus- 
pids and  incisors  ;  and  in  these  teeth  (the  pits  are  very  often  absent)  the 
decays  are  much  fewer  in  number.  The  time  of  their  occurrence'  may 
generally  be  reckoned  by  the  rule  given  above ;  but  it  will  be  noted 
that  in  those  teeth  in  which  decay  is  more  rare  the  age  at  which  it 
occurs  is  somewhat  greater.  This,  however,  is  probably  not  true  of  the 
pits  of  the  incisors.  These  occur  only  in  a  small  proportion  of  cases ; 
but  if  very  pronounced,  they  decay  at  about  the  same  time  as,  or  a  little 
later  than,  those  in  the  first  molars.  The  wisdom  teeth  often  decay 
much  sooner  after  their  eruption  than  the  other  teeth.  This  is  ex- 
plained by  the  fact  that  there  is  often  a  long  period  of  irritation  of  the 
tissues  by  which  they  are  surrounded  during  their  eruption,  and  that 
they  arc  injured  by  absorptive  jirocesses  or  by  acid  nmcus.  If  they 
escape  this — that  is,  if  they  come  through  the  gum  readily — they  decay 
relatively  later  than  any  other  teeth.  The  reasons  for  tlys  will  appear 
subsequently. 

The  second  class,  or  proximal  decays,  in  cases  in  which  the  predisposi- 
tion is  marked,  are  as  a  general  rule  a  year  or  two  later  in  their  appear- 


CLINICAL  HISTORY  OF  CARIES.  781 

ance  than  the  first  class,  and  also  follow  pretty  closely  the  order  of  the 
eruption  of  the  teeth.  But  if  in  the  individual  case  the  predisposition 
to  caries  is  but  slight,  they  will  usually  be  several  years  later  in  their 
appearance.  In  this  class  there  is  often  an  exception  in  the  mesial  sur- 
faces of  the  first  molars,  which  frequently  very  soon  after  their  erup- 
tion are  infected  from  a  close  contact  with  a  carious  surface  on  the 
second  milk  molar.  The  importanbe  of  this  class  of  carious  cavities  is 
evident  from  the  fact  that  they  outnumber  all  others  combined  in  the 
ratio  of  about  3.38  to  1.  (This  is  the  result  given  in  Charts  Nos.  1  and 
2.  In  these  it  is  probable  that  the  number  of  cavities  indicated  in  the 
proximal  surfaces  of  the  bicuspids  is  too  large,  on  account  of  the  number 
of  adults  who  require  refilling  of  these  cavities.  Refillings  in  cavities 
previously  filled  by  myself  have  been  carefully  eliminated,  but  cavities 
previously  filled  by  others  have  not  been  designated  in  my  records.) 

Occurring  on  smooth  surfaces  of  the  teeth,  where  the  enamel  is  gener- 
ally fairly  good  and  free  from  pits,  they  are  somewhat  slower  in  their 
beginnings  than  those  of  the  first  class,  probably  because  the  penetration 
of  this  enamel  is  more  difficult.  But  the  position  oifers  the  best  advan- 
tages for  lodgments  and  fermentation,  and  the  conditions  for  this  are 
more  constantly  present  than  in  any  of  the  other  positions  in  which 
caries  has  its  beginnings.  In  some  examinations  of  the  skulls  of  the 
older  Indian  races  made  a  few  years  ago  I  found  that  they  presented  a 
very  much  larger  proportion,  comparatively,  of  this  class  of  caries  than 
our  own  people.  Where  the  predisposition  to  caries  is  less,  this  class 
will  be  found  in  greater  relative  proportion,  and  the  cavities  will  appear 
later  in  life.  The  ratio  in  which  they  occur  on  the  individual  surfaces 
of  the  several  teeth  is  displayed  in  the  charts. 

The  beginnings  of  this  class  of  cavities  are  very  much  hidden.  The 
special  point  at  which  a  great  majority  of  them  occur  is  just  above 
(toward  the  root  of  the  tooth)  the  point  of  contact  of  the  teeth,  where 
the  cavity  cannot  be  seen.  If  observed  closely  at  the  right  time,  a  very 
minute  opening,  or  it  may  be  several  openings  not  far  apart,  will  be 
found,  the  enamel  about  these  being  softened  through  the  greater  part 
of  its  thickness,  and  generally  injured  for  a  space  on  either  side.  There- 
fore, in  preparing  small  proximal  cavities  for  filling,  very  wide  cutting 
is  required  to  remove  all  of  this  injured  enamel.  Very  often — gener- 
ally, I  may  say,  unless  revealed  by  a  delicate  exploring  instrument — 
the  first  discoverable  trace  of  these  cavities  is  a  discoloration  which 
shows  through  the  enamel  of  the  crown.  In  young  persons  this  has 
usually  an  ashy  opacity,  but  in  older  persons  it  is  likely  to  be  dark. 
When  this  appears,  caries  has  made  considerable  progress  in  the  dentine. 
It  is  not  very  unusual  for  the  pulp  to  become  exposed  before  the  ])atient 
is  aware  of  the  existence  of  a  cavity,  the  evidence  of  which,  in  molars 
and  bicuspids,  is  often  first  made  known  to  the  patient  by  the  sudden 
breaking  down  of  the  undermined  enamel  of  the  crown,  toothache  fre- 
quently following,  from  compression  of  the  exposed  pulp.  Of  the  four 
classes  of  caries  this  is  by  far  the  most  destructive. 

The  third  class:  comprises  but  comparatively  few  cases.  These  are, 
for  the  most  part,  seen  on  the  labial  surface  of  the  incisors  and  buccal 
surfaces  of  the  bicuspids  and  molars.     (This  and  the  fourth  class  are 


782 


DENTAL   CARIES. 


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DESCRIPTION   OP   CHARTS. 

These  charts  represent  the  iiuiiilter  of  curious  cavities  observed  in  one.  hundred  persona,  and  the  posi- 
tion of  these  cavities  on  the  individual  surfaces  of  the  teeth.  There  are  five  cohimns  of  squares 
devoted  to  each  tooth  of  one  side  of  the  mouth,  representing  the  five  surfaces  as  shown  on  the  left 
hand.  The  number  of  cavities  in  the  surface  represented  is  shown  by  the  number  of  squares  dark- 
ened, so  tliat  the  effect  of  the  diagram  as  a  whole  gives  a  striking  picture  of  the  frequency  of  decay 
in  the  individual  surfaces  of  the  several  teeth.  On  the  right  the  percentage  or  the  number  per  hun- 
dred persons,  is  given  in  figures  calculated  to  the  first  decimal  point.  On  the  left  th(»  percentage  of 
cavities  in  the  individual  teeth  for  all  surfaces  is  given  iu  the  same  way.    The  cavities  occurring  on 


CLINICAL  HISTORY  OF  CARIES. 


783 


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one  side  of  the  mouth  only  are  represented.  And  only  one  decay  in  an  individual  surface  is  counted ; 
that  IS,  It  two  or  more  pits  are  found  decayed  in  the  srinding  surface  of  a  molar,  but  one  is  counted ; 
and  the  same  rule  is  followed  with  all  of  the  other  surfaces. 

Charts  No.  1  and  2  (upper  and  lower  jmwi  are  made  up  from  my  records  of  fillings  for  Gl'S  persons  of 
all  ages,  and  therefore  represent  what  is  seen  in  practice  rather  than  the  actual  number  that  may 
occur.  ■' 

('harts  No.  3  and  4  (upper  and  lower  jaw)  are  made  from  100  of  my  own  patients  between  the  ages 
ot  ten  and  twenty-five  years,  for  whom  I  have  filled  a'l  cavities  Hnd  know  the  condition  at  present 
I  hey  represent  the  actual  number  of  cases  in  which  the  individual  surfaces  have  decayed  in  these 
lUO  persons. 


784 


DENTAL   CARIES. 


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CLINICAL   HISTORY   OF  CARIES. 


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, 

^ 

Vol.  I.— 50 


786  DENTAL   CARIES. 

not  distinguished  on  the  charts,  being  mixed  with  others  that  appear  on 
the  same  surfaces.)  In  the  incisors  their  beginning  is  usually  marked 
by  the  dark  color  of  the  enamel  near  the  gum.  This  face  of  the  tooth 
is  habitually  gummed  over  with  half-dried  mucus  and  debris,  thus  giv- 
ing opportnniti/  for  fermentation  and  caries.  Inquiry  will  generally  dis- 
close the  fact  that  the  person  habitually  sleeps  with  the  mouth  open, 
this  often  being  traceable  to  some  obstruction  in  the  nasal  passages. 
These  cavities  occur  chiefly  in  persons  under  eighteen  years  of  age, 
and  not  uufrequently  before  the  twelfth  year.  In  the  bicuspids  and 
molars  this  form  of  decay  also  occurs,  and  apparently  from  habitual 
uncleanliness,  which,  however,  does  not  seem  to  be  traceable  to  the 
same  causes. 

The  fourth  clas-s  is  always  accompanied  by  a  diseased  condition  of 
the  gums.  They  have  their  beginnings  very  close  to  the  margin  of  the 
gum,  or  even  beneath  it,  just  at  the  junction  of  the  enamel  and  cement. 
The  gum,  however,  is  usually  everted  or  shrunken  from  the  neck  of  the 
tooth  before  caries  proper  is  demonstrable.  The  manner  of  the  begin- 
ning of  these  cavities  has  been  described  in  the  consideration  of  acid 
mucus  and  absorptions  in  their  relations  to  caries.  They  do  not  often 
occur  in  children,  but  are  generally  seen  in  middle  life  or  old  age.  In- 
deed, this  form  of  caries  may  almost  be  said  to  be  the  only  tyjie  that 
attacks  elderly  persons.  Occasionally  it  wrecks  a  denture  after  danger 
from  the  other  classes  of  caries  has  long  since  passed. 

The  characterisfk'S  presented  by  caries  of  the  teeth  in  individual  cases 
are  of  great  importance  in  the  clinical  sense.  The  rule  is  that  if,  after 
beginning  in  a  tooth,  the  caries  advances  rapidly,  it  will  do  so  in  all 
other  cases  occurring  in  that  individual.  If  it  is  seen  to  proceed  slowly 
in  the  teeth  first  attacked,  its  progress  will  be  slow  in  those  that  are 
attacked  later.  This  may  be  denominated  a  characteristic  observed  in 
individual  cases.  It  must  be  noted,  however,  that  the  number  of 
beginnings  of  caries  hold  but  little  correspondence  to  the  progress  after 
a  beginning  has  been  made.  In  some  cases  decay  commences  early  in 
a  few  teeth  only,  and  they  are  very  quickly  destroyed  ;  in  other  cases 
the  individual  teeth  are  attacked  at  intervals  of  considerable  duration, 
and  in  each  case  are  quickly  destroyed.  It  is  not  uncommon  in  the 
examination  of  cases  in  ^\hich  there  have  been  no  dental  operations  to 
find  that  several  teeth  have  been  destroyed  by  caries,  while  all  the 
others  have  entirely  escaped,  or  that  in  a  very  few  others  decay  has 
begun  and  is  running  the  same  rapid  course.  In  another  series  of  indi- 
viduals an  opposite  condition  will  be  found.  Several  carious  cavities 
may  have  formed,  while  very  few  of  them  have  progressed  so  far  as  to 
do  serious  injury,  continued  observation  showing  that  they  are  still 
making  compai-atively  slow  progress.  In  other  cases  verv  few  cavities 
will  be  found,  these  few  remaining  almost  stationary. 

Thus  it  will  be  seen  that  caries  in  individual  cases  presents  special 
characteristics  in  reference  to  the  liability  to  the  beginning  of  decay,  and 
also  as  to  the  progress  of  that  decay  after  the  beginning  has  been  made. 
As  these  characteristics  are  combined  in  each  individual  case,  thev  may 
be  fornndated  as  follows  : 

First  Characteristic :  Many  decays  start  and  progress  rapidly. 


CLINICAL  HISTORY  OF  CARIES.  787 

Second  Characteristic:  A  few  decays  start  and  progress  rapidly. 

Third  Characteristic :  Many  decays  start  and  progress  slowly. 

Fourth  Characteristic:  A  few  decays  start  and  progress  slowly. 

These  characteristics  seem  to  be  dependent  on  two  conditions  and 
tlieir  opposites — namely,  the  activity  of  the  cause  of  caries  in  the  indi- 
vidual case,  and  the  opportunity  presented  for  attack  by  the  condition 
of  the  surfaces  of  the  individual  teeth.  If  the  cause  of  caries  be  active, 
if  the  condition  of  the  fluids  of  the  mouth  be  such  as  to  favor  it,  caries 
that  has  gained  a  start  will  progress  rapidly  to  the  destruction  of  the 
tooth.  After  the  causative  agent  is  once  implanted  in  the  dentine, 
the  circumstances  giving  or  withholding  opportunitt/  no  longer  affect 
its  progress.  This  progress  may  be  modiHed  by  one  of  two  influ- 
ences or  by  both — namely,  by  the  condition  of  the  fluids  penetrating 
the  cavity,  and  by  the  condition  of  the  tissue  being  destroyed.  The 
latter  modifying  influence  occurs  only  in  individual  cases  in  which  the 
dentine- is  of  faulty  formation,  which  abnormality  has  been  sufficiently 
described  in  connection  with  the  phenomena  of  caries.  The  princijjal 
condition  modifying  the  general  rate  of  progress  of  caries  is  the  state  of 
the  fluids  entering  the  cavity.  It  will  be  seen,  from  the  studies  con- 
tained in  the  preceding  pages,  that  the  food-material  upon  which  the 
fungus  must  depend  for  its  acid-producing  power,  and  without  which 
caries  cannot  progress,  is  not  found  within  the  dentine,  but  must  be 
absorbed  from  without.  This  circumstance  is  of  much  importance  in 
this  connection — not  from  the  probability  that  this  food-material  is 
likely  to  be  scarce  in  ^he  buccal  fluids,  but  as  showing  the  dependence 
of  the  active  agents  in  the  production  of  caries  upon  the  fluids  external 
to  the  cavity. 

The  beginnings  of  caries  are  dependent  largely  on  those  predisposing 
causes  that  give  opportunity.  Without  the  presence  and  activity  of  the 
cause  there  can  be  no  caries ;  and  the  degree  of  that  activity  will  tend 
to  modify  the  nCimber  of  cavities,  because  a  certain  degree  of  action  will 
be  sufficient  to  make  a  breach  under  conditions  in  which  a  less  degree 
of  activity  would  fail.  This  is  not  the  principal  circumstance  modify- 
ing the  beginnings  of  caries ;  for  if  it  were,  we  would  not  see  those 
cases  in  which  one  or  two  teeth  have  been  quickly  destroyed,  while 
the  others  have  escaped  altogether.  The  principal  circumstances  giving 
opportunity  for  the  beginnings  of  caries  are  unfavorable  forms  of  the 
teeth  and  habits  of  uncleanliness.  This  is  illustrated  by  the  tendency 
of  carious  cavities  to  occur  in  pairs  on  certain  surfaces  of  similar  teeth 
on  opposite  sides  of  the  mouth,  where  the  form  is  presumably  the  same. 
The  predisposing  conditions  due  to  faults  of  form  giving  opportunity 
for  the  beginnings  of  caries  have,  however,  been  sufficiently  discussed 
on  a  previous  page,  to  which  the  reader  is  referred. 

These  characteristics  are  seen  in  every  possible  degree  of  intermixture 
and  affect  all  classes  of  caries.  I  have  seen  some  cases  in  M'hich  the 
teeth  seemed  to  have  been  attacked  in  every  possible  position,  and  rap- 
idly destroyed,  very  soon  after  emerging  from  the  gum.  In  tliese  cases 
the  condition  of  the  fluids  of  the  mouth  is  certainly  such  as  to  favor 
that  process  of  fermentation  which  is  the  basis  of  caries,  and  the  forms 
of  the  teetli  are  of  a  kind  to  favor  the  beginnings  at  numerous  points.    It 


788  DENTAL   CARIES. 

is  doubtful,  however,  if  any  formation  or  structure  of  the_  teeth,  be  they 
ever  so  perfect,  could  withstand  the  conditions  present  in  such  cases. 
The  activity  of  the  processes  calculated  to  decompose  them  is  so  ener- 
getic that  the  strongest  teeth  would  be  destroyed  in  a  short  time.  The 
Avorst  cases  I  have  seen  were  those  of  two  Swedish  girls,  twin-sisters,  • 
eighteen  years  old,  who  came  to  me  for  advice  a  few  years  ago.  In 
these  most  of  the  teeth,  including  the  lower  incisors,  which  are  so 
generally  exempt  from  caries,  were  already  decayed  to  the  gums,  and 
those  that  still  retained  a  portion  of  the  crown  were  attacked  at  from 
one  to  four  points.  Fortunately,  such  cases  are  rare.  With  this  as  the 
worst  representative  of  the  beginnings  and  the  destructiveness  of  caries, 
we  might  give  cases  illustrating  all  forms  of  gradation,  doM-n  to  a  case 
in  which  an  individual  tooth  shows  a  dark  spot  indicating  that  at  some 
time  in  the  past  the  i)roducts  of  fermentation  had  injured  the  enamel.' 

Cay'ien  of  the  tedh  u  easentialhi  a  dhease  of  i/ovtJi  (compare  charts). 
This  is  especially  the  case  with  the  first  and  second  classes  of  caries, 
which  comprise  the  great  mass  of  cases.  It  is  a  notable  fact  that  the 
predisposition  to  caries  diminishes  as  age  advances.  It  is  usually 
strongest  in  childhood  or  youth,  and  the  greater  number  of  cavities 
have  begun  at  the  age  t)f  eighteen.  Very  nearly  all  of  the  first  and 
.second  classes  have  begun  before  the  age  of  twenty-five.  Perhaps 
there  is  more  than  one  reason  for  this.  If  we  suppose  that  the  dis- 
position to  caries  remains  the  same,  it  is  presumable  that  at  the  age  of 
twenty-five  years  all  points  favorable  to  the  beginnings  of  decay  have 
been  attacked.  All  except  the  wisdom  teeth  have  for  a  dozen  years  or 
more  been  exposed  to  the  agents  productive  of  caries;  and  if  beginnings 
have  not  been  made  within  this  time,  it  is  presumable  that  they  Avill  not 
be  made  unless  there  is  some  change  in  the  conditions.  This  is  prob- 
ably the  ])rincipal  condition  of  tlie  cessation  of  the  beginning  of  new 

^  Some  years  ago  I  proposed  the  terms  vIk  inita  (beginning  ))ower),  from  ris,  power, 
force,  and  ineo,  to  begin;  and  vi-t  delela  (destroying  power),  from  delco,  to  blot  out,  to 
destroy,  to  represent  these  cliaracteristics.  These  terms  may  readily  be  used  for  the 
purpose  of  expressing  the  conditions  in  any  given  case,  and  for  this  purpose  I  asso- 
ciate with  them  numbers  to  show  the  degree  of  the  special  characteristic.  The  follow- 
ing gives  the  extremes  of  the  possible  combinations  : 

Vis  inita  1,  combined  with  vis  deleta  1  to  100. 

Vis  deleta  1,  combined  with  vis  inita  1  to  100. 

These  may  be  used  in  the  description  of  cases  for  the  purpose  of  the  more  ready  and 
accurate  representation  of  the  facts  that  may  exist  or  of  the  conditions  observed,  without 
reference  to  the  causes  which  may  be  supposed  to  underlie  these  effects.  For  instance, 
in  describing  the  conditions  found  in  case  of  the  two  Swedi.sh  girls  spoken  of  in  the  text, 
I  should  say  there  was  present  vis  inita  100  and  vis  deleta  100.  Tliis  exjjresses  my 
conception  of  caries  of  the  worst  characteristics  or  tlie  most  violent  i'orm  in  which  it 
is  manifested.  In  a  case  in  which  a  medium  number  of  decays  made  their  appear- 
ance, and  each  of  these  was  running  a  very  rapid  course  to  the  destruction  of  the  teeth 
attacked,  I  would  represent  it  as  vis  inita  50,  vis  deleta  100.  In  another  case,  in  which 
a  medium  numljcr  of  Iteginnings  of  decay  was  apparent,  and  these  presented  rather  a 
dark  color  and  showed  other  characteristics  indicating  that  the  progress  was  rather 
slow  and  yet  decided,  I  would  state  it  as  vis  inita  50,  vis  deleta  25.  In  this  way  all 
gradations  of  tlie  duiracterislics  of  caries  as  manifested  in  the  individual  case  may 
l)e  readily  presented  without  imnecessary  circumlocution.  The  use  of  tliis  plan  is 
also  of  great  advantage  in  teaching. 

In  this  use  the  term  v/.s  inita  represents  the  actual  exercise  of  the  opportunities  pre- 
sented for  the  beginnings  of  caries  in  the  individual  case,  and  vis  deleta  the  activity 
of  the  progress  after  the  beginnings  are  made.  The  terms  themselves  are  purely 
arbitrary. 


CLINICAL   HISTORY  OF  CARIES.  789 

cavities.  There  is  much  reason,  however,  to  believe  that  the  environ- 
ment of  the  causative  agent  becomes  with  advancing  age  less  favorable 
to  progress.  The  first  of  the  permanent  teeth  to  take  their  places  in 
the  arch  are  those  most  frequently  affected  by  caries  (see  charts).  Caries 
already  begun  advances  less  rapidly  in  older  persons,  and  in  some  cases 
cavities  cease  to  progress.  The  cases  of  general  spontaneous  cessation 
of  progress  in  carious  cavities  are  few,  no  matter  what  the  age,  yet  a 
number  of  such  cases  have  occurred  under  my  observation.  The  dis- 
position to  caries  is  not  steady,  however,  but  presents  fluctuations  more 
or  less  marked.  These  are  sometimes  seen  following  an  illness.  In 
women  it  is  often  noted  in  pregnancy,  especially  in  first  and  second  preg- 
nancies. Other  conditions  have  from  time  to  time  been  noted  which 
seemed  temporarily  to  dispose  the  individual  to  an  exacerbation  of  the 
tendency  to  caries.  Yet  in  the  great  majority  of  cases  this  disposition 
is  gradually  diminished  with  increasing  age  to  such  an  extent  that  if 
the  cavities  are  well  treated  but  few  decays  will  begin  after  the  patient 
is  thirty  or  thirty-five  years  old,  and  the  beginning  of  these  will  gener- 
ally be  found  to  depend  upon  some  change  in  the  conditions  giving 
opportunity. 

This  leads  to  the  consideration  of  the  infectious  nature  of  caries, 
which  is  best  shown  by  the  results  of  treatment  in  cases  which  mani- 
fest a  strong  predisposition  to  the  disease.  Many  times  I  have 
undertaken  cases  in  which  there  seemed  to  be  but  little  hope  of 
success ;  yet  I  have  found  that  if  caries  could  be  eradicated  from  the 
mouth,  and  its  exclusion  maintained  for  a  time,  the  tendency  to  the 
disease  rapidly  diminished,  and  to  such  an  extent  as  to  make  its  con- 
trol a  matter  of  but  little  difficulty.  Infection  is  always  a  strong 
element  in  the  beginning  of  caries.  I  have  had,  in  numbers  of  cases, 
opportunity  to  study  this  feature  in  the  children  of  the  same  family, 
where  some  would  be  careless  and  others  fairly  careful  in  attendance  for 
operations.  Those  who  were  careless,  and  in  this  way  allowed  the  con- 
tinuance of  the  conditions  favoring  infection — namel}",  a  number  of 
cavities  continuing  in  progress  and  adding  to  the  amount  of  the  fungus 
growing  in  the  mouth — have  almost  uniformly  had  much  the  larger 
number  of  cavities  at  the  age  of  twenty  or  twenty-five.  It  is  doubtful 
if  this  fungus  grows  well  in  the  mouth  where  it  is  fully  exposed  to  the 
saliva.  Partial  seclusion  seems  more  favorable  to  it.  Certainly  it  does 
not  produce  results  unless  it  is  fairly  well  secluded  and  sheltered  from 
the  fluids  of  the  mouth.  Possibly,  as  already  explained,  this  may  be 
due  to  the  washing  away  of  its  products. 

In  a  considerable  number  of  cases  there  is  a  spontaneous  cessation 
of  caries  in  cavities  that  have  made  considerable  progress.  This  is,  in 
most  instances,  connected  with  some  change  in  the  form  of  the  cavity, 
usually  the  breakage  of  one  or  more  of  its  walls  in  such  a  manner  as 
to  give  to  all  of  its  parts  free  access  of  the  fluids  of  the  mouth.  This, 
if  the  individual  is  approaching  middle  life  and  the  predisposition  to 
caries  has  not  been  very  considerable,  will  be  sufficient  to  stop  the  prog- 
ress of  the  decay.  In  case  the  predisposition  to  caries  is  strong,  it  is 
necessary  that  the  whole  surface  decayed  be  exposed  to  the  friction  of 
mastication  to  bring  about  a  cessation  of  the  decay.     In  this  case  the 


790  DENTAL  CARIES. 

^vhole  of  the  injured  tissue  will  become  intensely  black.  In  a  number 
of  instances  I  have  seen  the  spontaneous  cessation  of  a  considerable 
number  of  decays  under  conditions  that  showed  plainly  that  the  cause 
had  ceased  to  act.     The  fungus  was  dead. 

The  fourth  class  of  caries  is  occasionally  seen  to  become  very  trou- 
blesome after  the  other  classes  have  ceased  altogether.  It  is  the  class  of 
decay  that  is  most  likely  to  give  trouble  in  old  age.  Its  beginnings  are 
determined  almost  entirely  by  irritations  of  the  gingivae,  giving  rise  to 
absorptions  about  the  necks  of  the  teeth,  which,  becoming  exposed 
through  the  recession  of  the  gums,  become  the  seat  of  caries.  They  are 
usually  broad  cavities  that  are  shielded  partially  from  the  free  entrance 
of  the  fluids  of  the  mouth,  either  by  debris  or  by  adjoining  teeth  or  by 
an  overhanging  gum.  The  teeth  are  attacked  one  or  two  at  a  time, 
probably  at  considerable  intervals  or  very  irregularly  as  to  time. 
Occasionally  the  teeth  in  a  certain  part  of  the  mouth  may  be  attacked 
together.  Caries  of  this  character  is  sometimes  very  destructive — more 
for  the  reason  that  the  position  is  such  that  the  pulp  of  th(^  tooth 
is  exposed  with  but  little  destruction  of  tissue  than  on  account  of 
the  decay.  The  beginnings  are  usually  in  the  cementum  near  its 
junction  with  the  enamel,  and  in  the  molars,  especially,  the  pulp- 
canals  are  often  in  close  proximity.  Decays  very  much  resembling 
these  are  often  seen  in  younger  persons  who  wear  partial  plates  abut- 
ting against  the  remaining  teeth. 


APPENDIX. 


FERMENTATION  IN  THE  HUMAN  MOUTH: 

ITS  RELATION  TO  CARIES  OF  THE  TEETH. 

THE    INFLUENCE     OF     ANTISEPTICS,    FILLING    MATERIALS,    ETC., 
UPON  THE  FUNGI  OF  DENTAL  CAEIES. 

THE   FUNGI  OF  DENTAL  CAEIES;  THEIR   PURE  CULTIVATION  AND 
EFFECT  UPON   LOWER  ANIMALS. 

BIOLOGICAL  STUDIES  ON  THE  FUNGI  OF  THE  HUMAN  MOUTH. 

By  De.  W.  D.  miller,  Berlin,  Gebmany.  ^ 


During  the  last  two  years  I  have  stated  at  diiferent  times  and  places, 
as  the  result  of  many  experiments,  that  "  the  first  stage  of  dental  caries 
consists  in  a  decalcification  of  the  tissue  of  the  teeth  by  acids  which  are 
for  the  greater  part  generated  in  the  mouth  by  fermentation."  The 
object  of  the  investigations  described  in  this  and  the  following  papers  is 
to  determine  this  ferment  and  the  conditions  essential  to  its  action.  I 
shall  seek  in  wliat  follows  to  present  no  views  which  are  not  the  legiti- 
mate and  necessary  results  of  rigid  and  exact  experiment,  and  I  shall 
give  in  detail  a  description  of  each  series  of  experiments,  in  order  that 
every  one  may  have  an  opportunity  to  judge  of  the  accuracy  of  the 
work  and  the  justice  of  the  conclusions  drawn  from  it. 

It  is,  nevertheless,  with  some  hesitancy  that  I  venture  to  present 
before  the  dental  profession  the  results  of  my  last  six  months'  labor, 
having  learned  by  experience  the  almost  endless  number  of  agents 
which  combine  to  vitiate  such  a  series  of  experiments  as  that  wiiich 
I  am  about  to  offer,  and  the  exceeding  great  care  which  is  necessarv 
in  excluding  or  eliminating  all  irrelevant  factors.  If,  therefore,  I  have 
been  guilty  of  any  oversight  or  failed  to  take  all  possible  precautions  to 
guard  against  error,  I  hope  that  some  one  will  kindly  show  me  where 
I  have  gone  astray  and  put  me  in  the  right  course  again. 

The  larger  apparatus  necessary  for  these  experiments  are  : 

^Reprinted  from  the  Independent.  Practitioner,  February,  March,  and  May,  1884,  and 
May  and  June,  1885. 

791 


792 


DENTAL   C ABIES. 


Damp  Chamber :  n,  shallow  glass 
vessel  partially  filled  with  water; 
h,  glass  globe  lined  with  wet  bib- 
ulous paper ;  c,  metallic  >taiid  lor 
culture-tubes. 


1.  A  large  double-walled  incubator,  with  gas-regulator  for  maintain- 
ing any  desired  constant  temperature. 
Fig.  407.  2.  A  Koch  sterilizer. 

3.  A  damp  chamber.    (See  Fig.  407.) 

4.  A  drying-oven  for  sterilizing  instru- 
ments, glass  vessels,  etc.,  at  a  temperature 
of  150°  C. 

5.  A  good  microscope  with  either  water  or 
oil  immersion. 

It  is  not  necessary  to  mention  the  smaller 
instruments,  glass  vessels,  etc.,  etc.,  nor  the 
ai)paratus  necessary  for  making  a  chemical 
analysis  of  the  products  of  the  fermentation ; 
these  are  sufficiently  familiar  to  every  one. 
To  avoid  repetition,  I  will  say  here  that 
all  vessels  and  instruments  used  in  the  cul- 
ture experiments  were  purified  in  the  flame 
of  a  J^unsen  burner  when  practicable,  otherwise  by  exposing  for  fifteen 
minutes  in  the  drying-oven  to  a  temperature  of  150°  to  160°  C.  (302° 
to  320°  F.),  and  that  all  substances  used  as  culture  substrata  M^ere  ster- 
ilized four  times  by  exposure,  at  intervals  of  twelve  hours,  for  half  an 
hour,  to  steam  at  100°  C,  in  a  Koch  sterilizer.  Furthermore,  all  infec- 
tions from  carious  dentine  were  made  as  follows  :  The  cavity  of  a 
freshlv-extracted  carious  tooth  is  cleared  of  food  and  carefully  brushed 
over  with  a  pledget  of  cotton  dij^ped  in  carbolic  acid  (90  per  cent.). 
The  acid  is  then  thoroughly  absorbed  by  means  of  bibulous  paper,  and 
layer  after  layer  of  the  soft  dentine  removed  with  a  repeatedly  purified 
instrument  until  the  deeper  jiarts  are  reached ;  then  a  portion  of  the 
clean  soft  dentine  scarcely  as  large  as  a  pin-head  is  removed  and  quickly 
brought  into  or  upon  the  culture  medium. 

Infections  from  the  mouth  were  made  by  scratching  upon  the  surface 
of  the  mucous  membrane  of  the  cheek  or  the  margin  of  the  gum  with 
the  end  of  a  clean  platinum  wire,  and  then  dipping  it  into  the  culture 
medium.     The  materials  used  for  culture  were : 


Ao.  /.     Sterilized  saliva 50.0 

Sugar ' 1.0 

Starch 0.5 

No.  2.     Sterilized  milk. 


No.  3.     Decoction  of  malt 
Sugar     .... 


50.0 
1.0 


The  malt  decoction  is  made  by  boiling,  with  slight  evaporation,  20.0* 
dry  malt  with  120.0  water  for  ten  minutes,  and  filtering. 

No.  J/,.     Sterilized  saliva 50.0 

Water 50.0 

Starch 20.0 

Sugar 2.0 


FERMENTATION  IN  THE  HUMAN  MOUTH.  793 

The  starch  is  addetl  to  the  cold  sohition  of  water  and  saliva  and 
stirred  until  it  becomes  evenly  divided  throughout  the  solution  ;  it  is 
then  poured  into  shallow  glass  vessels  with  glass  covers  and  put  into 
the  sterilizer  for  complete  sterilization ;  it  there  congeals  and  forms  a 
solid  mass,  upon  the  surface  of  which  the  infections  may  be  made.  It 
possesses  all  the  advantages  of  gelatin,  with  one  great  additional  one, 
in  that  it  does  not  liquify  at  blood-temperature. 

No.  5.     Decoction  of  malt 100.0 

Sugar 2.0 

Starch 20.0 

Prepared  in  the  same  way  as  No.  4. 

No.  6.     Beef-extract 2.0 

Water 100.0 

No.  7.     Water 100.0 

Beef-extract 2.0 

Sugar 2.0 

No.  8.     Fresh-baked  potato  cut  into  slices  one-half  inch 
thick  with  a  clean  knife. 

Other  substances  were  used,  but  need  not  be  considered  here.  Ad- 
ditional sugar  is  not  absolutely  necessary  where  malt  is  used,  though 
I  have  so  far  obtained  better  results  by  adding  a  small  quantity.  The 
kind  of  sugar  is  immaterial,  provided  it  be  fermentable ;  even  cane- 
sugar,  though  not  directly  fermentable,  is  converted  into  a  fermentable 
variety  in  the  culture.  Where  small  quantities  of  any  culture  material 
were  used  the  cultures  were  kept  in  the  damp  chamber,  to  prevent  their 
drying  up  or  becoming  too  concentrated  by  evaporation.  All  cultures 
were  made  under  a  temperature  of  36°  to  38°  C. 

We  will  begin  with  the  fundamental  experiments. 

Exp.  1.  Fresh  saliva  is  mixed  with  sugar  or  starch,  1-40,  and  kept 
at  blood-temperature.  It  invariably  becomes  acid  in  four  to  five  hours. 
But  some  one,  no  doubt,  will,  say  that  this  is  a  result  of  no  consequence, 
because  the  experiment  was  not  made  within  the  oral  cavity ;  for  his 
personal  benefit  we  give  the  following : 

Exp.  '3.  A  glass  tube  2  cm.  long  and  3  mm.  wide  is  filled  with  starch, 
sterilized,  and  fastened  to  a  molar  tooth  in  the  mouth  on  soina;  to  bed : 
next  morning  the  contents  of  the  tube  will  have  a  strong  acid  reaction. 
A  cavity  in  a  tooth  or  a  piece  of  linen  which  may  be  saturated  ^vith  a 
solution  of  starch  will  answer  the  purpose  as  well  as  the  glass  tube. 
That  the  acid  is  the  same  in  each  case  will  be  further  established  below. 

Exp.  3.  The  mixture  of  saliva  with  starch  or  sugar  is  kept  for  a  half 
hour  in  the  sterilizer  at  100°  C,  and  then  placed  in  the  incubator ;  it 
does  not  become  sour  in  four,  nor  in  twenty-foiu^,  hours — in  fact,  not  at 
all.  We  conclude  that  the  ferment  is  rendered  inactive  by  a  tempera- 
ture of  100°  C. 

Exp.  4-  The   starch  is  heated  to  150°   C.   before  mixing  with  the 


794  DENTAL   CARIES. 

saliva ;  the  solution  still  becomes  sour.  Conclusion  :  The  ferment 
exists,  not  in  the  starch,  but  in  the  saliva. 

We  have  now  to  determine  the  question,  Is  it  an  organized  ferment 
(fungi),  or  is  it  an  unorganized  ferment  (ptyalin)? 

This  question  is  determined  by  the  following  experiments  : 

Exp.  5.  From  6  to  8  grams  of  saliva  are  agitated  in  a  test-tube  with 
as  much  suli)huric  ether  as  it  will  take  up,  starch  added,  and  the  whole 
put  in  the  incubator.  On  examination  after  a  few  hours  Ave  will  find 
sugar  in  the  solution,  but  no  acid  ;  in  other  words,  the  acid-forming 
ferment  has  been  rendered  inactive,  but  the  unorganized  sugar-forming 
ferment  not. 

Exp.  6.  Instead  of  ether,  enough  carbolic  acid  is  added  to  make  the 
solution  one-half  per  cent,  strong ;  the  result  is  the  same.  These  two 
experiments  show  that  the  ])tyalin  of  the  saliva  (which  was  not  injured 
by  the  presence  of  the  ether  or  the  carbolic  acid,  as  proved  by  the  fact 
that  it  retained  its  diastatic  action)  is  not  the  cause  of  the  acid  reaction. 

Exp.  7.  According  to  Paschutin,  ptyalin  is  devitalized  by  exposure 
twenty  minutes  to  a  temperature  of  67°  C  Organized  ferments  could 
not  be  killed  by  the  same  means.  We  accordingly  subject  a  mixture  of 
saliva  and  grape-sugar  to  the  given  temperature  for  twenty  minutes. 
We  thereby  destroy  the  ptyalin ;  the  mixture,  nevertheless,  becomes 
sour  if  allowed  to  stand  in  the  incubator  for  twenty  hours.  This 
experiment  confirms  the  result  of  experiments  5  and  6,  and  we  begin 
to  suspect  that  we  have  to  deal  with  an  organized  ferment.  This  sup- 
position is  confirmed  by  the  following  experiment. 

Exp.  8.  Six  to  eight  drops  of  a  j)erfectly  sterilized  solution  of  sugar  in 
saliva  (1-40)  in  a  miniature  test-tube  with  cotton  cork  are  infected  from 
the  mouth  or  with  carious  dentine,  as  described  above ;  in  twenty-four 
hours  the  solution  will  be  acid.  With  a  fraction  of  a  drop  of  this  solu- 
tion a  second  tube  is  infected  ;  it  will  likewise  become  acid.  From  this 
a  third,  etc.,  etc. ;  each  becomes  acid  in  turn,  while  the  control  tube 
(containing  the  same  solution  not  infected)  remains  neutral. 

The  conclusion  is  plain  that  we  have  to  do  with  a  ferment  M'hich  is 
capable  of  reproducing  itself;  in  other  words,  an  organized  ferment. 
It  therefore  becomes  evident  that  not  only  free  in  the  mouth,  but  in  the 
deeper  parts  of  carious  dentine,  we  have  a  fungus  which  is  capable  of 
producing  an  acid  reaction  in  characteristic  substrata. 

Exp.  9.  Each  of  thirty  small  tubes  was  furnished  with  eight  drops 
of  solution  No.  1,  and  each  of  thirty  other  tubes  with  as  many  drops 
of  solution  No.  3,  and  all  were  sterilized.  Twenty-four  were  then 
infected  from  the  mouth,  twenty-four  with  carious  dentine,  and 
twelve  were  left  as  controls.  In  twenty-four  hours  all  forty-eight 
of  the  infected  solutions  were  acid,  while  the  twelve  controls  remained 
neutral. 

Exp.  10.  Make  a  solution  of  40.0  of  saliva  and  1.0  of  starch;  ])ut 
equal  portions  in  two  fiasks,  a  and  b,  and  cover  the  surface  of  the  solu- 
tion in  a  with  a  layer  of  pure  oil,  to  prevent  the  free  access  of  air ;  or, 

Exp.  11.  Place  flask  a  in  an  air-tight  bottle  containing  a  fresh  alka- 
line solution  of  pyrogallic  acid  (which  abstracts  the  oxygen  from  the 
air) ;  or, 


FERMENTATION  IN  THE  HUMAN  MOUTH.  795 

Exp.  1'2.  Exhaust  flask  a  by  means  of  the  air-pump,  so  as  to  produce 
a  tolerably  complete  vacuum.  The  quantity  of  acitl  produced  in  a  will 
be,  (jn  an  average,  the  same  as  that  produced  in  h. 

We  conclude  from  experiments  8,  9,  and  10  that  the  fungus  in  ques- 
tion is  independent  of  the  free  access  of  air  or  oxygen  for  its  develop- 
ment and  characteristic  action — a  conclusion  Avhich  would  exclude  the 
fungus  of  vinegar  {^Mycoderma  aeeti),  and  which  is  of  the  utmost  prac- 
tical importance,  since  it  signifies  that  this  fungus  can  develop  and  per- 
form its  work  deep  in  the  dentinal  tubules  or  under  fillings,  provided 
the  necessary  materials  are  furnished  it. 

Kvp.  IS.  Place  a  piece  of  carious  dentine  upon  the  surface  of  the 
culture  material  described  in  number  4,  5,  or  6  ;  in  twelve  hours  the 
dentine  will  be  surrounded  by  a  white  ring  from  4  to  8  mm.  in  diam- 
eter ;  the  material  within  this  ring  will  be  partially  liquefied  and  have 
an  acid  reaction.  The  same  result  follows  when  the  infection  is  made 
from  the  mouth. 

Exp.  14-.  Produce  10.0  of  saliva  by  chewing  a  sterilized  quill  tooth- 
pick, add  0.5  starch  or  sugar,  and  place  in  the  incubator.  Then  give 
the  oral  cavity  a  most  thorough  cleansing  with  pure  water,  using  tooth- 
pick, brush,  and  floss,  the  object  being  to  free  the  mouth  from  micro- 
organisms as  completely  as  possible.  Then  produce  again  10.0  saliva, 
add  0.5  starch  or  sugar,  and  put  in  the  incubator ;  the  amount  of  acid 
produced  in  a  given  time  will  in  the  latter  case  be  often  as  low  as  one- 
fourth  of  that  in  the  former.  Conclusion  :  By  thoroughly  cleansing  the 
mouth  we  no  doubt  remove  the  greater  portion  of  the  fungi ;  hence  the 
small  amount  of  acid  produced.  By  using  strong  antiseptics  or  by  repeat- 
edly filtering  the  saliva  we  may  reduce  the  amount  of  acid  produced  in 
twenty-four  hours  almost  to  0.  An  experiment  yet  to  be  made  is  to  take 
the  saliva  direct  from  the  gland  before  it  becomes  infected  with  the  organ- 
isms of  the  mouth ;  it  should  not  then  become  sour  when  mixed  with  starch 
and  allowed  to  stand  at  blood-temperature.  In  every  case  a  careful 
microscopic  examination  of  the  cultures  was  made,  revealing  the  constant 
presence  of  a  fungus,  chiefly  in  the 

form  of  diplococci,  either  single  or  V^^-  408. 

in  chains,  less  often  in  the  form  of  /'  - 

bacteria,    bacilli,    or    even    threads.  ■^  ,/  /  /  / 

(See  Fig.  408.)    Sometimes  all  these  j^'^^'^ry^    '    / 

forms  are  found  on  a  single  thread,  ^^    •*•*    ^     J    / 

thus  proving  what  I  have  already  /  ^^  y     !       ^ 

demonstrated  for  Leptothrix  bvccaUs  /   I      ^     i     J         \ 

and  Leptothrix  c/igantea  (Miller),  the        '  ^*^    ^        j*****  ' 

genetic  connection  of  these  different         /  g^   i   /^' 

forms.   The  particular  form  in  which     /  ^      ••*8       **tJ^L 

the  fungus  occurs  depends  somewhat  •    ^     S    <^9r^ 

upon  the  culture  medium,  as  well  as  \      ^  "^  J'^  t  ^ 

u])on   the  age  of  the  culture.     By  ••••  |  J^ 

using  a  glass  tube  as  culture  vessel 

we   may   demonstrate  that,  whether    '-""^ '^^  ^''l^U^TuJ^i^^.^^""^ '"''^' 
the  culture  is  made  in  the  mouth  or 
out  of  it,  under  similar  conditions  the  fungus  is  the  same.     The  fungus 


796  DENTAL   CARIES. 

is  not  capable  of  producing  an  acid  reaction  of  all  substances  in  which 
it  may  vegetate.  A  luxuriant  growth  may  be  obtained  in  beef-extract, 
but  no  acid  is  produced  unless  sugar  is  present.  It  is  only  from  carbo- 
hydrates (especially  sugar)  that  it  appears  to  be  able  to  produce  acid  in 
any  considerable  quantity  or  at  all.  This  question,  however,  as  well  as 
the  morphology,  physiology,  development,  and  life-conditions  of  the 
fungus,  will  receive  subsequent  consideration. 

We  have,  then,  a  micro-organism  which  agrees  morphologically  with 
the  Bacterium  acidi  laciici,  and  which,  A\ithout  the  presence  of  oxygen^ 
produces  acid  from  sugar ;  so  that  we  m^ouIcI  probably  not  be  far  from 
right  if  we  were  to  say  that  the  organism  in  question  is  simply  the  fun- 
gus of  lactic  acid.  We  will,  however,  reserve  our  decision  for  another 
page,  where  the  analysis  of  the  product  of  the  fermentation  will  be 
given,  that  being  the.  one  sure  method  for  determining  the  species 
of  any  ferment  bacterium. 

In  all  cultures  it  is,  of  course,  essential  that  the  culture  substratum 
be  neutral  when  the  inoculation  is  made ;  should  it  be  acid,  it  must 
be  neutralized.  This  is  best  accomplished  by  very  carefully  adding  the 
carbonate  of  sodium.  Without  this  precaution  it  would  be  somewhat 
difficult  to  determine  whether  acid  had  been  produced  by  the  action  of 
the  fungus  or  not. 

In  the  light  of  these  experiments,  the  thorough  decalcification  of  the 
tooth-substance  in  caries  is  easily  accounted  for.  The  saliva  is,  no  doubt, 
always,  particularly  in  mouths  of  uncleanly  persons,  impregnated  with 
sugar,  either  taken  directly  into  the  mouth  or  formed  there  by  the  action 
of  the  ptyalin  of  the  saliva  upon  starch.  The  question  of  the  presum- 
able diastatic  action,  as  well  as  of  a  presumable  inverting  power  on  the 
part  of  the  organisms  themselves,  Avill  be  considered  in  the  section  on 
Physiology. 

Wherever  this  stagnates  between  the  teeth  in  fissures,  etc.,  etc.,  espe- 
cially during  sleep,  it  7nnst  become  acid.  When  a  portion  of  the  dentine 
has  become  decalcified,  it,  as  is  well  known,  takes  up  the  liquids  of  the 
mouth,  and  the  fungi  with  them,  like  a  sponge,  and  the  fungi,  being 
independent  of  the  free  access  of  air,  go  on  producing  acid  within  the 
dentinal  tubules.  As  each  layer  of  dentine  becomes  softened  in  turn 
the  micro-organisms  follow  offer,  continually  producing  new  acid. 
Hereby  the  zone  of  softened,  non-infected  dentine  is  readily  under- 
stood. The  production  of  acid  is  entirely  independent  of  the  reaction 
of  the  saliva  as  it  enters  the  mouth ;  hence  the  uselessness  of  "  testing 
the  saliva"  for  acid.  That  the  liquid  squeezed  out  of  the  tubules  of 
decaj/inr/  dentine  lias  an  acid  reaction  every  dentist  in  America  who  has 
a  piece  of  blue  litnms-paper  and  is  not  color-blind  can  easily  prove  for 
himself. 

The  result  of  experiment  6  ])lainly  shows  one  cause  of  the  good  effects 
which  the  profession  has  seen  from  the  use  of  carbolic  acid. 

The  fact  that  a  pure  culture  was  obtained  in  most  cases  by  the  first 
inoculation  seems  to  indicate  that  the  fungus  exists  in  a  state  of  tolerable 
purity  in  the  deeper  parts  of  the  carious  dentine.  This  question  will, 
however,  receive  consideration  later.     The  action  of  the  fungus  upon 


FERMENTATION'  IN   THE  HUMAN  MOUTH.  797 

substances  which  contain  no  carbohydrates  Avill  also  be  considered 
under   Pliysiology. 

In  addition  to  these  experiments,  I  add  the  following  :  A  sound 
bicuspid  tooth  was  sawed  into  sections,  varying  from  ^  to  1  mm.  in 
thickness,  and  an  equal  number  of  these  sections  placed  in  each  of  two 
test-tubes.  Into  one  of  these  test-tubes  were  then  brought  5  c.c.  of  a 
})erfectly  neutralized  2-per-cent.  aqueous  solution  of  beef-extract ;  into 
the  other  the  same  solution,  with  the  addition  of  0.2  cane-sugar.  Both 
tubes,  with  their  contents,  were  then  sterilized,  and  upon  cooling  infected 
from  a  pure  culture  of  the  fungus  under  consideration. 

The  solution  in  the  second  tube  became  acid  in  a  few  hours  ;  not  so, 
however,  with  that  in  the  first  tube,  it  being  non-fermentable.  At  the 
end  of  one  week  the  thinner  sections  in  the  second  tube  were  so  far  soft- 
ened that  one  of  them,  removed  for  examination,  could  be  easily  bent 
between  the  fingers.  At  the  end  of  the  second  week  all  but  the  thicker 
sections  were  completely  decalcified.  One  of  these  sections  was  now 
placed  upon  the  freezing  microtome  and  made  into  cuts,  which  were 
stained  in  fuchsin  and  mounted  in  Canada  balsam.  A  microscopic 
examination  showed  that  the  fungi  had  penetrated  many  of  the  tubules 
to  a  considerable  de])th,  the  invaded  tubules  being  at  the  same  time 
slightly  extended.  At  the  close  of  the  third  week  the  invasion  was 
found  to  have  become  much  more  extensive,  the  tubules  much  dilated, 
and  in  some  places  the  walls  were  broken  through,  leading  to  the  forma- 
tion of  oval  spaces  or  caverns  in  the  dentine.  In  short,  we  had  a  typi- 
cal case  of  caries. 

It  is  hardly  necessary  to  state  that  the  thinnest  sections  in  the  first 
tube,  where  the  development  of  the  fungus  was  not  accompanied  by  an 
acid  fermentation,  did  not  show  even  the  traces  of  softening,  to  say 
nothing  of  caries. 

I  had,  then,  produced  caries  by  inoculating  sound  dentine  from  a 
pure  culture  of  a  fungus  found  in  carious  dentine  in  the  presence  of  the 
same  fermentable  substances  that  occur  in  the  mouth.  It  seems  that  a 
clearer  solution  of  the  problem  can  at  present  scarcely  be  expected.  Of 
course  the  thought  at  once  suggests  itself  to  every  one  that  this  decay  is 
quite  independent  of  putrefaction  ;  all  evidence  points  to  the  conclusion 
that  putrefaction  at  most  does  nothing  more  than  dispose  of  the  already 
devitalized  and  much  riddled  remains  of  tissue,  and  we  are  in  danger  of 
overrating  its  influence  even  at  this  stage. 

Pieces  of  dentine  in  a  solution  kept  constantly  pure  and  sour  by  fer- 
mentation not  only  become  softened  and  show  the  microscopic  changes 
characteristic  of  carious  dentine,  but  finally,  after  some  months,  disap- 
pear altogether,  as  has  repeatedly  been  the  case  in  my  cultures.  From 
this  we  must  infer  that  the  process  commonly  known  as  putrefaction  is 
absolutely  essential  at  no  stage  of  caries ;  especially  is  this  the  case  in 
caries  of  enamel. 

It  has  been  intimated  that  the  active  agent  in  this  process  is  nearly 
related  to,  if  not  identical  with,  the  fungus  of  sour  milk.  Bacterium 
nckli  lactici.  The  analysis  of  the  product  of  fermentation  will  show 
the  truth  or  falsity  of  this  supposition. 

The  method  of  carrying  out  such  an  analysis  wall  now  be  given  :  200 


798 


DENTAL   CARIES. 


c.c.  fresh  saliva  are  mixed  M'itli  2.0  starch  and  allowed  to  stand  forty- 
eight  hours  at  blood-temj)erature  ;  the  mixture  is  then  filtered  and 
heated  to  100°  C,  to  stop  the  fermentation.  This  process  is  repeated 
until  about  a  litre  of  the  solution  has  accumulated.  It  is  then  placed 
in  a  retort  and  reduced  to  a  volume  of  about  75  c.c.  It  will  be  very 
strongly  acid.  A  few  drops  of  this  liquid  are  added  to  a  thin  solution 
of  methyl-violet,  and  leave  it  unchanged  ;  from  this  we  conclude  that 
we  have  to  deal  with  an  organic  acid,  as  an  inorganic  acid  ^vould  turn 
it  first  blue,  and  then  green.  Since  the  acid  did  not  distill  during  the 
prolonged  boiling,  we  may  set  it  down  as  non-volatile ;  hence  a  non- 
volatile, organic  acid.  The  distillate  was  ver}'  slightly  acid ;  we  will 
call  it  distillate  No.  1,  as  we  wish  to  refer  to  it  again. 

The  solution  was  further  reduced  in  volume  to  about  40  c.c.  over  the 
water-bath,  and  then  transferred  to  a  large  glass  vessel,  briskly  shaken 
with  1^  to  2  litres  of  sulphuric  ether,  and  allowed  to  stand  until  the  ether 
became  perfectly  transparent.  This  was  then  filtered  into  a  large  retort 
and  distilled,  proper  precautions  being  observed  to  prevent  accidents. 
AMien  the  volume  had  been  reduced  to  about  50  c.c,  the  solution  was 
filtered  into  a  porcelain  vessel  and  still  further  reduced  over  the  water- 
bath.  A  portion  of  the  solution  tested  in  the  short  tube  of  a  Mitscher- 
lich  double-shadoM' polaristrobometer  gave  as  a  mean  of  nine  readings  a 
rotation  of  the  plane  of  polarization  equal  to  0.015°,  or  0°  0.9'.  In 
other  words,  the  solution  w^as  optically  inactive,  the  0°  0.9'  being  fiir 
within  the  range  of  the  error  of  experiment,  especially  as  the  solution 
was  not  absolutely  transparent. 

An  excess  of  freshly-prepared  oxide  of  zinc  was  then  added  to  the 
solution  and  the  whole  slowly  and  carefully  boiled,  Avater  being  added 

as  it  was  found  necessary,  till  the  reaction 
became  neutral,  or  nearly  so,  filtered  into  a 
large  glass  evaporating  dish,  and  put  away  at 
the  temperature  of  the  room  for  the  salt  to 
crystallize.  A  drop  of  this  solution  placed 
uj)on  a  glass  slide  gave  upon  crystallization 
the  forms  seen  in  Fig.  409,  which  are  at 
once  recognized  as  crystals  of  lactate  of  zinc. 
In  a  few  days  a  quantity  of  a  whitish  crystal- 
line powder  had  formed.  This  was  placed 
upon  a  filter,  the  mother-liquid  squeezed  out, 
washed  in  absolute  alcohol,  dissolved  in  hot 
water,  recrystallized,  and  dried  over  sulphuric 
acid  ;  it  then  weighed  0.343.  After  exposing  to  a  temperature  of  100° 
C,  or  a  little  more,  till  the  weight  became  constant,  it  weighed  0.2816  ; 
it  lost,  accordingly,  17.9  per  cent.^  of  water  of  crystallization,  corre- 
sponding to  3  molecules  of  water.  The  salt  was  then  dissolved  in 
Mater,  the  zinc  precij^itated  as  carbonate  and  burned.  The  burned 
mass  (zinc  oxide)  weighed  0.0970.     AVe  have,  consequently, 

Substance  analyzed  (a  zinc  salt)  =  0.343 

Oxide  of  zinc  *  =  0.097 

^  Theoretically,  18.2,  or  0.3  per  cent.  more. 


Fk;.  409. 


FERMENTATION  IN  THE  HUMAN  MOUTH.  799 

The  zinc  oxide  is  seen  to  be  equivalent  to  28.2  per  cent,  of  the 
substance  analyzed. 

The  formula  for  the  inactive  ethylidene  lactate  of  zinc  is 

ri'S'R'  \  Zii  +  SH.O  =  243  +  54. 

Dried  at  ordinary  temperature,  it  contains  27.3  per  cent,  zinc  oxide. 
The  result  obtained  from  the  analysis  differs,  therefore,  from  that 
deduced  from  the  formula  by  less  than  1  per  cent.,  and  settles  beyond 
doubt  the  fact  that  the  substance  analyzed  was  the  lactate  of  zinc,  or 
that  the  acid  generated  by  the  fermentation  is  lactic  acid — or,  more 
exactly,  inactive  ethylidene  lactic  acid,  since,  as  shown  above,  the  acid 
solution  was  optically  inactive  and  the  zinc  salt  contained  3  molecules 
of  water  of  crystallization.  The  salt  was  furthermore  soluble  in  62 
parts  water  at  14°  C. 

I  repeated  the  analysis  with  the  following  solution  : 

Water,  1000  c.c. 

Saliva,  300  c.c. 

Bouillon,  200  c.c,  made  by  boiling  125.0  beef  ten 

minutes  in  300  c.c.  of  water. 
Sugar,  10.0. 

This  solution,  being  slightly  acid,  was  neutralized  with  the  carbonates 
of  lime  and  sodium,  sterilized,  and  infected  from  a  pure  culture  of  the 
fungus  in  question.  It  was  treated  throughout  exactly  in  the  manner 
above  described,  except  that  the  zinc  salt  was  converted  into  the  sul- 
phide instead  of  the  carbonate,  and  burned  with  powdered  sulphur  in  a 
stream  of  hydrogen.     The  result  was  as  follows  : 

Substance  analyzed    —     1.0540 

Zinc  sulphide  =     0.415 

Zinc  =  26.38  per  cent. 

instead  of  26.74  per  cent.,  as  deduced  from  the  formula — a  difference 
of  only  ^  of  1   per  cent. 

In  this  case  the  substance  was  dried  at  100°  C.  before  weighing,  and 
the  formula  becomes 

Wk }  ^" = '"'■ 

One  more  analysis  was  made,  using — 

Water,  .     1000  c.c. 

Liquid  beef  extract,       20  c.c. 
Sugar,  10.0 

The  result  was  the  same,  and  need  not  be  given,  the  two  analyses 
above  described  being  abundantly  sufficient  to  show  that  the  acid  gen- 
erated by  the  fungus  in  question  is  the  common  ferment,  lactic  acid. 

Distillate  No.  1,  referred  to  above,  owed  its  slight  acidity,  we  now 
know — in  part,  at  least — to  lactic  acid,  since,  when  an  aqueous  solution 


800  DENTAL   CARIES. 

of  lactic  acid  is  boiled,  a  small  fraction  of  the  acid  goes  over  with  the 
water.  To  ascertain,  however,  whether  any  other  acid,  especially  vola- 
tile, was  present,  the  distillate  was  boiled  with  carbonate  of  lime, 
filtered,  evaporated  to  dryness,  a  small  amonnt  of  dilute  sulphuric 
acid  added,  and  heated  in  a  retort  over  the  water-bath.  A  few  drops 
of  an  oilv  acid  came  over,  which  when  taken  upon  the  fingers  smelled 
like  butyric  acid ;  the  amount,  however,  was  so  small  that  no  attempt 
could  be  made  to  analyze  it. 

I  have  been  able  with  some  degree  of  certainty  to  establish  the  pres- 
ence of  lactic  acid  in  carious  dentine  by  a  method  theoretically  so 
simple  that  it  seems  strange  it  has  never  been  made  use  of  before,  but 
which,  however,  in  practice,  is  carried  out  only  with  great  difficulty. 
My  first  and  second  attempts  were  only  partially  successful ;  the  third 
succeeded  sufficiently  well  to  justify  its  description  here. 

In  this  experiment  I  made  use  of  fifteen  teeth,  all  containing  consid- 
erable quantities  of  carious  dentine,  and  all  extracted  on  the  day  of  use. 
The  remains  of  food  were  first  removed  from  the  cavities,  but  none  of 
the  softened  dentine ;  then  all  the  softened  dentine  was  taken  out  and 
placed  in  a  porcelain  vessel,  cut  or  picked  into  fine  pieces,  placed  in  a 
test-tube  with  1  c.  c.  of  water  and  two  drops  of  a  lO-jier-cent.  solution 
of  hydrochloric  acid  added.  Any  free  la(:tic  acid  in  the  carious  den- 
tine would  remain  free,  and  any  existing  in  combination  with  lime 
would  be  set  free  by  the  hydrochloric  acid.  It  Avas  then  gently  shaken 
with  about  25  c.c.  sulphuric  ether,  and  the  latter,  holding  the  lactic  acid 
in  solution,  was  after  some  minutes  j)oured  off  into  a  second  test-tube ; 
here  it  must  be  allowed  to  stand  fi'om  twenty-four  to  forty-eight  hours, 
till  it  becomes  perfectly  clear.  It  was  then  filtered  into  a  porcelain 
dish,  evaporated,  a  few  drops  of  distilled  water  and  a  small  quantity  of 
freMy-prepared  zinc  oxide  added,  gently  boiled  (water  being  added  as 
necessary)  for  ten  minutes,  the  three  or  four  dro})s  of  liquid  remaining 
filtered  on  to  a  glass  slide  and  allowed  to  crystallize.  I  obtained  the 
forms  seen  in  Fig.  410.  Their  close  resemblance  to 
Fig.  410.  ^^iQ  crystals  of  the  lactate  of  zinc  (Fig.  409)  will  be 

seen  at  once.  There  can,  in  fact,  scarcely  be  a  doubt 
that  they  are  lactate-of-zinc  crystals.  The  lactic  acid 
concerned  in  their  formation  must,  of  course,  have 
existed  in  the  carious  dentine. 

I  have  noticed  in  the  dental  journals  a  tendency  on 
the  part  of  some  writers  on  this  subject  to  derive  a 
large  amount  of  satisfaction  from  the  statement  that, 
after  all,  what  I  have  done  to  clear  up  the  subject  of  dental  caries  was 
done  and  known  long  ago.  One  writer  even  states  that  he  might 
almost  have  said  two  years  ago  something  that  I  said  but  a  few  months 
since.  Let  me  say,  once  for  all,  that  I  have  too  little  sjiare  time  to 
devote  any  of  it  to  the  discussion  of  the  (jue.stion  who  said  this  or  that 
first,  or  even  who  mir/ht  almod  have  said  something  two  years  ago. 
There  is  perhaps  no  human  disease  about  which  more  has  been  said 
than  about  caries  of  the  teeth  ;  and  when  the  subject  shall  have  received 
its  final  settlement,  there  will  be  hundreds  Avho  may  say,  "  I  told  you 
so."     Malassez  and  Vignal  very  justly  say  of  Baumgarten,  who  claims 


FERMENTATION  IN  THE  HUMAN  MOUTH  801 

priority  over  Kocli  in  the  discovery  of  the  tubercle  bacilkis,  "11  ne  siuffit 
pas  de  trouver,  il  faut  prouver;"  and  I  do  not  hesitate  to  say,  with 
reference  to  some  of  the  discussions  which  for  years  have  been  carried 
on  concerning  the  cause  of  dental  caries,  "11  ne  sivffit  pas  de  deviner,  il 
faut  trouver  et  prouver,'^ 

It  is  not  enough  to  guess  the  cause,  or  guess  at  it :  we  must  find  the 
cause,  and,  having  found  it,  prove  that  it  is  the  cause  sought  for. 

If  we  infect  a  beef-extract-sugar  solution  with  carious  dentine,  as 
already  described  in  this  paper,  using  every  possible  precaution  to 
obtain  perfectly  pure  material  and  to  prevent  the  access  of  germs 
from  without,  and  keep  the  solution  at  37°  C,  we  may  observe  the 
following  phenomena  :  In  from  eight  to  ten  hours  the  solution  will 
show  a  slight  cloudiness,  which  at  no  time,  however,  amounts  to  com- 
plete opacity.  Tested  with  sensitive  litmus-paper,  it  will  be  seen  that 
the  acid  reaction  has  already  appeared.  In  fifteen  to  twenty  hours  the 
fermentation  will  generally  have  reached  the  most  active  state,  and 
soon  afterward  a  colorless,  flocky  precipitate  will  begin  to  form  on  the 
bottom  of  the  vessel,  accompanied  by  a  corresponding  clarifying  of  the 
solution  and  a  diminution  of  the  feriuentative  activity.  After  the  lapse 
of  forty-eight  hours  the  sediment  will  have  completely  formed,  and  the 
solution  will  be  almost  as  transparent  as  when  the  experiment  began. 
The  time  required  for  the  completion  of  this  series  of  phenomena  will, 
however,  naturally  depend  somewhat  upon  the  amount  of  dentine  taken 
for  the  infection  and  the  amount  of  the  solution  used. 

Impurities  in  the  culture  manifest  themselves  in  various  ways — it 
may  be  by  an  excessive  cloudiness  of  the  liquid,  or  by  the  formation  of 
a  skin  upon  the  surface  of  the  solution,  or  the  failure  of  the  latter  tO' 
become  clear  after  the  regular  lapse  of  time,  etc.,  etc. 

Dentine  is  an  excellent  medium  for  separating  the  different  fungi- 
found  in  the  mouth,  the  most  of  them  not  being  able  to  exist  in  the 
deeper  parts,  partly  on  account  of  the  acidity  of  the  medium,  partly  on' 
account  of  the  lack  of  free  oxygen.  We  may,  therefore,  with  the 
proper  amount  of  care,  obtain  material  of  such  purity  as  to  produce 
a  pure  culture  in  the  first  generation. 

If  we  microscopically  examine  the  sediment  which  has  formed  on  the 
bottom  of  the  vessel,  we  shall  find  it  to  consist  of  cocci  and  diplococci, 
either  single  or  in  chains — in  either  case,  without  motion.  Under  a  low 
power  they  appear  round  and  regular ;  with  -^  oil  immersion  they  are 
seen  to  be  round  or  oval,  regular  or  irregular,  involuted,  etc.,  present- 
ing the  most  various  shapes  and  sizes.  I  have  never  been  able  to  detect 
the  existence  of  spores,  and  reproduction  takes  place  only  after  the  scheme 
presented  in  Fig.  411,  Nos.  1,  2,  3,  4,  5,  6,  7.  A  coccus  which  may  be 
round  in  the  beginning  by  extension  in  one  axis  becomes  oval  or  elon- 
gated ;  soon  after,  it  shows  a  contraction  in  the  middle,  resulting  in  the 
production  of  a  diplococcus  or  two  cocci,  each  of  which  may  produce 
two  cocci  in  the  same  manner. 

We  find,  consequently,  in  a  chain  taken  from  a  growing  culture,  some 
of  the  cocci  round,  others  oval ;  some  of  the  diplococci  but  slightly  con- 
tracted, while  in  others  the  contraction  amounts  almost  to  a  complete 
division.     (See  Fig.  411,  d,  e,f.)     Frequently  the  cells  acquire  a  pro- 
VoL.  I.— 51 


802  DENTAL   CARIES. 

nounced  bacterium  form  ;  so  that  if  they  did  not  occur  in  the  same  chain 
M'ith  the  ordinary  forms,  one  would  be  in  doubt  as  to  whether  they 
belonged  to  the  same  species. 

The  growing  cells  in  a  chain  sometimes  turn  upon  their  shorter  axis, 
and  then,  growing  out  in  the  new  direction,  produce  very  peculiar  fig- 


Fig.  411. 

..i8:{{ 

^  *^  °°o„ 

0   Of)  \ 

/  1  !  s         0  0   0 

^  0     0 

•     •^     f        ff 

r.-i    0  ^ 

^  I 

'Sfi 


°0P, 

ures  (Fig.  411,/,  g).  In  stagnant  cultures  the  cells  under  high  power 
are  mostly  very  irregular,  having  in  groups  the  appearance  of  the  bones 
of  the  wrist.     (See  Fig.  411,  a,  6.) 

Very  characteristic  are  the  involution  forms  produced  both  in  stag- 
nant cultures  and  in  media  which  are  not  well  adapted  to  the  needs  of 
the  fungus.  Here  the  forms  and  sizes  are  so  various  that  it  sometimes 
becomes  exceedingly  difficult,  if  not  impossible,  to  tell  if  certain  ones 
are  normal  or  abnormal.  (See  Fig.  411,  h,  i,j,  k.)  In  exceptional 
cases  the  threads  surround  themselves  with  a  thick  gelatinous  sheath. 

(See  Fig.  411,  c.)     The  protoplasm  of  the 

Fig.  412.  involuted  cells  generally  presents  a  gran- 

y***  V  ^^^''^^'  appearance  (Fig.  411,  h,k). 

^Ji  V  ^        ^         If  we  make  a  large  number  of  cultures 

f  /       /'  •  I     /      ^^  once,  we  will  in  about  one  case  out  of 

^N,   /  •  t   I        five  to  ten  (and  if  the  cultures  are  made 

I  \  ''*i/        I  /         in  a  decoction  of  malt  much  more  fre- 

/     %  *    ^  j  quently)    meet   with    a    second    fungus, 

\^^^     ^^*   /  essentially    different    from    the    one   just 

I       ^^      y  described.     It  occurs  chiefly  in  form  of 

I  •  bacilli,  but  also  as  leptothrix,   bacteria, 

^/l        •*  diplococci,    and    cocci    singly,    or,    as    is 

»        I  mostlv  the  case,  in  long  zig-zag  threads 

/      /  (Fig.  41 2). 

/  The  discovery  of  this  fungus,  with  its 

different  forms  of  development,  affords  a 

very  ready  explanation  of  the  fact  that  in  a  single  dentinal  tubule  we 

sometimes  find  a  transition  from  leptothrix  to  bacilli,  from  bacilli  to 

bacteria,  and  from  bacteria  to  cocci — an  occurrence  which  I  demon- 


FERMENTATION  IN  THE  HUMAN  MOUTH. 


803 


strated  nearly  two  years  ago  before  the  American  Dental  Society  of 
Europe,  before  the  Gesellschaft  fuer  Heilkuncle  in  Berlin,  and  to  vari- 
ous private  persons,  including  some  of  the  most  celebrated  mycologists 
in  Germany.  Those  who  maintain,  as  was  done  in  the  British  Dental 
Association,  that  such  cases  may  not  be  found,  are  responsible  for  their 
own  mistake. 

J/ac/"oscopically,  cultures  of  this  fungus  in  beef-extract-sugar  solution 
are  not  easily  to  be  distinguished  from  cultures  of  that  described  above. 
The  fungus  collects  as  a  sediment  on  the  bottom  of  the  vessel ;  it  never 
forms  a  skin  on  the  surface  of  the  liquid,  and  produces  but  a  moderate 
cloudiness  of  the  same.  In  most  decoctions,  however,  they  present 
some  peculiarities.  Sometimes  the  fungus  floats  about  in  the  solution 
in  semi-transparent  balls,  or  rises  up  from  the  bottom  of  the  vessel  like 
a  miniature  cloud  of  smoke,  or  collects  in  small  patches  on  the  sides  of 
the  vessel,  while  the  solution  itself  remains  almost  perfectly  clear.  The 
cells  are  motionless  and  do  not  form  spores. 

In  order  to  discriminate  between  these  two  fungi,  I  will  designate 
for  the  present  the  one  first  described  by  the 
prefix  .'/  (alpha),  and  the  one  under  considera- 
tion by  the  prefix  /3  (beta).  In  all  probability, 
the  /3-fungus  also  produces  lactic  acid  from 
sugar.  I  say  "  in  all  probability,"  because, 
though  I  have  always  been  able  to  detect  lactic 
acid  in  cultures  of  this  fungus,  I  could  not  say 
with  absolute  certainty  that  cocci  and  diplococci 
of  the  species  ./  were  not  present. 

We  have,  then,  in  carious  dentine  two  dis- 
tinct fungi — one  always,  the  other  often,  pres- 
ent ;  the  former  surely,  the  latter  probably, 
producing  lactic  acid  from  sugar.  If  these 
fungi  are  the  direct  cause  of  dental  caries,  we 
should  be  able  to  produce  caries  by  subjecting 
sound  dentine  to  their  action.  This  I  have 
accomplished,  as  already  described. 

In  Fig.  413,  a,  are  seen  in  outline  two 
tubules  of  dentine  melted  together  by  natural 
caries,  and  in  Fig.  413,  6,  two  tubules  melted 
together  by  artificial  caries. 

In  Fig.  414,  rt,  are  likewise  two  tubules 
from  natural  caries,  and  in  Fig.  41 4,  6,  two 
from  artificial  caries.  It  is  a  fact  of  consider- 
able interest  that,  though  the  fungi  themselves 
are  perfectly  colorless,  pieces  of  dentine  sub- 
jected to  their  action  become  yellowish,  light 
brown,  or  dark  brown,  etc.,  depending  upon 
the  medium  in  which  the  culture  is  made, 
while  diiferent  pieces  of  dentine  in  the  same 
culture  do  not  by  any  means  necessarily  acquire  the  same,  color. 

The  carrying  out  of  this  experiment  is  attended  with  difficulties,  and 
some  may  try  it  and  fail ;  I  have  failed  many  times.     The  necessity  of 


804 


DENTAL   CARIES. 


I' 
il 


I      V 

II' 


repeatedly  changing  the  solution  very  much  increases  the  danger  from 
impurities ;  especially  must  the  saccharomycetes  be  guarded  against. 
The  acidity  of  the  medium  caused  by  the  caries  fungi  renders  it  very 

favorable  for  their  development ;  and  when 
they  have  once  found  their  way  into  a  culture, 
it  might  as  well  be  thrown  away  at  once. 
Again,  notwithstanding  the  presence  of  the 
pieces  of  dentine,  the  solution  sometimes  be- 
comes sufficiently  acid  to  impair,  if  not  to 
destroy,  the  vitality  of  the  fungus.  In  this 
case  the  dentine  becomes  softened,  but  only  a 
slight  invasion  of  the  tubules  takes  place. 
Then,  of  course,  in  the  very  last  stage  of 
caries,  other  fungi,  especially  Lcptothrix  buc- 
calls,  are  present  in  the  decomposing  dentine, 
and  sometimes  produce  an  appearance  in  its 
superficial  layers  which  I  have  not  attempted 
to  reproduce  artificially.  It  is  not  difficult 
by  a  simple  microscopic  examination  of  the 
fluids  of  the  mouth,  as  well  as  of  carious  dentine,  to  find  forms  mor- 
phologically identical  with  those  described  above. 

In  Fig,  415  is  seen  in  outline  a  portion  of  an  epithelial  scale  from  the 

Fig.  415. 


Fio.  414. 
6 

W 

.«; 
it 

': 


'1) 


I 
1} 


Fig.  416. 


human  mouth,  highly  magnified,  with  the  fungi  lying  upon  the  surface. 
Theformssecnin  Fig.  416  were  obtained  fromaglass 
tul)e  filled  with  starch  and  kept  in  the  mouth  over- 
night, while  Fig.  41 7  is  from  carious  dentine.  The 
.7  caries  fungus  agrees  morpho-  ^xa.  417. 

I  '  logically  with  the  fungus  of  sour 

milk  as  delineated  by  Pasteur. 
Later  experiments,  however,  ren- 
der it  probal)lc  that  the  souring 
of  milk  is  ])roduced  by  an  alto-      * 
^       ^/  gether  diiferent  fungus,  a  short,  thick  badenum, 


/I 


//' 


I 
! 
I 


tU 


FERMENTATION  IN  THE  HUMAN  MOUTH.  805 

occurring  in  twos,  seldom  fours,  which  may  also  be  found  in  the  human 
mouth  (though  probably  not  deep  in  carious  dentine),  and  will  be  con- 
sidered at  another  time. 

In  the  case  of  both  fungi  the  fermentation  goes  on  independently  of 
the  presence  of  free  oxygen.  I  have  already  shown  that  where  only  a 
trace  of  oxygen  is  present  in  no  way  comparable  with  the  amount  of 
acid  produced,  the  degree  of  acidity  was  as  great  as  where  there  was 
free  access,  of  air.  Whether,  however,  this  trace  of  oxygen  is  essential 
to  the  life  of  these  fungi — /.  e.  whether  without  it  they  would  perish 
from  asphyxia — is  a  question  which  we  will  not  discuss  here. 

It  has  been  generjjlly  supposed  that  the  production  of  lactic  acid  by 
fermentation  from  sugar  is  accompanied  by  the  evolution  of  carbonic 
acid ;  in  fact,  Fluegge  says  that  no  fermentation  can  go  on  without  the 
production  of  carbonic  acid.  This  statement  will  hardly  be  borne  out 
by  a  study  of  the  fermentation  produced  by  the  fungi  of  tooth  caries. 

A  glass  vessel  of  500  c.c.  capacity  was  tilled  witli  becf-extract-sugar 
solution  infected  with  a  pure  culture  of  caries  fungi  and  made  air-tight 
with  a  rubber  stopper  carrying  an  efflux-tube  for  collecting  the  gas  over 
mercury.  After  twenty-four  hours,  during  which  time  1.75  c.c.  acid 
had  been  produced,  one  single  gas-bubble  was  collected,  which  may 
have  been  due  to  a  slight  change  of  temperature,  as  well  as  to  a  veritable 
gas-evolution.  The  splitting  appears,  therefore,  to  be  perfectly  smooth, 
and  to  take  place  in  accordance  with  the  simple  formula, 

CsHiaOg  =  2C3lIg03. 

It  presents  a  marked  contrast  to  the  stormy  character  of  the  butyric 
and  alcoholic  fermentations,  in  case  of  which  the  pressure  of  the  gas 
evolved  is  often  sufficient  to  burst  the  vessels  containing  the  cultures. 

There  is  perhaps  at  nearly  all  times  a  sufficient  amount  of  sugar  in 
the  oral  cavity  to  enable  the  fungi  of  caries  to  carry  out  their  charac- 
teristic ferment  action.  It  remains,  nevertheless,  an  interesting  question 
whether  they  have  the  power  to  form  sugar  out  of  starch — i.  e.  whether 
they  have  any  diastatic  action.  About  thirty  cultures  in  an  aqueous 
solution  of  beef-extract  and  starch  and  in  a  solution  of  starch  in  steril- 
ized saliva  gave,  for  the  most  part,  negative  results ;  in  exceptional 
cases  a  slight  diastatic  action  appeared  to  take  place,  which  I  am  in- 
clined to  regard  as  the  result  of  some  impurity  in  the  culture  or  an 
error  in  the  experiment. 

On  the  other  hand,  the  fungi  appear  without  doubt  to  possess  the 
power  to  invert  or  to  render  non-fcrmcntable  sugars  fermentable,  since 
cane-sugar,  which  is  not  fermentable  and  does  not  reduce  alkaline  solu- 
tions of  sulphate  of  copper,  acquires  both  these  properties  when  sub- 
jected to  their  action.  That  this  result  is  caused  by  the  action  of  a 
ferment  produced  by  the  organisms,  and  which  may  be  separated  from 
them,  is,  I  think,  demonstrated  by  the  following  experiment :  By  mak- 
ing a  number  of  cultures  at  one  time  in  vessels  of  200  to  500  c.c.  capa- 
city and  collecting  the  sediment  which  was  deposited  on  the  bottom  of 
the  vessels,  I  succeeded  in  bringing  together  a  considerable  quantity  of 
the  fungi;  this  was  then  treated  with  90-per-cent.  alcohol  filtered  and 
dried  in  a  porcelain  vessel,  thoroughly  rubbed  with  sand,  digested  with 


806  DENTAL   CARIES. 

water  at  23°  C,  and  again  filtered ;  the  filtrate  (which  must  be  clear 
and  should  contain  the  ferment  in  solution)  was  added  to  a  solution  of 
cane-sugar,  which  then  showed  in  the  long  tube  of  a  Mitscherlich  polar- 
iscope  a  rotation  equal  to  5.19°.  The  solution  was  now  allowed  to 
stand  four  hours  at  a  temperature  of  38°  C,  after  which  time  it  pro- 
duced a  rotation  of  only  4.54°,  indicating  a  decrease  of  about  two- 
thirds  of  a  degree.  The  solution  also  produced  a  slight  reduction  of 
an  alkaline  solution  of  sulphate  of  copper — i  e.  a  certain  portion  of  the 
cane-sugar  had  been  converted  into  invert  sugar. 

In  the  presence  of  the  fungi  the  non-fermentable  sugar,  by  the  action 
of  the  invertine  produced  by  the  fungi,  takes  up  oTie  molecule  of  water 
and  is  converted  into  invert  sugar,  a  mixture  of  levulose  and  dextrose, 
both  of  ^vhich  are  fermentable  : 

Cane  sugar.  Levulose.  Dextrose. 

We  may  say,  therefore,  that  the  micro-organisms  require  sugar  to 
produce  fermentation,  but  that  it  is  immaterial  which  kind  of  sugar  is 
furnished  them.  The  fermentation  is  most  active  between  the  tempera- 
tures 35°  and  40°  C.  Above  50°  and  below  15°  C,  little  or  no  pro- 
duction of  acid  takes  place. 

In  addition  to  these  two  species  of  fungi,  others  of  minor  importance 
are  occasionally  met  with  in  the  mouth,  and  will  receive  attention 
later  on. 

I  would  not  have  any  one  think  that  I  look  upon  the  above  as  a 
thorough  consideration  of  the  fungi  of  tooth  caries ;  to  me  it  a})pears 
very  imperfect.  Nevertheless,  I  have  thought  it  well  to  present  the 
matter  before  the  profession  in  the  hope  that  others  might  be  induced 
to  take  it  up  and  help  to  complete  the  work  thus  begun.  I  will  now 
present  the  results  of  experiments  relating  to  the  action  of  various 
antiseptics,  filling  materials,  etc.  upon  the  fungi   under  consideration. 


The  Influence  of  Antiseptics,  Filling  Materials,  etc.  upon 
THE  Fungi  op  Dental  Caries. 

Having  established  upon  an  experimental  and  scientific  basis  the  fact 
that  caries  of  the  teeth  is  to  a  certain  extent  the  direct  result  of  the  action 
of  ferment  acid  or  acids ^  upon  the  tissue  of  the  tooth,  followed,  particu- 
larly in  the  case  of  the  dentine,  by  the  action  of  the  ferment  organisms 
tliemselves  upon  the  decalcified  tissue,  it  becomes  a  matter  of  the  first 
importance  to  determine,  first,  by  what  means  we  may  counteract  the 
action  of  the  acids  or  ])revent  their  jiroduction ;  second,  by  what  means 
we  may  save  the  hi  ready  decalcified  dentine  from  complete  destruction. 

Evidently,  there  are  three  methods  by  which  the  desired  end  may  be 
partially  obtained  : 

1.  By  repeated,  thorough,  systematic  cleansing  of  the  oral  cavity  and 
the  teeth  we  may  so  far  reduce  the  amount  of  fermentable  substances  in 
the  mouth  and  the  number  of  ferment  organisms  as  to  materially  dimin- 

^  The  chief  work  in  tlie  production  of  caries  is  iierfornied  by  lactic  acid  ;  other  acids 
are  only  auxiliary  factors. 


FERMENTATION  IN  THE  HUMAN  MOUTH.  807 

ish  the  production  of  acid.      This  is  so  self-evident  that  it  needs  no 
further  comment. 

2.  By  the  repeated  application  of  alkaline  substances  we  may  to  a 
certain  extent  neutralize  the  acids  before  they  have  acted  upon  the  teeth 
to  any  considerable  degree. 

3.  By  a  proper  and  intelligent  use  of  antiseptics  we  may  destroy  the 
organisms  themselves,  or  at  least  render  them  inactive.  It  is  this  method 
which  is  especially  applicable  in  the  second  stage  of  dental  caries — /.  e. 
the  stage  M-hich  follows  the  decalcification — and  to  which  we  will  here 
give  exclusive  attention.  We  must,  however,  constantly  bear  in  mind 
that,  by  whatever  metliod  we  proceed,  a  previous  thorough  cleansing  of 
tlie  teeth  is  absolutely  indispensable.  There  is  no  known  solution,  alka- 
line or  antiseptic,  applicable  in  the  human  mouth  which  will  penetrate 
between  the  teeth  or  to  the  bottom  of  fissures  and  cavities  when  these 
are  filled  with  food  in  sufficient  quantity  to  have  any  appreciable  effect. 
Therefore  before  all  antiseptics  or  alkaline  washes  come  the  toothbrush, 
toothpick,  and  floss  silk. 

In  my  experiments  for  determining  the  action  of  various  antiseptics 
upon  the  fungi  of  tooth  caries  it  appeared  to  me  that  by  allowing  the 
antiseptic  to  act  upon,  the  fungi  in  their  natural  medium,  saliva,  I  could 
obtain  results  of  more  practical  value  tlian  by  experimenting  upon  them 
in  artificial  solutions  and  in  pure  cultures,  neither  of  which  ever  occurs 
in  the  human  mouth.  Furthermore,  since  the  fungi  can  attack  the 
teeth  only  after  a  partial  decalcification,  we  have,  in  tlie  first  place,  to 
demand  of  an  antiseptic  not  so  much  that  it  destroys  the  fungi  as  that 
it  prevents  the  production  of  acid  by  them.^  Consequently,  if  an  acid 
reaction  failed  to  appear  in  a  solution  of  saliva  and  sugar  to  which  a 
certain  antiseptic  had  been  added  as  soon  as  in  a  like  solution  to  which 
no  antiseptic  had  been  added  (control),  it  was  taken  as  evidence  of  the 
activity  and  value  of  the  antiseptic  used.  This  method  could,  of  course, 
be  used  only  with  substances  having  a  neutral  reaction.  The  solutions 
w^ere  also  subjected  to  a  microscopic  examination,  to  render  the  evidence 
doubly  sure. 

In  the  following  table  I  have  indicated  the  percentage  of  each  anti- 
septic experimented  upon  which  must  be  present  in  a  sweetened-saliva 
solution  to  prevent  the  appearance  of  an  acid  reaction  in  twenty-four 
hours,  or,  in  case  of  alkaline  or  acid  antiseptics,  to  prevent  the  develop- 
ment of  the  characteristic  fungi  in  the  same  time. 

For  example,  if  to  100,000  parts  of  sweetened  saliva  we  add  one 
part  of  bichloride  of  mercury,  the  solution  will  not  be  found  acid  after 
the  lapse  of  twenty-four  hours  even  though  the  control  become  sour  in 
four  or  five  hours.  If  we  add  only  one  part  to  500,000,  the  acid  reac- 
tion will  appear  somewhat  later  than  in  the  control. 

This  table  is  designed  to  show  the  comparative  strength  of  the  anti- 
septics most  commonly  used.  The  action  of  the  antiseptics  having  an 
acid  or  alkaline  reaction  upon  the  fungi  was  determined  by  the  use  of 
the  microscope  alone: 

'  The  production  of  acid  may  be  taken  as  synoTiymous  with  the  development  of  the 
fnngi,  though  the  faihire  of  the  acid  reaction  to  appear  after  a  certain  length  of  time 
does  not  necessarily  indicate  that  the  fungi  have  been  devdalized. 


808  DENTAL  CARIES. 

Production  of  Acid 

(Development  of  Fungi). 

Prevented.  Retarded. 

Bichloride  of  mercury    ' 1-100,000  1-500,000 

Nitrate  of  silver    . 1-50,000  1-100,000 

Iodoform 1-5,000  1-10,000 

Naphthaline 1-4,000  (?)       1-9,000 

Iodine                                 1-6,000  1-15,000 

Oil  of  mustard 1-2,000  1-5,000 

Permang?;nate  of  potas 1-1,000  1-2,000 

Eucalyptus  oil 1-600 

Carbolic  acid 1-500  1-1,000 

Hydrochloric  acid 1-500  1-1,000 

Phenylicacid    .    . l-'-OO  l-oOO 

Liquid  of  Agate  Cement 1-250 

Liquid  of  Excelsior  Cement 1-225 

Lactic  acid 1-125  1-250 

Carbonate  of  sodium 1-100  1-200 

Salicylic  acid  (Cone,  alcohol  sol.) 1-75  1-125 

Alcohol 1-10  1-20 

The  experiments  show  that  bichloride  of  mercury  is  about  two  hun- 
dred times  as  powerful  as  carbolic  acid,  and  demonstrate  very  clearly 
the  mistake  of  substituting  weak  solutions  of  this  antiseptic  (1-1000,  as 
I  have  seen  recommended)  for  concentrated  carbolic  acid.  One  (jnc- 
thousandth  is  only  one-fifth  as  powerful  as  pure  carbolic  acid,  which  in 
many  cases  may  be  used  with  impunity.  It  is  consequently  useless  to 
attempt  to  introduce  the  sublimate  solution  for  the  purpose  of  sterilizing 
root-canals,  cavities  before  filling,  etc.,  unless  we  may  use  at  least  a 
i_per-cent.,  if  not  a  1-per-cent.,  solution.  I  see  no  reason,  however, 
why  this  may  not  be  done.  In  a  few  cases  I  have  used  a  1-per-cent. 
solution  for  treating  root-canals,  and  do  not  hesitate,  particularly  with 
the  rubber  dam  adjusted,  to  wipe  out  cavities  before  filling  with  a  2-per- 
cent, solution,  and  see  no  possible  evil  which  could  result  from  it.  A 
well-known  physiologist  in  Berlin  has  told  me  that  he  uses  a  1-per-cent. 
solution  in  his  own  mouth  for  aphthae,  and  with  excellent  results.  We 
should  not,  however,  overlook  the  fact  that  a  1-per-cent.  sublimate  solu- 
tion is  only  one-fifth  as  powerful  as  pure  iodoform. 

As  a  raouth-wash  I  have  frequently  used  a  ^-per-cent.  (1-1000) 
solution  myself,  and  have  seen  no  bad  results  from  it ;  I  would  not, 
however,  recommend  it  to  my  patients  in  this  strength.  It  has,  besides, 
for  me,  an  exceedingly  disagreeable  and  lasting  taste  which  it  is  difficult 
to  disguise,  and  produces  an  immediate  increased  secretion  of  saliva  and 
mucus  which  is  very  annoying.  A  ^^Q^-per-cent.  solution  (1-5000)  may 
eventually  be  brought  into  u.se ;  in  this  concentration  it  is  four  times  as 
powerful  as  a  1-per-cent.  solution  of  carbolic  acid.  The  very  high 
antiseptic  power  of  nitrate  of  silver  is  particularly  noteworthy.  Why 
may  it  not  be  employed  in  place  of  the  much  more  dangerous  mercuric 
chloride  ? 

The  action  of  tobacco  upon  the  fungi  is  worthy  of  notice.  Five 
"■rammes  of  old  Virginia  plug  were  boiled  fifteen  minutes  in  50  c.c.  of 
water,  the  loss  by  evaporation  being  constantly  replaced ;  the  decoction 
was  then  filtered  and  a  portion  added  to  an  equal  volume  of . "saliva  with 
sugar.  Tliis  jirodnced  a  mixture  scarcely  .stronger  than  that  which 
many  veteran  chewers  carry  around  in  their  mouths  all  day,  and  in  it 


FERMENTATION  IN  THE  HUMAN  MOUTH. 


809 


Fig.  418. 


V 


a 


the  fungi  led  only  a  miserable  existence.  Much  more  remarkable,  how- 
ever, was  the  action  of  tobacco-smoke  upon  the  fungi,  the  smoke  from 
the  first,  third,  or  last  quarter  of  a  Colorado  Claro  cigar  being  found 
amply  sufficient  to  sterilize  10  c.c.  of  a  beef-extract-sugar  solution  pre- 
viously richly  infected  with  caries  fungi. 

The  apparatus  used  for  this  experiment 
(see  Fig.  418)  explains  itself.  A  current 
of  water  passing  through  the  part  B  in  the 
direction  indicated  by  the  double-headed 
arrow  produces  a  current  of  air  through  the 
part  A  in  the  direction  shown  by  the  single- 
headed  arrow  which  draws  the  smoke  from 
a  lighted  cigar  through  the  solution.  The 
rate  at  which  the  cigar  smokes  may  be  regu- 
lated at  will  by  the  cock  of  the  hydrant. 

In  consideration  of  the  strong  antiseptic 
power  of  tobacco-smoke,  we  might  be 
inclined  to  infer  that  tobacco-smokers 
should  never  suffer  from  caries  of  the 
teeth ;  it  is  evident,  however,  that  there 
are  very  many  points  in  the  dental  arch  to 
which  the  smoke  never  penetrates. 

In  the  preparation  of  cavities  for  in- 
serting fillings  it  is  naturally  often  next 
to  impossible  to  remove  all  the  carious 
dentine,  and  in  all  such  cases  it  is  espe- 
ciallv  desirable  that  the  filling;  material 
itself  should  possess  antiseptic  properties, 
since  we,  in  using  such  a  material,  not  only 
destroy  those  organisms  existing  in  the 
carious  tissue,  but  the  material,  if  it  re- 
mains permanently  antiseptic,  retards  the 
working  of  the  ferment  organisms  from 
without  and  the  appearance  of  secondary 
decay.  We  need,  therefore,  a  material  for 
filling  which  is  not  only  antiseptic  at  the  time  of  insertion,  but  which 
remains  permanently  so  after  being  inserted.  I  have  endeavored  to 
determine  the  relative  antiseptic  power  of  different  filling  materials 
(cements,  amalgams,  etc.)  not  only  at  the  moment  of  mixing,  but  after 
they  were  thoroughly  dry,  af^er  they  had  lain  some  hours  in  sweetened 
saliva,  and  after  they  had  been  an  indefinite  time  in  the  human  mouth. 

A  large  number  of  miniature  test-tubes  (homeopathic  pill-tubes)  were 
provided  with  cotton  stoppers  and  sterilized.  Into  each  was  brought 
h  c.c.  of  beef-extract-sugar  solution  previously  infected  with  carious 
fungi  (pure  culture).  To  the  first  tube  was  added  a  small  drop  of  a 
1-per-cent.  sublimate  solution,  the  second  tube  was  left  untouched,  and 
into  the  third,  fourth,  fifth,  etc.  wei^e  brought  the  filling  materials  whose 
antiseptic  virtues  were  to  be  tested ;  these  were  in  the  form  of  cylinders 
2  ram.  in  diameter  and  3  mm.  long ;  if  old  fillings  from  the  mouth  were 
used,  pieces  were  taken  having  approximately  the  same  size. 


a,  glass  cylinder  with  infected  solu- 
tion ;  6,  c,  glass  tubes;  </,  d',  d",  rub- 
ber tubing;  f,  cigar  (Colorado  Cla- 
ro) ;  B,  water  air-i)unip.  A  current 
of  water  passing  through  B  in  the 
direction  indicated  by  the  double- 
headed  iirrow  produces  a  partial 
vacuum  in  the  bulb,  and  conse- 
quently a  current  of  air  in  the  di- 
rection shown  by  the  single-headed 
arrow,  or  through  the  cigar,  which 
if  lighted  will  smoke  at  a  I'ate  deter- 
mined by  the  pressure  under  which 
the  water  is  llowiug. 


810  DENTAL   CARIES. 

These  tubes  now  being  placed  in  the  incubator,  their  contents  became 
cloudy  one  after  the  other.  In  those  tubes  which  contained  fillings  of 
but  slight  antiseptic  power  the  development  of  the  fungi  proceeded 
rapidly  and  the  cloudiness  soon  appeared  ;  if,  on  the  other  hand,  the 
filling  was  strongly  antiseptic,  the  development  of  the  fungi  was  hin- 
dered and  the  cloudiness  appeared  later.  The  first  tube  to  which  the 
sublimate  solution  had  been  added  of  course  remained  clear,  and  by 
comparing  the  others  with  this  it  was  easy  to  see  just  when  the  turbidity 
began  to  show  itself;  the  second  tube,  containing  no  antiseptic  and  no 
filling,  served  as  control,  and  the  space  that  intervened  alter  the  control 
became  turbid  till  any  one  of  the  other  tubes  became  turbid  was  a  meas- 
ure of  the  antiseptic  power  of  the  material  in  that  tube. 

As  the  result  of  a  great  number  of  experiments,  I  have  been  able  to 
get  together  the  following  table. 

When  the  control  tube  becomes  turbid  in  five  hours,  then — 

A  tube  containing  an  old  oxyphosphate  filling  becomes  turbid  in 5    hours. 

"  "  an  old  oxychloride  filling  becomes  turbid  in 5  '' 

"  "  a  gold  cylinder  becomes  turbid  in      5  " 

"  "  a  Hill's  stopping  cylinder  becomes  turbid  in 5  " 

"  "  an  amalgam  cylinder  (kept  twelve  hours  in  saliva)  becomes 

turbid  in b\  " 

"  "  an  agate  cylinder  (kept  twelve  hours  in  saliva)  becomes 

turbid  in b\  " 

"  "  an  old  amalgam  filling  becomes  turbid  in b^^     " 

"  "  an  amalgam  cylinder  (mixed  dry)  becomes  turbid  in  .    .    5|  " 

"  "  an  amalgam  cylinder  (mixed  wet)  becomes  turbid  in  .    .     Sj  " 

"  "  an  oxy.pliosphate  cylinder  (twelve  hours  in  saliva)  becomes 

turbid  in  .    / 5^  " 

"  "  an  amalgam  cylinder   (twelve  hours  old)  becomes  tui'bid 

i"-.-    •':    ; .• ^       " 

"  "  an  old  filling  ot  tin  and  gold  becomes  turbid  in  ....    5f       " 

"  "  an  oxyphosphate  cylinder  (twelve    hours  old)    becomes 

turbid  in       .    ' 6         " 

"  "  an  agate  cylinder  (twelve  hours  old)  becomes  turbid  in  .    6|       " 

"  '*  an    iodoform    cement   cylinder    (twelve  hours  in  saliva) 

becomes  turbid  in 6f       " 

"             "             a  pyrophosphate  cylinder  (mixed  dry)  becomes  turbid  in  7\       " 
"             "             a  pyroplifjspluite  cylinder  (mixed  wet)  becomes  turbid  in  7|        " 
"             "             an  oxychloride  cylinder  (twelve  hours  old)  becomes  tur- 
bid in 9         " 

"  "  a  piece  of  dentine  from  a  tooth  impregnated  by  a  cojiper 

amalgam  filling  becomes  turbid  in 11         " 

"  "  an  iodoform  cement  cylinder  (twelve  hours  old)  becomes 

turbid  in 12         *' 

"  "  an  iodolbrm  cement  cylinder  (fresh)  becomes  turbid  in  .     ?         " 

"  "  a  globule  of  mercury  becomes  turbid  in — 

"  "  a  cylinder  of  black  oxide  of  mercury  becomes  turbid  in  .  — 

"  "  a  cylinder  of  any  copper  amalgam   becomes  turbid  in  .  — 

"       -      "  any  old  copper  amalgam  filling  becomes  turbid  in  .    .    .  — 

"  "  a  cylinder  of  oxychloride  (fresh)  becomes  turbid  in  .    .  — 

The  ( — )  signifies  that  the  solution  remained  permanently  clear. 

We  see  from  these  results  that  the  only  filling  at  present  in  use  which 
exerts  a  continual  antiferment^  action  upon  the  walls  of  the  tooth  and 
its  immediate  surroundings  is  the  old  copper  amalgam ;  not  only  that, 
but  the  very   substance  of  the  tooth  containing  such  a  filling  itself 

*  I  use  the  terms  antiferment  and  antiset)tic  interchangeably,  though  the  former  is 
perhajis  preferable,  since  we  are  treating  of  ferment,  and  not  septic  organisms. 


FERMENTATION  IN  THE  HUMAN  MOUTH.  811 

becomes  antiseptic,  a  piece  of  bluish  or  bluish-green  dentine  from  such 
a  tooth  very  powerfully  retarding  the  development  of  the  fungi^  and, 
indeed,  in  two  cases  completely  destroying  them.  Secondary  decay  in 
such  a  case  would  be  next  to  impossible  where  anything  like  cleanliness 
was  observed. 

This  result  is  well  supported  by  observations  which  I  have  had 
abundant  opportunity  to  make  for  the  last  five  years  here  where  this 
material  is  so  extensively  used,  and  I  do  not  hesitate  to  say  that  if  our 
only  object  is  to  check  the  destruction  of  tissue  by  caries  there  is  no 
material  at  present  in  use  with,  which  this  object  may  be  so  surely 
accomplished  as  with  a  good  copper  amalgam.  It  is  a  material,  how- 
ever, which  I  have  never  used,  though  I  am  not  aware  of  any  bad 
effect  produced  by  it  beyond  the  discoloration  of  the  tooth.  Skogs- 
berg's  iodoform  cement  came  into  my  hands  too  late  to  complete  the 
experiments  with  it.  It  has  undoubtedly  strong  antiseptic  properties, 
which  it  does  not  completely  lose  even  when  exposed  to  the  saliva,  and 
might,  no  doubt,  be  used  to  great  advantage  as  a  foundation  for  perma- 
nent fillings.  Old  fillings  of  tin  and  gold  possess  slight  antiseptic  power, 
still  less  (almost  zero)  old  amalgam  fillings  (not  copper).  The  very 
inconsiderable  power  of  amalgams  to  prevent  the  development  of  fer- 
ment fungi  is  a  source  of  some  surprise,  since  we  have  been  accustomed 
to  look  upon  them  as  very  active  in  this  r&spect.  It  is  probably  a  mis- 
take to  attribute  the  hardening  of  dentine  under  amalgam  fillings  to  the 
antiseptic  action  of  the  amalgam,  since  in  the  first  place  it  possesses  this 
power  to  but  a  slight  degree,  and  in  the  second  place  the  hai'dening 
may  take  place  under  fillings  of  gutta-percha  equally  well.  If  we  dry 
the  cavity  but  indifferently  well  and  then  choose  a  piece  of  gutta-percha 
which  we  think  will  about  fit  the  cavity,  warm  it,  and  stuti'  it  into  the 
cavity,  we,  of  course,  can  expect  only  bad  results.  If  we  proceed  as 
follows,  we  will  obtain  excellent  results,  as  I  have  seen  time  and  again  : 
Adjust  the  dam,  excavate  carefully,  especially  the  margins,  wash  with  a 
strong  antiseptic,  dry  thoroughly  with  bibulous  paper,  and  then  with 
the  hot-air  syringe,  till  the  surface  of  the  dentine  becomes  whitish, 
paint  with  a  thin  solution  of  copal  varnisli,  dry  again  with  warm  air, 
then  put  in  the  gutta-percha  in  small  pieces,  one  after  the  other,  being 
sure  that  each  piece  sticks  to  its  place,  especially  along  the  margin,  just 
as  if  you  were  making  a  filling  of  gold.  A  piece  which  has  once  moved 
in  its  place  must  not  be  allowed  to  remain,  as  a  leak  will  be  the  result. 
Remove  such  a  filling  after  two  years,  and  the  cavity  will  often  be  found 
in  an  excellent  condition  for  a  gold  filling. 

The  oxychlorides,  when  first  mixed,  are  powerfully  antiseptic,  but 
soon  lose  their  energy  when  exposed  to  the  action  of  saliva. 

The  oxy phosphates  are  very  much  inferior  to '  the  oxychlorides  in 
antiseptic  power,  and  should  never  be  used  in  cavities  where  there  is 
much  soft  dentine.  This  conclusion  is  borne  out  by  my  own  experience 
in  practice,  and  by  that  of  others  with  ^\•hom  I  have  conversed  on  the 
subject.  Dr.  Paetsch  first  called  my  attention  to  the  disastrous  results 
of  such  a  practice,  and  his  testimony  was  confirmed  by  that  of  Dr. 
F.  P.  Abbott  and  others. 

It  must  not  be  expected  that  the  results  given  in  the  above  table  are 


812  DESTAL   CARIES. 

absolutely  free  from  error.  The  experiment  is  attended  ■with  more  diffi- 
culties than  are  at  first  sight  apparent ;  especially  does  the  sterilization 
of  the  tilling  materials  themselves  involve  much  time  and  labor,  and  the 
results  are  not  always  constant ;  this  was  especially  the  case  with  iodo- 
form cement.  Amalgams  and  phosphates  gave  quite  constant  results. 
The  tests  with  some  of  the  materials  were  made  over  twenty-five 
times ;  with  others,  such  as  copper  amalgams,  where  there  was  no 
doubt  as  to  the  result,  only  a  few  experiments  were  made. 

Caries  of  the  teeth,  except  in  the  later  or  last  stage,  is  the  result  of  a 
ferment  process,  and  the  organisms  found  in  the  deeper  parts  of  decay- 
ing dentine,  which  I  have  isolated  and  obtained  in  pure  culture,  are  fer- 
ment organisms.  The  decomposition  of  the  pulp  and  contents  of  the 
root-canal,  attended  by  bad-smelling  products,  is,  on  the  other  hand,  a 
putrefactive  process  in  which  entirely  different  species  of  fungi  are  con- 
cerned. Whether  or  not  the  results  which  I  have  obtained  for  the  fungi 
of  caries  would  apply  equally  well  to  those  putrefactive  fungi  is  a  ques- 
tion which  can  be  settled  only  by  experiment  upon  pure  cultures  of  the 
same. 

Although  I  have  now,  as  I  think  will  be  granted,  established  upon  a 
sure  basis  the  fact  that  caries  of  the  teeth  may  result  directly  from  the 
action  of  acid-producing  fungi  in  the  presence  of  fermentable  carbo- 
hydrates, the  conclusion  would  hardly  be  justifiable  that  by  keeping 
the  mouth  constantly  and  perfectly  free  from  all  fermentable  substances, 
or  by  repeated  application  of  antacids  or  antiseptics  to  all  parts  of  the 
teeth,  or  by  all  these  means  together,  we  could  ever  banish  dental  caries 
from  the  oral  cavity.  A  most  powerful  influence  which  we  do  not  well 
understand  is  exerted  by  the  nutritive  processes  in  the  teeth  themselves. 

I  am  assured  by  men  who  have  grown  old  in  the  practice  of  dentistry 
that  mouths  which  have  long  been  under  their  observation,  and  which 
practically  have  been  completely  free  from  caries  for  years,  at  once,  on 
account  of  some  sudden  change  of  health,  show  a  general  breaking  down 
or  crumbling  of  the  teeth  en  masse  in  the  space  of  a  few  weeks.  It  has 
also  been  my  ex])erience  that  ]iatients  Avho  have  been  dismissed  by  their 
dentists  in  America  with  the  assurance  that,  according  to  previous  expe- 
rience, their  dentures  Mould  require  no  treatment  for  one  or  two  years, 
have  come  to  me  a  few  weeks  later  with  teeth  looking  as  though  they 
had  not  been  under  the  hands  of  a  dentist  for  years.  Some  say  the 
ocean-voyage  spoiled  their  teeth  ;  others  attribute  it  to  a  change  in 
the  climate,  food,  health,  etc. 

At  any  rate,  we  have  here  a  cause  which  lies  without  the  domain  of 
both  bacteria  and  acids  (either  ferment  or  otherwise).  The  lime  salts  of 
the  teeth  are  supposed  to  form  with  the  organic  matter  of  the  tooth  a 
definite  chemical  compound,  and  it  is  probal)ly  due  to  this  fact  that  sim- 
ple salts  of  lime  are  so  nnich  more  readily  soluble  in  weak  acids  than 
pulvcri/X'd  tooth-})one,  or  tiiat  the  tartar  upon  the  teeth  is  so  much  more 
easily  soluble  than  the  teeth  themselves ;  so  that  when  any  one  rinses 
his  mouth  with  vinegar,  and  afterward  finds  lime  in  the  vinegar,  we 
know  that  the  lime  in  by  far  the  greater  part — if,  indeed,  we  may  not 
say  altogether — came  from  the  tartar.  Now,  though  there  is  no  posi- 
tive evidence  for  the  supposition,  it  is  cei*tainly  not  altogether  improb- 


FERMENTATION  IN  THE  HUMAN  MOUTH.  813 

al)le  that,  as  a  consequence  of  certain  derangements  in  the  nutritive 
functions  of  the  teeth  resulting  from  a  change  of  health,  etc.,  etc.,  a  dis- 
solution of  the  affinity  between  the,  lime  salts  and  the  organic  matter 
mav  take  place,  thus  setting  free  the  easily  soluble  lime  salts,  which  are 
then  carried  away  in  solution  or  washed  out  mechanically.  This  is  a 
supposition  only,  which  I  bring  forward  because  facts  in  this  case  are 
absolutely  wanting.  If  it  should,  perchance,  contain  a  trace  of  truth, 
then  adult  and  pulpless  teeth  should  be  less  subject  to  these  sudden 
attacks  of  caries  than  young  teeth  with  living  pulps. 

There  still  remains  much  hard  work  to  be  done  before  the  subject  of 
dental  caries  may  be  dismissed  as  having  received  a  final  solution  in  all 
its  different  phases.  There  are  men  enough  in  the  profession,  however, 
w^ho  are  willing  to  work,  and  who  do  not  shrink  from  the  tasks,  yet  to 
be  performed. 

The  Fungi  of  Dental  Caries  :   Their  Pure  Cultivation  and 
Effect  upon  Lower  Animals. 

In  the  preceding  pages  will  be  found  the  description  and  illustrations 
of  two  species  of  micro-organisms  obtained  from  carious  dentine.  These 
species  I  isolated  by  inoculating  culture  liquids  with  very  small  pieces 
of  carious  dentine  taken  from  near  the  border  of  the  normal  tissue.  If 
the  fungus  was  not  at  once  obtained  in  tlie  pure  state,  a  second  culture 
tube  was  inoculated,  after  the  method  of  fractional  culture,  with  a  min- 
imum portion  of  the  first,  and  so  on.  It  soon,  however,  became  appar- 
ent that  the  capture  of  these  two  species  by  no  means  ended  the  work ; 
on  the  other  hand,  new  forms  continually  presented  themselves,  and,  in 
order  to  be  able  to  determine  definite  characteristics  for  each  species, 
resort  was  had  to  the  culture  on  plates  of  gelatin  prepared  with  beef 
extract,  calf's  broth,  malt  decoction,  etc. 

The  beef-extract  gelatin,  for  example,  I  prepare  as  follows :  200  c.c. 
water  +  3.0  beef  extract  +  3.0  sugar  are  first  neutralized,  then  slowly 
boiled  for  five  minutes  and  filtered  (filter  and  all  other  vessels,  of  course, 
sterilized).  After  cooling,  8.0  of  the  finest  gelatin  is  added  and  grad- 
ually heated  till  the  gelatin  is  dissolved  ;  it  is  then  cleared  with  the 
white  of  an  e^g,  and  all  together  kept  at  the  boiling-point  for  about  five 
minutes,  stirring  constantly  to  prevent  burning;  it  is  then  passed  through 
a  filter  surrounded  by  a  bath  of  boiling  Avater  into  gla&s  tubes  with  cot- 
ton stoppers  (both  sterilized),  and  kept  in  a  refrigerator.  When  to  be 
used,  it  is  melted  in  warm  water  and  poured  upon  sterilized  cold  glass 
plates,  which  may  be  0.15  m.  long  by  0.07  m.  wide,  and  placed  in  the 
moist  chamber.     The  layer  of  gelatin  should  be  about  2  mm.  thick. 

Suppose,  now,  we  have  a  culture  containing  diiferent  species  of  fungi 
and  we  wish  to  separate  them.  A  thin  platinum  wire  with  one  end 
melted  into  a  glass  rod  is  sterilized  in  the  flame  of  a  Bunsen  burner, 
and  on  cooling  dipped  into  the  impure  culture  and  lightly  drawn  across 
the  surface  of  the  gelatin  ;  the  fungi  which  adhered  to  the  platinum 
wire  are  thereby  scattered  in  a  row  upon  the  surface  of  the  gelatin,  and 
in  a  short  time  we  will  find  that  at  certain  points  in  the  row  one  form 
of  fungus  has  developed  and  at  other  points  other  forms.     Now,  if  we 


814 


DENTAL   CARIES. 


take  upon  the  end  of  our  platinum  wire  a  small  quantity  of  fungi  from 
one  of  these  points  and  draw  it  across  the  surface  of  a  second  plate,  we 
will  in  parts  of  this  line  invariably  obtain  a  pure  culture  of  one  of  the 
species  in  the  original  impure  culture,  nearly  every  species  being  dis- 
tinguished by  some  characteristic  in  the  form  which  it  takes  in  growing 
and  in  its  action  upon  the  gelatin.  Having  obtained  a  pure  culture  in 
this  manner,  test-tubes  containing  gelatin  are  inoculated  M'ith  it.  In 
these  it  may  be  kept  in  a  pure  state  for  weeks  or  months,  while  the 
plates  are  always  short-lived. 

The  gelatin  method  of  pure  culture  has  one  great  disadvantage  in 
the  low  melting-point  of  the  gelatin  :  24°  to  25°  C.  is  the  highest  tem- 
perature to  which  they  can  be  exposed  without  danger 
of  melting,  and  this,  to  fungi  which  are  accustomed  to 
a  temperature  of  37°  C,  is  not  always  a  matter  of 
indifference.     I  have  succeeded  in  isolating  three  spe- 
cies   besides    the    ones   previously   described    (see    p. 
802),    and — only    for    the    purpose    of    distinguishing 
them — I  will  designate  them  by  the  Greek  letters  y,  o, 
and    £.     These    fungi    are  shown    in   Figs.   420,  421, 
and  425.     In  Fig.  419  I  have  reproduced  the  fungus 
described  on  page  802  as  a  caries  fungus,  for  the  sake  of  comparison. 
When  the  species  a,  y,  and  o  are  isolated,  it  is  not  difficult  to  tell  one 

from  the  other ;  Mhen,  however. 
Fig.  421.  they  are  mixed  together,  it  is  next 

^^%g  @f®  &    to  impossible  to  determine  which 

VJ*^^^^'      *^  which,  and   especially  is   this 


Fig.  420. 


:t 


"'n 


Fig.  422. 


the  ca.se  with  a  and  y.  Their 
modes  of  development  on  gelatin 
are,  however,  so  different  that  we 
possess  therein  a  ready  means  of 
distino;ui.shino;  between  them.  The 
a-fungus,  sparingly  inoculated 
into  gelatin  tubes,  presents  in  a  few  days  the  appearance  which  I 
have  attempted  to  represent  in  Fig.  422.     It  may  be  compared  to  a 

bunch  of  grapes  which  pre- 
FiG.  423.  Fig.  424.        sents  all  gradations  from  the 

fully-developed  berry  to  the 
little  green  one ;  the  masses 
of  fungi  are  globular  or 
ovoid,  exceedingly  fine,  and 
semi-transparent,  presenting 
altogether  a  strikingly  beau- 
tiful culture  which  it  is  im- 
possible to  even  approx- 
imately represent  by  draw- 
ing. It  furthermore  forms 
a  button  upon  the  surface 
of  the  gelatin ;  the  latter 
becomes  softened,  but  not 
liquefied.     On  the  plates  it 


.     FERMENTATION  IN  THE  HUMAN  MOUTH.  815 

presents  soft,  milky  ridges  or  knots  raised  sometimes  a  millimeter  above 
the  surface  of  the  gelatin  and  obtaining  a  width  at  the  base  of  3  to  6 
mm.  The  y-fungus  differs  from  all  other  fungi  that  I  have  yet  found 
in  decaying  dentine  in  tliat  it  completely  liquefies  the  gelatin.  The  cul- 
ture tubes  present,  therefore,  a  funnel-shaped  area  of  liquefied  gelatin, 
while  the  fungi  themselves  fall  to  the  bottom  of  the  funnel.  (See  Fig. 
423.) 

This  fungus  forms  furrows  in  the  plates ;  and  if  the  plate  is  turned 
on  its  edge,  the  w^hole  mass  of  fungus  flows  from  one  end  of  the  furrow 
toward  the  other  or  slides  quite  off  the  plate. 

The  o-fungus  (Fig.  421)  forms  completely  opaque  masses  wdiich  may 
have  a  slight  yellowish  tinge,  provided  the  gelatin  itself  is  yellowish. 
It  has  a  small  surface-growth  and  liquefies  the  gelatin  only  to  a  slight 
extent.  In  cultures  on  plates  which  are  two  or  three  days  old,  the  row 
of  fungus  appears  to  lie  in  a  trough  or  depression  in  the  gelatin.  It 
does  not  move,  however,  when  the  plate  is  turned  on  edge.  (See  Fig. 
424.) 

For  the  funo-us  of  Fio;.  425  I  have  not  yet  been  able  to  establish 
definite  peculiarities  of  growth.     As  far  as  my  observations  have  at 
present  extended,  it  differs  from  that  of  Fig. 
421   in  that  it  is  almost  entirely  wanting  in  ^^^-  "^^S. 

surface-growth    and    forms    colorless    masses         iJ^C*  ^'*'-v        \> 
even  in  colored   media.     It  does    not  liquefy     ^1^   vV?**    "^^1'''*'^"' 
the  gelatin.     Viewed  by  transmitted  light,  it         lOi^"*      |        ^^-,4 
appears  to  have  a  bluish  tinge  and  a  slight         >^    ^    ^         \\ 
opalescence.     It  grows,  however,  very  slowly,         '^*      V  *' 

and  I  have  consequently  as  yet  been  unable  to         ,,1' 
establish  certain  and  definite  characteristics  for 

it.  The  fungus  described  on  page  802  grows  still  more  slowly  at  gel- 
atin temperature,  and  I  cannot  at  present  give  any  microscopical  feat- 
ures by  which  cultures  on  gelatin  may  be  distinguished. 

The  most  important  feature  connected  with  all  these  fungi,  especially 
the  coccus-forms,  is  that  they  possess  a  ferment  activity — in  other  words, 
they  are  capable  of  producing  acid  out  of  sugar,  or,  in  the  human  mouth, 
out  of  starch,  by  the  aid  of  the  diastatic  action  of  the  saliva.  They  may 
consequently  all  be  looked  upon  as  factors  in  the  decay  of  the  teeth.  I 
Avould  not  venture  to  say  that  the  «-fungus  is  more  concerned  in  the 
process  of  caries  than  all  the  rest  together ;  nevertheless,  such  is  the 
constancy  with  which  I  have  found  it  that  if  any  one  else  should  make 
the  assertion  I  would  have  no  reason  for  contradicting  him.  Cultivated 
in  liquid  substrata,  none  of  them  form  films  or  skins  upon  the  surface 
of  the  liquid,  but  powdery  or  fleecy  precipitates  upon  the  bottom  and 
sides  of  the  vessel.  NoneJ  so  far  as  I  have  observed,  produce  an  evolu- 
tion of  carbonic  acid  in  solutions  containing  sugar,  nor  do  they  appear 
to  suffer  when  the  access  of  oxygen  is  restricted. 

A  question  of  great  importance  not  only  for  dentists,  but  for  general 
physicians — and,  in  fact,  for  everybody — is  that  relating  to  the  ])ossible 
pathogenic  nature  of  these  fungi.  We  find  in  the  works  of  Leyden  and 
Jaffe,  Haussman,  Bollinger,  James  Israel,  etc.,  sufficient  ground  for  the 
statement  that  "  these  fungi,  in  all  parts  of  the  human  body  which  they 


816  DENTAL   C ARIES. 

reach,  can  play  the  same  malignant  role  as  upon  the  teeth."  Gangrene 
of  the  lungs^  abscesses  of  the  mouth  and  throat,  chronic  pyaemia,  etc.,  etc. 
have  bv  various  authors  been  ascribed  to  the  action  of  the  fungi  of  the 
human  mouth.  Raynaud,  Lannelongue,  and  Pasteur  produced  what 
they  called  maladie  nouveUe  by  inoculating  rabbits  with  the  saliva  of  a 
child  bitten  by  a  mad  dog,  and  A.  Fraenkel  has  in  a  number  of  cases 
produced  sputum-septicaemia  by  inoculating  rabbits  with  his  own  saliva. 

We  ask  ourselves,  then,  the  question,  ]\Iay  not  many  of  our  obscure 
cases  of  infectious  disease  which  now  and  then  appear  after  extraction 
or  other  dental  operations,  and  which  are  without  further  examination 
attributed  to  the  unclean  instruments  or  hands  of  the  dentist,  be  the 
result  of  an  infection  produced  by  micro-organisms  in  the  patient's  own 
mouth?  If  a  man's  saliva  contains  organisms  which  when  brought  into 
the  blood  of  a  rabbit  occasion  death  in  twenty-four  hours,  would  it  be 
a  matter  of  no  consequence  to  produce  so  large  a  wound  in  his  mouth 
as  that  caused  by  the  extraction  of  a  tooth  ?  For  the  purpose,  if  pos- 
sible, of  throwing  some  light  upon  this  question,  I  have  undertaken  a 
series  of  experiments  for  determining  whether  the  organisms  which  are 
most  commonly  found  in  the  human  mouth  possess  the  power  of  pro- 
ducing death  (by  septicaemia  or  otherwise)  by  inoculation.  These  exper- 
iments, as  well  as  the  others  recorded  in  this  article,  I  have,  in  fact,  only 
begun.  My  absence  from  lijome,  however,  prevents  my  carrying  them 
on  during  the  summer  months,  and  I  have  determined,  therefore,  to  pre- 
sent the  results  which  I  have  already  obtained,  few  and  imperfect  as  they 
are.  » 

The  inoculations  have  thus  far  been  performed  on  three  rabbits,  one 
rat,  and  six  white  mice.  They  were  made  partly  with  a  mixture  of  the 
two  fungi  a  and  y,  and  partly  with  saliva  which  had  been  kej^t  in  ster- 
ilized calf's  broth  for  fifteen  hours  at  blood-temperature. 

Each  rabbit  received  1  c.c.  of  the  infected  liquid,  injected  directly  into 
the  lung  or  abdominal  cavity ;  the  rat  0.2  c.c,  and  the  mice  0.1  c.c. 

Exj).  1.  Small  rabbit  inoculated  with  1  c.c.  in  the  abdominal  cavity : 
In  the  course  of  a  few  hours  the  rabbit  appeared  evidently  ill,  refused 
to  eat,  and  remained  quiet  in  the  corner  of  the  cage.  In  twenty-four 
hours  diarrhcca  appeared,  with  a  slight  elevation  of  temperature.  These 
svmptoms  increased  during  the  next  day,  till  fifty  hours  after  the  time 
of  inoculation  it  was  found  at  the  point  of  death.  The  examination 
showed  the  blood  to  be  almost  entirely  free  from  organisms  and  no 
indication  of  septicaemia.  Living  fungi  were  found,  however,  in  the 
abdominal  cavity,  and  a  large  part  of  the  right  lobe  of  the  liver  was 
completely  riddled  with  masses  of  fungi ;  also  in  the  faeces  were  found 
enormous  numbers,  which  morphologically  were  identical  with  those  in 
the  liver,  their  entrance  into  the  alimentary  canal  from  the  liver  being 
easily  accom])lislied.  I  unfortunately  neglected,  however,  to  establish 
their  identity  by  the  proper  cultures. 

Exp.  2.  Rabbit  inoculated  as  in  Exp.  1  :  The  animal  manifested  a 
slight  indisposition  on  the  second  day,  from  which  it  soon  recovered. 

Exp.  3.  Rabbit  inoculated  in  the  right  lung  Avith  saliva  M'hich  had 
been  kept  in  sterilized  calf's  broth  for  fifteen  hours  at  37°  C.  :  No 
eifect  apparent. 


FERMENTATION  IN  THE  HUMAN  MOUTH.  817 

Exp.  If..  White  rat,  injection  in  abdominal  cavity :  The  animal 
remained  well, 

Exps.  5—11.  Seven  white  mice ;  five  inocnlated  in  abdominal  cavity 
with  a-  and  }/-fungi ;  two  in  the  lungs  with  saliva  in  calf's  broth  :  Of 
the  former  two  died  at  about  the  fortieth  hour  under  the  same  symp- 
toms as  in  Exp.  1.  Great  numbers  of  fungi  were  found  in  the  abdom- 
inal cavity,  which  by  culture  on  gelatin  proved  to  be  the  y-fungus.  A 
number  of  colonies  were  likewise  found  in  the  liver.  Microtome  sec- 
tions of  the  liver  of  the  rabbit  stained  in  fuehsin  show,  when  examined 
under  the  microscope  with  sufficient 
liglit  to  drown  the  tissue,  a  distribution  Fig.  426. 

of  the  fungi  verv  similar  to  that  often  srw    /^^^^ 

seen  in  the  outermost  layei's  ot  carious      ^  —^     ^.Tiji-   "    '      " 
dentine.    (See  Fig.  426.)     Of  course  no       Jt'l''^'^   i'  jA 

definite  conclusion  can  be  drawn   from        ''""V''  '     .. 

a  few  experiments.     They  are,  however,  .  .      ^      .    '  i,; 

sufficient  to  show  that  these  fungi  cer-        i^  %    l*-'^? 

tainly  do  possess  a  pathogenic  character,     ■%^.  %     ^C^^'    ^ 
and  when   brought  into  other  parts  of        %'\^   ,^  ^  a  %        ik 
the    human   bodv   mav   be  able,   under  ^   ''b  mM     \    0? 

predisposing  conditions,  to  produce  dis-  ^  ^' 

astrous  results.  Especially  the  contin- 
ual swallowing  of  these  fungi  in  great  numbers  may  by  their  ferment 
activity  alone  in  the  course  of  time  produce  very  serious  derangements 
of  the  stomach  and  alimentary  canal,  since  the  small  percentage  of 
hydrochloric  acid  in  the  stomach,  even  in  the  presence  of  the  normal 
quantity  of  pepsin,  is  not  sufficient  to  devitalize  them.  It  was  with  a 
certain  degree  of  satisfaction  that  I  have  failed  thus  far  to  find  the 
coccus  of  sputum-septicaemia  in  my  own  saliva.  It  is,  however,  very 
desirable  that  experiments  should  be  made  with  the  saliva  of  many  per- 
sons, for  the  purpose,  if  possible,  of  determining  in  what  proportion  of 
eases  this  fungus  is  present. 

Messrs.  Underwood  and  Milles  have  endeavored  to  repeat  some  of 
my  earliest  experiments  in  the  production  of  artificial  caries,  but,  under 
those  very  abnormal  conditions  against  which  I  entered  warning  in  the 
Lidependent  Practitioner,  failure  was  the  necessary  result.  They  per- 
formed, further,  a  very  elaborate  experiment,  lasting  six  months,  in 
which  the  baths  became  so  putrid  and  offi^nsive  that  "  they  quit  the 
experiment  with  relief."  They  naturally  produced  no  caries,  thereby 
furnishing  an  admirable  confirmation  of  the  fact  to  which  I  have  so 
often  called  attention — that  it  is  impossible  to  produce  even  a  trace  of 
caries  by  putrefaction  alone.  •  They  tried  a  third  experiment,  putting 
the  fungi  under  such  abnormal  conditions  that  they  could  not  produce 
acid,  and  of  course  failed  again,  once  more  confirming  the  fact  that  I 
have  long  since  estal^lished — that  we  can  have  no  caries  without  acid. 
With  these  experiments  they  risk  the  statement  that  artificial  caries  is 
probably  an  impossibility.  The  production  of  artificial  caries  is  a  fait 
arcompli,  and  to  deny  its  possibility  is  only  to  endanger  the  reputation 
of  him  who  denies.  They  state  further  that  they  can  find  no  softened 
dentine  which  does  not  contain  micro-organisms.    This,  however,  is  con- 

VoL.  I.— 52 


818  DENTAL   CARIES. 

trary  to  the  experience  of  a  great  many  American  microscopists,  and, 
moreover,  as  I  have  elsewhere  stated,  I  shall  take  with  me  to  the  next 
meeting  of  the  American  Dental  Society  of  Europe  several  hundreds  of 
specimens  of  carious  dentine,  and  be  ready  to  show  the  areas  of  softened, 
non-infected  dentine  on  any  one  or  on  all  of  them. 

Messrs.  Underwood  and  ]\Iilles  understand  me,  in  the  third  place,  as 
being  of  the  opinion  that  all  the  micro-organisms  connected  with  caries 
of  the  teeth  are  only  different  forms  of  one  fungus.  The  readers  of  the 
Independent  Practitioner  know  better.  I  have  stated  simply  that  one 
of  the  many  fungi  found  in  the  human  mouth  in  connection  with  caries 
of  the  teeth  may  produce  different  forms  of  development.  This  is  the 
fungus  which  I  have  designated  by  the  prefix  /?.  It  is  scarcely  neces- 
sary to  add  that  I  am  ah\'ays  prepared  to  prove  its  existence  micro- 
scopically, as  well  as  on  the  authority  of  many  of  the  best  mycologists 
of  Germany. 

No  one,  I  think,  will  deny  that  wuthin  the  last  few  years  I  have  done 
a  large  amount  of  work  and  contributed  some  evidence  toward  the  solu- 
tion of  the  problem  of  dental  caries.  The  amount  of  material  dealt  with 
and  the  ground  gone  over  have  been  so  extensive  that  it  has  been  abso- 
lutely impossible,  with  the  greatest  efforts,  to  remain  as  long  by  each 
step  as  would  have  been  desirable.  It  may  be,  therefore,  that  at  some 
points  the  subject  has  not  been  presented  with  sufficient  clearness  or 
decisiveness ;  it  may  be,  too,  that  at  some  points  the  conclusions  have 
been  faulty,  since  I  make  no  pretension  to  infallibility.  Time  will  show 
whether  this  is  the  case.  At  present  I  know  of  no  important  change 
wdiich  I  could  make  if  I  were  to  rewrite  all  my  contributions  of  the  last 
three  years. 

I  desire  to  give,  in  closing,  a  very  short  resume  of  the  work  which  I 
have  accomplished : 

1 .  I  convinced  myself  by  the  examination  of  some  thousands  of  slides 
of  carious  dentine  that  micro-organisms  were  always  present,  and  that 
they,  without  any  doubt,  were  the  cause  of  various  anatomical  changes 
which  Avere  found  to  take  place  in  the  structure  of  the  dentine  during 
caries.  (Here,  of  course,  the  question  of  priority  does  not  suggest  itself: 
Leber  and  Rottenstein,  as  is  well  known,  were  the  first  to  give  definite 
expression  to  this  fact.) 

2.  I  proved,  at  the  same  time,  that  the  invasion  of  the  micro-organ- 
isms was  not,  in  the  majority  of  cases,  simultaneous  with  the  softening 
of  the  dentine,  but  that  large  areas  of  softened  dentine  could  be  found 
that  contained  no  fungi.  Of  all  those  who  examined  my  preparations 
in  America,  no  one,  whatever  his  theory,  ever  once  denied  this  fact.  I 
concluded  from  this  that  the  softening  of  the  dentine  went  in  advance 
of  the  invasion  of  the  organisms. 

3.  I  determined  by  analyses  of  masses  of  carious  dentine  sufficiently 
large  to  give  reliable  results  that  the  softening  of  the  dentine  is  of  the 
nature  of  a  true  decalcification ;  that  the  decalcification  of  the  outer 
layers  is  almost  complete  and  diminishes  in  degree  as  we  advance 
toward  the  normal  dentine ;  furthermore,  that  the  same  relations 
maintain  in  dentine  softened  in  a  mixture  of  saliva  and  bread  or  in 
weak  organic  acids ;  also,  that  in  a  mass  of  carious  dentine  the  lime 


BIOLOGICAL  STUDIES  ON  FUNGI  OF  HUMAN  MOUTH.       819 

salts  had   been  removed  to  a  much  greater  extent  than   the  organic 
matter. 

4.  I  maintained  from  the  first  that  the  softening  of  the  dentine  was 
produced  by  acids  for  the  most  part  generated  in  the  mouth  by  fer- 
mentation.    I  had,  however,  no  direct  proof  of  this. 

5.  I  proved  that  fungi  exist  in  great  numbers  in  the  human  saliva 
and  in  carious  dentine  which  have  the  power  to  produce  acid  under 
conditions  which  are  constantly  present  in  the  human  mouth.  I  deter- 
mined this  acid — for  one  of  the  fungi,  at  least — to  be  the  ordinary 
ferment,  lactic  acid. 

6.  I  produced  caries  artificially  which  under  the  microscope  cannot 
be  distinguished  from  natural  caries  by  subjecting  sound  dentine  to  the 
action  of  these  fungi  in  fermentable  solutions. 

7.  I  determined  the  influence  of  various  antiseptics  and  filling  mate- 
rials upon  the  fungi  of  caries. 

8.  I  isolated  various  forms  of  these  fungi  and  determined,  in  part,  the 
conditions  most  favorable  to  their  development,  their  characteristic  reac- 
tion upon  gelatin,  their  physiological  action,  their  effect  when  inoculated 
into  the  system  of  lower  animals,  and  their  possible  connection  with  cer- 
tain obscure  diseases  generally  attributed  to  the  carelessness  of  the  dentist. 

My  continual  search  has  been  after  facts,  and  such  facts  as  I  have 
obtained  I  have  presented  before  the  profession,  never  putting  before 
them  either  theory  or  speculation,  nor  anything  which  was  not  the  result 
of  severe  and  continued  labor ;  and  in  this  spirit  I  propose  to  prosecute 
this  work,  as  well  as  any  other  that  I  may  undertake  in  the  interest  of 
the  profession. 

Berlin,  May  21,  1884. 

Note. — Since  writing  the  above  I  have  succeeded  in  producing  death  by  septicfemia 
of  both  mice  and  rabbits  by  injecting  into  the  lung  saliva  from  the  mouth  of  a  per- 
fectly healthy  person. 


BIOLOGICAL  STUDIES  ON  THE  FUNGI  OF  THE  HUMAN 

MOUTH/ 

In  order  to  be  able  to  determine  upon  the  proper  course  to  be  taken 
in  the  attempt  to  remove  or  check  the  progress  of  any  disease,  it  is 
necessary  that  our  ideas  of  the  cause  and  course  of  that  affection  be 
established  upon  the  most  certain,  exact,  and  scientific  data  which  we 
are  capable  of  attaining.  Unfortunately  for  the  dental  profession,  the 
attempt  to  furnish  a  scientific  solution  of  the  problems  of  dental  caries 
has  until  recently  been  confined  to  a  very  few,  and  even  now  a  majority 

'  German  mycologists  use  the  term  P'dz  indiscriminately  to  designate  either  schizo- 
mycetes,  blastomycetes,  hyphomycetes  or  myxomycetes.  When  it  is  desirable  to  refer 
to  any  one  of  these  groups  in  particular,  they  use  the  prefixes  Spall,  Sproi^s,  Srhimmel 
or  Fadpn,  and  Schhiin,  giving  Sp'iltpih,  Sprof^f^pilz,  Schimmel-  or  Fadenpiiz,  and  Schhim- 
pilz.  Following  their  example,  I  have  in  previous  papers  used  the  term  "fungus"  for 
all  of  the  four  groups  of  mycetes  mentioned  above,  and  shall  also  use  the  term  in  this 
paper,  in  which  only  schizomycetes  are  treated  of. 


820  DENTAL   CARIES. 

of  the  investigators  in  dental  pathology  are  content  to  restrict  tlieir 
observations  to  the  clinical  aspect  of  the  question — a  course  which 
could  never  produce  a  satisfactory  solution — while  others  even  openly 
advocate  a  speculative  course  and  do  not  hesitate  to  ascribe  to  every  new 
factor  discovered  in  nature  a  role  in  the  production  of  caries  of  the  teeth. 
Consequently,  we  have  had  presented  to  us,  in  turn,  worms,  acids,  inflam- 
mation, electricity,  infusoria,  bacteria,  putrefaction,  toxic  agents,  etc.,  etc., 
as  causes  or  conditions  of  caries  dentinuin,  some  of  these  theories  con- 
taining some  truth  and  some  a  surprising  amount  of  absurdity.  In  the 
last  two  or  three  years,  however,  a  great  advance  has  been  made  in  the 
methods  of  study  and  a  number  of  important  points  have  been  firmly 
established : 

1.  The  observation  of  Leber  and  Rottenstein  that  micro-organisms 
are  constantly  present  in  decaying  dentine  has  been  confirmed  (Weil, 
Milles,  Underwood,  Miller). 

2.  The  softening  of  dentine  in  caries  has  been  shown  to  be  chemically 
identical  with  that  produced  by  certain  weak  organic  acids  (Miller,  Jese- 
rich,  Bennefeld). 

3.  It  has  been  established  that  various  organisms  found  in  the  human 
mouth  produce  the  decalcifying  acid  by  first  converting  non-fermentable 
sugars  into  fermentable  varieties,  and  secondly  by  splitting  fermentable 
sugars  into  lactic  acid  (Miller,  Hueppe). 

4.  The  same  organisms  have  been  found  capable  of  dissolving  decal- 
cified dentine,  while  they  have  no  apparent  effect,  even  after  two  or  three 
years,  on  sound  dentine  (Miller). 

5.  Caries  of  dentine  chemically  and  morphologically  identical  with 
natural  caries  has  been  produced  outside  of  the  mouth  (Miller). 

6.  It  has  been  furthermore  shown  that  certain  of  the  organisms  of 
the  human  mouth  are  capable  of  developing  under  exclusion  of  air, 
thus  making  it  possible  for  them  tg  propagate  within  the  substance  of 
the  dentine  (Miller,  Hueppe). 

I  propose  to  describe  in  the  following  pages  a  series  of  experi- 
ments made  for  the  purpose  of  obtaining  more  definite  information 
respecting  the  number  and  morphology  of  the  fungi  of  the  human 
mouth,  and  their  physiology,  as  far  as  is  necessary  to  an  understanding 
of  the  part  which  they  may  perform  in  the  production  of  caries  of  the 
human  teeth. 

At  the  meeting  of  the  American  Dental  Association  at  Saratoga  a 
number  of  tubes  containing  pure  cultures  of  fungi  were  passed  around  ; 
with  regard  to  these  a  reporter  remarked  that  "  they  were  evidently 
beyond  the  information  of  the  majority."  It  is  not  very  flattering  to 
American  dentistry  if  its  representative  association  allows  a  question  of 
so  great  imjiortance  to  remain  beyond  its  comprehension,  nor  is  there 
any  excuse  for  such  a  condition  of  things  now,  so  widespread  have  the 
methods  of  jTTU'e  culture  become.  I  rather  incline  to  the  opinion  that 
the  reporter  misinterpreted  the  apathy  of  the  members  of  the  society. 
I  siiall,  at  any  rate,  here  describe  in  a  few  words  the  methods  now  uni- 
versally employed  in  isolating  any  given  fungus,  and  then  more  in  detail 
give  tlie  means  Avhich  I  have  used  to  ascertain  the  physiological  charac- 
teristics of  the  different  fungi  when  obtained  in  pure  culture. 


BIOLOGICAL  STUDIES  ON  FUNGI  OF  HUMAN  MOUTH.       821 

We  will  start  with  a  solution  densely  impregnated  with  micro-organ- 
isms and  a  number  of  tubes  of  culture  gelatin  perfectly  sterilized.  The 
gelatin  being  melted,  we  add  to  the  first  tube  one  bead  (on  a  loop  of 
sterilized  platinum  wire)  of  the  solution  ;  this  is  called  the//-s^  dilution. 
From  this  tube  we  add  two  or  three  beads  to  a  second  tube  (second  dilu- 
tion), and  from  the  second  five  or  six  beads  to  a  third  tube  (tJdrd  dilu- 
tion). The  gelatin  is  then  poured  upon  horizontally  placed  sterilized 
cold  glass  plates.  It  congeals  in  a  few  seconds,  and  the  three  plates  are 
placed  in  a  pile  (on  glass  benches)  in  a  moist  cell.  The  plates  are  exam- 
ined after  twenty-four  to  thirty-six  hours  under  a  magnification  of  100 
diameters.  By  this  means  the  fungi  are  so  separated  that  on  the  third 
plate  there  will  generally  not  be  more  than  two  to  ten  (on  the  second 
there  may  be  one  hundred  or  two  hundred,  while  on  the  first,  of  course, 
there  are  very  many  more).  As  each  micro-organism  develops,  being 
fixed  in  the  gelatin,  we  will  have  at  that  point  a  pure  culture  of  that 
particular  kind ;  at  another  point  we  obtain  a  colony  of  a  second  kind ; 
and  so  on.  In  general,  colonies  of  different  fungi  may  be  distinguished 
with  the  greatest  ease  by  their  microscopic  appearance.  With  a  steril- 
ized platinum  wire  bent  at  right  angles  at  the  end  we  now  pick  up  a 
number  of  the  colonies  of  each  kind  under  the  microscope  (100  diam- 
eters), and  transfer  them  directly  to  tubes  of  culture  gelatin,  only  one 
colony  to  each  tube.  We  have  then  (except  in  case  of  a  possible  acci- 
dental air-infection)  pure  cultures.  Some  experience  is  necessary  to 
enable  one  to  pick  up  the  colonies  under  the  microscope.  Beginners 
should  not  attempt  it  with  plates  where  more  than  one  colony  is  in  the 
field  at  once. 

The  method  described  on  page  813  may  also  sometimes  be  used  to 
great  advantage.  For  fungi  which  do  not  grow  on  gelatin,  agar-agar  or 
congealed  blood-serum  should  be  used.  The  former,  1  to  1^  per  cent., 
has  a  higher  melting-point  than  gelatin,  10  per  cent.,  and  remains  solid 
at  the  temperature  of  the  human  blood.  When  it  is  used  for  plate-cul- 
tures, it  must  be  melted  in  hot  water  and  the  infection  made  at  a  tem- 
perature of  40°  to  42°  C.  Below  this  temperature  it  becomes  solid  and 
cannot  be  poured ;  above  it  the  germs  would  be  liable  to  suffer.  In 
other  respects  the  agar-agar  media  are  treated  as  the  gelatin.  Congealed 
blood-serum  cannot,  of  course,  be  poured  upon  plates.  It  is  prepared 
in  test-tubes  so  inclined  as  to  give  the  greatest  possible  surface,  and  a 
minimum  quantity  of  the  substance  containing  the  fungus  or  fungi 
spread  over  the  surface.  Having  obtained  a  pure  culture  of  any 
fungus,  the  points  to  be  determined   regarding    it  are  the  following : 

1.  Its  morphology  (bacillus,  spirillum,  micrococcus). 

2.  Is  it  movable  ?     Does  it  produce  spores  ? 

3.  What  are  its  growth-characteristics  on  various  media,  microscopi- 
cally and  to  the  naked  eye  ? 

4.  What  are  its  relations  to  oxygen  ? 

5.  Does  it  produce  fermentation  ?  If  so,  what  fermentation,  under 
what  conditions,  and  with  or  without  development  of  gas? 

6.  Does  it  cause  putrefaction  ? 

7.  Does  it  have  a  diastatic,  inverting,  or  peptonizing  action? 

8.  Has  it  a  J)athogenic  character? 


822  DENTAL  CARIES. 

9.  Does  it  produce  coloring-matter? 

10.  AVliat  is  its  susceptibility  to  the  action  of  the  various  antiseptics? 

The  first  and  second  of  these  questions  are,  of  course,  determined  by 
the  microscope  alone ;  the  third,  by  the  microscope  and  the  naked  eye 
combined  ;  the  fourth,  by  the  methods  described  on  page  814,  or  by 
placing  a  thin  strip  of  mica  upon  one  half  of  the  culture-plate  before 
the  gelatin  solidifies.  The  mica  then  adapts  itself  closely  to  the  surface 
of  the  gelatin,  excluding  the  air ;  and  if  the  fungus  requires  oxygen  for 
its  development,  the  colonies  beneath  the  mica  either  M'ill  not  develop  at 
all  or  they  will  be  very  small  compared  with  those  on  the  other  half  of 
the  plate,  their  growth  ceasing  as  soon  as  the  oxygen  in  the  gelatin  has 
been  consumed  (Koch).  The  fifth  point  is  answered  by  infecting  fer- 
mentable solutions  with  the  fungus  in  question,  placing  it  under  various 
conditions  of  temperature,  etc.,  and  determining  the  products  of  fermen- 
tation (if  any) ;  the  sixth,  by  analogous  methods  ;  the  seventh  question 
is  determined  by  the  action  of  the  fungi  upon  starch,  cane-sugar,  and 
albumen  (boiled  white  of  egg) ;  the  eighth,  by  experiments  on  animals  ; 
the  ninth,  by  the  appearance  or  non-appearance  of  color  in  the  vegeta- 
tion itself  or  in  the  surrounding  medium ;  the  tenth,  by  experiments 
that  will  readily  suggest  themselves.  Other  points  to  be  investigated 
will  be  mentioned  farther  on. 

Boiled  potato  is  a  medium  of  great  value  in  the  determination  of 
schizomycetes.  No  medium,  however,  requires  greater  care  in  prepara- 
tion and  after-treatment  than  this  in  order  to  obtain  satisfactory  results. 
Any  sound  potato  tvhich  does  not  become  laealy  or  crack  open  on  boiling 
will  do  for  the  purpose.  It  is  first  thoroughly  washed  and  brushed, 
and,  all  defective  spots  and  deep  eyes  being  removed,  it  is  placed  for 
one  hour  in  a  corrosive  sublimate  solution,  5  to  1000,  then  in  the  steam 
sterilizer  for  one-half  to  one  hour.  In  the  mean  time,  the  moist  cell  is 
sterilized  and  the  bottom  lined  with  filter-paper  wet  with  sublimate 
solution,  5  to  1000.  The  potatoes  are  while  hot  removed  from  the 
sterilizer  with  sterilized  forceps,  cut  into  halves  with  a  cold  sterilized 
knife,  and  placed  directly  upon  the  sublimate  paper  (the  cut  surface  up) 
and  the  cell  closed.  Potato-sections  prepared  in  this  way  should  remain 
unchanged  indefinitely.  When  the  potato  has  become  cool,  the  cover 
of  the  cell  is  carefully  removed  and  the  fungus  which  is  to  be  cultivated 
is  spread  upon  a  space  about  as  large  as  a  dime  in  the  centre  of  the  sec- 
tion. Fungi  which,  morphologically  as  well  as  in  their  reaction  upon 
gelatin,  agar-agar,  and  blood-serum,  show  no  appreciable  differences, 
may  sometimes  be  easily  distinguished  by  aid  of  the  potato  culture. 
The  potato  can  seldom  be  used  to  separate  fungi — /.  e.  to  prepare  pure 
culture.  It  is  chiefly  used  as  a  reagent  in  distinguishing  between  fungi 
already  in  pure  culture.  For  example,  all  comma  bacilli  yet  discovered 
grow  on  potato  excej>t  the  one  found  by  Dencke  in  old  cheese,  which 
does  not  develop  at  all  on  potato,  and  is  thereby  at  once  distinguished 
as  an  entirely  different  fungus. 

Eggs  may  often  be  used  to  great  advantage.  They  are  prepared  as 
follows  :  The  frenli  egg  is  placed  in  sublimate,  5  to  1000,  for  ten  min- 
utes, then  in  the  steam  sterilizer  for  one  hour.  The  cell  for  eggs  is 
prepared  as  for  potatoes,  except  that  a  sterilized  glass  plate  resting  on  a 


BIOLOGICAL  STUDIES  ON  FUNGI  OF  HUMAN  MOUTH.       823 

glass  bench  is  placed  in  the  bottom  to  support  the  egg-sections.  As  the 
eggs  must  be  handled  with  the  lingers,  the  hands  must  be  thoroughly- 
washed,  then  soaked  in  sublimate,  5  to  1000,  and  then  washed  again  in 
alcohol  absolutus,  to  remove  the  sublimate.  The  eggs  are  shelled  while 
still  hot  and  cut  into  two,  three,  or  four  sections.  They  are  vaccinated 
in  points  upon  the  M^iite ;  the  yellow  is  not  so  Avell  adapted  to  culture 
experiments,  since  it  cannot  be  cut  with  a  smooth  surface. 

I  always  keep  on  hand  sections  of  potato  and  egg,  also  tubes  of  gela- 
tin, agar-agar,  and  blood-serum  ;  and  when  in  my  practice  particularly 
good  material  or  anything  uncommon  presents  itself,  a  portion  of  it  is 
at  once  transferred  to  these  different  culture  media ;  so  that  it  is  pretty 
sure  to  develop  in  one  of  them,  at  least.  For  example,  I  have  several 
times  met  with  a  fungus  in  the  human  mouth  which  produces  a  yellow- 
ish coloring-matter,  and  which  absolutely  refuses  to  grow  on  anything 
which  I  have  tried  except  potato. 

By  use  of  the  methods  described  I  have  isolated  twenty-two  different 
fungi  from  the  secretions  or  deposits  of  the  human  mouth,  and  have 
endeavored  to  determine,  as  far  as  possible,  their  separate  peculiarities 
of  growth,  physiological  action,  etc.  It  will,  however,  at  once  suggest 
itself  to  every  one  that  a  thorough  study  of  twenty-two  different  fungi 
involves  an  enormous  amount  of  labor  and  might  constitute  almost  a 
life-task  for  one  experimenter.  The  task  is,  moreover,  rendered  still 
more  difficult  by  reason  of  the  fact  that  many  of  these  fungi  show  dif- 
ferences of  action  when  cidtivated  in  different  media,  rendering  the 
number  of  experiments  necessary  to  come  to  a  definite  conclusion  doubly 
great.  I  shall,  therefore,  not  attempt  to  present  an  exhaustive  treatment 
of  the  subject,  but  rather  an  introduction,  hoping,  at  the  same  time,  to 
establish  some  points  which  may  be  of  use  in  bringing  about  a  clearer 
understanding  of  the  factors  involved  in  the  production  of  dental 
caries. 

Regarding  the  first  point  to  be  considered — the  morphology  of  the 
fungi — it  is  not  at  all  necessary  to  enter  into  a  minute  description  of  all 
the  different  forms  here  presented ;  the  figures  will  give  a  sufficiently 
clear  idea  of  their  diversity  and  the  appearance  of  their  colonies  under 
a  low  power.  For  the  rest,  suffice  it  to  say  that  ten  of  them  are  micro- 
or  dijilococci,  •five  are  bacteria,  and  six  bacilli.  Some  show  more  than 
one  form  of  development.  It  would,  however,  lead  us  too  far  from 
our  subject  to  discuss  this  fact  here. 

In  liquid  media  three  grow  out  into  long  leptothrix,  forming  bundles 
or  meshes  of  intertwining  uni-  or  multicellular  threads,  while  one 
develops  into  spirilli ;  eight  are  motile,  fourteen  are  non-motile,  while 
three  only  have  been  seen  to  form  spores.  The  others  multiply  by 
division  alone. 

With  reference  to  the  latter  point,  however,  I  have  not  made  exam- 
inations sufficiently  careful  or  extensive  to  be  able  to  speak  decidedly. 
Eight  liquefy  nutritive  gelatin,  one  converts  it  into  a  paste, 
thirteen  leave  it  unchanged.     On  agar-agar  the  differences        Fig.  427. 
of  grrowth  are  not  sufficiently  pronounced  to  deserve  par-  " 

ticular   mention.     In  gelatni  the  microscopic  appearance      ^  >  •*  ^^ 
of  the  colonies  of  a  sufficient  number  of  these  fungi  is        ^        \3 


824  DENTAL   CARIES. 

shown  in  the  figures  (b).  It  Mill  be  seen  that  the  appearance  of  the 
colonies  forms  a  much  safer  means  of  differentiation  than  the  morpho- 
logical characteristics  of  the  fungi,  it  being  very  seldom  that  in  growing 
two  fungi  present  exactly  the  same  appearance.  An  exception  is,  how- 
ever, presented  by  6  and  7,  ^\'hich  to  the  naked  eye  and  under  the 
microscope  grow  on  gelatin  exactly  alike ;  moreover,  on  potato,  white 
of  egg,  blood-serum,  agar-agar,  and  milk  their  effect  is  identical.  One, 
however,  produces  a  yellow  coloring-matter,  the  other  not ;  and  thereby 
they  are  easily  distinguished.  The  others  may  all  be  readily  distin- 
guished by  their  growth  on  potato. 

In  relation  to  oxygen  they  show  great  differences.     Ten  are  strictly 
aerobian — i.  e.  they  grow  only  where  the  air  has  free  access ;  four  are 
not  strictly  aerobian — i.  e.  they  propagate  also  when  the  atmospheric 
Fi  •  428        ^^^  '^^  excluded,  though  not  so  rapidly  ;  eight  grow  equally 
^      '       well  with  or  without  access  of  air ;  sixteen  produce  an  acid 
i^^    J     ^^^ction  in  a  solution  of  beef-extract,  peptone,  and  sugar; 
"*  t?  «i  (^     four  produce  an  alkaline  reaction  without  the  appearance 
of  bad-smelling  products  and  appear  to  leave  the  solution 
neutral.     AYitli  regard  to  the  six,  however,  the  results  were  not  satis- 
factory, sometimes  the  reaction  being  acid,  at   other  times  neutral  or 
alkaline,  depending  somewhat  upon  the  material  used  for  the  cultures. 
Some  which  produce  an  acid  reaction  in  fermentable  solutions  give 
rise  to  an  alkaline  reaction  in  non-fermentable  solutions.    The  acid  pro- 
duced is  probably  in  all,  or  in  nearly  all,  these  cases,  lactic  acid.     This 
fact  I  established  for  No.  1  by  chemical  analysis,  for  No.  2  by  forming 
the  zinc  salt  and  crystallizing,  for  No.  5  by  the  color  test.'     In  the 
other  cases  the  acid  was  not  determined.     Thirteen  were  repeatedly  cul- 
tivated on  potato.     Of  these,  five  grew  rapidly,  one  in  particular  cov- 
ering the  whole  surface  of  the  section  in  forty-eight  hours  and  completely 
liquefying  it  to  a  depth  of  1  to  2  mm.,  the  liquefied  mass  flowing  off  at 
the  sides ;  the  others  develop  very  slowly  and  attain  only  a  limited 
growth.     I  am   not   able  to   say  whether  any  of  them 
^^'   ^  '         possesses  a  diastatic  action.     It  is,  however,  highly  prob- 
able.    Fifteen  were   cultivated  on  boiled  white  of  egg. 
Four  grew  very  rapidly.  No.  19  (see  Fig.  439)  in  par- 
ticular in  from  two  to  four  days,  converting  the  egg  into 
a  semi-transparent  pasty   mass  which   gradually  disap- 
peared.   In  the  first  two  days  large  quantities  of  sulphuretted  hydrogen 
are  developed  ;  later,  ammonia.     Seven  grew  slowly  on  the  white  of 
egg,  and  four  scarcely  at  all.     The  nourishment  of  the  fungi  naturally 
takes  place  at  the  expense  of  the  albumen  of  the  egg,  w^hich  is  converted 
into  a  soluble  variety  by  the  peptonizing  action  of  the  fungus.     In  two 
cases  the  presence  of  peptone  could  be  detected  in  the  dissolved  mass 

^  Two  drops  carbolic  acid.  1  drop  cliloride  of  iron,  20  c.cm.  water,  produce  a  violet  color 
whidi  becomes  yellow  on  ihe  addition  of  lactic  acid,  even  in  very  dihite  form.  I  am 
not  prepared  to  say  that  this  is  an  absolutely  sure  test  for  lactic  acid.  It  is  the  test 
used  by  Prof.  Ewald  and  others  for  detecting  lactic  acid  in  the  stomach,  and  is  con- 
sidered by  them  to  be  decisive.  Of  course  the  culture  material  itself  must  not  give 
this  reaction.  I'cef-extract,  for  example,  cannot  be  used,  as  it  already  contains  lactic 
acid.  A  few  other  substances  also  give  this  reaction,  but  none,  I  believe,  which  are 
likely  to  be  produced  in  these  cultures. 


BIOLOGICAL  STUDIES  ON  FUNGI  OF  HUMAN  MOUTH.       825 

after  separation   from  the  albumen  by  the  biuret  reaction,         Fig.  430. 
the  organisms  producing  more  peptone  than  they  needed 
for  their  own  consumption. 

Some  of  them  produce  in  fermentable  solutions  con-  "  "^  ""^^^ 
siderable  quantities  of  gas.  If  a  glass  bulb  with  a  fine 
stpui  drawn  out  to  a  point  be  filled  with  milk  inoculated  with  No.  3 
(see  Fig.  428),  otherwise  sterile,  and  kept  at  blood-temperature,  in 
twenty-four  hours  so  much  gas  will  be  generated  that  on  breaking  off 
the  pi)int  the  whole  contents  of  the  bulb  will  be  ejected  with  consider- 
able force.  The  same  effect  may  sometimes  be  produced, 
though  not  so  markedly,  when   non-fermentable  solu-  a       ^ 

tions  are  used.  We  may  expect  a  similar  action  to  take  ^g©^  * 
place  when  we  seal  up  a  dead  pulp  in  a  tooth,  the  gas  ^^^  @ 
itself  not  only  escaping  through  the  apical  foramen,  but, 
if  its  exit  is  hindered,  ultimately  forcing  particles  of  the  decomposino" 
pulp  througli  with  it.  The  question  suggests  itself  whether  certain 
configurations  seen  in  carious  dentine  may  not  owe  their  origin  in 
part  to  the  pressure  of  gas. 

Four  produce  coloring-matter,  Nos.  5  and  7  (Figs.  430  and  431)  in 
gelatin  cultures  some  days  old,  forming  brick-yellow  masses  such  as 
may  be  seen  occasionally  on  the  buccal  surface  of  teeth  which  are  not 
kept  well  cleaned. 

On    potato    they   appear    bright    yellow.      Nos.    10    and    13    give 
the  gelatin  for  a  space  1  cm.  in  diameter  around  the  colony  a  grass- 
green   tinge.     I   doubt  very  much  whether    either    of  these 
organisms  has  anything  to  do  with  the  production  of  green    ^^^-  ^^^• 
stain,  all  my  attempts  to  isolate  a  chromogenic  fungus  directly     ^,  "  ^ 
from  green  stain  having  thus  far  failed.     Cultures  of  some  of        \"v. 
these  fungi  were  made  on  dentine  and  enamel.     Sections  of         x 
dentine,  when  decalcified,  neutralized,  and  soaked   in   saliva  "^s^ 

and  sugar,  formed,  when   kept  in  a  perfectly  damp  cell,  a 
medium  on  which  a  considerable  development  took  place,  microtome 
sections  of  the  dentine  after  two  weeks  showing  a  destruction  of  sub- 
stance at  the  point  of  inoculation. 

On  sections  of  normal  dentine  the  fungi  in  some  cases  appeared  to 
maintain  an  existence  until  tlie  organic  matter  exposed  upon  the  surface 
of  the  section  was  consumed,  after  which  the  development  ceased,  while 
normal .  enamel,  as  might  have  been  expected,  formed  about  as  good  a 
culture  substratum  as  glass  or  porcelain. 

A  description  of  the  cultures  in  milk,  blood-serum,  etc.  is  not  neces- 
sary for  our  present  purpose ;  also,  experiments  on  animals  have  been 
made  in  too  limited  a  number  to  lead  to  accurate  results. 
It  is  very  plain,  however,  that  a  study  of  the  pathogenic 
character  of  twenty-two  fungi  is  out  of  the  question.  No. 
19,  which  possesses  peculiar  interest  on  account  of  its 
similarity  to  the  cholera-bacillus,  was  tested  on  mice, 
guinea-pigs,  and  rabbits.  A  small  quantity  from  a  pure 
culture  injected  into  the  abdominal  cavity  of  mice  almost 
invariably  caused  death  in  a  few  hours.     Guinea-pigs  and  rabbits  have 


826  ^  DENTAL  CARIES. 

thus  far  shown  themselves  proof  against  it  even  when  large  quantities 
were    injected   into   the  duodenum   (the  ductus  choledochus  not  being 
ligated).     Experiments    Mere    made  with  a   number  of  antiseptics  in 
addition  to  those  given  on  page  810.     Arsenious  acid, 
Fig.  434.         contrary    to    the    repeated    statements   of   one    of   our 
journals,  possesses   an  antiseptic  power  at  least  half  as 
great   as    that    of   carbolic  acid,   and   about  twenty-five 
times  greater  than  absolute  alcohol.     Chlorate  of  potas- 
sium, on  the  other  hand,  possesses  scarcely  any  available 
power  whatever.    Peroxide  of  hydrogen  proved  to  be  particularly  active. 
The  following  practical  conclusions  appear  to  follow  from  the  experi- 
ments above  recorded  : 

1.  A  great  majority  of  the  fungi  found  in  the  human  mouth  are 
capable  of  producing  acid  from  cane-  or  grape-sugar,  and  it  is  proba- 
ble that,  icith  vei-y  few  exceptions,  all  can  when  the  proper  conditions  are 
presented  to  them.  In  nearly  all  cases  which  have  been  examined  with 
special  reference  to  this  question  the  acid  has  appeared  to  be  lactic.  The 
acetic-acid  fermentation,  which  cannot  go  on  at  temperatures  above  35° 
C.  (Fluegge),  is  out  of  the  question  in  the  human  mouth,  nor  is  there 
as  yet  any  proof  of  the  presence  of  more  than  minute  traces  of  butyric 
acid. 

2.  In  non-fermentable  substances  the  reaction  will  be  found  either 
neuti'al  or  alkaline,  in  some  cases  considerable  quantities  of  ammonia 
and  sulphuretted  hydrogen  being  produced.  If,  therefore,  a  decom- 
posing pulp  is  sealed  up  in  a  tooth,  its  reaction  cannot  be  acid,  and 
caries  cannot  take  place  in  either  the  pulp-chamber  or  the  root- 
canals. 

3.  Of  considerable  interest  is  the  fact  that  the  same  fungus  may  produce 
an  acid  reaction  in  one  substratum  and  an  alkaline  in  another.     If,  for 

example,    No.    19   (Fig.   439)    be 
Fig.  435.         cultivated  in  certain  neutral  non- 
fermentable  substances,  an  alkaline 
reaction  will  appear  ;  if  then  sugar 
be  added,  the  reaction  will  in  a  few 
hours  change  to  acid.     In  such  a 
case  we  undoubtedly  have  two  dis- 
tinct processes  going  on — first,  the  nutrition  of 
tlie  organism,  accompanied  by  the  appearance  of 
alkaline  products  ;  and  secondly,  its  fermentative 

action,  accompanied  by  acid  products.  Ordinarily,  the  latter  so  out- 
weigh the  former  that  the  resultant  reaction  will  be  acid.  This  is, 
however,  by  no  means  necessarily  the  case.  On  the  other  hand,  condi- 
tions may  readily  be  produced  under  which  the  resultant  reaction  will 
be  neutral  or  alkaline,  especially  in  the  human  mouth,  where  so  many 
different  fungi  and  so  various  conditions  are  present.  In  such  a  case 
the  result  would  be  to  put  a  temporary  check  upon  the  advance  of  the 
decalcifying  process — in  otlier  words,  upon  the  caries  itself.  In  the  case 
of  particularly  foul-mouthed  persons  the  foulness  itself  may  become  a 
preventive  of  caries. 


BIOLOGICAL  STUDIES  ON  FUNGI  OF  HUMAN  MOUTH.       827 


Fig.  437. 


4.  The  po.ssession  of  a  peptonizing  action  by  a  large  number  of  these 
fungi  readily  accounts  for  the  solution  of  the  decalciiied  dentine.^ 

5.  Any  one  of  these  fungi  which  can  produce  acid  by  fermentation  of 
carbohydrates  or  can  dissolve  the  decalciiied  dentine  may  aid  in  the  pro- 
duction of  caries,  while  any  one  which  combines  both 
these  properties — as  many  of  them  do — may  alone 
bring  about  the  phenomenon  of  dental  caries.  A  solu- 
tion of  the  dentine  or  enamel  without  previous  decalci- 
fication cannot  take  place.  The  fact  which  I  have  so 
often  affirmed,  and  which  was  denied  by  Milles  and 
Underwood — that  one  continually  meets  with  large 
tracts  of  softened,  non-infected  dentine — has  been  com- 
pletely confirmed  by  Arkovy  and  Matrai.  They  say  :  ''  The  invasion 
extends,  however,  only  to  a  certain  depth,  and  only  isolated  tubules 
show  a  deeper  invasion,  sometimes  to  twice  the  depth,  and  reach  the 
border  of  the  normal  dentine,"  the  whole  territory  between  the  isolated 
tubules  being  free  from  invasion. 

6.  The  comparative  or  complete   independence   of  many   of  these 
organisms   of  the  free  access  of  air  renders  their  propagation  within 

the  dentine  or  under  fillings  M^here  softened,  non- 
sterilized  dentine  has  been  left  an  easy  matter. 

7.  The  fact  that  dentine  and  enamel  form  so 
exceedingly  poor  culture  substrata  for  schizomy- 
cetes  is  an  additional  proof  of  the  position  that 
their  attack  upon  the  teeth  is  only  secondary — 
i.  e.  they  owe  their  rapid  devel- 
opment to  the  secretions,  deposits, 
etc.  of  the  oral  cavity ;  and  not 
until  the  tissue  of  the  tooth  has 
undero^one  a  certain  change — first 
decalcification,  second  peptoniza- 
tion— can  they  adapt  it  to  their 
nourishment.  The  decalcification 
is  produced  chiefly  by  acid  resulting  from  the  action  of  the  organisms 
upon  certain  carbohydrates  in  the  human  mouth,  while  the  peptoniza- 
tion is  produced  either  by  the  direct  action  of  the  protoplasm  of  the 
organisms  upon  the  decalcified  dentine  or  by  the  action  of  a  ferment 
which  they  produce. 

A  knowledge  of  the  properties  of  the  fungi  of  the  human  mouth,  as 


Fig.  438. 


Fig.  439. 


'  Not  a  little  confusion  has  been  introduced  by  attempted  artificial  definitions  of 
putrefaction  and  fermentation.  The  idea  that  every  chansje  in  nitrogenous  organic 
substances  must  be  of  the  nature  of  putrefaction  is  particularly  misleading.  A  ferment 
of  the  nature  of  pepsin  which  dissolves  coagulated  albumen  is  widely  distributed  among 
the  fungi  of  fermentation  as  well  as  putrefaction,  and  the  schizomycetes  in  general 
require  nitrogenous  substances  in  some  shape  for  their  nutrition.  The  dissolution  of 
the  organic  portion  of  dentine  is  by  no  means  dependent  upon  tlie  ])res'^nce  of 
putrefactive  organism,  but  may  be  accomplished  equally  well  by  fermentation.  As 
previously  stated,  I  never  found  a  putrefactive  organism  in  the  deeper  portions  of  carious 
dentine.  Moreover,  the  acid  reaction  of  carious  dentine  is  highly  unfavorable  to  the 
development  of  such  organisms.  I  intend  to  repeat  and  extend  my  experiments  on 
this  point.  The  presence  of  putrefactive  organisms,  while  it  would  accelerate  the  sec- 
ond stage  of  caries,  could  only  retard  the  first. 


828  DENTAL   CARIES. 

given  above,  combined  with  a  microscopic  and  chemical  examination  of 
carious  tissue  and  comparative  studies  of  caries  of  living  and  dead  teeth, 
appear  to  me  to  furnish  a  fair  solution  of  the  phenomena  of  dental 
caries.  That  other  agents  than  those  of  a  parasitic  nature  are  also 
often  concerned  there  can  be  no  doubt.  To  say  nothing  of  predispos- 
ing causes,  an  acid  reaction  of  the  oral  secretions,  acid  medicines,  acid 
foods,  etc.  may  give  rise  to  caries  at  points  which  otherwise  probably 
would  have  escaped. 


PATHOLOGY  OF  THE  DENTAL  PULP. 


By  G.  V.  BLACK,  M.D.,  D.  D.  S. 


The  dental  pulp  comprises  the  soft  tissue  that  occupies  the  central 
cavity  of  the  crown  of  the  tooth  and  the  canals  in  the  roots  to  the 
apical  foramen.  It  is  thus  divided  into  two  portions — the  coronal 
portion  or  bulb,  which  occupies  the  crown-cavity,  and  the  canal  por- 
tion, which  occupies  the  roots  or  root-canals.  Aside  from  this,  the 
coronal  portion  has  a  projection  of  its  tissue  under  each  of  the  cusps  of 
the  tooth,  as  in  the  molars,  which  are  called  the  horns  of  the  pulp. 
These  horns  are  often  quite  long  and  slender,  especially  in  young 
teeth  with  long  cusps.  Generally,  the  form  of  the  pulp  corresponds 
pretty  closely  to  that  of  the  tooth,  except  that  it  is  every  way  more 
slender. 

The  Tissue  of  the  dental  pulp  is  of  the  connective-tissue  group,  and 
supports  an  abundant  supply  of  blood-vessels  and  nerves.     Its  mass  is 


Margin  of  Dental  Pulp:  a,  a,  dentinal  fibrils,  pulled  out  of  the  dentine;  b,b,  membrana  eboris 
or  layer  of  odontoblasts;  r,  c,  transparent  zone  between  the  odontoblasts  and  the  cells  of  the  pulp 
proper;  d,(l,  layer  of  cells  closely  packed  together;  r,  f,  blood-vessels;  /,/,  cells  less  closely 
placed  toward  the  central  portions  of  the  pulp  (Wales'  immersion  ^  in.  objective). 

made  up  of  a  semi -gelatinous  matrix,  which  is  quite  thickly  studded 
with  cells,  but  these  cells  do  not  in  themselves  form  a  complete  tissue, 
in  that  they  are  not  placed  in  contact  with   each  other.     They  are 

829 


830 


PATHOLOGY  OF  THE  DENTAL  PULP. 


imbedded  in  the  gelatinous  matrix,  always  a  little  apart  from  each 
other,  even  where  most  thickly  set.  The  accompanying  illustration  (Fig. 
440)  gives  a  good  idea  of  the  pulp-tissue  as  seen  with  a  high  power  in 
thin  sections  stained  with  hsematoxylin.  This  is  from  the  crown  portion 
of  the  pulp,  and  in  this  the  cells  are  set  in  no  particular  position  rela- 
tively to  each  other,  but  seem  to  be  placed  as  if  by  accident  in  every 
conceivable  position.  In  the  root  portion  this  is  different :  the  cells 
are  there  placed  with  their  long  axis  parallel  with  the  long  axis  of  the 
canal ;  which  arrangement  gives  the  tissue  quite  a  different  appearance. 
The  Cells  are  generally  spindle-shaped,  with  a  delicate  filament  or 
process  extending  from  either  end.  The  form,  however,  varies  con- 
siderably, especially  in  the  coronal  portion  of  the  pulp.  Some  may 
be  seen  so  delicate  and  slender  that  they  seem  but  little  else  than  a 
filament,  while  others  are  nearly  round  and  much  larger  in  their 
central  part.  Again,  we  meet  with  many  cells,  especially  in  the 
coronal  portion,  that  have  three  and  four  filaments  extending  in  as 
many  directions.  In  the  normal  pulp  these  filaments  are  very  slender 
and  are  lost  in  the  gelatinous  matrix.  These,  in  all  well-prepared  sec- 
tions, appear  as  minute  threads  in  all  parts  of  the  tissue  (as  shown  in 
the  illustration). 

77?e  Distribution  of  the  Cells  varies  considerably  in  different  portions 
of  the  pulp.  They  are  fewest  in  number  in  the  central  parts  of  the 
coronal  portion.  All  around  the  periphery  of  the  pulp,  just  a  little 
inside  the  layer  of  odontoblasts,  we  find  a  zone  that  is  much  more 

thickly  studded  with  cells  (r/).  This  is  seen 
in  all  parts  of  the  pulp  periphery.  Between 
this  and  the  layer  of  odontoblasts  there  is  a 
narrow  zone  that  is  usually  almost  or  quite 
destitute  of  cells.  In  sections  so  prepared 
as  to  show  them  this  is  found  to  be  occupied 
by  a  very  fine  plexus  of  nerves. 

The  Odovtoblasts  form  the  periphery  of 
the  pulp,  and  lie  in  contact  with  the  dentine 
(Fig.  440,  6).  As  seen  with  hematoxylin 
staining,  they  seem  to  be  flask-shaped  cells 
with  a  process  extending  into  the  dentine, 
the  fibrils  of  Tomes,  or  the  dentinal  fibrils. 
There  is  also  a  process  extending  from 
the  pulpal  end  of  the  cell  which  does  not 
take  the  stain  and  cannot  be  seen  by  this 
mode  of  preparation.  In  Fig.  441, 1  have 
shown  these  cells  as  they  apj^ear  in  plain 
unstained  section,  mounted  in  glycerin, 
with  the  one-sixteenth  inch  immersion 
objective.  The  cells  are  shown  just  as 
they  happened  to  lie,  without  correcting 
any  of  the  distoi  tion  caused  by  the  mount- 
ing. In  this  section  the  odontoblasts  seem 
to  have  been  pulled  oif  from  the  tisssue  of  the  pulp  in  pressing  down 
the  cover-glass,  and  the  fibrils  are  evidently  somewhat  stretched  out  of 


Fig.  441. 


iiD^ 


\ 


Odontoblast^  cliiuinR  to  i  Fngnient 
ot  Iniperlecih  clt\ eloped  lieiitme. 
llie  ti^'iiie  ^^  is  pii  kd  ^^^  i\  in 
niuuiiiiiig    tlitr     ^tr^;tlull         llit;     uells 

are  drawn  just  as  ihey  lay  distorted 
in  the  mounting,  hut  a  good  idea  is 
given  of  their  true  form  (glycerin 
mounting,  y'gth  inch  obj.). 


STRUCTURE  OF  THE  DENTAL  PULP. 


831 


Fig.  442. 


the  dentine ;  otherwise  the  drawing  may  be  regarded  as  representing 
very  closely  the  true  form  and  relations  of  these  cells  to  each  other  and 
to  the  dentine. 

The  Blood-vessels  of  the  pulp  are  very  numerous.  In  young  teeth,  the 
roots  of  which  are  not  yet  fully  formed,  there  are  usually  a  number  of  small 
arteries  entering  the  pulp  ;  but  as  the  apical  foramen  becomes  narrower 
these  diminish  in  number,  until  finally  there  are  not  more  than  two  or 
three,  and  in  a  very  large  number  of  cases  only  one.  This  divides  and 
subdivides  until  the  entire  tissue  of  the 
pulp  is  filled  with  a  network  of  capil- 
laries, which  is  especially  rich  in  the  per- 
iphery of  the  organ  immediately  beneath 
the  odontoblasts.  Fig.  442  gives  a  good 
idea  of  this.  The  veins  are  usually  a 
little  larger  than  the  arteries,  and  anasto- 
mose with  each  other  very  freely.  The 
blood-vessels  of  the  pulp  are  remarkable 
for  the  thinness  of  their  walls — a  fact  that 
becomes  very  important  in  the  study  of 
its  pathological  conditions.  The  smaller 
veins  are  generally  nothing  more  than  the 
endothelial  cells  placed  edge  to  edge  or 
maro;in  to  marg-in.  The  arteries  have  a 
circular  and  a  longitudinal  layer  of  mus- 
cular fibres,  but  these  are  very  thinly 
distributed. 

The  Nerves  of  the  Pulp  enter  the  apical 
foramen  usually  in  a  single  bundle,  which 
breaks  up  but  little  in  the  canal  portion 
of  the  pulp,  but  in  the  coronal  subdivides 
in  every  direction  to  send  filaments  to  the 
periphery.  Immediately  beneath  the  layer  of  odontoblasts  there  is  a 
very  delicate  plexus  of  fine  naked  nerve-filaments.  These  are  not  well 
seen  in  sections  stained  with  hematoxylin,  but  with  chloride  of  gold  or 
by  treating  with  caustic  potash,  as  recommended  by  Boll,  they  come  into 
view. 

This  makes  up,  in  brief,  the  sum  of  the  pulp-tissue.  The  only  ele- 
ment really  peculiar  to  it  is  the  odontoblast  or  dentine- forming  cell. 
Tlie  tissue  may  be  regarded  as  semi-foetal  in  type ;  that  is  to  say,  it  is 
a  true  connective  tissue  which  seems  not  to  have  reached  mature  devel- 
opment. It  is  only  occasionally  in  the  root  portion  that  we  see  the  cells 
so  placed  in  relation  to  each  other  asrto  form  a  tissue  by  their  conjunc- 
tion during  the  health  of  the  organ.  They  seem  to  be  simply  imbedded 
in  the  gelatinous  matrix,  as  is  seen  so  markedly  in  the  tissues  of  the 
foetus.  The  gelatinous  matrix  contains  no  areolae  during  the  health  of 
the  organ,  but,  as  we  shall  see,  often  becomes  areolar  in  chronic  hyper- 
emia and  chronic  inflammation  of  the  pulp.  The  dental  pulp  seems  to 
be  destitute  of  lymphatics — a  fact  of  considerable  moment,  as  will  be 
seen  in  the  study  of  its  pathology  and  symptomatology.  With  these 
points  well  in  mind  we  are  prepared  to  study  the  changes  that  occur  in 


Point  of  the  Pulp  of  an  Incisor  in- 
jected with  Beale's  blue  to  show  the 
blood-vessels  (X  2.5). 


832  PATHOLOGY  OF  THE  DENTAL  PULP. 

the  diseases  of  the  pulp.  But  before  proceeding  to  this  it  may  be  well 
to  examine  the  sensory  Junctions  of  the  pulp,  with  the  view  of  a  better 
understanding  of  its  symptomatology. 

The   Sensory  Functions   and   Symptomatology   of   the 

Dental  Pulp. 

A  proper  understanding  of  the  sensory  fimctions  of  the  dental  pulp 
is  so  important  to  the  correct  interpretation  of  its  symptomatology  that 
it  seems  to  me  necessary  to  introduce  here  its  consideration.  It  is  gen- 
erally and  correctly  considered  that  the  physical  function  of  the  pulp  is 
the  formation  of  the  dentine  and  the  maintenance  of  its  vitality.  But 
aside  from  this  the  pulp  has  a  special  sensory  function  which  is  limited 
in  the  most  remarkable  manner,  and  M'hich,  so  far  as  I  am  able  at  pres- 
ent to  determine,  has  no  parallel  among  the  organs  and  tissues  of  the 
body.   This  function  consists  in  a  'peculiar  resentment  to  thermal  changes} 

It  requires  both  the  pulp  and  peridental  membrane  to  make  up  the 
sum  of  the  sensory  functions  of  the  tooth.  The  sense  of  touch  resides 
wholly  in  (he  peridental  membrane,  which  receives  the  impression  of 
even  the  slightest  touch  upon  any  part  of  the  surface  of  the  tooth.  The 
pulp,  on  the  other  hand,  has  not  the  sense  of  touch.  If  it  had,  it  is 
clear  that  it  would  not  be  able  to  exercise  it  in  the  normal  condition  of 
complete  encasement  within  its  dentinal  chamber.  It  is  completely 
shielded  from  contact  with  the  outer  world,  and  in  this  condition  has 
no  need  for  the  sense  of  touch  or  the  tactile  sense.  This  is  true  also  of 
the  dentine.  Indeed,  the  dentine  derives  its  sensory  function  directly 
from  the  pulp  through  the  fibrils  of  Tomes  or  dentinal  fibrils,  and, 
except  that  it  is  more  limited,  agrees  in  all  respects  Avith  the  pulp.  The 
dental  pulp  responds  very  promptly  to  injury — not  by  means  of  a  sense 
of  touch,  but  by  means  of  the  sense  of  pain.  There  is  a  sharp  distinc- 
tion to  be  made  between  these  two  functions — a  distinction  having  a  spe- 
cial bearing  upon  the  symptomatology  of  the  organ.  The  tactile  sense 
is  a  localizing  sense.  The  sense  of  pain  when  standing  alone  is  not  a 
localizing  sense.  It  may  be  said  that  the  mind  takes  no  cognizance  of 
organs  that  have  not  the  tactile  sense.  It  does  not  folloM^  that  these 
organs  fail  to  respond  to  injurious  impressions  through  the  sense  of 
]-)ain,  though  some  organs,  as  the  retina,  have  not  even  this  property. 
Pain,  however,  is  not  accurately  located  by  the  mind  without  other  aid 
than  the  mere  sense  of  suffering.  For  instance,  a  patient  can  form  no 
conception  as  to  whether  a  painful  sensation  proceeds  from  the  stomach, 
the  transverse  colon,  or  other  organ  in  the  neighborhood,  for  tlie  simple 
reason  that  these  organs  are  destitute  of  the  tactile  sense.  Patients,  in- 
deed, learn  to  associate  certain  pains  with  certain  affections — as  much, 
perhaps,  by  the  qualities  of  the  pains  as  by  any  sense  of  localization. 
This  quality  of  localization  is  purely  a  matter  of  education  and  not  a 
matter  of  special  endowment.  On  the  other  hand,  an  injury  to  the  sur- 
face of  the  body  involving  the  skin  is  accurately  located  by  the  associa- 

^  Tliis  is  spoken  of  in  the  introduction  to  the  article  on  Diseases  of  the  Peridental 
jMenibrane ;  Hut  on  account  of  its  intrinsic  importance,  and  a  desire  to  make  each  arti- 
cle complete  in  itself,  it  will  be  treated  here  as  if  not  mentioned  elsewhere. 


SYMPTOMATOLOGY.  833 

tion  of  the  sense  of  pain  with  the  tactile  sense  ;  and  the  more  pronounced 
and  acute  the  tactile  sense  of  the  part,  the  more  precisely  will  a  minute 
injury  be  located.  Hence  we  find  in  practice  that  pain  from  injuries  to 
the  surface  is  correctly  located  by  the  patient  whether  he  has  the  oppor- 
tunity of  individual  inspection  of  the  parts  or  not.  This,  as  I  have 
indicated,  is  not  the  case  with  internal  parts  that  have  not  the  tactile 
sense ;  and  it  is  in  disease  of  these  parts  that  we  have  what  is  known 
as  refleeted  pain.  Reflected  pain  is  a  pain  located  by  the  mind  of  the 
patient  at  a  distance,  more  or  less  great,  from  the  seat  of  injury  or  dis- 
ease by  which  it  is  caused.  This  is  probably  divisible  into  two  quali- 
ties or  kinds  of  reflection.  In  the  one  variety  the  pain  is  simply 
wrongly  located  by  the  mind ;  in  the  other  the  pain  is  actually  induced 
in  another  place  through  a  perversion  of  nervous  function.  Our  meagre 
knowledge  of  the  modus  operandi  of  the  production  of  pain  renders  the 
very  accurate  following  of  this  subject  extremely  difficult ;  but  when  we 
see  muscular  contractions  occurring  in  different  parts  of  the  body,  the 
eifect  of  disturbance  of  nervous  function  by  local  disease,  it  is  reason- 
able to  suppose  that  jDain  also  may  be  thus  produced.  Indeed,  these 
muscular  contractions  may  be  the  source  of  reflected  pains  which  are 
accurately  located  through  what  is  known  as  the  sixth  or  muscular  sense. 
Much  of  the  pain  in  the  muscles  of  the  back  occurring  in  woman  in  con- 
nection with  disorders  of  the  uterus  is  of  this  character.  Pleurodynia 
may  occur  as  an  expression  of  disturbed  nervous  function,  the  result 
probably  of  intense  tonic  contraction  of  a  few  fibres  of  some  one  of  the 
intercostal  muscles,  or  it  may  be  of  isolated  fibres  of  several  of  them. 
Much  of  what  we  know  as  reflected  pain  is,  however,  generally  of  a 
different  character  from  these  latter  examples,  and  its  mode  of  produc- 
tion is  different.  A  patient  complains  of  a  persistent  pain  in  the  knee, 
and  the  surgeon  recognizes  it  as  a  symptom  of  disease  of  the  hip-joint. 
The  cause  of  the  pain  is  in  the  hip-joint,  but  the  diseased  tissue,  being 
destitute  of  the  tactile  sense — indeed,  in  this  case  of  any  nerves  of  sense — 
the  pain  is  wrongly  referred  by  the  mind  of  the  patient.  A  patient  has 
pain  in  and  retraction  of  a  testicle,  and  the  surgeon  will  probably  be 
suspicious  of  stone  in  the  urinary  bladder,  and  look  for  the  other  symp- 
toms with  which  the  presence  of  a  calculus  is  usually  associated.  An- 
other complains  of  a  pain  in  the  region  of  the  scapula  (shoulder-tip 
pain),  from  which  the  physician  diagnoses  disease  of  the  liver.  In 
inflammation  of  the  iris  the  principal  seat  of  pain  is  in  the  brow.  In 
this  manner  we  might  go  on  indefinitely  enumerating  examples  of  re- 
flected pain,  and  in  every  instance  it  will  be  found  that  the  diseased 
organ  is  one  that  has  not  the  tactile  sense.  The  instances  given  are 
among  the  best  known,  and  most  constantly  associated  with  the  organs 
named,  that  occur  in  symptomatology,  and  serve  to  illustrate  the  general 
]:)rinciples  of  the  subject.  But  in  very  many  instances  there  is  no  well- 
defined  point  at  which  pain  is  felt  in  diseases  of  a  given  internal  organ. 
Pain  may  be  felt  at  various  points,  and  may  be  shifting  from  one  point 
to  another ;  may  be  in  close  proximity  to  the  diseased  organ  or  remote 
from  it ;  may  be  slight  or  severe.  For  instance,  in  case  of  stone  in  the 
urinary  bladder,  besides  radiating  pains  and  the  symptoms  that  have 
their  seat  in  the  neck  of  the  bladder  and  urethra,  "spasmodic  con- 

VoL.  I.— 53 


834  PATHOLOGY  OF  THE  DENTAL  PULP. 

tractions  in  tiie  rectum,  vagina,  testes,  neighborhood  of  the  kidneys, 
perineum,  or  thighs,  burning  sensations  in  the  soles  of  the  feet,  in  the 
heels,  or  in  the  elbows,  may  be  present,  occurring  mostly  in  paroxysms" 
(Ziemssen). 

I  have  spoken  of  reflected  pain  as  the  product  of  muscular  contractions 
through  perversion  of  nerve-function.  There  is  another  mode  of  the 
production  of  pain  closely  akin  to  this,  which  occurs  through  disturb- 
ance of  the  vaso-motor  nerves,  producing  contractions  or  dilatations  of 
the  muscular  coats  of  the  arteries,  thereby  causing  variations  in  the 
blood-supply  to  local  parts  or  organs.  In  the  following  pages  I  give 
experimental  proof  of  the  association  of  intense  pain  with  hypersemia; 
and  it  seems  to  be  conceded  that  local  deprivation  of  blood  (ansemia)  is 
also  a  cause  of  pain,  and  to  which  form  of  disturbance  are  referred  many 
of  the  types  of  so-called  neuralgia. 

The  true  office  of  symptomatology  is  the  accurate  observation,  record- 
ing, and  grouping  of  these  reflected  pains,  so  that  the  combined  results 
of  investigators  will  be  of  use  to  the  practitioner  in  the  determination 
of  the  ailments  of  his  patients.  It  is  to  the  general  principles  of  this 
subject,  as  established  in  the  field  of  general  practice,  that  we  must  go 
for  the  basis  on  which  to  found  our  study  of  the  symptomatology  of  the 
dental  pujp.  In  order  that  this  shall  be  of  most  service  to  us,  we  should 
first  understand  as  accurately  as  possible  the  actual  sensory  functions  of 
the  organ  in  health.  I  have  explained  above  that  the  dental  pulp  has 
not  the  tactile  sense.  In  this  respect  it  is  a  true  internal  organ,  and  as 
such  its  symptomatology  must  be  studied. 

The  dental  pulp  manifests  a  very  decided  sensibility  to  thermal 
changes ;  not  that  it  readily  determines  degrees  of  temperature  or  dis- 
tinguishes heat  from  cold  ;  in  fact,  the  pulji,  unaided  by  the  nerves 
of  other  parts,  as  the  lips,  gums,  and  peridental  membrane,  seems 
incapable  of  so  discriminating. 

Experiment. — Select  a  normal  tooth ;  one  standing  alone  is  to  be  pre- 
ferred ;  adjust  the  rubber  dam  ;  then  pack  cotton  or  other  non-conduct- 
ing material  around  the  neck  of  the  tooth.  When  this  is  done  apply 
another  piece  of  rubber  dam  to  the  tooth  over  the  cotton.  About  one- 
half  of  the  crown  may  be  left  exposed  after  the  second  piece  of  rubber 
dam  has  been  applied.  Both  pieces  of  rubber  should  be  sufficiently 
large  to  allow  water  to  be  used  with  a  syringe  without  danger  of  com- 
ing in  contact  with  the  patient's  face  or  clothing,  and  between  them 
napkins  and  cotton  should  be  so  placed  that  a  very  perfect  non-con- 
ductor shall  be  formed.  Any  tooth  may  be  used  by  placing  the  first 
piece  of  dam  over  three  teeth,  one  on  either  side.  When  all  is  satis- 
factorily arranged  and  the  patient's  eyes  are  shielded,  throw  alternately 
a  jet  of  ice-water  and  a  jet  of  hot  water  on  the  exposed  crown  of  the 
tooth.  It  will  be  found  that  the  patient  feels  a  sharp  twinge  of  pain 
from  the  contact  of  each  jet,  but  does  not  experience  the  sensation  of 
heat  or  cold  at  all. 

The  teaching  of  this  curious  little  experiment  is  of  great  importance 
in  the  study  of  the  symptomatology  of  the  dental  pulp  ;  normally,  this 
sense  of  pain  upon  sudden  changes  of  temperature  is  the  only  sensation 
conveyed  to  the  sensorium  from  this  organ.     That  sense  by  which  we 


SYMPTOMATOLOGY.  835 

recognize  heat  and  cold  is  contributed  by  the  lips  and  gums,  but  the 
pulp  itself  resents  thermal  change  by  the  sense  of  pain.  This  general 
fact  we  see  exemplified  almost  every  day  :  a  person  taking  a  drink  of 
ice- water,  if  not  accustomed  to  it — and  generally  if  he  is — experiences  a 
twinge  of  pain  in  the  teeth  :  this  resentment  to  heat  and  cold  is  the  special 
sense  of  the  dental  'pulp;  under  normcd  conditions  it  has  none  other  what- 
ever. 

In  diseases  of  organs  having  a  special  function  the  expressions  of 
disease  are  exao-oerated  durino;  the  exercise  of  that  function,  and  the 
case  is  generally  made  worse  for  the  time.  In  affections  of  the  uterus 
this  is  seen  during  the  performance  of  the  function  of  menstruation,  and 
so  on  with  other  organs.  With  many  organs  of  the  body  the  perform- 
ance of  their  peculiar  function  is  necessary  to  the  continued  existence  of 
the  individual,  and  cannot  be  suspended ;  but  in  all  cases  where  rest 
can  be  had  without  endangering  the  patient  it  seems  to  be  the  plain  duty 
of  the  physician  to  secure  it.  The  oculist  should  shield  from  the  light 
an  inflamed  retina  or  iris,  accompanied  witli  photophobia,  in  order  that 
the  diseased  tissue  may  have  rest  from  the  performance  of  its  peculiar 
function.  On  the  same  principle,  a  diseased  dental  pnlp  should  be 
shielded  rigorously  from  thermal  change.  Indeed,  it  may  be  stated 
that  a  very  large  proportion  of  the  difficulty  that  arises  in  the  pulps 
of  teeth  under  treatment  is  due  to  inattention  to  this  one  point.  The 
careless  handling  of  the  burr  or  sand-paper  disc  may,  simply  from 
over-heat,  instantly  precipitate  a  condition  of  disease  from  which,  as 
we  shall  see  farther  on,  the  pulp  of  the  tooth  will  never  recover. 

In  the  symptomatology  of  the  pulp  of  a  tootli  there  are  certain  points, 
based  on  its  structure  and  sensory  functions,  that  are  peculiar  to  it,  as 
distinguished  from  the  diseases  of  the  peridental  membrane  and  neigh- 
boring tissues,  and  are  constant  for  all  of  its  diseases.  This  being  the 
case,  it  may  be  well  to  consider  these  peculiarities  separately.  We  have 
already  seen  that  the  pulp  is,  in  its  symptomatology,  an  internal  organ, 
and  as  such  fails  to  locate  its  ailments.  This  is  so  marked  a  peculiarity, 
and  has  come  to  the  notice  of  the  observant  specialist  so  frequently,  that 
it  need  only  be  mentioned  to  be  understood.  Yet  the  full  force  of  this 
proposition  seems  not  to  be  appreciated.  It  may  be  stated  that  no  one 
can  locate  with  reasonable  certainty  a  single  diseased  pulp  among  the 
teeth  by  the  sensation  of  pain  alone.  When  it  is  properly  located  it  is 
done  by.  other  means.  By  the  sensation  alone  the  patient  is  generally 
able  with  certainty  to  refer  the  pain  to  a  given  side  of  the  face,  but 
nothing  more.  The  more  definite  location  of  the  pain  is  left  to  the 
chance  notion  of  the  patient,  or  is  determined  by  some  accompanying 
circumstance,  as  the  existence  of  a  cavity  :  a  sudden  pain  is  felt,  and  the 
tongue  finds  a  crumb  crowded  into  the  cavity  in  a  certain  tooth ;  this 
occurring  repeatedly,  the  location  of  the  ailment  becomes  in  this  manner 
definitely  and  correctly  fixed  in  the  mind.  In  some  such  way  as  this 
most  of  the  cases  that  present  themselves  for  treatment  are  correctly 
located  by  the  patient.  But  in  any  case  in  Avhich  the  patient  is  left 
without  some  such  guide  the  pain  is  more  likely  to  be  located  Avrongly 
than  rightly ;  and  especially  if  there  exist  circumstances  calculated  to 
lead  the  patient  astray,  he  is  very  sure  to  err. 


836  PATHOLOGY  OF  THE  DENTAL  PULP. 

Recently  I  was  called  on  by  a  lady  "svho  had  for  some  days  been 
suffering  severely  with  a  pulpitis.  I  found  that  before  calling  on  me 
she  had  been  to  three  practitioners,  but  failed  to  obtain  relief,  oM'ing  to 
the  fact  that  she  had  located  the  pain  in  one  tooth,  while  each  of  the 
dentists  whom  she  had  consulted  had  located  it  in  another.  The  patient 
was  certain  she  was  right,  and  her  advisers  were  equally  sure  that  their 
diagnosis  was  correct,  and  in  the  disagreement  nothing  could  be  done 
for  her  relief.  Upon  examination  I  found  that  she  referred  the  pain  to 
a  second  molar  that  had  recently  been  filled,  and  that  the  cause  of 
trouble  was  in  the  first  liicuspid,  as  shown  by  the  temperature  test.  The 
patient  imperatively  demanded  the  removal  of  the  offending  molar. 
After  trying  in  vain  to  explain  to  her  her  mistake,  and  finding  that  in 
her  disturbed  mental  state  the  sacrifice  of  a  tooth  was  the  only  possible 
way  out  of  the  difficulty,  I  seized  a  pair  of  forceps  and  removed  the 
offending  bieuspid  before  she  was  aware  that  I  had  "fastened  on  the 
wrong  tooth,"  as  she  expressed  it.  The  relief  from  pain  which  followed 
had  the  effect  to  bring  her  to  her  senses  and  to  the  admission  that  she 
"  must  have  been  mistaken  as  to  the  tooth ;"  but  this  required  some 
days. 

Cases  of  such  absolute  insanity  as  this  are  not  very  common,  but 
cases  of  pain  wrongly  located  are  of  very  frequent  occurrence.  Some 
months  ago  I  had  a  patient  who  for  several  Meeks  had  suffered  with 
recurring  pain  in  the  superior  bicuspids  of  the  right  side.  She  had 
forced  cotton  saturated  with  some  harmless  nostrum  between  them  for 
the  relief  of  the  pain  until  they  stood  apart  one-eighth  of  an  inch.  The 
teeth  were  perfectly  sound,  and  responded  normally  to  the  temperature 
test.  The  cause  of  pain  was  found  in  an  exposed  and  hypersemic  pulp 
in  the  second  lower  molar  of  the  same  side,  A\hich  had  a  carious  cavity 
under  the  margin  of  the  gum  that  had  escajied  the  observation  of  the 
patient. 

The  pain  in  these  cases  is  not  always  referred  to  the  teeth.  One  of 
the  most  constant  localities  of  reference  is  in  the  ear  of  the  same  side. 
It  may,  however,  be  referred  to  the  temple,  the  infraorbital  foramen, 
the  malar  prominence,  the  angle  of  the  lower  jaw,  the  side  of  the  neck, 
and  other  localities  more  remote. 

The  teeth  in  these  cases  are  never  sore  to  the  touch.  Pressure,  or 
even  the  stroke  of  an  instrument,  calls  out  nothing  abnormal,  but  a 
dash  of  cold  water  upon  the  offending  member  will  usually  excite  a 
vigorous  paroxysm  of  pain. 

In  acute  diseases  of  the  dental  pulp  its  sensitiveness  to  thermal 
changes  is  augmented,-  usually,  to  a  very  marked  degree.  In  most 
cases  this  is  the  first  symptom  that  attracts  the  attention  of  the  patient, 
and  is  oflen  present  for  some  time  before  other  symptoms  are  noticed ; 
and  even  after  the  suffering  becomes  severe  the  paroxysms  may  occur 
only  after  exposure  to  thermal  change.  As  a  rule,  any  pain  in  the 
region  of  the  face  or  ear  that  is  markedlv  increased  bv  filling  the  mouth 
with  cold  or  warm  water  has  its  origin  in  disease  of  the  pulp  of  a  tooth. 
The  most  notable  exceptions  to  this  rule  are  to  be  found  in  some  of  the 
rarer  types  of  neuralgia  of  the  branches  of  the  fifth  pair  of  nerves  in  the 
form  of  painful  tic,  and  in  the  earlier  stages  of  apical  pericementitis 


DENTAL  NEURALGIA.  837 

caused  by  the  expansion  in  the  pulp-cavity  of  gas  arising  from  decom- 
position of  pulp-tissue,  in  which  case  warm  water  causes  an  increase  of 
pain  by  increasing  the  expansion.  In  the  later  stages  of  acute  disease 
as  the  pulp  approaches  a  moribund  condition  its  sensibility  is  lessened, 
and  is  finally  lost. 

The  DIFFERENTIAL  DIAGNOSIS  between  diseases  of  the  dental  pulp 
and  the  different  forms  of  pericementitis  is  usually  easily  made  out,  if  it  is 
remembered  that  the  peridental  membrane  is  the  organ  of  the  tactile 
sense  for  the  tooth.  If  the  peridental  membrane  is  inflamed,  the  tooth  is 
sensitive  to  the  touch,  and  is  not  sensitive  to  reasonable  thermal  changes  ; 
while  in  acute  and  painful  diseases  of  the  pulp  the  tooth  is  not  sensitive 
to  the  touch,  but  is  very  sensitive  to  changes  of  temperature.  Reflected 
or  radiating  pains  do  not  occur  in  diseases  of  the  peridental  membrane 
without  the  presence  of  a  tooth  that  is  sore  to  the  touch.  In  case  of 
reflected  pain  from  disease  of  the  pulp  the  tooth  is  not  sore  to  the  touch. 

In  Degenerations  of  the  dental  pulp  its  sensibility  to  thermal  change 
is  generally  markedly  diminished.  In  some  cases  I.  have  noticed  that 
painful  sensations  came  on  some  minutes  after  excitation  by  thermal 
change,  as  though  the  pulp  was  incapable  of  the  usual  quick  response. 
This  may  be  true  even  though  the  pulp  is  in  a  condition  to  cause  very 
severe  pain,  and  under  these  conditions  I  have  thought  that  there  was 
a  greater  tendency  to  reflected  pain.  In  such  cases  unusual  difficulty 
is  encountered  in  the  differential  symptomatology  between  neuralgia  and 
reflected  pain  from  the  dental  pulp.  The  greater  tendency  to  reflected 
pain  in  these  cases  is  probably  on  account  of  the  comparative  insensi- 
bility of  the  pul])  to  local  disturbances. 

Dental  Neuralgia  is  a  form  of  the  affection  which  has  its  immediate 
exciting  cause  in  some  disease  of  the  dental  pulp.  This  should  not  be 
confounded  with  the  reflected  pains  spoken  of  above.  In  many  cases, 
however,  a  differential  diagnosis  is  difficult  to  arrive  at,  on  account  of 
the  close  similarity  of  the  symptoms.  Dental  neuralgia  very  rarely,  if 
ever,  occurs  in  other  than  persons  who  are  of  what  may  be  called  a  neur- 
algic diathesis ;  that  is  to  say,  disease  of  the  dental  pulp  alone  is  not 
a  sufficient  cause  of  neuralgia,  but  in  persons  who,  by  virtue  of  their 
nervous  constitution,  are  subjects  of  neuralgic  affections,  or  in  persons 
who,  on  account  of  malaria,  anaemia,  or  other  form  of  nervous  depres- 
sion or.  exhaustion,  have  temporarily  come  into  a  neuralgic  condition, 
the  irritation  of  a  diseased  pulp  may  be  the  exciting  cause  determining 
an  attack  in  the  branches  of  tlie  fifth  pair  of  nerves,  or  even  in  more 
remote  parts.  In  making  this  statement  the  reflected  pains  of  which  I 
have  spoken  above  are  excraded.  They  do  not  properly  come  under  the 
denomination  of  neuralgic  affections,  though  they  seem  to  have  been 
widely  recognized  as  such  by  members  of  the  profession.  It  is  rather 
to  the  credit  of  the  scientific  following  of  the  symptomatology  of  disease, 
that  many  of  the  painful  maladies  heretofore  regarded  as  neuralgic  have 
been  assigned  names  in  accord  with  their  true  character.  Still,  after  the 
exclusion  of  these  forms  of  reflected  pain  cases  occur  now  and  then  that 
undoubtedly  present  the  characteristics  of  neuralgia.  It  seems  that 
irritation  of  terminal  nerves  will  slowly  bring  about  an  unusual  excita- 
bility of  the  region  supplied  by  the  nerve-trunk  from  which  the  branch 


838  PATHOLOGY  OF  THE  DENTAL  PULP. 

involved  in  the  irritation  proceeds,  and  often  of  others  in  close  sym- 
pathetic relation  therewith.  This  is  especially  noted  in  the  hyperses- 
thetic  condition  of  the  first  branch  of  the  fifth  pair  dnring  jjainful  dis- 
eases of  the  eye,  and  equally  so  in  the  second  and  third  in  diseases  of 
the  pulps  of  the  teeth.  This  hyperesthesia  of  the  second  and  third  is 
to  be  explained  by  the  fact  that  both  contribute  to  the  nerve-supply  of 
the  teeth,  and  are  thus  brought  into  close  relations  with  each  other. 
Therefore  in  neuralgic  conditions  of  the  general  system  a  peripheral 
irritation  may  inaugurate  a  true  neuralgia.  But  while  this  is  true,  it 
must  be  remembered  that  the  fifth  pair  of  nerves  is  a  frequent  seat  of 
neuralgia  from  causes  entirely  occult  or  remote  from  the  teeth  ;  and 
these  may  even  affect  the  teeth  themselves  prominently.  It  will  be  seen, 
therefore,  that  I  cannot  go  into  the  details  of  this  subject  without  treat- 
ing of  the  general  subject  of  neuralgia,  which  would  be  out  of  place  in 
this  article. 

However,  those  forms  of  the  affection  that  arise  in  antemic  individ- 
uals from  the  irritation  caused  by  a  diseased  tooth-pulp  have  usually 
certain  peculiarities  that  serve  in  some  degree  to  distinguish  them  from 
those  that  arise  from  causes  more  occult.  These  I  Avill  try  to  point  out 
as  they  have  appeared  to  me  in  practice. 

Neuralgias  of  the  fifth  pair  of  nerves  arising  from  occult  causes  or  from 
irritation  which  is  probably  central  or  in  the  course  of  the  nerve-trunk, 
usually  affects  one  or  the  other  of  its  three  principal  branches.  This 
may  be  the  first,  second,  or  third,  but  the  second  or  third  is  more  fre- 
quently the  seat  of  the  affection  than  the  first.  The  pain  may  apparently 
be  located  in  the  trunk  of  the  nerve  or  in  its  terminal  branches,  and 
therefore  may  appear  prominently  on  the  skin.  It  is  somewhat  rarely 
that  it  is  found  affecting  two  of  the  branches  of  the  fifth  at  the  same 
time.  In  the  forms  of  neuralgia  that  have  as  their  exciting  cause  a  dis- 
eased dental  pulp,  the  pain  is  first  felt  in  the  second  or  third  branch  of 
the  fifth  pair,  but  very  soon  aflPects  both,  the  pain  alternating  betAveen 
the  two,  or  there  may  be  painful  points  referable  to  both  at  the  same 
moment.  The  pain  does  not  appear  in  the  terminal  branches  or  in  the 
skin.  After  some  time  the  pain  manifests  a  peculiar  tendency  to  pass 
doAvn  the  side  of  the  neck,  and  finally  into  the  chest  or  arm  of  the 
affected  side ;  and  there  is  pain  in  the  ear  in  a  very  large  number  of 
cases;  which  is  not  the  case  in  neuralgia  from  other  causes.  Paroxysms 
of  pain  are  liable  to  be  excited  by  trifling  circumstances,  as  in  other 
forms  of  neuralgic  affections,  l)ut  more  particularly  by  changes  of  tem- 
perature affecting  the  teeth,  or  they  come  on  during  eating  or  after 
meals.  In  some  cases  the  recumbent  position  has  seemed  to  increase 
the  pain.  But  the  most  reliable  symptom  of  this  form  of  neuralgia  is 
the  fact  that  the  disturbance  of  a  particular  tooth  is  sufficient  to  induce 
a  paroxysm  ;  not  the  rapping  of  the  tooth  with  an  instrument  or  any 
form  of  violence  applied  to  the  surface  of  the  tooth,  but  the  touching 
of  the  pulp  with  an  instrument  or  sudden  changes  of  temperature. 

I  have  usually  found  this  form  of  disease  to  be  connected  with  the 
degenerations  of  the  pulp  described  hereafter.  Sometimes  several  cases 
have  occurred  that  seemed  to  indicate  a  particular  pathological  condition 
of  the  organ,  attended  with  a  tendency  to  neuralgia,  but  further  investi- 


SWELLING   OF  THE  DENTAL  PULP.  839 

gation  has  again  dispelled  this  idea,  and  now  it  seems  to  me  fairly  well 
settled  that  it  is  the  condition  of  the  patient  that  determines  this  form 
of  pain,  rather  than  the  particular  form  of  disease  of  the  dental  pulp 
by  which  it  is  excited.  It  appears,  however,  that  neuralgia  rarely 
results  from  acute  affections  of  the  pulp. 

Swelling  (that  is  apparent)  is  uniformly  absent  in  the  diseases  of  the 
dental  pulp.  In  diseases  of  the  peridental  membrane  swelling  occurs 
uniformly,  either  in  slight  degree  or  extensively.  Especially  is  there 
apt  to  be  some  swelling  and  tenderness  of  the  lymphatics  of  the  angles 
of  the  neck.  This  does  not  occur  in  any  of  the  diseases  of  the  dental 
pulp.  The  only  instances  in  which  I  have  noted  exceptions  to  this  rule 
have  been  in  inflammations  of  the  pulp  in  children,  in  teeth  of  which 
the  roots  were  not  yet  fully  developed,  and  consequently  were  still  Avide 
open  at  the  apex.  But  even  in  these  cases  it  is  of  rare  occurrence.  This 
fact  is  to  be  explained  by  the  consideration  of  the  anatomy  of  the  parts, 
together  with  the  theory  of  oedema  and  the  cause  of  the  swelling  of  the 
lymphatics  in  inflammatory  diseases.  In  regard  to  the  latter,  it  seems 
that  in  inflammations  the  tissue-changes  are  imperfectly  performed, 
resulting  in  the  formation  of  abnormal  waste  products  which  are  taken 
up  by  the  lymphatics.  These  cause  swelling  and  tenderness  of  the  first 
lymphatic  glands  at  which  they  arrive  in  their  course  toward  the  central 
parts  of  the  body.  This  being  the  case,  it  is  clear  that  different  inflam- 
mations will  differ  as  to  the  amount  of  swelling  they  will  cause  in  these 
glands,  those  of  a  septic  character  usually  causing  the  most,  for  the 
reason,  perhaps,  that  the  poisonous  products  of  micro-organisms  are 
added  to  that  produced  by  the  abnormal  tissue-changes.  Thus  a  com- 
mon "  canker  sore "  on  the  mucous  membrane  will  often  cause  more 
trouble  to  the  glands  in  the  angles  of  the  neck,  than  an  alveolar  abscess. 
Th«  principal  reason  why  we  have  no  lymphatic  swellings  in  connection 
with  inflammations  of  the  dental  pulp  is  probably  to  be  found  in  the 
fact  that  the  pulp  has  no  lymphatics  ;  therefore  the  altered  products  of 
inflammation  are  not  removed  by  that  system  of  vessels. 

The  absence  of  oedema  in  inflammations  of  the  dental  pulp  is  evi- 
dently owing  to  the  confinement  of  the  organ  in  its  dentinal  chamber, 
together  with  the  absence  of  areolae  in  its  tissue.  These  two  causes  com- 
bine primarily  to  prevent  the  escape  of  the  serum  of  the  blood  from 
the  vessels,  and  secondarily  to  prevent  its  infiltrating  the  surrounding 
tissues.  It  cannot  pass  through  the  dentine,  and  in  the  normal  condi- 
tion the  apical  foramen  is  too  narrow  to  allow  of  much  escape  by  that 
route,  especially  as  inflammation  is  for  the  most  part  confined  to  the 
bulb  of  the  pulp  at  some  distance  from  the  apical  foramen.  For  these 
reasons,  anv  effusions  that  occur  in  the  pulp  are  necessarily  removed  by 
the  veins,  if  removed  at  all,  and  therefore  do  not  cause  swelling  of  con- 
tiguous parts.  Ordinarily,  the  effusions  must  be  very  slight,  for  the 
sim])le  reason  that  there  is  no  space  for  their  accommodation.  That 
sioeUinfi  of  the  pulp  occurs,  however,  must  be  plain  to  every  one  who  has 
noticed  its  protrusion  into  a  cavity  of  decay  through  an  orifice  exposing 
its  tissue. 

In  widespread  diffusive  inflammation  or  hyperemia  of  the  pulp  there 
may  be  some  effusion  into  the  apical  space,  causing  the  tooth  to  be 


840  PATHOLOGY  OF  THE  DENTAL  PULP. 

lifted  slightly  in  its  socket,  and  giving  symptoms  resembling  apical 
pericementitis.  I  have  noted  symptoms  of  this  kind  a  few  times  in 
intense  hyperemia  induced  primarily  by  thermal  changes ;  but  it  seems 
most  likely,  when  all  of  the  facts  are  considered,  that  these  symptoms, 
when  occurring  in  teeth  with  living  pulps,  are  the  result  of  some  slight 
traumatic  injury  to  the  peridental  membrane,  such  as  would  occur  from 
inadvertently  catching  a  hard  substance  betNseen  the  teeth  in  mastica- 
tion. At  any  rate,  in  the  preparation  of  sections  of  the  pulp  I  have  as 
yet  been  unable  in  any  instance  to  connect  this  class  of  symptoms  M'ith 
either  inflammation  or  hyperemia  of  the  organ ;  and  I  have  made  a 
number  of  selections  with  this  special  end  in  view^,  but  in  each  instance 
have  found  the  pulp  healthy.  These  results  are  contrary  to  my  pre- 
vious convictions.  The  only  class  of  cases  in  which  I  have  been  able 
to  demonstrate  the  existence  of  inflammatory  products  at  the  apical 
foramen  have  been  those  in  which  the  pulp  was  almost  wholly  disor- 
ganized. 

Hyperemia  of  the  Dental  Pulp. 

Hyperseraia  of  the  dental  pulp  is  probably  the  most  important  of  its 
pathological  conditions,  for  the  reason  that  it  is  among  the  most  com- 
mon that  the  dentist  has  to  combat,  and  for  the  fact  that  it  so  often 
terminates  in  the  destruction  of  the  organ.  By  the  term  hyperaemia  is 
meant  the  over-filling  of  the  vessels  of  the  pulp  with  blood.  This  sub- 
ject seems  to  have  been  in  the  past  very  generally  overlooked  by  writers 
on  dental  pathology,  probably  on  account  of  the  difficulties  of  examina- 
tion and  discovery  of  the  exact  conditions  at  the  moment  of  extraction. 
Heretofore,  this  condition  has  been  studied  subjectively  for  the  most 
part ;  that  is,  symptoms  have  been  depended  upon  to  reflect  the  co^^di- 
tion  of  the  organ,  and  while  hyperemia  has  had  recognition,  it  has 
usually  been  regarded  as  an  accompaniment  of  the  inflammatory  pro- 
cess. This  is  a  grave  mistake :  there  is  probably  no  organ  or  tissue  in 
the  body  in  which  hyperaemia  unaccompanied  by  other  morbid  process 
is  so  common  or  so  dangerous  to  the  tissue  involved.  For  these  rea- 
sons, together  with  the  intrinsic  importance  of  the  subject,  I  have  fol- 
lowed its  study  as  closely  as  the  limited  time  of  a  busy  practitioner 
w^ould  allow,  and  since  determining  to  write  this  treatise  have  taken 
pains  to  make  a  practical  reinvestigation  of  the  whole  subject,  for  the 
purpose  of  the  correction  of  any  possible  error  of  previous  studies. 

Before  proceeding  farther  it  may  be  well  to  give  in  some  detail  the 
modes  of  study  that  I  have  found  best  calculated  to  give  correct  infor- 
mation on  this  subject ;  and  it  may  as  well  be  said  now  that  these  ]>lans 
of  research  apply  to  the  study  of  all  of  the  morbid  processes  of  the 
organ,  but  more  especially  to  hyperaemia.  For  the  purposes  of  micro- 
scopic section  the  dental  pulp  furnishes  but  a  small  amount  of  tissue, 
and  it  will  be  seen  at  once  that  it  cannot  be  handled  for  the  purpose  of 
preparation  as  can  tissues  that  may  be  had  in  larger  amounts.  The 
eff'orts  that  have  been  made  at  decalcifying  the  tooth  and  afterward 
hardening,  and  then  making  sections  of  the  pulp  in  situ,  have  not  given 
satisfactory  results — partly  on  account  of  the  action  of  the  acid  upon  the 


HYPERyEMIA    OF  THE  DENTAL  PULF.  841 

pulp-tissue,  and  partly  on  account  of  the  distortion  of  the  tissues  by 
shrinkage.  Then,  too,  the  blood  in  the  vessels  at  the  time  of  extraction 
has  generally  been  lost.  The  question  of  retaining  and  displaying  in 
microscopic  section  the  natural  injection  occurred  to  me  a  number  of 
years  ago ;  and  after  some  experiment  I  found  it  possible  to  do  this  in 
such  a  manner  as  to  display  the  difference  between  the  healthy  and  the 
hyperciemic  pulp  in  very  striking  contrast.  The  first  object  to  be  accom- 
plished in  this  study  is  to  capture  the  condition,  or,  in  other  words,  to 
be  able  finally  to  place  the  pulp  in  section  under  the  lens  with  the  ves- 
sels containing  the  blood  just  as  they  did  at  the  moment  the  tooth  was 
removed  from  the  alveolus,  at  least  without  their  having  lost  the  red 
blood-globules.     This  process  I  will  give  very  briefly. 

When  a  suitable  case  is  presented,  first  examine  the  condition  of  the 
tooth  itself  as  seen  in  the  mouth.  Tlien  obtain  its  history,  the  symp- 
toms it  has  presented  from  the  first  painful  impressions  until  the  pres- 
ent. If  the  pain  has  been  paroxysmal,  find  if  possible  what  has  been 
the  disturbing  cause  that  has  ushered  in  the  paroxysms,  the  duration  of 
the  paroxysms,  the  occurrence  of  soreness  on  closing  the  mouth,  and,  in 
short,  a  full  history  of  the  case.  The  condition  of  the  tooth  at  the  mo- 
ment of  extraction,  especially  as  to  pain,  is  a  matter  of  pjritne  importance 
in  this  study. 

Now  extract  the  tooth  and  drop  it  at  once  into  Miiller's  fluid.  It 
should  not  be  handled  nor  disturbed  in  any  way.  It  should  lie  in  this 
fluid  for  at  least  one  week,  at  the  expiration  of  which  time  it  will  be 
found  that  the  blood  in  the  vessels  has  become  so  hard  that  it  will  not 
be  displaced  if  carefully  handled,  and  that  the  red  globules  have  pre- 
served their  form  perfectly,  and  will  do  so  during  the  subsequent  hand- 
ling. After  the  expiration  of  this  period  the  tooth  should  be  cracked 
in  the  vise,  as  recommended  by  Salter.  This  is  done  by  wrapping  it  in 
muslin  and  placing  it  in  the  jaws  of  a  powerful  vise  (this  should  be  so 
strong  that  there  will  be  no  springing  together  of  the  jaws  on  cracking 
the  tooth,  as  that  would  be  liable  to  crush  the  pulp),  and  l)ringing  them 
together  steadily  until  the  tooth  cracks  open.  If  it  is  skilfully  placed, 
the  line  of  fracture  will  generally  follow  the  long  axis.  Then  place  the 
tooth  in  clear,  freshly-filtered  Miiller's  fluid  and  carefully  remove  the 
pulp  from  its  bed.  In  some  instances  the  layer  of  odontoblasts  will 
remain  adherent  to  the  walls  of  the  pulp-chamber,  in  others  they  will 
remain  with  the  pulp,  and  often  the  dentinal  fibrils  will  be  pulled 
out  of  the  dentine  to  a  considerable  length.  The  pulp  is  now  to  be 
placed  in  a  thin  solution  of  gum  arable  to  which  some  gum  camphor 
has  been  added  to  prevent  mould.  The  strength  of  this  solution  is  very 
important ;  it  should  in  no  case  be  strong  enough  to  float  the  pidp.  This 
should  be  the  test  of  its  strength.  If  the  fluid  be  of  greater  specific 
gravity  than  the  pulp,  its  tissue  w'ill  shrink,  otherwise  not.  The  gum- 
arabic  solution  should  now  be  slowly  evaporated  in  any  convenient  way, 
so  that  it  is  not  done  too  rapidly,  to  the  consistence  of  very  thick  jelly. 
This  should  require  three  or  four  days,  and  it  will  be  found  that  the 
impregnation  of  the  pulp-tissue  with  the  gum  will  keej)  even  j^ace  with 
the  thickening  of  the  solution,  and  that  the  tissue  will  remain  at  the 
bottom  of  the  vessel.    When  the  solution  has  become  as  thick  as  is  con- 


842  PATHOLOGY  OF  THE  DENTAL  PULP. 

sistent  with  handlings  the  pulp  sliould  be  taken  up  with  as  much  niiici- 
hige  as  will  conveniently  adhere  to  it,  and  placed,  in  such  a  position  as 
may  be  desirable  for  cutting,  on  a  bit  of  fine  cork,  which  is  then  floated 
on  alcohol  with  the  side  on  which  the  pulp  is  placed  down.  In  from 
twelve  to  thirty-six  hours,  according  to  the  amount  and  consistence  of 
the  mucilage,  the  surface  will  become  hard  from  the  abstraction  of  the 
water  by  the  alcohol.  It  should  not  be  allowed  to  become  too  hard  or 
the  tissue  will  be  injured.  A  little  experience  and  judgment  will  enable 
one  to  control  this.  When  the  drying  has  reached  the  right  point,  the 
tissue,  cork,  and  all  should  be  invested  in  the  microtome  in  the  proper 
position  for  cutting,  using  paraffin  or  other  suitable  substance  for  imbed- 
ding, and  allowed  to  stand  for  twelve  or  twenty-four  hours.  The  moist- 
ure remaining  in  the  mass  will  by  this  time  have  become  evenly  dis- 
tributed, so  that  it  will  be  of  equal  consistence  throughout.  It  should 
now  be  just  hard  enough  to  cut  smoothly  when  kept  wet  with  alcohol. 
If  all  has  been  properly  done,  it  Mill  be  found  that  very  fine  sections 
can  be  made.  Every  particle  of  the  tissue  can  be  cut,  and  if  desirable 
the  sections  can  be  munbcred  and  examined  in  their  order,  and  every 
part  of  the  tissue  brought  under  the  lens.  The  sections  may  be  mounted 
directly  in  glycerin  without  dissolving  out  the  mucilage,  and  every  cell 
retained  in  position,  or  the  mucilage  may  be  dissolved  out  in  tepid 
water,  and  afterward  the  section  may  be  stained  or  prepared  in  any  way 
desirable,  just  as  can  those  obtained  by  any  other  process ;  and  it  will 
be  found  that  the  blood  will  remain  in  all  but  the  largest  vessels. 

For  the  illustration  of  this  subject  I  have  chosen  sections  stained  with 
hsematoxylin,  except  in  a  few  cases  which  will  be  noted.  -  This  is  done, 
not  for  the  reason  that  this  staining  is  thought  better  than  any  other, 
but  rather  for  the  sake  of  uniformity  of  illustration.  In  the  study  of 
any  such  subject  the  various  modes  of  preparation  should  be  employed. 

Hypersemia  may  occur  in  any  degree,  from  a  slight  distension  of  the 
vessels  of  the  pulp  to  an  expansion  that  seems  enormous,  and,  consider- 
ing the  close  encasement  of  the  organ  in  its  dentinal  envelope,  almost 
inexplicable.  The  distension  of  the  vessels  is  usually  seen  iij  the  great- 
est degree  in  the  bulb  or  coronal  portion  of  the  pulp,  and  is  apt  to  be 
very  unevenly  distributed  ;  but  it  is  not  uncommon  to  find  the  vessels  of 
the  whole  of  the  bulb  of  the  pulp  greatly  expanded  and  overfilled  with 
blood.  Fig.  443  represents  a  field  from  the  margin  of  a  section  of  the 
pulj)  of  a  tooth  extracted  during  a  sev^ere  jjaroxysm  of  pain,  the  vessels 
containing  the  natural  injection  except  at  some  points,  as  at  c,  c,  e,  c, 
from  which  the  coagulum  has  fallen  in  the  handling  of  the  section. 
This  was  a  case  of  extreme  sensitiveness  to  thermal  changes,  in  which 
severe  paroxysms  of  pain,  lasting  for  an  hour  or  more,  were  occasionally 
occurring,  seemingly  excited  by  very  trivial  changes  of  temperature. 
This  condition  had  continued  for  several  weeks.  The  tooth  was  much 
decayed,  but  the  l>ulp  was  not  actually  exposed,  though  but  a  thin  cov- 
ering of  dentine  remained.  The  examination  reveals  no  signs  of  inflam- 
matory changes  whatever.  This  I  find  common  in  those  cases  in  which 
a  pulp  has  become  abnormally  sensitive  to  thermal  changes  without 
exposure  or  irritation  from  external  sources  other  than  changes  of  tem- 
perature.    This  forms  an  important  feature  of  the  pathology  of  the 


hyperjEmia  of  the  dental  pulp. 


843 


dental  pulp,  for  the  reason  that  its  causes  are  so  constantly  present  and 
their  action  augmented  in  every  case  of  filling  with  metal.  It  is  liable 
to  occur  in  the  pulp  of  any  tooth,  however  sound  and  otherwise 
healthy. 

Sensitiveness  to  thermal  changes  in  a  certain  degree  is,  as  has  been 
explained  above,  the  normal  sensory  function  of  the  pulp.  In  each 
instance  of  the  exercise  of  this  function  there  is  an  unusual  amount  of 


Hj-pertemia  of  the  Dental  Pulp,  showing  the  natural  injection  of  the  vessels:  a,  a,  membrana  ehoris, 
or  layer  of  oduiioblasts;  /),  b,  b,  b,  vessels  distended  with  blood;  c,  c,  c,  c,  points  from  which  the 
blood  has  fallen  in  handling  the  section. 

blood  sent  to  the  organ.  This,  when  in  a  reasonable  degree,  is  purely 
physiological — a  temporary  physiological  hypersemia  which  calls  out  a 
simple  warning  in  the  form  of  an  unpleasant  sensation,  and  immediately 
passes  away.  It  is  evident  in  this  case  that  no  injury  results  ;  but  when 
this  is  repeated  frequently  with  a  degree  of  thermal  change  that  is  inor- 
dinate, the  vessels  finally  fail  to  contract  in  a  normal  manner  and  remain 
overfilled  with  blood,  and  at  the  same  time  acquire  an  unusual  degree 
of  susceptibility  to  thermal  influences,  so  that  very  slight  changes  pro- 
duce great  results.  This  is  evidently  in  a  large  degree  a  nervous  jihenom- 
enon.  The  tension  of  the  blood-vessels,  the  degree  of  their  contraction 
upon  their  contents,  is  under  the  control  of  the  nerves  of  the  vaso-motor 
system,  and  in  the  derttal  pulp  these  are  prominently  affected  by  ther- 
mal change  in  such  a  way  tliat  the  vessels  in  some  degree  let  go  their 
grasp  on  the  blood  and  expand  passively  before  the  pressure  of  the  cir- 
culation. This  condition  becomes  pathological  when  the  part  has  become 
inordinately  excitable  by  over-stimulation  or  the  vessels  fail  to  resume 
their  normal  tonicity  after  the  momentary  excitement  has  passed. 


844  PATHOLOGY  OF  THE  DENTAL  PULP. 

Irritation  of  the  distal  ends  of  the  dentinal  fibrils  augments  the  sus- 
ceptibility of  the  pulp  to  thermal  changes,  and  in  this  way  contrib- 
utes to  the  development  of  the  condition  of  hypersemia.  This  is  a 
matter  of  observation,  or  is  based  on  the  fact  that  very  much  the  larger 
number  of  observed  cases  of  hypertemia  are  to  be  found  in  teeth  in  which 
the  dentine  is  largely  exposed  by  decay  or  some  of  the  forms  of  abra- 
sion. This  can  in  part  be  explained  by  the  fact  that  the  covering 
of  dentine  is  reduced  in  thickness,  thereby  contributing  to  the  ease  with 
which  thermal  changes  may  penetrate  to  the  interior ;  but  we  are  con- 
tinually witnessing  the  rise  of  this  condition  in  case  of  cavities  that  are 
so  hidden  away  between  the  teeth  that  this  cause  cannot  operate.  In 
many  of  these  cases  there  is  actual  exposure  of  tiie  pulp  with  inflamma- 
tion, but  hyperemia  occurs  repeatedly  without  exposure  of  the  organ. 
It  is  evident,  however,  that  this  cause  only  renders  the  pulp  more  sus- 
ceptible by  increasing  the  excitability  of  its  nerves.  That  this  condi- 
tion is  by  no  means  dependent  on  any  lesion  of  the  tooth  for  its  origin 
is  exemplified  by  its  frequent  occurrence  in  perfectly  sound  teeth. 

The  Pain  in  hy])er?emia  is  sharp  and  lancinating,  and  paroxysmal  in 
its  character,  especially  in  the  earlier  stages.  It  is  usually  referred  to 
the  teeth,  though  it  very  often  happens  that  the  patient  is  unable  to 
refer  it  to  a  particular  tooth  or  designates  the  wrong  one.  In  case  the 
pain  has  been  shnvly  developed  in  a  particular  tooth  without  a  cavity 
that  has  attracted  the  patient's  attention,  or  in  case  there  are  many  cav- 
ities in  the  teeth,  it  is  very  liable  to  be  referred  to  any  jiart  of  the  dis- 
tribution of  the  fifth  pair  of  nerves,  and  may  exhibit  the  peculiar 
changes  of  position  so  characteristic  of  some  of  the  forms  of  facial  nein- 
algia.  The  reference  of  the  pain  to  the  ear  is  very  common.  A  close 
study  of  the  symptoms  will  connect  the  beginning  of  the  paroxysms 
with  some  form  of  thermal  change.  This  sometimes  requires  more  care 
in  the  inquiry  than,  from  the  nature  of  the  case,  would  be  expected.  It 
often  liap])ens  that  a  patient  has  insensibly  learned  so  perfectly  to  shield 
the  tooth  from  direct  contact  with  cold  water  that  he  may  drink  ice-water 
with  impunity  even  when  a  tooth  is  so  sensitive  to  thermal  change  that 
a  breath  of  cold  air  is  sufficient  to  precipitate  a  severe  j)aroxysm  of  pain, 
or  the  pain  may  come  on  shortly  after  drinking  from  the  cooling  of  the 
contiguous  parts.  Patients  have  often  told  me  that  ice-water  taken  in 
the  mouth  did  not  cause  pain,  when  on  examination  I  have  found  that 
water  twenty  degrees  lower  in  temperature  than  the  blood  thrown 
directly  on  the  tooth  would  cause  the  most  excruciating  suffering.  It 
is  quite  remarkable  how  perfectly  some  persons  learn  to  shield  their 
teeth  from  the  effects  of  ice-water.  Recently  in  conversation  with  a 
physician  on  this  point  he  contended  that  thermal  change  did  not  affect 
his  teeth  any  more  than  other  tissues  of  his  body ;  he  could  drink  ice- 
water  without  any  disagreeable  sensation  whatever,  and  had  done  so  for 
years.  I  asked  liim  to  fill  his  mouth  with  ice-water  and  distend  his 
cheeks  with  it ;  which  he  did  at  once.  The  result  Mas  a  paroxysm  of 
pain  (described  by  liim  as  "  awful  ")  which  continued  for  some  minutes. 
He  had,  as  most  people  do  who  use  ice-water,  learned  unconsciously  to 
shield  his  teeth  from  contact  with  the  water  while  in  the  act  of  drink- 
ing.    This  is  the  reason  so  many  people  come  to  us  wath  hypersemia  of 


HYPER.EMIA    OF  THE  DENTAL  PULP. 


845 


the  pulp  and  give  a  history  in  which  pain  from  changes  of  temperature 
has  no  place.  The  painful  tooth  is  actually  shielded  from  contact  with 
cold  water  unwittingly,  but  every  breath  of  cold  air  affects  it.  This  is 
markedly  exemplified  by  the  comfort  afforded  by  completely  covering 
in  the  affected  tooth  with  a  closely-fitting  gutta-percha  cap ;  Mhich,  I 
may  add,  is  almost  the  sole  treatment  that  I  have  employed  in  this  con- 
dition for  some  years  past.  The  point  is  simply  to  obtain  absolute  rest 
from  thermal  change  until  there  is  complete  recovery  of  the  normal  tone 
of  the  vessels. 

Tissue-change  in  hypersemia  unaccompanied  by  inflammation  is  con- 
fined to  the  walls  of  the  vessels,  and,  so  far  as  is  yet  determined,  con- 
sists of  a  passive  distension  resulting  from  a  semi-paralysis  of  the  local 
action  of  the  vaso-motor  nerves  of  the  part.  This  may  be  more  or  less 
complete,  and  the  distension  slight,  or  it  may  be  very  great.  This  dis- 
tension may  be  recovered  from  very  quickly,  as  is  usually  the  case  in 
the  early  stages  of  the  affectiou,  or  as  the  case  progresses  recovery  of  the 
normal  calibre  of  the  vessels  does  not  occur  for  days  together,  or  possi- 
bly not  at  all.  There  is  no  change  in  the  coats  of  the  vessels  that  can 
be  determined  by  microscopic  investigation  except  the  one  of  distension. 
This  distension,  as  most  commonly  seen  in  well-prepared  sections,  is 
fairly  represented  in  Fig.  444.  This  is  from  a  case  that  had  been  sub- 
ject to  paroxysms  of  pain  for  some  weeks,  and  was  extracted  during 
one  of  these.  During  the  greater  part  of  this  time,  however,  it  had 
remained  free  from  pain.  In  some  cases  of  a  similar  character — i.  e. 
presenting  similar  symptoms,  but  extracted  during  the  interval  of  quiet 
— nothing  remarkable  is  presented ;  the  veins  in  the  bulb  of  the  pulp 
may  be  abnormally  large  and  contain  more  blood  than  usual,  Avhile  the 
arteries  will  be  almost  or  quite  empty  and  the  injection  of  the  capillary 
system  wanting.     This  difference  is  very  striking  when  the  sections  of 


Fig.  444. 


Dilated  Blood-vessels  from  the  Dental  Pulp  in  Hypersemia,  from  tooth  extracted  during  a  paroxysm 

of  intense  pain. 

a  mmiber  of  pulps  of  known  history  are  carefully  compared,  and  shoM's 
the  wonderful  degree  of  recuperation  from  this  condition  of  engorge- 
ment. 

As  the  case  progresses,  the  cause  continuing  to  act  at  frequent  inter- 
vals— i.  e.  in  cases  that  present  a  history  of  frequent  and  very  severe 


846 


PATHOLOGY  OF  THE  DENTAL  PULP. 


pain,  usually  attributable  to  thermal  changes — the  blood-vessels  lose 
their  regular  outline  and  become  more  or  less  varicose.  In  Fig.  444 
I  have  represented  quite  a  remarkable  group  of  these  varicosities  as 
they  appeared  in  the  pulp  of  a  tooth  extracted  during  a  paroxysm  of 
pain.  In  my  studies  of  this  subject  I  have  met  Avith  so  large  a  number 
of  cases  presenting  this  varicose  enlargement  of  the  vessels  that  I  must 
think  it  quite  common.  They  occur  in  every  possible  form  of  contor- 
tion. Occasionally  a  vein  will  be  seen  presenting  a  peculiar  nodulated 
appearance  and  seemingly  crowded  with  blood-globules  to  the  point  of 
bursting,  as  shown  in  Fig.  445.     In  some  instances  single  protuber- 

FiG.  445. 


A  Small  Vein  from  a  Hypersemic  I'uip,  greatly  distended  and  nodulated. 


ances  will  be  seen  upon  the  side  of  a  ves.sel,  as  though  it  had  jjeen  a 
weak  point  distended  by  force  from  within.  Salter  has  noticed  these 
aneurismal  enlargements,  but  seems  to  have  connected  them  with  the 
sloughing  or  ulceration  of  the  pulp;  in  which  he  is  quite  right,  for  I 
have  also  seen  them  in  the  position  named  by  him.  It  seems  to  me 
quite  curious  that  he  had  not  also  noticed  this  condition  of  the  vessels 
separate  from  ulceration.     In  Fig.  446,  I  have  copied  his  illustration. 


Fig.  446. 


Dilated  Vessels  from  the  Dental  Pulp  (Salter's  Denfal  Pathohfiy,  p.  154):  a,  from  the  root  portion; 

6,  from  the  coronal  portion. 

This  is  also  an  enlargement  of  paralyzed  vessels,  and  certainly  belongs 
to  the  condition  of  hyperremia  as  associated  with  the  inflammatory 
process,  which  will  be  presently  considered. 

This  enlargement  of  the  vessels  is  only  the  beginning  of  the  story  of 
hypersemia,  When  the  enlargement  becomes  excessive,  and  in  some 
instances  in  which  it  does  not  seem  so  very  great,  another  phenomenon 
presents  itself  This  is  the  migration  of  the  red  blood-corpuscles  from 
the  vessels,  as  in  infarction,  described  in  the  article  of  this  work  on  Gen- 
eral Pathology,  to  which  the  reader  is  referred  for  the  general  principles 
involved  in  the  snbject.  In  the  dental  pulp,  however,  this  is  not  by  any 
means  always  a  complete  infarction,  but  the  escape  of  blood-globules 


HYPER.EMIA   OF  THE  DENTAL  PULP. 


847 


Fig.  447. 


here  and  there  through  the  pulp-tissue,  where  the  distension  of  vessels 
seems  to  be  the  greatest.  This  is  often  interspersed  with  what  seem  to 
be  slight^  extravasations  of  blood.  In  Fig.  447  is  presented  an  illus- 
tration of  this  taken  from  the 
pulp  of  a  tooth  which  I  ex- 
tracted during  a  most  intense 
paroxysm  of  pain  that  had 
been  continuous  for  several 
hours  :  nearly  tiie  whole  of 
the  tissue  of  the  bulb  of  the 
pulp  contained  red  blood-cor- 
puscles scattered  through  its 
substance.  A  large  proportion 
of  the  veins  Avere  enormously 
enlarged,  as  shown  at  a,  a,  and 
splotches  of  red  blood  were  seen 
at  many  points  in  the  tissue,  as 
shown  at  b,  b,  b.  I  have  noted  ^ 
this  condition  in  a  considerable 
number  of  cases,  and  also  have 
evidence  in  the  remains  of 
partly-absorbed  clots  in  my 
sections  that  even  this  may 
be  recovered  from ;  at  least, 
the  condition  of  occasional  ex- 
travasations. This  lesion  evi- 
dently leads,  in  many  cases,  to 
the  complete  infarction  of  the 
pulp,  in  which  its  tissue  is  en- 
tirely filled  wdth  red  blood- 
globules,  resulting  in  its  de- 
struction. It  has  not  been  my 
fortune  to  prepare  sections  of  a  pulp  in  a  state  of  complete  infarction, 
but  I  have  no  doubt  that  many  of  the  sudden  deaths  of  the  pulp  en 
masse  occur  in  this  way. 

Hypercemia  leads  to  diffuse  inflammation  of  the  pulp  whenever  any 
considerable  amount  of  red  blood  has  escaped  into  the  tissues ;  it  is 
doubtful  if  it  will  occur  before  this.  j\Iy  own  observations  have  not 
decided  the  point,  but  the  experiments  of  Cohnheira  seem  conclusive  in 
showing  that  inflammation  does  not  result  from  the  most  extreme 
hypersemia  that  can  be  induced  by  the  paralysis  of  the  vaso-motor 
nerves.  In  his  experiments  there  was  probably  no  extravasation  of 
red  blood  to  act  as  a  nidus  of  the  inflammatory  movement.  ]\Iy  obser- 
vations seem  to  show  conclusively  that  in  almost  every  extravasation 
a  mild  form  of  inflammatory  action  is  set  up,  by  which  new  elements 
are  thi-own  out  which  act  the  part  of  absorbents  in  the  removal  of  the 
extravasated  blood,  and  that  in  this  way  a  general  diffusive  inflamma- 
tion of  the  pulp  may  be  brought  about  as  a  result  of  hyperseraia.  In 
this  way  also  diffusive  inflammation  of  the  pulp  very  often  occurs  with- 
out the  exposure  of  the  organ  to  any  external  irritation  whatever. 


Section  of  Hyperaeniic  Pulp,  showing  aneurisranl  dilata- 
tions of  the  vessels,  extravasations  of  blood,  and  red 
blood-discs  escaped  apparently  by  diapedesis  :  a,  «.  di- 
lated vessels;  A,  6,  A,  extravasated  blood.  Besides  this, 
red  blood  discs  are  plentifully  distributed  everywheie 
in  the  neighborhood  of  the  veins.  The  tooth  was  ex- 
tracted during  a  paroxysm  of  pain. 


848  PATHOLOGY  OF  THE  DENTAL  PULP. 

The  causes  of  hypersemia  have  probably  been  sufficiently  indicated  by 
what  has  been  said  above.  It  should  be  added,  however,  that  heat 
operates  as  powerfully  in  its  production  as  cold,  and  that  the  dentist, 
by  the  careless  use  of  the  burr  in  the  engine,  but  especially  by  the  heat- 
ing of  the  sand-paper  disk  in  the  finishing  of  fillings,  is  constantly  liable 
to  precipitate  a  condition  of  hypersemia  from  which  recovery  is  very 
difficult  or  impossible.  Inordinate  heating  in  this  way  operates  power- 
fully to  dilate  the  vessels  of  the  pulp ;  and  from  the  observations  I  have 
made  I  am  confident  that  extravasations  occasionally  occur  from  this 
cause,  resulting  finally  in  the  death  of  a  pulp  which  at  the  time  of  the 
filling  of  the  tooth  was  in  good  condition.  I  have  noted  these  unto- 
ward results  in  my  own  practice  and  in  that  of  others. 

Inflammation  of  the  Dental  Pulp. 

There  is  probably  no  tissue  in  the  body  in  which  inflammation,  with 
its  characteristic  tissue-changes,  can  be  studied  in  prepared  sections  to 
better  advantage  than  in  the  dental  pulp.  This  is  owing  chiefly  to  the 
fact  that  its  cells  are,  comparatively,  sparsely  distributed  in  its  matrix, 
and  for  this  reason  are  not  so  much  in  the  way  of  the  observation  of  the 
inflammatory  elements  ;  then,  too,  the  normal  cells  have  so  nearly  the  same 
general  form  and  character  that  changes  in  them  are  easily  noted.  I  think 
I  may  say  that  I  have  studied  the  characteristics  of  this  ])rocess  as  it 
occurs  in  the  dental  pulp  with  more  pleasure  than  in  any  other  tissue. 
But,  however  interesting  this  phase  of  the  subject  may  be,  I  must  refer 
the  reader  to  the  article  on  General  Pathology,  where  he  will  find  it  dis- 
cussed in  detail ;  here  I  will  consider  the  subject  only  as  it  relates  to  the 
dental  pulp. 

Inflammation  of  the  dental  pulp  has  been  discussed  in  some  degree 
by  almost  every  writer  who  has  taken  up  the  subject  of  dental  pathol- 
ogy. It  is  therefore  well  known  to  the  profession.  There  are,  how- 
ever, some  conditions  surrounding  the  pulp  of  a  tooth  which  render 
inflammation  of  this  organ  peculiar  in  some  of  its  phases,  and  which  I 
wish  especially  to  notice.  One  of  these  is  the  peculiar  relation  of  the 
pulp  to  thermal  changes,  and  the  consequent  augmentation  of  the 
inflammatory  movement  by  the  frequent  exacerbations  of  the  hyper- 
emia accompanying  it.  Most  inflammations  are  accompanied  by 
hypersemia,  and  I  know  of  no  difference  between  the  hypersemia 
occurring  as  an  accompaniment  of  inflammation  and  that  occurring 
from  other  causes.  It  must  be  plain  to  every  one  that  in  an  organ  so 
prone  to  hypersemia  as  is  the  dental  pulp,  and  in  which  the  blood-ves- 
sels are  so  liable  to  injury  from  this  cause,  inflammation  will  be  more 
likely  to  assume  a  serious  form  than  under  other  conditions.  To  this 
is  added  the  fact  that  it  is  encased  in  solid  walls  of  dentine,  and  is  thus 
prevented  from  obtaining  relief,  as  do  other  organs  of  the  body,  by 
swelling.  For  these  reasons  the  dental  pulp  is  more  liable  to  destruc- 
tion of  tissue  from  the  inflammatory  process  than  other  structures. 

The  rise  of  inflammation  of  the  pulp  of  the  tooth  as  a  result  of  hyper- 
emia has  already  been  sufficiently  discussed,  and  need  not  occupy  our 
attention  now. 


INFLAMMATION  OF  THE  DENTAL  PL' LP.  849 

The  chief  causes  of  inflammation  of  the  pulp  of  the  teeth  are,  either 
exposure  of  the  organ  by  decay,  some  one  of  the  forms  of  abrasion, 
mechanical  violence  in  the  form  of  accident,  or  the  operations  of  the 
dentist  in  the  preparation  of  cavities  and  the  insertion  of  fillings.  Sim- 
ple exposure  of  the  pulp  to  the  fluids  of  the  mouth  is  usually  sufficient 
to  set  up  an  inflammatory  action  at  the  point  exposed ;  at  least  in  my 
cuttings  of  the  pulp  I  have  found  no  case  of  complete  exposure  of  the 
organ ^n  which,  on  microscopic  examination,  the  usual  signs  of  inflam- 
matory action  were  not  present  at  the  point  of  exposure  This  inflam- 
mation is,  in  many  cases,  limited  to  a  very  small  amount  of  tissue ;  often 
to  a  very  small  portion  at  the  immediate  point  of  exposure.  Inflam- 
mations that  are  strictly  localized  are  very  common.  Occasionally,  how- 
ever, widespread  inflammations  are  found  which  involve  large  portions 
of  the  pulp-tissue,  but  this  is  an  exception  to  the  general  rule.  Even 
in  cases  where  the  pulp  is  destroyed  by  the  inflammatory  process,  it  is 
usually  accomplished  little  by  little  by  the  process  of  suppuration  or 
ulceration,  the  invasion  of  the  tissue  showing  a  decided  tendency  to  fol- 
low the  course  of  the  veins  as  they  take  their  way  toward  its  central 
parts  and  thence  into  the  root  portion,  in  such  a  way  that  the  pulp  is 
hollowed  out,  leaving  its  periphery  intact  until  its  blood-supply  is  cut 
off"  by  the  destruction  of  the  vessels  supplying  it.  In  many  of  my  sec- 
tions this  manner  of  invasion  is  very  marked.  If  a  tooth  is  extracted 
during  a  paroxysm  of  pain,  inflammation  of  the  pulp  is  almost  uni- 
formly accompanied  by  the  signs  of  hypersemia,  they  being  present  in 
a  marked  degree  in  the  immediate  neighborhood  of  the  seat  of  inflam- 
mation ;  but  if  the  tooth  is  removed  during  a  period  of  quiet,  the 
hypersemia  is  limited  to  the  vessels  within  the  inflamed  area.  This  is 
so  constant  that  I  am  forced  to  the  conclusion  that  the  condition  of 
pain  depends  very  largely  on  the  hypersemia. 

Wedl,  Tomes,  Salter,  and  Harris  all  speak  of  the  very  frequent  occur- 
rence of  inflammation  of  the  pulp  before  exposure  of  the  organ.  Much 
as  I  regret  to  differ  with  these  gentlemen,  to  whom  we  owe  so  much 
of  our  present  knowledge  of  dental  pathology,  my  examinations  have 
forced  me  to  a  different  opinion.  That  inflammations  do  occur  without 
exposure  of  the  organ  is  no  doubt  true,  as  I  have  already  indicated  ;  but 
certainly  the  great  mass  of  the  cases  occur  coincidently  with  the  expo- 
sure or  afterward.  If  the  pulp  be  examined  by  breaking  open  the  tooth 
directly  after  extraction,  and  the  existence  of  abnormal  redness  of  its 
tissues  or  fulness  of  its  vessels  be  regarded  as  evidence  of  inflammation, 
and  this  judgment  be  not  corrected  by  careful  preparation  of  the  tissue 
for  examination  with  reasonably  high  powers  of  the  microscope,  the 
cases  of  hypersemia  that  I  have  described  would  all  be  regarded  as  cases 
of  inflammation.  From  the  fact  of  the  general  absence  of  any  consid- 
eration of  the  subject  of  hypersemia  in  the  works  mentioned,  I  suspect 
that  this  is  the  true  explanation  of  the  difference  of  opinion. 

The  tissue-changes  due  to  inflammation  are  very  easily  followed  in 
the  dental  pulp,  especially  in  fine  sections  stained  with  hsematoxylin  or 
fuchsin.  Other  modes  of  preparation  may  be  better  for  the  determina- 
tion of  difficult  points  in  the  morbid  process,  but  for  the  simple  deter- 
mination of  its  presence  I  know  of  no  method  superior  to  this.     In 

Vol.  I.— 54 


850 


PATHOLOGY  OF  THE  DENTAL  PULP. 


Fig.  448  I  give  an  illustration,  with  a  high  power,  taken  from  the 
margin  of  a  iielcl  of  inflammation,  showing  the  inflammatory  elements 
distributed  among  the  normal  tissue-cells,  a,  a  point  out  the  normal 
cells  of  the  part ;  these  are  all  more  or  less  swollen,  especially  their  pro- 


FiG.  448. 


Inflammation  of  Dental  Pulp:  a,n,  normal  cells;  6,  6,6,  6,  inflammatory  elements;  r,  cells  in  process 

of  division  (^^  in.). 

cesses.  At  6,  b,b,b  L  have  pointed  out  the  inflammatory  elements ;  these 
are  leucocytes  in  the  process  of  development  and  self-division,  derived 
from  the  blood  (white  corpuscles)  or  from  the  rejuvenation  of  the  original 
cells  of  the  part.  I  have  draAvn  the  outline  of  each  individual  cell  and 
its  relation  to  its  neighbors  as  perfectly  as  possible  by  aid  of  the  camera 
lucida,  and  it  will  serve  to  show  of  what  the  inflammatory  change  con- 
sists, and  how  clearly  it  is  seen  by  this  mode  of  preparation. 

As  the  inflammatory  process  proceeds,  the  normal  cells  of  the  part 
disappear  and  are  replaced  by  the  inflammatory  elements,  which  are  in 
fact  young  cells  destined  to  develop  and  re-form  the  tissue,  or  degener- 
ate and  form  pus,  as   they  are 
Fig.  449.  more   or   less   favorably  placed. 

The  mode  of  origin  of  these  ele- 
ments is  discussed  at  length  in  the 
article  on  General  Pathology.  In 
some  instances  we  may  see  in  our 
sections,  if  not  the  actual  diape- 
desis  of  the  white  globules  from 
the  veins,  the  results  of  this  dia- 
pedesis  in  the  most  unmistakable 
manner.  In  Fig.  449  I  give 
an  illustration  of  this  as  it  ap- 
^  pears  in  a  section  of  a  pulp  that 
seems  to  have  been  caught  with 
the  inflammatory  process  rapidly 
invading  its  substance.  The  illus- 
tration shows  a  group  of  distended 
veins  at  a  point  just  before  they  enter  the  root  portion  of  the  pulp ; 
and  the  tissue  immediately  around  each  of  the  veins  is  thickly  studded 


Section  oT  Dental  Pulp,  showing  the  invasion  of  the 
inflaiiiniatoi  y  process  along  the  course  of  the  veins 
—the  diapedesis  of  the  white  blood-corpuscles. 


INFLAMMATION  OF  THE  DENTAL  PULP.  851 

with  leucocytes  that  have  evidently  escaped  from  the  veins  within  a  very 
short  time  before  the  extraction  of  the  tooth.  This  part  of  the  section 
resembles  very  much,  except  tliat  the  staining  renders  the  cellular  elements 
far  more  apparent,  what  is  seen  in  the  early  stages  of  inflammation  in  the 
mesentery  or  web  of  the  foot  of  the  frog.  In  searching  over  sections  of 
inflamed  pulps  I  often  see  little  islands  of  inflammation  in  the  midst 
of  apparently  healthy  tissue,  as  though  a  new  nidus  had  been  formed 
at  a  little  distance  from  the  point  of  irritation  or  exposure  of  the  organ. 
It  seems  evident  that  these  are  occasionally  the  central  points  for  the 
formation  of  those  minute  abscesses  that  are  so  often  formed  in  the  midst 
of  the  pulp-tissue.     In  Fig.  450  is  given  an  illustration  of  one  of  these 


u 

Minute  Inflammatory  Focus  within  the  Tissues  of  the  Pulp:    n,  a,  arterial  twigs  ;    6,  a  nerve-hundle ; 

c,  collection  of  leucocytes. 

— a  very  small  one  indeed,  but  one  that  cannot  be  mistaken.  In  this 
the  inflammatory  elements  are  very  closely  grouped  together,  with  but 
few  leucocytes  scattered  in  the  neighborh(jod.  This  is  seen  only  occa- 
sionally in  my  sections.  More  frequently  such  islands  of  inflammation 
ai'e  seen  in  the  diifusive  inflammation  that  results  from  the  condition  of 
hypersemia  and  slight  extravasations  of  red  blood.  In  these  cases  the 
tissue  is  apt  to  be  stained  with  the  coloring  matter  of  the  red  blood-cor- 
puscles that  have  been  broken  up  in  the  process  of  absorption.  I  have 
made  sections  of  a  few  pulps  the  tissues  of  which  were  thickly  studded 
with  these ;  and  occasionally  appearances  indicate  very  certainly  that 
extravasations  have  occurred  at  different  times,  some  being  advanced  in 
the  process  of  absorption,  and  others  being  comparatively  fresh. 

This  breaking  up  of  the  red  blood-corpuscles — or,  rather  the  efl*ect 
of  it — has  been  noticed  by  several  writers.  AVhen  it  occurs  in  large 
amount  the  coloring  matter  is  absorbed  into  the  dentinal  fibrils,  occa- 
sionally in  such  quantities  as  to  give  the  dentine  a  red  color,  making  it 
appear  as  though  it  were  hyper^emic  or  as  if  the  blood  had  really  entered 
the  dentine.  This  is  most  likely  to  be  noticed  about  the  juncti<5n  of  the 
enamel  and  cementum,  where  there  is  the  least  thickness  covering  the 
dentine  from  view.  I  think,  hoM'ever,  that  this  redness  of  the  dentine 
occurs  oftenest  after  death  of  the  pulp  from  infarction.     In  this  case 


852  PATHOLOGY  OF  THE  DENTAL  PULP. 

there  is  a  breaking  up  of  the  red  blood-discs  in  the  process  of  disinte- 
gration, and  a  krge  amount  of  coloring  matter  is  set  free  in  solution, 
and  frequently  will  be  found  in  the  crystalline  form  in  blood-clots. 
While  in  the  state  of  solution  this  may  enter  the  tubules  in  large 
amounts,  and  cause  the  discoloration  of  the  entire  dentine.  In  this 
case  it  is  apt  to  be  much  blackened  by  the  formation  of  the  dark  sul- 
phurets,  giving  to  the  tooth  a  blue-black  or  even  a  black  color,  instead 
of  a  dark  red. 

I  have  seen  but  few  cases  in  which  there  was  a  clear  and  unmistak- 
able deposit  of  inflammatory  lymph  making  space  for  itself  within  the 
pulp-chamber.  One  quite  notable  case  occurred  in  the  pulp  of  a  second 
molar  removed  from  a  robust  girl  of  fourteen  years.  This  presented  a 
history  of  a  severe  toothache,  lasting  for  two  days,  two  weeks  previous  to 
the  time  of  extraction.  The  pulp  was  very  slightly  exposed  from  decay, 
and  the  deposit  of  lymph  was  in  the  neighborhood  of  this  exposure, 
spreading  over  perhaps  one-eighth  of  the  surface  of  the  pulp,  and  seemed 
to  have  been  beneath  the  layer  of  odontoblasts.  At  least,  it  lay  on  the 
periphery  of  the  pulp,  and  the  odontoblasts  were  wanting  ;  and  it  is  fair 
to  presume  that  they  had  adhered  to  the  wall  of  the  pulp-chamber  when 
the  pulp  was  removed  from  its  bed — a  thing  that  occurs  in  fully  one- 
third  of  the  cases  in  pulps  that  are  fairly  healthy.  I  cannot,  therefore, 
assume  that  the  odontoblasts  had  been  destroyed,  though  they  were  cer- 
tainly placed  in  a  very  unfavorable  position.  This  pulp  presented  also 
evidences  of  previous  extravasations  of  blood  from  hypersemia.  These 
deposits  are  occasionally  seen  within  the  tissues  of  the  pulp  in  the  form 
of  islands,  and  usually  seem  remarkably  free  from  cellular  elements. 

It  seems  to  me  that  these  facts  show  that  the  dental  pulp  has  consid- 
erable power  of  recuperation  from  the  inflammatory  state.  It  is  certain 
that  moderate  extravasations  of  blood  are  disposed  of  successfully,  and 
that  a  considerable  bulk,  considering  the  size  of  the  organ,  of  inflam- 
matory lymph  is  tolerated  without  destroying  it,  and  would  undoubtedly 
be  disposed  of  by  the  tissues  if  the  case  were  placed  under  favorable 
conditions. 

The  symptoms  of  inflammation  of  the  pulp  cannot  be  very  certainly 
differentiated  from  those  of  hypersemia.  It  seems  to  me  evident  that  in 
both  cases  the  pain  is  for  the  most  part  dependent  on  the  hypersemia, 
and  therefore  very  nearly  the  same  line  of  symptoms  are  present.  The 
pain  in  inflammation,  however,  is  less  paroxysmal  or  is  more  inclined  to 
be  continuous.  The  paroxysms  continue  for  a  longer  time,  and,  instead 
of  the  pain  ceasing,  it  is  dull,  heavy,  and  persists  with  more  or  less 
pertinacity.  The  pain,  too,  is  much  more  liable  to  come  on  at  night 
after  retiring.  It  seems  that  in  some  instances  the  difference  in  the 
blood-pressure  in  the  upright  and  the  recumbent  posture  is  sufficient  to 
determine  a  state  of  pain  by  the  greater  expansion  of  the  injured  vessels 
in  the  inflamed  tissue.  It  is  probable  that  this  may  happen  also  when 
the  vessels  have  been  repeatedly  injured  by  hypersemic  distension ;  but 
it  is,  I  think,  less  liable  to  occur  under  such  conditions.  At  all  events, 
the  differential  diagnosis  is  in  many  cases  very  difficult  to  make  out 
satisfactorily.  I  may  say  that  in  the  cases  that  I  have  selected  for 
making  sections  I  have  tried  this  very  carefully  for  the  purpose  of 


INFLAMMATION  OF  THE  DENTAL  PULP.  853 

deteriuining  the  diiferential  symptomatology ;  but  my  success  has  not 
been  such  that  I  can  speak  very  positively  of  any  especial  symptoms 
that  are  diagnostic.  The  general  rule  has  been  that  I  have  found  ex- 
posed pulps  inflamed,  whether  there  have  been  symptoms  of  any  kind 
or  not.  (I  do  not  mean  here  pulps  covered  by  softened  dentine  that 
would  be  exposed  in  excavating,  but  pulps  that  are  actually  exposed  to 
the  fluids  of  the  mouth.)  I  am  satisfied  that  there  are  a  great  many 
cases  in  which  exposed  pulps  become  inflamed  and  go  on  to  suppura- 
tion and  the  final  destruction  of  the  organ  without  presenting  any  symp- 
toms whatever;  indeed,  it  is  by  no  means  uncommon  to  find  the  pulj)  in 
a  state  of  suppuration  or  ulceration  in  such  cases.  I  am  inclined  to  the 
opinion  that  inflammation  without  decided  hyperemia  is  not  a  painful 
affection.  Certainly,  it  may  destroy  the  pulp  of  the  tooth  without  pro- 
ducing pain. 

The  causes  of  inflammation  of  the  dental  pulp  seem  to  be,  in  most 
cases,  external  violence  and  the  contact  of  the  saliva.  I  have  uniformly 
found  the  pulp  inflamed  if  it  had  been  so  exposed  that  the  saliva  had 
had  free  access  to  it,  whether  it  had  presented  any  symptoms  or  not.  It 
must  be  admitted,  however,  that  the  number  of  pulps  obtained  for  exam- 
ination, exposed  but  presenting  no  symptoms,  have  been  comparatively 
limited.  The  part  that  micro-organisms  play  in  the  production  of  in- 
flammation of  the  pulp  is  uncertain,  but,  all  tilings  considered,  I  have 
been  inclined  to  the  opinion  that  it  is  a  very  important  one.  Still,  in 
my  microscopic  examinations  I  have  not  yet  been  able  to  find  the  tissues 
of  the  pulp  invaded  by  them ;  possibly  this  may  be  the  result  of  faulty 
manipulation,  yet  the  same  processes  that  I  have  used  successfully  in 
other  situations  have  failed  to  reveal  them  here.  They  are  plentiful, 
however,  in  the  pus  from  suppurating  pulps,  and  undoubtedly  their 
waste  products  have  much  to  do  with  the  initiation  of  the  inflammatory 
process. 

Of  the  ability  of  the  dental  pulp,  when  placed  in  good  hygienic  con- 
ditions, to  recover  from  inflammation,  there  can  be  no  doubt  whatever. 
The  observed  facts  given  in  the  previous  pages  fully  warrant  this  state- 
ment, and  it  is  also  justified  by  clinical  experience,  judged  in  the  light 
of  microscopic  investigation. 

Suppuration  op  the  Pulp 

is  of  very  frequent  occurrence ;  indeed,  it  seems  that  the  dental  pulp  is 
especially  prone  to  suppuration  when  fully  exposed  to  the  fluids  of  the 
mouth.  In  the  greater  number  of  cases  in  -which  I  have  made  careful 
examination  suj^erficial  suppuration  has  been  present ;  yet  I  have  found 
a  considerable  number  of  cases  in  which  the  organ  had  evidently  been 
widely  exposed  for  a  considerable  time,  and  in  which  inflammation  had 
made  considerable  progress,  without  any  evidence  of  suppuration,  and 
in  which  the  layer  of  odontoblasts  was  still  in  position.  Again,  cases 
are  found,  and  are  by  no  means  rare,  in  which  suppuration  has  begun 
in  the  form  of  abscess  within  the  substance  of  the  pulp  at  a  little  dis- 
tance from  the  exposed  point.  In  the  great  majority  of  cases,  however, 
the  suppuration  begins  superficially,  and  the  layer  of  odontoblasts  at 


854 


PATHOLOGY  OF  THE  DENTAL  PULP. 


the  point  of  exposure  is  destroyed.  In  Fig.  451,  A,  I  liave  repre- 
sented in  diagram  a  first  molar  with  a  proximal  decay  exposing  the  pulp. 
The  darkened  portion  of  the  pulp  at  b  shows  the  extent  of  the  invasion 
of  the  pulp-tissue  by  the  inflannnatory  process.  In  B  is  given  an  illus- 
tration of  the  tissue  which  I  have  taken  from  a  central  section,  and 
which  includes  the  most  of  the  inflamed  area.     In  this  I  have  left  the 

Fig.  451. 


A,  Diagram  of  Lower  Molar,  with  caries  at  a  which  exposes  the  pulp.  The  darkened  portion  at  6 
shows  the  extent  of  the  iiiflaiiiniation.   The  rest  of  the  organ  was  free  from  inflammatory  change. 

£,  Illustration  of  the  Inflamed  Tissue,  showing  a  part  destroyed  hy  suppuration  at  a.  The  odonto- 
blasts are  uuderniiued  at  (*.  The  blood-vessels  which  were  filled  with  blood-clot  in  the  section 
are  left  blank  here,  that  they  may  be  more  apparent. 

blood-vessels  blank,  that  they  may  be  more  ap])arent,  though  in  the 
section  they  are  filled  with  clotted  blood.  It  will  be  noted  that  in  the 
greater  part  of  the  field  the  normal  cells  of  the  part  have  disappeared 
and  given  place  to  inflammatory  elements,  and  that  at  the  immediate 
point  of  exposure  the  odontoblasts  are  wanting,  and  the  tissue  has  been 
invaded  by  the  suppurative  process  forming  a  deep  pocket  in  its  sub- 
stance. The  undermining  of  the  layer  of  odontoblasts  at  the  point  b  is 
worthy  of  especial  note  (See  Fig.  452  also.).  This  undermining  of  the 
odontoblasts  occurs  so  often  that  I  may  say  that  it  is  the  general  rule  in 
what  may  be  called  progressive  suppuration  of  the  pulp,  which  is  the 
form  that  I  have  most  generally  found.  Occasionally  I  have  found 
suppuration — or  more  properly,  perhaps,  ulceration — folloSving  a  very 
superficial  inflammation,  in  Avhich  the  tissue  was  apparently  melting 
down  into  a  sanious  pus  thickly  inhabited  by  micro-organisms.  In 
thesis  instances  there  is  a  very  superficial  area  of  the  tissue  in  which  the 
blood  seems  to  be  clotted  in  the  vessels,  whether  the  tooth  be  extracted 
during  a  paroxysm  of  pain  or  not,  and  the  melting  down  of  the  tissue 
is  evidently  on  account  of  the  deprivation  of  blood  by  this  clotting  pro- 


SUPPURATION  OF  THE  DENTAL  PULP. 


855 


Fig.  452. 


cess,  as  has  been  suggested  by  Salter.    It  is  probable  that  the  micro-orgaii- 

isms,  by  the  molecular  changes  which 

they  produce  in  their  life-processes, 

yield  a  material  that  determines  this 

persistent  clotting  in  the  superficial 

capillaries,  and  in  this  way  keep  up 

the  ulcerative  process. 

In  most  cases,  however,  as  has 
been  said,  the  invasion  of  the  inflam- 
mation precedes  the  breaking  down 
of  the  tissue  in  a  much  wider  zone; 
and  it  is  often  seen  to  penetrate 
deeply  into  the  substance  of  the 
pulp,  following  the  direction  of  the 
veins.  This  tendency  is  well  seen 
in  Fig.  452,  taken  from  a  section  of 
the  pulp  of  a  superior  lateral  incisor 
in  which  about  one-fourth  of  the 
pulp  at  the  coronal  j)ortion  had  been 
destroyed.  This  section  also  gives 
an  excellent  showing  of  the  tendency 
to  the  undermining  of  the  layer  of 
odontoblasts.  In  this  way  the  pulp 
is  progressively  destroyed  from  the  (2- 
point  of  exposure  toward  the  apex 
of  the  root.  In  many  cases  this  pro- 
cess is  evidently  in  progress  for  many 
weeks  together,  during  which  time 
the  suppuration  alternates  with  ef- 
forts, always  unsuccessful,  at  repair. 
In  this  way  the  pulp  is  destroyed, 
little  by  little,  until  only  a  small  por- 
tion remains  in  the  root-canal  toward 
the  apical  portion.  In  other  cases, 
however,  the  entire  organ  is  destroy- 
ed at  once  by  gangrene  or  infarction. 
That  the  pulp  ever  becomes  cica- 
trized and  capable  of  performing  its 
functions  after  suppuration  has  been 
established  I  have  no  direct  proof 
that  is  entirely  satisfactory.  In  some 
clinical  cases  I  have  thought  that  this 
had  been  accomplished,  but  there  is  so 
much  liability  to  error  in  these  obser- 
vations that  this  judgment  must  be  taken  with  a  considerable  degree  of 
allowance. 

Abscess  of  the  Dental  Pulp 

is  of  frequent  occurrence ;  and  it  seems  to  me  probable  that  the  suppu- 
rative process  very  often  makes  its  beginnings  in  the  form  of  a  minute 


Progressive  Suppuration  of  the.  Pulp  of  an  In- 
cisor: </,  healthy  tissue;  h,  odontoblast  layer, 
or  iiienibrana  eboris;  c,  inflamed  tissue,  in 
which  the  veins  are  seen  to  be  dilated ;  il,  line 
of  demarcation  of  the  suppurative  process;  e, 

|1US. 

A  part  of  the  crown  portion  of  the  pulp  had 
been  destroyed  by  suppuration,  and  in  the 
remaining  portion  it  will  be  noted  how  tlie 
pulp  is  hollowed  out,  the  process  pursuing  the 
course  of  the  veins  and  converging  to  the 
centre  (X  100,  reduced). 


856 


PATHOLOGY  OF  THE  DENTAL  PULP. 


abscess  just  within  the  layer  of  odontoblasts.  These  cells  exhibit  less 
disposition  to  change  under  the  influence  of  inflammation  than  the  other 
cells  of  the  pulp,  and  I  have  often  found  them  retaining  their  form  and 
position  when  the  tissue  in  immediate  juxtaposition  witli  them  had  been 
destroyed.  Therefore,  it  seems  probable  that  the  first  formations  of 
pus  would  be  retained  behind  them  for  a  time  in  the  form  of  a  tiny 
abscess ;  at  least,  this  is  suggested  by  the  facts  observed. 

Abscesses  lying  deeper  in  the  tissue  of  the  organ  are  seen  to  form  by 
the  aggregation  of  the  inflammatory  elements  into  a  compact  mass  or 
little  masses  that  lie  near  each  other  and  run  together  in  the  process  of 
increase.     These  cells,  on  account  of  the  unfavorable  conditions  of  their 

environment,  degenerate  in- 
to pus-cells,  and  the  result 
is  the  formation  of  an  ab- 
scess. Fig.  450  represents 
very  fairly  a  beginning  of 
the  collection  of  inflamma- 
tory elements  that  might  well 
serve  as  the  nidus  of  an  ab- 
scess if  the  conditions  were 
unfavorable  to  their  contin- 
ued vitality.     In  Fiff.   453 


Fig.  453. 


is  given   an   illustration  in- 


Abscess  within  the  Tissues  of  the  Pulp.   The  field  includes 
about  one-half  of  the  little  pocket  of  pus  (X  2oU). 


eluding  about  the  half  of  a 
minute  abscess  that  I  dis- 
covered in  the  sections  of 
the  pulp  of  a  central  incisor 
about  midway  of  its  length. 
The  coronal  portion  was  sup- 
purating, and  the  inflamma- 
tion was  rather  more  ex- 
tended in  its  tissue  than  is 
common.  I  have  seen  abscess  in  the  pulps  of  the  molars  much  oftener 
than  in  the  single-rooted  teeth.  Here  it  is  not  very  uncommon  to  find 
several  minute  pockets  of  pus  at  a  little  distance  from  the  point  of 
exposure  in  cases  in  which  the  pulp  has  been  exposed  for  a  consider- 
able period.  When  we  note  the  swelling  that  usually  accompanies  the 
formation  of  an  abscess  in  the  soft  parts,  we  can  gain  some  idea  of  the 
destructive  effect  produced  by  the  formation  of  an  abscess  in  the  tissue 
of  the  dental  jjulp,  encased  as  it  is  in  the  dentine  Avithout  the  opportunity 
of  obtaining  the  increased  space  necessary  for  the  accommodation  of  the 
forming  pus.  This  applies  with  the  same  force  to  the  formation  of 
})us  on  the  surface  of  the  organ  when  there  is  not  a  complete  exposure 
that  will  allow  of  its  escape,  the  formation  of  pus  after  a  filling  has 
been  inserted,  or  under  a  capping.  In  any  of  these  conditions,  if  the 
amount  of  pus  formed  is  more  than  can  find  room,  the  compression  and 
strangulation  of  the  organ  are  inevitable ;  and  I  have  every  reason  for 
believing  that  this  form  of  strangulation  and  destruction  of  the  pulp  is 
not  infrequent.  This  conclusion  is  based  on  the  frequent  finding  of 
minute  abscesses  in  the  living  pulp  as  prepared  for  microscopic  exami- 


CHEOXIC  INFLAMMATION  OF  THE  DENTAL  PULP.        857 

nation,  the  occasional  discharge  of  minute  quantities  of  pus  from  such 
abscesses  by  puncture,  and  also  from  the  surface  of  the  pulp  after  the 
removal  of  cappings,  which  I  have  noticed  in  practice,  as  well  as  the 
speedy  relief  from  pain  afforded  by  these  operations. 

The  pain  in  abscess  of  the  pulp  is  often  very  violent.  It  seems  to 
arise  differently  from  that  occasioned  by  hypersemia,  in  that  the  onset 
of  the  attack  is  not  sudden  and  violent,  but  beo-ins  with  a  slitrht  ffnawins: 
pani  that  persistently  nicreases  ni  severity,  often  until  it  becomes  very 
intense.  If  relief  is  not  obtained  by  the  discharge  of  the  pus  in  some 
direction,  strangulation  will  sooner  or  later  occur,  the  pain  then  ceasing. 
This,  within  from  six  to  twenty-four  hours,  will  probably  be  replaced 
by  symptoms  of  apical  pericementitis.  Hyperaemia  may  of  course  be 
coincident  with  the  formation  of  abscess  and  may  mask  its  svmptoms. 

Small  amounts  of  pus  may  be  retained  in  the  pulp-chamber  indef- 
initely, and  in  this  position  may  possibly  undergo  absorption.  I  have 
noted  some  instances  in  which  it  had  undergone  fatty  degeneration,  and 
seemed  to  be  partially  converted  into  an  emulsion,  as  described  by  Salter. 
Under  these  circumstances  gas  is  occasionally  formed  by  a  process  of 
decomposition.  Only  a  few  days  ago  I  was  removing  the  pulp  from  a 
central  incisor  after  it  had  lain  in  Miiller's  fluid  for  a  week,  and  imme- 
diately on  cracking  the  tooth  I  discovered  in  its  tissue  a  cavity  that 
contained  a  bubble  of  gas.  Possibly  this  may  have  formed  afler  pla- 
cing it  in  the  fluid,  but  the  conditions  for  its  formation  must  have  been 
present  before  the  extraction  of  the  tooth,  for  they  could  not  have  arisen 
after  it  was  placed  in  the  fluid.  Upon  section  of  the  pulp  I  found 
unmistakably  that  the  gas-bubble  was  in  an  abscess-cavity.  This  is  the 
only  instance  in  which  I  have  found  evidence  of  the  formation  of  gas 
within  the  living  organ;  and  even  in  this  I  cannot  say  that  the  for- 
mation was  not  post-mortem.  The  generation  of  gas  within  the  closed 
pulp-chamber,  in  which  suppuration  of  the  pulp  is  going  on,  undoubtedly 
takes  place  in  some  instances.  In  such  cases  warm  liquids  should 
increase  the  pain  by  expanding  the  gas,  while  cold  would  relieve  it 
by  the  opposite  effect. 

Chronic  Inflammaton  of  the  Dental  Pulp 

may  take  any  one  of  three  forms.  The  more  common  forms  are  chronic 
inflammation  with  the  continuous  shedding  of  pus,  which  has  been  suffi- 
ciently described ;  chronic  inflammation  with  the  addition  of  new  ele- 
ments, or  inflammatory  hypertrophy ;  and  chronic  inflammation  accom- 
panied with  degeneration  of  structure,  or  inflammatory  degeneration. 
No  considerable  hypertrophy  of  the  pulp  can  occur  while  it  is 
enclosed  in  a  normal  pulp-chamber,  for  the  simple  reason  that  there  is 
no  room  for  its  expansion.  In  cases  of  exposure  of  the  organ,  however, 
a  very  considerable  hypertrophy  occasionally  occurs,  the  new  growth 
pushing  out  into  the  cavity  of  decay  which  has  caused  the  exposure. 
This  is  seen  as  a  fleshy  mass  in  the  carious  cavity,  and  is  often  much 
greater  in  bulk  than  the  pulp  from  which  it  has  sprung.  This  growth 
does  not  all  take  place  outside  of  the  cavity,  for  there  is  often  evidence 
in  the  arrangement  of  the  tissue  that  shows  us  plainly  that  much  of  the 


858 


PATHOLOGY  OF  THE  DENTAL  PULP. 


growth  has  taken  place  within  the  cavity,  and  has  gradually  been 
squeezed  out  through  the  opening.  In  other  instances  the  growth 
seems  to  have  occurred  mostly  at  or  without  the  orifice,  exposing  the 
pulp.  In  the  greater  number  of  the  cases  I  have  examined  the 
growth  seems  to  have  been  determined  by  the  continual  irritation  of 
the  tissue  of  the  pulp  by  the  sharp  corners  of  the  opening  into  the  pulp- 
chamber.  The  growth  itself  is  almost  uniformly  composed  of  granula- 
tion-tissue of  rather  a  low  type,  which  remains  in  a  very  primitive  state. 
The  accompanying  illustration  will  give  a  good  idea  of  this  (Fig.  454). 

Fig.  454. 


-4,  A  Diagram  of  a  First  Lower  Molar,  with  a  ta\it}  at  a  toiuplttch  filled  by  a  hypertrophy  of  the 
pulp,  which  has  urown  out  through  the  onhce,  exposing  the  pi.lp  at  ft. 

B,  A  Held  illustrating  the  Tissue  of  the  Growth,  which  is  coiiijiosed  almost  entirely  of  granulation- 
tissue  of  a  very  primitive  type:  a,  a  covering  of  epithelium  presenting  papilla;;  ft,  epithelium 
apparently  without  papillae. 

Occasionally  I  have  seen  the  tissue  much  more  developed,  approaching 
fibrous  tissue  in  its  structure.  Many  of  these  growths  are  covered  on 
the  exposed  surface  with  the  usual  squamous  epithelium  of  the  mucous 
membrane  of  the  mouth.  This,  evidently,  has  not  developed  from  the 
tissues  of  the  ])ul]),  but  is  a  transplantation  from  the  epithelium  of  the 
adjacent  gum,  which  has  occurred  after  the  fashion  of  skin-grafting. 
With  the  frequent  abrasions  that  occur  in  the  act  of  mastication  I  can 
readily  understand  how  the  epithelium  could  be  transplanted,  but  I  can- 
not understand  how  this  form  of  epithelium  could  be  developed  from  the 
tissues  of  the  pulp.  In  a  few  i nuances  such  a  growth  has  been  known 
to  become  calcified.  John  Tomes'  figures  a  case  in  M'hich  the  pulp 
seems  to  have  Ix-come  somewhat  hypertrophied  after  breakage  of  the 
crown  of  the  tooth,  and  afterward  to  have  become  calcified.     Heider 

^  Dental  Surgery,  p.  540. 


DEGENERATION  OF  THE  DENTAL  PULP.  859 

and  Wedl,  in  their  eighth  plate/  also  give  a  figure  of  a  similar  case 
which  occurred  in  an  incisor  tooth  of  the  antelope.  I  have  seen  a  very 
curious  case  of  this  kind  occurring  under  a  metallic  capping.  Some  of 
the  older  members  of  the  profession  will  remember  that  before  the  intro- 
duction of  the  cements  there  was  a  considerable  effort  to  preserve  the 
pulps  of  teeth  by  bridging  over  with  thin  plates  of  metal.  Owing  to 
a  threatened  alveolar  abscess,  it  became  necessary  for  me  to  remove  a 
filling  made  by  Dr.  Isaiah  Forbes  of  St.  Louis,  which  the  patient  told 
me  had  had  a  capping  of  this  kind  in  position  for  twelve  years.  The 
case  was  a  lower  wisdom  tooth  standing  alone,  with  a  very  large  amal- 
gam filling  occupying  the  anterior  part  of  the  crown.  There  was  a 
little  caries  about  its  margin  that  enabled  me  to  insert  a  point  and 
pry  the  filling  out  en  masse.  This  disclosed  a  large  piece  of  gold  plate 
which  had  been  laid  over  an  exposure  of  the  pulp,  leaving  a  consider- 
able space  between  it  and  the  bottom  of  the  cavity.  I  was  surprised  to 
find  this  filled  completely  with  what  was  evidently  a  calcification  of  the 
hypertrophied  pulp,  which  had  grown  out  and  filled  the  space  left  under 
the  capping.  The  mass  was  slightly  movable,  showing  that  it  was  not 
attached  to  the  original  dentine,  but  extended  into  the  pulp-chamber  in 
such  a  way  that  it  was  necessary  to  cut  it  to  pieces  to  remove  it.  This 
form  of  calcification  is  evidently  very  rare. 

Another  result  of  inflammatory  hypertrophy  of  the  pulp — one  that 
is  very  rarely  seen,  however — is  the  absorption  of  dentine  from  the 
inner  walls  of  the  pulp-chamber,  causing  its  enlargement.  I  have  never 
met  with  a  case  in  which  I  had  the  opportunity  of  a  systematic  exam- 
ination of  this  process,  but  in  practice  have  seen  several  well-marked 
cases,  and  just  now  have  under  observation  a  first  lower  molar  in  which, 
on  removal  of  the  pulp,  I  found  the  whole  of  the  floor  of  the  pulp- 
chamber  missing.  Ten  years  ago,  as  my  record  shows,  I  capped  a  very 
ugly  exposure  in  this  tooth  and  made  a  large  gold  filling.  For  two  or 
three  years  the  pulp  has  been  irritable,  and  I  finally  determined  to 
remove  it ;  and  upon  doing  so  found  the  pulp-chamber  enormously 
enlarged,  and  that  an  opening  to  the  peridental  membrane  between  the 
roots  had  been  formed.  Another  case  was  that  of  a  central  incisor  in 
which  the  enlargement  of  the  pulp-chamber  was  not  so  great,  but  was 
unmistakable. 


-Degeneration  op  the  Structure  of  the  Pulp 

may  occur  from  long-continued  inflammation  of  a  low  grade.  From 
my  personal  observations  I  should  think  that  the  tissue  does  not  at  any 
time  become  the  seat  of  a  high  grade  of  inflammatory  action ;  if  so,  the 
inflammatory  elements  must  be  removed  by  some  process  of  degener- 
ation and  absorption.  The  original  cells  of  the  part  also,  for  the  most 
part,  disappear  or  lose  their  nucleus,  and  become  converted  into  very 
fine  fibres.  Areolae  develop  in  the  matrix,  and  all  the  histological  cha- 
racters of  the  tissue  are  profoundly  changed.  Fig.  455  is  given  as  an 
illustration  of  this,  from  a  pulp  thus  affected  in  an' extreme  degree.  These 
areolae  were  evidently  filled  with  fluid ;  hence  a  kind  of  oedema  of  the 

^  Atlas  of  the  Paiholoyy  of  the  Tteth, 


860 


PATHOLOGY  OF  THE  DENTAL  PULP. 


organ  must  have  existed  which  in  the  enclosed  pulp-chamber  has  prob- 
ably gradually  destroyed  the  cellular  elements,  and  new  elements  thrown 
out  in  the  inflammatory  process  have  suffered  the  same  fate.  At  any 
rate,  those  that  are  seen  are  all  more  or  less  shrivelled  in  appearance. 

This  particular  case  was  taken  from 
Fig.  455.  the  mouth  of  a  young  lady  seven- 

teen years  old,  and  presented  a  his- 
tory of  rather  severe  pain  at  several 
different  times  during  four  or  five 
months;  it  was  "often  uneasy."  It 
had  not  given  severe  pain  for  two 
months  before  extraction.  Cases 
are  met  with  that  present  every 
possible  grade  of  change,  from  the 
occasional  appearance  of  areolee  to 
the  complete  areolation  of  large 
portions  of  the  pulp,  as  shown  in 
the  illustration.  But  in  the  most 
cases  I  have  seen  the  areolation  has  not  extended  to  the  whole 


Chronic  Inflamniation  of  the  Pulp,  areolation 
and  desreneratiun. 


extreme 

tissue.  All  grades  wdll  be  found  in  the  same  pulp.  The  bulb  suffers 
most,  and  often  that  part  of  the  bulb  nearest  an  exposure,  while  the  rest 
of  the  organ  seems  to  retain  its  tone  more  or  less  perfectly.  How  much 
hypersemia  may  have  to  do  in  the  production  of  this  condition  I  cannot 
say.  The  evidence  of  oedema  presented  by  the  abnormal  areolae  would 
indicate  that  the  effusion  was  hypersemic  rather  than  inflammatory,  but 
in  all  of  these  cases  I  have  found  the  evidences  of  inflammatory  action 
unmistakable. 

My  observations  of  this  condition  of  the  pulp  lead  me  to  the  opinion 
that  the  sensibility  of  the  organ  is  markedly  diminished  as  this  con- 
dition is  developed.  I  have  not,  however,  found  a  sufficient  number  of 
well-marked  cases  in  the  cuttings  I  have  made  to  feel  very  certain  of 
the  symptomatology.  From  what  I  have  seen  I  would  suggest  that 
this  is  probably  the  manner  of  the  death  of  those  pulps  that  we  some- 
times find  dried  up  (mummified)  in  their  chambers. 


Deposits  of  Calcoglobulin 

are  found  associated  with  inflammation  in  a  considerable  number  of 
cases.  I  have  not  seen  this  deposit  mentioned  in  any  writings  on  this 
subject,  yet  it  is  so  prominent  that  I  fail  to  understand  how  it  could 
have  been  overlooked.  To  my  mind,  this  formation  is  associated  with 
the  formation  of  what  are  known  as  pulp-nodules.  It  possesses  the 
same  form  of  elements  common  to  the  pulp-nodule,  including  the  forms 
of  the  calcospherite,  but  is  soft  enough  to  be  readily  cut  with  the  knife 
in  the  preparation  of  sections,  while  the  pulp-nodule  is  very  hard.  It 
has  been  present  in  a  number  of  the  pulps  th.it  I  have  cut,  always  in 
the  inflamed  portion,  and  usually  near  the  point  of  exposure,  often 
Iving  immediately  beneath  the  layer  of  odontoblasts,  but  occasionally 
much  deeper  within  the  tissues  of  the  pulp.  It  usually  occurs  in 
irregular  masses,  occasionally  of  considerable  size;  and  scattered  about 


DEPOSITS  OF  CALCOGLOBULIN. 


861 


^^^^«iP^ 


Deposit  of  Calcoglobulin  within  the  Tissues  of  an 
Inflaiued  Pulp. 


these  there  are  generally  a  number  of  small  globular  forms,  many  of  which 
have  the  onion-like  layers  of  the  calcospherite  quite  distinctly  marked. 
In  Fig.  456  I  give  an  illustration  of  one  of  these  masses  as  it  occurred 

in  the  pulp  of  a  second  molar 
Fig.  456.  from  the  mouth  of  a  girl  of 

fifteen  years.  About  one-half 
of  the  coronal  portion  of  the 
pulp  was  involved  in  inflam- 
mation, which,  from  the  his- 
tory of  the  case,  must  have 
been  present  for  as  much  as 
two  months,  the  tooth  re- 
maining quiet  most  of  the 
time,  but  subject  to  par- 
oxysms of  pain  lasting  from 
a  few  moments  to  two  or 
three  hours.  There  were  sev- 
eral such  masses  as  the  one 
represented  in  the  pulp-tissue,  all  lying  a  little  inside  of  the  odontoblast 
layer  and  having  globular  forms  in  their  mass  or  attached  to  their  mar- 
gins. In  one  part  of  the  pulp  there  were  a  number  of  detached  globules 
similar  to  those  attached  to  the  specimen  shown.  When  mounted  in 
glycerin,  without  staining,  these  masses  are  very  transparent  and  show 
no  color  whatever.  They  stain  an  intense  red  with  fuchsin,  and  are  not 
bleached  by  immersion  in  alcohol  for  five  or  six  hours.  With  hsema- 
toxylin  they  are  stained  blue  or  purple.  Judging  from  the  forms  pre- 
sented by  these  bodies,  I  suppose  them  to  be  calcoglobulin  :  I  have  not 
made  the  chemical  examination  that  would  be  required  to  demonstrate 
this.  They  are  entirely  different  from  lymph-deposits,  and  do  not 
show  the  reactions  peculiar  to  amyloid  deposits. 

The  idea  that  calcoglobulin  is  deposited  in  the  pulps  of  teeth  in  the 
soft  state  has  been  arrived  at  with  some  difficulty,  from  the  fact  that  it 
was  known  only  as  the  basis  of  the  pulp-uodule,  the  calcospherite^  and 
perhaps  of  the  dentine  and  bones,  which  remained  after  the  solution  of 
the  lime  salts  with  which  it  was  originally  combined.  It  thus  forms 
the  matrix  of  these  bodies,  and  the  assumption  that  this  is  calcoglobulin 
necessarily  embraces  the  idea  that  the  basis  substance  may  be  formed  in 
the  absence  of  sufficient  lime  salts  for  the  complete  calcification  of  the 
matrix.  I  know  of  no  record  of  the  accomplishment  of  this  by  arti- 
ficial means,  and  certainly  the  subject  needs  further  investigation. 

The  only  situations  of  the  natural — or,  I  might  say,  the  pathological — 
formation  of  the  calcospherite  is  in  the  dental  pulp  and  in  varicose  veins. 
The  formation  of  these  bodies  artificially  seems  to  require  the  presence 
in  solution  of  albumen,  the  salts  of  lime,  and  carbonic  acid  (carbon 
dioxide).  When  these  materials  are  brought  together  in  a  tightly-stop- 
pered bottle,  calcospherites  closely  resembling  those  found  in  the  dental 
pulp  and  in  varicose  veins  are  slowly  deposited  at  the  bottom.  This 
subject  has  been  very  closely  investigated  by  Rainie,  Ord,  Harting,  and 
others,  and  the  identity  of  the  artificial  forms  with  those  found  in  the 
situations  named  seems  well  established.      Now,  the  fact  that  these 


862  PATHOLOGY  OF  THE  DENTAL  PULP. 

bodies,  called  in  this  situation  phlebolites  or  phleboliths,  are  found  only 
in  varicose  veins  where  there  is  a  condition  of  congestion  or  venous 
hypersemia — in  which  cases,  as  is  well  known,  there  is  a  supersaturation 
of  the  "blood  with  carbonic  acid — seems  to  have  an  important  bearing  on 
the  conditions  of  their  formation  wherever  found.  When  there  is  venous 
congestion,  as  in  the  varicosities  of  the  veins,  the  blood  often  becomes 
intensely  venous,  or,  in  other  words,  an  unusual  amount  of  carbonic 
acid  has  accumulated  in  it,  and  the  blood  may  at  the  same  time  hold  a 
sufficient  quantity  of  the  salts  of  lime.  In  this  case  we  have  the  con- 
ditions found  necessary  for  the  formation  of  these  bodies  by  the  arti- 
ficial process,  and  in  the  blood-vessels  such  locations  are  the  only  ones 
in  which  these  bodies  are  found.  This  suggests  the  inference  that  in 
the  dental  pulp  the  formation  of  these  bodies  is  dependent  on  a  con- 
dition of  congestion ;  which  inference  is  strengthened  by  the  finding 
of  these  soft  forms  only  under  the  conditions  of  inflammation. 

In  this  connection  the  question  arises  as  to  whether  this  soft  form  is  the 
usual  mode  of  origin  of  these  bodies,  they  becoming  more  heavily  im- 
pregnated with  lime  salts  afterward.  In  favor  of  this  idea  is  the  state- 
ment made  by  most  authors — and  with  which  I  concur — that  in  the 
growth  of  enamel  and  dentine  there  is  a  stratum  constantly  presented 
that  has  not  acquired  its  full  amount  of  lime  salts,  and  is  still  compara- 
tively soft.  In  the  preparation  of  developing  teeth  I  have  often  cut 
quite  a  little  thickness  of  this  without  difficulty.  Yet  in  all  of  my 
examinations  I  have  never  found  a  pulp-nodule  in  a  soft  shell  or  with 
a  fsofter  portion  on  the  outside ;  and  it  seems  to  me  that  if  the  above 
were  the  true  mode  of  their  origin,  I  should  have  found  this.  This 
question  has  an  important  bearing  on  the  subject  of  pathology  as  con- 
nected with  the  pulp-nodule.  If  these  bodies  are  formed  in  the  tissues 
of  the  pulp  only  under  the  conditions  of  venous  congestion  or  inflam- 
mation, their  presence  has  a  signification  that  I  bad  not  attached  to 
them.  There  can  be  no  doubt  but  their  presence  in  the  pulps  of  teeth 
has  some  relation  to  irritation  of  the  dentinal  fibrils,  for  I  have  cer- 
tainly found  an  increased  number  in  the  teeth  of  those  who  had  suffered 
much  from  decay  or  abrasion,  each  of  which  exposes  the  fibrils  to  irri- 
tation. 

The  facts  given  above  as  to  the  mode  of  the  formation  of  these  bodies 
suggest  the  idea  that  calcoglobulin  and  the  pulp-nodule  originate  in  the 
veins  of  the  pulp  as  a  result  of  venous  congestion  or  hyperseraia,  and 
that  the  vessel  is  obliterated  thereby  ;  and  it  must  be  admitted  that 
those  conditions  that  are  known  to  be  favorable  to  the  promotion  of 
such  congestions  are  the  conditions  under  which  we  find  the  greatest 
number  of  pulp-nodules.  I  have,  however,  looked  for  evidences  of 
their  formation  within  the  veins  without  success.  Certainly,  we  find 
the  congestions  and  the  varicose  veins,  and  most  of  these  bodies  have 
about  them  a  condensation  of  tissue  resembling  in  some  degree  a  mem- 
brane ;  which  fact  has  been  noted  by  Wedl  and  a  number  of  other 
writers.  But  I  have  not  been  able  to  make  out  in  this  any  resemblance 
to  the  structure  of  the  walls  of  the  veins.  Again,  the  forms  of  these 
bodies  as  seen  in  the  dental  pulp  give  no  indication  of  their  formation 
in  the  veins. 


PULP-NODULES. 


863 


Fig.  457. 


A  Small  Pulp-nodule,  as  seen  with  a  low  power, 
showing  its  nodulation :  a  represents  the  nat- 
ural size  (X  15;. 


The  Pulp-nodule  may  be  found  in  any  part  of  the  pulp-ti.s.sue,  but 
occurs  mostly  in  the  coronal  portion  or  near  the  junction  of  this  with 
the  root  portion.  It  is  of  irreg- 
ular form,  and  in  mo.st  specimens 
it  is  irregularly  nodulated,  as  if 
made  up  of  an  aggi-egation  of 
smaller  nodules.  In  Fig.  457  is 
given  a  representation  of  one  of 
these  magnified  (the  true  size  be- 
ing represented  at  a),  which  gives 
a  good  idea  of  the  surface  aj^pear- 
ance  of  the  mass.  In  respect  to 
the  nodulation  there  is  the  great- 
est variety,  some  specimens  pre- 
senting a  very  smooth  outline. 
These  are  usually  the  large  ones, 
but  even  Avith  these  the  nodulated 
surface  is  the  rule.  They  are  very 
hard,  and  are  composed  of  the 
same  material  as  the  dentine,  but 
have  not  the  same  structure.  In 
Fig.  458  I  have  represented  this 
as  seen  in  section.  The  bodies  made  up  of  concentric  rings  are  the  cal- 
cospherites.  These  rarely  make  up  any  very  considerable  portion  of  the 
bulk  of  the  nodule ;  indeed, 

I  think  they  are  as  plenti-  ^^^-  ^■^'^• 

fully  distributed  in  this  sec- 
tion as  in  any  that  I  have  cut. 
The  balance  of  the  mass  is 
made  up  of  calcific  material 
that  shows  no  structure  what- 
ever, or  may  have  some  irreg- 
ular lines  or  faults  running 
through  it  without  any  def- 
inite arrangement.  Usually, 
this  is  very  clear  and  trans- 
parent, but  a  considerable 
number  of  specimens  are  ir- 
regularly clouded.  These  are 
not  calcifications  of  the  tissue 
of  the  pulp,  but  are  formed  in 
the  midst  of  the  tissue,  mak- 
ing room  for  them.selves  by 
pushing  the  ti.ssue  aside,  or, 
possibly,  they  may  be  formed  in  varicose  veins,  as  suggested  above. 
This  distinction  is  important  as  dividing  calcific  degenerations  of  the 
pulp-ti.ssue,  in  which  the  tissue  itself  is  impregnated  with  lime  salts, 
from  the  pulp-nodule.  Both  forms  are  found  in  the  form  of  irregular 
bodies,  and  are  not  unfrequently  a.ssociated  in  the  same  calcific  deposit. 

The  nodules  found  in  the  root  portion  of  the  pulp  arc  usually  smoother 


Section  of  a  Pulp-nodule  showins;  many  calcospherites, 
as  pointed  out  by  u,  n. 


864 


PATHOLOGY  OF  THE  DENTAL  PULP. 


in  their  outline,  and  are  much  more  likely  to  contain  calcified  tissues,  than 
those  found  in  the  coronal  portion.  These  are  often  associated  with 
calcific  degeneration  of  the  pulp-tissue,  which  will  be  considered  pres- 
ently.    In  Fig.  459,  I  give  an  illustration  of  a  group  of  these  nodules. 

Fig.  459. 


Pulp-nodules  in  the  Canal  Portion  of  the  Pulp  (X  o'J). 

There  has  been  a  disposition  on  the  part  of  the  profession  to  attach 
considerable  importance  to  pulp-nodules  in  the  pathological  sense. 
After  a  very  close  investigation  of  the  subject  I  cannot  share  this  feel- 
ing. Whatever  may  be  the  circumstances  attending  their  formation, 
they  seem  to  do  no  injury  after  they  are  once  formed  ;  at  least,  that  is 
the  inference  to  which  I  am  driven  after  a  very  large  number  of  exami- 
nations of  these  bodies  in  teeth  of  known  history.  Carefully-conducted 
examinations  show  that  they  are  more  abundant  in  the  teeth  of  the  mid- 
dle-aged and  the  old  than  in  those  of  the  young.  They  are  also  more 
plentiful  in  the  teeth  that  have  been  worn  by  mastication  or  have  suf- 
fered from  any  of  the  forms  of  abrasion  than  in  others.  In  these  cases 
the  individual  teeth  that  may  have  escaped  the  abrasion  are  about  as 
liable  to  contain  the  nodules  as  the  worn  ones.  I  also  find  an  increased 
number  in  teeth  from  mouths  of  persons  that  have  suffered  much  from 
caries.  Indeed,  any  circumstances  that  may  expose  the  dentinal  fibrils 
and  subject  them  to  irritation  seem  to  contribute  to  the  formation  of 
pulp-nodules,  not  only  in  the  teeth  directly  affected,  but  also  in  those 
that  are  not  affected.  Only  a  short  time  ago  I  selected  four  sound 
teeth,  the  enamel  of  which  seemed  very  perfect  (removed  from  the 
mouth  of  a  woman  twenty-five  years  old,  the  greater  part  of  whose 
teeth  had  been  destroyed  by  caries),  and  endeavored  to  make  sections 
of  them.  Every  part  of  the  tissue  was  studded  with  these  nodules  to 
such  an  extent  that  I  obtained  but  few  sections  good  enough  to  display 
the  condition  of  the  tissue.  These  showed  the  tissue  to  be  perfectly  nor- 
mal. In  studying  the  pulps  of  teeth  of  known  history  I  have  been 
unable  to  find  that  those  with  pulp-nodules  have  given  any  peculiar 
symptoms  or  have  given  more  pain  than  those  without  these  bodies. 
It  is,  however,  quite  possible  that  these  may  occur  of  such  size  near 
the  conjunction  of  the  coronal  and  root  portion  of  the  pulp,  or  in  the 
root  portion,  as  to  interfere  with  the  circulation,  and  in  this  way  con- 
tribute to  the  degeneration  of  the  organ;  or  they  may  by  their  volume 
interfere  with  its  functions. 


Hard  Formations  within  the  Pulp-chamber. 

Classification. — A  classification  of  the  hard  formations  within  the 
pulp-chamber  seems  desirable,  yet  it  is  doubtful  if  tliis  can  be  done  in  a 


SECONDARY  DENTINE.  865 

perfectly  satisfactory  way  at  the  present  time ;  and,  besides,  it  does  not 
seem  best  to  attempt  to  consider  these  entirely  apart  from  the  diseases 
of  the  soft  parts,  for  the  reason  that  the  one  seems  in  many  cases  to  be 
directly  dependent  on  the  other.  Some  attempt  at  classification  will, 
however,  serve  the  purpose  of  simplifying  description  ;  I  therefore  give 
the  following : 

1st.  Secondary  Dentine. — A  new  growth  of  dentine  more  or  less 
regular  in  formation,  excited  by  abrasion,  decay,  or  other  injury,  by 
which  the  dentinal  fibrils  are  subjected  to  irritation  at  their  distal  ends. 

2d,  Dentinal  Tumor  within  the  Pulp-chamber. — An  erratic  growth  of 
dentine  into  the  pulp-chamber  united  to  the  wall  by  a  pedicle.  The 
structure  is  usually  very  irregular. 

3d.  Nodular  Calcifications  among,  but  not  of,  the  Tissues  of  the  Pulp. 
— These  are  the  irregular  nodulated  masses  so  frequently  seen  either  as 
very  small  stones  or  irregular  masses.  They  contain  many  calcospher- 
ites.  These  were  considered  with  the  soft  parts  for  the  sake  of  con- 
venience. 

4th.  Interstitial  Calcifications  of  the  Tissues  of  the  Pulp. — This  is  the 
counterpart  of  calcifications  elsewhere  in  the  body,  as  in  the  arteries,  etc. 

5th.  Cylindrical  Calcifications  of  the  Pulp,  the  tissues  of  Avhich  are 
probably  in  a  state  of  fibrous  degeneration.  Usually  seen  in  the  pulp- 
canals. 

6th.  Osteo-dentine. — Erratic  formations  showing;  both  the  lacunse  of 
bone  and  dentinal  tubes. 

Calcospherites  may  be  seen  in  connection  with  any  of  these.  Many 
irregular  formations  are  found  that  are  scarcely  assignable  to  any  of 
these  forms,  and  it  is  not  unusual  to  find  them  intermixed  with  each 
other. 

Secondary  Dentine  is  the  result  of  a  new  growth  excited  by  some 
abnormal  condition  of,  or  injury  to,  the  tooth.  It  is  always  deposited 
upon  the  walls  of  the  pulp-chamber,  and  results  in  the  reduction  of  its 
size.  This  must  be  distinguished  from  the  normal  growth  of  the  dentine. 
In  the  young  the  pulp-chamber  is  comparatively  very  large,  and  dimin- 
ishes in  size  for  some  time  (which  cannot  be  definitely  stated)  after  the 
tooth  has  otherwise  completed  its  growth  or  has  attained  the  full  form 
of  its  root  and  crown.  This  growth  is  continuous  with  the  general 
structure  of  the  dentine,  without  break  or  demarcation  of  any  kind  so 
long  as  it  continues  normal ;  but  in  case  a  new  growth  is  excited  by 
abnormal  conditions  there  is  generally  a  departure  from  the  normal 
structure  that  distinguishes  it  sharply  from  the  original  dentine,  and 
enables  us  to  make  out  the  original  form  of  the  pulp-chamber.  This 
departure  from  the  normal  structure  varies  greatly  in  different  cases. 
It  is  occasionally  marked  by  a  sharp  curve  or  change  in  the  direction 
of  the  tubules  only,  or  there  may  be,  and  generally  there  is,  a  marked 
diminution  of  their  numbers.  Occasionally  the  sudden  diminishing  of 
the  number  of  the  tubules  will  be  the  only  distinguishing  mark,  and  in  a 
very  few  instances  I  have  seen  what  seemed  to  be  a  great  reduction  in 
the  size  of  the  chamber,  tiiat  had  occurred  with  such  perfect  regularity 
of  structure  as  to  leave  no  line  of  demarcation  whatever ;  but  this  is  rare. 
Generally  there  is  a  marked  difference  in  the  color  of  the  new  structure 

Vol.  I.— 55 


866 


PATHOLOGY  OF  THE  DENTAL  PULP. 


as  compared  with  the  primary  dentine,  by  which  it  is  readily  distin- 
guished with  the  naked  eye.  This  is  seen  in  teeth  that  have  been  so 
worn  by  abrasion  as  to  expose  the  new  structure  in  the  form  of  a  yel- 
lowish spot  which  marks  out  the  original  form  of  the  pulp-chamber. 

The  extent  to  which  secondary  dentine  may  be  formed  is  a  question  of 
much  importance.  There  seems  to  be  a  widespread  opinion  that  the  pulp- 
chamber  may  be  obliterated  by  the  formation  of  secondary  dentine.  This 
is  an  error.  At  least  I  know  of  no  well-authenticated  case  of  this  kind. 
The  secondary  deposit  seems  to  be  limited  within  certain  but  not  very 
definite  bounds,  which  always  stop  short  of  the  complete  filling  of  the 
chamber.  This  deposit,  as  compared  with  the  size  of  the  pulp-cavity,  is 
more  extensive  in  the  single-rooted  teeth,  as  the  incisors  and  cuspids, 
than  in  the  molars.  In  the  former  it  is  not  unusual  to  see  considerable  of 
the  crown  portion  completely  filled,  so  that  the  secondary  formation  will 
do  good  service  in  the  protection  of  the  pulp  from  exposure.  In  Fig.  460 
is  given  an  illustration  of  this  as  it  is  usually  seen  in  the  anterior  teeth 
affected  by  abrasion.     It  will  be  noticed  that  the  pulp-cavity  is  per- 

FiG.  461. 


Fig.  460. 


Fig.  460. — Secondary  Dentine,  filling  the  pulp-chamber  in  case  of  abrasion  of  a  cuspid  tooth  :  a,  por- 
tion lost  by  abrasion;  c,  abraded  surface;  (/,  secondary  dentine,  filling  a  portion  of  the  pulp- 
chamber,  and  acting  as  a  protection  to  the  pulp;  c,  slender  point  of  the  pulp  ;  irregular  deposits 
are  seen  on  the  walls  of  the  pulp-chamber,  as  at/;  g,  cylindrical  calcifications  in  the  root  portion 
of  the  pulp-chamber. 

Fig.  461.— Secondary  Dentine,  from  the  same  specimen  as  Fig.  460,  magnified  sufficiently  to  show  the 
difference  in  primary  and  secondary  tissue:  a.  abraded  surface  of  crown  ;  ft,  secondary  dentine ; 
c,  primary  dentine;  d,  junction  of  primary  with  secondary  dentine;  e,  remains  of  pulp-tissue; 
/,  small  oval  masses  of  calcific  material. 

fectly  filled  for  only  a  very  short  distance  in  advance  of  the  abrasion. 
This  is  more  definitely  shown  in  Fig.  461,  from  the  same  specimen, 
magnified  sufficiently  to  show  the  structure  as  compared  with  the  ])ri- 
mary  dentine.     In  this  case  it  will  be  seen  that  the  secondary  formation 


SECONDARY  DENTINE. 


867 


is  fairly  regular,  but  that  the  number  of  dentinal  tubes  is  much  dimin- 
ished. This  is  quite  the  common  form  of  secondary  formations  in  the 
incisors  and  cuspids  when  they  are  slowly  worn  by  attrition.  This 
kind  of  formation  is  always  limited,  though  some  cases  present  much 
more  of  the  secondary  formation  than  others  before  the  final  degener- 
ation and  death  of  the  pulp ;  which  seems  very  certain  to  follow  sooner 
or  later,  probably  from  exhaustion.  In  the  root  portion  of  this  speci- 
men (Fig.  460)  there  is  an  extensive  deposit  of  cylindrical  calcifications 
(to  be  described  presently),  which  very  surely  mark  the  last  perform- 
ances of  the  organ. 

In  the  pulps  of  the  molar  teeth  affected  by  abrasion  we  find  similar 
deposits  of  secondary  dentine ;  but  in  this  case  there  are  certain  pecu- 
liarities that  deserv^e  mention,  especially  as  they  are  of  importance  in 
the  clinical  sense.  In  all  of  the  double-  or  triple-rooted  teeth  there  is 
a  very  distinct  enlargement  of  the  pulp  in  the  coronal  portion,  from 
which  the  several  root  portions  diverge  into  their  canals.  This  forms 
the  bulb  of  the  pulp,  which  is  absent  in  the  single-rooted  teeth.  Now, 
in  this  case  the  formation  of  secondary  dentine  is  confined  almost  ex- 
clusively to  the  bulb  of  the  pulp,  extending  into  the  root  portion  verv 
little,  if  at  all,  or,  we  may  say,  it  is  confined  to  the  very  orifice  of  these 
canals.  Otherwise  than  this  the  deposit  is  very  nearly  uniform  on  all 
parts  of  the  walls  of  the  chamber,  or  if  differ- 
ences exist  the  deposit  is  least  on  the  anterior 
and  posterior  walls  and  greatest  on  the  floor 
and  roof.  In  Fig.  462  I  have  accurately  drawn 
the  outline  of  a  section  of  the  crown  of  a  supe- 
rior molar  abraded  but  slightly  (though  its  as- 
sociates were  badly  worn),  for  the  purpose  of 
illustrating  the  position  of  the  secondary  de- 
posits as  they  are  most  generally  seen  in  cases 
of  extreme  reduction  of  the  size  of  the  pulp. 
The  lightly-shaded  portion  represents  the  orig- 
inal form  and  size  of  the  chamber,  and  the  dark 
shading  that  portion  not  filled  by  the  second- 
ary deposit.  It  will  be  noted  in  this  case  that 
the  deposit  is  as  great,  or  nearly  so,  rootwise 
from  the  remaining  portion  of  the  pulp,  as 
that  dejjosited  next  the  crown  ;  and  in  the  one 
root  which  appears  in  the  drawing  the  narrow- 
ing of  the  canal  is  confined  to  the  portion  orig- 
inally within  the  pulp-chamber.  So  far  as 
deposits  of  secondary  dentine  are  concerned, 
this  remains  quite  constant  in  all  of  my  sec- 
tions. In  some  cases  the  rootwise  deposit  is 
the  greatest,  but  the  difference  is  never  very  great.  The  narrowing  of 
the  root-canals  within  the  original  pulp-chamber  is  occasionally  so  ex- 
treme that  it  is  difficult  to  get  a  broach  through  them ;  but  the  root- 
canal  is  usually  about  the  normal  size,  provided  always  that  there  are  no 
other  hard  formations  except  the  secondary  dentine.  There  arc,  how- 
ever, occasional  exceptions  to  this  rule  in  which  there  is  considerable 


Illustration  of  the  Narrowing  of 
the  Pulp-chamber  in  a  Slolar 
(superior)  by  the  deposit  of  sec- 
ondary dentine  resulting  from 
aljrasion,  showing  the  portions 
of  the  chamber  in  which  the 
deposit  usually  occurs.  The 
light-shaded  portion  (li)  shows 
the  original  dimensions  of  the 
chamber,  which  in  this  in- 
stance seems  to  have  been  pret- 
ty large ;  a,  a  point  of  deep 
abrasion  ;  c,  c,  remaining  pulp- 
chamber,  which  is  mostly  filled 
with  irregular  masses ;  rf,  one 
of  the  root-canals.  It  will  be 
observed  that  the  narrowing  of 
the  root-canal  is  within  the 
original  pulp-chamber. 


868  PATHOLOGY  OF  THE  DENTAL  PULP. 

narro^A'ing  of  the  canals,  but  I  have  seen  very  few.  In  those  cases  in 
which  the  root-canal  is  obstructed  I  have  generally  found  it  to  be  with 
pulp-nodules,  cylindrical  calcifications,  or  general  calcification  of  the 
tissues  of  the  pulp.     In  Fig.  463,  at  c,  c,  there  is  a  blocking  of  the 


Reduction  of  the  Size  of  the  Pulp-chambev  by  deposit  of  secondary  dentine  excited  by  abrasion. 

A,  Diagram  of  a  Lower  Molar  badly  worn,  showing  narrowing  of  the  pulp-chamber. 

B,  Illustration  of  the  Tissue  of  the  Secondary  Deposit:  a,  «,  </,  a,  outline  of  the  original  pulp-ehani- 

ber,  from  which  the  secondary  growth  has  begun  ;  in  the  rootwise  portion  theie  iippears  a  second 
line  of  beginning;  b,  gloliuhir  dentine,  in  which  a  few  dentinal  tubes  may  be  seen  traversing  the 
the  globules  ;  c,  irregular  crystalline  deposits. 

entrance  to  the  root-canals  by  calcific  deposits  in  the  form  of  irregular 
crystalline  masses.  In  this  figure,  at  A,  is  represented  a  lower  molar 
with  the  crown  very  much  abraded  by  mastication,  the  pulp-cavity  of 
which  is  very  much  reduced  by  the  growth  of  secondary  dentine.  The 
lines  «,  rt,  o,  a  point  out  the  original  outlines  of  the  pulp-chamber,  and 
the  new  tissue  formed  is  seen  to  be  quite  regular  in  its  structure.  The 
rootwise  portion  of  the  new  formation  shows  two  lines  of  the  beginning 
of  new  growth,  showing  that  there  had  been  a  cessation  and  rebeginning 
of  the  process.  In  passing  I  will  call  attention  to  the  peculiar  structure 
at  6,  in  which  a  series  of  globules  are  seen  to  have  a  few  dentinal  tubes 
passing  through  them.  Here  the  secondary  growth  has  become  mark- 
edly abnormal ;  and  tliis  abnormality  is  expressed  in  some  form  in 
almost  every  case  in  which  the  pulp  has  died  from  exhaustion  follow- 
ing large  deposits  of  secondary  dentine. 

It  is  found  that  these  growths  of  secondary  dentine  caused  by  abra- 
sion are  not  confined  to  the  particular  teeth  worn,  but  if  there  is  con- 
siderable wear  of  the  teeth  generally,  those  that  may  have  escaped 
abrasion  will  have  the  growth  of  secondary  dentine  in  very  nearly  the 
same  degree  as  those  that  have  actually  suffered  from  the  wear. 

Grovths  of  Secondary  Dentine  excited  by  Carief^  present  some  features 
that  differ  markedly  from  those  excited  by  abrasion.  As  has  been  seen, 
deposits  of  secondary  dentine  excited  by  abrasions  are  very  generally 
equally  distributed  on  the  inner  walls  of  the  pulp-chamber.  In  their 
structure  and  in  the  direction  of  their  tul)ules  they  resemble  very  closely 
the  normal  dentine.  In  the  study  of  secondary  dentine  the  growth  of 
Avhich  lias  been  excited  by  the  irritation  of  caries  this  is  quite  different 
in  a  large  proportion  of  cases.     The  irritation  is  confined  to  a. smaller 


SECONDARY  DENTINE. 


869 


number  of  fibrils,  and  the  new  growth  is  very  generally  confined  to  a 
small  part  of  the  pulp-ehaniber  immediately  opposite  the  fibrils  irritated 
— not  generally,  indeed,  to  the  exact  fibrils  that  are  involved  in  the 
decay,  but  to  that  portion  of  the  pulp-cavity.     In  Fig.  464  I  gis^e  an 


Fig.  464. 


Calcification,  or  Deposit  of  Secondary  Dentine,  resulting  from  caries  of  an  incisor. 

A,  Diagram  of  Section  of  Incisor,  showing  caries  at  a,  and  secondary  dentine  at  li. 

B,  Illustration,  magnified  2Ui)  diameters,  to  show  the  tissue  of  tlie  secondary  dentine:  a,  pulp-rbani- 

ber;  6,  h,  secondary  dentine;  c,  primary  dentine.     It  will  be  noticed  that  the  dentinal  tubes  in 
the  secondary  dentine  gftidually  disappear,  giving  place  to  a  clear  calcification. 

illustration  of  this.  At  A  is  represented  a  section  of  a  central  incisor  with 
a  small  dark  decay  in  the  proximal  surface  at  «,  and  a  growth  of  sec- 
ondary dentine  at  6,  which  is  confined  to  the  side  of  the  pulp-chamber 
toward  the  decayed  point.  At  B,  I  give  an  illustration  of  the  tissue  of 
the  new  growth,  in  which  it  will  be  seen  that  there  is  a  marked  diver- 
sion of  the  tubules  from  the  normal  direction  at  the  beginning  of  the 
new  growth,  and  also  that  the  tubules  soon  become  irregular,  and  finally 
disappear,  leaving  the  portion  next  to  the  pulp  simply  a  clear  calcifica- 
tion, showing  that  the  pulp  has  degenerated  and  become  incapable  of  the 
proper  performance  of  its  physiological  functions — a  sure  precursor  of 
its  complete  destruction.  This  tooth  was  from  the  mouth  of  a  negro 
woman  who  came  to  me  with  an  acute  apical  pericementitis.  She  was 
sure  the  tooth  had  not  given  her  pain  before  the  present  attack.  The 
pulp  was  not  exposed,  and  no  cause  could  be  assigned  for  its  death.  I 
should  say  that  in  grinding  the  section  I  found  that  the  pulp-chamber 
contained  numerous  calcific  masses,  which  were  lost,  unfortunately,  with- 
out their  character  having  been  ascertained.  As  there  were  many  decayed 
teeth  in  the  mouth,  much  of  this  may  have  been  excited  by  sym]xathy. 
Yet  the  case  illustrates  very  well  the  general  nature  of  secondary  dentine 
excited  by  decay.  It  is  of  medium  type  as  to  the  regularity  of  structure, 
and  the  result  is  that  which  we  may  expect  to  follow  in  ca.ses  of  consid- 


870 


PATHOLOGY  OF  THE  DENTAL  PULP. 


erable  secondary  deposit — death  of  the  pulp  from  degeneration  of  its 
structure. 

In  Fig.  465  is  presented  another  case  in  which  the  exciting  cause  of 
the  new  growth  was  apparently  about  the  same  as  that  in  Fig.  464. 
This  case  presented  a  history  of  hypersemia  from  thermal  changes.  At 
A  is  given  a  diagram  of  the  tooth  considerably  enlarged,  showing  the 

Fig.  465. 


Secondary  Deutine,  resulting  from  irritation  of  the  dentinal  fibrils  by  caries. 

A,  Diagram  of  an  incisor  having  a  decay  in  the  labial  surface,  a,  and  a  deposit  of  secondary  dentine  at 

h.    The  point  from  which  the  illustration  B  is  taken  is  sliown  by  c. 

B,  Illustration  of  the  Tissue  of  the  Secondary  Deposit  in  A  :  a,  primary  dentine ;  h.  secondary  dentine  ; 

c  seems  to  be  a  blood-vessel  that  has  become  calcified  ;  d,  an  irregular  fault  having  some  resem- 
blance to  the  lacunse  of  bone  :  e,  pulp-chamber.  It  will  be  noted  tliat there  are  irregular  deposits 
of  granular  matter  in  the  substance  of  the  secondary  dentine,  and  that  the  tubules  wind  about 
them. 

relative  position  of  the  decay  and  the  growth  of  secondary  dentine,  c 
indicates  the  point  from  which  the  field  B  was  taken.  In  this  case  the 
secondary  formation  was  very  irregular,  and  presented  many  fields  of 
granular  calcific  material  interspersed  among  the  dentinal  tubules.  At 
c  a  blood-vessel  seems  to  have  been  caught  in  the  new  growth,  and  has 
become  calcified.  At  d  there  is  a  curious  form  resembling  in  some 
degree  the  lacunse  of  bone,  but  I  am  inclined  to  the  opinion  that  it  is 
simply  a  fault.  This  case  presents  a  curious  specimen  of  irregular 
formation.  If  space  permitted  a  great  variety  of  these  might  be 
presented. 

Fig.  466  is  an  illustration  of  a  ca.se  in  which  the  seondary  formation 
has  been  excited  by  a  very  small  decay  on  the  labial  surface  of  an  incisor, 
and  is  confined  almost  entirely  to  the  fibrils,  the  distal  ends  of  which 
are  irritated  by  the  carious  process.  Such  cases  have  been  spoken  of 
by  a  number  of  writers,  but  within  my  personal  observation  secondary 
dentine  so  strictly  limited  as  this  has  been  rare.  It  serves  well  to  illus- 
trate the  fact  recognized  by  most  of  those  who  have  critically  examined 
this  subject,  of  the  effect  that  is  occasionally  produced  within  the  pulp- 
chamber  by  the  irritation  of  the  distal  ends  of  the  dentinal  fibrils  by  the 
processes  of  caries.  It  must  not  be  supposed,  however,  that  such  effects 
as  those  illustrated  here  or  in  other  writings  on  this  subject  are  uniformly 


SECONDARY  DENTINE. 


871 


present  in  the  pulp-chamber  in  cases  of  caries  of  the  dentine.  The  facts 
are  quite  the  reverse ;  and  it  is  well  that  it  is  so,  for,  unless  my  observa- 
tion is  at  fault,  any  very  considerable  deposits  of  secondary  dentine  mean 
exhaustion  and  degeneration  of  the  pulp,  followed  finally  by  its  complete 
destruction.  In  the  search  among  decayed  teeth  for  secondary  dentine 
we  may  indeed  find  many  examples  and  an  indefinite  variety  of  forms, 


Fig.  466. 


3 


-4,  Section  of  an  Incisor  having  a  small  dark  decay  in  the  buccal  (or  labial)  surface:  a,  the  tubules 
leading  from  this  to  the  pulp-chamber  are  pointed  Out  at  6.  At  c  a  small  deposit  of  irregular 
secondary  dentine  has  occurred,  Avhieh  is  seen  magnitied  in  B.  The  shading;  at  e  shows  some 
secondary  deposit  along  the  wall  of  the  pulp-chamber.  The  turning  of  the  tubules  away  from 
the  principal  deposit,  as  shown  at  a,  a  in  B,  is  very  singular. 

but  the  great  majority  of  decayed  teeth  present  no  secondary  formations. 
The  circumstances  that  determine  the  formation  of  secondary  dentine  in 
the  one  case  or  fail  to  bring  it  about  in  another  are  by  no  means  well 
known.  My  personal  observations  on  this  point  seem  to  show  that  the 
greater  number  of  these  formations  are  found  in  connection  with  decays 
that  have  progressed  very  slowly,  or,  in  other  words,  cases  in  which  the 
dentinal  fibrils  have  for  a  long  time  been  continuously  exposed  to  irri- 
tation. I  have  found  them  mostly  in  persons  of  middle  age,  though 
occasionally  in  those  not  yet  past  their  teens.  They  are  not,  there- 
fore, confined  to  any  time  of  life,  nor,  so  far  as  I  am  able  to  determine, 
to  any  peculiar  condftion  of  the  teeth  or  the  patient.  I  think  they  will 
be  found  oftener  in  cases  in  which  the  teeth  have  many  cavities  than  in 
those  in  which  the  cavities  are  few.  The  teeth  seem  bound  together  by 
a  bond  of  sympathy  that  is  very  marked,  and  any  cause  that  produces  a 
considerable  effect  upon  one  tooth  has  its  effect  upon  all,  often  in  a  very 
great  degree.  This  is  seen  most  prominently,  perhaps,  in  the  second- 
ary deposits  excited  by  abrasions,  in  which  all  the  pulps  of  the  teeth 
suffer  from  the  wear  of  a  part  of  the  number.  But  it  is  seen  also  in  all 
of  the  diseases  to  which  the  teeth  are  subject.  Decay  that  causes  irrita- 
tion with  deposits  of  pulp-nodules  in  one  tooth  is  certainly  liable  to 


872 


PATHOLOGY  OF  THE  DENTAL  PULP. 


bring  about  similar  results  in  the  pulps  of  those  otherwise  unaffected. 
Inflammation  of  the  pulp  of  a  single  tooth  will  induce  hypersesthesia 
of  the  pulps  of  the  whole  denture,  etc.  This  is  seen  in  other  organs  of 
the  body  as  well.  If  one  eye  is  seriously  diseased,  the  other  suffers  from 
sympathy,  and  in  certain  pathological  conditions  oculists  often  extirpate 
one  eye  in  order  to  save  the  other.  The  effect  of  one  diseased  tooth  upon 
others  is  in  every  respect  similar,  though  not  so  great  in  degree. 

Dentinal  Tumors  within  the  Pulp-chamber  are  rare  forms  of  the  growth 

Fig.  467. 


^, Section  of  an  Upper  Molar  Tooth:  a,  a  carious  cavity;  h,  fairl)-  regular  secondary  dentine;  r,  a 
dentinal  tumor  which  has  grown  into  the  pulp-chaniber,  occupying  the  greater  part  ol'  it.  This 
was  attached  to  the  wall  of  the  chamber  by  a  rather  narrow  pedicle.  The  structure  is  extremely 
irregular,  and  varies  much  iu  its  different  parts.  The  section  was  saturated  witli  balsam  and 
ground  thin  and  polished  ;  afterward  the  balsam  was  dissolved  out  in  turpentine,  and  it  was  then 
soaked  in  chloroform  to  remove  tlie  turpentine,  and  finally  mounted  dry. 

.B(Fig.  4(;7)  iiiircsents  one  field  of  view,  and  I'igs.  468  and  469  two  otliers.  The  tubules  are  quite 
remarlvable  for  the  large  number  of  their  branches  and  the  irregularity  of  their  direction. 

of  secondary  dentine,  in  which  a  more  or  less  considerable  calcific  mass 
is  attached  to  the  wall  of  the  pulp-chamber  by  a  pedicle.  These  growths 
are  occasionally  notable  for  the  singular  irregularity  of  their  structure. 


DENTINAL  TUMORS. 


873 


I  ha%'e  met  with  some  very  remarkable  examples.  One  of  these  is  rep- 
resented in  Figs.  467,  468,  and  469.  In  Fig.  467,  at  A,  is  given  a 
diagrammatic  representation  of  a  molar  which  had  a  small  cavity  in 
the  anterior  proximal  surface.  Opposite  this  there  appears  an  ordinary 
growth  of  secondary  dentine,  pointed  out  by  6  ;  c  is  a  large  pediculated 
tumor  arising  from  the  growth  of  secondary  dentine,  and  composed  of 
the  most  extravagantly  irregular  dentine  that  has  been  my  fortune  to 
see.  At  B  is  given  an  illustration  representing  a  field  from  this,  and 
in  Figs.  468  and  469  two  more,  which,  taken  together,  illustrate  the 
characteristics  of  the  tissue  Very  fairly.  The  illustrations  will  do  more 
to  convey  a  correct  idea  of  the  structure  of  this  tumor  than  any  verbal 
descrii)tion  that  I  am  able  to  give.  It  is  very  transparent,  except  in 
some  })oints  where  it  is  shaded  by  extremely  fine  tufts  of  tubules,  as  in 
some  })arts  of  each  of  the  figures.  These  tufts  form  one  of  t-lie  prom- 
inent characteristics  of  the  tissue,  and  appear  here  and  there  throughout 
its  mass.  These  seem  to  unite  in  many  places  to  form  unusually  large 
dentinal  tubes,  which,  after  pursuing  a  straight  course  for  a  short  dis- 
tance, are  apt  to  be  abruptly  curved  and  lost,  generally  by  passing  out 
of  the  section,  but  sometimes  seeming  to  end  in  blind  extremities.  There 
are  also  many  very  curious  groupings  of  these  tufts,  as  though  odonto- 

FiG.  470. 


Dentinal  Tumor  within  the  Pulp-chamber:  .J,  diagram  of  the  tooth,  with  dotted  line  showing  the  posi- 
tion of  the  section  B.  In  B  the  pLilp-chamber  is  shown  in  section,  nearly  natural  size,  showing  the 
tumor  witliin.  Cis  an  illustration  of  the  tissue  of  the  tumor;  a.  a.  the  primary  dentine  ;  h,  irreg- 
vdar  tubules  connecting  the  new  growth  with  the  primary  dentine — most  of  these  are  very  dark 
and  irregular;  c,  a  calcospherite  included  in  the  mass:  rf,  apparently  a  blood-vessel  calcified;  ^, 
calcified  tissue;  ./',  a  finely  granular  mass;  g,  a.  spur  of  very  transparent  dentine.  Dentinal 
tubules  appear  at  A,  /(. 


blasts,  or  at  least  dentinal  fibrils 
some  fields,  of  which  Fig.  468 


,  had  originated  at  these  localities.     In 
is  an  example,  the  tubules  are  very 


874  PATHOLOGY  OF  THE  DENTAL  PULP. 

sparsely  distributed.  In  others  they  are  quite  thickly  placed,  or  even 
crowded,  as  in  Fig.  469.  But  the  more  general  character  is  that  of 
irregular  grouping  of  the  tubules  with  intervening  clear  spaces,  as  seen 
in  B,  Fig.  467.  Now  and  then  there  are  seeming  faults  filled  in  with 
very  fine  granular  matter,  one  of  which  occurs  in  Fig.  468. 

In  Fig.  470  another  case  is  illustrated,  in  which  the  new  growth 
seems  to  consist  partly  of  secondary  dentine,  which  is  intermixed  with 
granular  calcific  material,  calcified  tissue,  and  calcospherite.  These  two 
specimens  represent  the  extremes  of  tissue-formation  occurring  in  these 
tumors.  They  are  universally  connected  ^fith  the  walls  of  the  pulp- 
chamber  by  a  pedicle,  either  narrov/  or  broad,  by  which  the  dentinal 
tubes  have  passed  into  the  tumor.  It  happens  many  times  in  the  prep- 
aration of  sections  of  these  pathological  growths  that  the  pedicle  is  lost, 
giving  the  impression  that  the  dentinal  fibrils  are  developed  within  the 
tissues  of  the  pulp.  I  cannot  but  regard  this  as  an  error.  In  every 
case  in  which  I  have  had  the  proper  opportunity  for  the  examination 
of  these  masses  presenting  dentinal  tubes  they  have  sprung  from  the 
walls  of  the  pulp-chamber,  and  some  portion  of  the  tubes  are  con- 
tinuous with  those  of  the  primary  dentine.  And  now  I  should  regard 
the  appearance  of  undoubted  dentinal  tubes  in  any  mass  Avithin  the 
pulp-chamber  as  a  sufficient  proof  of  that  fact. 

This  form  of  tumor  is  confined  exclusively  to  the  pulp-chamber.  I 
have  never  seen  such  a  growth  in  the  root  portion.  The  causes  which 
lead  to  the  growth  are  evidently  the  same  as  those  leading  to  forma- 
tions of  secondary  dentine  generally.  AVhat  circumstances  determine 
the  erratic  tumor-like  form  of  the  growth  is  entirely  unknown.  So  far 
as  the  symptomatology  is  concerned,  I  know  of  no  observations  that 
throw  any  light  whatever  on  the  subject.  The  existence  of  the  growth 
cannot  be  known  until  after  the  destruction  of  the  organ,  and  its  occur- 
rence is  so  rare  that  we  are  not  likely  to  obtain  much  light  by  having 
known  the  history  of  the  chance  cases  discovered. 

Chlcificaiions  of  the  Tissues  of  the  Pvlp  are  probably  the  most  difficult 
of  the  problems  presented  in  the  consideration  of  the  pathological  forma- 
tions within  the  pulp-chamber.  Many  specimens  are  presented  which 
it  is  impossible  to  assign  to  any  specific  class,  no  matter  how  skilfully 
we  may  arrange  our  classification  ;  yet  in  most  of  these  cases  we  will 
find,  if  we  have  the  proper  opportunity  of  examination,  that  some  part 
of  the  tissue  is  incorporated  in  the  calcific  mass,  or  so  attached  to  it  as 
to  show  that  it  is  also  undergoing  the  process  of  infiltration  with  lime 
salts.  There  are  very  few  cases  presented  that  show  the  form-elements  of 
the  tissue  calcified  in  such  a  manner  that  it  can  be  certainly  identified ; 
but  after  a  large  number  of  examinations  with  the  object  of  determining 
this  point,  it  is  fimnd  that  there  are  certain  characteristic  differences 
between  these  calcifications  and  the  pulp-nodules  that  distinguish  them 
with  a  considerable  degree  of  certainty.  They  do  not  present  the  nod^ 
ulated  appearance  of  the  pulp-nodules,  but,  on  the  other  hand,  have 
rather  a  regular  outline  with  generally  a  smooth  surface.  When 
prominences  are  present,  they  are  in  the  direction  of  the  trend,  as 
it  may  be  called,  of  the  tissue  l)eing  calcified  or  the  direction  pursued 
by  the  blood-vessels  of  the  part.     The  characteristics  of  the  tissue, 


CALCIFICATIONS  OF  THE  DENTAL  PULP. 


875 


if  it  may  be  so  termed,  will  be  discussed  in  connection  with  the 
illustrations. 

Heretofore  there  seems  to  have  been  no  effort  to  distinguish  between 
these  formations  and  the  pulp-nodule.  To  my  mind,  the  distinction  is 
important  in  the  pathological  sense.  The  presence  of  a  few  pulp-nod- 
ules in  a  tooth  is  of  very  little  significance  so  far  as  the  future  health 
of  the  pulp  is  concerned.  We  find  no  degeneration  of  the  tissues  of 
the  pulp  associated  with  them,  unless,  indeed,  there  are  other  causes 
of  ill  health  of  the  organ.  But  tissue-calcification  is  uniformly  asso- 
ciated with  degeneration  of  the  uncalcified  tissues  of  the  pulp.  It  is  true 
that  pulp-nodules  may  be  seen  in  pulps  that  are  rapidly  undergoing  the 
l)rocesses  of  degeneration,  and  may  also  be  included  within  these  calcifi- 
cations. When  once  formed  they  do  not  disappear,  and  they  will  be 
connected  with  any  diseased  condition  which  may  afterward  overtake 
the  organ.  On  the  other  hand,  tissue-calcifications  are  never  met  with 
in  healthy  tissue. 

In  Fig.  471,  I  have  illustrated  a  case  of  calcification  which  seems  to 
include  within  it  the  form-elements  of  an  inflamed  pulp.     At  A,  I  have 


A,  Diagram  of  a  Section  of  a  Central  Incisor,  w  itli  .i  proximal  decay  at  a  which  seems  to  have  pene- 

trated the  original  pulp-chamber,  but  the  opening  is  closed  by  a  calcification  at  h.    c  marks  the 
position  of  a  detached  mass  of  calcific  material  th:it  was  lost  in  mounting  the  section. 

B,  Illustration  showing  the  Appearance  of  the  Calcific  Deposit.    This  seems  to  be  a  calcification  of 

indamed  or  cicatricial  tissue.    At  a  there  is  the  appearance  of  a  blood-vessel ;  b,  pulp. 

represented,  diagrammatically,  a  central  incisor  with  a  proximal  decay 
at  a  which  opeiis  the  original  pulp-cavity.  This  opening  is  closed  by 
a  calcific  mass  at  6.  At  c  there  was  a  large  elongated  mass  unattached 
to  the  walls  of  the  pulp-chamber  which  was  lost  in  mounting  the  sec- 
tion after  it  was  ground  At  B,  I  give  an  illustration  of  a  field  of  the 
mass  b  \n  A,  in  which  the  form-elements  appear  quite  distinctly.  At  a 
there  is  the  api^earance  of  a  blood-vessel  with  its  branches.  My  suppo- 
sition is  that  this  calcification  occurred  after  the  exposure  of  the  pulp  by 
decay  and  inflammation  of  the  ])ulp-tissue,  and  that  for  the  time,  no 
doubt,  the  pulp  was  protected.     But  in  the  formation  of  this  protective 


876 


PATHOLOGY  OF  THE  DENTAL  PULP. 


covering — or,  we  may  say,  primarily  by  the  inflammation — processes  of 
degeneration  were  inaugurated  that  resuhed  finally  in  the  destruction  of 
the  organ. 

Many  calcifications  of  this  order  are  found  from  time  to  time  that  are 
very  large — as  large,  indeed,  as  the  capacity  of  the  pulp-chamber  will 
allow.  But  the  attachment  of  the  mass  to  the  walls  of  the  pulp-cham- 
ber, as  was  the  case  in  Fig.  471,  is  rather  an  exception  to  the  rule.  I 
have  often  seen  these  so  perfectly  fitting  to  the  walls  of  the  chamber  in 
such  cases  that  they  appeared  to  be  attached  until  I  had  ground  a  sec- 
tion.    Fig.  472  is  an  illustration  of  a  case  of  this  character.     At  A,  I 


Calcification  of  the  Dental  Pulp.  At  A  is  shown  tliu  outline  ot  .i  low  ei  molar  w  itb  a  cavity  at  6.  Tlie 
pul|j-chamber  is  much  reduced  in  size  and  filled  with  calcific  material,  iis  shown  in  B.  n.  a  large 
granular  mass  of  calciiic  material,  which  is  very  transparent,  but  finely  granular.  A  few  very 
irregular  lines  are  seen  in  the  centre,  which  slightly  resemble  dentinal  tubes ;  /;,  an  erratic  growth 
of  irregularly  formed  and  unusually  transparent  dentine;  c,  line  of  the  growth  of  dentine  from 
the  floor  ol  the  pulp-chamber:  the  growth  from  other  directions  is  so  perfectly  regular  as  to  leave 
no  markings;  '/,  margin  of  the  cavity  of  decuy  ;  f, a  bundle  of  cylindrical  forms  of  calcific  mate- 
rial extendiiig  down  into  the  root-canal.    1  hese  extended  to  the  apex  of  the  root. 

give  an  illustration  showing  a  lower  molar  with  a  proximal  decay  at  the 
junction  of  the  enamel  and  cementum,  exposing  the  pulp.  In  this  case 
there  has  been  a  marked  reduction  in  the  size  of  the  pulp-chamber  by  a 
secondary  growth  of  dentine  that  is  remarkable  for  its  regularity,  as  will 
be  seen  by  the  inspection  of  the  illustration  of  the  tissue  as  shown  in  B. 
The  line  of  the  new  growth  is  clearly  marked  in  the  root  wise  portion  at 
e,  but  in  other  directions  there  exists  no  demarcation  whatever.  At  b 
there  is  a  distinct  dentinal  tumor  in  the  form  of  a  spur  having  its  base 
at  c,  where  it  springs  from  the  rootwise  portion  of  the  original  wall  of 
the  pulp-chamber,  and  its  point  turns  in  under  the  calcific  de])osit  (f.  At 
a  is  a  calcification  that  fills  nearly  the  entire  pulp-chamber.  The  mass  is 
very  clear  and  transparent,  and  presents  a  finely  granular  appearance, 
Avithout  any  sign  of  structure  except  some  irregular  lines  in  its  centre. 
With  the  low  power  with  which  the  drawing  was  made  these  resemble 


CALCIFICATIONS  OF  THE  DENTAL  FULP. 


877 


dentinal  tubes,  but  with  higher  powers  they  are  found  to  present  cha- 
racters which  show  them  to  be  fliults.  At  either  extremity  of  the  mass 
the  degenerated  tissue  is  apparent  in  the  form  of  minute  irregular 
threads  Avhich  give  these  parts  a  clouded  appearance.  At  the  root- 
wise  extremity  it  is  connected  with  some  cylindrical  calcifications  {e) 
which  extend  down  into  the  root-canal. 

These  two  illustrations  may  be  regarded  as  exhibiting  the  extremes 
that  appear  in  the  study  of  this  subject — the  first  showing  most  clearly 
the  form-elements  of  the  tissue  calcified,  and  the  last  exhibiting  the  few- 
est traces.  Generally,  nothing  can  be  clearly  made  out  except  some  fine 
lines  that  seem  to  represent  fibres  that  have  persisted  or  the  perverted 
forms  of  cells  which  seem  to  have  escaped  impregnation  with  lime  salts. 
This  may  occur  in  groups,  as  I  suppose,  resulting  in  faults  of  irregular 
form,  or  single  cells  may  remain,  distorted  perhaps  beyond  recognition. 
In  some  such  Avay  most  of  the  tissue-calcifications  possess  a  great  diver- 
sity of  markings  of  which  nothing  definite  can  be  made  by  microscojjic 
examination.     In  Fig.  473  is  represented  a  field  from  a  calcification 

Fig.  473. 


A,  Outline  of  Incisor,  with  crown  destroyed  by  decay.    There  is  a  calcific  deposit  in  the  root  portion 

of  the  pulp-chamber  |  inches  long,  pointed  out  by  a. 

B,  Illustration  showing  the  characters  of  the  calcification.    Some  of  the  forms  resemble  somewhat 

the  lacunae  of  boue  (X  ti50). 

occurring:  detached  from  the  dentinal  walls  in  the  root  of  a  carious  inci- 
sor.  A  is  a  diagram  of  the  tooth,  and  the  calcific  mass  was  about  half 
an  inch  in  length,  nearly  filling  the  canal  in  the  position  pointed  out  by 
a.  In  B  the  peculiar  markings  are  shown.  The  mass  is  very  ti-ans- 
])arent,  so  that  these  forms  are  seen  as  clearly  as  if  mounted  alone. 
They  have  some  resemblance  to  the  lacunae  occurring  in  the  cementum, 
and,  while  there  might  be  a  reasonable  ground  for  difference  of  o])inion, 
I  suppose  them  to  be  faults  formed  by  the  persistence  of  tissue-cells  that 
resisted  calcification.  A  large  portion  of  this  mass  presented  no  mark- 
ings of  any  kind.  Something  of  this  class  oi  fault  occurs  in  almost 
every  tissue-calcification,  and  the  forms  of  them  are  as  various  as  can 
be  imao;ined. 


PATHOLOGY  OF  THE  DENTAL  PULP. 


The  size  and  form  of  these  masses  vary  indefinitely.  They  may  be 
large  enough  to  fill  the  pulp-chamber  or  they  may  be  very  minute. 
They  are  evidently  formed  very  slowly,  and  may  have  their  beginnings 
at  several  or  many  centres ;  and  these  separate  pieces  will  coalesce  as 
they  enlarge  in  the  same  manner  as  is  seen  in  the  calcific  plates  that 
occasionally  occur  in  the  walls  of  the  arteries.  It  would  be  interesting 
to  know  if  there  is  any  connection  between  this  calcification  in  the 
dental  pulp  and  in  the  arteries.  I  know  of  no  observations  in  this 
direction. 

Cylindrical  Calcification  is  a  peculiar  form  of  interstitial  calcification 
of  the  pulp  occurring  only  in  the  root-canal,  and  is  connected  with  the 
most  marked  degeneration  of  the  tissues  of  the  whole  organ.  At  least 
I  have  not  met  with  this  form  of  calcification  passing  considerably  into 
the  coronal  portion  of  the  pulp  in  any  case  that  I  have  examined.  I 
present  illustrations  of  this  form  in  its  varying  degrees  in  Figs.  474, 


Fig.  474. 


A,  Outtine  of  a  Lower  Molar,  with  a  large  carious  cavity  at  o;  h,  pulp-chamber.    'Ihe  shaded  portion, 

c,  was  occupied  by  cylindrical  calcifications. 

B,  Illustration  of  the  Cylindrical  Calcifications  (X  100). 

475,  476.  It  occurs  in  patients  of  all  ages,  but  perhaps  is  seen  most 
frequently  in  middle-aged  people  who  have  suifered  much  from  decay 
of  the  teeth  or  from  abrasions.  In  the  earlier  stages  of  the  process 
the  calcific  points  are  found  within  the  tissues  in  very  small  cylinders 
or  spindle-shaped  masses  too  small  to  be  seen  with  the  naked  eye. 
In  this  condition  the  pulp,  when  rolled  in  the  fingers,  will  have  a  dis- 
tinct gritty  feeling,  as  if  it  contained  particles  of  sand.  It  is  difficult 
to  make  fine  sections  of  such  a  pulp,  for  the  reason  that  these  hard 
grains  will  destroy  the  edge  of  the  section  knife.  But  when  a  section 
is  had,  it  will  be  found  that  the  cellular  elements  have  mostly  disap- 
peared, or  have  lengthened  out  into  slender  spindle-cells  to  such  an 
extent  as  to  give  the  tissue  a  veiy  distinct  fibrous  appearance ;  and 
Iving  parallel  with  these  are  found  the  little  cylinders  of  calcific  mate- 
rial, as  seen  in  B,  Fig.  474.  At  A,  in  the  same  figure,  I  give  a  diagram 
of  the  tooth,  a  lower  molar  with  a  large  crown  decay,  from  which  the 
specimen  was  taken,  in  which  the  shaded  portions  of  the  pulp  show  the 
parts  in  which  this  form  of  calcification  was  found.  This,  I  will  say, 
agrees  well  with  other  cases  that  I  have  examined.  In  Fig.  475  the 
preparation  was  picked  to  pieces  and  spread  out  with  needles,  and  it 
gives  a  better  exhibition  of  the  fibres  seen  in  the  tissue  :  it  will  be  noticed 
in  the  fibres  lying  across  the  main  trend  of  the  tissue  in  the  field  how 


CALCIFICATIONS  OF  THE  DENTAL  PULF. 


879 


Fig.  475. 


the  cylinders  are  attached  to  them  by  their  ends.  In  picking  these  apart 
in  the  field  of  the  microscope  this  is  still  more  observable,  and  then  it 
is  found  that  each  cylinder  is  firmly  attached  at  either  end  to  a  little 
bundle  of  fibrous  material ; 
and  it  is  hard  to  escape  the 
conviction  that  these  fibres 
are  being  infiltrated  with 
lime  salts.  A  pulp  containing 
these  calcifications  will  be  dis- 
tinctly stiffened,  and  may  be 
bent  about  and  will  retain  the 
curve  given  it  like  lead  wire. 
Indeed,  this  is  uniformly  the 
condition  of  those  pulps  that 
seem  stiff  wdien  removed  by 
the  broach. 

Fig.  476  represents  an 
extreme  degree  of  this  form 
of  calcification.  Here  is  a 
more  curious  phenomenon 
still.  The  cylinders  have 
grown  and  run  together,  but 
instead  of  coalescing  end  to 
end,  forming  rods,  as  might 
have  been  expected,  they  are 
irregularly  jointed,  and  in  the  effort  to  pick  these  apart  with  needles  it  is 
found  that  these  joints  are  held  together  quite  firmly  by  fibres  passing 
from  the  one  to  the  other.  In  this  condition  the  root  portion  of  the  pulp 
becomes  very  stiff;  yet  it  may  still  be  bent,  and  will  retain  its  bent  posi- 
tion like  annealed  wire.  I  do  not  think  that  this  form  of  calcification 
ever  runs  together  into  a  solid  mass.  It  is  evidently  a  distinct  form,  and 
dependent  on  a  peculiar  condition  of  the  tissue  of  the  pulp.     I  have  seen 

Fig.  476. 


Cylindrical  Calcification  of  the  Pulp.  This  has  hefn 
spread  with  needles,  ami  the  filires  that  lay  across  tlie 
general  trend  show  how  the  calcifications  are  attached 
at  the  end  to  the  fibres.  It  will  also  be  noticed  that  the 
tissue  has  lost  its  normal  forms  and  degenerated  into 
an  irregular  fibrous  mass  (.X  lOU). 


Cylindrical  Calcification,  more  advanced  than  in  Figs.  47-1  and  475.    Instead  of  running  together  and 
forming  a  solid  mass,  they  are  irregularly  jointed  (X  100). 

nothing  in  other  parts  of  the  body  with  which  to  compare  it.  AYe  indeed 
find  long,  flattened  calcifications  in  the  arteries,  but  I  have  seen  none  with 
the  distinctly  jointed  appearance  shown  in  Fig.  476.  What  forces  are  in 
operation  to  produce  these  peculiar  forms  I  am  unable  to  say.     I  am 


880  PATHOLOGY  OF  THE  DENTAL  PULP. 

equally  at  a  loss  as  to  the  symptomatology  of  this  class  of  cases.  I 
think  there  is  no  doubt  that  the  death  of  the  pulp  follows  closely  in 
the  wake  of  the  calcification.  Mr.  Salter  has  also  examined  this  form 
of  calcification  and  described  it  in  some  detail.  I  agree  with  him  in 
saying  that  "  the  whole  of  the  tissues,  cells,  nuclei,  connective  tissue, 
blood-vessels,  and  multitudes  of  nerves,  are  swallowed  up  and  obliter- 
ated in  the  calcific  process."  .  .  .  .  "  The  calcification  is  clearly  not  in- 
terstitial in  the  sense  of  being  between  the  fibres,"  but  the  whole  tissues 
are  impregnated  with  the  calcific  material.  They  are  not  pushed  aside, 
as  in  the  formation  of  pulp-nodules,  but  are  involved  in  the  calcific  pro- 
cess in  the  sense  of  being  infiltrated,  and  thus  converted  into  the  hard 
substance  and  completely  destroyed  as  tissue.  But  the  calcific  process 
is  not  the  primary  change,  for  before  the  calcification  has  begun  the 
tissue  is  already  profoundly  changed,  as  has  been  indicated  already,  so 
that  the  cells  have  mostly  disappeared. 

This  form  of  calcification  does  not  as  a  rule  stand  alone,  but  is  asso- 
ciated with  other  forms.  Generally,  there  is  more  or  less  calcification 
of  the  tissues  of  the  coronal  portion  of  the  pulp  at  the  same  time.  This 
may  be  of  any  of  the  varieties,  but  Avith  the  exception  of  deposits  of 
secondary  dentine  it  is  more  commonly  associated  with  interstitial 
calcifications  in  the  form  of  smooth,  round  boulders,  such  as  is  shown 
in  Fig.  472,  or  there  may  be  several  smaller  stones  of  this  variety. 

Ostco-deiitine  is  the  rather  inappropriate  name  that  has  been  applied 
to  osseous  formations  within  the  pulp-chamber.  In  the  human  teeth 
these  formations  are  very  rare,  but  in  the  teeth  of  animals  they  are  seen 
quite  often,  especially  in  the  very  large  animals.  I  have  seen  a  number 
of  these  from  the  tusks  of  the  elephant  in  which  there  seemed  to  be  a 
mixture  of  dentinal  tubes  and  bone-corpuscles.  But  to  enter  into  a 
discussion  of  these  peculiar  formations  in  the  animal  kingdom  generally 
would  lead  us  too  far  for  the  purposes  of  this  article.  It  has  been  my 
intention  to  adhere  strictly  to  the  human  teeth  both  in  description  and 
illustration,  notwithstanding  the  very  great  interest  presented  in  the 
comparative  study  aiforded  in  the  diseases  and  accidents  of  the  teeth 
of  the  animals. 

The  undoubted  osseous  formations  met  with  in  the  pulp-chamber  of 
the  human  teeth  are  very  rare.  In  making  this  statement  I  exclude  all 
hard  formations  in  which  bone-corpuscles  are  not  present.  This  seems 
not  to  have  been  done  by  many  who  have  written  on  this  subject ;  but, 
on  the  other  hand,  some  writers  seem  to  have  called  almost  all  irregular 
formations  ostco-dentine.  The  great  bulk  of  these  have  not  the  slightest 
resemblance  to  bone. 

The  cases  of  osseous  formation  within  the  pulp-chamber  that  I  have 
met  with  have  all  presented  the  general  characters  of  cementum,  and 
have  been  found  in  the  root-canal  attached  to  the  dentinal  wall  or  resting 
n])on  some  irregular  formation  which  separates  them  slightly  from  the 
dentine.  This  is  different  from  the  reflection  of  the  cementum  slightly 
into  the  pulp-chamber  from  the  apical  foramen,  which  occasionally  occurs 
in  such  a  way  that  I  should  not  consider  it  in  any  sense  pathological.  It 
seems  to  me  evident  that  bone  M'ill  not  form  in  these  positions  until  after 
the  atrophy  of  the  layer  of  odontoblasts ;  at  least,  the  specimens  that  I  have 


OSTEO-DENTTNE. 


881 


examined  all  indicate  this.  I  present  two  illustrations  of  this  in  Figs. 
477  and  478,  both  taken  from  incisor  teeth  that  have  been  considerably 
abraded  and  the  pulp-chamber  partially  filled  by  secondary  deposits. 


Fig.  477. 


Osteo-dentine. 


A,  Outline  of  Abraded  Incisor,  with  point  of  pulp-chamber  {a)  closed  by  secondary  dentine;  6  points 

out  a  narrowing  of  the  root-canal  by  a  deposit  of  osteo-dentiue. 

B,  niustration  of  the  Tissue  of  the  Deposit:  «,  pulp-chamber ;  6,  ossific  material;  c,  layer  of  very 

small  calcosphetites;  (/,  primary  dentine  {X  350). 

Fig.  478. 


Osteo-dentine. 

A,  Outline  of  Incisor,  showing  a  narrowing  of  the  ro'it-canal  at  6  bj^  a  deposit  of  osteo-dentine. 

B,  Illustration  of  the  Tissue:  n,  primary  dentine;  '),  line  of  the  beginning  of  a  growth  of  secondary 

dentine:  t,  secondary  dentine;  (/,  layer  of  granular  matter;  e,  osteo-dentine.  This  has  the 
lacunae  at  n  and  dentinal  tubes  at  k.  f  seems  to  be  the  surface  of  the  osseous  deposit;  i,  irregu- 
lar crystalline  deposits;   A,  the  pulp-chamber  ()<  350). 

They  are  enough  alike  in  every  respect  to  have  been  taken  from  the 
same  mouth,  though,  as  a  fact,  they  were  not.     In  each  I  present  a  dia- 
gram of  the  tooth  at  A,  with  the  position  of  the  osseous  deposit  pointed 
Vol.  I.— 56 


882  PATHOLOGY  OF  THE  DENTAL  PULP. 

out  by  b.  It  will  be  noticed  that  in  each  case  the  pulp-chamber  is  very 
much  narrowed  at  the  point  of  the  bony  deposit,  and  is  wider  again 
toward  the  apex  of  the  root.  The  only  other  position  in  which  I  have 
seen  a  similar  deposit  was  in  the  palatine  root  of  an  upper  molar,  and 
in  this  the  same  narrowing  occurred.  In  B  of  each  of  these  figures  the 
tissue  is  illustrated,  and  affords  a  better  description  than  I  can  give  in 
words.  I  will  call  attention  to  the  fact  that  in  Fig.  477  the  bone  is 
deposited  upon  a  layer  of  small  calcospherites,  at  which  the  dentinal  tubes 
stop  suddenly  and  completely.  This  growth  seems  to  be  in  all  respects 
a  true  cementum,  presenting  quite  perceptibly  the  peculiar  stratified 
appearance  so  generally  seen  in  that  structure.  In  Fig.  478  this  is 
entirely  different.  There  is  a  secondary  dentine  of  very  imperfect 
structure  in  which  the  dentinal  tubes  gradually  disappear,  and  then  the 
osseous  formation  is  deposited  upon  a  layer  of  granular  matter.  At  k 
there  seems  to  be  a  return  of  dentinal  tubes.  This  particular  section 
more  nearly  merits  the  name  "  osteo-dentine  "  than  anything  else  that  I 
have  seen  from  the  human  mouth.  It  is  possible  that  osteo-dentine  may 
occur  in  other  portions  of  the  pulp  of  human  teeth,  or  even  in  isolated 
nodules,  as  is  undoubtedly  the  case  in  the  teeth  of  animals,  but  as  I 
have  not  met  with  them  in  all  my  cuttings,  I  think  they  must  be  very 
rare. 

The  Condition  of  the  Layer  of  Odontoblasts  in  the  varying  states  of 
the  dental  pulp  is  a  point  of  the  greatest  interest,  and  I  have  delayed 
the  consideration  of  it  until  this  time,  for  the  reason  that  I  wished  to 
present  the  other  tissue-changes  first,  in  order,  as  far  as  possible,  to  sim- 
plify description  and  prevent  repetition.  It  will  be  seen  that  in  all  of 
the  deposits  of  secondary  dentine,  except  it  be  some  of  the  more  rare 
forms  of  dentinal  tumor,  the  dentinal  tubes,  if  not  markedly  dimin- 
ished at  the  very  beginning,  soon  begin  to  disappear ;  and  if  the  case 
has  met  with  no  mishap  in  the  way  of  exposure  or  hyperaemia  of  suf- 
ficient severity  to  cause  death  of  the  pulp,  the  dentinal  tubes  disappear 
entirely,  giving  place  to  clear  calcification,  deposits  of  graiuilar  matter, 
calcospherites,  or  other  irregular  structures.  I  believe  this  conclusion 
of  the  deposits  of  secondary  dentine  is  universal  if  it  is  not  brought  to 
a  stop  by  the  premature  death  of  the  pulp.  This  means  exhaustion  of 
the  organ  to  such  an  extent  that  it  is  no  longer  capable  of  physiologi- 
cal function  ;  for,  no  matter  by  what  cause  it  may  be  excited,  we  must 
regard  the  formation  of  true  dentine  in  normal  form  as  a  physiologi- 
cal product  of  the  organ,  and  whatever  may  be  the  differences  of  view 
in  regard  to  the  matter,  all  must  regard  the  layer  of  odontoblasts  as 
very  nearly  related  to  the  formation  of  the  dentine.  The  processes 
emanating  directly  from  these  cells  are  the  occujmnts  of  the  dentinal 
tubes — are  the  dentinal  fibrils ;  and  without  these  there  is  no  dentine, 
for  it  is  the  presence  of  these  that  gives  the  structure  the  characteristics 
by  which  it  is  known  to  the  histologist.  Hence  without  the  odonto- 
blasts we  cannot  have  the  formation  of  dentine.  There  may  be  calcific 
material,  but  it  will  not  have  the  form  of  dentine.  This  is  exempli- 
fied in  most  of  the  illustrations  that  I  have  presented  of  the  secondary 
formations  within  the  pulp-chamber.  These  considerations,  together 
with  the  ever-present  fact  that  the  characters  of  the  secondary  deposits 


CHANGES  IN  THE  ODONTOBLASTS.  883 

of  dentine  soon  begin  to  show  a  failure  as  to  the  normal  number  of  the 
tubes,  has  led  me  into  the  study  of  the  condition  of  these  cells  in  the 
varying  conditions  of  the  pulp  as  regards  secondary  deposits.  I  have, 
however,  found  this  an  exceedingly  difficult  study.  In  cases  of  calci- 
fication it  is  very  difficult  to  get  good  sections  without  decalcifying  the 
hard  tissues,  and  in  so  doing  the  tissue  is  so  deranged  and  otherwise 
injured  as  to  be  of  little  use.  Again,  in  removing  the  pulp  from  its 
chamber  the  layer  of  odontoblasts  so  often  remains  clinging  to  the  den- 
tinal walls,  either  as  a  whole  or  in  part,  as  to  cause  much  vexation. 
Witli  all  of  these  troubles  in  the  way  it  is  not  surprising  that  the  study 
of  this  layer  of  cells  in  its  diseases  has  made  so  little  progress. 

I  have  already  alluded  to  the  fact  that  this  layer  of  cells  seems  to 
persist  unchanged  in  acute  inflammations  of  the  pulp  until  it  is  under- 
mined by  the  processes  of  suppuration.  This,  however,  does  not  argue 
the  greater  vitality  of  these  cells,  but  rather  the  reverse,  for  it  shows 
that  they  are  less  susceptible  to  changes  of  form  than  the  other  cells 
of  the  organ.  The  facts  already  given  speak  plainly  of  the  atrophy  of 
the  odontoblasts  before  the  death  of  the  pulp  as  a  whole.  Indeed,  some 
of  my  observations  seem  to  indicate  that  the  pulp  may  remain  alive  for 
a  considerable  time  after  the  atrophy  of  a  large  proportion  of  the  odon- 
toblasts. In  many  of  my  sections  of  pulps  that  had  been  long  in  a 
state  of  disease  the  peculiar  structure  of  the  margin  of  the  pulp  in  which 
the  odontoblasts  lie  has  been  present,  but  without  the  odontoblasts,  or 
with  one  here  and  there  only,  or  with  patches  from  which  they  Avere 
missing,  very  much  the  same  as  we  often  see  in  secondary  dentine  where 
the  tubes  fliil  in  patches  or  become  fewer  in  number  and  finally  disap- 
pear. Again,  I  have  found  in  some  sections  that  all  signs  of  the  nor- 
mal periphery  of  the  pulp  were  missing,  and  yet  along  the  margin 
there  was  an  occasional  odontoblast  which  took  the  stain  in  a  very 
unusual  manner,  as  though  profoundly  clianged  in  its  chemical  con- 
dition. 

In  Figs.  479  and  480  are  given  illustrations  of  these  changes.  These 
can  be  better  appreciated  by  comparison  with  Fig.  440,  in  which  the 
full  number  of  odontoblasts  that  occupy  the  periphery  of  the  pulp  are 
present.  This  form  of  failure  of  these  cells  seems  to  accompany  the 
degenerative  changes  of  the  tissues  of  the  pulp  that  have  been  described, 
and,  taken  together  with  the  evident  persistence  of  these  cells  during 
the  changes  due  to  acute  inflammations,  show  us  plainly  that  it  is  in  the 
cln-onic  diseases  that  we  must  expect  the  atrophy  of  this  layer.  This 
agrees  also  with  what  is  seen  in  secondary  dentine.  It  seems  that  these 
cells  are  profoundly  affected  by  irritation  of  the  distal  ends  of  the 
fibrils,  for  we  often  find  them  depositing  secondary  dentine  in  cases  of 
abrasion,  as  has  been  indicated,  and  in  connection  with  tliis  perform- 
ance the  cells  disappear.  Not  only  this,  but  they  disappear  in  many 
cases  in  which  there  has  been  no  deposit  of  secondary  dentine  whatever. 
This  has  appeared  prominently  in  two  cases  in  which  there  had  been 
long-continued  inflammation,  accomjmnied  with  hypertrophy  of  the 
pulp  which  was  projected  into  the  cavity  of  decay,  as  shown  in  Fig.  454. 
In  neither  of  these  cases  were  there  any  secondary  deposits  except  a  few 
pulp-nodules  and  a  few  masses  of  calcoglobulin ;  but  over  a  consider- 


884 


PATHOLOGY  OF  THE  DENTAL  PULP. 


able  part  of  the  coronal  portion  of  the  pulp  there  were  patches  from 
which  the  odontoblasts  had  disappeared  from  their  matrix.  The  pos- 
sibility that  these  had  been  pulled  out  of  their  matrix  in  the  removal 
of  the  pulp  from  its  chamber  has  been  fully  considered.  This  ])ulling 
out  occurs  in  a  considerable  number  of  cases,  so  that  I  have  become 
acquainted  with  its  indications ;  and  in  the  cases  mentioned  these  indi- 
cations are  entirely  wanting.  Fig.  479  was  taken  from  the  coronal 
portion  of  the  pulp  of  a  tooth  that  had  a  considerable  hypertrophic 
growth  extending  into  a  carious  cavity,  and  from  the  history  given  by 
the  patient  it  had  evidently  for  five  or  six  months  been  subject  at  inter- 
vals to  severe  attacks  of  inflammation ;  and,  though  there  had  been  a 
large  increase  of  its  tissue,  showing  a  tenacious  vitality  and  a  strong 
tendency  toward  reconstruction,  the  odontoblasts  had  disappeared  from 
many  parts  of  its  surface,  and  in  other  parts  there  ^vere  but  few  left  in 
the  matrix  of  the  membrana  eboris,  as  is  shown  in  the  figure.  In  this 
pulp  there  was  another  abnormal  condition  of  this  membrane  that 
deserves  mention,  though  it  is  but  an  accidental  disturbance :  Along 
the  dentinal  wall,  extending  from  the  point  of  exposure  through  which 
the  hy[)ertrophic  growth  was  extruded,  the  dentinal  fibrils  had  been 
drawn  considerably  out  of  the  dentine,  and  the  layer  of  odontoblasts 
turned  so  that  their  long  axis  was  almost  parallel  with  the  dentinal 
wall,  with  their  pulpal  ends  inclined  toward  the  opening  :  this  was  evi- 


FiG  479 


Fig.  480. 


Atrophv    of  the  Odfmtol)!  ists  (compire  with 
l-i^.  440)  (i"nih  iiitli  iimutrsioi.). 


Atrophy  of  the  Odontobla<<ts  /  odoi  tobli^ts 
that  have  taken  tlit  staii.  ii.  .,i.  iii„j,i.Ur 
manner.  There  is  also  a  peculiar  variation 
in  their  size.  Some  areolations  appear  in 
the  tissue  ^ jVth  inch  immersion). 


dcntly  done  by  the  swelling  of  the  pulp  and  the  protrusion  of  its  mass 
through  the  opening. 

Fig.  480  is  an  illustration  of  the  condition  of  the  membrana  eboris  in 
a  pulp  that  had  been  somewhat  reduced  in  size  by  the  deposit  of  sec- 


CHANGES  IN  THE  ODONTOBLASTS.  885 

ondary  dentine  excited  by  abrasion.  It  had  also  suiFered  from  hyperfemia 
and  extravasations,  as  was  shown  by  both  tlie  history  and  the  appearance 
of  old  clots  in  its  tissue,  and  finally  was  found  to  be  in  a  state  of  chronic 
inflammation  at  the  time  of  extraction.  The  odontoblasts  had  disap- 
peared from  a  great  portion  of  the  periphery,  and  in  many  places  all 
indication  of  the  membrana  eboris  was  lost.  The  illustration  was  taken 
from  a  point  at  which  a  few  scattering  odontoblasts  remained.  It  will 
be  seen  that  the  usual  demarcation  of  the  membrana  eboris  is  wanting, 
and  the  odontoblasts  that  remain  are  sticking  in  among  the  other  cells 
and  the  inflammatory  elements.  They  also  present  a  singular  variation 
in  size,  and  the  staining  is  ditferent  from  the  healthy  cells.  The  general 
structure  of  the  pulp  -was  also  much  changed,  areolations  appearing  in 
its  matrix  at  a  number  of  points. 

In  cases  of  much  less  degenerative  change  in  the  general  structure  of 
the  pulp  there  are  often  observed  changes  of  a  more  or  less  marked  cha- 
racter in  the  odontoblasts  ;  and  my  observations,  taken  as  a  whole,  seem 
to  indicate  that  these  changes  are  quite  common  to  the  chronic  affections 
of  the  organ,  and  especially  so  where  there  have  been  considerable  sec- 
ondary deposits  of  any  kind  except  the  pulp-nodules.  It  is  probable 
that  it  accompanies  them  also  if  the  pulp-nodules  are  very  consider- 
able in  bulk. 

The  influence  of  the  destruction  of  the  membrana  eboris  with  its 
odontoblasts  in  cases  of  exposure  of  the  pulp  is  a  question  of  great 
interest.  It  is  to  be  regretted  that  there  is  no  direct  observation  on 
this  point  that  will  assist  us  in  arriving  at  conclusions.  I  have  many 
times  seen  a  hard  formation  that  closed  the  breach,  and  for  the  time 
seemed  to  shield  the  pulp  from  external  injury  in  cases  which  I  had 
capped  at  a  time  when  the  pulp  was  fully  exposed,  and  in  such  con- 
dition that  I  think  there  could  be  no  doubt  of  the  destruction  of  the 
odontoblast  layer.  But  I  have  never  had  the  opportunity  of  micro- 
scopic examination  of  such  a  case.  A  number  of  times  I  have  drilled 
through  these  deposits  to  remove  a  dead  pulp  ;  and,  so  far  as  I  was  able 
to  judge  of  the  condition  by  such  a  mode  of  examination,  it  is  not  dif- 
ferent from  that  found  in  death  of  the  pulp  following  secondary  deposits 
excited  in  other  ways.  A  sufficient  number  of  examinations  of  the  sec- 
ondary deposits  in  cases  of  exposure  and  known  destruction  of  a  portion 
of  the  surface  of  the  pulp  would  settle  the  question  as  to  whether  these 
cells  may  be  re-formed  after  they  have  once  been  destroyed.  Until  such 
observations  have  been  carefully  conducted  in  sufficient  number,  or  until 
direct  evidence  of  their  re-formation  has  been  had,  the  question  must 
remain  an  open  one.  At  the  present  time  what  evidence  we  possess  on 
this  point  is  certainly  against  such  re-formation  with  the  restoration  of 
physiological  function.  In  some  cases  of  dentinal  tumor — such,  for 
instance,  as  that  presented  in  Fig.  467 — there  seem  to  have  been  new 
dentinal  tubes  originated,  and  with  these  there  must  have  been  odonto- 
blasts. The  number  of  the  tubes,  and  the  peculiar  tufts  uniting  to  form 
tubes,  seem  to  me  to  be  evidence  that  odontoblasts  have  come  into 
existence,  but  the  tissue  formed  is  in  no  sense  physiological.  Still, 
in  these,  in  every  instance,  some  portion  of  the  dentinal  tubes  comes 
directly  from  the  primary  dentine. 


886  PATHOLOGY  OF  THE  DENTAL  PULP. 

General  Considerations. 

In  the  foregoing  pages  I  have  frequently  alkided  to  the  fact — which 
is  apparent  in  a  very  large  proportion  of  my  microscopic  preparations 
— that  any  of  the  secondary  calcific  formations  within  the  pnlj)  of  the 
tooth  result  in  exhaustion  and  the  final  death  of  the  pulp.  This  fact 
is  so  prominent  that  it  seems  to  me  that  it  cannot  well  be  overlooked, 
and  yet  in  the  capping  of  exposed  pulps  it  seems  to  have  been  the 
thought  of  the  profession  that  to  be  able  to  obtain  a  secondary  dejiosit 
under  such  circumstances  was  to  ensure  the  permanence  of  the  health 
of  the  pulp.  This  was  my  own  thought  some  years  ago,  but  further 
clinical  experience,  combined  with  the  closer  microscopic  study  of  the 
subject,  has  convinced  me  that  this  is  a  mistake.  Secondary  deposits 
may,  and  do,  ensure  temporary  quiet,  but  so  far  from  ensuring  health 
are  they  that,  as  a  matter  of  fact,  they  bring  about  the  very  state  of 
matters  that  we  most  wish  to  avoid — the  degeneration  and  final  destruc- 
tion of  the  pulp.  In  a  large  majority  of  cases,  however,  this  result  is 
bi'ought  about  very  slowly,  and  thus  has  escaped  the  notice  of  most 
observers.  For  if  an  exposed  pulp  is  capped  and  the  cavity  filled,  and 
the  case  seems  to  do  well  for  a  year  or  two,  it  is  regarded  as  a  success, 
and  is  lost  sight  of.  When  this  returns  some  years  later  with  a  dead 
pulp,  it  is  treated  as  one  of  the  great  mass  of  such  cases  that  are  con- 
stantly presenting  themselves,  and  probably  no  note  is  made  of  the  fact 
that  it  was  capped  at  a  certain  time  and  was  one  of  the  many  successful 
cases.  And  precisely  the  same  thing  is  true  of  a  large  number  of  teeth 
in  which  very  large  fillings  are  made  in  cases  in  which  there  is  no  ex- 
posure of  the  pulp,  as  well  as  in  many  in  which  the  fillings  were  not  so 
verv  large.  The  fact  seems  to  be  that  anv  condition  of  abnormal  irri- 
tation  is  liable  to  produce  these  results  whether  it  be  from  a  capping,  a 
large  filling  that  increases  the  thernial  changes  by  the  greater  conduct- 
ing power  of  the  metal  of  which  the  filling  is  composed,  the  exposure 
of  the  fibrils  by  abrasion,  or  other  deleterious  influence.  And,  taking 
my  own  records  as  a  guide,  I  should  be  compelled  to  say  that  very  large 
fillings  without  non-conductors  in  teeth  with  pulp  not  exposed  are  more 
destructive  than  well-made  cappings  with  non-conducting  material 
where  pulps  are  fully  exposed  ;  provided  that  the  capping  material  be 
at  the  same  time  non-irritating.  It  will  be  seen  that  in  all  of  these 
cases  the  cause  of  difficulty  lies  in  the  fact  of  continuous  irritation,  and 
it  makes  but  little  difierence  from  whence  that  irritation  comes ;  it  will 
in  time  do  its  work  of  destruction. 

The  time  that  pulps  may  live  after  the  beginning  of  secondary  de- 
posits is  a  question  of  great  importance.  At  jiresent  we  are  almost 
without  exact  observation  on  this  point.  Undoubtedly,  the  time  varies 
■\Aidely  in  different  cases,  and  may  be  said  to  extend  from  a  year  or  two 
to  half  a  lifetime  or  even  more.  A  very  large  proportion  of  these  pulps, 
however,  are  lost  within  ten  years.  Some  of  these  cases  will  result  in 
abscess,  but  very  many  pass  on  for  years  in  a  state  of  perfect  tran- 
quillity, giving  no  indication  of  the  death  of  the  organ.  The  only 
cases  in  wliich  I  have  had  the  o]>])ortunity  of  making  microscopic 
examination  have  been  those  of  death  of  the  pulp  from  causes  other 


CAPPING   OF  THE  DENTAL  PULP.  887 

than  exposures  capped  by  myself,  and  have  not  inckided  cases  in  which 
I  have  had  certain  knowledge  of  the  state  of  the  pulp  at  the  time  of 
capping  by  others ;  but  from  the  gross  examination  of  clinical  cases  I 
have  no  doubt  that,  with  the  exception  of  the  nature  of  the  deposit,  the 
general  pathological  changes  are  the  same  as  those  seen  in  very  slow  or 
stationary  caries ;  that  is,  function  becomes  more  and  more  irregular  or 
abnormal  until  the  pulp  fails  entirely. 

Very  many  cases  of  capping  pass  on  for  years  without  any  deposit 
whatever,  and  seem  to  remain  in  a  perfectly  healthy  condition.  This 
we  must  regard  as  the  most  desirable  resulj:  that  can  be  obtained. 
Enough  of  these  cases  have  been  noted  to  demonstrate  the  possibility 
of  rendering  the  conditions  so  nearly  normal  that  no  disturbance  of  the 
functions  of  the  organ  occurs. 

In  relation  to  the  symptomatology  of  the  dental  pulp  more  exact 
information  is  to  be  desired,  especially  as  to  the  differential  diagnosis 
of  its  different  states.  This  will  require  that  cases  of  known  history 
be  prepared  in  large  number  for  microscopic  examination  and  the 
results  classified.  The  old  plan  of  judging  of  the  condition  of  the  pulp 
by  the  symptoms  presented  is  of  but  little  scientific  value  until  we  shall 
have  more  direct  knowledge  of  the  conditions  by  which  the  symptoms 
are  produced ;  and  this  can  be  gained  only  by  the  methods  of  study 
indicated. 


DISEASES  OF  THE  DENTAL  PULP,  AND 
THEIR  TREATMENT. 

By  JAMES    TRUMAN,   D.  D.  S. 


The  diseases  of  the  dental  pulp,  while  not  numerous,  are  an  import- 
ant part  of  tlie  pathological  conditions  coming  under  the  care  of  the 
dentist.  It  has  been  the  aim  of  the  writer  to  present  the  subject  in  the 
clearest  manner  possible,  without  undue  overloading  with  quotations. 
As  the  minute  anatomy  of  the  dental  pulp  is  fully  treated  elsewhere  in 
this  volume,  no  allusion  has  been  made  to  it.  Considerable  space  has 
been  given  to  the  consideration  of  thermal  influence,  as  that  important 
factor  in  pulp-irritation  has  measurably  been  neglected  and  its  influence 
underrated  in  the  production  of  pulpitis,  etc. 

The  subjects  treated  are  embraced  under  the  following  headings : 


Thermal  Influences. 

Changes  from  Normal.  < 


Nodular  Deposits. 
Polypus  of  the  Pulp. 


1st.  Simple  Exposure. 

2d.  Superficial  Pulpitis. 

3d.  Deep-seated  Pulpitis. 

4th.  Devitalization. 

5th.  Gangrene. 

6th.  (So-called)  Dry  Gangrene. 


Thermal  Influences. 

The  pathological  condition  of  the  pulp  cannot  be  properly  understood 
without  devoting  some  consideration  to  the  primary  causes  of  inflamma- 
tion in  that  organ,  originating  in  external  influences  which  bear  more 
or  less  directly  upon  the  diseases  subsequently  manifested. 

The  prolongations  of  the  odontoblastic  layer  through  the  tubuli 
practically  extend  the  pulp  to  the  remotest  ramifications  of  these  passages, 
and,  as  they  occujw  the  largest  proportion  of  the  dentine,  it  follows  that 
the  pulp  cannot  l)e  considered  simplv  as  a  central  organ  of  the  tootli- 
body,  but  nuist  hohl  important  relations  to  all  parts  of  the  tooth,  and 
in  return  nuist  receive  all  impressions  made  at  the  peri])heral  ter- 
minations ;  and  in  proportion  to  the  extent  of  these  will  the  effect  be 
tem])orary  or  destructive.  When  it  is  understood,  therefore,  that  in  all 
exposed  dentine  surfaces  we  are  dealing  directly  with  the  central  organ 


THERMAL  INFLUENCES.  889 

through  its  vital  extensions,  the  importance  of  carefully  considering  the 
causes  of  irritation  will  be  properly  appreciated. 

The  pulp  proper,  while  it  undoubtedly  receives  impressions  through 
the  enamel,  is  never  seriously  affected  by  these  unless  disturbed  by  some 
sudden  concussion  or  movement  of  the  tooth  or  by  deposits  of  calcific 
matter,  but  remains  in  the  quiet  performance  of  its  function  as  one 
of  the  sources  of  nutrition  to  the  entire  structure.  When,  however,  the 
dentine  becomes  exposed  by  the  progress  of  caries,  the  contents  of  the 
tubes  are  kept  in  a  continuous  state  of  irritation.  While  the  tube-con- 
tents have  not  as  yet  been  demonstrated  as  consisting  of  a  nerve-fibre  or 
fibres,  it  is  demonstrably  true  that  sensation  is  carried  from  periphery 
to  centre  through  this  channel ;  and  where  sensation  is,  a  certain  amount 
of  inflammation  is  always  possible.  While  this  is  true  in  theory,  it  is 
practically  demonstrated  by  the  fact  that  the  exposed  tubes  are  a  source 
of  inflammation  in  the  pulp,  oftentimes  through  quite  thick  layers  of 
dentine ;  and  this  is  only  possible  under  the  supposition  that  the  irrita- 
tion of  the  surface  layer  has  extended,  by  the  general  law  governing 
inflammations,  to  the  central  tissue. 

Pulpitis  may,  therefore,  be  said  to  have  its  origin  in  quite  remote 
irritation ;  and  this  irritation  may  be  produced  by  any  of  the  many 
sources  of  disturbance  present  in  the  oral  cavity,  or  it  may  originate 
from  the  action  of  the  varying  temperatures  to  which  all  teeth  are 
exposed.  The  direct  and  most  positive  cause  is  in  the  progress  of  caries. 
The  extent  and  rapidity  of  inflammation  will  de]:)end  on  the  density  of 
the  tooth  affected.  In  soft-structured  teeth  with  great  deficiency  of 
inorganic  material  the  chemical  action  leaves  exposed  a  greater  propor- 
tion of  organic  matter,  and  necessarily  opens  up  a  larger  surface  of  inner 
tubular  tissue  to  the  irritating  action  of  the  acid  fluids,  debris  of  decay, 
fungi,  etc.  The  result  is  not  only  a  more  rapid  destruction  of  the  tooth, 
but,  at  the  same  time,  a  more  speedy  increase  of  the  inflammation  along 
the  inner  tubular  contents.  In  very  dense  teeth  the  irritation  is  reduced 
to  a  minimum,  and  it  is  therefore  rare  to  And  the  pulp  affected.  This 
is  to  be  attributed  to  the  contracted  calibre  of  the  tubes  and  the  ex- 
tremely slow  progress  of  the  disease.  Between  these  two  extremes  there 
exist  all  grades  of  structure  dependent  on  age  and  systemic  conditions. 

The  causes  already  described  rarely  result  in  inflammation  of  the  pulp 
prior  to  actual  exposure,  and  may  be  regarded  as  simply  placing  the 
tube-contents  in  a  condition  suitable  for  the  more  positive  action  of 
atmospheric  influence.  This,  from  its  continuous  and  more  decided 
impression,  becomes  a  serious  factor  in  the  preliminary  irritations,  with 
results  more  frequently  injurious  to  the  pulp  than  all  the  other  causes 
combined.  As  before  stated,  the  density  of  the  tooth  contributes  a  pro- 
portionate degree  to  its  eftect,  and  it  therefore  follows  that  the  age  must 
be  considered  in  any  treatment  given  teeth.  Young  or  imperfectly- 
developed  dentine,  for  reasons  already  enumerated,  is  more  liable  to 
these  impressions,  while  old  age  is  scarcely  affected  at  all ;  hence  the 
treatment  adapted  to  the  latter  is  clearly  inadmissible  in  the  former. 
Cold  and  heat,  whether  communicated  through  fluids  or  by  draughts  of 
air,  have  a  similar  effect,  producing  a  violent  shock  and  acute  pain,  which, 
if  long  continued,  will  result,  as  before  stated,  in  pulp-irritation  and 


890        DISEASES  OF  THE  DENTAL  PULP,   AND   TREATMENT 

final  devitalization.  In  moderately  or  very  dense  teeth  this  may  produce 
but  slight  irritati(jn,  and,  following  the  general  law,  may  result  in  extra 
development  of  secondary  dentine,  an  ett'ectual  barrier  being  thus  inter- 
posed against  further  irritation.  The  operation  of  this  law  is  beautifully 
illustrated  in  the  formation  of  secondary  dentine  by  occlusion  in  teeth 
worn  down  on  the  cutting  edges  and  in  the  development  of  extra-cemen- 
tal  tissue  in  exostosis,  and  also  in  the  calcification  of  the  tubuli  in  caries 
in  dense  teeth.  This  is,  however,  only  possible  under  favorable  condi- 
tions— conditions  rarely  or  never  present  in  young  teeth.  Hence  the 
filling  of  all  such  teeth  with  good  conductors,  without  some  intervening 
media  to  prevent  the  irritating  influence,  -must  be  regarded  as  an  ob- 
jectionable practice.  In  exact  ratio  to  the  sensitiveness  of  the  tissue 
will  be  the  danger  of  thermal  action,  and  this  hypersesthetic  state  will 
be  in  proportion  to  the  conditions  already  described. 

It  is  important  to  bear  in  mind  the  possible  pathological  contingencies 
in  the  treatment  of  so-called  sensitive  dentine.  Over-stimulation  from 
an  irritant  will  have  a  very  deleterious  effect  if  too  long  continued  or  if 
applied  over  a  too  thin  layer  of  dentine.  The  peculiar  and  quite  diifer- 
ent  action  of  various  obtundents  must  be  carefully  studied  in  their  pos- 
sible relations  to  the  pulp,  those  being  the  best  to  use — if  used  at  all — 
that  confine  their  action  to  the  superficial  layer ;  and  those  of  great 
penetrating  power,  of  violent  action,  or  that  continue  their  devitalizing 
power  through  absorption  should  be  used  sparingly  or  be  abandoned 
altogether.  Among  those  of  great  penetrating  power  may  be  classed 
chloride  of  zinc,  and  of  devitalizing  power,  arsenic. 

The  possible  changes  that  may  arise  through  thermal  action  necessi- 
tate care  in  the  treatment  of  all  teeth,  no  matter  what  may  be  the  struc- 
ture. While  it  does  not  come  within  the  province  of  this  paper  to  dis- 
cuss the  question,  it  will  not  be  out  of  place  to  suggest  that  as  a  general 
rule  no  very  sensitive  teeth  should  be  filled  with  as  good  a  conductor  as 
gold  without  a  preparatory  layer  of  gutta-percha,  tin,  or  some  equally 
reliable  non-conducting  material.  Especially  is  this  applicable  to  im- 
mature teeth  or  the  teeth  of  children  between  the  ages  of  twelve  and 
fifteen.  Indeed,  so  liable  is  the  pulp  to  be  affected  during  this  period 
that  it  is  very  questionable  whether  gold  should  ever  be  used  in  that 
class  of  tecitli. 

The  destructive  action  through  conditions  heretofore  alluded  to  result 
eventually,  if  not  checked  by  remedial  agents,  in  direct  irritation  of  the 
central  organ.  This  opens  up  a  long  chain  of  tissue-disturbance  that 
may  end  in  the  total  destruction  of  tiie  tooth,  and  possibly  to  more 
remote  and  serious  lesions.  These  changes  from  the  normal  to  abnor- 
mal may  be  classified  as  follows : 

1st.    Simple  exposure. 

2d.    Superficial  pulpitis. 

3d.     D('e])-seated  pulpitis. 

4th.  Devitalization. 

5th.  Gangrene. 

6th.  (So-called)  Dry  gangrene. 

Simple  Expomrc. — The  jirogress  of  the  destructive  forces  eventually 
removes  all  intervening  layers  of  dentine,  and  the  pulp  lies  directly 


CHANGES  FROM  NORMAL.  891 

exposed  to  their  influence.  While  this  organ^  from  its  large  supply  of 
nerve-ti-bres,  is  very  sensitive  and  easily  disturbed  by  impingement  of 
foreign  matter,  it  very  frequently  bears  this  exposure  without  indications 
of  pain  ;  indeed,  it  not  unfrequently  happens  that  it  passes  through  all 
the  stages  enumerated  A\ithout  any  sign  more  than  an  occasional  imcom- 
fortable  sensation.  This  is  not,  however,  always  the  case.  Fresh  expos- 
ures always,  when  visible,  present  a  rich  red  appearance,  from  the  fact 
that  the  red  blood-corpuscles  have  not  been  given  time  to  take  on  the 
condition  of  stasis,  or  stagnation,  in  the  progress  of  inflammation.  The 
bright-red  spot  so  familiar  to  all  practitioners  has,  therefore,  only  a  lim- 
ited duration,  and  gives  place  to  the  secondary,  or  dark,  stage  peculiar 
to  areas  of  inflammation,  whether  limited  to  minute  or  covering  large 
surfaces.  The  red  spot  is  therefore  the  indication  of  a  pulp  in  a  nor- 
mal condition,  or  as  near  that  as  it  is  possible  to  have  it  and  still 
require  treatment.  The  exposure  may  not  be  visible  to  sight,  as  it 
may  have  occurred  through  the  cracks  always  possible  in  dentine  in 
defects  of  structure  or  by  accident.  It  M'ill,  therefore,  in  such  cases,  be 
manifestly  impossible  to  diagnose  its  condition  or  judge  the  length  of 
time  of  exposure  or  the  extent  of  the  inflammation.  The  red  presenta- 
tion is  the  indication  for  a  favorable  judgment  as  to  the  propriety  of  the 
so-called  process  of  capping.  In  proportion  as  the  pidp  has  degenerated 
toward  pulpitis  will  the  possibility  of  success  be  decreased.  This  has 
been  the  experience  of  the  writer,  and  is  fully  in  accord  with  the  gen- 
eral professional  sentiment  on  this  subject. 

The  difficulty  in  diagnosing  a  slight  exposure  is  oftentimes  very  great, 
and,  as  it  is  of  vital  importance  that  this  should  be  correctly  done,  the 
examination  should  be  thorough.  The  simulation  of  exposure  of  the 
pulp  by  sensitive  inner  tubular  fibres  is  always  a  source  of  difficulty. 
If  it  has  been  exposed  to  irritation  for  some  days,  the  excavator  may 
foil  to  find  it ;  resort  must  be  had  then  to  some  agent  that  will  penetrate 
minute  openings  and  act  as  a  searcher.  For  this  purpose  nothing  is 
superior  to  finely-carded  cotton.  The  fibres  of  this  insinuate  themselves 
into  minute  orifices,  and  the  opening  must  be  very  small  indeed  that 
will  not  be  entered  by  them.  The  result  is  momentary  pain,  more  or 
less  acute,  depending  on  the  size  of  the  aperture.  While  this  simple 
test  is  not  Avholly  to  be  relied  on,  it  is  the  best  at  present  at  command, 
as  it  certainly  is  a  very  delicate  one.  Sensitive  dentine  is  not  affected 
by  it,  for  the  reason  that  the  test  is  only  available  after  excavation  of 
all  debris  of  decay ;  and  this  process  cuts  off*  all  fibres  level  with  the 
orifices .  of  the  tubes,  into  which,  on  account  of  their  microscopical 
minuteness,  the  fibres  of  cotton  cannot  penetrate. 

Superficial  Pulpitis. — Inflanmiation  of  the  pulp  proceeds  by  the  usual 
stages  accompanying  other  inflammations — first,  the  irritation  caused  by 
the  foreign  matter ;  then  the  period  of  excitement  or  increased  flow  of 
blood,  followed  by  the  static  period ;  then  gradual  loss  of  vitality  in  the 
part  most  affected  ;  eventual  death,  followed  by  a  putrescent  condition. 
The  first  stage  is  that  comprised  under  this  heading,  which  may  be 
described  as  superficial  pulpitis  from  the  fact  that  it  frequently  retains 
that  character  for  a  long  time,  and  may  therefore  be  properly  considered 
as  a  distinct  variety.     When  it  assumes  a  chronic  character,  it  is  evi- 


892         DISEASES  OF  THE  DENTAL  PULP,   AND   TEEATMENT. 

dently  due  to  a  large  amount  of  vitality  in  the  individual,  giving  a 
resisting  power  to  the  encroachment  of  disease.  This  peculiarity  is 
often  manifested  in  the  power  of  resistance  some  pulps  possess  against 
the  action  of  arsenic.  Ordinarily,  however,  superficial  pulpitis  is  of  but 
short  duration,  and,  following  the  general  law,  continues  to  the  destruc- 
tion of  the  whole  organ.  The  possible  error  in  diagnosis  will  be  found 
in  the  difficultv  of  determining  the  extent  of  the  lesion  and  ^vhether  it 
may  not  possiblv  have  reached  the  condition  of  deep-seated  pulpitis,  the 
latter  condition  being  generally  accompanied  by  more  or  less  periosteal 
disturbance,  which  will  at  times  furnish  a  guide  to  judgment,  though 
the  violence  of  the  inflammation  will  have  to  be  the  general  diagnostic 
sign.  If  there  is  but  little  activity,  if  pain  is  not  excessive  and  is  not 
coupled  with  periostitis,  the  pulpitis  may  be  regarded  as  superficial ; 
but,  on  the  other  hand,  if  acute  with  the  other  accompaniments,  it  has 
reached  a  point  where  devitalization  is  certain  to  result,  and  any  effort 
to  abort  the  inflammatory  state  must  result  in  failure.  The  usual 
attempt  to  quiet  such  pulps  and  then  cap  with  some  foreign  material 
has  but  little  to  recommend  it,  and  the  final  result  is  almost  invari- 
ably devitalization. 

The  destruction  of  the  life  of  the  pulp  is  by  no  means  dependent  on 
exposure  by  caries.  The  organ  holds  its  vitality  by  the  slight  connec- 
tions with  the  main  vessels  and  nerves  through  the  oftentimes  very  con- 
tracted canal,  the  apical  foramen  of  the  tooth.  It  requires  but  a  very 
slight  disturbance  at  this. point  to  cut  oif  all  sources  of  nutrition  in  this 
direction,  and  the  pulp's  life  is  sacrificed.  This  is  much  more  easily 
accomplished  than  is  generally  supposed,  judging  by  the  very  rough 
appliances,  and  the  still  rougher  modes  of  using  them,  that  have  been 
adopted  from  time  to  time  for  the  purpose  of  moving  teeth.  The  sepa- 
ration of  teeth  by  the  wedge  and  hammer  and  powerful  screws  is  but 
one  sample  of  the  wrong  application  of  force  upon  a  delicate  tissue. 
Tiie  elasticity  of  the  pericementum  admits  of  a  limited  movement,  and 
any  force  used  beyond  that  must  be  cautiously  applied,  to  jirevent 
strangulation  of  the  vessels  of  the  pulp  at  the  apex.  The  pulp  may 
be  devitalized  and  give  no  immediate  sign,  or  it  may  result  in  sudden 
congestion  or  rapid  discoloration.  A  sudden  blow  has  the  same  eflect, 
and,  as  this  is  peculiarly  liable  to  occur  to  children,  the  largest  percent- 
age of  loss  from  this  cause  occurs  in  the  earlier  years  of  life  and  very 
frecpiently  fails  of  recognition  until  a  later  period,  when  discoloration 
gives  the  usual  indication.  Devitalization  occurring  under  these  cir- 
cumstances is  not  necessarily  a  source  of  discomfort  to  the  individual. 
Tiie  pulp-tissue  is  gradually  decomposed  or  mummified,  and  the  matter 
is  gradually  absorbed  into  the  body  of  the  tooth,  and,  in  connection 
with  the  dead  material  already  there,  produces  the  dark  appearance 
before  alluded  to.  Such  a  tooth  may  remain  comparatively  comfortable 
for  years.  It  recpiires  the  ingress  of  atmospheric  germs  to  produce 
the  j)n)ducts  of  decomposition  which  render  the  treatment  the  mo^t 
troublesome  and  uncertain  of  any  of  the  pathological  conditions  of 
which  the  dentist  is  called  to  take  charge.  This  can  be  more  properly 
considered  under — 

Gangrene. — This  term  is  applied  to  the  pulp  in  the  last  stages  of 


GANGRENE.  893 

•fleconiposition,  for  it  is  death  preceded  by  inflammation.  This  may 
have  been  superinduced  by  the  exposure  of  the  organ,  or,  as  previously 
described,  by  a  too  suddenly  applied  force.  The  destruction  of  the 
vitality  leaves  a  mass  of  dead  matter  confined  within  narrow  limits. 
This,  even  when  exposed  to  the  air,  may  remain  quiescent  for  a  long 
time,  provided  there  is  free  egress  for  the  products  of  decomposition. 
One  of  these — sulphuretted  hydrogen — is  formed  rapidly.  If  by  any 
means  the  aperture  becomes  closed,  the  excessive  irritation  from  pres- 
sure that  this  produces  rouses  the  pericementum  into  activity ;  the  result 
is  periostitis.  This  will  give  rise  to  symptoms  more  or  less  aggravated, 
depending  largely  on  temporary  or  permanent  systemic  conditions.  The 
state  of  the  pulp  at  this  pathological  period  is  of  far  more  importance 
than  has  generally  been  conceded.  Unless  great  care  is  exercised,  com- 
])lications  of  a  serious  character  are  certain  to  result.  The  septic  poison 
so  infiltrates  the  surrounding  tissue  by  long  continuance  that  the  treat- 
ment very  often  becomes  exceedingly  tedious,  and  in  some  cases  ineffect- 
ual, especially  in  cachectic  individuals.  Atmospheric  air  as  a  factor  in 
decomposition  is  in  no  case  more  clearly  demonstrated  than  in  pulps  of 
this  character.  When  confined  in  a  sealed  cavity,  as  in  teeth  without 
caries,  they  may  remain,  as  previously  stated,  for  years  without  any  dis- 
turbance ;  but  a  free  opening  brings  in  a  new  element,  and  the  destruc- 
tive process  immediately  begins.  In  the  exposed  pulp  this  is  always 
present ;  hence  pulps  of  this  character  are  loaded  with  germs.  This  is 
not  the  place  to  discuss  the  influence  of  bacteria  on  inflammatory  con- 
ditions, but  the  observations  of  the  writer  point  unerringly  to  the  fact 
that  their  presence  is  quite  necessary  to  the  progress  of  such  conditions, 
and  their  destruction  is  absolutely  essential  before  any  good  result  can 
be  effected.  Careful  microscopic  examinations  in  'pyrori'hcea  alveolaris 
have  demonstrated  that  very  positively.  Treatment  of  gangrene,  there- 
fore, must  be  based  on  this  fact  first,  and,  secondly,  must  be  directed  to 
an  elimination  of  the  gaseous  products.  This  part  of  the  subject  will  be 
more  thoroughly  treated  hereafter. 

Dn/  Gangrene. — This  peculiar  state  of  the  pulp,  subsequent  to  de- 
struction of  its  vitality,  is  not  easy  of  explanation,  but  there  are  cases 
which  are  undoubtedly  produced  by  the  development  of  secondary  den- 
tine, and  a  consequent  stagnation  in  the  circulation,  as  in  r/angrena 
senilis.  This  is  often  observed  in  teeth  of  old  persons,  but  is  more 
rarely  seen  where  death  of  the  pulp  has  taken  place  in  a  closed  cavity. 
It  has  been  termed  the  "  mummified  condition  of  the  pulp."  It  is  a 
frequent  result  of  capping  with  oxychloride  of  zinc,  and  in  such  cases  it 
is  evidently  due  to  its  great  penetrating  property,  dependent,  probably, 
upon  its  affinity  for  the  water  and  power  of  combining  with  the  albu- 
men of  the  tissues.  It  is  for  this  reason,  to  a  large  degree,  that  oxy- 
chloride of  zinc  is  the  most  valuable  capping  material,  as  it  produces 
this  very  desirable  state — a  state  in  which  the  tooth  is  generally  effect- 
ually preserved  from  the  results  described  under  the  head  of  Gangrene. 
Teeatmext. — The  treatment  of  simple  exposure,  as  Avell  as  tJie  other 
more  complicated  pathological  changes,  has  assumed  increased  import- 
ance with  the  development  of  dentistry  ;  indeed,  it  may  be  said  to  base 
its  progress  and  right  to  be  deemed  worthy  to  be  called  a  profession 


894        DISEASES  OF  THE  DENTAL  PULP,   AND   TREATMENT. 

upon  the  intelligent  conception  of  the  management  of  this  organ.  The 
feeble  and  generally  futile  efforts  to  treat  it  made  by  the  older  dentists 
were  necessarily  failures,  as  they  were  of  a  purely  empirical  character 
and  a  continual  violation  of  what  are  now  Avell-understood  principles. 
The  old  method  of  destruction  by  the  actual  cautery,  while  theoretically 
correct,  was  impossible  of  application  Nvith  the  then  imperfect  appli- 
ances, and  the  knowledge  of  the  proper  subsequent  treatment  ^yas 
whoUv  wanting.  There  was  little  or  no  progress  until  after  the  in- 
troduction of  arsenic  as  a  devitalizer  by  Spooner,  in  1836.  It  came 
into  use  very  slowly,  and  Dr.  Harris,  the  ablest  of  the  pioneer  dentists, 
for  several  years  tailed  to  perceive  any  advantage  in  its  use,  and  he 
passed  from' his  laborious  aud  useful  life  before  the  pulp  and  its  entire 
pathological  relations  were  understood.  It  is  very  doubtful  whether  the 
half  century  that  has  been  given  to  its  study  has  clearly  solved  all  the 
problems  connected  with  it. 

The  two  modes  of  treatment  that  have  been  adopted  are — the  one 
being  conservative,  and  the  other  destructive — diametrically  opposed, 
yet  both  lead  directly  to  the  same  end,  the  preservation  of  the  tooth. 
The  former  is  effected  by  Avhat  is  known  now  as  capping,  and  the  other 
by  devitalization  and  removal. 

Capping  was  very  early  adopted,  in  accordance  with  the  theory  that 
if  the  pulp  could  be  protected  from  pressure  it  would  maintain  its 
vitality  and  perform  its  proper  function  for  an  indefinite  period.  This 
was  based  on  erroneous  conceptions  of  the  character  of  the  central 
organ,  and  also  on  defective  knowledge  of  the  powerful  influence  of 
other  sources  of  irritation.-  It  was  not  then  clearly  understood  that 
the  surface  of  the  pulj)  from  the  period  of  first  exposure  is  in  a  patho- 
logical condition,  and  that  this  must  progress  unless  measures  be  taken  to 
abort  it,  and  that  the  mere  interposing  of  some  media,  though  nearly 
allied  to  dentine  in  character,  would  not  avail  to  prevent  this  gangrenous 
destruction.  The  germ  theory  of  disease  was  then  unknown,  and  it  is 
not,  therefore,  remarkable  that  the  efforts  at  pulp-preservation  usually 
ended  in  pulp-destruction.  The  earliest  attempts  were  sim])ly  to  protect 
the  pulp  from  contact  with  the  filling.  The  first  cappings  were  made 
of  gold  and  lead  cut  in  circular  form  of  a  size  sufficient  to  rest  on  the 
adjacent  solid  tissue.  These  were  stamped  to  form  a  concave  surface 
over  the  pulp.  For  this  purpose  gold  was  generally  used,  though  lead, 
owing  to  its  poorer  conducting  property,  was  regarded  by  many  as  pref- 
erable. Harris  advocated  the  forming  of  the  filling  by  so  packing  the 
gold  that  the  caps  would  be  formed  out  of  the  filling — a  very  difficult, 
and  always  an  uncertain,  operation.  The  results  were  not  satisfactory. 
In  subjects  of  great  recuperative  power  the  pulp  would  be  preserved  in 
spite  of  the  defective  process,  but  the  number  was  so  limited  and  the  cases 
of  failure  were  so  numerous  that  the  process  was  abandoned  by  all  good 
operators.  Attemjits  were  made  to  modify  the  supposed  injurious  effect 
of  the  metals  by  the  substitution  of  a  material  nearly  allied  to  dentine, 
under  the  supposition  that  irritation  would  be  thus  reduced  to  a  min- 
imum ;  ivory,  quill,  and  gutta-percha  were  therefore  substituted,  with 
but  little  better  results.  These  were  followed  by  asbestos,  plaster  of 
Paris,  goldbeater's  skin,  collodion,  court-plaster,  tissue-paper  saturated 


CAPPING.  895 

with  solution  of  Canada  balsam,  lactophosphate  of  lime,  and  finally 
oxychloride  of  zinc,  oxyphosphate  of  zinc,  and  oxysulphate  of  zinc. 

While  these  have  been  introduced  nearly  in  the  order  named,  there 
was  an  interregnum  of  years  after  the  use  of  the  metals  before  much 
reliance  was  placed  on  any  form  of  capping,  and  the  operation  regarded 
as  most  satisfactory  was  the  destruction  and  removal  of  the  pulp  and 
the  filling  of  the  canals.  This,  however,  involved  tedious  operations, 
with  a  constant  percentage  of  failures  in  inaccessible  roots.  So  frequent 
were  these  that  the  active  minds  of  the  profession  continued  experi- 
menting with  various  agents,  but  no  good  results  were  attained  until 
the  introduction  of  oxychloride  of  zinc  as  a  filling  material.  It  is 
uncertain  who  was  the  first  to  suggest  this  as  a  covering,  but  its  use 
developed  such  surprising  results  that  its  almost  universal  adoption  is 
one  of  the  remarkable  revolutions  in  the  history  of  dentistry.  This 
was  owing  partially  to  the  general  desire  to  make  dental  operations 
shorter  if  equally  good  results  could  be  attained,  and  also  to  the  general 
feeling  that  the  destruction  of  the  pulp  cut  off  the  principal,  if  not  the 
only,  source  of  nutrition  to  the  dentine,  practically  rendering  it  a  dead 
tooth  with  a  partial  vitality  maintained  through  the  cementum. 

The  theory  of  the  action  of  the  oxychloride  was  not  well  understood 
at  this  period,  but  the  results  were  manifested  in  pulps  retaining  their 
full  vitality  for  (juite  long  periods  of  time  and  remaining  perfectly  com- 
fortable. The  number  of  years  that  have  elapsed  since  its  introduction 
for  this  purpose  have  given  ample  time  to  arrive  at  intelligent  conclusions 
regarding  it  and  other  similar  materials,  and,  while  the  writer  does  not 
propose  to  dogmatize,  it  w^ould  seem  appropriate  to  the  subject  to  give 
his  views  in  connection  with  a  description  of  the  different  modes  of 
capping  at  present  in  use  and  a  statement  as  to  the  direction  in  which 
failure  or  success  may  be  looked  for. 

That  capping  can  be  made  an  invariable  success  must  ever  remain  an 
impossibility.  The  delicate  nature  of  t4ie  organ  upon  M'hich  we  are 
called  to  operate — endowed,  as  it  is,  with  sensory  nerves  inviting  the 
inflammatory  condition  upon  the  slightest  irritation — makes  any  treat- 
ment at  once  difficult  and  uncertain.  Systemic  peculiarities,  the  anaemic, 
the  scrofulous,  the  syphilitic  diatheses, — all  operate  against  a  satisfactory 
prognosis  ;  and  so  common  are  these  antagonistic  forces  that  it  is  some- 
what remarkable  that  there  has  been  any  degree  of  success. 

The  pulp  from  the  moment  of  exposure  being  irritated  by  atmo- 
spheric germs,  etc.,  it  becomes  necessary  that  the  treatment  attempted 
should  first  aim  to  overcome  this  condition.  If  the  inflammation  has 
not  advanced  too  far,  the  action  of  some  sedative  combined  with  an  anti- 
septic may  be  all  that  is  requisite  as  a  preliminary  treatment.  Oil  of 
cloves,  oil  of  cajeput,  iodoform,  or  a  10-per-cent.  solution  of  carbolic 
acid  may  be  used  at  this  period  with  markedly  good  results.  It  must 
be  remembered,  however,  that  capping  over  freshly-exposed  pulps  is 
alone  under  consideration. 

The  theory  of  the  action  of  the  oxychloride  of  zinc  has  been  that  its 
escharotic  action  is  limited — that  it  preserves  not  only  all  the  superficial 
tissue  destroyed,  but  in  case  of  devitalization  of  the  balance  of  the  pulp 
will  preserve  it  also  in  the  before-mentioned  dry-gangrenous  state ;  so 


890        DISEASES  OF  THE  DENTAL  PULP,  AND  TREATMENT. 

that  even  if  death  supervenes  the  disastrous  results  usually  following 
the  death  of  the  pulp  are  averted.  That  this  is  true  experience  has 
amply  demonstrated.  Its  jjorous  character  makes  it  a  good  absorbent, 
and  its  poor  conducting  quality  is  an  additional  element  in  its  favor. 
In  discussing  the  merits  of  an  agent  the  requirements  to  be  met 
must  be  taken  into  consideration ;  they  are — 1st.  Close  contact,  to 
exclude  air ;  2d.  Porosity  ;  3d.  Non-conduction  ;  4th.  Property  of  pre- 
serving tissue  in  case  of  death.  AVith  our  present  knowledge,  these  seem 
to  be  necessarv ;  and  an  agent  foiling  to  meet  all  of  these  requirements 
Mill  be  a  failure  except  under  most  favorable  conditions — conditions  of 
extraordinary  vitality  and  resisting  power.  There  is  at  present  but  one 
airent  known  that  meets  all  these  demands — the  oxychloride  of  zinc. 
This  is  regarded  by  some  as  too  powerfidly  escharotic,  but  this  eifect 
can  be  modified  by  an  intermediate  capping.  Gutta-percha  has  no 
superiority  over  horn,  quill,  etc. ;  for,Mhile  it  may  be  applied  in  solution 
and  be  perfectly  adapted,  it  is  still  a  foreign  element  without  any  of  the 
peculiar  therapeutic  properties  of  some  of  the  other  substances.  The  same 
may  be  said  of  collodion,  the  resins,  etc.  The  deep-penetrating  property 
of  oxychloride  of  zinc  gives  it  decided  therapeutical  advantage  over 
anv  other  agent.  This  is  very  marked  in  the  treatment  by  it  of  other 
pathological  states,  as  in  chronic  pericementitis,  alveolar  abscess,  etc.  It 
is  this  penetrating  power  which  ensures  the  pulp  from  decomposition  in 
case  of  death,  as  the  effect  has  been  transmitted  to  the  farthest  extrem- 
ity of  the  tissue.  As  oxyphosphate  of  zinc  does  not  possess  this  quality, 
it  is  quite  valueless  in  comparison  with  the  first  named,  and  will  neces- 
sarily fail  of  good  results.  Hence,  while  each  of  the  agents  named  has 
one  or  more  of  the  required  properties,  success  can  be  attained  in  the 
largest  number  of  cases  only  by  the  use  of  that  material  possessing 
these  in  the  fullest  degree ;  and  in  the  judgment  of  the  writer,  until 
some  other  material  can  be  demonstrated  as  superior,  reliance  must  still 
be  placed  on  oxychloride  of  zinc.  It  must  be  said,  however,  that  this 
opinion  is  Avidely  at  variance  with  some  very  good  authorities. 

Coleman '  gives  the  preference  to  nitric-acid  treatment.  He  says : 
"  The  softened  dentine  having  been  cleared  away  and  the  cavity  other- 
wise prepared,  the  sensitiveness  of  the  exposed  pulp  is  lessened  by  a  free 
a])j>lication  of  carbolic  acid  ;  and  then  a  small  disc  of  card  but  little 
larger  than  the  exposed  surface,  and  well  saturated  with  the  strongest 
nitric  acid,  is  laid  gently  upon  it,  and  so  retained  for  about  half  a  min- 
ute. At  times  a  sensation  like  toothache,  but  never  severe,  is  felt  for  a 
few  moments  afterward.  After  removal  of  the  nitric  acid  a  cap  of  thick 
])aper  moistened  with  carbolic  acid  is  placed  over  the  pulp,  and,  if  the 
tooth  is  to  be  filled  with  foil,  over  the  paper  cap  one  of  metal,  concave 
on  the  pulp-surface,  to  guard  the  pulp  from  all  pressure.  The  filling 
is  then  completed."  In  amalgam  fillings  he  recommends  "  to  give  a 
coating  of  oxychloride  over  the  first  jiaper  cap,  in  place  of  the  metal 
one."     Tliis  is  done  to  prevent  change  of  temperature. 

In  considering  the  action  of  any  agent  in  its  eifect  on  the  pulp  the 
]>ossibility  of  the  development  of  osteo-dentine  must  enter  as  a  factor. 
If  this  were  possible  under  all  conditions,  nothing  more  could  be  hoped 

'  Dental  Surgery  and  Pathology. 


CAPPING.  897 

for  or  desired  ;  but  that  sucli  is  not  the  result,  except  in  the  fewest  num- 
ber of  cases,  must  be  clear  to  every  observer,  and  the  reasons  for  this 
must  be  apparent.  If  it  occurs  at  all,  it  must  be  where  the  pulp  is  the 
nearest  possible  to  a  normal  condition,  the  full  normal  state  being  very 
seldom  met  with.  The  vitality  of  the  subject  must  be  above  the  aver- 
age, and — of  equal  importance — the  agent  used  must  have  a  limited 
power  of  stimulation.  It  is,  therefore,  if  this  position  be  correct,  use- 
less to  expect  ncM'  formations,  except  in  limited  degree,  from  the  direct 
action  of  any  of  the  usual  agents.  Oxychloride  is  too  powerful  an 
escharotic ;  oxyphosphate  is  preferable ;  and  so  on  through  the  list. 
But  little  dependence  can  be  placed  upon  this  result,  and  until  we  have 
some  gauge  to  determine  the  actual  amount  of  excitation  necessary  to 
produce  new  tissue  a  favorable  result  may  be  regarded  only  in  the  light 
of  an  accident. 

The  introduction  of  oxychloride  of  zinc  as  a  filling  and  capping  mate- 
rial M'as  naturally  followed  by  investigation  in  other  directions;  efforts 
were  made  to  avoid  the  direct  injurious  escharotic  effect  of  this  and 
other  valuable  agents.  Dr.  J.  S.  King  in  1871  suggested  covering  the 
pulp,  prior  to  the  insertion  of  the  oxychloride,  with  a  paste  made  of 
carbolic  acid  and  oxide  of  zinc.  The  anaesthetic  and  antiseptic  proper- 
ties of  the  former  were  su])posed  to  meet  the  necessary  requirements, 
while  the  latter  furnished  a  convenient  means  of  retaining  it  in  a  soft 
magma,  and  effectually  excluding  the  air  and  giving  a  cushion  on  which 
to  rest  the  denser  filling,  and  thus  avoid  the  effect  of  pressure.  This 
theoretical  view  was  sustained  in  practice.  It  was  found  that  by  pla- 
cing a  very  small  quantity  directly  over  the  pulp  no  pain  folloMcd  the 
introduction  of  the  oxychloride,  and  the  results  were  apparently  more 
satisfactory.  Carbolic  acid  of  full  stroigth  should  not  be  used,  a  20- 
per-cent.  solution  being  quite  strong  enough.  This  mixture  can  be 
prepared  at  the  time  needed  and  gently  pressed  in  position  by  a  piece 
of  spunk  or  bibulous  pa])er,  which  at  the  same  time  absorbs  any  excess 
of  fluid.  Then  cover  this  with  the  oxychloride,  either  as  a  cap  or  as  a. 
filling  of  the  entire  cavity. 

Dr.  J.  E.  Cravens  in  1873  suggested  the  following  practice  as  hasten- 
ing the  formation  of  secondary  dentine.  After  careful  drying  of  the 
cavity  the  pulp  is  covered  \vith  a  jiaste  prepared  as  follows  :  ''  Upon  a 
warm  slab  of  ground  glass  put  a  drop  of  Merck's  lactic  acid  and  twice 
that  volume  of  magma  or  freshly-precipitated  phosphate  of  lime  ;  then 
rub  until  a  complete  solution  is  effected.  This  is  laetophosphate  of  lime. 
To  this  solution  add  dry  phosphate  of  lime  until  the  paste  is  of  i)roper 
consistence  for  application.  Place  the  paste  directly  on  the  exposed 
pulp  so  as  to  occupy  all  the  space  and  yet  make  no  pressure  upon  it ;-. 
then  remove  the  moisture  from  the  surface  of  the  paste  with  spunk  or 
some  absorbent;  then  cover  it  with  two  or  three  pieces  of  bibulous 
paper  cut  to  fit  the  cavity  and  moistened  with  sweet  oil.  Press  this 
carefully  upon  the  paste,  especially  upon  the  border ;  then  cover  this, 
and  fill  with  oxychloride.  No  preparative  treatment  is  required." 
This  dressing  should  remain  for  from  two  to  six  weeks,  and  must  not  be 
disturbed  during  that  time. 

For  the  purpose  of  protecting  the  pulp  a  film  of  collodion  has  been 
Vol.  I.— 57 


898        DISEASES  OF  THE  DENTAL  PULP,  AND   TREATMENT. 

used,  a  drop  being  placed  over  the  exposed  portion  and  the  ether  allowed 
to  evaporate  before  covering  it  with  the  capping.  Dr.  Francis  of  New 
York  suggested  the  saturation  of  tissue  or  Japanese  paper  with  Canada 
balsam  and  laying  this  gently  over  the  pulp.  This  plan  has  been  quite 
extensively,  adopted  by  some  prominent  operators,  who  regard  it  as 
superior  to  other  modes.  A-^arious  other  processes  have  been  suggested, 
all  looking  to  the  same  end,  each  and  all  having  the  same  percentage 
of  success  and  failure.  One  of  the  most  satisfactory  in  the  writer's 
hands  has  been  a  modification  of  Dr.  King's  method,  which  he  has 
used  almost  exclusively  since  it  was  first  mentioned ;  and  that  is  the 
addition  of  a  small  amount  of  iodoform  to  the  paste  of  carbolic  acid 
and  oxide  of  zinc.  The  value  of  this  agent  as  an  antiseptic  can  hardly 
be  overestimated,  and  as  an  obtunder  of  pain  it  is  second  only  to  chlo- 
roform. Its  non-irritant  quality  renders  it  peculiarly  adapted  for  this 
purpose.  The  two  objectionable  features  are  the  odor  and  the  tendency 
to  nauseate ;  hence  it  must  be  used  only  in  minute  quantities  for  this 
purpose,  as  it  is  presumed  that  this  will  remain  on  the  pulp  for  an 
indefinite  period. 

The  practice  in  regard  to  subsequent  treatment  varies,  and  its  discus- 
sion does  not  fall  to  the  province  of  the  writer.  Suffice  it  to  say  that 
some  make  use  of  the  material  adopted — whether  it  be  gutta-percha, 
oxychloricle,  oxyphosphate,  or  oxysulphate — simply  as  a  cap,  filling  the 
balance  of  the  cavity  with  the  permanent  material.  The  safest  plan, 
however,  is  to  pre])are  the  capping  of  sufficient  thickness  to  support  a 
metal  filling,  if  that  is  decided  upon,  doing  this  while  the  capping 
material  is  in  a  semiplastic  condition  ;  then  fill  temporarily  with  gutta- 
percha, to  test  results.  At  a  future  sitting  the  filling  can  be  finished 
without  risk  of  disturbing  the  capping  first  placed— ^a  consideration  of 
very  great  importance. 

In  closing  this  portion  of  the  subject  it  may  be  said  that  no  plan  has 
as  yet  been  proposed  that  gives  a  satisfactory  solution  of  the  problem 
under  discussion  ;  and,  while  it  remains  true  that  the  pulp  ought  to  be 
saved,  no  treatment  has  as  yet  been  devised  and  no  specific  been  intro- 
duced to  accomplish  this  in  all  cases,  and,  as  before  stated,  it  would 
seem  impossible  that  this  can  ever  be  done  while  conditions  are  as  we 
find  them.  From  the  great  discrepancy  in  reports  from  different  sec- 
tions, it  is  very  evident  that  localities  have  much  to  do  with  success. 
This  ought  to  be  expected.  Healthy  locations,  giving  vigorous  organi- 
zations, would  result  more  favorably  than  the  opposite,  and  the  treat- 
ment that  would  give  a  large  percentage  of  success  in  the  one  would 
result  in  almost  total  failure  in  the  other. 

The  discussion  of  treatment  has  been  wholly  confined  to  freshly- 
exposed  judps  or  those  but  slightly  affected  by  long  exposure.  Those 
in  the  first  or  secondary  stages  of  pulpitis  have  not  been  mentioned,  but 
will  be  more  fully  considered  in  the  proper  place.  It  may  be  stated  as 
a  rule  that  in  proportion  to  the  extent  of  the  inflammation  in  the  pulp 
will  be  the  probability  of  failure. 

Before  entering  into  the  treatment  of  inflamed  pulps  it  will  be  con- 
sistent with  the  plan  marked  out  to  consider  the  subject  of  entire  devital- 
ization and  removal.    This  mode  of  procedure  antedated  that  of  capping, 


DEVITALTZATION.  899 

and  was  for  many  years  the  only  mode  of  overcoming  the  difficulties 
arising  from  exposures ;  but  the  treatment — if  it  may  be  dignified  by 
this  title — was  confined  to  the  anterior  teeth.  This  was  necessarily  so, 
as  no  appliances  were  then  in  use  adapted  to  the  posterior  teeth.  The 
plan  then  adopted  was  that  before  described — destroying  the  pulp  by 
the  actual  cautery,  or,  by  what  was  in  more  general  use,  hooked  or  barbed 
instruments,  to  tear  it  out  by  force.  It  is  needless  to  say  that  either  of 
these  operations  was  so  barbarous  in  its  infliction  of  pain  that  it  is 
scarcely  presumable  that  many  submitted  to  it.  The  removal  at  the 
present  time  may  be  performed  with  a  minimum  amount  of  pain  by 
the  use  of  local  anaesthetics  and  the  galvano-cautery,  but  at  the  period 
referred  to  neither  of  these  agents  was  known.  Up  to  the  time  when 
Spooner  introduced  arsenic  as  a  means  of  devitalization  the  canals  from 
which  pulps  had  been  removed  were  allowed  to  remain  unfilled ;  the 
result  was  decomposition  of  the  remaining  organic  matter,  followed 
by  pericementitis,  alveolar  abscess,  etc.  The  reasons  for  this  were  not 
then  understood,  and  the  untoward  results  were  ascribed  to  the  operation, 
and  not  to  the  true  cause — the  leaving  unclosed  canals  to  become  recep- 
tacles for  eiiete  matter  with  its  train  of  evils.  It  was  not  until  long 
after  the  introduction  of  arsenic  that  this  imperfect  mode  of  operating 
was  in  part  remedied.  The  credit  of  this  is  due  to  Dr.  Maynard  of 
Washington,  D.  C,  who  perfected  the  process  noAV  known  as  filling  the 
canals.  Until  this  was  demonstrated  as  an  effectual  remedy  when  per- 
fectly performed,  the  filling  of  teeth  was  of  very  little  service.  Atten- 
tion was  immediately  turned  to  improving  the  mode  of  introducing 
arsenic  and  of  limiting  its  action.  Since  that  period  the  experience 
derived  has  more  clearly  demonstrated  its  value,  and  it  remains  the  only 
agent  that  will  effect  the  destruction  of  the  pulp  with  certainty  and  with 
comparatively  little  pain  to  the  indiyidual.  To  accomplish  this,  how- 
ever, certain  things  are  to  be  considered. 

Arsenic  acts  by  first  exciting  the  sensory  nerves  and  then  paralyzing 
them,  arousing  inflammation  violent  in  proportion  to  the  amount  used. 
This  first  stage  of  excitement  passes  off',  and  the  arsenic  is  gradually 
absorbed.  Death  of  the  organ  does  not  immediately  follow ;  indeed, 
cases  have  been  noticed  where  sensation  returned  after  apparent  death. 
As  the  irritation  is  violent  at  the  earlier  stages,  and  is,  as  before  stated, 
in  proportion  to  the  quantity  used,  it  follows  that  an  overdose  will  pro- 
duce an  amount  of  excitation  that  will  defeat  the  object  of  its  use ;  or, 
in  other  words,  the  inflammation  suddenly  aroused  will  resist  the  ab- 
sorption, probably  through  the  action  of  the  well-known  law  that  pres- 
sure of  fluids  on  one  side  of  a  membrane  tends  to  prevent  the  passage 
of  fluids  or  substances  in  solution  upon  the  other  side,  and  thus  arsenic 
will  fail  to  do  more  than  increase  the  congestion.  The  same  result  is 
manifest  in  the  use  of  large  quantities  in  the  stomach,  the  sudden 
inflammation  frequently  producing  a  similar  effect  on  a  larger  scale. 
The  recognition  of  this  well-known  fact  rendere  the  application  of 
arsenic  to  inflamed  pulps  of  doubtful  value ;  indeed,  it  is  very  well 
understood  that  the  irritated  tissue  will  resist  its  action,  and  the 
application  must  be  delayed  until  the  inflammation  has  been  reduced 
by  treatment.     It  therefore  follows  that  the  destruction  by  arsenic  will 


900        DISEASES  OF  THE  DENTAL  PULP,  AND  TREATMENT. 

be  m(3re  satisfactorily  performed,  as  in  the  case  of  capping,  npon  pnlps 
the  least  irritated  or  nearly  freshly  exposed.  The  fact  also  having  been 
demonstrated  that  quantity  increases  inflammation,  and  proportionately 
so  to  the  amount  used,  it  follows  as  a  necessary  sequence  that  it  is  better 
and  safer  to  use  minute  quantities ;  and  it  has  been  further  found  by 
experience  that  this  amount,  -when  properly  applied,  may  be  reduced  to 
the  Y^Q  ^^  ^  grain  and  be  effectual  to  the  extent  of  destruction  desired. 
It  has  been  further  demonstrated  that  an  amount  sufficient  to  devitalize 
the  entire  pulp  at  one  application  is  too  large,  as  the  destructive  effect 
may  be  continued  through  the  tissue  in  the  apical  foramen  to  the 
periosteum,  and  that  the  limitations  of  amount  should  be  confined 
to  the  quantity  that  will  carry  destruction  to  the  upper  third  of  the 
tissue  in  the  canal  Avithout  comprising  all  of  it.  Keeping,  then, 
this  general  statement  in  mind,  its  preparation  and  use  may  be 
described. 

The  preparation  of  arsenious  acid  for  use  in  devitalizing  the  pulp  was 
in  the  earlier  days  of  its  introduction  regarded  as  of  more  importance 
than  at  present.  Various  agents  were  from  time  to  time  suggested 
either  to  reduce  the  pain  or  to  limit  the  action  of  the  arsenic  to  the  part 
for  which  it  was  intended,  or  else  to  give  bulk  to  the  mass.  For  the 
first  purpose  morphia  was  recommended,  and  for  the  second  charcoal 
and  othei-  materials.  AVliy  charcoal  should  have  been  used  is  not  very 
clear,  nor  did  it  come  into  general  use.  Morphia,  however,  still  retains 
its  place  with  many,  but  the  majority,  probably,  of  operators  use  at 
present  arsenic  without  any  other  combination  than  creasote  or  carbolic 
acid.  One  of  the  first  to  recommend  morphia  in  connection  with  arse- 
nious acid  and  creasote  was  Dr.  J.  D.  White  of  Philadelphia.  His  for- 
mula was : 

I^.  Acidi  arseniosi,  gr.  j  ; 

Morphinse  sulphatis,  gr.  ij  ; 

Creasoti,  q.  s.*    M. 

S.  To  be  made  into  a  thick  paste  by  severail  hours'  trituration. 

The  proportional  amounts  of  arsenic  and  morphia  varied  with  differ- 
ent ojierators,  and  Dr.  Foster  Flagg  suggested  the  use  of  acetate  of 
morphia  in  place  of  the  sulphate.     His  formula  was : 

^.  Acidi  arseniosi, 
MorphiujB  acetatis 
Acidi  carbolici,        gtt.  iij.     M. 

Garretson  makes  it  equal  quantities  of  arsenious  acid  and  acetate  of 
morjihia.  Dr.  J.  D.  AVhite  regarded  thorough  trituration  as  of  great 
iui])()rtauce,  to  the  end  that  the  arsenic  and  morphia  might  be  com- 
])U'tcly  combiued,  but,  the  specific  gravity  of  the  former  being  greater 
than  that  of  the  latter,  the  arsenic  would  mainly  sink  to  the  bottom  of 
the  receptacle,  thus  introducing  an  element  of  uncertainty  in  its  applica- 
tion ;  so  that  the  preparation  of  small  amounts  and  the  spreading  the 
mass  over  a  consid(>rab]c  surface  became  a  necessity  if  the  operator  would 
make  the  application  with  a  reasonable  degree  of  certainty  of  having 
received  sufficient  arsenic  to  accomplish  the  end  desired.     Owino;  to  the 


gr. 

,1 ; 

gr. 

ij ; 

gtt. 

iij 

DEVITALIZATION.  901 

separation  produced  by  the  greater  specific  gravity  of  the  arsenic  even 
after  the  long  trituration,  the  simple  mixing  of  these  ingredients  in  the 
glass  or  porcelain  vessel  in  which  it  was  to  remain  came  to  be  the  usual 
mode  adopted ;  for  this  purpose  the  ordinary  glass  or  porcelain  tooth- 
powder  boxes  are  all  that  is  required.  Very  little  creasote  or  carbolic 
acid  should  be  used  ;  for  the  thicker  the  paste  is,  the  more  convenient 
will  be  its  application. 

It  is  very  questionable  whether  the  addition  of  morphia  is  any  im- 
provement, as  it  has  never  been  satisfactorily  demonstrated  that  it 
diminishes  the  pain  of  the  process.  Adding  bulky  foreign  substances 
is  a  decided  detriment,  as  this  prevents  any  approach  to  exactness  of 
measurement — a  matter  which  is  of  great  importance. 

The  amount  of  jjain  following  the  application  of  arsenic  is  dependent 
on  two  conditions :  first,  the  state  of  the  pulp  at  the  time ;  and  sec- 
ondly, the  amount  of  pressure  given  to  it  by  the  covering  used.  Pulps 
will  always  give  a  painful  response  to  pressure,  but  this  Avill  be  aggra- 
vated in  proportion  to  the  inflammation  already  present  in  the  tissue. 
In  a  highly-inflamed  pulp  the  pain  will  be  severe  and  continuous,  and 
the  arsenic,  as  already  stated,  will  fail  to  act  upon  it.  The  patient  will 
have  hours  of  suifering  with  negative  results.  On  the  other  hand,  if 
there  has  been  little  or  no  irritation  of  this  organ,  the  application  causes 
pain  which  lasts  for  an  hour  and  then  ceases.  The  remarkable  uni- 
formity of  this  period  leads  to  the  conclusion  that  direct  pressure  must 
have  something  to  do  with  the  pain,  but  this  does  not  entirely  explain 
it.  It  Avould  seem  as  though  this  amount  of  time  was  required  to  par- 
alyze the  nerves  of  sensation,  while  a  longer  period  is  necessary  for  the 
entire  devitalizing  process.  This  would  appear  to  be  the  only  reason- 
able explanation,  as  the  pain  is  present  when  the  utmost  care  has  been 
taken  to  avoid  pressure,  and  this  Mill  continue  to  the  time  specified.  So 
certain  is  this  that  in  non-irritated  pulps  the  operator  can  safely  prom- 
ise his  patient  relief  at  the  expiration  of  the  hour.  Continuation  of 
pain  over  this  period  is  a  certain  indication  that  the  pulp  was  in  an 
inflamed  condition  prior  to  the  apjilication.  The  patient  should  in 
all  cases  be  instructed  to  return  if  the  pain  continues  after  the  period 
named. 

Exactness  in  administration  is  of  great  importance,  for  the  rapidity 
of  absorption  of  arsenic  in  non-inflamed  tissue  renders  any  excess  of  the 
agent  a  possible  danger — a  danger  proportionate  to  the  density  of  the 
tooth  and  the  age  of  the  patient.  The  destruction  of  the  life  of  the 
entire  pulp  is  not  required,  nor  is  it  desirable.  The  upper  third  should, 
if  possible,  be  kept  in  a  nearly  normal  condition  ;  its  removal  does  not 
produce  much  pain  and  the  parts  in  and*  around  the  foramen  are  left  in 
a  much  better  state.  The  danger  of  an  excess  of  arsenic  passing  through 
to  the  pericementum  is  always  imminent  and  should  be  carefully  guarded 
against ;  the  smallest  quantity,  therefore,  of  the  paste  should  be  taken  : 
if  ap]ilied  directly  to  the  pulp,  a  very  minute  amount  will  answer.  It 
is  difficult  to  give  any  clear  idea  of  this  in  fractions  of  a  grain,  espe- 
cially when  paste  is  used,  but  an  approximation  may  be  arrived  at  by 
stating  that  an  amount  sufficient  to  lie  on  the  point  of  a  small  hatchet- 
shaped  excavator  will  be  sufficient.     From  the  2V  to  -gLj,  or  even  3-^, 


902         DISEASES   OF  THE  DEXTAL   PULP,   A  SB   TEEATMEXT. 

of  a  graiu  of  the  powder  may  be  used,  depending  on  the  position  and 
character  of  the  exposure.  Tlie  most  feasible  mode  of  arriving  at  this 
is  to  divide  a  grain  on  a  slab  into  the  number  of  parts  desired ;  this 
will  familiarize  the  mind  with  the  required  amount. 

It  must  be  remembered  that  arsenic  is  rapidly  absorbed  by  any 
organic  matter  with  which  it  is  brought  in  contact,  so  that  foreign 
matter  will  prevent  its  action  on  the  pulp-tissue  just  in  proportion  to 
the  amount  present ;  hence,  the  debris  from  decay  should  all  be  removed 
before  making  the  arsenical  application,  and  in  the  use  of  covering  mate- 
rials those  of  a  nature  to  absorb  should  be  discarded  or  their  contact 
Avith  the  arsenic  be  prevented  by  an  intermediate  layer  of  metal. 

The  preparation  of  the  cavity  having  been  completed,  the  tooth  should 
be  carefully  invested  Avith  the  rubber  dam,  especial  care  being  taken  to 
have  it  bind  closely  at  the  gum-margin.  Dry  out  the  cavity,  and  then 
make  the  application  direct  to  the  pulp.  Cover  this  with  a  lead  cap, 
and  then  fill  the  balance  of  the  cavity  with  gutta-percha.  This  part 
of  the  operation  should  be  carefully  j)erformed,  to  avoid  the  possibility 
of  the  arsenic  rciichiug  the  gum-tissue.  Care  must  also  be  exercised 
that  no  arsenic  adheres  to  the  shank  of  the  instrument,  as  this  may 
accidentallv  hxlge  where  it  is  not  desirable  to  have  it.  For  this  reason 
wide-moutlied  vessels  as  receptacles  are  the  only  ones  fit  to  use,  and  the 
narrow-necked  bottles  so  universally  sold,  containing  arsenic  and  car- 
bolic acid,  should  be  condemned  for  this  purpose. 

Where  the  tooth  is  so  badly  broken  that  it  is  difficult  to  secure  proper 
support  for  the  retaining  filling,  recourse  may  be  had,  on  proximal 
surfiices,  to  the  adjoining  tooth  ;  where  this  fails,  the  filling  should  be 
ligatured  in  place.  The  difficulty  of  treating  fractured  teeth  with 
arsenic  has  been  very  great,  as  these,  in  the  case  of  anterior  teeth,  are 
frequently  broken  in  such  a  manner  that  no  supporting  walls  are  left. 
Ail  application  of  very  minute  amount  should  be  made  ;  cover  this  with 
a  thin  layer  of  gutta-percha  and  ligature  it  in  position.  This  may 
destroy  only  a  portion  of  the  pulp,  but  still  sufficient  to  enable  the 
ojierator  to  secure  a  place  for  a  second  application,  which  generally  is 
reijuircd.  A  very  neat  mode  of  accomplishing  this  is  suggested  by  Dr. 
Kirk  of  Philadelphia  :  he  uses  the  surgeon's  rubber  plaster  where  but 
a  portion  of  the  tooth  is  left,  carrying  it  round  the  tooth.  It  will  adhere 
satisfactorily  for  several  days,  or  long  enough  to  accomplish  the  object. 
The  destructive  character  of  arsenic  is  so  well  understood  that  any  care- 
lessness in  its  use  in  this  operation  amounts  to  malpractice,  and  should 
be  condemned  as  such.  AVhen  ])roperly  applied  and  carefully  guarded, 
no  agent  is  more  thorijughly  under  control  or  more  safely  used  ;  but  in 
careless  hands  nothing  can  l)e  more  dangerous  to  the  life  of  the  tooth 
and  surrounding  tissues.  Extensive  sloughings  have  been  produced  by 
a  lack  of  caution.  While  this  is  true,  the  very  remarkable  stories  of 
the  supposed  bad  results  in  its  use  have,  generallv,  no  foundation  in 
fact. 

The  application  should  remain  about  twenty-four  hours  before  exam- 
ination. If  the  operation  has  been  performed  with  judgment,  the  pulp 
will  lie  partially  destroyed — sufficiently  so  to  be  removed. 

This  operation,  though  apparently  simple,  is  attended  with  consider- 


DE  VITALIZA  TIOX.  903 

able  difficulty  if  attempted  immediately  after  the  devitalization  by 
arsenic.  In  the  singk-rooted  tuutli  the  instrument  is  readily  passed  to 
the  farthest  extremity  of  the  canal.  The  canals  of  the  superior  bicus- 
pids and  the  molars,  superior  and  inferior,  are  far  more  difficult  of 
acc-ess.  The  extreme  minuteness  of  the  canals  in  the  buccal  roots  of  the 
su])erior  first  and  second  molars  and  the  anterior  root  or  roots  of  the 
inferior  molars  increases  the  difficulty.  The  operation  is  also  rendered 
more  uncertain  by  the  bent  form  of  the  roots.  Enlargement  of  the 
canal  by  drilling  is  possible  to  a  portion  of  its  extent,  though  great 
care  is  required  to  avoid  passing  the  drill  through  the  root.  Cavities  on 
the  distal  surfaces  of  molars  require  special  treatment.  Entrance  to  the 
canals  through  this  surface  is  accomplished  only  by  a  sacrifice  of  a  large 
portion  of  the  tooth.  Entrance  to  the  pulp  can  be  effected  more  satis- 
tactorily  by  drilling  through  the  buccal  surface  in  the  direction  of  the 
roots,  or,  what  is  preferable,  to  enter  through  the  mastic-ating  surface, 
provided  a  cavity  has  previously  existed  on  that  surface ;  otherwise,  the 
amount  of  labor  required  hardly  justifies  the  ojxration. 

The  instrument  generally  used  to  remove  the  pulp  is  made  from  a 
watchmaker's  broach,  temper  drawn  and  the  steel  barbed.  This  would 
be  a  very  satisfactory  instrument  had  it  any  lasting  property,  but  the 
barbs  naturally  flatten  or  the  steel  breaks  after  one  or  two  operations. 
The  best  instrument  for  this  purpose  is  probably  one  made  from  steel 
wire,  filed  down  to  the  proper  size,  then  flattened  at  the  extremity,  bent 
in  the  form  of  a  delicate  hook,  and  tempered  at  this  portion. 

To  remove  the  pulp  the  instrument  must  be  passed  carefully  up  the 
canal  as  far  as  possible  and  then  rotated,  in  order  to  cut  ofl"  the  pulp- 
connections.  When  the  barbed  instrument  is  used,  the  danger  of  break- 
ing is  always  present ;  and  when  this  occurs,  the  fractured  end  is  removed 
with  difficulty.  It  may  be  accomplished  by  passing  a  second  instrument, 
wrapped  with  cotton,  up  by  the  side  of  the  first.  The  barbs  become 
entangled  in  the  cotton,  and  the  broken  piece  is  thus  removed.  A  mag- 
netized instrument  has  been  recommended  for  this  purpose,  but  the 
attractive  force  is,  as  a  rule,  insufficient  to  accomplish  the  removal. 
The  operation  will  be  found  at  all  times  difficult  and  tedious,  and  some- 
times impossible.  When  this  proves  to  be  the  case,  the  piece  should  be 
carefully  located  and  the  filling  material  carried  directly  to  the  most 
constricted  portion  of  the  canal  and  the  balance  carefully  and  very 
solidly  filled.  Where  this  has  been  well  done,  the  writer  has  never 
known  any  unpleasant  results  to  follow  the  leaving  of  the  fragment 
of  steel  in  the  canal. 

The  pulp  on  removal  will  show  the  dividing-line  between  the  part 
affected  by  the  agent  and  that  still  in  the  normal  state,  provided 
that  the  amount  of  arsenic  used  has  been  small. 

The  proper  time  for  filling  the  roots  after  the  removal  of  the  pulp  has 
been  a  subject  of  much  controversy.  The  safest  plan  is  to  place  a  mild 
antiseptic,  as  euctdyptus  oil  or  oil  of  cloves  or  eugeuol,  in  the  canal  and 
let  it  rest.  The  objection  to  immediate  filling  lies  in  the  fact  that  there 
must  be  a  collection  of  fluid  and  lymph  in  the  canal  from  the  apical 
foramen,  and  possibly  from  the  canaliculi  of  the  dentine,  in\'iting  putre- 
factive processes.     It  is  necessary,  therefore,  to  place  the  canal  or  canals 


904        DISEASES  OF  THE  DENTAL  PULP,  AND   TREATMENT. 

under  proper  treatment  before  inserting  the  filling.  Those  Avho  advo- 
cate inniiediate  tilling  contend  that  delay  in  closing  the  canal  increases 
this  collection  of  fluid,  ^vhile  the  filling  arrests  it.  Whatever  force  there 
may  be  in  this  reasoning,  it  is  certainly  the  safest  plan  to  wait  for  a 
restoration  to  normal  conditions.  Dr.  Litch  recommends,  before  filling, 
repeatedly  to  pass  up  each  canal  a  probe  heated  to  white  heat,  thus  not 
only  desiccating,  but  superficially  carbonizing,  the  walls  of  the  canals. 

A  second  ap};lication  of  arsenic  should  not  be  made  upon  a  pulp  par- 
tially destroyed  by  this  agent.  If  a  poi'tion  of  the  pulp  has  been  devi- 
talized, except  in  the  case  of  fractured  teeth,  it  is  better,  and  altogether 
more  prudent,  to  let  the  pulp  rest  a  day  or  two  before  attempting  its 
removal.  Some  pulps  are  affected  very  slowly  and  require  more  than 
the  usual  twenty-four  hours.  In  some  cases  repeated  applications  of 
arsenic  fail  to  have  any  immediate  effect,  and  in  one  case  coming  under 
the  observation  of  the  writer  this  was  repeated  several  times,  when,  fail- 
ing to  get  any  results,  the  tooth  was  capped,  and  at  the  expiration  of 
a  year  was  examined,  under  the  supposition  that  possibly  a  small 
amount  of  arsenic  might  have  been  absorbed  and  death  followed ; 
but  the  pulp  still  retained  its  full  vitality,  and  was  recapped. 

The  resisting  power  of  the  tissue  of  the  pulp  after  devitalization  by 
arsenic  is  very  clearly  demonstrated  in  the  tenacity  with  which  the 
organ  resists  the  attempt  to  remove  it.  Even  with  the  best-arranged 
barbed  instruments  this  is  by  no  means  an  easy  matter,  and  frequently 
ends  in  its  coming  out  in  torn  portions.  This  demonstrates — if  demon- 
stration be  needed — ^that  arsenic  has  no  effect  upon  the  tissue  itself. 
The  force  of  the  retention  is  very  easily  understood  when  it  is  remem- 
bered that  the  })ulp,  M-ith  its  microscopic  connections,  has  intimate  rela- 
tions with  almost  the  entire  dentine,  exclusive  of  its  attachments 
through  the  foramen. 

Arsenic,  to  a  limited  extent,  is  a  preserver  of  tissue,  but  this  does  not 
prevent  ultimate  decomposition,  which  at  the  expiration  of  ten  days  will 
have  progressed  so  far  as  to  make  the  removal  of  the  pulp  or  pulps  a 
very  easy  matter ;  indeed,  they  may  be  drawn  out  by  a  pair  of  small 
surgical  forceps.  A  delay,  however,  in  removal  to  this  period  of  change 
is  wrong,  as  any  approach  to  putrescence  endangers  the  success  of  the 
subsequent  treatment  necessary  to  restore  to  healthy  conditions. 

Tiiat  the  pulp  is  very  easily  removed  is  true,  but,  from  what  has  been 
already  said,  it  will  be  understood  that  waiting  for  putrescence  is  a  very 
reprehensible!  practice.  The  effect  is  })recisely  the  same  as  in  other  forms 
of  devitalization  ;  indeed,  pericementitis  is  seemingly  more  certain  to 
follow  than  where  death  has  occurred  from  causes  enumerated.  The 
best  plan  is  to  remove  at  once. 

Treatment  of  Superficial  Pulpitis. — Inflaramation  of  the  pulp 
may,  as  already  stated,  be  limited  in  its  area  of  action,  not  spreading  to 
any  extent  Ixyond  the  crown  portion  ;  this  slight  irritation  may  or  may 
not  be  accom])anied  l)y  acute  pain.  The  tooth,  however,  is  never  wholly 
comfortable.  Attempts  have  constantly  been  made  to  save  these  pulps 
by  capping,  but  it  must  be  acknowledged  Avith  only  a  moderate  degree 
of  success.  Tiie  reasons  for  this  have  already  been  fully  stated,  and  it 
therefore  only  remains  to  give  the  general  treatment. 


TREATMENT  OF  SUPERFICIAL   PULPITIS.  905 

If  pain  is  an  accompaniment,  the  inflammation  must  be  reduced  by 
mechanical  and  antiphlogistic  measures.  These  consist  in  the  removal 
of  all  decayed  matter  pressing  upon  and  continuing  the  irritation  of  the 
pulj) ;  local  depletion  of  the  congested  vessels  by  bleeding  and  then 
thoroughly  syringing  with  lukewarm  water,  to  remove  all  particles 
of  loose  matter.  The  pulp  may  be  temporarily  capped  by  an  agent  or 
combination  of  agents.  These  should,  first,  destroy  all  bacterial  germs  ; 
second,  obtund  pain  ;  and,  third,  destroy  septic  emanations.  To  effect  the 
first  result,  the  agents  that  may  be  used  are  numerous.  Of  these,  car- 
bolic acid  justly  holds  a  liigh  place  ;  but  this,  while  superior  as  a  germ- 
destroyer,  is  a  powerful  escharotic,  and  in  practice  its  use  in  full  strength 
has  been  found  not  altogether  satisfactory.  Its  valuable  properties  are, 
however,  manifested  when  reduced  to  about  20-per-cent.  solution.  C^ar- 
bolic  acid  is  a  local  anaesthetic  of  considerable  importance  and  can  usually 
be  depended  upon  to  relieve  the  pain  of  pulpitis,  but  is  more  effective  when 
combined  with  iodoform.  The  fact  that  this  has  the  dual  properties  of  an 
antiseptic  and  an  anaesthetic  of  nearly  equal  value  to  chloroform  renders 
it  superior  to  all  other  agents  for  this  purpose.  As  these  two  agents  cover 
the  three  desired  qualities,  they  are  recommended  as  fulfilling  the  require- 
ments of  an  excellent  and  very  effective  application.  The  medium  to 
retain  these  in  position  may  be  the  oxide  of  zinc ;  they  should  be  com- 
bined at  the  moment  of  using  and  placed  gently  over  the  pulp.  If  it  is 
found  necessary  to  dismiss  the  patient  for  the  time,  a  temporary  filling 
of  gutta-percha  should  be  placed  over  this,  care  being  taken  not  to  press 
upon  the  temporary  covering.  To  avoid  the  possible  disturbance  from 
the  products  of  decomposition — ahvays  a  possible  factor  of  disturbance 
in  these  pathological  states — it  is  safer  to  leave  a  passage  through  the 
temporary  filling  for  the  escape  of  an  excess  of  gas.  This  is  readily 
made  by  building  the  material  round  a  canal-plugger  and  upon  comple- 
tion withdrawing  it.  Treatment  of  these  teeth  should  never  be  attempted 
without  this  precautionary  measure.  Ordinarily,  one  or  two  applica- 
tions will  give  satisfactory  results ;  but  if  systemic  conditions  are  unfa- 
vorable, the  inflammation  will  not  easily  yield  to  palliative  treatment, 
and  resort  must  be  had  to  the  destruction  of  the  pulp  either  by  the 
arsenical  application  or  by  the  removal  of  the  portion  of  the  pulp  most 
diseased  and  the  capping  of  the  balance.  This  latter  treatment  is  pref- 
erable in  both  cases,  for,  as  already  stated,  arsenic  does  not  act  readily 
on  inflamed  surfaces,  and  a  removal  of  a  section  before  applying  it  is 
a  matter  of  necessity.  The  plan  of  cutting  out  a  portion  of  the  pulp 
was  probably  first  suggested  by  Dr.  Allport  of  Chicago.  It  consists  in 
the  excision  of  a  portion  of  the  pulp  at  the  orifice  of  exposure,  drawing 
the  edges  of  the  incised  part  together  and  inducing  their  union,  and  in 
this  manner  closing  the  wound.  From  the  "  extreme  delicacy  of  the 
operation,"  Dr.  Allport  regards  it  as  ''  rarely  a  practical  one."  Witzel 
of  Germany  suggested  in  1879  a  modification  of  this.  His  plan  was  to 
treat  with  arsenious  acid,  and  then  after  a  limited  time  to  cut  out  the 
crown  portion  and  preserve  the  balance,  or  stump,  of  the  pulp  by  cap- 
ping. As  the  use  of  arsenic  must  necessarily  sooner  or  later  destroy  the 
entire  pulj),  this  mode  cannot  be  recommended.  Cases  very  frequently 
occur  in  chronic  pulpitis  where  this  operation  of  partial  extirpation  is 


906         DISEASES  OF  THE  DENTAL  PULP,   AND   TREATMENT. 

necessary;  this  is  readily  performed  with  a  minimum  amount  of  pain 
by  the  use  of  local  anaesthetics.  The  pulp  may  be  placed  under  the 
influence  of  chloroform,  a  di'op  or  two  being  sufficient ;  or  it  may  be 
benumbed  by  rhigolene,  ether-spray,  or  cocaine ;  or  an  application  may 
be  made  of  iodoform  paste — iodoform,  carbolic  acid,  and  oxide  of  zinc. 
If  either  the  first  or  the  last  be  used,  time — from  five  to  ten  minutes 
— must  be  given  for  the  action  of  the  agents.  Then  Avith  a  sharp  burr 
revolved  rapidly  by  a  dental  engine  the  most  highly-inflamed  portion 
can  quickly  be  removed.  This  accomplished,  the  pulp  may  be  placed 
under  a  non-irritant  antiseptic  dressing,  as  oil  of  cajeput,  and  event- 
ually be  capped  or  destroyed  by  arsenic,  as  may  be  desired. 

The  treatment  of  deep-Heated  pulpitis  is  substantially  the  same  as 
for  that  just  described,  except  that  any  attemjjt  at  amputation  must, 
from  the  nature  of  the  case,  be  futile.  The  indications  here  are  acute 
pain,  generally  complicated  with  slight  i^ersistent  irritation,  which  will 
be  manifested  by  pain  upon  striking  the  teeth.  The  aim  must  be  to 
reduce  the  inflammation  as  much  as  possible  by  the  means  proposed  in 
superficial  pulpitis.  Avoid  any  attempt  at  destruction  by  arsenic,  as 
the  effect  of  this  would  simply  be  to  increase  the  irritation.  It  is  better 
and  safer  to  keep  the  pulp  under  the  dressing  until  the  acute  inflamma- 
tion destroys  the  vitality,  and  then  remove  before  the  period  of  putres- 
ence.  The  point  to  be  enforced  is  to  avoid  over-treatment.  Removal 
of  the  pulp  is  the  only  effectual  course  to  pursue,  for  anything  less  than 
this  is  almost  sure  to  end  in  disappointment. 

The  management  of  gangrenous  or  putrescent  pulps  is  probably  one 
of  the  most  difficult  and  unsatisfactory  of  any  of  the  operations  the 
dentist  is  called  upon  to  perform.  These  may  be  classed  under  two 
forms — the  one  where  death  has  occurred  from  extrinsic,  and  the  other 
from  intrinsic,  influences.  The  liability  of  the  anterior  teeth  in  early 
life  to  receive  blows  makes  the  presentation  of  teeth  having  dead  pulps, 
and  yet  being  at  the  same  time  free  from  decay,  not  unusual.  Again, 
regulating  teeth  frequently  produces  a  similar  result.  Thermal  action 
in  young  teeth  too  early  filled  with  metal,  exposures,  etc.  may  produce 
devitalization.  Blows  or  any  sudden  movement  may  result  in  strangu- 
lating the  sources  of  nutrition  at  the  apical  foramen,  or  they  may  cut 
off"  the  delicate  connections  entirely ;  but  in  the  writer's  judgment  the 
effect  is  doubtless  produced  by  strangulation.  The  reason  for  this  con- 
clusion is  found  in  the  fact  that  in  regulating  teeth  where  the  movement 
is  comparatively  regular  and  Mithout  sudden  jar  the  same  result  is  some- 
times apparent.  The  fact  that  this  occurs  at  all  should  relegate  to  the 
obscurity  of  tlie  past  the  practice  of  the  rapid  separation  of  teeth  by  the 
M-edge,  mallet,  screws,  and  other  barbaric  instruments  of  the  earlier 
professional  life,  for  they  certainly  no^v  have  no  place  in  the  proper 
treatment  of  teeth. 

From  whatever  cause  death  occurs,  the  fact  must  be  remembered  that 
the  appearance  of  quiescence  and  comfort  in  the  organ  is  wholly  decep- 
tive, and  that  it  is  ready  to  arouse  to  violent  inflammation  the  connect- 
ing and  surr(tun<ling  tissues  on  apjiarently  very  slight  disturbance.  A  dead 
])ulp  may  remain  for  years — and,  it  may  be,  for  life — very  quiet  if  not 
exposed  by  caries,  but  may  in  a  fe\y  hours  produce  violent  pericementitis 


TREATMENT  OF  GANGRENOUS  PULPS.  907 

if  exposed  to  the  action  of  the  atmosphere.  It  is,  therefore,  oftentimes 
a  question  in  the  diagnosis  of  such  a  tooth  whether  the  great  risk  war- 
rants meddling  with  it  at  all.  The  prognosis  must  take  in  the  })ossible 
results  from  systemic  conditions.  If  these  are  unfavorable,  it  would  be 
much  better  to  allow  the  tooth  to  remain  quiet  rather  than  risk  the 
more  serious  evil  of  acute  pericementitis,  alveolar  abscess,  and  possibly, 
in  a  depraved  habit  of  body,  necrosis.  All  teeth  with  dead  pulps  are 
subject  to  this,  but  those  sealed  in  a  cavity  are  peculiarly  liable  to  take 
on  extreme  manifestations.  The  preliminary  treatment  must  first  be,  if 
devitalization  has  occurred  in  a  tooth  without  pulp-exposure,  to  make  an 
opening  through  the  enamel  and  dentine  into  the  pulp-chamber.  This  is 
best  accomplished  in  the  anterior  teeth  by  the  use  of  the  engine,  to  pene- 
trate the  enamel  at  the  basilar  ridge.  Then  take  up  the  hand-drill,  care 
being  taken  to  point  the  drill  in  the  direction  of  the  long  axis  of  the 
root.  The  entrance  of  the  drill  in  the  pulp-chamber  will  be  manifested 
by  a  sudden  dropping  into  a  cavity.  This  accomplished,  drilling  should 
cease  and  an  application  of  an  antiseptic  be  made — eucalyptus  oil,  per- 
manganate of  potash,  or  iodoform — and  sealed  up,  care  being  taken  to 
leave  the  before-described  vent  through  the  filling ;  the  object  of  this 
care  is  to  avoid  any  undue  irritation  and  to  prevent  the  development 
of  germs.  On  the  second  visit  the  devitalized  pulp  may  be  removed. 
Whether  the  odor  of  decomposition  be  present  or  not,  the  treatment 
should  always  be  based  on  the  supposition  that  putrescence  has  com- 
menced. Ordinarily,  there  is  no  difficulty  in  the  removal  of  the 
decomposed  pulp  :  a  slight  twist  of  the  barbed  broach  will  bring  away 
all  that  may  remain. 

The  odor  of  putrescence  is  ordinarily  present.  The  product  of  this 
decomposition — ])rincipally  sulphuretted  hydrogen — is  undoubtedly  the 
prime  factor  in  pericemental  disturbance,  and  the  importance  of  elim- 
inating this  cannot  be  overestimated.  The  amount  of  pressure  from 
this  rapidly-developing  gas  is  very  great,  and  until  this  is  overcome 
filling  of  the  roots  must  be  regarded  as  a  very  dangerous  operation. 
It  is  difficult,  owing  to  the  contracted  space  in  the  canal,  to  make  any 
application  that  will  reach  all  ])arts  of  the  tooth  and  chemically  change 
the  gaseous  products ;  hence  a  vent  must  be  left,  as  described.  The 
philosophy  of  the  treatment  must  be  based  on  the  conditions  present, 
the  rapid  development  of  bacteria,  the  generation  of  gas,  and  septic 
poison  requiring  an  agent  or  agents  that  will  meet  these  distinct 
conditions.  While  it  is  true  that  an  ordinary  antiseptic,  such  as  car- 
bolic acid,  boracic  acid,  salicylic  acid,  etc.,  may  destroy  the  bacteria 
present  and  prevent  further  decomposition,  it  is  equally  true  that  the 
conditions  are  not  fully  met;  besides,  the  former  in  full  strength  is 
too  irritating,  and  is  not  very  effective  in  reduced  form.  It  does 
not  act  chemically  on  the  products  of  decomposition  before  mentioned, 
nor  do  any  of  the  ordinary  antiseptics.  The  subject  was  first  clearly 
stated  by  Dr.  Litch  of  Philadel])hia,^  and  it  is  to  his  M'ork  that  we 
are  really  indebted  for  the  only  intelligent  answer  to  the  query, 
What  shall  be  done  with  putrescent  pulps?  After  discussing  the 
character  of  antiseptic  agents,  he  says  : 

^  Cof-mos,  February,  1882. 


908        DISEASES  OF  THE  DENTAL  PULP,  AND   TREATMENT. 

"A  careful  discrimination  must  be  made  between  the  powers,  respect- 
ively, of  such  antiseptics  as  carbolic  acid,  creasote,  oil  of  cloves,  oil  of 
thyme,  oil  of  cajeput,  etc.,  and  such  other  antiseptics  as  chlorine,  bro- 
mine, and  iodine,  which,  in  addition  to  their  antizymotic  power,  are 
true  chemical  antagonists  of  those  sulphuretted-hydrogen  compounds 
of  which  putrefactive  gases  are  constituted,  such  gases  being  immedi- 
ately decomposed  by  them,  their  hydrogen  element  going  either  to  the 
chlorine,  bromine,  or  iodine,  to  form,  respectively,  hydrochloric,  hydro- 
bromic,  or  hydriodic  acids,  the  sulphur  being  in  each  case  precipitated. 

"  This  can  readily  be  demonstrated  by  acting  upon  a  small  portion 
of  ferrous  sulphide  with  dilute  sulphuric  acid  and  passing  the  sulphur- 
etted-hydrogen gas  which  will  result  from  the  reaction  through  tincture 
of  iodine.  A  milky  precipitate  of  sulphur  will  at  once  appear,  and  at 
the  same  time  the  characteristic  color  of  the  iodine  will  disappear  in 
consequence  of  the  conversion  of  the  iodine  into  hydriodic  acid,  a 
heavy,  colorless  gas  which  remains  in  solution  in  the  water  present  in 
the  alcohol  of  which  the  tincture  is  made 

"  If  the  sulphuretted  hydrogen  is  passed  through  the  strongest  possi- 
ble solution  of  carbolic  acid,  no  such  precipitation  of  sulphur  occurs; 
no  change  either  in  the  appearance  or  chemical  constitution  of  the  car- 
bolic acid  is  manifest No  matter  how  thoroughly  the  odor  of 

putrefaction  in  a  room  or  in  a  tooth  may  be  masked  or  disguised  by  the 
characteristic  odor  of  carbolic  acid,  creasote,  oil  of  cloves,  or,  indeed, 
any  antiseptic  oil,  the  gases  are  none  the  less  present,  although  their 
odor  is  neutralized ;  the  disinfection  is  only  apparent,  not  real.  The 
further  formation  of  putrefactive  gases  may  be  prevented,  but  the 
decomposition  of  those  already  formed  must  be  accomplished  by  those 
chemical  agents  bromine,  chlorine,  or  iodine." 

It  is  questionable  whether  the  position  of  Prof.  Litch  can  be  sucess- 
fully  refuted.  Practice  demonstrates  fully  the  correctness  of  the  theory, 
and  since  the  adoption  of  this  mode  of  treatment  the  writer  has  had 
more  satisfaction  and  far  less  anxiety  in  the  management  of  these  cases 
than  at  any  former  period.  The  mode  he  adopts  is  to  syringe  out  the 
canal  thoroughly  with  warm  water  to  which  a  small  amount  of  listerine 
has  been  added.  Then  take  about  the  twentieth  part  of  a  grain  of  iodo- 
form^ and  moisten  it  with  a  20-per-cent.  solution  of  carbolic  acid;  carry 
tills  on  a  few  fibres  of  cotton  to  the  extremity  of  the  canal  and  then  seal 
up  the  crown  with  gutta-percha,  leaving  the  vent  through  the  filling. 
It  may  require  repeated  applications  to  remove  the  odor  of  iiutrefaction. 
The  same  effect  has  been  said  to  be  produced  rapidly  by  the  perman- 
ganate of  potash,  but  it  is  questionable  whether  its  low  germ-destroying 
power  makes  it  as  valuable  as  some  other  agents.  Dr.  Miller^  has  very 
satisfactorily  demonstrated  the  comparative  value  of  various  antiseptics, 
the  bichloride  of  mercury  standing  at  the  head  of  the  list  as  a  germ- 
destroyer.  Wliile  this  is  true  of  a  very  minute  quantity  of  this  agent, 
it  may  be  equally  true  of  a  larger  quantity  of  a  weaker  one.     But  in- 

'  The  writer  does  not  wish  to  be  understood  as  asserting  that  iodoform  stands  in  the 
same  chemical  relation  to  II.^S  as  iodine,  but  that  in  its  clinical  presentations  it  seems 
to  he  e(|ually  as  etlectual. 

'^Denial  Practitioner,  June,  1884. 


TREATMENT  OF  GANGRENOUS  PULPS.  909 

crease  in  quantity  is  not  always  possible,  as  a  very  strong  solution  of 
j^ermanganate  of  potash  would  probably  result  in  discoloration  of  the 
tooth.  Other  antiseptics  can,  however,  be  used  in  large  quantities  with- 
out risk,  and  with  results  equally  good  as  with  the  bichloride  of  mer- 
cury. In  illustration  of  this,  sulphate  of  quinia  is  one  of  the  very  best 
germicides  in  and  around  inflamed  gums.  The  writer  has  had  better 
results  from  this  than  from  any  other  remedy.  The  theory  of  its  action 
is  that,  in  addition  to  its  germ-destroying  power,  it  inhibits  the  migra- 
tory movements  of  the  white  blood-corpuscle,  and  thus  retards  inflam- 
matory processes. 

The  removal  of  all  odor  from  the  pulp-canals  is  supposed  to  be  the 
guide  to  determine  the  time  for  filling  them.  It  must  be  borne  in  mind 
that  the  pulp  practically  extends  throughout  the  dentine,  and  that  there 
must  be  a  vast  amount  of  microscopic  tissue  necessarily  left  in  the 
canaliculi  for  future  decomposition  or  discoloration  ;  this  is  undoubt- 
edly the  cause  of  the  change  of  color,  more  or  less  pronounced,  in  all 
these  teeth.  Care  should  be  taken  to  have  the  antiseptic  fluids  pass 
well  into  the  tubes,  and  to  accomplish  this  by  imbibition  time  must  be 
given.  A  tooth  should,  therefore,  be  kept  under  an  antiseptic  for  sev- 
eral weeks  before  filling.^ 

The  next  consideration  is  as  to  the  filling  material  to  use  for  this  pur- 
pose. This  is  of  far  more  importance  than  is  generally  conceded.  The  old 
plan  was  to  fill  always  with  metal,  gold,  or  tin,  and  the  results,  while 
excellent,  were  not  equal  to  those  effected  by  other  modes,  for  reasons 
now  well  understood.  Wood,  and  even  cotton  saturated  with  carbolic 
acid,  have  been  used.  Gutta-percha,  the  oxyphosphates,  and  the  oxy- 
chlorides  have  each  found  earnest  advocates. 

The  necessity  of  having  a  thoroughly  compact  and  solid  filling  would 
seem  to  require  no  argument,  yet  there  are  many  who  appear  to  think 
facility  of  removal  a  prime  requisite.  The  writer's  judgment,  based  on 
a  long  experience  in  filling  canals,  is  that  no  canal  can  with  safety  be 
left  loosely  filled  even  with  the  best  germicide  present.  That  a  gold 
filling  will  give  better  results,  provided  it  is  packed  solidly,  than  a 
cotton,  felt,  or  any  other  loose  substance,  has  been  demonstrated  too 
often  to  be  now  successfully  controverted.  It  is  certainly  settled  that 
a  canal  must  be  impervious  to  fluids  and  the  entrance  of  atmospheric 
air  made  impossible.  If  a  material  that  combines  solidity  with  anti- 
septic properties  can  be  used,  that  should  take  precedence.  Of  the  jilas- 
tics,  the  oxychlorides  alone  meet  this  requirement ;  the  peculiar  property 
of  these  and  their  deep-penetrating  power  should  bring  them  into  more 
general  use.  The  writer's  attention  was  early  called  to  this  by  the 
remarkable  results  attained  by  the  use  of  oxychloride  in  the  treatment 
of  alveolar  abscess,  in  w'hich  teeth  have  repeatedly  been  rendered  com- 
fortable, loose  teeth  tightened,  the  production  of  pus  stopped,  and  the 
fistula  closed  by  simply  filling  the  canal  with  oxychloride  of  zinc.  The 
constant  repetition  of  these  results  led  to  the  abandonment  of  gold  or 
tin  and  the  substitution  of  this  material,  and  years  of  practice  have 

'  Dr.  Kirk  (Cosmon)  suggests  the  use  of  sodium  carbonate  in  pnlps  of  this  eliaracter. 
He  dries  out  the  cavity  and  introduces  a  small  particle  of  this  agent,  leaving  it  there  a 
short  time.     It  can  be  used  in  crvstals  or  in  solution. 


910        DISEASES  OF  THE  DENTAL  PULP,   AND   TREATMENT. 

served  only  to  confirm  this  judgment.  Chronic  pericementitis,  or  even 
chronic  alveolar  abscess,  is  oftentimes  best  treated  by  simply  filling  the 
canals. 

The  mode  of  insertion  is  quite  a  simple  one.  A  few  fibres  of  cotton 
dipped  in  a  thin  batter  of  the  oxychloride  are  passed  into  and  packed 
solidlv  in  the  canal  or  canals.  This  becomes  a  solid  mass  in  a  short 
time,  and  if  properly  placed  will  be  impenetrable  to  any  of  the  fluids 
permeating  the  tooth.  A  method  proposed  by  Dr.  Hullihen  of  Wheel- 
ing, Va.,  in  these  cases  was  to  leave  the  canal  unfilled  and  make  a  vent 
at°the  free  margin  of  the  gum  by  drilling  a  hole  through  the  root  to  the 
canal.  This  makes  it  a  drainage-conduit,  and,  while  the  tooth  may  be 
comparatively  comfortable,  it  is  always  malodorous  and  liable  at  any 
time  to  take  on  more  complicated  pathological  conditions.  This  opera- 
tion should  be  used  only  as  a  means  of  temporary  relief.  A  mode  of 
filling  roots  adopted  by  many  good  operators  is  to  pass  cedar  saturated 
with  carbolic  acid  into  the  canal ;  the  swelling  of  the  wood  is  supposed 
to  perfectly  fill  the  canal.  Theoretically,  this  seems  a  very  faulty  ope- 
ration. There  is  no  certainty  as  to  the  length  of  time  carbolic  acid  will 
retain  its  power,  and  wood  is  always  a  good  absorbent.  Reference  need 
only  be  made  to  the  condition  of  old  wooden  pivots  and  the  adjacent 
tissue  to  furnish  argument  against  the  practice. 

The  dry  gangrene — so  called  in  contradistinction  to  the  previously- 
described  moist  gangrene — is  not  of  much  pathological  significance. 
The  pulp  is  shrivelled  and  the  canal  is  entirely  free  from  the  results  of 
decomposition.  The  tooth  retains  its  color.  The  reason  for  this  state 
of  the  pulp  is  not  very  clear.  It,  however,  according  to  the  observation 
of  the  writer,  occurs  principally  in  very  dense  teeth,  especially  in  the 
teeth  of  old  age.  This  leads  directly  to  the  supposition  that  there  has 
been  a  gradual  filling  up  of  the  tubuli  with  secondary  dentine,  preventing 
the  free  circulation  of  fluids,  if  not  stopping  them  entirely  ;  this  is  evi- 
dently the  case  in  senile  dentine.  AVhile  the  possibility  of  this  process 
is  doubted  by  Wedl,  who  regards  the  translucency  described  by  Tomes 
as  dependent  on  the  continuation  of  the  "  process  of  the  dentine  cells 
existing  in  the  translucent  portions  of  senile  dentine,  and  that,  as  they 
still  retain  the  property  of  imbibition,  it  may  be  assumed — with  a  certain 
degree  of  plausibility,  at  least — that  these  processes  as  well  as  other  tis- 
sues in  the  decay  of  advanced  age  have  lost  more  or  less  their  distensi- 
bility,  that  their  central  vitreous  substance  has  disappeared,  and  that, 
together  with  the  investing  walls  of  the  dentinal  tubules,  they  have 
become  closed  in  such  a  manner  that  the  entrance  of  atmospheric  air 
is  no  longer  possible."  The  writer's  observations  on  senile  teeth,  and 
also  on  teeth  lost  at  an  early  period  of  life  through  extreme  density, 
are  fully  in  accord  with  the  conclusion  of  the  elder  Tomes.  If  these 
conclusions  be  accepted,  the  dryness  observable  in  senile  dentine,  result- 
ing in  dry  gangrene  of  the  pulp,  can  be  readily  understood  and  the 
latter  condition  accounted  for. 

Teeth  with  mummified  pulps  (dry  gangrene)  require  no  attention  on 
the  part  of  the  operator  further  than  to  remove  the  remains  and  fill. 
They  never,  so  far  as  observed,  are  a  source  of  irritation,  and  it  is  rare 
that  thev  come  into  the  hands  of  the  dentist  for  treatment. 


NODULAR  DENTINE.  911 

Nodular  Dentine. 

Under  this  name  are  classified  the  secondary  deposits  found  in  pulps. 
They  may  be  purely  physiological  in  character,  and  are  not  necessarily 
pathological.  Indeed,  it  is  difficult  to  draw  the  dividing-line  between 
these  two  conditions,  for  the  one  may  run  into  the  other  through  the 
ordinary  processes  of  development. 

The  formation  of  secondary  tissue  is  dependent  on  so  many  and  such 
diverse  conditions  that  it  is  impossible  to  class  it  as  belonging  to  any 
particular  period  or  state.  It  may  be  found  at  all  ages,  in  all  teeth, 
and  it  has  been  observed  even  in  deciduous  teeth.  There  is  one  law, 
however,  that  seems  universal  in  its  application,  and  that  is  that  the 
structure  must  average  a  superior  grade.  In  other  words,  teeth  of 
strong,  dense  character,  yellowish  color,  are  peculiarly  liable  not  only 
to  new  formations,  but  to  have  this  extra  development  assume  the  nod- 
ular or  granulated  form. 

The  relations  sustained  by  the  pulp  to  dentine  and  the  part  the 
former  takes  in  the  development  of  the  latter  are  better  understood 
to-day  than  at  any  former  period,  but  no  satisfactory  explanation  has  been 
attempted  throwing  light  on  the  peculiar  form  dentine  assumes  or  show- 
ing why  at  a  certain  period  in  development  it  changes  its  character.  It 
is,  however,  well  known  that  the  new  ibrmation  differs  from  the  normal, 
or  regular  dentine,  in  the  irregularity  of  the  tubuli,  there  being  a  dis- 
tinctive line  of  demarcation  between  the  new  and  the  old.  All  that  is 
really  understood  in  regard  to  it  is  that  up  to  an  uncertain  period  nor- 
mal tissue  is  developed,  and  after  that  the  formation  assumes  the  cha- 
racter of  secondary,  or  osteo,  dentine. 

Before  considering  the  character  of  these  formations  it  may  be  well  to 
examine  into  the  probable  causes  that  lead  to  their  origin.  They  may 
be  classified  under  two  heads : 

1st.  Increase  of  density. 

2d.  Irritation. 

The  increase  of  density  may  occur  at  any  age,  and  the  familiar  exam- 
ple of  senile  dentine,  with  its  superabundance  of  secondary  tissue,  is  a 
common  presentation.  Between  these  two  extremes  may  be  found  all 
degrees  of  formation,  ending  frequently  in  loss  of  the  teeth,  they  being 
thrown  out  as  foreign  bodies.  Increase  of  density  necessarily  means  an 
increased  deposition  of  the  inorganic  material  in  the  organized  body. 
If  it  be  accepted  that  the  pulp  is  capable  of  forming  dentine,  either  nor- 
mal or  abnormal  in  character,  at  all  periods — and  this  is  not  disj)uted — 
it  follows  as  a  natural  sequence  that  the  cellular  formative  elements 
must  possess  unlimited  power  of  development  which  is  not  confined  to 
the  peripheral  cell-layer,  but  is  equally  distributed  throughout  the  pulp : 
that  every  portion  must  be  so  endowed  and  be  equally  amenable  to  the 
universal  law  of  formation.  Secondary  dentine  is,  therefore,  not  con- 
fined to  the  pulp  proper  in  the  form  of  minute  grains  or  larger  nodular 
calcifications,  but  is  manifested  in  the  translucent  dentine  of  Tomes, 
M'hich  is  but  another  state  of  the  same  development.  Wedl  does  not 
regard  this  as  proved,  as  by  the  use  of  "  heated  dilute  hydrochloric 
acid  "  he  was  able  to  demonstrate  that  the  "  processes  of  the  dentinal 


912        DISEASES  OF  THE  DENTAL  PULP,  AND  TREATMENT. 

cells "  were  brought  into  view.  "  In  these  experiments  no  essential 
dilferences  could  be  discovered  between  the  translucent  and  less  diapha- 
nous portions  of  the  dentine."  ^  These  experiments  would  seem  con- 
clusive, especially  those  subsequently  made  to  demonstrate  the  power  of 
imbibition  remaining  in  the  fibrils  or  odontoblastic  prolongations  ;  but 
the  means  resorted  to  seem  fatal  to  the  conclusions.  Secondary  dentine 
is  "  not  as  dense  as  normal  dentine  and  has  less  carbonate  and  more 
])hosphate  of  lime  "  (Sehlenker),  and  consequently  would  be  less  able  to 
resist  the  action  of  powerful  reagents.  The  result  would  necessarily  be 
a  reopening  of  the  canals  in  the  dried  specimens,  and  because  coloring- 
matter  could  be  injected  into  the  tubuli  it  does  not  necessarily  follow 
that  the  tibrilltie,  while  retaining  the  form,  also  retained  normal  vital 
powers.  The  inference  drawn  by  Wedl  does  not  seem  justified  by 
the  results.  The  importance  of  determining  this  must  be  apparent 
when  it  is  considered  that  if  the  transparent  zone  is  not  recognized  as 
a  consolidation  into  secondary  dentine  it  will  be  difficult  to  understand 
the  law  of  its  formation  anywhere,  and  the  nodular  deposits  must 
remain  an  enigma.  Experiments  with  reagents  are  not  always  satis- 
factory, for  the  reasons  stated,  and  the  matter  must  be  determined  prin- 
cipally by  inference,  by  analogy,  and  by  results.  The  secondary  forma- 
tions in  the  tubuli  occur  in  exceptionally  dense  teeth ;  the  color  simulates 
that  of  normal  tissue,  and  its  power  to  resist  the  encroachment  of  caries 
proves  its  comparative  density.  The  well-known  fact  is  that  so-called 
eburnated  dentine  is  but  a  form  of  arrested  decay,  and  that  in  all  very 
dense  teeth  caries  progresses  with  extreme  slowness — and  in  these  the 
transparent  zone  is  marked — indeed,  is  never  seen  in  soft-structured 
teeth.  In  exceptional  cases  of  extreme  density  there  appears  to  be  a 
total  cessation  of  nutrition ;  the  power  of  imbibition  by  natural  pro- 
cesses is  in  a  great  measure  lost  and  the  connection  with  the  perice- 
mentum broken  up.  This  is  remarkably  illustrated  in  the  loss  of  single 
and  entire  sets  of  otherwise  perfectly-formed  teeth,  and  that  through  no 
pathological  changes,  as  in  pyrorrhoea  alveolaris.  A  patient  of  the 
writer,  aged  thirty-five,  with  a  remarkably  beautiful  and  dense  set  of 
teeth,  gradually  lost  them  all,  until,  edentulous,  he  w'as  forced  to  resort 
to  artificial  substitutes.  Microscopic  examination  of  thin  sections  by 
high  powers  failed  to  show  the  slightest  trace  of  tubular  formation  ex- 
cept in  the  inner  third  nearest  the  original  pulp-canal.  The  whole  tissue 
was  diaphanous  and  apparently  homogeneous.  It  was  clearly  a  case  of  non- 
nutrition.  Dr.  Kirk^  in  a  paper  on  the  care  of  the  children  of  the  Insti- 
tution of  the  Deaf  and  Dumb  of  Philadelphia  illustrates  the  possibility 
of  increasing  the  density  as  well  as  producing  nodular  deposits  at  a  very 
early  age.  Pie  says:  "The  majority  of  pupils  are  admitted  between  the 
ages  of  ten  and  twelve  years.  After  a  year's  residence  in  the  institution 
— fluring  which  time  they  are  given  excellent  care  in  all  that  relates  to 
their  physical  welfare — a  marked  improvement  will  be  observed  in  the 
character  of  their  teeth  :  they  will  be  found  exceedingly  hard  and  dense, 

making  the  wear  and  tear  on  cutting  instruments  very  great But 

the  most  conclusive  evidence  which  I  have  met  with  of  the  value  of  the 

'  Wedl,  Pdlholofj,/  of  the  Teeth. 

^  "Kelation  of  Food  to  Teeth,"  Denial  Office  and  Laboraiory. 


NODULAR  DENTINE.  913 

diet-table,  so  far  as  the  nutrition  of  their  teeth  is  concerned,  is  the  un- 
usual number  of  cases  of  arrested  caries  and  the  formation  of  so-called 

secondary  dentine As  showing  still  further  the  abundance  of 

bone-forming  material  with  which  the  blood  is  supplied,  I  have  re- 
moved in  two  cases  large  pulp-nodules  from  the  sixth-year  molars  of 
children  not  over  eleven  years  of  age." 

Without  extending  the  argument  farther,  it  may  be  assumed  that  the 
facts  warrant  the  opinion  that  the  new  formation  in  the  tubuli  is  in 
direct  ratio  to  the  density. 

The  eifect  of  irritation  is  well  known  to  be  a  cause  of  new  formations. 
The  increased  development  of  the  cementum  at  the  apex  of  roots — 
familiarly  known  as  exostosis — is  produced  by  a  slight  irritation,  as  the 
wearing  of  a  plate  over  a  root,  the  jar  of  clasps  attached  to  a  plate,  the 
malocclusion  of  teeth,  etc.,  etc.  On  the  other  hand,  an  excessive  irrita- 
tion produces  absorption  or  destructive  pathological  conditions.  Rea- 
soning from  this  well-understood  fact,  it  would  be  expected  that  the  law 
of  hypertrophy,  as  applied  to  bone,  would  give  equal  results  with  den- 
tine, so  nearly  allied  to  it  in  character.  The  very  familiar  example  of 
the  wearing  away  of  the  anterior  teeth  furnishes  us  with  an  answer  to 
this  proposition.  New  formations  proceed  equally  in  proportion  to 
wear,  provided  that  wear  is  not  too  rapid.  If  the  process  is  very  slow, 
secondary  dentine  will  develop  gradually  until  the  entire  coronal  pulp 
is  obliterated  and  the  tooth  worn  down  to  the  gum-border.  On  the 
other  hand,  if  too  rapid,  the  pulp  is  quickly  exposed.  This  is  exactly 
a  repetition  of  the  before-mentioned  result  in  slow  caries.  The  progress 
of  the  disease  produces  an  amount  of  irritation  to  develop  new  forma- 
tion. In  medium-  or  soft-structured  teeth  this  is  not  possible ;  hence 
rapid  destruction. 

AVhen  we  extend  this  familiar  process  of  formation  and  destruction  to 
the  growth  of  new  formations  of  the  pulp,  we  are  led  at  once  to  the 
conclusion  that  irritation  is  the  principal — though  possibly  not  the  only 
— cause  of  secondary  deposits.  It  is  very  probable  that  the  process  of 
mastication  has  very  much  to  do  with  nutrition  and  increased  inorganic 
deposits.  It  has  long  been  observed  that  those  teeth  in  constant  use  are 
more  perfectly  formed  and  resist  caries  better  than  (hose  rarely  brought 
under  the  forces  of  mastication.  This  can  be  accounted  for  only  by  the 
constant  jar  and  slight  irritation  producing  the  before-mentioned  result. 
It  has  yet  to  be  demonstrated  by  actual  observation  whether  these  teeth 
are  more  liable  to  nodular  calcifications  than  others,  but  theoretically  this 
should  be  the  case. 

The  effect  of  caries  in  producing  new  formations  in  direct  line  with 
the  disease  is  beautifully  shown  in  an  illustration  from  Schlenker.^  In 
this  case  the  new  formation  is  clearly  the  result  of  irritation  carried 
through  the  tissue  and  proceeding  in  proportion  to  the  caries.  The 
same  result  is  seen  in  Fig.  482,  from  the  same  author,  in  which  the  new 
formation  extends  over  a  still  greater  surface.  By  the  wear  from  a 
clasp,  a  metal  filling,  especially  gold,  may  produce  a  similar  result  by 
the  constant,  though  slight,  irritation  through  changes  of  temperature. 
A  similar  effect  is  usually  expected  from  capping  pulps ;  but  this  expec- 

'  Untersuchungen  iiber  die  Verknocherung  der  Zahnnerven.  Vierteljahrsschrift.  f.  Z. 
Vol.  I.— 68 


914        DISEASES  OF  THE  DENTAL  PULP,  AND   TREATMENT. 


tation  is  rarely  realized,  as  here  the  irritation  is  excessive  and  becomes 
a  destructive  force.     In  absolute  inflammation  of  the  pulp  new  fornia- 


FiG.  481. 


o,  caries;  h,  adhering  dentine  forma- 
tion; c,  a  free  nodule  with  the  con- 
nection dissolved. 


Longitudinal  Section  through  Ca- 
nine. Secondary  dentine  the 
result  of  a  clasp  (Schlenker). 


Fig.  483. 


tion  is  impossible.  Schlenker  says  of  inflammation  of  the  periosteum 
followed  by  abscess  that  "  if  in  such  teeth  secondary  dentine  is  found  it 
must  not  be  accepted  as  positive  that  this  is  the  result  of  inflammation 
of  the  pulp.  If  the  pulp  is  inflamed,  all  new  for- 
mations cease  in  hard  tooth-structures." 

The  same  author  divides  the  new  formations  into 
six  distinctive  sections  :  1.  Enameloid  ;  2.  Enamel- 
dentoid  ;  3.  Dentoid  ;  4.  Dentine-osteoid  ;  5.  Oste- 
oid ;  6.  Calcoid.  In  regard  to  the  former,  the 
enamel  nodule,  he  says  :  "  At  the  yearly  meeting 
of  the  Central  Society  of  German  Dentists  held  at 
Freiburg,  1875,  I  exhibited  two  free  enamel  nod- 
ules found  in  the  pulp-tissue,  since  which  time  I 
have  added  three  others  free  and  two  specimens 
of  adhering  enamel  formations." 

From  the  enamel-dentoid,  or  combination  of 
enamel  and  dentine,  he  has  two  examples.  In  the 
dentine-osteoid  the  combination  of  cement  and  den- 
tine takes  place.  The  osteoid,  as  its  name  implies, 
consists  wholly  of  cement,  and  the  calcoid  the  cal- 
cification, in  the  connective  tissue  of  the  pulp,  and 
felt  as  grains  of  sand. 

The  calcification  of  the  tissue  of  the  pulp  into 
nodules  is  finely  represented  by  an  illustration  from 
the  same  author.  The  symptoms  of  calcification 
are  not  sufficiently  marked  to  render  the  diagnosis  an  easy  one  ;  indeed, 
the  de(Msion  must  rest  largely  on  the  character  of  the  teeth  and  the 
exclusion  of  other  sources  for  the  neuralgic  pains  present.     The  usual 


Section  ilii..ii;;ii  I  aiiine, 
with  the  I'ulp:  n.  entire 
pulp;  b,  partial  calcifica- 
tion; c,  part  of  the  pulp 
without  nodules  (Schlen- 
ker). 


POLYPUS  OF  THE  PULP.  915 

mode  of  diagnosing  pericementitis  fails  here,  for,  as  before  stated,  vio- 
lent inflammation  renders  new  formations  an  impossibility.  The  pain 
is  in  paroxysms,  worse  during  the  night  and  accompanied  with  a  boring 
sensation. 

Ordinarily,  the  new  development  is  not  a  cause  of  neuralgia ;  indeed, 
it  may  be  considered  quite  exceptional  that  this  occurs,  for  in  some  one 
of  its  forms  secondary  tissue  may  be  said  to  exist  in  every  mature  tooth. 
When,  however,  it  assumes  the  granulated  form,  producing  unequal  pres- 
sure on  the  sensory  nerves  of  the  pulp,  the  result  is  pain — oftentimes  of 
the  most  aggravated  character.  This  may  be  confined  to  one  tooth,  but 
frequently  will  be  repeated  in  one  tooth  after  another  until  the  entire 
denture  is  involved.  Dr.  Garretson  mentions  a  case  of  this  character 
where  each  tooth  in  turn  was  extracted,  and  all  presented  nodular  calcifi- 
cation.    Schlenker  also  gives  a  large  number  of  cases. 

The  TREATMENT  must  be  either  to  destroy  the  pulp  or  to  extract  the 
tooth  ;  in  most  cases  the  former  course  will  give  relief.  The  suspected 
tooth  must  be  carefully  drilled  through  to  the  pulp  and  the  usual  appli- 
cation of  arsenic  made.  If  devitalization  fails,  nothing  remains  but  to 
extract. .  Efforts  have  been  made  to  reimplant  these  teeth,  after  remov- 
ing all  calcific  deposits,  and  with  some  degree  of  success. 

Polypus  of  the  Pulp. 

In  teeth  much  broken  down  by  caries  there  is  necessarily  a  constant 
irritation  of  the  exposed  pulp.  This  does  not  always  result  in  a  slow 
destruction  of  the  organ,  but  eventuates  in  a  hypertrophied  condition 
that  in  time  fills  up  the  cavity  of  decay.  In  the  experience  of  the 
writer  these  polypi  are  more  frequently  found  in  the  inferior  molar  teeth 
where  the  croMu  has  been  hollowed  out  to  a  thin  external  wall.  The 
increased  development  may  be  of  small  size  or  it  may  fill  the  entire 
cavity.  Its  character  is  readily  determined  by  pressing  it  to  one  side, 
when  it  will  be  found  to  be  a  bulbous  formation  attached  by  a  con- 
stricted neck  to  the  coronal  pulp.  This  will  distinguish  it  from  an 
epulis,  M'hich  is  attached  to  the  alveolar  walls.  It  is  not  ordinarily 
very  sensitive.  It  has  a  dark-red  color  and  is  of  a  "  spongy  or 
fleshy  consistence."  "  It  contains  an  abundance  of  roundish  and 
spindle-shaped  cells,  the  bodies  of  the  cells  varying  slightly  in 
extent,  which,  together  with  a  small  amount  of  fibrous  intercellular 
substance,  comprise  the  principal  portion  of  the  tumor.  The  groups 
of  cells  are  in  long  rows  and  have  a  radiated  arrangement.  The  cells, 
which  are  provided  with  processes,  unite  here  and  there  to  form  a  net- 
work ;  rows  of  spindle-shaped  cells  also  are  met  with ;  the  blood-vessels 
pursue  a  tortuous  course  from  the  interior  toward  the  periphery,  are 
numerous,  comparatively  large;  and  invested  with  thick  fibrous  sheaths. 
The  type  presented  by  the  capillary  ramifications  is  different  from  that 
found  in  the  pulp.     Nerves  or  the  remains  of  the  parenchyma  of  the 

pul]->  are  not  to  be  seen The  parenchymatous  connective  tissue 

is  the  seat  of  the  proliferation  described  as  sarcoma  of  the  pulp,  in  AAhich 
the  parenchyma  gradually  is  destroyed,  as  is  indicated  by  the  absence  of 
nerves  and  the  altered  character  of  the  blood-vessels.     As  the  sarcoma 


916        DISEASES  OF  THE  DENTAL  PULP,  AND  TREATMENT. 

is  located  upon  the  outside  of  the  remains  of  the  pulp,  it  serves  in  a 
measure  to  protect  the  latter"  (Wedl). 

The  tumor  may  be  purulent  in  character,  though  the  amount  of  pus 
is  limited.  A  number  of  such  cases  in  the  experience  of  the  writer  gave 
no  evidence  of  pus-formation. 

This  proliferation  of  the  pulp  is  principally  confined  to  comparatively 
young  teeth  and  teeth  imperfectly  calcified.  They  bleed  readily  at  the 
slightest  touch,  but  the  ordinary  result  of  inflammation  of  the  pulp  is 
not  present.  They  do  not  end  in  pulp-devitalization,  pericementitis,  alve- 
olar abscess,  nor  are  they  usually  very  uncomfortable.  They  seem  to 
be,  as  Wedl  expresses  it,  secondary  formations,  and  furnish  a  protection 
to  the  central  organ. 

In  cases  of  fracture  where  the  pulp  has  been  suddenly  and  violently 
irritated  there  may  be  an  enlargement  of  the  pulp  of  a  somewhat  differ- 
ent character.  This  will  be  extremely  sensitive.  In  other  respects  it  is 
similar  to  the  ordinary  polypus.  "  In  microscopic  structure  this  sprout- 
ing of  the  pulp  differs  little  from  the  insensitive  polypus,  but  its  vitality 
implies  a  more  abundant  nerve-supply  "  (Salter). 

Treatment. — The  difficulty  of  giving  any  treatment  to  cases  of 
fungous  growth  has  long  been  understood.  The  polypus  can  readily 
be  cut  away,  but  it  will  return,  and  for  the  reason  laid  down ;  under 
the  destruction  of  the  pulp  by  arsenic  it  resists  that  agent,  and  henge 
success  has  not  warranted  prolonged  effort  in  this  direction.  Coleman  ^ 
gives  a  mode  of  treatment  that  in  his  hands  has  been  satisfactory.  He 
says  :  "  We  first  dose  the  growth  with  carbolic  acid,  to  deaden  its  sensi- 
tiveness, and  then  with  a  scythe-shaped  lancet  cut  away  as  much  as  pos- 
sible. After  the  bleeding  has  ceased  we  carry  out  the  nitric-acid  process." 
This  was  described  at  length  in  considering  the  subject  of  capping.  It 
consists  of  applying  the  strongest  nitric  acid  on  a  disk  of  cardboard  to 
the  pulp  and  retaining  it  there  for  about  thirty  seconds.  It  is  then 
removed  and  the  pulp  capped. 

Dr.  B.  G.  Msercklein  recommends  the  continued  use  of  iodine  upon 
and  around  the  fungous  growth.  He  says  :  "  After  removing  all  for- 
eign substances,  dry  the  cavity  as  carefully  and  thoroughly  as  possible, 
and  then  ajiply  the  tincture  of  iodine  with  a  pledget  of  absorbent  cotton 
or  bibulous  paper  until  the  entire  growth  has  been  covered  with  the 
iodine  ;  after  which,  seal  the  cavity  in  the  usual  manner.  This  should 
be  repeated  every  twenty-four  hours  until  it  has  been  entirely  destroyed. 
If  any  portion  of  the  pulp  in  tlie  canals  resists  this  treatment,  it  should 
after  the  expiration  often  days  be  devitalized  by  arsenic  and  the  root  or 
roots  filled  in  the  usual  maimer.  For  this  purpose  I  prefer  the  oxy- 
chloride  of  zinc  to  anv  other  material.  If  the  fungous  o-rowth  should 
nil  the  entire  cavity,  as  is  sometimes  the  case,  it  is  necessary  to  modify 
the  first  part  of  the  treatment.  In  such  cases  proceed  as  follows  :  Take 
small  pledgets  of  bibulous  paper  or  absorbent  cotton  saturated  with  tinc- 
ture of  iodine  and  place  them  between  the  fungoid  and  the  walls  of  the  cav- 
ity until  as  much  pressure  has  been  made  as  is  consistent  with  the  comfort 
of  the  patient,  but  in  no  case  should  it  be  carried  to  the  extent  of  giving 
pain.     This  dressing  is  to  be  repeated  daily  until  sufficient  room  has 

'  Dental  Surgery  and  Pathology. 


POLYPUS  OF  THE  PULP.  •917 

been  obtained  to  proceed  as  in  the  first  case.  Some  of  the  last  class 
of  fungoid  growths  are  very  persistent  in  resisting  treatment,  but  I  have 
never  seen  a  case  that  did  not  yield  where  treatment  was  kept  up  for 
any  length  of  time." 

The  writer's  experience  in  various  modes  of  treatment  does  not  justify 
a  hopeful  prognosis  in  these  cases,  and  the  final  result  has  been  a  resort 
to  extraction  as  the  only  effectual  remedy. 


DISEASES  OF  THE  PERIDENTAL  MEM- 
BRANE. 

By  G.  V.  BLACK,  M.D.,  D.D.S. 


The  peridental  membrane  covers  the  root  of  the  tooth  and  serves  to 
unite  it  with  its  alveolus.  In  its  structure  it  is  very  diiferent  from  a 
periosteum,  and  its  functions  are  diiferent.  The  connection  of  the  tooth 
with  the  wall  of  the  alveolus  is  more  that  of  an  immovable  joint,  and 
yet  a  joint  that  permits  a  certain  passive  motion  by  which  the  tooth  is 
cushioned,  so  to  speak,  against  the  hardships  of  severe  blows  and  con- 
cussions that  it  is  liable  to  receive  in  the  performance  of  its  peculiar 
functions  of  tearing  and  grinding  food.  This  joint  has,  however,  none 
of  the  elements  of  tjie  joints  that  are  movable  by  the  muscles.  There 
is  no  cartilage  and  none  of  the  other  elements  of  the  movable  joints 
intervening  between  the  root  of  the  tooth  and  the  bony  walls  of  its 
alveolus  :  the  joint  is  effected  by  the  interposition  of  fibrous  tissue,  with 
a  sparse  intermixture  of  cellular  elements.  In  the  formation  of  this 
joint  the  fibrous  tissue  is  disposed  in  a  definite  form  relative  to  the  root 
of  the  tooth  and  the  alveolar  process.  This  is  found  to  be,  for  the 
grejiter  part  of  the  root,  in  the  form  of  a  set  of  fibres  running  down- 
ward (toward  the  crown  of  the  tooth)  and  outward  (toward  the  alveolus), 
connecting  with  the  alveolus.^  These  fibres  serve  to  swing  the  tooth  in 
such  a  way  that,  while  it  is  permitted  a  very  slight  motion  in  its  socket 
in  any  direction  in  response  to  a  strain  that  may  be  brought  against  it, 
its  position  is  regained  at  once  when  the  strain  is  removed.  This  par- 
ticular disposition  of  the  fibres  is  found  all  over  the  body  of  the  root 
of  the  tooth,  but  on  the  apex  of  the  root  and  near  the  neck  of  the  tooth 
the  disposition  of  the  fibres  is  diiferent.  At  the  apex  the  space  between 
the  end  of  the  root  and  the  alveolar  wall  is  a  little  greater  than  else- 
where. This  I  shall  call  the  apical  space  (Fig.  484).  In  this  space  the 
fibres  radiate  from  the  apex  of  the  root  to  the  alveolar  wall  in  various 
directions  without  much  regularity  ;  yet  it  can  generally  be  seen  that 
tiiere  is  a  disposition  to  radiate  fanlike  from  the  apex  of  the  root  to  the 
alveolus.  Toward  the  rim  of  the  alveolus  the  downward  trend  of  the 
fibres  is  rapidly  lost,  and  as  the  rim  of  the  alveolus  is  passed  this  trend 
is  reversed.     In  this  way  the  fibres  are  gathered,  as  they  pass  from  the 

^  In  tlie  descriptions  given  thronghont  this  article  I  sliall  regard  the  tooth  as  a  cone, 
with  the  crown  as  the  base  and  the  end  of  tlie  root  as  tlie  apex.    Therefore,  toward  the 
crown,  or  hase,  is  downward,  and  toward  the  apex  of  the  root  is  upward,  no  matter 
whether  the  tooth  be  in  tlie  upper  or  lower  jaw. 
918 


BLOOD -SUPPLY. 


919 


Fig.  484. 


tooth,  into  rather  a  thick  mass  just  over  the  rim  of  the  alveolus,  where 
they  are  continuous  with,  or  merge  into,  the  periosteum,  which  covers 
the  outer  surface  of  the  alveolar  process.  This  forms  what  has  been 
termed  the  dental  ligament.  I  will  describe  the  gingivae  in  connection 
with  the  diseases  which  have  their  beginnings  in  them. 

The  blood-supply  of  the  pulp  of  the  tooth  and  its  peridental  mem- 
brane is  admitted  to  the  api- 
cal space,  usually,  by  a  single 
arterial  twig  for  each  root. 
A¥hen  within  this  space,  it 
breaks  up  into  a  number  of 
branches,  and  one  of  these 
enters  the  apical  foramen, 
while  the  others  pass  down 
toward  the  crown  of  the 
tooth  within  the  structure 
of  the  peridental  membrane. 
These  are  generally  found 
about  midway  between  the 
root  of  the  tooth  and  the 
alveolar  wall,  and  in  unin- 
jected  sections  cut  lengthwise 
will  often  give  the  impression 
that  the  membrane  is  com- 
posed of  two  layers,  as  we 
find  it  described  in  some  of 
the  older  works.  As  these 
arteries  proceed  down  the 
sides  of  the  root  they  send 
out  branches  into  the  walls 
of  the  alveolus  that  anasto- 
mose freely  with  the  arteries 
that  supply  the  gums.  And 
just  at  the  rim  of  the  alveo- 
lus   there    is    a    pretty    rich 

plexus  formed    by  union  with    Eoot  and  Membrane  of  Tooth:    p,p,  perid 
ii  ,       •  f»   ■!  -J.  brane :  ap,  apical  space :  a,  artery:   al,  al,  a 

the  arteries  ot  the  periosteum      cess;  M.dentai  ligament. 
and  of  the  gum — the  gingival 

plexus.  This  being  the  case,  it  is  evident  tliat  the  peridental  mem- 
brane may  receive  its  blood-supply  from  either  of  these  two  opposite 
sources.  In  alveolar  abscess  the  blood-vessels  of  the  apical  space  are 
often  completely  destroyed,  but,  as  the  anastomosis  with  the  vessels  of 
the  gum  over  the  alveolar  rim  and  through  the  alveolar  wall  is  so  rich, 
the  membrane  does  not  suffer  from  lack  of  blood. 

The  nerve-supply  of  the  peridental  membrane  is  also  derived  from 
two  sources.  These  correspond  perfectly  with  the  sources  of  the  blood- 
supply,  and  need  no  further  description  except  to  say  that  in  this  instance 
the  principal  supply  seems  to  be  from  the  direction  of  the  gum  and 
through  the  alveolar  wall.  This  may  not  so  plainly  apj^ear  from  ana- 
tomical examination,  but  experimental  observation  demonstrates  that  the 


ental   mem- 
alveolar  pro- 


920  DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 

sensibility  of  the  peridental  membrane  is  not  appreciably  impaired  by 
the  destruction  of  the  nerves  in  the  apical  space. 

The  peridental  membrane  is  the  organ  of  touch  of  the  tooth;  the 
enamel  has  no  sense  of  touch.  And  the  pulp  is  so  encased  within  the 
hard  structures  of  the  tooth  that  it  could  not  exercise  the  sense  of  touch 
if  it  possessed  it;  which,  as  a  matter  of  fact,  it  does  not.  The  pulp  of 
a  tooth  conveys  painful  impressions  only,  and  under  normal  conditions 
these  impressions  are  aroused  only  by  thermal  changes.  By  means  of 
the  nerves  of  the  peridental  membrane,  however,  every  touch  upon  the 
tooth  is  reported  to  the  sensorium.  These  nerves  are  the  proper  nerves 
of  touch  for  the  tooth — as  much  so  as  are  the  nerves  distributed  to  the 
finger-ends  for  the  fingers.  No  other  nerves  of  the  tooth  are  so  situated 
as  to  receive  impressions  made  upon  the  tooth,  and  these  must  receive 
the  impressions  in  a  secondary  way  (which,  by  the  way,  is  the  case  with 
all  nerves  of  touch.  In  the  fingers'  ends  these  nerves  are  covered  by 
the  epithelium).  When  a  tooth  is  touched,  as  by  the  tongue,  by  articles 
of  food  taken  into  the  mouth,  or  by  the  finger,  the  peridental  membrane 
receives  the  pressure,  and  through  its  nerves  a  sensation  of  touch  is  con- 
veyed to  the  brain.  Such  a  touch  cannot  affect  the  pulp  of  the  tooth, 
because  it  cannot  reach  it ;  therefore  the  peridental  membrane  is  the  only 
organ  of  touch  possessed  by  the  tooth.  This  sense  of  touch  is  in  normal 
conditions  rather  feeble,  yet  sufficiently  pronounced  to  respond  readily 
to  very  slight  pressure  on  any  tooth.  That  these  nerves  of  touch  are  not 
distributed  principally  by  way  of  the  apical  space  I  have  satisfied  my- 
self by  examination  of  the  sensibility  of  this  membrane  after  removing 
everything  from  the  apical  space.  One  of  the  most  noteworthy  observa- 
tions I  have  made  on  this  point  was  in  the  case  of  a  young  lady  who  had 
lost  the  pulp  of  the  first  bicuspid  at  a  time  when  the  apical  foramen  was 
still  widely  open,  and  through  which  another  operator  had  inadvertently 
passed  quite  a  large  pellet  of  cotton.  I  found  it  necessary  to  cut  through 
the  alveolar  wall  in  order  to  remove  it,  and  I  took  particular  care  to 
remove  everything  in  the  apical  space.  The  space  was  much  enlarged 
by  absorption,  and  was  in  a  septic  condition.  In  this  case  the  pulp  of 
the  tooth  was  gone ;  the  nerves  entering  the  peridental  membrane  by 
way  of  the  apical  space  were  gone ;  and  yet  this  tooth,  at  the  earliest 
date  at  which  the  sense  of  touch  could  be  differentiated  from  the  sense 
of  pain,  was  found  to  possess  the  sense  of  touch  in  a  high  degree.  As 
progress  toward  recovery  was  made  the  sense  of  touch  in  this  tooth 
became  the  same  as  in  the  others — or,  in  other  words,  it  became  nor- 
mal. This  and  similar  cases  in  which  the  same  results  were  observed, 
establish  the  fact  that  the  nerves  of  touch  of  the  tooth  are  to  be  found 
in  the  peridental  membrane,  and  that  they  are  received — for  the  most 
part,  at  least — by  way  of  the  nerv^es  distributed  to  the  gum  through  the 
wall  of  the  alveolus. 

Therefore  we  find  that  the  teeth  are  normally  well  supplied  with 
nerves  and  blood  from  at  least  two  different  sources,  and  that,  though 
one  of  these  sources  of  supply  may  be  cut  off,  they  seem  not  to  suffer 
materially  on  that  account — at  least,  this  is  the  case  with  the  peridental 
membrane.  Now,  the  cementum  of  the  tooth  is  supplied  with  nutrient 
material   from  the  peridental  membrane.     It  follows  that  the  loss  of 


CLASSIFICATION.  921 

some  of  tlie  avenues  by  which  this  nutrient  material  may  reach  it  will 
not  materially  impede  its  continued  nutrition,  and  therefore  will  not 
materially  lower  its  standard  of  health.  This  agrees  substantially  with 
what  is  seen  in  daily  clinical  experience.  Teeth  that  have  lost  their 
pulps  go  on  decade  after  decade  continuing  in  the  most  perfect  health. 
The  sense  of  touch  remains  perfect ;  the  connection  of  the  tooth  with 
the  neighboring  parts  shows  no  signs  of  disturbance. 

Diseases  of  the  Peridental  Membrane. 

One  of  the  first  things  that  the  student  should  recognize  in  the  study 
of  the  pathology  of  the  peridental  membrane  is  the  fact  that  it  is  sub- 
ject to  various  forms  of  disease.  Among  these  there  are  several  dis- 
tinct varieties  of  inflammation,  which  arise  from  distinct  causes  and 
require  different  treatment  for  their  cure.  No  classification  can  at  pres- 
ent be  made  that  will  be  free  from  objections ;  yet  a  classification,  even 
if  not  perfect,  will  assist  in  the  comprehension  of  the  details  of  the 
subject. 

Classification. — 1st.  Traumatic  pericementitis,  or  inflammation  of  the 
peridental  membrane  resulting  from  injuries. 

2d.  Absorption  of  the  roots  of  the  permanent  teeth  :  (o)  In  diseased 
conditions  of  the  peridental  membrane;  (6)  After  injuries  and  trans- 
plantations, replantations,  etc. 

3d.  Pericementitis,  or  inflammation  of  the  peridental  membrane,  hav- 
ing its  seat  in  the  apical  space  and  following  the  death  of  the  pulp  of 
the  tooth.  This  is  the  only  inflammation  of  this  membrane  to  which 
this  term  should  be  applied  without  the  use  of  a  descriptive  adjective, 
and  even  here  I  think  it  is  better  to  use  the  term  apical  j)ericeme7ititis. 

4th.  Alveolar  abscess.  This  abscess  always  has  its  seat  in  the  apical 
space,  and  is  a  result  of  apical  pericementitis  following  the  death  of  the 
pulp  of  the  tooth. 

5th.  Gingivitis,  inflammation  of  the  gingival  border  of  the  gum  and 
lower  border  of  the  peridental  membrane,  occurring  mostly  from  con- 
stitutional causes,  including  salivation  from  mercury,  iodide  of  potassi- 
um, etc. 

6th.  Calcic  inflammation  of  the  gums  and  peridental  membrane,  a 
diseased  condition  dependent  upon  deposits  of  calculus,  salivary  or 
serumal,  on  the  necks  of  the  teeth. 

7th.  Phagedenic  pericementitis,  a  specific,  infectious  inflammation 
having  its  beginnings  in  the  gingivte  and  accompanied  with  destruc- 
tion of  the  peridental  membranes  and  alveolar  walls. 

It  will  be  noted  that  in  this  classification  we  have  two  distinct  groups 
of  pathological  manifestations,  the  one  having  its  beginnings  in  the  apical 
space,  and  the  other  having  its  begimiings  in  the  gingivae. 

Those  conditions  resulting  from  injuries  to  the  roots  of  the  teeth,  and 
from  replantations,  transplantations,  etc.,  will  be  treated  in  another 
article,  to  which  the  reader  is  referred.  I  will  only  treat  of  the  pathol- 
ogy of  absorption  of  the  roots  of  the  permanent  teeth  in  those  cases  in 
which  no  previous  injury  has  been  observed. 

On  this  point  it  may  be  stated  as  an  axiom  that  such  absorption  never 


922  DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 

occurs  during  the  maintenance  of  the  health  of  the  peridental  membrane. 
As  to  the  conditions  of  this  absorption  Ave  have  very  positive  informa- 
tion ;  I  cannot  speak  so  certainly  as  to  the  nature  of  the  causes  which 
bring  about  these  conditions.  Absorption  of  the  roots  of  the  temporary 
teeth  is  in  all  respects  a  physiological  process ;  the  absorption  of  the 
roots  of  the  permanent  teeth  cannot  be  so  regarded ;  and  yet  an  exam- 
ination of  the  process  in  the  two  instances  reveals  the  fact  that  they  are 
identical  in  their  nature,  although  the  causes  by  which  the  process  is  set 
in  action  in  the  two  instances  are  entirely  different.  Resorption  of  the 
roots  of  the  temporary  teeth  is  effected  by  certain  cells  known  as  odon- 
toclast;  resorption  of  bone  in  the  physiological  processes  of  change  of 
form  is  effected  by  cells  known  as  osteoclasts.  Each  of  these  processes 
is  physiological,  and  the  cell  or  tissue  that  performs  this  function  in 
each  instance,  is  the  same,  the  only  difference  being  one  of  position.  In 
each  instance,  as  the  calcific  material  is  removed,  the  space  is  filled  with 
ne\\ly-fbrmed  cells  that  crowd  into  the  breach  ;  so  that  newly-formed 
cells  are  always  presented  to  the  surface  being  absorbed.  It  is  certain 
that  these  cells  form  a  solvent  that  effects  the  solution  of  the  calcific 
material,  though  it  is  not  yet  known  precisely  what  this  solvent  is.  It 
has  been  suggested  by  Rustizky  and  Krause  that  it  contains  lactic  acid. 
This  suo;";estion  seems  to  have  arisen  from  noting  the  behavior  of  these 
cells  toward  stainino;  agrents,  and  cannot  be  reo;arded  as  conclusive. 

These  cells  not  only  effect  the  solution  of  the  living  bone,  but  they 
burrow  into  necrosed  bone  or  pieces  of  ivory  that  are  thrust  into  the 
tissues  for  the  purpose  of  experiment  (Billroth,  DelNIorgan,  Tomes, 
Krause,  Koelliker),  and  in  this  case  the  peculiar  cells  are  to  be  found 
in  the  burrowings,  the  same  as  in  the  ordinary  resorption  of  the  bones 
or  the  roots  of  the  temporary  teeth.  This  shows  us  that  the  process  of 
absorption  is  in  no  wise  dependent  upon  the  life  of  the  tissue  being 
absorbed.  Further,  other  substances  than  bone  may  be  absorbed. 
It  has  become  quite  customary  among  surgeons  to  use  ligatures  of 
animal  membrane,  such  as  catgut,  silkworm-gut,  etc.,  for  deep  su- 
tures ;  these  are  left  in,  and  are  absorbed.  In  the  microscopic 
study  of  this  process  it  has  been  found  that  the  leucocytes  aggre- 
gate themselves  about  the  ligature,  and  that  in  their  presence  its 
substance  disappears  in  such  a  way  as  to  foi'ui  irregular  pockets,  the 
same  as  is  seen  in  the  absorption  of  bone.  The  cells  crowd  into  the 
S])ace  gained,  keeping  it  completely  filled,  until,  finally,  when  the  last 
particle  of  the  ligature  is  removed,  it  is  accurately  represented  by  a 
solid  cord  of  newly-formed  living  tissue.  In  case  of  the  sponge-c/raft 
the  sponge  is  removed  in  precisely  the  same  manner,  and  is  replaced  by 
newly-formed  tissue.  In  modus  operandi  these  several  processes  are 
identical.  In  each  instance  an  excitation  of  the  tissue  in  the  neighboi'- 
hood  of  the  substance  to  be  absorbed  is  necessary,  and  it  is  also  neces- 
sary that  this  excitation  be  not  so  great  as  to  cause  the  formation  of  pus, 
as  this,  among  other  causes,  w^ill  prevent  the  cells  from  performing  their 
pliysiological  function.  In  cases  where  a  ligature  has  been  used  any 
considerable  pus-formation  in  the  immediate  neighborhood  is  known  to 
defeat  the  absorptive  process.  The  presence  of  pus  similarly  arrests  the 
absorption  of  other  substances  or  tissues. 


CONDITIONS  OF  ABSORPTION.  923 

Now,  by  the  application  of  the  facts  here  presented  we  can  know  the 
conditions  under  which  the  roots  of  the  permanent  teeth  are  absorbed. 
There  must  in  each  instance  be  a  mild  form  of  irritation  that  will 
keep  up  local  excitement  of  a  particular  kind.  In  the  physiological 
processes  this  excitation  is  probably  furnished  by  the  nervous  system. 
In  the  pathological  processes  of  absorption  the  excitation  is  undoubtedly 
furnished  by  some  local  irritant  which  acts  more  or  less  continuously. 
What  this  irritant  may  be  must  be  determined  for  each  case  inde- 
pendently. In  many  of  the  cases  of  absorption  it  will  be  found 
extremely  difficult  to  determine  the  exact  cause  of  the  excitation,  but  in 
all  cases  that  have  come  under  my  observation  the  tissues  in  the  imme- 
diate neighborhood  of  the  destructive  process  have  been  found  hypersemic 
and  presenting  the  macroscopic  appearance  of  granulation-tissue. 

In  many  cases  that  present  themselves  to  the  practitioner  it  will  be 
very  difficult  to  assign  a  cause  for  this  chronic  irritation.  One  of  the 
most  frequent  causes  in  my  experience  has  been  the  protrusion  of 
root-fillings  beyond  the  apical  foramen  into  the  tissues  of  the  apical 
space,  where  they  keep  up  a  very  low  degree  of  ii'ritation.  I  have 
seen  many  cases  in  which  this  was  the  only  cause  that  I  was  able  to 
assign  for  the  difficulty.  These  cases  have  nearly  all  been  those  in 
which  I  have  myself  filled  the  roots  with  gold.  But  since  the  filling 
of  root-canals  with  gutta-percha  has  come  in  vogue  I  have  met  Avith 
a  few  cases  in  which  the  protrusion  of  that  substance  seemed  to  have 
acted  as  a  cause.  It  is  plain,  however,  that  these  materials  will  not 
invariably  produce  this  result;  for  I  have  seen  cases  where  the  root- 
filling  had  extended  into  the  tissues,  and  so  remained  for  years  without 
evil  consequences. 

Some  of  the  cases  that  have  come  before  me  have  seemed  to  arise  from 
some  cause  entirely  hidden.  In  one  very  remarkable  case  eight  teeth  of 
the  upper  jaw  had  lost  their  roots  by  absorption.  Three  of  the  eight  had 
root-fillings  that  I  had  introduced  fourteen  years  before ;  in  the  other 
five  the  pulps  were  alive.  The  process  seemed  to  have  been  about  the 
same  in  those  with  living  pulps  as  in  those  in  which  the  pulps  were 
dead.  The  woman  had  become  very  intemperate  and  excessively  fat. 
A  number  of  cases  have  come  to  my  notice  in  which  this  absorption 
has  occurred  on  the  roots  of  teeth  otherwise  healthy.^ 

The  absorptive  process  in  these  cases  is  usually  very  irregular.  It 
may  attack  the  root  at  any  point  and  remove  its  substance  in  the  most 
irregular  manner,  or  the  root  may  be  removed  almost  as  are  the  roots 
of  the  temporary  teeth.  Irregularity  of  absorption  is,  however,  the 
rule.  This  affection  presents  no  symptoms  by  which  it  can  be  recog- 
nized before  it  becomes  manifest  by  the  loosening  of  the  crown  of  the 
tooth.     It  is  not  amenable  to  treatment. 

Apical  Pericementitis,  or  Pericementitis  foJJoicing  the  Death  of  the 
Dental  Pulp. — This,  together  with  its  resultant,  alveolar    abscess,   is 

^  Since  writing  the  above  I  have  met  with  a  case  in  which  all  of  the  posterior  root 
and  the  floor  of  the  pulp-chamber  of  a  lower  molar  has  disappeared  by  absorption. 
The  tooth  had  a  large  contour-filling  occupying  the  posterior  half  of  the  crown,  which 
I  placed  there  ten  years  ago,  after  capping  the  pulp.  The  pulp  was  alive,  as  I  found  by 
drilling  into  the  pulp-chamber. 


924  DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 

the  most  painful  affection  to  which  the  teeth  are  liable.  It  consists  of 
an  inflammation  of  the  peridental  membrane,  always  beginning  in  the 
apical  space,  in  the  immediate  neighborhood  of  the  apical  foramen.  It 
never  occurs  during  the  life  of  the  pulp  of  the  tooth,  or,  if  so,  not  until 
the  pulp  is  irreparably  inflamed.  The  tissue  involved  in  the  inflamma- 
torv  process  is  encased  between  the  walls  of  the  alveolus  and  the  root  of 
the  tooth  in  such  a  way  as  to  hinder  its  expansion  when  engorged  by 
the  influx  of  blood.  The  tissue,  although  in  normal  conditions  not 
unusually  sensitive,  is  richly  supplied  with  nerves,  and  in  the  inflam- 
matory state  soon  becomes  exquisitely  painful.  This  inflammation  is 
very  prone  to  terminate  in  suppuration,  with  the  formation  of  alveolar 
abscess.  The  affection  may  be  ushered  in  inmiediately  upon  the  death 
of  the  pulp  of  the  tooth,  or  it  may  be  indefinitely  delayed.  In  some 
instances  this  inflammation  may  precede  the  death  of  the  pulp,  the 
inflanunation  of  the  latter  seeming  to  be  projected  through  the  apical 
foramen.  This,  however,  very  rarely  occurs,  the  rule  being  that  the 
death  of  the  pulp  precedes  the  beginning  of  the  inflammation  in  the 
apical  space,  usually  some  days,  or  until  putrescence  of  the  pulp  has 
proceeded  so  far  as  to  give  rise  to  poisonous  material,  which  escapes 
into  the  tissues  by  way  of  the  apical  foramen.  In  very  many  cases 
this  is  delayed  for  weeks  or  months,  or  may  not  occur  even  during 
a  lifetime.  Tlie  rule,  however,  is  that  it  does  occur  sooner  or  later. 
It  may  be  very  positively  stated  that  no  tooth  with  an  empty  pulp- 
chamber  is  safe  from  apical  pericementitis. 

The  SYMPTOMS  of  acute  apical  pericementitis  vary  much  in  different 
cases,  but  this  variation  is  more  as  to  the  severity  of  the  pain  than  as  to 
the  character  of  it.  It  is  usually  ushered  in  by  a  dull  pain  referred  to 
the  affected  tooth.  Usually  this  is  at  first  somewhat  relieved  by  pres- 
sure, but  as  the  inflammation  increases  in  severity  pressure  of  the  oppos- 
ing teeth  causes  extreme  pain ;  and,  as  the  swelling  of  the  tissues  in  the 
apical  space  causes  a  slight  elevation  of  the  tooth  in  its  socket,  thus 
bringing  the  whole  force  of  the  occlusion  upon  this  tooth,  this  becomes 
the  source  of  extreme  suffering.  Now  the  mucous  membrane  over  the 
affected  root  begins  to  present  signs  of  inflammation ;  it  becomes  a 
deeper  red  than  the  other  parts  of  the  mucous  membrane,  and  the  pres- 
sure of  the  finger  causes  pain.  As  the  case  progresses  still  farther  the 
gum  is  liable  to  assume  a  purplish  hue.  The  pain  is  continuous  and 
becomes  throbbing,  each  pulsation  causing  an  exacerbation  of  the  pain. 
Pus  is  usually  formed  in  the  apical  space  very  quickly — within  twenty- 
four  hours — but  sometimes  is  delayed  for  several  days.  With  the 
formation  of  pus  the  case  becomes  one  of  acute  alveolar  abscess,  which 
will  be  described  presently. 

The  DIAGNOSIS  of  acute  apical  pericementitis  usually  presents  very 
little  difficulty.  Pain  caused  by  pressure  on  the  affected  tooth  is  a  con- 
stant symptom  that  distinguishes  it  sharply  from  hypersemia,  or  inflam- 
mation of  tlie  ])ulp  of  the  tooth.  In  diseases  of  the  dental  pulp  the 
affected  organ  does  not  become  tender  to  the  touch — at  least,  not  until 
the  inflammation  has  passed  through  the  apical  foramen,  thus  ushering 
in  ajiical  inflammation.  In  apical  pericementitis  the  pain  is  always  re- 
ferred definitely  to  the  particular  tooth.    In  pulpitis  the  patient  is  often 


CHRONIC  APICAL  PERICEMENTITIS.  925 

uncertain  as  to  the  exact  location  of  the  pain  ;  such  an  uncertainty  on 
the  part  of  the  patient  is  in  all  cases  sufficient  to  exclude  acute  apical 
pericementitis.  Pain  referred  to  different  parts  of  the  face,  the  ear,  or 
other  remote  points,  in  the  absence  of  a  tooth  sore  to  pressure,  also 
excludes  this  disease  as  the  cause,  while  it  is  characteristic  of  the 
affections  of  the  pulp  of  the  tooth.  If  the  practitioner  will  keep  well 
in  mind  the  functions  of  the  two  organs,  there  cannot  be  much  difficulty. 
The  peridental  membrane  is  the  organ  of  touch  of  the  tooth,  and  there- 
fore definitely  locates  its  ailments.  The  pulp  of  the  tooth  is  not  an 
organ  of  touch,  and  therefore  does  not  definitely  locate  its  ailments, 
but  is  especially  prone  to  cause  reflected  pain,  or  pain  referred  to  asso- 
ciate or  distant  parts.  This  is  characteristic  of  the  diseases  of  those 
organs  that  have  no  nerves  of  touch,  as  is  seen  in  pain  referred  to  the 
knee  in  hip-joint  disease,  pain  referred  to  the  region  of  the  scapula  in 
disease  of  the  liver,  pain  referred  to  the  brow  in  inflammation  of  the 
iris,  etc.  This  peculiarity  occurs  so  frequently  in  diseases  of  organs 
having  no  sense  of  touch  as  to  make  it  a  general  law^  of  symptomatol- 
ogy. Another  point  of  prime  importance  is  the  fact  that  the  dental 
pulp  is  especially  sensitive  to  thermal  changes,  and  that  this  sensibility 
is  markedly  increased  in  its  diseases.  The  peridental  membrane,  on  the 
other  hand,  has  no  special  sensitiveness  to  thermal  changes,  and  such 
sensitiveness  is  not  developed  to  any  considerable  degree  in  its  diseases. 
Therefore  the  existence  of  special  sensitiveness  to  thermal  changes  in 
connection  with  a  given  case  marks  it  at  once  as  an  affection  of  the 
pulp.  There  seems  to  be  but  one  condition  in  which  thermal  change 
causes  marked  pain  in  acute  or  chronic  apical  pericementitis,  and  this  is 
in  cases  when  the  pulp-chamber  of  the  tooth  is  filled  with  gas  in  such  a 
w;ay  as  to  cause  pressure  on  the  tissues  of  the  apical  space.  In  this  case 
heat  will  give  rise  to  an  expansion  of  the  gas,  increasing  the  pressure 
and  the  pain,  while  the  application  of  cold  will  relieve  it.  This,  then, 
is  diagnostic ;  for  in  affections  of  the  pulp  both  heat  and  cold  cause  pain 
when  suddenly  applied. 

Chronic  apical  pericementitis  has  all  of  the  characters  of  the  acute 
variety  in  a  modified  form.  The  patient  usually  complains  of  sore- 
ness of  a  particular  tooth.  This  may  be  considerable,  or  it  may  be  so 
slight  as  to  occasion  annoyance  only.  This  condition  may  remain  sta- 
tionary for  an  indefinite  time,  or  it  may  come  and  go,  lasting  a  day,  or 
two  or  three  days,  at  a  time.  In  some  cases  there  will  be  marked  con- 
gestion of  the  gum  about  the  affected  tooth ;  others  will  present  no 
signs  whatever  to  the  eye.  In  most  cases  there  will  be  some  sensitive- 
ness to  pressure  made  with  the  finger  over  the  root  of  the  affected  tooth ; 
in  these  cases  the  tooth  is  not  sensitive  to  thermal  changes.  The  pres- 
ence of  such  sensitiveness  is  sufficient  for  the  exclusion  of  this  affection 
from  the  diagnosis. 

This  form  of  disease  is  more  likely  to  be  confounded  with  phagedenic 
pericementitis  than  any  other.  They  agree  in  many  of  their  manifesta- 
tions, but  an  examination  of  the  peridental  membrane  as  directed  in 
treating  of  that  affection  cannot  fail  to  render  the  diagnosis  clear. 

The  CAUSE  of  apical  pericementitis,  acute  or  chronic,  is  always  some 
irritating  agent  that  finds  its  way  into  the  tissues  of  the  apical  space  by 


926  DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 

way  of  the  apical  foramen.  Tliis  agent  is  usually  furnished  by  products 
of  die  decomposition  of  the  pulp  of  the  tooth.  The  tooth  will  in  most 
instances  be  found  with  a  cavity  of  sufficient  depth  to  expose  the  pulp- 
chamber,  the  palp  being  in  a  state  of  active  decomposition,  or,  the  pulp 
having  been  long  dead,  its  chamber  is  found  crowded  with  decomposing 
filth.  The  instances  are  not  few,  however,  in  which  the  atfected  tooth 
is  found  to  be  perfectly  sound.  In  these  cases  the  pulp  has  previously 
died  from  some  of  the  diseases  or  accidents  to  which  it  is  liable,  and 
decomposition  of  the  contents  of  the  pulp-chamber  has  taken  place.  A 
large  number  of  the  cases  seen  in  practice  are  those  in  which  the  pulp, 
after  the  insertion  of  a  filling,  has  died  from  thermal  changes  or  from 
pressure  on  the  pulp.  In  those  cases  in  which  there  is  no  external 
opening  into  the  pulp-chamber  it  is  not  uncommon  for  the  case  to  go 
on  for  a  long  time  after  the  death  of  the  pulp  before  painful  symptoms 
manifest  themselves — probably  from  the  fact,  so  repeatedly  noticed,  that 
the  pulp  dries  up,  or  becomes  mummified,  instead  of  undergoing  decom- 
position. Sooner  or  later,  however,  serum  will  percolate  into  the  cham- 
ber and  decompose,  furnishing  the  necessary  poisonous  material  for 
lighting  up  inflammation  in  the  apical  space.  According  to  recent 
observations  in  regard  to  the  influence  of  micro-organisms — their  neces- 
sity to  the  process  of  putrefaction — it  is  difficult  to  understand  how 
decomposition  can  take  place  in  the  closed  pulp-chamber,  it  having 
never  been  open  ;  but,  however  this  may  be,  the  fact  remains  that  such 
decompositions  do  occur.  In  very  many  instances  this  is  postponed, 
as  stated  above,  and  during  this  time  the  peridental  membrane  retains 
its  health. 

Aside  from  this,  there  are  many  instances  in  which  the  pulp-chamber 
is-  filled  with  decomposing  filth  for  indefinite  periods  and  no  inflamma- 
tion results.  It  is  probable  that  in  these  instances  the  apical  foramen 
has  become  so  closed  with  debris  as  effectually  to  prevent  the  passage 
of  poisonous  material. 

In  the  TREATMENT  of  apical  pericementitis  the  first  thing  that  should 
receive  attention  is  the  pulp-chamber  of  the  affected  tooth.  If  there  is 
a  cavity  opening  into  it,  this  should  be  enlarged,  so  as  to  gain  free  access 
to  the  root-canais  ;  the  decomposing  pulp,  or  anything  else  that  may  be 
in  the  chamber  or  root-canals,  should  be  removed  in  the  most  perfect 
manner  possible,  and  the  interior  subjected  to  the  most  thorough  cleans- 
ing. The  best  instruments  for  the  purpose  are  the  barbed  broaches  well 
known  in  the  shops  of  dealers  in  dental  instruments ;  these  are  usually 
put  u])  in  assorted  sizes  very  suitable  for  this  operation.  Each  broach 
should  be  examined  before  using,  to  see  that  none  of  the  cuts  for  form- 
ing t!ie  barbs  are  so  deep  as  to  weaken  the  shaft  at  that  point,  rendering 
it  liable  to  break.  The  use  of  the  broach  requires  considerable  practice 
to  obtain  the  best  results.  It  should  usually  be  passed  up  beside  the 
pulp  with  the  l)arbs  turned  toward  the  wall  of  the  chamber ;  and  when 
the  point  has  gone  far  enough,  the  barbs  should  be  turned  against  the 
soft  tissue  and  the  broach  withdrawn.  Usually,  the  entire  pulp  will 
come  out  with  it  if  the  motion  is  skilfully  executed ;  but  sometimes  the 
tissue  will  simply  be  torn  up  and  the  broach  will  come  aMay  without 
the  pulp,  especially  when  it  is  in  a  state  of  partial  decomposition.    Then 


CHRONIC  APICAL  PERICEMENTITIS.  927 

it  Avill  be  necessary  to  twist  the  tissue  around  the  broach.  In  doing  this 
the  greatest  care  should  be  exercised  not  to  break  the  instrument  and 
leave  a  part  of  its  shaft  in  the  root-canal.  I  have  usually  found  it  well 
to  pass  a  fine  broach  carefully  through  the  apical  foramen,  to  make  sure 
that  it  is  open,  so  that  if  any  pus  has  already  formed  it  may  be  dis- 
charged through  the  root-canals.  After  this  is  done  the  interior  of  the 
pulp-chamber  and  root-canals  should  be  bathed  with  some  good  disin- 
fecting agent.  In  practice  I  have  found  that  it  matters  little  what  this 
is,  so  that  it  is  not  an  irritant  and  accomplishes  the  office  for  which  it 
is  intended — the  thorough  disinfection  of  the  parts.  For  this  purpose 
I  have  used  carbolic  acid  more  than  any  other  agent,  and  I  think 
this  is  most  used  by  the  profession.  Other  substances  seem  to  act  just 
as  well,  such  as  iodoform,  sanitas,  eucalyptus,  iodine,  salicylic  acid,  and 
a  number  of  others.  An  objection  to  the  use  of  carbolic  acid  has  been 
raised  by  some  operators  on  the  ground  that  it  is  liable  to  close  the  api- 
cal foramen  prematurely  by  the  coagulation  of  albuminous  material. 
Theoretically,  the  objection  would  seem  to  be  well  taken,  but  in  prac- 
tice I  have  not  experienced  any  difficulty  from  this  cause. 

After  disinfecting,  the  pulp-chamber  should  be  loosely  filled  with  cot- 
ton which  has  been  dipped  in  some  antiseptic  lotion,  and  the  cavity  tem- 
porarily sealed.  In  a  large  majority  of  cases  this  treatment  will  he 
sufficient  to  terminate  the  difficulty.  Within  a  few  hours  the  pain 
will  subside  and  the  soreness  disappear.  In  all  cases  the  cavity 
should  be  sealed  moisture-tight,  and,  if  pus  is  forming,  should  be 
changed  with  sufficient  frequency  to  prevent  pressure  from  accumu- 
lation. 

Cases  are  now'  and  then  met  with  in  which  this  treatment  is  insuf- 
ficient— that  is,  the  pain  persists.  In  such  cases  various  means  have 
been  resorted  to  for  the  arrest  of  the  inflammatory  process.  Counter- 
irritation  is  one  of  the  simplest,  and  is  often  a  very  effective  remedy.  The 
form  of  counter-irritation  that  I  most  resort  to  is  this  :  Cut  a  piece  of 
soft  blotting-paper  the  size  desired  and  stick  it  on  a  small  bit  of  rub- 
ber dam.  Moisten  the  paper  with  chloroform,  and  place  it  over  the 
root  of  the  tooth  in  such  a  way  that  the  rubber  will  protect  the  lips  or 
cheeks  from  the  action  of  the  agent.  This  will,  if  the  mucous  mem- 
brane is  dried  before  it  is  applied,  make  a  blister  within  three  or  four 
minutes.  I  have  thought  it  more  effective,  however,  not  to  carry  it  to 
that  extent,  but  to  apply  it  until  there  is  sharp  burning,  then  remove, 
then  reapply  in  the  same  way  after  an  interval ;  and  keep  repeating  this 
as  long .  as  seems  necessary.  Any  means  by  which  the  chloroform  can 
be  applied  to  the  parts  and  its  evaporation  prevented  will  be  effective. 
I  not  unfrequently  use  it  on  a  bit  of  punk,  under  my  finger.  Many 
plans  for  the  application  of  counter-irritation  in  these  cases  have  been 
devised  from  time  to  time,  such  as  pepper-bags,  plasters  into  the  com- 
position of  which  some  one  or  more  of  the  vesicants  or  irritants  are 
incorporated.     These,  if  well  made,  are  effective  and  convenient. 

Local  blood-letting  will  often  be  effective,  and  is  to  be  recommended 
in  those  cases  in  which  local  congestion  is  a  prominent  factor.  This  is 
best  clone  by  a  cut  encircling  the  tooth  at  its  neck  or  by  a  cut  in  the 
mucous  membrane  immediately  over  the  affected  root.     This,  to  be 


928  DISEASES  OF  THE  PERrDENTAL  MEMBRANE. 

most  effective,  should  be  carried  to  the  bone.  In  persistent  cases  it  is 
better  to  penetrate  the  bone  and  lacerate  the  tissues  of  the  apical  space. 
This  is  quickly  done  by  means  of  a  well-directed  drill  driven  by  the 
engine.  It  is  needless  to  say  that  this  is  an  instrument  that  should  be 
used  with  great  care. 

A  still  better  result  is  usually  obtained  by  the  use  of  carbolic  acid  for 
the  painless  penetration  of  the  apical  space.  It  is  best  done  in  this  wise: 
The  mucous  membrane  is  first  dried  at  the  point  at  which  it  is  desired 
to  make  the  opening,  and  napkins  are  so  placed  as  to  keep  it  dry.  Then 
a  plugging-instrument  with  fairly  sharp  serrations  and  of  convenient 
shape  is  selected.  The  point  of  this  is  dipped  into  a  95-per-cent.  solu- 
tion of  carbolic  acid,  and  a  drop  conveyed  to  the  mucous  membrane ; 
this  will  at  once  produce  a  white  eschar.  Then  a  slight  scratching 
motion  with  the  serrated  point  is  begun,  with  the  view  of  removing  the 
tissue  that  is  whitened.  This  is  continued  until  the  carbolic  acid  is 
thick  with  the  debris  of  the  tissue  torn  up,  then  it  is  dried  out  and 
another  drop  added,  as  before,  and  the  process  continued.  This  is 
repeated  as  often  as  may  be  necessary,  going  deeper  and  deeper  into  the 
tissue  in  the  desired  direction  until  the  bone  is  laid  bare.  Then  a  fresh 
drop  of  the  acid  is  placed  on  the  bone  and  the  periosteum  carefully 
raised  over  a  sufficient  space ;  then  with  a  sharp  chisel  cut  through  to 
the  peridental  membrane.  This  will  generally  cause  some  pain  and 
some  bleeding,  but  after  giving  a  little  time  for  this  to  cease,  and  add- 
ing more  of  the  acid,  the  apical  space  can  usually  be  reached  without 
difficulty.  No  blood  should  be  drawn  at  any  time  during  the  opera- 
tion except  in  penetrating  the  wall  of  the  alveolus.  In  doing  this  no 
tissue  is  removed  until  it  is  anaesthetized  by  the  carbolic  acid.  This  is 
a  little  tedious,  but  it  is  almost  painless,  and  the  general  effect  is  usu- 
ally better  than  by  other  modes  of  penetrating  the  apical  space.  The 
carbolic  acid  has  the  effect  of  modifying  the  pain,  and  the  opening  left 
does  not  close  so  readily.  I  have  frequent  occasion  to  use  this  process 
with  very  sensitive  patients,  and  have  found  it  to  be  quite  satisfactory. 

These  means  of  relief  may  with  advantage  be  supplemented  by  con- 
stitutional treatment,  especially  in  the  more  severe  acute  forms.  Hot 
foot-baths  at  bedtime  are  usually  found  effective  in  combating  the 
inflammation,  if  made  use  of  before  pus  has  formed.  A  brisk  saline 
cathartic  is  still  better,  and  it  is  well  to  follow  it  with  quinine  on  the 
following  day.  This  treatment  is  especially  recommended  in  those 
obstinate  chronic  forms  occasionally  met  WMth.  In  those  it  is  well  to 
repeat  this  several  times  within  a  few  days.^ 

^  Exclusive  reliance  upon  local  medication,  so  common  in  dental  practice,  is  an  evil 
which  slionld  be  amended.  At  the  request  of  Dr.  Black  the  writer  presents  the  lollow- 
ing  summary  of  a  line  of  constitutional  treatment  which  in  a  large  percentage  of  cases 
has  in  his  hands  proved  effective  in  preventing  suppuration.  It  will  be  observed  that 
it  varies  in  detail,  but  not  in  principle,  from  that  recommended  in  the  text. 

1st.  After  the  evacuation  of  purulent  matter  or  {)ent-up  gases  from  the  pulp-cham- 
ber, apply  to  the  gums,  over  the  implicated  tooth,  one  or  two  good  Swedish  leeches. 
American  leeches  are  unruly  and  difHcult  to  manage  in  the  mouth  or  upon  any  circum- 
scribed surface.  Each  leech  will  draw  about  a  fluidrachm  of  blood.  After  theirremoval 
the  hemorrhage  can  be  almost  indefinitely  prolonged  by  wiping  away  the  clot  as  fast  as 
it  forms  in  the  wound  made  by  the  leech  aud  directing  the  patient  to  rinse  the  mouth 
with  warm  water  as  long  as  it  may  be  desirable  to  continue  the  bleeding.     In  this  way 


ALVEOLAR  ABSCESS.  929 

Alveolar  Abscess. — Alveolar  abscess  results  from  inflammation  having 
its  seat  in  the  apical  space  proceeding  to  the  formation  of  pus ;  there- 
fore the  location  of  alveolar  abscess  is  always  in  its  inception  the  apical 
space,  no  matter  where  it  may  afterward  extend.  If  this  be  not  the 
case,  it  is  not  alveolar  abscess  even  though  it  be  an  al^scess  within  the 
alveolus  of  a  tooth.  This  term  has  been  employed  from  time  immemo- 
rial to  designate  this  special  form  of  abscess,  and  it  should  be  strictly 
confined  to  this  one  form,  so  that  all  may  know  exactly  what  is  meant. 
If  an  abscess  occurs  on  the  side  of  a  root  of  a  tooth  as  the  result  of 
injury,  and  be  not  the  effect  of  the  death  of  the  pulp  of  the  tooth,  it  is 
properly  a  traumatic  alveolar  abscess.  If  such  an  abscess  occurs  from 
any  of  the  diseases  that  attack  the  sides  of  the  root  of  the  tooth  and  it 
is  thought  well  to  designate  it  as  alveolar,  the  word  should  in  all  cases 
be  accompanied  by  an  adjective  expressing  the  fact.  This  is  necessary 
to  accuracy. 

Alveolar  abscess,  then,  is  in  all  cases  a  result  of  apical  pericementitis. 
If  the  case  is  not  seen  until  the  formation  of  pus  has  begun,  or  if  the 
means  employed  for  subduing  the  inflammation  have  proved  ineffectual, 
all  the  symptoms  will  show  an  aggravation.  The  gums  over  the 
aflected    tooth   will    become    deej^ly  congested,    and    perhaps    actually 

from  a  fluidounce  to  a  fluidounce  and  a  half  of  blood  may  readily  be  abstracted  from 
each  leech-bite,  in  addition  to  the  amount  originally  drawn.  "When  leeches  are  not 
obtainable,  the  method  of  scarification  of  the  gum  recommended  in  the  text  should  be 
ibllowed.  Leeching  not  only  ])ossesses  the  great  advantage  of  being  an  entirely  pain- 
less method  of  abstracting  blood,  but  secures  a  greater  outflow  than  that  obtainable 
from  a  simple  incision.  It  should  always  be  practised  before  any  local  medication  is 
attempted,  as  the  pi'esence  of  any  foreign  substance  upon  the  gum  interferes  with  the 
biting  of  the  leech,  if  it  does  not  entirely  prevent  it. 

'2d.  After  the  removal  of  the  leeches  give  a  full  dose — from  6  to  10  grains — of 
quinine.  This  somewhat  reduces  the  temperature  and  the  force  of  the  circulation,  and 
possibly  tends  to  retard  the  inflannnatorv  process  by  arresting  the  migration  of  the 
leucocytes  through  the  walls  of  the  congested  capillaries,  although  in  the  ordinary 
medicinal  dose  this  may  be  considered  doubtful. 

3d.  Following  the  quinine,  give  one  drop  of  tincture  of  aconite- root  evei\v  hour  until 
bedtime.  For  safety,  place  the  recpiired  number  of  drops  (and  no  more)  in  a  small  bottle, 
carefully  instructing  the  patient  as  to  dosage.  Ten  or  twelve  drops  are  usually  sufficient 
for  tiie  required  number  of  hours,  and  this  amount,  even  if  taken  at  once  by  an  adult, 
would  not  prove  fatal.  P^rom  such  small  doses  no  very  marked  effect  upon  the  force  or 
frequency  of  the  circulation  can  be  expected,  but  they  will  at  least  liolcl  the  inflamma- 
tion in  ciieck  and  prevent  an  increased  pulse-rate.  Larger  closes  of  aconite  should  not  be 
given  unless  the  patient  can  be  kept  constantly  under  observation  and  the  eflect  of  each 
dose  noted — a  precaution  which  the  exigences  of  dental  practice  usually  make  imprac- 
ticable. Under  proiter  safeguards  a  reduction  below  the  normal  of  from  five  to  ten  beats 
per  minute  in  tiie  i)ulse-rate  is  desirable  and  safely  attainable. 

4th.  At  bedtime  give  a  full  dose  (10  grains)  of  Dover's  powder.  This  is  to  be  taken 
in  conjunction  witii  a  liberal  amoimt  of  hot  lemonade,  the  feet  to  be  previously  Mell 
soaked  in  hot  water,  and  the  patient,  when  in  bed,  well  covered,  to  promote  sweating. 
This  treatment  is  a  most  effective  feature  in  general  medication  in  tiiis  class  of  cases. 
The  opium  eases  pain,  cjuiets  nervous  irritation,  lowers  the  circulation,  and  in  conjunc- 
tion with  ipecacuanha  promotes  diaphoresis,  thus  diverting  to  the  cutaneous  surface 
perverted  blood-currents,  draining  the  congested  vessels  of  their  contents,  and  dimin- 
ishing the  force  and  frequency  of  the  circuhitory  impact  upon  the  inflamed  area. 

5th.  T/(e/o//oM'mf/wioramr/ give  a  brisk  saline  cathartic.  If  given  during  the  previous 
day,  its  operation  is  likely  to  take  the  patient  out  of  bed  at  night,  and  thus  to  interfere 
■with  the  action  of  the  Dover  powder. 

6th.  Quinine,  aconite,  and  oijium  to  be  continued  (according  to  indications)  until 
inflammation  subsides,  on  the  one  hand,  or  the  abscess  has  formed  and  discharged, 
on  the  other.     (See  Treatment  of  Alveolar  Abscess.) — Ed. 

Vol.  I.— 59 


930 


DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 


The  pain  becomes  in  many  instances  intolerable,  and  there 
rigor  followed  by  fever.  In  a  number  of  instances  I  have 
of  103°    and    104°   F.    in   severe  cases   of  acute  alveolar 


Acute  Alveolar  Abscess  of  Supe- 
rior lucisor  puiutiug  on  the 
Gum:  ti,  abscess-cavity  in  the 
bone ;  ft,  floor  of  the  nostril ;  c, 
lip ;  (/,  tooth. 


inflamed, 
may  be  a 
seen  fever 
abscess. 

The  first  pus  farmed  is  pent  up  in  the  apical  space  by  bony  walls  on 
all  sides,  and  the  pressure  becomes  very  great ;  this  results  in  rapid 
absorption  of  the  surrounding  bone.     The  rule  in  such  cases  is  that  the 

pus  will  burrow  in  the  direction  of  the  least 
resistance,  and,  as  the  bone  about  and  enclos- 
ing the  apical  space  is  softer  than  the  exter- 
nal lamina,  it  usually  happens  that  notable 
destruction  of  bone  occurs  before  the  surface 
is  reached,  thus  forming  a  considerable  pus- 
cavity  (Fig.  485).  Even  in  this  case,  how- 
ever, the  tissues  of  the  peridental  membrane 
occupying  the  apical  space  are  not,  as  a  rule, 
destroyed.  The  fibres  are  swollen  and  great- 
ly elongated,  and  the  pus  usually  occupies 
s])aces  between  them.  This  swollen  tissue 
forms  the  mass  so  often  seen  attached  to  the 
end  of  the  root  of  a  tooth  extracted  while  in 
this  condition,  or  later,  after  the  abscess  has 
become  chronic.  The  explanation  of  this 
seems  to  be  that  the  fibres  are  loosened  from 
the  alveolus  by  absorption  of  the  bone,  but, 
the  root  of  the  tooth  not  being  absorbed,  the  attachment  of  the  fibres 
to  the  cementum  is  not  broken  up.  This  is  the  usual  condition  of  the 
tissues  in  alveolar  abscess,  but  in  some  cases  it  happens  that  this  tissue 
is  destroyed  and  the  end  of  the  root  denuded  of  its  membrane,  which 
complicates  the  healing  process.  It  seems  from  my  own  observation, 
however,  that  this  occurs  but  rarely  in  the  acute  forms ;  in  the  chronic 
form  it  is  more  frequently  met  with. 

During  the  time  that  the  pus  is  burrowing  in  the  bone  the  pain  con- 
tinues to  be  very  severe  and  is  of  that  throbbing  character  so  peculiar 
to  abscess-formation.  The  gums  over  the  affected  root  become  deeply 
congested  and  often  much  thickened  by  engorgement  with  blood,  and 
the  lymphatics  about  the  angle  of  the  jaw  are  liable  to  become  very 
sore  and  swollen.  There  is  not  often  during  this  time  much  swelling 
of  the  tissues  of  the  face.  Finally,  the  pus  will  find  an  exit  from  the 
bone.  This  usually  occurs  on  the  buccal  side  of  the  arch  (the  mouth  is 
regarded  as  consisting  of  two  cavities — the  lingual  cavity,  inside  the 
dental  arch ;  the  buccal  cavity,  outside  the  dental  arch  and  inside  the 
checks  and  lips),  as  shown  in  Figs.  485,  486,  but  may  occur  in  any 
direction,  the  rule  being  that  it  will  burrow  in  the  direction  of  the  least 
resistance.  It  is  in  obedience  to  this  law  that  the  large  cavity  is  formed 
in  the  bone  about  the  apical  space.  This  portion  of  the  bone  is  of  a 
cancellated  structure,  and  is  much  more  raj)idly  absorbed  than  the  denser 
portions  near  the  surface ;  therefore  there  is  usually  a  very  considerable 
cavity  formed  in  this  portion  of  the  bone  in  the  ifirst  stage  of  the  pro- 
cess, but  after  the  penetration  of  the  outer  lamina  of  the  bone  the  pus 


ACUTE  ALVEOLAR  ABSCESS. 


931 


Fig.  486. 


finds  its  way  into  the  soft  tissues,  where  the  resistance  is  less  and 
the  destruction  of  the  bone  ceases  or  progresses  less  rapidly.  With 
the  escape  of  the  pus  from  its  imprisonment  within  the  bone  comes 
a  modification  of  all  the  symptoms.  There  is  usually  a  marked 
abatement  of  the  intense  pain.  This,  however,  is  only  an  abatement, 
not  a  cessation  :  the  pain  continues  in  a  less  intense  form.  The  feat- 
ures, which  up  to  this  time  had  shown  but  little  of  the  effects  of  the 
malady  except  the  expression  of  suffering,  now  become  swollen,  often 
with  great  rapidity.  Frequently  all  the  tissues  of  the  side  of  the  face 
affected  become  intensely  oedematous  and  distorted,  the  eye  closed,  and 
the  jaws  so  stiffened  that  the  mouth  can 
be  but  slightly  opened.  In  this  condition 
an  examination  will  show  a  large  tumor 
of  the  gum  over  the  affected  root.  This 
may  be  in  either  the  lingual  or  the  buccal 
cavity,  but  in  a  great  majority  of  cases  it 
is  found  in  the  buccal.  The  tumor  will 
be  found  fluctuating,  aud  if  left  to  itself 
will  very  generally  open  on  the  gum,  just 
over  the  root  of  the  tooth.  This  result 
should,  however,  be  anticipated  by  opening 
with  the  bistoury,  for  it  not  very  unfre- 
quently  happens  that  the  tissues  of  the 
gum  are  raised  from  the  bone  and  the  pus 
finally  gains  an  exit  at  the  gingival  mar- 
gin ;  which  complicates  the  process  of  re- 
covery. 

After  the  discharge  of  pus  the  inflam- 
matory symptoms  usually  abate  very  rap- 
idly. The  pain  generally  subsides  within 
a  few  hours,  and  the  swelling  within  a  day 
or  two,  though  pus  may  continue  to  be  dis- 
charged indefinitely.  The  amount  of  pus 
formed  in  these  cases  is  often  very  consid- 
erable, the  discharge  being  profuse  and  con- 
tinuing for  a  number  of  days.  The  quan- 
tity, however,  gradually  lessens,  and  after  four  or  five  days  it  is  usually 
reduced  to  a  comparatively  small  amount.  The  abscess,  if  left  to  itself, 
usually  assumes  the  chronic  form,  the  pus  continuing  to  be  discharged, 
but  in  lessened  volume.  With  the  exception  of  the  fistula  and  the 
slight  discharge  of  pus,  the  parts  now  assume,  so  far  as  the  eye  can 
detect,  their  normal  condition.  This  is  the  chronic  form  of  alveolar 
abscess. 

Acute  alveolar  abscess  presents  three  forms  in  respect  to  the  manner  in 
ichich  the  pus  leaves  its  bony  enclosure.  It  may  at  once  penetrate  into 
the  soft  tissues,  as  described  above  (Figs.  485,  486)  ;  it  may  separate  the 
periosteum  from  the  bone  and  form  a  cavity  for  itself  between  the  two, 
as  shown  in  Fig.  487  ;  or  it  may  follow  the  peridental  membrane  down 
the  side  of  the  root  and  be  discharged  at  the  margin  of  the  gum.  The 
second  is  the  form  of  abscess  that  is  most  likelv  to  be  attended  with 


Acute  Alveolar  Abscess  of  the  Lower 
Incisor  poiuting  on  the  Gum:  a,  ab- 
scess-cavity in  the  bone ;  c,  lip ;  d, 
tooth. 


932 


DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 


necrosis  of  portions  of  bone,  and  for  this  reason  should  receive  prompt 
attention  for  the  purpose  of  preventing  or  limiting  this  very  unfavorable 
result.  This  seems  to  occur  mostly  in  those  cases  in  which  the  inflamma- 
tion has  run  very  high,  and  in  which  there 
has  been,  or  exists  at  the  time  of  the  escape 
of  the  pus  from  the  bone,  a  very  considerable 
inflammation  of  its  substance  and  of  its  peri- 
osteum, by  which  the  layer  of  osteoblasts  have 
become  so  softened  that  they  are  readily  sepa- 
rated from  the  bone  beneath.  In  this  condi- 
tion of  things  the  pus,  in  making  its  escape 
from  the  bone,  instead  of  penetrating  the  over- 
lying tissues,  raises  the  periosteum  in  the  same 
manner  as  in  subperiosteal  inflammations.  In 
this  way  separation  of  the  periosteum  from  the 
bone  over  a  considerable  surface  occasionally 

occurs  ;    and  if  the  parts  are  suffered  to  re- 
Acute  Alveolar  Abscess  with  Pocket  •     •     ii  •  Tj_'       i?  •!       1  1     x- 
of  Pus  between  the  Periosteum   uiaiu  lu  this  couditiou  tor  a  Considerable  tune, 

^^^.oi  of  ^^i;lr"   "ecrosis  more  or  less  extensive  will  result.    If; 
hp  ;rf,  tooth  ;e,  pus-cavity  beneath   qu  the  otlicr  liaud,  the  pus  bc  promptlv  dis- 

the  periosteum.  '  .^  ^  i"- 

charged,  so  that  the  periosteum  may  be  again 
brought  in  contact  with  the  parts  from  which  it  was  separated,  not  much 
harm  will  follow ;  it  will  readily  be- 
come reattached,  and  the  parts  will 
heal  without  difficulty.  Separation  of 
the  periosteum  is  to  be  suspected  when 
the  tumor  of  the  gum  is  broad  and  com- 
paratively soft.  After  discharge  of  the 
pus  by  means  of  the  bistoury  an  exami- 
nation with  a  probe  will  reveal  the  fact 
that  the  bone  is  more  or  less  extensively 
stripped  of  its  periosteal  covering.  This 
form  of  abscess,  when  left  to  itself,  is 
prone  to  discharge  at  the  gingival  mar- 

FiG.  488. 


Fig.  489. 


Necrosis  of  the  lUical  Plate  of  the  Alveolar  Pro- 
cess from  Alveolar  Abscess. 


Acute  Alveolar  Abscess  of  a  Lower  Incisor  with 
Pus-cavity  between  the  Bone  and  the  Perios- 
teum :  II,  pus-cavity  in  the  bone;  b,  pus  be- 
tween the  periosteum  and  bone;  e,  lip;  d, 
tooth ;  '■,  tongue. 


gin  after  having  separated  the  periosteum  from  the  outer  wall  of  the  alveo- 


ACUTE  ALVEOLAR  ABSCESS. 


933 


lar  process.  In  this  condition  the  only  blood-supply  that  this  portion  of 
the  process  can  obtain  is  that  which  may  come  from  the  other  side  of  the 
tooth  through  the  anastomosis  of  the  arterial  branches  in  the  peridental 
membrane,  already  in  a  more  or  less  inflamed  condition,  or  through  the 
Haversian  canals  of  the  septum  of  the  alveolar  process  between  the  teeth. 
This,  it  will  at  once  be  seen,  will,  in  the  inflamed  condition  of  the  parts, 
be  a  very  precarious  supply ;  and,  as  a  result  of  this  condition,  necrosis 
of  the  alveolar  plates  overlying  the  root  afi'ected  and  those  immediately 
adjacent  is  very  liable  to  occur.  Loss  of  these  plates  by  necrosis  occur- 
ring in  this  manner  is  shown  in  Fig.  488. 

This  form  of  abscess,  occurring  in  the  lower  jaw  (Fig.  489),  is  per- 
haps more  likely  to  point  on  the  face  than  any  other  of  the  acute  forms, 
on  account  of  the  tact  that  gravitation  carries  the  pus  in  that  direction. 
This  may  drop  gradually  down  and  the  pus  be  discharged  under  the  chin, 
forming  a  chronic  abscess  such  as  is  shown  in  Fig.  500  ;  or  if  it  be  an 
anterior  tooth,  it  may  open  in  front,  under  the  lip ;  or  if  it  be  a  posterior 
tooth,  on  the  lower  border  of  the  cheek.  Less  frequently  this  may  happen 
from  alveolar  abscess  in  the  upper  jaw,  the  abscess  pointing  almost  any- 
where on  the  face,  but  more  especially  just  under  the  prominence  of  the 
malar  bone,  in  front  of  the  attachment  of  the  masseter  nuiscle  (Figs. 
490  and  495). 

The  opening  of  an  alveolar  abscess  on  the  face  is  always  a  grave  mis- 
fortune because  of  the  scar  that  is  almost  inevitable,  and  for  this  reason 
such  a  result  should  be  guarded  against  with  the  utmost  care.  When  it 
is  apprehended,  the  pus  should  without  delay  be  discharged  into  the 
mouth  by  use  of  the  bistoury. 

Occasionally  this  form  of  abscess  is  seen  to  raise  the  periosteum  and 
soft  tissues  from  the  hard  palate,  the  pus  having  discharged  from  its 
bony  enclosure  in  that  direction  (Fig.  491).     My  observation  leads  me 


Fig.  490. 


Fig.  491. 


Upper  Molar  with  Acute  Abscess  at  the  Buccal 
Roots  and  Chronic  Abscess  at  the  Palatine  Root: 
a,  cavity  of  acute  abscess  in  the  bone  ;  h,  pus- 
cavity  between  the  bone  and  periosteum,  ex- 
tending out  under  the  prominence  of  the  malar 
process  ;  c,  tissues  of  cheek  ;  d,  tooth  ;  e,  maxillary 
sinus;./",  nostril;  c/,  malar  process;  h,  cavity  of 
chronic  abscess  discharging  at  i.  (Compare  with 
Figs.  495,  496,  and  504.) 


Upper  Incisor  with  Acute  Alveolar  Abscess 
the  Pus  from  which  has  raised  the  Perios- 
teum from  the  Hard  Palate:  a,  very  large 
abscess-cavity  in  the  bone  ;  ft,  pus-cavity  be- 
twi  en  the  periosteum  and  bone;  c,  lip;  d, 
tooth  ;  e,  floor  of  nostril. 


to  the  conclusion  that  in  this  case  there  is  not  the  same  tendency  to  dis- 
charge at  the  gingival  margin  as  in  cases  in  which  the  tumor  is  situated 


934  DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 

in  the  buccal  cavity.  When  the  abscess  points  in  the  hard  palate,  there 
is  about  the  same  liability  to  necrosis  of  the  alveolar  process,  yet  it 
usually  seems  to  be  limited  more  to  the  margins.  Occasionally  I  have 
seen  the  periosteum  stripped  from  the  bone  over  the  entire  roof  of  the 
mouth,  but  retaining  its  attachment  at  the  gingivae  and  along  the  line 
of  the  posterior  border  of  the  hard  palate,  forming  in  this  way  a  pus- 
cavity  filling  the  entire  palatine  arch.  In  these  cases,  extensive  as  is 
the  separation  of  the  periosteum,  necrosis  of  the  bone  but  rarely  occurs ; 
indeed,  I  have  nev^er  witnessed  a  perforation  of  the  hard  palate  from 
this  cause.  This  is  probably  due  to  the  fact  that  the  bones  are  thin  and 
their  blood-supply  from  the  mucous  membrane  of  the  opposite  surface 
is  not  interfered  w^ith.  This  accounts  for  the  fact  that  in  the  palate 
necrosis  of  bone  is  usually  limited  to  the  immediate  neighborhood  of 
the  teeth,  where  the  blood-supply  may  be  cut  off  by  the  tissue  injury. 

In  these  cases  we  recognize  two  causes  of  necrosis  of  bone.  One  is 
the  intensity  of  the  inflammatory  process,  which  destroys  by  producing 
stasis  over  a  considerable  territory.  This  may  cause  necrosis  in  any 
locality  whatever.  The  other  occurs  in  such  localities  as  may  be  de- 
prived of  their  blood-supply  by  the  injury  of  tissues  in  their  immediate 
neighborhood  upon  which  they  are  dependent.  This  is  confined,  for  the 
most  part,  to  the  alveolar  process,  which  receives  its  blood  from  two 
sources — through  the  vessels  of  the  gum  and  periosteum  of  the  outer 
surface  of  the  process,  and  through  the  vessels  that  enter  the  apical 
space  and  supply  the  alveolar  dental  membrane.  The  latter  vessels  are 
cut  off — temporarily,  at  least — by  the  formation  of  abscess  in  the  apical 
space.  Now,  if  the  periosteum  also  is  separated  by  the  burrowing  of 
pus  beneath  it,  the  death  of  this  portion  of  bone  seems  inevitable,  and 
clinical  observation  shows  that  this  result  does  take  place  if  this  con- 
dition of  things  remains  for  a  considerable  time ;  yet  it  does  not  neces- 
sarily occur  at  once,  and  even  here  necrosis  of  the  process  may  be  pre- 
vented by  prompt  action  in  discharging  the  pus  and  keeping  the  parts 
in  apposition. 

The  third  form  is  that  in  wdiich  the  pus,  instead  of  penetrating  the 
surface  of  the  bone,  finds  its  way  along  the  side  of  the  root,  following 
the  peridental  membrane  to  the  gingival  margin,  and  is  discharged  at 
that  point.  This  form  is  more  rare  than  either  of  the  others.  AVhen  it 
occurs,  it  destroys  a  considerable  part  of  the  peridental  membrane,  and 
the  alveolar  process  overlying  this  quickly  disappears.  This  condition 
is  readily  recognized  by  passing  a  thin,  flat,  pointed  instrument  up  by 
the  side  of  the  root  and  finding  the  peridental  membrane  wanting ; 
whereas,  if  the  pns  has  penetrated  to  the  surfiice  of  the  bone  above  and 
been  discharged  at  this  point,  the  peridental  membrane,  on  raising  the 
periosteum,  will  be  found  intact.  The  tliird  form  is  perhaps  more  liable 
to  be  mistaken  for  phagedenic  pericementitis  than  any  other  type  of 
alveolar  abscess. 

Occasionally  there  occurs  a  case  of  alveolar  abscess  accompanied  by  ex- 
tensive necrosis  of  the  bones  of  the  face.  I  have  seen  one  extreme  case 
in  which  all  of  the  lower  border  of  the  right  superior  maxilla,  including 
the  whole  floor  of  the  antrum  of  Highmore,  and  all  of  the  teeth  from 
the  central  incisor  to  the  wisdom  tooth,  were  carried  away.     I  did  not 


CHRONIC  ALVEOLAR  ABSCESS.  935 

see  the  case  until  the  necrosed  parts  were  loosened,  but,  from  the  history 
^iven  by  the  patient,  there  seemed  to  be  no  doubt  that  the  trouble  arose 
from  acute  alveolar  abscess  at  the  roots  of  tlie  first  molar.  That  tooth 
had  for  some  time  been  decayed,  and  the  patient  had  had  severe  tooth- 
ache several  times ;  in  one  of  these  attacks  the  face  began  to  swell,  and 
it  was  in  this  inflammation  that  the  necrosis  occurred.  The  patient  was 
a  young  man  about  twenty  years  old,  and  when  I  saw  him  was  quite 
antemic.  He  made  a  good  recovery  after  the  removal  of  the  necrosed 
portions  of  bone.  Another  extensive  case  was  that  of  a  boy  of  nine 
years,  in  which  all  of  the  teeth  from  the  cuspid  to  and  including  the 
t\velve-year  molar — which  had  not  erupted — came  away.  This  seemed 
to  have  arisen  from  alveolar  abscess  at  the  root  of  the  first  molar,  which 
had  been  allowed  to  run  its  course  without  attention.  Cases  so  exten- 
sive as  these  are,  f  )rtunately,  very  rare.  In  a  few  cases  I  have  seen 
extensive  necrosis  of  the  alveolar  processes  that  seemed  to  arise  from 
abscesses  occurring  independently  at  the  roots  of  various  teeth,  all  of 
which  had  been  neglected.  In  such  cases  the  general  health  of  the 
patients  has  usually  suffered  greatly,  and  they  generally  present  an 
ansemic  appearance. 

Chronic  alveolar  abscess  usually  follows  the  acute  form  if  the  case  is 
left  to  itself.  The  causes  of  this  abscess  are  such  that  they  are  not  self- 
limiting,  as  is  the  rule  with  a  large  proportion  of  the  abscesses  to  which 
the  human  frame  is  liable.  A  common  boil,  or  phlegmon,  is  cured 
spontaneously  by  the  discharge  of  its  contents ;  this  is  the  general  result 
in  abscesses  of  the  soft  tissues.  In  subperiosteal  abscess  the  discharge 
of  the  contents  results  in  a  spontaneous  cure  in  those  cases  in  which  no 
necrosis  of  bone  has  occurred ;  but  if  there  is  necrosis,  the  presence 
of  the  dead  bone  may  cause  the  abscess  to  assume  the  chronic  form 
by  its  continuous  irritation  of  the  tissues  with  which  it  is  in  contact. 
In  alveolar  abscess  we  may,  and  generally  do,  have  the  case  continu- 
ing in  the  chronic  form  without  the  presence  of  necrosed  bone.  In 
this  case  the  irritant  tliat  is  responsible  for  the  continuance  of  the 
abscess  is  derived  from  the  pul])-chamber  of  the  affected  tooth  ;  that 
is,  the  same  cause  that  brought  about  the  acute  form  remains  to 
keep  up  the  chronic — namely,  the  discharge  of  septic  matter  from  the 
pulp-chamber  of  the  tooth  into  the  ajjical  space. 

The  presence  of  this  abscess  is  known,  except  in  that  form  called 
blind  abscess,  by  a  fistulous  oj^ening  in  the  neighborhood.  The  position 
of  this  opening  and  the  direction  of  the  burrowing  of  the  pus  in  chronic 
abscess  furnish  a  great  variety  of  forms,  presently  to  be  considered  ; 
just  now  the  conditions  peculiar  to  the  apical  space  will  engage  our 
attention.  When  the  pus  is  discharged  from  the  acute  abscess,  the 
inflammation  subsides  and  the  paji'ts,  so  far  as  the  eye  can  detect,  return 
to  their  normal  condition,  except  that  a  fistulous  opening  remains. 
Even  this  may  close,  and,  though  rarely,  the  abscess  may  be  ctu'ed 
spontaneously.  The  rule,  however,  is  that  the  fistulous  opening  con- 
tinues, and  that  pus  may  be  found  at  the  orifice  at  any  time.  The  flow 
of  pus  is  often  profuse  for  the  first  few  weeks,  but,  as  a  ride,  it  is  gradu- 
ally reduced  until  it  is  quite  small  in  amount,  tmd  often  the  orifice  heals 
over  and  opens  again  every  few  days ;  sometimes  it  closes  permanently. 


936 


DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 


Fig.  492. 


Blind  Abscess  at  the  Root  of  an  Upper 
Incisor:  «.  abscess-cavity  iu  bone:  b, 
drill-hole  exposing  the  pulij-chamber 
for  treatment. 


Then  we  have  the  condition  of  blind  abscess  (Fig.  492),  in  which  there 
remains  a  mass  of  tissue  in  the  enlarged  apical  space  with  which  more  or 

less  pus  is  constantly  intermingled.  This 
condition  of  things  may  continue  almost 
without  change  for  any  length  of  time, 
or  the  pus  may  be  burrowing  through 
the  tissues  without  the  patient's  knowl- 
edge. A  tooth  in  this  condition  is  lia- 
ble to  periodic  fits  of  soreness  which  will 
from  time  to  time  attract  to  it  the  atten- 
tion of  the  patient.  In  such  a  case  the 
symptoms  differ  but  little  from  chronic 
pericementitis.  The  contents  of  the  pulp- 
chamber  are  in  a  state  of  constant  putre- 
faction, and  the  resulting  products  are 
as  constantly  being  discharged  into  the 
apical  tissues  in  a  quantity  sufficient  to 
prevent  healing.  In  this  chronic  form 
changes  in  the  enlarged  apical  space  take  place  very  slowly,  and  usu- 
ally are  not  very  marked  in  their  character.  It  seems  evident  from  the 
comparisons  I  have  made  from  time  to  time  that  the  absorption  of 
bone  about  the  apical  space  is  greater  in  the  chronic  than  in  the  acute 
forms ;  therefore  I  conclude  that  in  the  majority  of  chronic  alveo- 
lar abscesses  the  absorption  of  the  bone  is  slowly  progressing,  though 
this  is  not  necessarily  true  in  all  cases.  I  have  seen  some  chronic 
abscesses  of  long  standing  in  which  the  absorption  of  bone  was  very 
slight.  In  the  majority  of  cases,  judging  from  clinical  experience 
gained  in  the  treatment  of  these  forms,  the  tissues  of  the  apical  space 
do  not  seem  to  be  very  much  impaired  in  their  vitality ;  for  such  ab- 
scesses heal  with  the  greatest  facility  when  the  cause  by  which  they  are 
maintained — septic  matter  from  the  pulp-chamber — is  removed.  Still, 
there  is  a  considerable  number  in  which  this  is  not  the  case.  In  some 
of  these  cases  the  difficulty  seems  to  consist  solely  in  the  low  state  of  the 
vitality  of  the  tissues ;  so  that  time  is  required  for  them  to  recover  tone. 
In  others  there  is  an  actual  destruction  of  the  tissues  of  the  apical  space, 
this  proceeding  to  such  an  extent  that  a  portion  of  the  apex  of  the  root 
is  denuded  of  its  tissue.  This  is  always  a  very  grave  condition  as  re- 
gards the  prospect  of  recovery.  Another  complication  also  is  liable  to 
occur — the  deposit  of  senimal  calculus  on  that  portion  of  the  root  which 
has  lo.st  its  covering  of  tissue.  This  calculus  is  evidently  derived  from 
the  exuded  serum,  and  not  unfrequently  is  deposited  in  the  form  of 
crystalline  or  crystal-like  points ;  so  that  when  the  finger  is  passed  over 
it  one  is  strongly  impressed  with  the  similarity  of  the  sensation  to  that 
produced  by  a  l)urr.  This  calculus  is  an  irritant,  and  is  especially  so 
when  in  this  form,  and  of  course  it  is  impossible  that  the  case  can  heal 
while  it  remains. 

Cases  are  now  and  then  met  with  that  have  taken  on  a  septic  condi- 
tion and  assumed  a  more  aggravated  type.  In  all  of  the  cases  before 
mentioned  the  ]mis  is  of  *thc  character  known  as  laudable,  but  in  the 
septic  condition  it  becomes  sanious,  or  very  thin  and  watery.     Now  the 


THE  BURRO WIXG    OF  PUS.  937 

destruction  of  tissue  becomes  more  apparent.  Not  only  the  bone,  but 
the  neighboring  soft  tissues,  are  found  to  be  wasting  aAvay,  and  several 
openings  for  the  discharge  of  sanious  pus  are  likely  to  be  formed  ;  and 
the  case,  if  left  to  itself,  is  likely  to  terminate  in  the  spontaneous  loss  of 
the  tooth.  This  condition  has  been  described  by  Dr.  Ingersol  as  alveo- 
lar ulceration.  It  seems  to  be  caused  by  micro-organisms  different  from 
those  usually  found  in  the  pus  of  ordinary  alveolar  abscess ;  but  our 
knowledge  of  it  is  as  yet  too  indefinite  for  positive  statements  to  be  made. 

Chronic  alveolar  abscess  may  result  directly  from  chronic  apical  peri- 
cementitis without  acute  inflammation  having  been  present  at  any  time ; 
indeed,  it  may  take  place  so  quietly  and  with  so  little  disturbance  that 
the  patient  will  not  remember  that  the  tooth  has  ev^er  been  sore  or  that 
anvthing:  has  been  wrong  with  it.  The  tooth  affected  is  not  necessarily 
decayed.  Its  pulp  may  have  died  from  any  of  the  diseases  to  which  it 
is  liable,  and  the  tooth  may  present  the  appearance  of  the  most  per- 
fect health.  An  abscess  formed  in  this  quiet  way  subsequently  pre- 
sents no  symptoms  different  from  those  that  follow  the  acute  form. 

The  condition  of  the  tooth  in  chronic  abscess  is  not  necessarily  very 
characteristic.  Of  course  the  pulp  is  always  dead,  and  in  a  certain  pro- 
portion of  the  cases  the  tooth  will  be  discolored  by  the  absorption  of' 
the  coloring-matter  from  the  decomposing  pulp,  or  after  this  by  the 
formation  of  the  dark  sulphurets.  This  discoloration  may  exist  in  any 
degree,  from  the  slightest  perceptible  tinge  to  a  deep  black.  The  rule 
is  that  there  is  some  change  of  color  by  which  the  fact  can  be  recog- 
nized that  the  tooth  has  lost  its  pulp.  In  many  cases  this  is  only  a 
slight  loss  of  translucency.  Such  a  tooth  is  never  sensitive  to  cold,  and 
by  this  test  the  right  tooth  can  usually  be  selected  in  case  of  doubt  as 
to  which  of  a  number  of  teeth  may  have  an  abscess  supplying  the  pus 
discharged  from  a  fistulous  opening  in  the  neighborhood. 

The  hurroidng  of  jyns  in  the  chronic  forms  of  alveolar  abscess  forms 
a  very  important  element  in  their  history.  This  presents  the  widest 
variations,  and  is  occasionally  the  source  of  much  perplexity  to  the 
physician  and  the  surgeon.  The  general  rule  is  that  the  discharge  is 
continued  at  the  point  at  which  the  acute  abscess  at  first  opened — i.  e. 
upon  the  gum  over  the  affected  root  (Figs.  493,  494).  This  is,  how- 
ever, a  general  rule  to  which  there  are  many  exceptions.  The  point  of 
discharge  is  frequently  changed  during  the  continuance  of  the  chronic 
form  ;  the  fistulous  opening  heals  over,  and  after  a  time  the  pus  appears 
at  another  point,  which  may  be  at  a  distance  from  the  original  opening. 
This  change  may  be,  and  generally  is,  made  with  so  little  disturbance 
that  the  patient  is  not  cognizant  that  it  is  taking  place  until  the  new 
point  of  discharge  is  noticed.  Exceptionally,  considerable  disturbance 
occurs ;  in  fact,  the  abscess  may  again  assume  the  acute  form  and  force  a 
new  opening  in  a  different  direction  or  at  a  more  remote  point.  The 
cases  in  which  there  is  a  certain  soreness  and  stiffening  of  the  tissues 
through  which  the  abscess  is  burroAving  are  more  common.  This  is 
especially  the  case  if  the  parts  be  freely  movable  or  if  the  pus  is  finding 
its  way  through  muscular  tissue,  and  yet  it  is  singular  how  far  pus  may 
burrow  among  muscles  without  serious  inconvenience.  It  often  happens 
that  the  stiffening  of  the  muscles  is  all  that  is  complained  of. 


938 


DISEASES   OF  THE  PERIDENTAL  MEMBRANE. 


Among  these  burrowiiigs  of  pus  in  this  class  of  abscesses  some  gen- 
eral rules  may  be  pointed  out,  and  some  particular  forms  that  occur 
oftener  than  others  may  be  mentioned.  It  is  a  general  law  of  the  bur- 
rowing of  pus  that  it  will  go  in  the  direction  of  the  least  resistance ; 


Fig.  493. 


Fig.  494. 


Chronic  Alveolar  Abscess  at  the  Root  of  a 
Lower  IncLsor:  ",  abscess-cavity  in  the 
bone;  6,  fistula  discharging  on  the  gum; 
c,  lip;  </,  tooth. 


Chronic  Alveolar  Abscess  at  the  Root  of  an  Upper 
Incisor  with  P'istula  discharging  on  the  (lum: 
a,  abscess-cavity  in  the  bone ;  b,  mouth  of 
fistula ;  c,  lip ;  d,  tooth. 


this  law  pertains  more  especially  to  the  acute  forms  of  abscess.  In  the- 
chronic  forms,  in  which  the  movement  of  the  pus  is  very  gradual,  it  is 
guided  largely  by  gravitation,  and  therefore  sinks  to  a  lower  point. 
Now,  these  two  forces,  acting  together,  will  explain  most  of  the  move- 
ments of  })us  in  the  burrowings  of  chronic  abscess.  If,  in  the  down- 
ward wanderings  of  the  pus,  it  comes  in  contact  with  a  more  dense 
tissue,  it  will  usually  be  deflected  from  its  course  toward  that  of  less 
resistance ;  or  if  it  be  entangled  in  the  fibres  of  such  a  tissue  as  the 
muscular  and  these  run  at  an  angle  with  the  perpendicular,  there  will 
be  seen  a  tendency  to  follow  instead  of  to  cross  the  fibres.  Again,  if 
the  pus  is  burrowing  in  a  softer  tissue  and  in  its  course  comes  in  con- 
tact with  a  muscle,  it  will  usually  be  deflected  and  pass  around  the  more 
den.se  tissue  in  the  direction  most  favored  by  gravitation.  In  the  same 
way,  it  will  be  turned  from  its  course  by  dense  fascia  and  burrow 
beneath  it.  This  is  the  general  law  observed  in  studying  the  burrow- 
ings of  pus  in  cases  of  chronic  abscess,  but  it  is  by  no  means  univer- 
sal, for  cases  are  occasionally  presented  in  which  it  seems  to  be 
directly  disobeyed.  In  the  nutss  of  cases,  however,  these  will  be  found 
to  be  exceptional. 

Now,  by  the  ajijilication  of  the.se  laws  we  will  be  assisted  in  tracing 
a  discharge  to  its  source,  though  in  some  exceptional  cases  it  may  mis- 


THE  BURROWING   OF  PUS. 


939 


lead.  The  rule  is  that  we  will  find  the  point  of  discharge  below  the 
source  of  the  pus ;  hence  chronic  abscesses  of  tliis  class  that  burrow  to 
a  considerable  distance  are  likely  to  discharge  on  the  lower  portion  of 
the  face  or  on  the  neck,  and  occasionally  as  low  as  the  clavicle.  Dr.  E. 
D.  Swain  of  Chicago  lias  given  me  the  details  of  a  case  coming  under  his 
care  which  illustrates  this  tendency.  The  pus  from  a  chronic  abscess  at 
the  root  of  a  second  superior  molar  became  entangled  in  the  fibres  of 
the  masseter  muscle  and  followed  them  down  through  their  length. 
At  the  lower  border  it  emerged  from  this  muscle  beneath  the  border  of 
the  platysma  myoides,  and,  having  become  entangled  in  the  fibres  of 
this,  followed  their  direction  downward  and  backward  to  the  border 
of  the  trapezius,  where  it  discharged  on  the  skin.  The  masseter  muscle 
was  so  disabled  that  the  moiith  could  not  be  opened  to  the  usual  width, 
and  the  line  of  the  sinus  was  readily  traceable  under  the  surface  as  it 
followed  the  platysma. 

It  is  rather  unusual  for  the  pus  from  abscesses  in  the  upper  jaw  to 
follow^  such  a  course.     When  such  a  discharge  comes  to  the  surface,  the 


Fig.  496. 


Fig.  495. 


Alveolar  Abscess  at  the  Buccal  Roots  of  au  Upper  Molar 
discharging  on  the  Face:  a,  abscess-cavity  in  the 
bone;  t),  fistula  opening  on  the  face;  c,  maxillary 
sinus;  rf,  nostril :  e,  tooth  ;  f,  tissues  of  cheek.  (Com- 
pare with  Figs.  490,  496,  and  504.) 


Scar  caused  by  Alveolar  Abscess  dis- 
charging on  the  Face.  (Compare  with 
Figs.  495,  504,  and  490.) 


usual  point  is  just  beneath  the  prominence  of  the  malar  bone  ?,nd  in 
front  of  the  anterior  border  of  the  masseter  muscle  (Fig.  495) — at  least, 
of  the  abscesses  of  the  upper  jaw  discharging  on  the  face  which  have 
come  under  my  observation  more  have  presented  at  this  point  than  at 
all  others  together.  All  those  that  I  have  seen  in  tlie  act  of  pointing 
in  this  ])osition  have  been  of  the  acute  form,  but  the  history  given  me 
in  some  cases  indicates  that  the  chronic  forms  may  occasionally  point  in 
this  direction  after  the  closure  of  the  fistula  opening  on  the  gum  over 
the  affected  root.  The  particular  point  of  discharge  seen  in  Fig.  496 
forms  a  very  characteristic  scar,  and  on  that  account  is  of  special  inter- 


940 


DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 


est.  My  observation  leads  rae  to  the  conclusion  that  such  fistulse  are 
usually  the  result  of  acute  abscess  of  the  form  shown  in  Fig,  489,  in 
which  the  periosteum  is  separated  from  the  bone  far  out  under  the  nialar 
prominence.  When  the  new  tissue  formed  by  the  healing  of  the  sinus 
has  contracted,  the  skin  is  drawn  inward  under  the  malar  prominence 
in  such  a  way  as  materially  to  disfigure  the  face.  The  healing  of  the 
fistula  forms  a  strong  cord  of  new  tissue,  which  in  this  instance  has  one 
of  its  ends  attached  to  the  skin  and  the  other  to  the  periosteum.  This 
binds  the  skin  down  to  the  bone  permanently  unless  it  be  relieved  by  an 
operation.     (See  p.  952.) 

This  class  of  abscess  may  discharge,  also,  anywhere  in  the  region  below 
the  eye.  As  a  general  rule,  the  muscles  are  avoided,  the  pus  burrowing 
around  them  when  they  happen  to  lie  in  the  way.  For  this  reason, 
perhaps,  there  is  a  tendency,  when  an  abscess  at  the  root  of  an  anterior 
tooth  discharges  on  the  face,  for  the  discharge  to  appear  in  the  triangle 
between  the  levator  labii  superioris  alseque  nasi  and  the  levator  labii 
superioris.  In  two  cases  I  have  seen  the  discharge  from  an  abscess  of 
a  central  incisor  appear  close  to  the  wang  of  the  nose. 

Occasionally  we  find  an  alveolar  abscess  discharging  on  mucous 
membranes   other  than  those  of  the  mouth  ;    such   cases    are   usually 

from  abscesses  situated  in  the  upper  jaw. 
I  have  three  times  seen  abscesses  at  the 
root  of  the  incisors  discharging  into  the 
nasal  cavity  (Fig.  497).  In  these  instances 
the  pus  passed  through  the  bone,  and  in 
each  instance  the  abscess-cavity  was  very 
large.  I  have  also  met  with  one  instance 
in  which  the  pus  from  an  anterior  tooth 
passed  back  beneath  the  mucous  mem- 
brane and  discharged  at  the  junction  of 
the  hard  and  soft  palate.  Several  cases 
of  this  kind  have  been  reported  in  dental 
literature.  Such  cases  are  liable  to  cause 
the  patient  much  trouble  before  a  correct 
diagnosis  is  made  unless  he  falls  under 
the  care  of  one  wdio  has  given  them  some 
special  study. 

The  relation  of  the  antrum  of  High- 
more  to  the  roots  of  the  teeth  (Fig.  498)  is  such  that  alveolar  abscess 
is  liable  to  discharge  into  that  cavity.  This  sinus  presents  great  vari- 
ations in  individual  cases.  In  some  there  is  a  heavy  lamina  of  bone 
betMcen  the  roots  of  the  teeth  and  the  cavity,  but  occasionally  a  case  is 
met  with  in  which  the  roots  of  the  teeth  actually  project  into  it,  being 
covered,  however,  by  a  very  thin  lamina  of  bone  in  addition  to  the 
nuicous  membrane ;  in  this  case  an  abscess  occurring  at  the  end  of  the 
root  will  inevital)ly  discharge  into  that  cavity.  This  will  sometimes 
produce  serious  complications,  especially  if  the  pus  is  not  freely  dis- 
charged by  way  of  the  nostril.  The  pus  may  also  find  its  way  into  this 
cavity  when  there  is  considerable  bone  between  it  and  the  root  of  the 
tooth  (Fig.  499). 


Alveolar  Abscess  at  the  Root  of  a  Su- 
perior Incisor  discharging  into  the 
Nose :  a,  large  abscess-cavity  in  the 
bone ;  6,  mouth  of  fistula  on  the  floor 
of  the  nostril ;  c,  lip ;  (/,  tooth. 


ABSCESS  OF  THE  ANTRUM. 


941 


By  far  the  larger  number  of  alveolar  abscesses  discharging  on  the 
face  are  situated  in  the  lower  jaw ;  this  is  undoubtedly  for  the  reason 
that  in  this  position  the  tendency  is  for  the  pus  to  be  carried  downward 


Fig.  498. 


Skull  with  the  Malar  Process  cut  away,  exposing  the  Antrum  of  Hlghniore,  and  with  the  Buccal 
Plate  of  the  Alveolar  Process  removed,  exposing  the  Roots  of  the  Teeth,  thus  showing  the  rela- 
tions of  the  Koots  of  the  Teeth  to  the  Antrum. 

by  gravitation.  The  greater  number  of  these  cases  occur  after  the  abscess 
has  at  one  time  opened  on  the  gum,  but  finally  has  discharged  so  little  pus 
that  the  fistula  has  closed.  Then  the  pus  that  remains  burrows  little  by 
little  in  the  direction  in  which  it  is  carried  by  gravitation,  until  it  finally 
finds  its  way  to  the  surface — usually, 
somewhere  along  the  lower  border 
of  the  inferior  maxilla.  As  show- 
ing how  insidious  this  creeping  of 
pus  may  be,  I  recall  a  case  in  which 
I  was  treating  an  abscess  at  the  root 
of  a  lower  incisor  for  a  patient  in  my 
own  house  ;  the  case  did  not  progress 
very  favorably,  but  after  a  few  weeks 
the  discharge  ceased  and  the  fistula 
closed.  Some  time  after  this,  when 
I  was  congratulating  myself  that  the 
cure  would  be  permanent,  the  patient 
one  day  called  my  attention  to  a  ''  lit- 
tle pimple  "  under  the  chin, 
am  illation,  I  found,  to  my  astonish- 
ment, that  the  abscess,  which  I  had 
thought  well,  had  found  a  new  out- 
let in  that  position,  the  pus  having 

.shown  in  Fig.  500.  This  had  occurred  so  quietly  that  the  patient 
had  discovered  no  unpleasant  symptoms,  though  I  had  now  and  then 
inquired  after  his  conditon.  This  is  a  form  seen  quite  frequently, 
as  compared  with  other  abscesses  opening  on  the  face.  These  may, 
however,  present  anywhere  on  the  face  belo\v  the  lip,  though  just  under 


On  ex-  Alveolar  Abscess  at  the  Root  of  an  L'pper  Mo- 
lar discharging  into  the  Antrum  of  High- 
more:  »,  abscess-cavity  in  the  bone;  6,  mouth 
of  listula  on  the  floor  of  the  antrum;  c,  pus 
in  the  antral  cavitv. 


followed  along  the  periosteum  as 


942 


DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 


the  chill  seems  to  be  a  favorite  point  for  them  to  open.     Another  form 
that  opens  at  the  same  place  I  have  illustrated  in  Fig.  501  ;  in  this  the 

Fig.  501. 


Fig.  500. 


Chronic  Alveolar  Abscess  at  the  Root  of 
a  Lower  Incisor  with  Fistula  discharg- 
ing on  the  Face  under  the  Chin  :  a,  ab- 
scess-cavity in  the  bone;  6,  b,  h,  fistula 
following  the  periosteum  down  to  the 
lower  margin  of  the  body  of  the  bone 
and  discharging  on  the  skin. 


Chronic  Alveobir  Abscess  of  the 
Root  of  the  Lower  Incisor  with 
Absce-ss-cavity  jjassing  throufih 
the  Body  of  the  Bone  and  dis- 
charging on  the  Skin  beneath 
the  C'hin :  n,  very  large  abscess- 
cavity  ;  f),  mouth  of  the  fistula. 


pus  has  burrowed  directly  through  the  body  of  the  bone.     Such  cases 
as  this  must,  I  think,  usually  occur  from  abscesses  that  were  chronic 

from  the  first — hli)id  abscesses, 
Fig.  502.  the  pus  from  whicli  has  never 

penetrated  the  outer  lamina  of 
bone  over  the  affected  root.  In 
such  a  case  the  pus  may  very 
readily  make  its  way  through 
the  body  of  the  bone,  in  obe- 
dience to  gravitation. 

This  class  of  cases  is  not  ne- 
cessarily confined  to  the  anterior 
part  of  the  lower  jaw,  but  may 
occur  at  any  point  from  angle 
to  auffle.  Fio;.  502  illustrates 
rather  an  unusual  case  that 
was  presented  to  me  some 
years  ago.  There  was  a  fis- 
tulous opening  just  beneath  the  body  of  the  lower  maxilla,  about  the  point 
where  the  facial  artery  crosses  over  the  bone  in  ascending  to  the  face  ;  this, 


Fistula  pa.ssing  down  through  the  Body  of  the  Lower 
Maxilla.    (See  page  943.) 


DIAGNOSIS   OF  ALVEOLAE  ABSCESS.  943 

the  patient  stated,  had  been  discharging  for  more  than  eight  years.  Early 
in  the  history  of  the  case  he  had  had  a  tooth  extracted,  with  the  view 
of  effecting  a  cure ;  but  the  operation  failed  of  its  purpose.  Following 
up  the  sinus  with  a  small  probe,  I  found  that  it  came  from  the  body  of 
the  bone,  and  iinally  detected  a  loose  substance.  On  carefully  taking 
the  direction  and  length  of  my  probe,  I  found  that  this  must  be  in 
the  position  formerly  occupied  by  the  roots  of  the  tooth  that  had  been 
extracted.  Examination  of  the  gums  at  the  point  revealed  nothing 
unusual ;  the  parts  seemed  healthy,  but  the  space  formerly  occupied  by 
the  now  missing  molar  seemed  to  be  as  wide  as  when  it  was  removed. 
I  dissected  off  the  soft  tissue,  and  found  what  seemed  to  be  very  solid 
bone ;  but  with  the  first  stroke  with  the  chisel  and  mallet  the  chisel 
passed  into  a  cavity.  In  this  cavity  I  found  a  piece  of  necrosed  bone 
that  from  its  form  seemed  to  be  the  septum  that  had  been  between  the 
roots  of  the  extracted  molar ;  this  bit  of  necrosed  bone  was  the  irritant 
that  had  kept  up  this  discharge  for  so  many  years. 

Alveolar  abscesses  opening  on  the  skin  are  not  confined  to  the  face, 
but  they  may  point  still  lower  down,  as  on  the  side  of  the  neck  as  far 
as  the  clavicle.  I  have  myself  seen  quite  a  number  that  had  opened  at 
one-third  and  one-half  the  distance  between  the  os  hyoides  and  the  clav- 
icle. A  route  often  taken  in  these  cases  is  for  the  pus  to  follow  the 
fibres  of  the  platysma  until  the  anterior  border  of  the  sterno-cleido- 
mastoid  is  reached,  and  there  come  to  the  surface.  It  is  only  occasion- 
ally that  this  point  is  passed,  and  then  the  pus  may  continue  its  bur- 
rowing as  far  as  the  clavicle.  This  is  apt  to  carry  it  well  out  toward 
the  shoulder. 

The  DIAGNOSIS  of  alveolar  abscess,  especially  the  acute  form,  does 
not  often  present  much  difficulty,  for  there  is  nearly  always  a  very  sore 
tooth  to  which  the  ])atient's  attention  has  been  strongly  directed.  The 
great  dread  of  having  a  tooth  extracted  wnll,  however,  often  cause  a 
patient  to  keep  that  important  fact  from  the  physician.  I  have  seen 
a  number  of  patients  who  would  say  they  had  had  no  toothache,  when 
a  tooth  was  so  sore  that  they  dared  not  close  the  teeth  together.  This 
fact,  however,  hardly  furnishes  an  excuse  for  treating  a  case  of  acute 
alveolar  abscess  as  one  of  erysipelas — an  error  in  diagnosis  which  more 
than  once  I  have  known  made ;  the  tumor  of  the  gum  is  usually 
present  and  the  general  appearance  of  the  swelling  is  quite  character- 
istic after  the  case  has  reached  a  stage  in  which  it  could  be  mistaken 
for  that  disease.  In  some  cases  it  might  be  confounded  with  subperios- 
teal inflammations,  but  these  are  more  liable  to  be  mistaken  for  alveolar 
abscess  when  they  occur  on  the  maxillary  bones.  Indeed,  I  have  seen 
some  cases  in  which  it  was  very  difficult  to  determine  whether  the  be- 
ginning of  the  trouble  w^as  with  the  periosteum  covering  the  bones  or 
in  the  sockets  of  the  teeth.  The  case  from  which  Fig.  503  was  made 
occurred  under  my  own  observation.  I  saw  it  early,  and  it  was  clearly 
a  case  of  subperiosteal  inflammation  having  its  beginning  just  below  the 
infraorbital  foramen.  Pus  had  evidently  formed  there,  but  the  patient 
very  positively  refused  to  have  anything  done ;  and  when  I  saw  him 
again,  a  few  days  later,  there  was  extensive  necrosis  that  carried  away 
four  teeth  with  a  considerable  piece  of  the  superior  maxilla,  laying  open 


944 


DISEASES   OF  THE  PERIDENTAL  MEMBRANE. 


/,jaa 


Loss  of  Bone  and  Teeth  from  Subperiosteal  Inflam 
mation. 


the  antrum  of  Hiiihmore.  The  discharge  of  pus  was  at  the  free  margin 
of  the  gum  ;  and  if  I  had  not  seen  the  case  early,  I  should  certainly  have 
taken  it  to  be  one  of  alveolar  abscess.  Except  as  a  matter  of  accuracy, 
this  error  would  tlien  have  been  of  no  importance ;  for  it  could  have 
made  no  diiference  in  the  treatment. 

Subperiosteal   inflammation    occurring    under  the   temporal   muscle, 

especially  if  it  be  in  the  temporal 
Fig.  503.  fossa,  will  usually  discharge  its 

pus  into  the  mouth  near  the  last 
molar  tooth  of  the  upper  jaw,  or 
it  will  appear  on  the  face  from 
under  the  zygomatic  arch ;  and 
if  the  case  be  somewhat  chronic, 
it  may  be  mistaken  for  alveolar 
abscess.  The  temporal  muscle  is 
covered  by  a  very  dense  fascia 
w^liich  prevents  the  pus  from  com- 
ing to  the  surface,  and  the  fibres 
of  the  muscle  will  carry  it  in  the 
direction  indicated.  In  two  cases 
I  have  met  with  there  was  very  lit- 
tle pain  complained  of  in  the  tem- 
poral region ;  both  were  fatal  from 
the  resulting  necrosis  of  the  skull. 
In  chronic  abscess  discharging  at  any  distance  from  the  teeth,  as  on 
the  lower  margin  of  the  lower  jaw  or  on  the  side  of  the  neck,  the 
chances  that  the  pus  may  come  from  some  small  point  of  necrosis 
should  always  receive  consideration.  I  have  twice  seen  such  cases,  in 
which  the  discharge  ^vas  in  the  same  region  in  which  we  usually  find  it 
when,  starting  from  alveolar  abscess,  the  pus  has  burrowed  into  the 
tissues  of  the  neck ;  in  both  of  these  cases  the  discharge  was  found  to 
be  caused  by  necrosis  of  the  ramus  of  the  lower  jaw.  In  the  search  for 
the  source  of  the  discharge  the  condition  of  the  teeth  will  often  materi- 
ally aid  us.  It  must  always  be  remembered  that  it  is  not  necessary 
that  a  tooth  be  decayed  or  in  any  wise  painful  in  order  that  it  may  be 
the  subject  of  chronic  abscess  ;  but  it  must  have  lost  its  pulp,  and  there- 
fore will  not  respond  to  the  tests  for  vitality  in  that  organ.  Such  a 
tooth,  also,  will  very  generally  show  a  change  of  color — will  be  a  shade 
or  several  shades  darker  than  the  teeth  that  are  healthy.  These  points, 
in  those  cases  in  which  the  teeth  are  all  seemingly  good,  will  generally 
serve  to  indicate  the  affected  tooth  and  aid  materially  in  tracing  the  pus 
to  its  source.  It  must  be  remembered,  also,  that  almost  precisely  the 
same  symptoms  may  arise  from  impacted  teeth;  discharges  from  these 
very  generally  occur  on  the  face  if  they  lie  deep  in  the  bone.  I  have 
.seen  quite  a  number  of  these  cases,  in  which  the  only  way  of  distin- 
guishing them  from  the  more  common  form  of  alveolar  abscess  was 
the  tracing  of  the  sinus  and  finding  in  this  way  the  impacted  teeth. 
The  TRE.VTMEXT  of  alvcoUu'  abscess  in  the  vast  majority  of  cases  pre- 
sents but  little  difficulty.  It  consi.sts  in  the  simple  cases  in  the  removal 
of  the  irritant  that  has  acted  as  the  cau.se — i.  e.  septic  matter  from  the 


TREATMENT  OF  ALVEOLAR   ABSCESS.  945 

pulp-chamber  of  the  affected  tooth.  If  the  case  has  occurred  at  the  apex 
of  a  worthless  crownless  root,  or  if,  from  any  cause,  the  tooth  cannot  be 
rendered  useful  if  retained,  the  proper  course  is  to  extract  at  once,  which 
ends  the  case.  This  is  true  though  the  abscess  be  of  long  standing  and 
though  the  pus  may  have  burrowed  to  a  great  distance.  Even  in  those 
cases  in  which  the  pus  is  discharging  on  the  side  of  the  neck  no  other 
treatment  is  necessary,  provided,  always,  that  there  are  no  spiculse  of 
necrosed  bone  to  keep  up  the  irritation.  Except  in  rare  cases,  extrac- 
tion is  not  necessary  to  a  cure ;  and  if  the  tooth  is  otherwise  in  a  con- 
dition to  be  useful  to  the  patient,  extraction  would  be  very  improper 
treatment. 

In  acute  cases  it  is  generally  best  to  evacuate  the  pus  as  early  as  pos- 
sible and  then  allow  the  parts  rest  until  the  extreme  soreness  of  the  tooth 
has  somewhat  abated  before  undertaking  further  treatment.  I  have 
already  detailed  the  treatment  of  apical  pericementitis.  Alveolar 
abscess  is  merely  such  a  case  gone  on  to  the  formation  of  pus ;  there- 
fore the  treatment  must  be  varied  to  suit  the  different  conditions  that 
have  arisen.  If  no  tumor  has  as  yet  formed  on  the  gum  over  the  root 
of  the  affected  tooth,  and  the  condition  as  to  soreness  will  allow  of  its 
being  done,  the  pulp-chamber  should  at  once  be  opened  and  the  canals 
of  the  root  cleared  of  their  contents,  in  order  to  allow  the  pus  to  escape 
through  the  tooth.  This  course  is  generally  better  than  to  make  an 
opening  through  the  outer  lamina  of  bone  with  instruments ;  for,  as  a 
rule,  the  pus  will  escape  by  way  of  the  pulp-canal  sufficiently  well  for 
all  practical  purposes.  If  the  pus  does  not  escape  at  once  on  opening 
the  pulp-chamber  and  root-canals,  a  delicate  instrument  should  be  passed 
through  the  apical  foramen,  in  order  to  remove  any  hindrance  that  may 
be  lodged  there.  In  a  minority  of  cases  the  pus  will  not  es/3ape  by 
this  route,  although  the  apical  orifice  may  be  open — for  the  reason, 
probably,  that  some  part  of  the  tissue  of  the  apical  space  covers  the 
foramen  as  a  valve,  preventing  outflow.  In  case  the  pus  escapes  read- 
ily in  this  way,  it  should  be  allowed  some  time — from  half  an  hour  to 
two  hours — to  discharge,  and  then  some  disinfectant  should  be  placed  in 
the  pulp-canal  on  a  pledget  of  cotton  and  the  cavity  sealed  so  tightly  as 
to  exclude  saliva.  After  this,  if  found  necessary,  the  tooth  may  be 
opened  from  time  to  time  for  the  discharge  of  pus  that  may  accumulate; 
but  in  the  majority  of  cases  this  will  not  be  required.  Such  cases  will 
usually  heal  at  once  or  within  a  short  time  without  other  treatment.  So 
general  is  this  that  it  has  become  my  habit  to  dismiss  these  cases  for  a 
week  or  ten  days,  advising  the  patients,  however,  to  consult  me  imme- 
diately if  they  have  a  return  of  pain ;  and  I  find  that  it  is  only  occa- 
sionally that  anything  further  is  required,  the  case  being  well  at  the 
next  visit  of  the  patient.  If  pain  should  recur,  it  is  because  more  pus 
has  collected,  and  all  that  is  necessary  is  to  open  the  tooth,  discharge  it, 
and  again  treat  as  before. 

In  case  the  pus  cannot  be  discharged  in  this  manner,  an  opening  to 
the  apical  space  should  be  made  as  directed  in  the  treatment  of  apical 
pericementitis  and  the  pus  discharged  in  this  way.  It  is  best  in  this 
class  of  cases  to  place  in  the  opening  made  in  the  gum  a  pledget  of 
cotton,  which  should  be  moistened  in  a   95-per-cent.  solution  of  car- 

VoL.  I.— 60 


946  DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 

bolic  acid.  This  will  prevent  the  wound  from  closing  and  save  the 
necessity  for  another  operation  should  the  abscess  not  heal  at  once. 

In  those  cases  in  which  the  external  lamina  of  the  bone  has  already 
been  penetrated  by  the  burrowing  of  the  pus  and  a  tumor  is  present  on 
the  gum  over  the  aifected  root,  it  is  best  to  discharge  it  at  once  with  the 
bistourv,  and  if  the  tooth  is  very  sore — which  is  almost  always  the 
case — not  to  open  the  pulp-chamber  until  the  soreness  has  somewhat 
abated.  In  this  case  it  is  especially  necessary  to  place  something  in  the 
opening  in  the  gum  to  keep  it  patulous,  for  the  fistula  should  not  be 
allowed  to  close  until  the  pulp-chamber  has  been  opened  and  the  root- 
canals  cleared  of  offensive  material.  Usually,  after  two  or  three  days 
the  soreness  will  have  so  moderated  that  the  pulp-chamber  may  be 
entered  without  very  much  pain.  This  should  be  done  as  early  as 
practicable  and  the  root-canals  properly  disinfected,  after  which  the 
opening  in  the  gum  should  be  allowed  to  heal.  This  class  of  cases, 
when  they  occur  in  patients  of  reasonably  good  health,  heal  with  great 
facility.  It  is  not  unusual  for  cases  in  which  the  intense  swelling  of  the 
parts  has  caused  the  utmost  distortion  of  the  features,  accompanied  with 
the  most  intense  pain  and  fever,  to  be  to  all  appearance  perfectly  well 
in  a  week  or  ten  days,  while  some  of  the  milder  forms  are,  so  far  as 
pain  and  soreness  are  concerned,  well  within  a  day  or  two. 

Constitutional  treatment  in  the  graver  forms  of  acute  alv^eolar  abscess 
should  not  be  overlooked  nor  neglected.  The  nature  of  the  affection  is 
not  such  that  it  can  be  cured  by  the  internal  administration  of  remedies, 
and  that  is  in  no  wise  the  object  of  medication,  but  rather  to  limit  the 
intensity  of  the  inflammatory  action  on  the  one  hand  and  to  promote  the 
healing  process  on  the  other.  It  may  also  have  for  its  object  the  mitiga- 
tion of  the  pain.  In  very  many  of  the  cases  that  present  themselves  for 
treatment  the  inflammatory  process  will  have  reached  its  heiglit — that 
is,  it  will  begin  to  abate  at  once — on  the  discharge  of  the  accumulation 
of  pus ;  and  in  this  case  nothing  can  be  done  by  the  use  of  internal 
remedies  to  limit  the  extent  of  the  inflammation.  This  has  been  an 
argument  against  the  use  of  internal  medication.  But  even  in  the  cases 
stated  internal  medication  may  still  save  portions  of  bone  from  necrosis 
by  the  more  ready  reduction  of  the  oedematous  swelling  and  the  quicker 
restoration  of  the  normal  circulation  of  the  parts. 

The  duration  of  the  inflammation  is  almost  as  important  a  factor  in 
the  production  of  necrosis  as  its  intensity ;  therefore  in  all  cases  of  con- 
siderable severity  of  the  inflammatory  process  the  local  treatment  should 
be  supplemented  with  an  active  saline  cathartic  as  an  aid  in  the  speedy 
reduction  of  the  oedema  and  induration  of  the  parts,  wdth  the  view  of 
the  quicker  restoration  of  the  normal  circulation  to  the  alveolar  borders 
and  such  other  tissues  as  may  be  endangered.  This  treatment  will  also 
contribute  much  to  the  comfort  of  the  patient  by  reducing  the  duration 
and  intensity  of  the  suffering.  I  do  not  insist  that  the  cathartic  should 
be  saline,  but  it  should  be  such  as  will  produce  large  watery  stools  and 
be  prompt  in  its  action.  If  thought  necessary,  an  opiate  may  also  be 
given  for  the  mitigation  of  the  pain.  In  many  cases  the  pain  continues 
very  severe  for  several  hours  after  the  discharge  of  the  pus  unless  coun- 
teracted by  this  form  of  medication.     After  the  cathartic  has  acted  it 


TREATMENT  OF  CHRONIC  ALVEOLAR  ABSCESS.  947 

should  usually  be  followed  by  a  stimulant  tonic ;  this  should  be  pre- 
scribed on  general  principles,  and  will  vary  with  the  individual  con- 
ditions of  the  patient.  If  his  general  health  is  fairly  good,  10  or  15 
grains  of  quinine  in  divided  doses  will  suffice.  If  the  patient  be 
ansemie,  one  of  the  salts  of  iron  should  be  added ;  and  in  cases  in 
which,  from  the  nature  of  the  case,  extensive  necrosis  is  thought  prob- 
able, the  treatment  should  be  especially  vigorous. 

All  fomentations  or  poultices  applied  to  the  face  should  be  strictly  for- 
bidden in  acute  alveolar  abscess,  for  the  reason  that  they  invite  an  opening 
on  the  face ;  and  if  any  softening  in  this  direction  is  discoverable,  the 
freest  opening  and  drainage  into  the  mouth  should  at  once  be  estab- 
lished over  the  affected  root,  with  the  view  of  preventing  such  a  result. 
In  this  matter  special  care  is  required  in  cases  of  the  second  form  occur- 
ring in  the  lower  jaw  (Fig.  488). 

If  the  treatment  of  the  acute  form  fails  of  its  object — the  cure  of  the 
abscess — the  case  soon  passes  into  the  chronic  form,  which  will  now  be 
considered. 

The  TREATMENT  of  chrouic  alveolar  abscess  presents,  in  some  of  its 
phases,  characteristic  differences  from  the  treatment  of  the  acute  forms. 
There  is  generally  no  soreness  or  any  considerable  inflammation  to  con- 
tend with.  The  treatment  is  therefore  more  purely  local  and  relates 
more  especially  to  the  removal  of  the  cause  perpetuating  the  discharge 
of  pus — indeed,  I  may  say  wholly  to  this  ;  for  if  the  cause  be  removed, 
the  tendency  is  to  a  spontaneous  cure.  Cases  are  sometimes  presented 
to  the  practitioner  in  which  the  systemic  conditions  are  so  depraved 
and  recuperative  power  is  so  low  that  an  abscess  will  not  heal  without, 
in  addition  to  local  treatment,  the  use  of  remedies  directed  to  the  im- 
provement of  the  general  health. 

With  reference  to  local  treatment,  chronic  alveolar  abscess  is  best 
divided  into  five  forms,  according  to  the  conditions  present  in  the  apncal 
space : 

1st.  The  simple  form.  In  this  the  tissue  of  the  apical  space  has  not 
been  so  injured  as  to  prevent  a  ready  and  spontaneous  cure  upon  the 
removal  of  the  fetid  contents  of  the  pulp-chamber. 

2d.  Cases  in  which  injury  to  the  tissue  of  the  apical  space  has  been 
so  great  as  to  prevent  its  taking  on  a  healthy  action  readily,  or  in  which 
it  has  been  actually  destroyed  over  a  portion  of  the  apical  end  of  the 
root. 

3d.  Cases  in  which  the  tissue  at  the  apical  end  of  the  root  has  been 
destroyed  and  serumal  calculus  has  been  deposited  on  the  denuded 
portion. 

4th.  Septic  abscess. 

5th.  Cases  complicated  with  necrosis  of  bone. 

The  diagnosis  of  these  diiFerent  forms  is  not  always  easily  made,  for 
the  reason  that  the  apical  space  is  not  accessible  for  this  purpose  without 
either  considerably  enlarging  existing  openings  or  making  a  sufficient 
opening  artificially ;  and  if  the  abscess  be  of  either  the  first  or  the  second 
form — as  may  be  expected  in  a  great  majority  of  cases — this  is  entirely 
unnecessary  and  may  do  harm.  All  that  can  be  gained  by  an  exam- 
ination of  the  apical  end  of  the  root  is  to  ascertain  if  serumal  calculus 


948  DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 

is  deposited  upon  it  or  to  learn  whether  or  not  the  walls  of  the  alveolus 
are  necrosed.  In  case  the  apical  opening  is  sufficiently  large  to  do  this 
readily  without  very  material  disturbance  of  the  parts,  it  may  be  done 
at  once ;  otherwise,  the  treatment  should  be  begun  with  the  idea  that 
the  case  is  of  the  simple  form. 

The  treatment  of  the  simple  form  of  alveolar  abscess  consists  merely 
in  removing  tiie  debris  from  the  pulp-chamber  and  root-canals  of  the 
affected  tooth  and  thoroughly  disinfecting  them.  For  this  purpose  the 
pulp-chamber  should  be  well  opened  with  the  drill  and  burr,  no  matter 
whether  the  tooth  be  much  or  little  decayed  or  whether  it  be  decayed  at 
all,  so  that  free  access  shall  be  obtained  to  the  canals ;  and  then  these 
must  be  well  cleaned  with  the  broach.  The  enlargement  of  the  canals 
in  the  roots  of  teeth  with  any  sort  of  drill  is  not  to  be  recommended  ;  the 
chances  are  that  it  will  do  more  harm  than  good.  Indeed,  in  those 
cases  in  which  it  can  be  done  safely  it  is  not  needed,  and  where  it  is 
needed  it  cannot  be  done  safely.  I  have  seen  so  much  harm  from 
this  procedure  that  I  feel  that  I  cannot  too  strongly  condemn  it. 

AVhen  the  root-canals  are  well  cleaned  with  the  broach,  they  should 
be  bathed  with  a  good  antiseptic  and  a  pledget  of  cotton  moistened 
with  an  antiseptic  lotion  placed  in  the  root-canals  and  then  the  cavity 
in  the  tooth  temporarily  filled,  but  in  such  a  way  that  the  entrance  of 
the  fluids  of  the  mouth  will  be  thoroughly  prevented.  With  this  the 
patient  should  be  discharged  for  a  week  or  ten  days,  to  give  time  for 
the  spontaneous  cure  of  the  case.  The  rule  is  that  at  the  next  visit  of 
the  patient  the  abscess  will  be  healed.  As  to  the  medicament  used  to 
disinfect  the  root-canals  in  these  cases,  I  have  found  that  it  makes  but 
little  difference  what  is  used,  so  that  it  accomplishes  that  one  purpose 
well.  Carbolic  acid,  eucalyptus,  iodine,  salicylic  acid,  creasote,  iodoform, 
and  various  other  antiseptics,  seem  to  answer  equally  well.  In  some 
cases  in  which  there  is  a  large  quantity  of  pus,  and  especially  if  it 
be  rather  offensive  in  character,  it  is  well  to  wash  out  the  whole 
tract  of  the  abscess  thoroughly  at  the  first  sitting.  This  is  best  done 
by  means  of  Farrar's  syringe,  but  any  other  syringe  with  a  suitable 
nozzle  may  be  used.  This  having  been  charged  with  the  fluid,  its  noz- 
zle is  introduced  as  far  into  the  canal  as  may  be  necessary,  and,  having 
all  dry,  is  sealed  in  place  with  a  piece  of  warmed  gutta-percha  and  the 
contents  of  the  syringe  forced  through  the  apical  foramen  and  out  at 
the  fistulous  opening.  The  fluids  best  suited  to  this  purpose  are  sul- 
])!un'ic  ether  and  peroxide  of  hydrogen.  I  have  used  sulphuric  ether 
for  many  years,  and  have  always  been  pleased  with  it ;  it  cleans  the 
parts  well  and  seems  to  have  a  very  valuable  stimulating  effect  on 
the  tissues.  Since  the  introduction  of  the  peroxide  of  hydrogen  to  the 
profession  by  Dr.  A.  W.  Harlan  of  Chicago  I  have  made  considerable 
use  of  it  for  the  purpose  of  thoroughly  cleaning  abscesses,  and  find  it 
to  take  a  place  not  filled  by  any  other  drug  at  our  command.  When 
introduced  into  an  abscess-cavity,  oxygen  is  liberated,  producing  an 
expansion  of  twelve  times  the  volume  of  the  liquid  ;  thus  a  small 
amount  of  the  drug  will  with  its  effervescence  expel  the  contents  of  a 
large  abscess.  It  is  for  this  reason  especially  fitted  for  cleaning  blind 
abscesses,  into  which  a  little  of  the  drug  may  be  forced  through  the 


TREATMENT  OF  ALVEOLAR  ABSCESS.  949 

root-canal.  After  the  wasliing  is  completed  the  pulp-canals  should  be 
filled  with  cotton  saturated  \vith  a  disinlectant,  and  the  cavity  temporarily 
filled  as  directed  above. 

In  any  of  the  forms  of  alveolar  abscess  cases  will  occur  in  which  it 
will  be  impossible  to  open  the  apical  foramen  and  gain  access  to  the 
abscess  by  that  route.  This  is  always  to  be  regretted,  as  the  treatment 
succeeds  best  when  directed  through  the  canals ;  but  in  such  cases  the 
medicaments  may  with  a  fair  degree  of  success  be  applied  through  the 
fistulous  opening  by  injection  with  Farrar's  or  other  suitable  syringe. 
The  nozzle  of  the  syringe  should,  if  practicable,  be  carried  through  the 
fistula  directly  to  the  apex  of  the  root. 

For  some  years  I  have  quite  largely  used  the  following : 

Take  of  Oil  of  cinnamon,  1  part ; 

Carbolic  acid  (crystals),  2  parts  ; 
Oil  of  gaultheria,  3  parts.      Mix. 

This  I  use  in  those  cases  that  require  a  stimulant  disinfectant.  The 
compound  seems  to  possess  properties  quite  different  from  carbolic  acid. 
It  may  be  used  freely  on  the  mucous  membranes  of  most  persons  with- 
out the  least  danger  of  producing  an  eschar.  Its  antiseptic  properties 
are  sufficient  for  use  in  the  pulp-chamber  and  root-canals.  But  its 
principal  use  is  as  a  stimulant  antiseptic  to  tissues  that  have  lost  their 
tone  from  long-continued  inflammation ;  hence  it  is  especially  useful  in 
the  second  form  of  chronic  abscess.  It  may  be  injected  into  the  apical 
space  without  danger  of  destroying  tissue.  It  may  be  diluted  with  oil 
of  lemon  or  oil  of  anise. 

If  after  a  week's  time  the  fistulous  opening  should  still  be  maintained, 
or  in  case  of  blind  abscess  pus  should  appear  on  opening  the  root,  the 
treatment  should  be  repeated.  If  the  abscess  does  not  heal  in  the  course 
of  another  week  or  ten  days,  it  may  be  regarded  as  belonging  to  the 
second  class,  or  possibly  to  the  third  ;  and  an  examination  may  now  be 
made,  to  ascertain  whether  or  not  there  is  a  deposit  of  serumal  calculus 
on  the  end  of  the  root.  Whether  this  should  be  done  or  not,  however, 
will  depend  on  conditions  that  must  be  decided  in  each  case  for  itself. 
If  there  is  no  such  deposit,  the  case  will  generally  heal  after  time  is  given 
for  the  recuperation  of  the  tissues  of  the  apical  space.  A  stimulating 
treatment  is  indicated.  Caustics  can  do  no  good,  but,  on  the  con- 
trary, may  destroy  what  tissue  remains.  It  is  true  that  such  cases 
will  often  get  well  after  the  use  of  caustics,  but  my  experience  is 
that  they  will  require  more  time  than  if  the  caustics  were  not 
used.  My  observation  is  that  too  much  is  done  for  these  cases  by 
many  operators.  The  main  thing  is  to  keep  them  clean  and  give 
them  a  chance  to  get  well. 

If  the  case  does  not  heal  within  a  reasonable  time,  the  examination 
for  deposits  of  serumal  calculus  should  be  made.  An  opening  should 
be  effected  or  the  existing  fistula  should  be  sufficiently  enlarged  for  an 
examination  of  the  root ;  and  if  calculus  be  found,  it  should  be  thor- 
oughly removed  with  suitable  instruments.  There  is  positively  no 
chance  for  the  case  to  heal  as  long  as  any  of  this  deposit  remains.  It 
is  better  to  cut  away  the  end  of  the  root  than  to  leave  the  least  trace  of 


950  DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 

the  deposit.  After  the  calcukis  has  been  removed  in  a  satisfactory 
manner  the  case  sliould  again  be  left  to  itself  to  heal,  simply  keeping 
the  parts  clean.  The  prognosis  in  such  cases  is  always  doubtful ;  the 
greater  number  of  them  will  recover,  but  some  will  be  found  in  which, 
no  matter  what  the  treatment,  there  will  be  no  reattachment  of  the 
tissue  to  the  root.  This,  however,  is  rare.  When  we  remember  that 
Hunter  boiled  teeth  for  replantation,  and  yet  obtained  a  union  of  the 
pericementum  to  the  root  of  the  tooth,  we  should  expect  such  cases  to 
reform  the  lost  membrane  and  get  Avell. 

In  the  fourth  class  of  abscesses,  in  which  there  is  a  discharge  of  a 
thin,  watery,  and  offensive  pus  occasionally  tinged  with  blood,  con- 
nected with  a  more  or  less  rapid,  but  marked,  destruction  of  tissue,  a 
more  heroic  treatment  is  required.  In  these  cases  there  is  a  condition 
not  ordinarily  found  in  alveolar  abscess.  It  is  not  kept  up  simply  by  the 
escape  of  septic  matter  from  the  pulp-cliamber  of  the  tooth,  but  is  a  true 
septic  abscess,  in  which  the  poisonous  material  is  being  produced  among 
the  tissues  themselves.  For  a  remedial  effect  on  this  the  strongest  anti- 
septics are  needed.  The  whole  abscess  should  be  injected  with  either  a 
95-per-cent.  solution  of  carbolic  acid,  strong  tincture  of  iodine,  or 
ethereal  solution  of  iodoform.  The  injection  should  be  repeated  per- 
liaps  twice  within  four  days.  The  object  in  this  treatment  is  to  destroy 
this  septic  condition,  and  thus  to  convert  the  abscess  into  the  simpler 
form ;  and  as  soon  as  that  is  accomplished  the  severe  measures  should 
be  suspended  and  milder  treatment  substituted.  This  class  of  abscesses 
will  give  the  most  unsatisfactory  results  of  any  that  are  met  with  in 
practice.  There  is  generally  a  comparatively  great  destruction  of  tis- 
sue, and  a  correspondingly  long  time  is  required  for  the  healing  pro- 
cess. In  the  mean  time,  the  case  will  require  constant  care  to  keep  the 
parts  in  good  condition. 

Abscesses  that  are  complicated  with  necrosis  of  the  alveolar  process 
require  special  care  in  their  treatment.  If  this  lesion  is  discovered 
early  in  the  case,  the  parts  should  be  well  cared  for  until  by  the  nat- 
ural process  of  the  absorption  the  necrosed  portions  are  loosened  ;  they 
should  then  be  carefully  removed.  I  have  learned  by  clinical  experi- 
ence that  much  of  an  alveolar  process  may  be  destroyed  by  necrosis 
from  inflammation  without  necessarily  destroying  the  hope  of  saving 
the  tooth.  ]\Iany  of  those  cases  that  present  a  very  bad  appearance 
heal  with  surprising  facility  with  a  little  care.  In  Fig.  488  I  have 
represented  a  case  in  which  the  outer,  or  buccal,  plates  of  the  alveolar 
process  Avere  destroyed  from  an  alveolar  abscess,  with  more  than  half 
of  the  septum  between  two  of  the  teeth  ;  and  yet  those  teeth  are  in  very 
good  condition  to-day,  eight  years  after  the  occurrence.  The  sketch  was 
made  at  the  time  the  necrosed  portions  of  the  bone  were  removed,  and 
as  nearly  as  possible  represents  the  actual  condition  of  the  case.  The 
treatment  may  be  very  briefly  related.  Before  the  pieces  of  necrosed 
bone,  were  loose  enough  to  be  removed  the  teeth  were  found  to  be  so 
loose  that  it  was  thouglit  best  to  wire  them  together  and  to  their  neigh- 
Iwrs,  to  prevent  motion.  The  parts  were  kept  well  cleaned  by  use  of 
the  syringe.  As  soon  as  it  was  practicable  the  necrosed  portions  were 
removed.    Between  two  of  the  teeth  the  septum  of  necrosed  bone  passed 


TREATMENT  OF  ALVEOLAR  ABSCESS.  951 

SO  far  toward  the  lingual  side  that  I  had  some  trouble  in  removing  it 
without  disturl:>ing  the  teeth,  and  in  all  the  teeth  the  necrosed  portion 
extended  over  the  apices  of  the  roots.  The  removal  being  accomplished, 
the  soft  tissues  were  laid  in  place  over  the  roots,  and  maintained  by  a 
stitch  passed  around  the  central  tooth  of  the  series.  Mild,  stimulating 
antiseptic  washes  were  used  with  the  syringe  daily  until  the  discharge 
of  pus  ceased  :  this  was  in  about  a  week,  and  the  case  was  then  gradu- 
ally left  to  itself.  A  short  time  ago  this  patient  allowed  me  to  pass  a 
small  exploring-instrument  in  various  directions  through  the  tissues 
over  the  site  of  the  former  necrosis,  and  I  found  the  alveolar  process 
completely  restored. 

In  most  cases  of  necrosis  of  the  alveolus  where  I  have  seen  the  patient 
daily  I  have  succeeded  in  obtaining  a  restoration  of  the  part,  but  it 
requires  constant  care.  If  the  management  of  dressings,  etc.  is  left  to 
the  patient,  failure  will  generally  result,  for  the  reason  that  the  parts 
become  more  or  less  septic,  and  instead  of  healthy  granulations  there 
is  destruction  of  tissue.  Where,  however,  the  necrosis  is  less  extensive, 
recovery  is  brought  about  with  much  more  facility.  In  all  these  cases 
the  condition  of  the  pulp-chambers  of  such  teeth  as  have  lost  their 
pulps  should  receive  prompt  attention,  to  prevent  the  discharge  of 
poisonous  matter  by  way  of  the  apical  foramen. 

In  those  cases  discharging  on  the  face  there  is  not  necessarily  any 
difference  in  the  treatment  of  the  abscess  itself,  but  in  the  very  begin- 
ning of  the  treatment  the  sinus  should,  if  its  situation  is  such  as  to 
make  this  possible,  be  cut  off  as  near  as  practicable  to  the  root  of  the 
tooth  and  the  pus  directed  into  the  mouth.  The  sinus  will  then  heal 
without  further  treatment,  and  the  abscess  is  to  be  treated  as  usual.  In 
some  rare  cases  there  may  be  a  spicula  of  necrosed  bone  in  the  course 
of  the  sinus ;  this  may  have  floated  into  it  from  the  alveolus  and  lodged 
in  a  narrower  part,  or  it  may  have  come  from  a  slight  necrosis  of  bone 
that  the  pus  has  uncovered  in  its  burrowings.  Any  such  source  of 
irritation  as  this  will,  until  it  is  removed,  prevent  the  healing  of  the 
sinus. 

In  the  treatment  of  these  cases  many  complications  will  arise  that 
will  tax  the  ingenuity  of  the  operator.  Some  time  ago  I  found,  in 
a  case  of  abscess  at  the  root  of  a  lower  incisor,  that  the  pus  had  bur- 
rowed down  the  anterior  surface  of  the  lower  jaw  to  the  point  of  the 
chin,  though  the  fistulous  opening  was  still  maintained  on  the  gum  in 
the  usual  position.  The  abscess  was  of  the  second  class,  and  did  not 
heal  readily.  I  found  great  difficulty  in  preventing  the  pus  from  drop- 
ping into  the  pocket,  and,  fearing  that  it  would  come  through  the  skin, 
I,  after  unsuccessfully  trying  several  expedients,  finally  passed  a  bis- 
toury carefully  down  the  length  of  the  pocket  and  made  a  considerable 
cut  as  close  to  the  bone  as  possible,  laterally,  on  both  sides  of  the  sinus. 
I  then  put  a  compress  on  it  for  two  days,  so  arranging  it  as  not  to  hin- 
der the  escape  of  the  pus  on  the  gum.  This  produced  enough  adhesive 
inflammation  in  the  parts  to  close  the  sinus  at  once.  Afterward  the 
abscess  healed  by  the  slow  process  usual  in  such  cases.  In  all  cases  of 
this  kind  the  ingenuity  of  the  operator  must  be  depended  upon  to  over- 
come the  difficulties  that  may  present  themselves.    No  set  rules  to  accom- 


952 


DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 


plish  this  can  be  given  for  them,  for  the  reason  that  all  the  conditions 
cannot  be  foreseen ;  and  if  rnles  were  given,  the  intelligent  dental  sur- 
geon would  be  likely  to  follow  methods  of  his  own  devising  in  each 
case  as  presented. 

The  general  rule  is  that  the  sinus  will  need  no  attention  after  the 
abscess  has  healed.  It  often  makes  a  very  ugly  scar  ;  but  if  this  is 
under  the  chin,  it  will  not  be  much  exposed  to  view,  and  if  on  the  neck 
may  be  covered  by  the  clothing.  If  on  the  face,  however,  there  will  be 
disfigurement ;  each  case  must  be  studied  with  the  view  of  lessening 
this  as  much  as  possible.  The  cord  formed  by  the  healing  and  contrac- 
tion of  the  sinus  is  always  somewhere  attached  to  the  bone,  and  it  will 
often  draw  in  the  tissues  in  such  a  way  as  to  be  very  unsightly.  This 
is  especially  the  case  when  the  abscess  has  pointed  just  under  the  prom- 
inence of  the  malar  bone  in  front  of  the  attachment  of  the  raasseter 
muscle.  In  this  case,  if  the  finger  is  thrust  into  the  mouth  and  a  pull 
made  outward  against  the  scar,  the  round  cord  by  M^hich  it  is  held  down 
to  the  bone  will  be  plainly  felt.  Now  a  tenotomy-knife  may  be  passed 
in  through  the  tissues  of  the  cheek,  and  while  a  strong  pull  is  being 
made  on  the  cord  it  may  be  cut  off  where  it  is  attached  to  the  bone ; 
this  will  allow  the  cheek  to  come  out  to  its  proper  fulness  at  once. 
Then  a  pin  may  be  passed  through  the  central  part  of  the  scar  and  left 

lying  against  the  face,  to  keep  it 
lio.  o04.  jj^  ^j^^^  position  until  the  wound 

heals.     This  little  procedure  will 
greatly    diminish    the    deformity, 
ini  ^^^^^y  but  will  not  entirely  eradicate  the 

"^T^Av  ^"^^^^^^^^^^^^^^x  ®^^^   (-^^^-   '^0^)-     ii^   some   such 

way  most  of  the  cases  where  the 
scar  is  badly  drawn  inward  may 
be  improved. 

Finally,  the  case  must  be  put  in 
condition  to  prevent  the  recurrence 
of  abscess.  To  do  this,  the  con- 
tamination of  the  tissues  of  the 
apical  space  with  poisonous  mate- 
rial from  the  pulp-chamber  of  the 
affected  tooth  must  be  rendered 
impossible ;  this  is  effected  by  fill- 
ing the  root-cfinals  and  pulp-chamber  with  some  enduring  material. 
The  requirements  of  a  material  for  this  purpose  are  threefold — first, 
that  it  shall  be  enduring,  that  it  shall  neither  absorb  moisture  nor  be 
sul)ject  to  solution  in  any  of  the  fluids  of  the  body  ;  second,  that  it  shall 
be  unirritating  to  tissues  with  which  it  may  be  brought  in  contact ; 
third,  that  it  shall  be  capable  of  such  manipulation  that  the  root-canals 
can  be  perfectly  and  solidly  filled  with  it.  Many  materials  have  been 
j)roposcd  from  time  to  time  for  this  purpose,  but  of  them  all  only  two 
seem  to  me  to  possess  these  qualities  in  a  sufficient  degree  to  recommend 
them  for  the  ]Mn']5ose  ;  these  are  gold  and  gutta-percha.  The  gold  meets 
the  first  two  requirements  most  perfectly,  while  the  gutta-percha — 
which  was  first  recommended  for  this  purpose  by  Dr.  O.  A.  Glidden  at 


Illustration  of  Operation  for  the  Remedy  of  Scar 
on  the  Face  caused  by  Alveolar  Abscess.  (See 
p.  940.    Compare  with  Figs.  490,  495,  and  496.) 


DISEASES  OF  THE  PERIDENTAL  MEMBRASE,  ETC.         953 

the  meeting  of  the  Illinois  State  Dental  Society  of  1873 — is  superior  to 
it  in  the  last.  It  seems  Avell  demonstrated  that  either  of  these  materials 
can  be  so  manipulated  as  to  make  a  thoroughly  solid  root-filling,  but  in 
very  delicate  and  tortuous  canals  the  gutta-percha  can  be  more  easily 
forced  to  the  apex  than  the  gold.  When  the  pulp-chamber  and  root- 
canals  are  solidly  filled  with  either  of  these,  the  possibility  of  the  forma- 
tion of  septic  matter  within  them  is  at  an  end.  The  methods  of 
manipulation  by  which  the  filling  is  accomplished  belong  rather  to  the 
ojjerative  department,  and  their  consideration  in  detail  here  would  occupy 
too  much  space. 

The  time  at  which  a  permanent  root-filling  should  be  made  is  an 
important  consideration  which  must  depend  on  the  judgment  of  the 
operator  in  each  individual  case.  Except  in  some  peculiar  cases,  the 
healino;  of  the  abscess  should  be  assured  before  the  filling;  is  undertaken: 
it  is  best  that  the  abscess  be  actually  Avell.  When  the  operator  is  as- 
sured of  this,  the  sooner  the  root  is  filled,  the  better.  In  those  cases  in 
which  the  apex  of  the  root  is  cut  away  in  order  to  remove  from  its  dis- 
tal side  the  last  traces  of  a  deposit  of  serumal  calculus,  it  is  probably 
best  to  fill  the  root  at  once,  for  the  reason  that  the  foramen  may  be  cut 
to  a  })oint  where  it  is  rather  large ;  if  the  root  is  at  once  filled,  any 
material  that  is  forced  through  into  the  apical  space  can  readily  be 
removed  and  the  end  of  the  root  made  smooth.  Otherwise  than  in 
some  such  case  as  this  the  filling  of  the  root  before  the  abscess  is  well 
is  not  to  be  recommended.  The  principal  reason  for  delay  is  the  fact 
that  the  best  means  of  treatment  is  through  the  open  root-canals ;  there- 
fore this  avenue  should  not  be  closed  until  the  operator  is  assured  that 
it  will  no  longer  be  needed. 


Diseases  of  the  Peridental  Membrane  having  their  Begin- 
ning AT  THE  Margin  of  the  Gum. 

This  group  of  diseases  has  generally  been  passed  over  without  very 
accurate  description  by  authors  who  have  written  on  the  subject  in  past 
years.  They  have  universally  been  grouped  together  under  one  name 
without  clifFerentiation.  This  name  has  varied  with  the  different  writers 
to  such  an  extent  that  in  looking  over  the  literature  of  the  subject  we 
find  almost  as  many  names  as  authors.  Spongy  gums,  inflammation  of 
the  gums,  scurvy  of  the  gums,  false  scurvy,  diseased  gums,  gingivitis, 
pericementitis,  suppurati\'e  inflanmiation  of  the  gums,  pyorrhoea  alveo- 
laris,  odontolithus,  etc.,  are  among  the  terms  most  commonly  used.  The 
descriptions  of  this  class  of  affections  as  given  in  works  on  dental  sub- 
jects have  generally  been  very  short  and  imperfect,  and  even  to-day  I 
know  of  no  book  or  writing  that  can  be  said  to  give  a  complete  treat- 
ment of  this  branch  of  pathology.  There  have,  however,  appeared  in 
the  journals  during  recent  years  a  number  of  very  important  papers 
treating  of  special  phases  of  the  subject  which  have  had  the  effect  of 
calling  general  attention  to  and  of  awakening  interest  in  it-  In  this 
work  Dr.  J.  M.  Riggs  of  Hartford,  Conn.,  has  very  justly  the  credit  of 
having  taken  the  initiative.  Others  had  treated  of  the  subject  before 
Dr.  Riggs,  but  this  gentleman,  by  rej)eatedly  calling  attention  to  it  in 


954  DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 

society  meetings,  at  the  same  time  illustrating  it  by  clinical  operations, 
succeeded  in  awakening  the  general  interest  of  tlie  profession.  AVhat- 
ever  we  may  now  think  of  Dr.  Riggs's  explanation  of  the  pathology 
of  this  class  of  lesions  or  of  his  method  of  treating  them,  he  deserves 
the  profound  gratitude  of  the  profession  for  what  he  has  done.  Unfor- 
tunately, Dr.  iliggs  has  not  left  much  in  our  literature  on  the  subject, 
his  communications  having  been  oral,  not  written.  And  there  is  but 
little  in  the  works  of  previous  writers  tiiat  will  be  available  to  me  in 
the  preparation  of  this  portion  of  the  paper ;  but  of  what  I  find  I 
shall  make  free  use,  especially  of  what  I  have  from  time  to  time  written 
myself  The  classification  I  have  given  at  the  beginning  of  this  paper 
may  be  imperfect  and  the  growing  knowledge  of  the  profession  may  in 
time  suggest  improvement,  but  for  the  present  it  seems  to  be  the  best 
that  presents  itself,  and  I  give  it  with  the  hope  that  it  will  be  useful  in 
the  future  study  of  this  very  important  subject — a  subject  that  has 
hitherto  been  neglected  to  an  extent  hardly  creditable  to  the  dental  pro- 
fession. 

It  has  seemed  to  me  that  the  time  has  come  when  the  old  names 
should  be  dropped  and  others  introduced  that  are  more  in  harmony 
with  what  is  now  known  of  the  pathological  conditions  present  in  each 
case.  This  I  acknowledge  to  be  a  difficult  task,  but  it  is  absolutely 
necessary  to  accuracy.  It  cannot  be  expected  that  the  profession  at 
large  will  have  definite  ideas  of  these  diseases  until  we  have  definite 
descriptions  under  definite  names.  In  other  words,  so  long  as  the 
nomenclature  and  writings  on  a  given  subject  are  vague  and  indefinite, 
so  long  will  men's  ideas  of  that  subject  be  indefinite.  The  term  gingi- 
vitis I  limit  to  those  inflammations  of  the  gingivae  that  occur  from  con- 
stitutional causes  or  the  lighter  forms  of  inflammation  from  soft  deposits 
on  the  teeth.  It  may  be  argued — and  justly — that  all  of  the  diseases 
of  this  class  begin  with  an  inflammation  of  the  gingivae ;  but  when 
another  factor  has  entered  into  the  case,  probably  in  its  inception,  it  is 
jiroper  that  that  factor  should  be  expressed ;  hence  the  term  calcic  in- 
flammation, expressive  directly  of  the  nature  of  the  cause  that  perpet- 
uates the  disease.  This  is  seen  in  two  forms — serumal  calculus  and 
salivary  calculus ;  but  as  these  relate  to  the  origin  of  the  calculus 
that  induces  the  inflammation  rather  than  to  the  character  of  the 
inflammation  itself,  and  as  the  two  are  very  often  blended  together 
in  the  same  case,  it  has  hardly  seemed  to  call  for  a  separate  name. 

In  the  term  phagedenic  pericementitis  I  have  again  expressed  the 
most  prominent  factor  of  the  affection  that  is  at  the  present  time  defi- 
nitely determined — its  destructive  character.  It  is  true  that  the  calcic 
form  is  destructive,  but  not  to  the  same  extent.  This  disease  is,  in  my 
opinion,  caused  by  a  specific  form  of  micro-organism,  but  this  has  not 
been  determined  with  sufficient  accuracy  to  justify  a  name  expressive 
of  that  conce])tion.  If  in  the  future  this  should  be  determined  with 
that  definiteness  demanded  by  science,  a  nomenclature  should  be 
ado]>ted  expressive  of  the  fact. 

The  names  heretofore  in  use  have  been  applied  to  the  entire  group  of 
diseases,  and  among  them  no  distinctions  have  been  made ;  the  most  of 
them  are  now  no  longer  used.     The  term  pyorrhoea  alveolaris  expresses 


GINGIVITIS. 


955 


Fig.  505. 


one  fact  common  to  all  of  these  forms  after  they  have  made  consider- 
able progress,  including;  alveolar  abscess  as  well — a  flow  of  pus  from  the 
alveolus.  It  must  be  seen  by  all  that  when  we  come  to  a  classification 
of  these  affections  this  term  loses  all  distinctiveness  and  cannot  be  of 
use.  Possibly  this  name  might  be  retained  as  expressive  of  the  whole 
group  of  diseases  in  which  there  is  a  flow  of  pus  from  the  alveolus,  but 
this  could  not  be  of  much  value ;  especially  is  it  objectionable  after  the 
use  that  has  been  made  of  it  in  the  past.  I  therefore  think  it  best  to 
drop  it  altogether. 

Cringivitis. — Before  entering  upon  the  study  of  gingivitis  and  that 
group  of  diseases  having  their  beginnings  at  the  gingival  margin  of  the 
gums  it  may  be  well  to  call  attention  to  the 
structure  and  functions  of  the  pai'ts.  What 
are  known  as  the  gingivce,  or  gingival  margins 
of  the  gums,  are  those  parts  of  the  soft  tissues 
that  immediately  surround  the  necks  of  the 
teeth  and  are  in  conjunction  with  them — the 
free  margin  of  the  gum  (Fig.  505). 

The  exposed  surface  of  the  free  margin  of 
the  gum  is  covered  with  a  very  dense  squa- 
mous epithelium  which  fits  it  well  to  withstand 
the  severe  abrading  contact  with  food  necessary 
in  the  act  of  mastication.  This  rests  upon  a 
layer  of  softer  epithelial  cells,  which  cover  a 
series  of  papillae  projected  from  the  fibrous 
tissue  beneath  as  a  glove  covers  the  fingers ; 
the  whole,  M'hen  in  the  normal  condition,  rests 
on  the  rim  of  the  alveolus  and  is  drawn  snugly 
around  the  neck  of  the  tooth,  forming  a  strong, 
resistant,  yet  flexible,  cushion  to  the  tissues 
which  it  protects.  It  is  also  strongly  at- 
tached to  the  neck  of  the  tooth  and  periosteum 
of  the  wall  of  the  alveolus  by  radiating  bun- 
dles of  fibrous  tissue  that  have  become  known 
as  the  dental  ligament.  In  health  this  attach- 
ment to  the  tooth  is  from  one-eighth  to  three- 
eighths  of  an  inch  from  the  extreme  edge  of 
the  free  margin,  varying  somewhat  in  different 
persons  and  about  the  different  teeth  of  the 
same  person  and  the  different  surfaces  of  the 
individual  teeth.  That  part  of  the  gingival 
margin  that  lies  in  against  the  neck  of  the 
tooth  is  of  a  different  structure  from  its  other 
parts.  Here  it  is  clothed  w'ith  a  very  soft, 
round,  or  ])olygonal  gland-like  epithelium  that 
suggests  the  formation  of  a  gland,  but  fails  to  assume  the  glandular 
structure,  though  it  seems  to  have  been  regarded  as  such  by  Serres. 
This — which  I  shall  call  the  gingival  organ — emits  a  profusion  of  small 
rounded  cells  which  are  always  found  in  the  saliva  (Salter)  and  are 
usually  called  mucus-corpuscles.     It  is  not  probable  that  all  of  these 


The  Gingival  Border  :  a,  enamel 
of  the  tooth ;  6,  dentine :  c. 
eeraentum;  d,  peridentil 
membrane;  e,  epithelial 
covering  of  the  gingival  bor- 
der :  /,  gingival  organ  ;  <■/, 
dental  ligament;  fi,  subepi- 
thelial tissue ;  i,  bony  wall 
of  the  alveolus. 


956  DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 

are  derived  from  this  source,  but  niaDy  of  them  certainly  are,  for  they 
can  be  had  for  examination  any  time  by  passing  a  thin,  flat-pointed 
instrument  under  a  healthy  free  margin  of  gum  and  transferring  that 
Avhich  adheres  to  a  slide  for  microscopic  examination.  These  often 
accumulate  in  considerable  numbers  under  the  free  margin  of  the  gum, 
and,  mixed  with  micro-organisms,  form  the  bulk  of  those  soft  cheesy 
masses  that  to  the  naked  eye  so  nearly  resemble  pus  that  they  are  often 
mistaken  for  it.  Indeed,  Koelliker  seems  to  have  considered  these  cor- 
puscles as  a  modified  form  of  pus.  They  are,  however,  always  found 
in  this  position,  and  therefore  must  be  considered  normal.  Still,  it  is  a 
question  whether  these  little  masses  of  cells  or  rings  of  cells  that  sur- 
round the  necks  of  the  teeth  should  be  considered  glands.  If  so,  what 
is  their  function?  At  the  present  time  this  question  cannot  be  answered 
satisfactorily,  the  subject  not  having  been  sufficiently  studied.  We  have, 
however,  some  facts  bearing  on  the  question  in  the  direction  most  im- 
portant to  the  subject  in  hand.  It  is  well  known  that  certain  glands 
have  the  power  of  the  selection  and  excretion  of  certain  poisons,  and  in 
this  way  of  eliminating  them  from  the  system,  and  that  in  the  passage, 
if  the  substance  be  in  large  amount,  hyperemia,  or  even  inflammation, 
may  result.  It  is  also  known  that  mercury  and  iodide  of  potassium 
M'ill  produce  inflammation  of  the  free  margins  of  the  gums,  and  Salter 
has  found  that  these  cells  are  in  greater  abundance  under  these  circum- 
stances ;  also  that  the  cells  taken  from  the  gingival  border  and  submit- 
ted to  chemical  tests  after  the  person  has  taken  iodide  of  potassium  are 
found  to  yield  and  are  tinged  with  iodine.  We  have  here,  then,  a  suf- 
ficient proof  that  gingivitis  may  occur  from  constitutional  causes,  or,  in 
other  words,  from  poisons  that  circulate  in  the  blood  and  have  an  elect- 
ive affinity  for  this  gingival  organ.  Certain  medicinal  agents  are  known 
to  possess  this  property  ;  what  other  substances  there  may  be  having 
similar  affinities  is  as  yet  only  a  subject  for  conjecture.  AVe  can  now 
speak  positively  of  mercurial  gingivitis  and  gingivitis  from  iodide  of 
potassium.  Each  of  these  is  a  form  of  true  constitutional  gingivitis, 
usually  termed  salivation  because  the  salivary  glands  are  excited  at  the 
same  time.  Either  of  these  forms  of  the  disease  may  so  extend  that 
it  might  be  termed  a  pericementitis,  and  that  from  mercury  in  some 
cases  might  take  the  name  of  any  of  the  tissues  of  the  mouth  or  face ; 
but  this  is  in  all  cases  an  extension  of  the  inflammation  from  the  gingi- 
vae, which  are  uniformly  the  point  of  attack.  It  is  not  my  intention  to 
discuss  these  diseases  further,  as  they  are  sufficiently  treated  in  works 
on  general  medicine,  and,  thanks  to  a  wiser  use  of  remedies,  they  are 
now  very  rarely  seen. 

In  the  influences  that  jjroduce  scurvy  we  find  another  cause  of  con- 
stitutional gingivitis  that  is  unmistakable,  and  the  course  of  the  affec- 
tion, taken  ajiart  from  the  other  manifestations  of  the  disease,  has  much 
in  common  with  the  simpler  forms. 

Aside  from  these  three  well-known  forms  of  gingivitis,  a  form  occurs 
quite  often — mostly  in  young  persons — that  is  of  much  less  note  and 
recpiires  only  a  ])assing  notice.  This  is  an  inflammation  usually  con- 
fined to  the  gingiv.'c,  but  extending  to  most  of  the  teeth.  The  margins 
of  the  gums  become  red  and  swollen  and  bleed  from  trifling  causes. 


CALCIC  INFLAMMATION  OF  MEMBRANE  AND   GUMS.        957 

There  is  often  some  eversion  of  the  gnni,  and  the  pockets  thus  formed 
are  filled  with  the  peculiar  mucus-corpuscles,  pus-corpuscles,  and  the 
usual  micro-organisms  of  the  mouth.  This  inflammation  seems  not  to 
assume  a  destructive  character.  There  is  little  or  no  separation  of  the 
tissues  from  the  necks  of  the  teeth,  and  the  difficulty  is  usually  tran- 
sient, lasting  but  a  few  weeks.  In  those  cases,  however,  where  there  is 
a  disposition  to  accumulations  of  calculus  or  other  irritating  substances, 
it  may  serve  as  the  starting-point  of  a  more  permanent  local  irritation  ; 
it  therefore  rerjuires  the  attention  of  the  dentist.  It  will  always  be 
favorably  modified  by  habits  of  cleanliness,  and  will  soon  pass  away 
without  other  treatment ;  therefore  the  removal  of  the  accumulations  is 
usually  all  that  is  indicated.  Of  course  the  patient  should  be  instructed 
in  regard  to  tlie  matter  of  keeping  the  parts  well  cared  for.  Some  cases 
will  be  met  with  in  which  a  brisk  saline  cathartic  as  an  eliminant  will 
be  advisable,  and  this  may  be  followed  by  the  vegetable  acids  with 
advantage.  For  this  purpose  I  have  found  nothing  better  than  oranges 
or  lemons ;  indeed,  in  all  of  this  group  of  diseases  these  fruits  seem  to 
exert  a  very  salutary  effect. 

There  is  but  little  doubt  that  simple  gingivitis  is  often  the  starting- 
point  of  the  more  grave  diseases  of  the  peridental  membranes  pres- 
ently to  be  described.  The  inflamed  and  swollen  state  of  the  gingiviB 
favors  tlie  lodgment  of  calculus  by  interfering  with  the  natural  tendency 
to  cleanliness  which  results  from  the  unrestrained  use  of  the  teeth  in 
the  mastication  of  food.  This  tendency  is  readily  seen  in  most  mouths 
when  from  any  cause  one  portion  of  the  mouth  is  not  freely  used,  as  in 
the  case  of  a  sensitive  carious  tooth.  In  such  cases  the  effect  of  disuse  is 
generally  quickly  seen  in  accumulations  of  debris,  if  not  actual  deposits 
of  calculus,  about  the  necks  of  the  teeth  in  tlie  region  disused,  with  the 
consequent  tendency  to  calcic  inflammation.  Now,  in  case  of  simple 
gingivitis,  continuing  for  some  weeks,  the  patient  will  become  cautious 
about  the  use  of  the  teeth  and  will  avoid  those  things  that  hurt  the 
gums,  and  therefore  will  not  make  that  free  use  of  the  teeth  best  calcu- 
lated to  keep  them  freed  from  such  accumulations  in  the  natural  way. 
In  this  manner  Nature's  plan  for  cleanliness  is  thwarted,  and  the  condi- 
tion is  prone  to  pass  into  one  of  calcic  inflammation. 

Calcic^  Inflammation  of  the  Peridental  3Iemhrane  and  Gums, — I  use 
the  term  calcic  inflammation  of  the  peridental  membrane  and  gums  to 
express  that  condition  in  which  inflammation  of  these  parts  is  caused 
and  perpetuated  by  deposits  of  calculus  on  the  necks  of  the  teeth.  As 
deposits  on  the  teeth  will  be  the  subject  of  a  special  paper,  I  will  not 
enter  into  a  discussion  of  the  causes  that  lead  to  them,  further  than  these 
may  depend  on  the  local  conditions.  I  recognize  that  a  tendency  to 
calcific  deposits  may  be  a  constitutional  vice  Avhich  is  probably  hered- 
itary in  many  cases,  but  may  be  acquired.  This  constitutional  vice  may 
be  favored  by  conditions  of  the  teeth  themselves,  by  their  form,  by 
irregularities  in  their  arrangement,  by  the  condition  of  the  gums,  as  in 
the  swollen  state  found  in  simple  gingivitis,  by  vicious  personal  habits, 

^  In  the  use  of  the  term  "calcic"  denoting;  the  cause  of  inflammation  I  follow  an 
esta'ilislied  usage,  as  seen  in  the  terms  traumatic  inflammation,  traumatic  fever,  septic 
fevei',  etc.,  all  of  which  denote  the  cause,  not  tlie  result,  of  the  conditions  named. 


958 


DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 


such  as  want  of  cleanliness,  and  by  the  use  of  soft  foods  which  require 
but  little  use  of  the  teeth,  etc.  Calcic  inflammation  is  really  one  of  the 
most  grave  of  the  diseases  of  the  teeth — not  that  it  is  so  very  difficult 
of  management  when  rightly  understood,  but  from  the  great  number  of 
cases  that  occur  and  its  insidious  character,  by  which  it  so  often  destroys 
the  denture  before  the  patient  is  aware  of  the  danger.  Within  my 
observation  it  is  causing  the  loss  of  more  teeth  than  is  caries.  The 
subject,  therefore,  merits  the  closest  possible  attention. 

This  variety  of  inflammation  is  dependent  directly  upon  the  accu- 
mulation of  calculus  upon  the  necks  of  the  teeth,  and  presents  two  forms 
that  may  appear  distinct  from  each  other  or  may  be  blended  together  in 
the  most  intimate  way.  This  relates  to  the  source  of  the  calculus  and 
tlie  position  of  the  deposit.  One  form  is  derived  from  the  serum  that 
exudes  from  the  tissues  in  a  state  of  disease,  and  is  uniformly  deposited 
under  the  free  margin  of  the  gum  ;  the  other  is  derived  from  the  saliva, 
and  is  deposited  on  the  necks  of  the  teeth  close  up  against  the  free  mar- 
gin of  the  gum,  but  not  beneath  it.  Any  of  the  conditions  that  favor 
deposits  favor  thus  far  the  development  of  the  affection.  Simple  gin- 
givitis will  in  this  way  contribute  to  its  development.  Indeed,  one 
form  of  calculus  seems  to  be  dependent  for  its  production  upon  previous 
conditions  of  disease ;  this  is  not  properly  salivary  calculus,  but  the 
calcareous  deposit  from  the  serum.  This  I  shall  call  serumal  calculus. 
So  far  as  I  know,  this  form  of  calculus  was  first  noticed  by  Dr.  Brown 
of  Georgia  in  an  article  in  the  American  Jownal  (October,  1870).  It 
was  also  described  by  Dr.  Ingersol  {Ohio  Journal,  August,  1881)  some- 
what at  length  under  the  title  of  ''  Sanguinarv  Calculus."  I  have  not 
been  able  to  determine  that  this  form  of  calculus  is  characteristic  of  any 
one  form  of  disease ;  it  seems  to  be  a  result  of  any  pathological  state  of 
the  gingivae  causing  them  to  weep  a  serous  fluid.  It  is  not,  however, 
confined  to  the  gingivae,  but  may  occur  on  any  part  of  the  root  of  the 
tooth,  and  not  unfrequently  is  found  on  the  apex  of  the  root  in  old 


Fig.  506. 


Fig.  507. 


Section  of  an  Upper  Molar  with  its  Alveolus, 
etc.,  showing  Deposit  of  Serumal  Calculus 
under  the  Oingival  Borders:  a,  a,  serumal 
calculus. 


cases  of  alveolar  abscess. 


Section  of  an  Upper  Incisor  showing 
at  n,  ft  a  Deposit  of  Serumal  Calculus 
within  the  Free  Margin  of  the  Gum. 


Yet  it  occurs  much  more  frequently  than 
elsewhere  on  the  necks  of  the  teeth  immediately  beneath  the  gingival 
border  (Figs.  506,  507).    There  seems  to  be  in  the  location  and  circum- 


SERUM  A  L  CALCULUS. 


959 


stances  of  the  deposit  of  this  calcukis  on  tlie  necks  of  the  teeth  a  sug- 
gestion that  this  particular  deposit  may  be  from  the  secretion  of  the 
gingival  organ ;  there  is  not  enough  known  of  the  matter,  however,  at 
the  present  "time  to  warrant  any  definite  statements.  It  is  possible  that 
it  may  be  formed  without  previous  local  disease,  but  my  personal  obser- 
vations do  not  favor  this  idea. 

As  seen  in  this  position,  the  deposit  is  generally  in  the  form  of  a  very 
hard  brownish  crust,  but  it  is  often  deposited  in  little  nodules  adhering 
very  firmly  to  the  neck  of  the  tooth,  and  usually  extending  to  a  large 
number,  if  not  to  all,  of  the  teeth.  It  is  in  no  wise  limited,  even  in  its 
beginnings  or  in  its  greatest  accumulations,  to  the  neighborhood  of  the 
ducts  of  the  salivary  glands,  as  is  seen  so  prominently  in  the  deposits 
of  salivary  calculus.  My  observation  leads  me  to  the  conclusion  that 
this  deposit  is  determined  by  irritation  of  the  gingiva?.  This  may  be 
caused  by  neighboring  deposits  of  the  ordinary  salivary  calculus,  by 
accumulation  of  micro-organisms  or  of  food,  or  it  may  be  from  local 
irritation  arising  from  constitutional  causes.  When  a  slight  deposit  has 
once  taken  place,  it  becomes  an  irritant  which  will  in  itself  perpetuate 
the  disease.  It  seems  to  possess  peculiar  irritating  qualities,  keeping 
the  adjacent  gum  and  lower  border  of  the  peridental  membrane  in  a 
state  of  chronic  inflammation  resulting  in  the  continued,  though  very 
slow,  increase  of  the  deposit.  This  deposit,  when  it  is  the  sole  apparent 
cause  of  trouble,  may  be  many  years  in  accumulation  before  if  will  be 
productive  of  serious  conditions ;  finally,  however,  some  ulceration  of 
the  lower  border  of  the  peridental  membrane  will  occur,  and  it  will  be 

Fig.  50S. 


Section  of  an  Upper  Incisor  showing  at  n  a 
Deposit  of  Seriuual  Calculus  and  Destrnc- 
tion  of  the  Lower  Border  of  the  Alveolar 
Wall  and  Peridental  Membrane,  with  a 
slight  Recession  of  the  Gum,  exposing  the 
Calculus. 


Absorption  of  the  Septum  of  Bone  and  Re- 
cession of  the  Gum  between  the  Central 
and  I-ateral  Incisors  caused  by  Deposits 
of  Serumal  Calculus  under  the  Gingiva. 


very  gradually  destroyed,  exposing  the  neck  of  the  tooth.  As  fast  as 
the"^  membrane  is  detached  from  the  root  of  the  tooth  the  rim  of  the 
alveolar  wall  or  socket  of  the  tooth  is  absorbed,  and  the  gum  recedes 
with  it,  often  exposing  the  brownish  girdle  of  serumal  calculus  encir- 
cling the  neck  of  the  tooth  (Fig.  508).  Sometimes  this  condition  of 
shrinkage  is  manifested  by  the  subsidence  of  the  septum  of  gum-tissue 
that  drops  down  between  the  necks  of  the  teeth,  this  forming  a  very 


960 


DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 


characteristic  mark  of  the  progress  of  the  aifection  (Fig.  509).  In 
these  cases,  as  already  explained,  the  lower  border  of  the  peridental 
membrane  is  destroyed  and  the  septum  of  the  alveolus  absorbed,  this 
allov.ing  the  gingival  border  to  recede.  It  is  not  the  gum  that  suffers, 
so  much  as  the  peridental  membrane  and  alveolar  wall.  This  condition 
is  also  frequently  seen  in  connection  with  phagedenic  pericementitis,  but 
is  not  so  characteristic,  as  in  this  disease  there  is  less  tendency  to  shrink- 
age of  the  gums.  This  does  not  occur  in  the  same  way  from  deposits 
of  salivary  calculus,  on  account  of  the  greater  tendency  to  active  inflam- 
mation of  the  adjacent  parts.  More  rarely,  however,  even  with  none 
but  serumal  deposits,  the  gum  will  be  markedly  inflamed,  reddened, 
and  spongy,  and  will  bleed  at  the  slightest  touch.  In  either  case  pus 
will  be  found  beneath  the  inflamed  gum  and  usually  be  seen  exuding 
on  pressing  the  parts  with  the  finger.  If  now  the  incrustations  be 
removed,  the  peridental  membrane  will  be  found  intact,  though  in  an 
inflamed  condition,  just  above  the  attachment  of  the  crust,  making  a 
strong  contrast  to  the  conditions  found  in  phagedenic  pericementitis 
(presently  to  be  described),  in  which  the  peridental  membrane  is  de- 
stroyed and  deep  pockets  are  formed  extending  far  beyond  the  cal- 
careous deposits  that  may  be  present.  (Compare  Figs.  506,  507,  and 
508  with  Figs.  518,  519,  and  520.) 

As  these  conditions  continue  the  peridental  membrane  becomes  more 
and  more  diseased ;  the  formation  of  pus  is  more  and  more  profuse ; 
ordinary  salivary  calculus  is  now  deposited  on  the  root  above  the  rim 
of  brown  serumal  calculus,  or  this  form  may  also  extend  along  to^\■ard 
the  apex  of  the  root. 

At  this  stage  of  the  disease  all  the  symptoms  are  likely  to  become 
aggravated  and  there  is  a  continual  flow  of  pus  from  the  sockets  of  the 
Fig.  510. 


Fig.  511. 


Section  of  a  Lower  Incisor  with  a  large  De- 
posit of  Salivary  Calculus  impinging  upon, 
and  causing  Inflammation  of,  the  Gum. 


Section  of  an  Upper  Molar  with  Deposit  of 
Calculus  on  its  Buccal  Surface  causing  In- 
flammation and  Absorption  of  the  Gum 
and  Lower  Border  of  the  Peridental  Mem- 
brane and  Alveolar  Wall. 


diseased  teeth,  these  gradually  becoming  loosened.  In  this  condition 
that  portion  of  the  ])eridentnl  membrane  remaining  about  the  end  of 
the  tooth  becomes  much  thickened ;   so  that,  while  the  tooth  shakes 


CALCIC  INFLAMMATION  OF  MEMBRANE  AND   GUMS.       961 


about  in  every  direction,  it  is  still  held  in  position  with  considerable 
tenacity.  This  condition  of  things  is  quite  characteristic  of  the  disease, 
and  even  at  this  late  period  serves  to  distinguish  it  from  phagedenic 
pericementitis,  in  which  the  membrane  around  the  end  of  the  root  is 
usually  destroyed,  while  remaining  still  intact  on  some  portions  of  the 
side.     In  this  condition  the  teeth  are  irretrievably  lost. 

The  conditions  resulting  from  the  deposit  of  salivury  calculus  are  in 
all  of  their  manifestations  much  the  same  as  those  just  described.  In 
this  class  of  cases,  however,  the  deposit  is  generally  much  more  pro- 
nounced in  the  neighborhood  of  the  openings  of  the  ducts  of  the  sali- 
vary glands — that  is,  on  the  lingual  surfaces  of  the  lower  incisors  (Fig. 
510)  and  on  the  buccal  surfaces  of  the  upper  molars  (Fig.  511).  It  is 
not,  however,  confined  to  these  localities.  The  beginnings  of  the 
deposits  are  almost  always  at  these  points,  and  as  the  deposit  increases 
it  spreads  to  either  side,  finally,  in  many 
eases,  going  the  whole  round  of  the  den- 
tal arch.  Thus  the  deposit,  beginning 
on  the  lingual  surface  of  the  lower  in- 
cisors, will  gradually  creep  in  between 
the  teeth,  and  finally  encircle  them,  and, 
passing  from  tooth  to  tooth,  ultimately 
involve  the  entire  set.  This  also  may 
occur  in  the  upper  jaw,  beginning  with 
the  molars  of  either  side  (Figs.  512, 
518,  and  514)..  Again,  it  is  not  un- 
conmion  to  see  mixtures  of  the  two 
kinds  of  calculus,  the  salivary  occupy- 
ing the  necks  of  the  teeth  near  the  ducts  of  the  glands,  and  the  ser 


Fig.  512. 


Heavy  Deposits  of  Salivary  Calculus  caus- 
ing general  Calcic  Inflammation. 


Fig.  514. 


Fig.  513. 


Sectional  Illustration  of  a  heavy  Deposit 
of  Salivary  Calculus  on  a  Lower  In- 
cisor, with  pnrtial  Destruction  of  the 
Alveolus  of  the  Tooth. 


Sectional  Illustration  of  Inferior 
Incisor  with  Iiepo.sit  of  Salivary 
Calculus  less  heavy  than  that 
shown  in  Fig.  .512,  but  with 
greater  Destruction  of  the  Alve- 
olus. 


umal  occupying  those  more  remote.     The  salivary  calculus  is  usually 
Vol.  I.— 61 


962  DISEASES   OF  THE  PERIDENTAL  MEMBRANE. 

of  a  light-yellow  color,  but  is  sometimes  quite  dark ;  it  is  much  softer, 
is  deposited  in  very  much  larger  quantity  than  the  serumal  variety,  and 
is  much  more  rapid  in  its  destructive  effects.  It  seems  to  be  more  irri- 
tating to  the  surrounding  tissues  than  the  serumal.  No  tissue  retains  its 
hcdlth  if  in  contact  irith  salivary  calculus ;  wherever  it  accumulates  it 
carries  destruction.  Not  only  this,  but  it  is  very  prone  to  follow  up  its 
destructive  effects  by  fresh  deposits  in  the  space  gained,  and  in  this  way 
is  continually  on  the  aggressive.  Yet,  if  the  de^wsit  be  cleared  away 
from  the  teeth,  the  peridental  membrane,  just  above,  will  be  found 
intact ;  it  may  be  inflamed  and  changed  in  texture,  but  it  is  not  de- 
stroyed for  any  considerable  distance  in  advance  of  the  forming  calcu- 
lus. In  this  way  the  teeth  are  often  loosened  very  rapidly.  The  lower 
incisors  are  usually  the  first  to  suffer  and  the  first  to  be  lost,  after  which 
the  others,  one  after  the  other,  are  liable  to  suffer  the  same  fate,  until 
the  entire  denture  is  lost. 

Instances  are  now  and  then  met  with  of  very  large  deposits  of  this 
calculus ;  I  have  often  seen  several  molar  teeth  hidden  from  view  by 
being  covered  completely  in  by  them.  The  lower  incisors  sometimes 
bear  a  deposit  greater  in  bulk  than  themselves.  The  destructive  effects 
of  this  calculus  do  not  seem  to  depend  so  much  on  the  amount  of  the 
deposit  as  upon  its  distribution.  For  instance,  the  lingual  surfaces  of 
the  lower  incisors  may  carry  a  load  of  calculus  equal  to  their  own  bulk 
and  not  suffer  very  much  harm  so  long  as  their  proximal  and  labial 
surfaces  are  free,  while  a  much  less  amount  of  deposit,  when  extending 
entirely  around  the  neck  of  the  tooth,  will  cause  a  much  greater  destruc- 
tion of  the  peridental  membrane.  It  would  appear,  also,  that  when  the 
deposit  takes  place  very  rapidly  in  a  certain  position  there  is  less  tend- 
ency to  encroachment  upon  the  tissues ;  the  deposit  in  such  cases  seems 
to  override  the  tissues  instead  of  insinuatino;  itself  beneath  them  and 
around  the  root  of  the  tooth. 

In  any  case,  it  is  not  so  much  the  deposit  of  calculus  that  is  to  be 
feared  as  the  continuance  of  that  deposit  in  contact  with  the  tissues;  for 
this  it  is  that  brings  about  the  evil  results.  The  gums  and  peridental 
membrane  naturally  heal  kindly  and  quickly  even  after  very  consider- 
able mutilation,  and  will  do  the  same  after  an  active  inflammation  has 
been  developed  by  the  presence  of  calculus;  but  when  this  continues  for 
month  after  month  and  year  after  year,  a  time  comes  when  they  lose  the 
power  of  recuperation  :  the  tone  of  the  tissue  is  lost  and  they  become 
incapable  of  returning  to  health.  This  is  seen  in  every  degree.  Some 
cases  that  look  very  badly  will  heal  readily  ;  others,  only  after  much 
careful  nursing  has  given  them  time  and  opportunity  for  recuperation. 
Still  other  cases  refuse  to  heal  so  long  as  the  teeth  remain  in  their  sock- 
ets— a  clear  indication  that  the  tone  of  the  peridental  membrane  has 
been  irretrievably  lost.  I  wish  to  emphasize  this  statement.  It  is  not 
the  tooth  that  is  at  fludt,  as  many  seem  to  suppose,  but  the  peculiar  tis- 
sue of  the  peridental  membrane,  the  recuperative  capacity  of  which  has 
been  worn  out.  John  Hunter  hailed  teeth  for  replantation,  and  yet  the 
tissues  of  the  peridental  meml)rane  were  found  equal  to  the  task  of 
uniting  with  their  roots.  Teeth  have  been  replanted  successfully  after 
having  been  knocked  out  and  carried  about  in  the  pocket  for  hours 


TREATMENT  OF  CALCIC  INFLAMMATION.  963 

Can  we  imagine  that  the  teeth  in  the  mouth  could  be  in  a  much  worse 
condition  ?  Certainly  it  is  not  the  condition  of  the  teeth  themselves 
(provided,  always,  that  tiiey  are  properly  cleaned),  but  the  very  low 
state  of  the  vitality  of  the  remaining  portions  of  the  peridental  mem- 
brane, that  renders  the  process  of  repair  impossible. 

Treatment. — The  most  important  measure  in  the  treatment  of  cal- 
cic inflammation  of  the  peridental  membrane  and  gums  is  the  removal 
of  the  concretions  from  the  teeth,  and  next  the  arousing  in  the  mind  of 
the  patient  an  active  determination  to  keep  them  clean  in  the  future. 
These  two  measures  are  absolutely  necessary  to  success ;  nothing  can  be 
accomplished  unless  they  are  scrupulously  carried  out.  But  with  these 
two  points  attained  success  is  assured  in  all  cases  during  the  early  or 
middle  of  the  course  of  the  disease.  It  should  always  be  kept  in  mind 
that  this  is  purely  a  local  affection  dependent  solely  upon  the  irritation 
of  accumulations  of  calculus,  and  that  these  accumulations  form  the 
only  bar  to  a  restoration  of  the  health  of  the  parts.  Plspecially  should 
these  facts  be  impressed  on  the  mind  of  the  patient,  and  he  should  be 
made  to  understand  that  the  result  will  depend  largely  upon  his  own 
efforts.  The  removal  of  these  concretions  in  such  a  manner  as  to  assure 
success  is,  however,  one  of  the  most  difficult  operations  in  dental  sur- 
gery. Another  very  serious  difficulty  standing  in  the  way  of  success  is 
the  very  slack  and  inefficient  notions  that  have  been  held  in  regard  to 
it  by  the  profession  at  large.  When  dentists  learn  to  regard  tliis  opera- 
tion as  equal  in  importance  to,  and  requiring  as  much  thoroughness  as, 
the  filling  of  teeth,  and  when  they  apply  themselves  with  the  same  dil- 
igence to  acquiring  the  necessary  dexterity  in  its  performance,  they  will 
be  rewarded  with  success  ;  without  this,  success  in  the  treatment  of  this 
disease  cannot  be  attained.  Either  of  the  forms  of  calculus  is  an  irri- 
tant, and  this  remains  true  no  matter  how  small  the  quantity.  The 
leaving  of  a  small  portion — be  it  ever  so  small — of  calculus  on  the  side 
of  the  root  of  a  tooth  is  just  as  fatal  to  the  result  of  this  operation  as  is 
the  leaving  of  a  small  portion  of  carious  dentine  on  the  margin  of  a 
cavity  in  which  a  filling  is  to  be  inserted.  Absolute  thoroughness  is 
the  requirement.  (For  more  detailed  description  of  the  operative  pro- 
cedures in  the  removal  of  calculus  the  reader  is  referred  to  the  article 
on  Calcareous  Deposits  on  the  Teeth.) 

The  instruments  for  tliis  operation  should  be  formed  with  the  greatest 
care  and  delicacy.  They  should  for  the  most  part  be  fashioned  to  work 
with  a  jmshing  motion — that  is,  they  should  work  from  the  hand  in  the 
act  of  removing  the  concretions.  Curved  and  hooked  or  hoe-shaped 
instruments  formed  to  work  toioard  the  hand  with  a  jndling  motion  may 
be  of  service  in  the  removal  of  the  bulk  of  the  larger  concretions  of 
salivary  calculus,  but  they  are  of  inferior  value  in  the  removal  of  the 
last  portions  of  the  deposits  or  for  serumal  calculus  that  is  deposited 
high  up  under  the  gum.  For  this  purpose  all  the  hooked  instruments, 
no  matter  how  delicately  formed,  should  be  discarded  and  slender  points 
made  to  work  with  the  jmshing  motion  substituted.  These  should  be 
made  of  the  finest  steel.  The  points  should  be  from  one-sixteenth  to 
one-eighth  of  an  inch  in  width,  very  thin — not  thicker  than  ordinary 
writing-paper — and  very  gradually  thicken  up  toward  the  shank,  so  as 


964 


DISEASES   OF  THE  PERIDENTAL  MEMBRANE. 


to  form  a  good  spring.  This  part  of  the  instrument  should  be  of  a  fine 
spring  temper  to  within  three-sixteenths  of  an  inch  of  the  point,  and 
the  remainder  should  be  hard.  The  point  itself  should  be  ground 
square,  and  kept  sharp  with  the  hone.  These  should  be  made  in  a  suf- 
ficient number  of  forms,  as  regards  curve  of  the  spring  part  of  the 
instrument,  to  enable  the  operator  easily  to  reach  any  portion  of  the 
root  of  any  tooth.  Six  or  eight  of  these  will  be  found  sufficient  for 
anv  operation  that  may  present  itself,  and  the  instruments  have  the 

advantage  of  bei  ng  easy  of  manage- 
ment if  well  formed.  Those  known 
n  \  n  in  as  Dr.  George  H.  Cushing's  scalers 
seem  to  be  the  best  yet  in  the 
market  (Fig.  515).  These  instru- 
ments may  be  passed  freely  in  be- 
tween the  most  crowded  teeth  and 
reach  every  point  where  deposits 
adhere,  and  if  judiciously  nsed 
are  capable  of  removing  all  in- 
crustations Avith  the  least  possible 
inconvenience  to  both  patient  and 
operator.  They  may  be  used  with 
both  the  pushing  and  the  lateral 
motion,  but  the  pushing  motion 
should  be  especially  relied  upon 
for  the  bulk  of  the  work.  At 
present  no  rules  for  this  can  be 
given  that  seem  to  me  to  be  espe- 
cially useful.  The  particular  plans 
of  manipulation  will  depend  large- 
ly on  the  manipulative  habits  of 
the  operator. 

At   first   sight    the    oj^erations 
seem  very  simple.     The  principal 
difficulty    is    in    the    finding   and 
removal   of  the   last  particles   of 
calculus.     The  bulk  of  the  incrus- 
tations may  be  removed  in  a  few 
moments  by  the  merest  tyro,  but 
the  removal  of  the  last  traces  re- 
quire a  measure  of  skill  and  pa- 
tience that  can  be  developed  only  by  the  most  determined  effort 
aided  by  considerable  practice.     But,  after  all,  one  of  the  most 
difficult  points  is  the  obtaining  of  the  conception  of  the  require- 
ments in  its  full   force  and  completeness.     The  expression  of 
this  in  words   is  a  simple  impossibility  ;  it  must  be  learned  at 
the  chair ;  by  the  watchful   scrutiny  of  cases  in  practice ;  by 
carefully  searching  out  the  causes  of  failure  in  individual  cases; 
by  the  finding  of  small  scales  that  have  prevented  healing  where 
it  was  thought  all  had  been  removed  ;  by  the  finding  of  a  little 
pus  here  and  the  cause  of  its  continuance  in  a  small  particle 


Dr.  George  H.  Cushing's  Scalers. 

The  forms  and  general  character  of 
these  scalers  are  well  shown.  All  the 
instriinieiits  except  No.  6  are  intended 
to  be  used  with  the  push  stroke.  Nos. 
1  and  2  are  specially  intended  for  ap- 
plication to  the  posterior  surfaces  of 
lower  incisors ;  they  are  also  admirably 
adapted  for  removing  calculous  depos- 
its below  the  gum  between  molars  and 
bicuspids,  and  from  the  posterior  sur- 
faces of  tlie  last  molars.  No.  2  can  be 
passed  quite  to  the  extremity  of  mo.st 
roots  with  less  disturbance  to  the  sol't 
tissues  than  a  thicker  or  more  rigid 
instrument  would  cause.  Nos.  '■'•  and  4 
are  for  removing  deposits  at  and  below 
the  gum  between  the  teeth,  particularly 
the  lower  front  teeth.  They  can  also  be 
easily  used  upon  the  sides  of  the  roots 
of  many  teeth,  being  passed  toward 
the  ape.x  of  the  root  in  a  line  nearly  or 
quite  parallel  with  that  of  the  axis. 
No.  5  is  intended  to  be  passed  between 
the  lower  front  teeth  at  or  near  the 
gum  and  then  directly  upward,  to  re- 
move the  deposits  on  the  proximal 
surfaces.  No.  G  is  a  hoe,  and  is  in- 
tended to  be  passed  quite  to  the  apex 
of  the  roots  where  a  hoe  is  desired. 


TREATMENT  OF  CALCIC  INFLAMMATION.  965 

overlooked  high  up  under  the  gum  ;  by  the  finding  of  an  inflamed  point 
there,  and  the  discovery  of  its  cause  in  an  unremoved  scale.  In  a  word, 
the  proper  conception  of  the  absolute  perfection  required  in  this  operation 
nuist  be  learned  by  a  careful  scrutiny  of  one's  own  failures,  with  the  deter- 
mination to  correct  them. 

In  many  cases  there  will  be  found  small  incrustations  of  very  slight 
thickness  that  lie  so  closely  and  smoothly  to  the  root  of  the  tooth  that 
an  instrument  may  slide  over  without  removing,  or  even  detecting  them 
except  by  the  most  cultivated  touch.  These,  when  they  occur  in  out- 
of-the-way  places  hidden  by  the  gum,  will  tax  the  patience  and  skill  of 
the  most  experienced  operator,  and  it  will  require  repeated  efforts  to 
find  and  remove  them.  The  presence  of  all  such  points  will  after  some 
days  be  manifested  by  a  failure  of  the  healing  process,  and  they  must 
be  searched  out  before  the  case  is  discharged.  Generally,  such  scales  are 
dark-colored,  and  are  readily  seen  if  they  can  be  so  uncovered  as  to  make 
visual  search  available.  This  may  be  much  aided  and  extended  by  the 
plan  proposed  by  Dr.  Gilmer  of  Quincy,  111.,  which  consists  in  packing 
salicylized  cotton^  under  the  free  margin  of  the  gum  and  allowing  it  to 
remain  for  twenty-four  hours,  its  expansion  causing  the  gum  to  stand 
off  from  the  tooth,  so  that  small  scales  may.  be  seen.  This  must  be 
done  with  care  and  no  more  than  the  necessary  pressure  used,  or  the 
tissue  of  the  gum  wall  be  injured.  If  judiciously  done,  the  neck  of  the 
tooth  may  be  exposed  to  view  up  to  the  attachment  of  the  peridental 
mend)rane  and  without  causing  a  slough.  In  positions  where  these 
plans  of  search  cannot  be  made  available  the  touch  alone  must  be  de- 
pended upon.  The  cutting  away  of  the  gum  for  the  purpose  of  finding 
the  last  traces  of  calcareous  deposits  is  in  all  cases  to  be  deprecated ; 
such  deposits  should  be  found  and  removed  without  this,  for  unless  the 
gum  tissue  be  in  over-abundance  any  removal  of  it  is  detrimental  to  the 
future  usefulness  of  the  teeth  and  is  entirely  unnecessary  to  the  curative 
process.  Where  there  is  hypertrophy  of  the  gum,  removal  is  judicious 
treatment  and  will  expedite  a  cure.  It  is  true  that  cases  in  which  no 
hypertrophy  exists  are  more  easily  managed  by  cutting  away  the  gum 
as  far  as  it  is  diseased  than  by  the  more  conservative  method  of  treat- 
ment, but  in  the  calcic  forms  of  inflammation  there  seems  to  me  to  be 
but  little  excuse  for  this  procedure,  as  it  is  destructive  of  tissues  that 
can  be  restored  to  health  and  usefulness,  and  which,  when  one  c  de- 
stroyed, are  not  readily  reprodnced,  the  result  being  an  undue  and  per- 
manent exposure  of  the  root  of  the  tooth.  The  plan — so  much  practised 
of  late-^of  removing  the  lower  border  of  the  peridental  membrane  and 
alveolar  wall,  but  retaining  the  tissue  of  the  gum,  while  not  so  destruc- 
tive, is  entirely  unnecessary  in  the  calcic  forms  of  inflammation,  unless 
the  case  be  complicated  with  such  a  thickening  of  the  alveolar  border 
as  will  prevent  the  gum  tissue  from  approximating  closely  to  the  root 
of  the  tooth.  This  is  occasionally  seen  in  old  cases  of  serumal  deposits. 
Then  it  is  only  necessary  to  break  down  the  prominences  of  the  wall  of 
the  alveolus  in  such  a  way  that  the  tissue  may  assume  the  normal  posi- 

^  Salicylized  cotton  is  prepared  by  soaking  common  cotton  in  an  ethereal  solution  of 
salicylic  acid  (40  grains  to  the  ounce)  and  then  drying  it.  This  will  irritate  the  gum 
much  less  than  cotton  alone — or,  indeed,  than  any  other  substance  that  I  have  tried. 


966  DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 

tion.  Especial  care  should  be  had  in  all  cases  to  preserve  as  much  of 
the  gum  as  possible,  for  upon  that  depends,  for  the  most  part,  the 
renewal  of  the  lost  tissue.  The  rule  is  that  the  destruction  of 
the  gum  is  in  any  chronic  case  fatal  to  such  restoration,  the  root 
of  the  tooth  remaining  denuded  as  far  as  the  gum  has  been  de- 
stroyed. 

In  all  inflammations  of  the  peridental  membranes  and  gums  originat- 
ing in  irritation  from  calculus,  of  whatever  variety,  or  kept  up  by  these 
causes,  the  tendency  is  to  speedy  recovery  after  their  removal,  provided, 
as  has  already  been  remarked,  this  is  done  before  a  certain  stage  of  the 
destructive  process  has  been  reached.  This  stage  of  the  affection  is 
marked  by  a  very  distinct  enlargement  of  what  remains  of  the  alveoli 
of  the  teeth — the  rim  o1  the  alveolus  having  already  been  lost  by  ab- 
sorption— and  the  tlilcke  'j  of  the  peridental  membrane.  In  this  case 
the  teeth  loosen  in  their  sockets  and  the  peridental  membrane  becomes 
profoundly  changed  in  its  character  and  qualities.  But  before  this  time 
there  is  little  else  to  do  than  to  keep  the  teeth  clean  after  once  removing 
all  the  crusts.  There  is  usually  seen  an  increased  tendency  to  the 
growth  of  the  fungi  of  the  mouth  about  the  necks  of  the  teeth  during 
the  healing  process,  and  this  cause  alone  is  very  often  sufficient  mate- 
rially to  retard  the  cure.  These  should  be  carefully  removed  at  least 
twice  a  day  for  a  time,  using  for  the  purpose  a  soft  brush  and  some  dis- 
infectant lotion ;  water  strongly  acidulated  with  lemon  or  orange,  or 
even  water  alone,  will  answer.  The  motion  of  the  brush  should  always 
be  lengthwise  of  the  teeth  instead  of  across  them,  as  is  the  manner  of  most 
persons  in  cleaning  the  teeth ;  this  point  is  important,  and.  the  patient 
should  be  very  carefully  instructed  in  regard  to  it.  The  brush,  used  in 
this  way,  will  clean  the  teeth  better,  and  at  the  same  time  injure  the 
inflamed  gum  less,  than  in  any  other  way.  In  the  greater  number  of 
cases  this  is  all  that  is  required  to  complete  the  cure.  But  the  operator 
should  keep  every  case  ujider  his  care  until  it  is  quite  well,  for  it  will 
often  happen  that  some  points  will  need  attention  that  have  seemed  to 
be  doing  well  for  a  week  or  two,  and  examination  will  sIioav  additional 
calculus  requiring  removal. 

In  cases  of  long  standing  in  which  there  has  been  considerable  wast- 
ing of  the  alveolus  and  general  enlargement  of  tlie  sockets  of  the  teeth, 
Avith  thickening  of  the  peridental  niembrane,  still  more  care  should  be 
taken  with  the  after-treatment.  Much  more  time  will  be  required  for 
the  return  of  the  tissues  of  the  peridental  membrane  and  gum  to  the 
normal  condition.  Indeed,  the  normal  condition  of  the  parts  will  never 
be  completely  restored.  The  case  will^  usually  recover,  if  at  all,  with 
more  or  less  of  the  root  of  the  tooth  denuded  of  peridental  membrane 
and  gum,  which  tooth  will  ever  after  be  more  liable  to  deposits  of  cal- 
culus ;  it  will,  therefore,  require  more  vigilance  on  the  part  of  the 
patient  to  keep  it  well  after  health  is  attained. 

In  many  cases  of  calcic  inflammation  the  tissues  will  be  found  in  a 
state  of  active  inflammation,  turgid,  and  much  thickened.  In  this  con- 
dition I  have  found  a  from  2()-to-30-per-cent.  solution  of  chloride 
of  zinc,  applied  carefully  about  the  teeth,  very  effective  in  con- 
stringing  the  gum   and    removing   from    the  tissue  the  condition  of 


TREATMENT  OF  CALCIC  INFLAMMATION. 


967 


Fig.  516. 


extreme  congestion.  This  is  applied  to  the  best  advantage  by 
wliat  is  known  as  Farrar's  syringe  (Fig- 
Si  6),  by  the  use  of  which  the  remedy  is 
placed  in  the  exact  position,  and  in  the 
amount  desired.  This  instrument,  or  some 
instrument  that  possesses  its  advantages, 
should  be  u.sed  for  the  application  of  any 
of  the  remedies  for  this  disease,  except,  it 
may  be,  the  milder  washes  with  which  the 
patient  may  be  entrusted.  Without  such  an 
appliance  it  is  simply  impossible  to  place 
the  remedies  in  the  position  required.  The 
only  ])oint  at  which  the  application  of  rem- 
edies is  especially  effective  is  under  the  frep 
margin  of  the  gum,  and  instruments  must  be 
iised  by  which  this  can  be  accomplished.  In 
these  cases  escharotics  should  not  be  used  in 
the  after-treatment,  except  within  the  first 
few  days.  Remedies  of  this  class  reduce  the 
vitality  of  the  tissues  to  which  they  are  ap- 
plied ;  indeed,  unless  they  are  used  for  the 
purpose  of  destroying  something  that  serves 
to  keep  up  the  irritation,  such  as  micro- 
organisms in  the  outer  strata  of  partially 
dead  tissue,  or  for  the  complete  destruction 
of  tissue  so  low  in  the  scale  of  vitality  as  to 
make  this  advisable,  they  should  not  be  ap- 
plied at  all.  With  this  end  in  view,  it  is 
occasionally  well  to  use  carbolic  acid  full 
95  per  cent,  in  the  beginning  of  the  treat- 
ment. Magitot  has  advised  the  use  of 
clu'omic  acid  ;  other  cauterants  also  may  be 
used.  But  after  one  or  two  applications  any 
of  these  substances  should  be  discarded  in 
favor  of  those  remedies  that  tend  more  to 
the  stimulation  of  the  tissues.  For  this 
purpose  there  is  perhaps  nothing  better  than 
tlie  oil  of  cinnamon.  The  ordinary  cinna- 
mon water  makes  a  very  agreeable  wa.sh, 
but  is  not  of  sufficient  strength  to  be  very 
effective.  Where  there  is  great  tissue-injury,  I  have  found  the  fol- 
lowing an  excellent  remedy  : 

Take  of  Oil  of  cinnamon,  dr.  iv. 

Oil  of  gaultheria,  dr.  iv. 

Carbolic  acid  (crystals),  dr 


Farrar's  Syringe  for  the  Application 
of  Remedies  in  Diseases  of  the 
Peridental  IVJembrane. 


Mix. 


This  may  be  freely  used  on  the  brush,  or  may  be  made  into  an  emul- 
sion in  water  at  the  time  of  using,  and  in  that  way  used  as  a  wash. 
This  is  at  once  a  fairly  good  antiseptic  and  stimulant,  and  is  a  very 
efficient  remedy.     The  principal  indication  is  to  keep  the  parts  clean, 


968  DISEASES   OF  THE  PERIDENTAL   MEMBRANE. 

and  to  stimulate  mildly  those  tissues  that  have  been  in  a  state  of  inflam- 
mation for  so  long-  as  to  have  lost  their  tone,  until  they  have  recovered 
their  vigor.  Any  plan  of  treatment  that  will  effect  this  will  answer  all 
the  requirements.  Our  materia  medica  contains  a  large  number  of 
ap])ropriate  remedies. 

In  those  cases  of  long  standing  in  which  the  alveolus  is  so  much 
destroyed  that  the  teeth  have  already  become  very  loose  not  much  can 
be  done  (Fig.  517) ;  the  rule  is  that  the  patient  will  do  better  with  arti- 

FiG.  517. 


The  Alveoli  irreparably  destroyed  by  Calcic  Inflammation. 

ficial  teeth.  If,  however,  it  is  only  the  four  lower  incisors  that  have 
become  very  loose — as  often  happens — and  the  remaining  teeth  can  be 
readily  cured,  these  incisors  may  be  secured  to  the  others  by  wiring  or 
by  slender  clasps,  thus  keeping  them  moderately  firm,  and  so  fitting 
them  to  do  fairly  good  service,  often  for  a  long  time,  if  sufficient  care 
is  taken  to  keep  them  clean.  They  will  often  serve  better  than  artificial 
teeth  in  this  position. 

The  general  law  as  regards  prognosis  is  this :  If  the  gum  covers 
the  root  sufficiently  to  form  an  alveolus  of  sufficient  depth  to  hold  the 
tooth  with  the  necessary  firmness,  it  may  be  expected  that  care  and  time 
will  restore  the  membrane  to  health  and  the  bony  parts  will  be  suf- 
ficiently rebuilt  to  serve  the  purpose  of  holding  the  tooth  in  its  posi- 
tion ;  but  if  the  gum-tissue  is  gone  as  shown  in  Fig.  517,  there  is  prac- 
tically no  hope  for  a  restoration.  Then  the  continual  looseness  of  the 
teeth  will  in  itself  serve  as  an  irritant  to  perpetuate  the  inflammation. 

Pliacjcdcnlc  Pcv'wementitiH,  or  Destructive  Inflammation  of  the  Peri- 
dental INIembrane. — Phagedenic  pericementitis  is  a  disease  distinct  from 
those  previously  described,  yet  it  has  many  features  in  common  with 
them.  It  may  have  its  beginning  in  a  gingivitis  that  in  its  inception 
cannot  be  distinguished  from  the  simple  form,  or  its  character  may  be 
masked  by  deposits  of  either  serumal  or  salivary  calculus.  On  some 
accounts  it  would  seem  to  merit  the  name  of  infectious  pericementitis, 
but  I  do  not  regard  the  infectious  character  of  the  affection  as  suf- 
ficiently well  established  to  warrant  such  an  appellation,  and  for  this 
reason  must  therefore  regard  the  term  "  infectious  alveolitis " — used 
by  Dr.  Adolph  Witzel  of  Essen,  Germany — as  premature.  Further- 
more, it  seems  to  me  that  the  disease  is  essentially  one  of  the  peridental 
membrane  rather  than  of  the  walls  of  the  alveolus,  as  would  be  indi- 
cated by  the  use  of  Dr.  Witzel's  terminology.     If  the  disease  were  of 


PHAGEDENIC  PERICEMENTITIS.  969 

tlie  bony  walls  instead  of  the  contents  of  the  alveolns,  I  see  no  reason 
why  the  ailment  should  be  cured  simply  by  the  removal  of  the  teeth  ; 
certainly,  if  the  disease  were  essentially  of  the  bone,  this  result  Avoidd 
not  so  invariably  follow.  But,  on  the  other  hand,  it  can  be  readih- 
understood  how,  the  disease  being  essentially  of  the  peridental  mem- 
brane, the  removal — the  destruction — of  this  would  terminate  the 
case.  This  agrees  also  with  my  observations  as  to  the  starting-point 
and  the  order  of  progress  of  this  pathological  condition. 

The  disease  under  consideration  consists,  then,  in  an  inflammation  of 
a  peculiar  character  wliich  results  in  the  destruction  of  the  peridental 
membrane.  This  destruction,  also,  is  closely  followed  by  the  absorption 
of  the  walls  of  the  alveolus;  so  that  in  the  end  both  are  destroyed.  The 
disappearance  of  the  two  is  so  nearly  synchronous  that  it  is  often  diffi- 
cult to  say  which  has  gone  first ;  indeed,  they  seem  to  go  together.  In 
its  least  complicated  form  the  disease  is  not  accompanied  with  salivary 
calculus,  or  calculus  of  any  kind.  It  seems  to  consist  essentially  in  an 
inflammation — which  may  be  acute  or  chronic — by  which  the  peridental 
membrane  is  separated  from  the  root  of  the  tooth  and  destroyed  fibre 
by  fibre,  cell  by  cell,  very  much  as  bone  is  destroyed  molecule  by  mole- 
cule in  the  disease  known  as  caries.  In  the  progress  of  this  destruction 
the  membrane  first  becomes  swollen ;  its  individual  fibres  are  very 
much  enlarged  and  lengthened  and  intermixed  with  an  abundance  of 
inflammatory  elements.  The  fibres  seem  first  to  separate  from  the  root 
of  the  tooth  and  then  to  melt  down,  but  still  to  retain  their  hold  on 
the  alveolar  wall  until  completely  destroyed.  There  is  not  necessarily 
any  considerable  inflammation  of  the  gums ;  they  are  generally  but 
slightly  aflected.  In  the  chronic  forms  the  disease  is  often  limited  very 
strictly  to  the  peridental  membranes.  So  fiir  as  I  have  had  opportunity 
to  observe  its  beginnings,  it  seems  to  take  the  form  of  a  simple  gingi- 
vitis, presenting  a  reddening  of  the  gingival  margins  about  the  teeth 
attacked,  this  soon  disappearing  as  the  disease  advances,  or  possibly 
becoming  less  apparent  on  account  of  the  more  general  reddening 
of  the  neighboring  gum  tissue.  At  first  there  will  be  seen  only  an 
irritation  of  the  gingivae,  but  after  this  has  persisted  for  some  time 
close  examination  will  show^  that  the  lo^ver  margin  of  the  membrane 
is  destroyed  here  and  there  in  such  a  way  that  a  thin,  flat,  but  dull, 
blade  ^vill  pass  up  along  the  side  of  the  root  farther  than  it  should. 
A  destruction  of  the  tissue  of  the  peridental  membrane  has  begun, 
and  already  there  is  a  slight  j^ocket  that  contains  a  very  little  pus.  This 
destructive  process  extends  gradually  toward  the  apex  of  the  root — /.  e. 
follows  the  length  of  the  fibres  of  the  membrane — and  in  most  cases 
narrow,  deep  pockets  are  formed  beside  the  root  of  the  tooth  (Figs.  518 
and  519).  This  may  occur  only  at  one  side  of  the  root  or  at  two  or 
three  points,  which  may  be  on  the  lingual  or  buccal  sides  of  any  of 
the  teeth,  or  it  may  attack  the  proximal  sides — indeed,  any  part  of  the 
mend^rane.  As  tlie  destructive  process  extends  lengthwise  of  the  root 
it  also  more  slowly  widens,  often  quite  irregularly,  extending  around  the 
root ;  so  that  the  tendency  is  to  the  destruction  of  the  entire  root-mem- 
brane. It  is  usually  very  irregular  in  its  attacks ;  cases  are  seen  in 
which  the  disease  is  for  some  time  confined  to  one  side  of  the  root  of  a 


970 


DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 


single  tooth  or  of  two  or  three  teeth.  But  the  infectious  character  of 
the  aifection  is  shown  by  the  tendency  to  attack  the  neighboring  teeth, 
for  in  this  way  they  are  liable  to  fall  one  by  one.     This  lial)ility  is  not 

^^'"•'^^^-  Fig.  519. 


Mi- 


Section  of  an  Upper  Molar  showing  De- 
struction of  its  Membrane  and  Alveolar 
Wall  by  Phagedenic  Pericementitis:  a, 
deposit  of  serumal  calculus;  6,  ft,  gum 
covering  pus-cavity  (r,  <•)  formed  by  the 
destruction  of  the  peridental  membrane 
and  alveolar  wall.  (Compare  with  Pigs. 
5uii  and  507.) 


Section  of  Upper  Incisor  showing 
Destruction  of  its  Peridental 
ISIembrane  and  Alveolus  by 
Phagedenic  Pericementitis  :  a, 
gum-tissues  covering  pus-cavity 
ifc)  formed  by  the  destruction  of 
the  peridental  membrane  and 
alveolar  wall. 


confined  to  particular  groups  of  teeth,  as  is  the  case  with  inflammation 
from  salivary  calculus  attacking  the  lower  incisors  or  upper  molars,  but 
seems  to  attack  any  of  the  teeth  indifferently,  no  particular  one  being 
more  liable  to  it  than  others.  When  the  disease  is  confined  to  one  side 
of  the  root,  as  the  lingual  sides  of  the  upper  incisors,  the  teeth  are  very 
liable  to  be  gradually  displaced,  moving  in  a  direction  jrom  the  diseased 
surface ;  so  that  the  teeth  mentioned  will  slowly  protrude  forward.  This 
is  probably  to  be  accounted  for  by  the  swelling  of  the  membrane.  In 
this  manner  the  teeth  may  be  gradually  distorted  as  to  their  relative 
positions.  This  is  frequently  seen  in  the  separation  of  particular  teeth 
when  the  proximal  sides  of  the  roots  are  the  points  of  attack. 

INIore  rarely  the  entire  gingival  margin  of  the  peridental  membrane 
is  attacked  at  once  and  all  destroyed  together.     I  have  seen  this,  how- 
ever, in  but  few  instances,  the  formation 
of  pockets  being  the  rule.     These  pock- 
Q,  ^^^^^-0      cts  deepen  and  waden,  and  finally  encir- 

^'^.■-••.  f/'  \?  cle   the    root    of  the   tooth,    but    much 

j^  _, Ob     ofitener  pass  up  the  length  of  the  root 

to  its  apex  before  it  has  completely  en- 
circled it.  When  the  disease  is  not 
com])licated  wnth  deposits  of  calculus, 
it  often  happens  that  the  entire  apex 
of  the  root  is  stripped  of  its  membrane, 
while  the  tooth  is  still  held  in  place  by 

Illustration    of   a   Case    of   Phagedenic       r\  \  c  •  i         i*  j.1  „    ,  „„I 

Pericementitis:   «,«,  dotted  lines  rep-       tilC    membrane    of    OUC    Sldc    ot    tllC    I'OOt, 

resenting  the  outlines  of  the  roots  of       \vhiV»h  lint^    it;    vpt  bpPTi  but  littlp  nffpctpd 
the  teeth;   ft.  ft,  irregular  lines  repre-       ""/<-'!  "^'^    ^^    ^^^   "^t!U   OUl  lltXie  ailCLlLU 

senting  the  extent  of  the  destruction       (Ficrs.    521      522).        EvCll    in     tllis     COll- 
of  the  peridental  membrane  and  walls       \.    .^   '     ,         '  ''  ,  />  •    i  i 

of  the  alveolus.   It  will  be  noted  that     ditiou  the  guuis  mav  havc  a  lairJy  good 

the  nums  appear  nearly  perfect.  (Com-  .i  'mi       I  .^,„,I.^  '  ,.^^1 

pare  with  Figs.  -yi\  and  527.)  appearaucc  ;    they  wall  show  more   red- 


FiG.  520. 


PHA  GEDENIC  PERICEMENTITIS. 


971 


ness  than  normal  and  will  occasionally  be  deeply  injected,  especially  if 
the  tooth  has  periods  of  soreness.     Usually  there  is  little  or  no  recession 
of  the  gum,  and  casual  observation  might  not  detect  the  presence  of  the 
Fig.  521. 


Fig.  522. 


Fig.  523. 


The  same  case  shown  in  Fig.  519  denuded  of  the  soft  Loss  of  Bone  and  thickening  of  the  Eorders 

tissues  to  show  more  plainly  the  loss  of  the  walls  of  the  Lost  Portion  from  Phagedenic  Peri- 

of  the  alveolus.    This  drawing  was   made   after  cemeutitis.     Shown    denuded    of    the    soft 

raising  a  semicircular  flap  ol  the  soft  tissues  over  tissues, 
each  root  for  the  purpose  of  thorough  exploration. 
(See  Fig.  527.) 

disease.     In  respect  to  the  outward  appearance  of  disease,  however,  there 
may  be  observed  the  greatest  variety. 

The  margins  of  the  alveolar  processes  usually  disappear  as  the  de- 
struction of  the  peridental  membrane  advances.  Whether  this  precedes 
or  follow\s  the  destruction  of  the  membrane  is  often  difficult  to  deter- 
mine, but  I  have  seen  enough  cases  in  which  it  was  clearly  demonstra- 
ble that  the  destruction  of  the  peridental  membrane  preceded  the  wast- 
ing of  the  process  to  convince  me  that  such  wasting  is  simply  a 
result  of  the  loss  of  the  membrane,  as  is  the  case  when  a  tooth  is 
extracted.  There  is,  however,  something  more  than  this ;  for  effects 
of  di.sea.>^e  of  the  process  other  than  absorption  are  found.  In  a  consid- 
erable number  of  cases,  especially  those  of  the  more  chronic  forms  of 
the  disea.^e,  we  may  discover  a  definite  thick- 
ening of  the  alveolar  wall  at  or  near  its  mar- 
gin w^hich  is  clearly  the  result  of  exostosis 
brought  about  by  the  irritation  in  the  imme- 
diate neighborhood.  In  most  if  not  all  of 
these  cases  the  peridental  membrane  will  be 
found  destroyed  between  this  thickened  rim 
and  the  root  of  the  tooth.  Furthermore,,  if 
the  gum  be  slit  up  and  turned  back,  giving 
time  for  the  blood  to  be  sufficiently  cleared 
away  to  get  a  good  view  of  the  parts,  it  is 
readily  determined  that  the  portion  of  the 
alveolus  lying  next  the  tooth  has  been  ab- 
sorbed. We  have,  therefore,  an  absorption 
of  the  inner  portion  of  the  alveolar  wall  and 
at  the  same  time  a  deposit  of  bone  on  the 
outer  portion  ;  so  that  finally  the  margin  of 
the  alveolar  wall  is  decidedly  thickened  in 
such  a  w^ay  that  the  gum-tissue  is  held  away 
from  the  root  of  the  tooth.  .  This  usually  occurs  on  the  buccal  or  pala- 
tine wall ;  this,  as  it  causes  the  gum  to  project,  can  be  seen,  and  may  be 


Section  of  an  Upper  Incisor  show- 
ing Destruction  ot  the  Peridental 
Membrane  and  Eversiou  of  the 
Alveolar  Wall  wiih  thickening 
of  its  Border:  o,  serumal  calcu- 
lus; 6,  thickened  border  of  the 
alveolar  wall;  c,  pus-cavity. 


972  DISEASES  OF  THE  PERIDENTAL   MEMBRANE. 

readily  felt  with  the  finger.  In  these  cases  the  absorption  of  the  inner 
wall  of  the  alveolus  is  readily  determined  by  thrusting  a  delicate  poir.t 
through  the  tissues  inside  of  this  rim  and  exploring  the  widened  alveo- 
lus (Fig.  523).  Even  in  slowly-progressive  cases  this  thickening  of 
the  rim  of  the  alveolus  is  by  no  means  constant,  and  then  the  rim 
of  the  alveolus  is  simply  destroyed ;  in  this  case  there  is  often  a  cha- 
racteristic falling  away  of  the  gum  if  the  destructive  process  has  eaten 
awav  the  whole  septum  between  two  teeth.  The  appearance  is  much 
the  same  as  that  often  seen  in  calcic  inflammation,  already  described. 
But  many  cases  will  be  found  where  there  is  a  deep  pocket  on  the 
proximal  side  of  the  root  of  one  tooth,  while  the  membrane  of  its 
neighbor  is  uninjured  ;  and  in  this  case  the  gum  will  usually  be  sup- 
ported in  its  position  by  a  lamina  of  bone  that  will  remain  next  to  the 

sound  membrane  and  may  appear  complete 
Fk;.  o'24.  (Fig.  524).     The  thickening  of  the  rim  of 

the  alveolus  is  usually  very  irregular  and 
but  rarely  fully  encircles  the  tooth.  It  may 
border  the  destructive  process  in  any  posi- 
tion, and  may  sometimes  be  seen  bordering 
a  deep  pocket  over  which  the  whole  thick- 
ness of  the  alveolus  is  destroyed  (Figs.  521 
and  524);  in  this  way  oddly-shaped  prom- 
"^Zf aM  twcLnini  of 'Ihe-Ror:  i»ences  of  the  alvcolus  are  occasionally  seen. 
(1  rs  of  the  Lost  Portion  from     And,  as  the  destructivc  proccss  is  ffoiup;  on 

Phagedetiic     Perieeiuentilis.      It       ,  ',       ^,.       .i-i         •  p    l^        i  i 

will  be  observed  that  only  half  l)eneatli  tliis  tliickenuig  ot  the  Doiie,  there 
McSidl'^s'desiV'ovId- th'rpl:"  will  often  be  found  jagged  prominences  that 
^^J^^s^X^l^^^l     ^^'^11  "^  themselves  interfere  with  the  healing 

the   bone    immediately   adjacent  proCCSS    if    thcv  are    UOt    rcmOVcd    at    the    bc- 

to  the  sound  membrane  is  main-  ^  .        .  o     ^  mi  •        i  •    i 

tained.     Also  note  tlie  sel)aration  ginUHlg  OI    the    treatment.        ilUS   thickcmng 

oyhe  teeth.    ,<  on.pare  with  Fig.  ^^  ^^^  alvColuS    is    UOt  SCCU  iu  the    CaSCS  that 

progress  very  rapidly.  The  destruction  of 
bone  in  the.se  cases  seems  to  be  a  process  of  absorption  rather  tlian 
molecular  necrosis,  and  is  in  part  the  result  of  the  pressure  caused  by 
the  swelling  of  the  membrane  in  its  inflamed  state  and  partly  from  the 
condition  of  irritation  of  the  membrane  causing  it  to  take  on  an  absorp- 
tive action.  I  have  seen  but  few  cases  in  Avhich  actual  necrosis  of  the 
alveolar  border  could  be  determined — so  few  that  I  must  regard  this 
condition  as  resulting  from  some  accidental  condition  not  necessarily 
pertaining  to  the  disease. 

]M.  iSIagitot  has  spoken  of  absorption  of  the  roots  of  the  teeth  in 
connection  with  this  disease  ;  I  had  not  seen  this  until  recently.  Within 
the  past  year  I  have  met  with  two  marked  cases,  in  which,  so  for  as  I 
am  able  to  determine,  the  absorption  Mas  due  to  the  irritation  of  the 
membrane.  It  seems  evident  from  the  nature  of  the  aflection  that 
this  would  occur  l)ut  rarely.  The  membrane  is  first  separated  from 
the  root,  and  absor])tion  of  that  part  of  the  root  could  not  take 
place  afterward,  for  the  reason  that  the  pus  would  prevent  the  contact 
of  tiie  living  tissue.  I  have  expected  trouble  from  the  absorption 
of  the  roots  after  healing,  but  as  yet  have  met  with  no  cases.  Tlie 
absorption  of  the  alveolar  wall  is  easily  understood,  for  the  living  tis- 


PHA  GEDENIC  PERICEMENTITIS. 


973 


Fig.  525. 


sue  usually  remain.s  in  contact  with  it — at  least,  for  a  considerable  time 
— and  even  when  it  is  entirely  denuded  it  contains  -within  its  bony 
structure  the  elements  necessary  to  bring  about  its  absorption.  How 
much  of  the  eversion  of  the  wall  of  the  alveolus  may  be  due  to  the 
pressure  caused  by  the  swelling  of  the  membrane  is  hard  to  determine. 
In  some  cases  that  I  have  recently  studied  very  closely  I  cannot  account 
for  the  eversion  in  any  other  way,  impossible  as  this  seems  at  first 
glance.  All  of  these  seemed  to  be  acute  cases.  In  one  I  made  a 
very  critical  examination  after  slitting  the  gum  and  laying  it  off  from 
the  bone.  I  found  the  width  of  the  space  between  the  root  of  the  tooth 
and  the  bone  to  be  three-sixteenths  of  an  inch.  The  shape  of  the  space 
is  shown  in  the  drawing  (Fig.  525).  In 
this  case  there  had  been  no  complaint  of 
trouble  in  this  locality  dating  back  more 
than  two  Aveeks,  and  I  had  carefully  exam- 
ined the  mouth  six  weeks  before  without 
discovering  anything  of  this  nature.  Two 
years  before,  I  had  treated  this  patient  for 
phagedenic  pericementitis  affecting  a  num- 
ber of  the  u]ipcr  teeth,  and  ever  since  had 
kept  watch  of  it  to  note  the  progress  of  the 
reformation  of  the  alveolar  walls  lost  at  that 
time,  some  of  which  are  as  yet  represented 
only  by  soft  tissue.  My  own  observation, 
together  with  the  statements  of  the  patient, 
would  indicate  that  this  eversion  had  oc- 
curred within  the  space  of  t^'o  or  three 
weeks.  There  had  been  considerable  pain 
for  about  a  week ;  and  when  I  first  saw  it, 
the  gum  was  inflamed  and  swollen  and  pus 
Avas  discharging  freely  from  under  the  free 
margin.  I  cut  out  the  everted  portion  of 
the  bone,  and  after  washing  thoroughly  with  peroxide  of  hydrogen  in 
which  1  grain  of  bichloride  of  mercury  to  the  ounce  was  dissolved  I 
stitched  the  gum  back  snugly  about  the  neck  of  the  tooth,  and  it  healed 
almost  as  readily  as  an  incised  wound.  This  case  seems  quite  novel ; 
and  if  it  had  not  occurred  in  a  mouth  that  had  previously  been  infected 
with  phagedenic  pericementitis,  I  might  have  passed  it  by  for  the  time 
as  an  abscess  occurring  from  some  accidental  cause.  The  other  cases 
of  similar  character  that  I  have  seen  have  not  run  so  rapid  a  course. 
The  following  case  may  be  regarded  as  representative  of  the  most 
acute  form  of  this  disease.  About  one  year  ago  Miss  D.,  a  teacher, 
called  on  me  for  advice,  saying  that  for  three  months  she  had  had  pain 
in  the  teeth  of  the  right  side  of  her  mouth  which  came  on  every  week 
or  two,  would  last  two  or  three  days,  and  then  subside.  The  pain  was 
not  very  .severe  at  any  time,  but  radiated  more  or  less  to  the  cheeh,  malar 
process,  and  temple.  At  these  times  the  teeth  on  the  affected  side  were 
sore  to  the  touch  and  she  was  not  able  to  chew  on  that  side  of  her  mouth, 
and  latterly  some  of  the  molars  were  sore  almost  continuously.  An 
examination  of  the  teeth  revealed  no  decay.     The  eye  detected  a  pro- 


Acute  Pericementitis  with  Eversion 
of  the  Alveolar  Wall:  a,  swollen 
gum,  which  is  raised  above  its 
normal  position  on  the  crowji  of 
the  tooth;  fc,  everted  alveolar 
wall ;  c,  pus-cavity,  which  al>o 
apiiears  to  contain  fibres  of  the 
peridental  membrane  clinging  to 
the  wall  of  the  alveolus. 


974  DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 

noimced  hyperemia  of  the  gums  about  the  molars  of  the  affected  side, 
especially  of  the  upper  jaw — not  particularly  of  the  margins  of  the 
gums,  but  extending  over  their  entire  buccal  surface.  The  gums,  how- 
ever, fitted  properly  to  the  teeth  without  any  sign  of  shrinkage.  The 
teeth  showed  signs  of  good  care ;  there  was  no  calculus  or  other  accu- 
mulation to  be  seen  about  them  anyAvhere.  The  second  upper  molar 
had  too  much  motion  in  its  socket,  but  would  not  be  called  very  loose. 
Taking  a  thin,  flat  scaling-instrument,  I  passed  it  up  under  the  free 
margin  of  the  gum  of  this  tooth,  and  found  the  peridental  membrane 
completely  destroyed  over  the  entire  surface  of  the  buccal  roots.  By 
passing  a  small  needle-like  exploring-instrument  through  the  tissues  in 
various  directions  I  fouiid  that  the  entire  buccal  wall  of  the  alveolus 
was  gone,  and  also  nnich  of  that  part  of  the  bone  between  the  buccal 
and  palatine  roots.  The  third  molar  had  a  narrow,  deep  pocket  at  the 
posterior  part  of  the  buccal  surface.  About  the  first  molar  there  were 
two  pockets,  which,  taken  together,  almost  encircled  the  tooth,  but  were 
not  very  deep.  The  first  bicuspid  had  a  deep,  narrow  pocket  extending 
up  two-thirds  of  the  length  of  the  root.  On  the  buccal  side,  extending 
around  to  the  proximal  side  of  the  anterior  root  of  the  lower  first 
molar,  there  was  a  pocket  extending  almost  the  length  of  the  root,  with 
a  corresponding  loss  of  bone.  There  were  a  few  other  points  of  attack 
of  less  note  in  other  parts  of  the  mouth.  By  reference  to  my  records 
I  found  that  I  had  not  examined  the  lady's  mouth  for  fourteen  months. 
I  had  made  a  large  number  of  fillings  for  her  in  the  years  past,  and  had 
kn()^vn  her  as  a  very  careful  patient.  I  feel  very  certain  that  there 
could  have  been  no  beginning  of  this  disease  prior  to  my  last  examina- 
tion of  the  mouth,  therefore  all  of  this  destruction  had  occurred  since 
that  time.  The  patient  had  noticed  it  only  three  months  before.  I 
extracted  the  upper  second  molar,  and  then  found  that  the  only  part  of 
the  peridental  membrane  that  was  perfect  was  that  of  the  palatine  side 
of  the  palatine  root ;  all  of  tlie  membrane  was  destroyed  but  this.  No 
salivary  or  serumal  deposits  whatever  were  found  upon  the  tooth  or  its 
root.  The  remaining  teeth  were  at  once  put  under  treatment,  and 
by  the  use  of  antiseptic  stimulants  a  cure  was  readily  effected,  with 
complete  restoration  of  the  membranes. 

In  another  instance  a  lady  came  to  me  with  one  of  her  bicuspids  in 
her  hand.  She  said  that  on  account  of  its  apparent  looseness  she  had 
called  the  attention  of  her  dentist  to  it  only  a  month  before,  and  had 
been  informed  that  no  disease  could  be  found.  Two  days  before  calling 
on  me  she  had  picked  it  out  with  the  thumb  and  finger.  An  examina- 
tion revealed  the  fact  that  there  Avas  very  serious  destruction  going  on 
al)out  the  roots  of  a  number  of  the  remaining  teeth.  Usually,  the  gums 
do  not  sliow  much  inflammation  unless  the  case  is  complicated  with  de- 
posits of  calculus,  and  in  this  case  there  was  so  little  appearance  of  any 
serious  disease  that  a  dentist  of  good  repute  had  failed  to  discover  it, 
though  his  attention  had  been  directly  called  to  it  by  the  patient. 

These  I  regard  as  the  most  typical  cases  of  the  acute  form  of  the  dis- 
ease when  not  complicated  with  deposits  of  calculus.  The  rule  is  that 
the  progress  is  slower  and  there  is  more  appearance  of  disease  to  be  seen 
in  the  neighboring  parts  than  in  the  cases  just  cited.     I  have  one  case 


PHAGEDENIC  PERICEMENTITIS. 


975 


Fig.  526. 


now  under  observation  that  for  five  years  I  have  been  watching  without 
using  anything  more  than  a  little  palliative  treatment.  When  I  first 
ob.served  it,  it  was  in  its  inception,  and  I  have  had  the  opportunity  of 
frequent  examination ;  and,  fortunately,  there  has  been  only  very  little 
salivary  calculus  to  complicate  the  case,  and  this  is  confined  to  the  lower 
incisors.  In  this  time  eight  teeth  have  been  lost,  and  some  others  are  in 
a  very  precarious  condition.  Soreness  of  the  affected  teeth  comes  on  at 
irregular  intervals,  lasting  a  few  days  at  a  time  and  then  passing  away. 
This  is  common  to  the  most  of  these  cases,  though  I  have  seen  a  number 
that  had  made  considerable  progress  without  any  complaint  of  pain  at 
any  time. 

A  class  of  cases  occur  on  the  lingual  sides  of  the  superior  incisors  that 
seem  rather  different  from  the  usual  types,  and  yet  are  evidently  of  the 
same  nature.  They  are  generally  compli- 
cated with  serumal  deposits  on  the  necks 
of  the  teeth,  and  I  think  occur  oftenest 
in  those  persons  that  breathe  mostly 
through  the  mouth.  They  have  generally 
been  rather  persistent.  Fig.  527  is  a  sec- 
tional illustration  from  one  of  these.  The 
gum  is  usually  thickened  from  the  inflam- 
mation of  its  tissue  and  on  account  of  the 
lo.ss  of  the  alveolar  wall  recedes,  exposing 
more  or  less  of  the  roots  of  the  teeth.  The 
teeth  are  often  protruded  to  such  an  extent 
as  to  render  them  unsightly.  They  are 
usually  very  slow  in  their  progress,  and 
are  apt  to  have  serumal  deposits  extending 
high  up  toward  the  apex  of  the  root. 

Thus  far  I  have  spoken  mostly  of  that 
class  of  cases  that  have  not  been  complicat- 
ed with  deposits  of  salivary  or  serumal  cal- 
ulus.  This  may.  be  said  to  be  the  simplest 
form,  but  it  is  not  the  least  destructive 
one,  for  I  have  seen  the  peridental  membrane  destroyed  as  rapidly 
without  deposits  of  calculus  as  with  them.  Indeed,  so  far  as  the  results 
are  concerned,  the  presence  of  calculus  seems  to  make  but  little  differ- 
ence. The  great  majority  of  the  cases  are  complicated  with  these  deposits. 
The  rule  is  that  we  find  nodules  of  serumal  calculus  under  the  margin 
of  the  gum  even  though  the  mouth  has  been  well  cared  for ;  and  if  there 
has  not  been  good  care  as  to  cleanliness,  there  will  usually  be  deposits 
of  salivary  calculus  also.  When  this  occurs  in  considerable  quantity, 
the  appearance  of  disea.se  becomes  much  more  apparent  because  of  the 
greater  inflammation  of  the  gum-tissue  cau.sed  by  the  calculus.  Here 
we  have,  in  fact,  the  two  diseases  existing  together — calcic  inflammation 
from  the  deposits  of  calculus,  and  phagedenic  inflammation  farther  up 
toward  the  apex  of  the  root  of  the  tooth.  It  is  evidently  this  dual  form 
so  often  presented  by  these  affections  that  has  so  long  delayed  the  recog- 
nition of  the  phagedenic  variety  as  an  independeiTt  disease.  Every  one 
who  has  had  any  considerable  experience  in  the  treatment  of  this  class 


Phagedenic  Pericementitis  compli- 
cated witli  Serumal  Calculus  on 
the  Lingual  Surface  of  the  Upper 
Incisors  (sectional  view):  cr,  ser- 
umal calculus;  b.  inflamed  and 
thickened  gum  that  has  fiillen 
into  the  space  made  by  the  loss 
of  bone,  exposing  a  part  of  the 
serumal  calculus;  c,  pus-cavity. 


976  DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 

of  cases  must  have  noticed  the  great  differences  they  manifest  in  regard 
to  healing  after  the  removal  of  the  calculus.  This  is  not  to  be  explained 
in  all  cases  by  imperfections  in  the  performance  of  the  operation.  A 
certain  minority  of  the  cases  \\\\\  not  heal,  no  matter  how  perfectly  this 
is  done ;  but  the  turgescence  of  the  gum  will  diminish  while  the  dis- 
charge of  pus  continues  and  the  destructive  process  is  still  in  unabated 
progress.  This  is  the  one  fact  that  has  so  discouraged  the  profession 
with  the  treatment  of  these  cases.  It  often  has  happened  that  the  cases 
that  promised  the  best  results  have  proved  the  most  rapidly  destructive ; 
it  thus  becomes  a  matter  of  the  greatest  importance  that  we  be  able  to 
determine  whether  we  have  in  a  given  case  only  an  inflammation  of 
the  gums  from  deposits  of  calculus — calcic  inflammation — or  whether 
there  is  in  addition  a  phagedenic  inflammation  of  the  peridental  mem- 
brane. Our  prognosis  Avill  be  far  more  favorable  if  we  determine  that 
we  have  only  a  calcic  inflammation  to  deal  with.  The  absence  of  pock- 
ets extending  up  beside  the  roots  of  the  teeth  above  the  deposits  of  cal- 
culus (toward  the  apex  of  the  root)  is  the  surest  indication  of  the  absence 
of  the  phagedenic  form  of  the  disease.  If  this  disease  is  not  present,  it 
will  be  found,  when  the  last  of  the  salivary  calculus  is  removed,  that  the 
peridental  membrane  is  intact  just  above — that  is,  it  is  attached  to  the 
root  of  the  tooth.  There  are  no  points  where  the  peridental  membrane 
is  destroyed  much  farther  than  the  calculus  has  extended.  The  calcu- 
lus may,  however,  have  extended  so  far  as  to  cause  the  loosening  of  the 
teetli,  and  thus  bring  about  their  loss.  In  this  case  there  is  usually  far 
more  wasting  of  the  tissue  of  the  gum  than  in  phagedenic  pericementi- 
tis, and  there  is  usually,  perliaps  generally,  a  peculiar  thickening  of  the 
tissue  of  the  peridental  membrane  at  the  apex  of  the  root — the  tissue  of 
the  apical  space — which  holds  the  tooth  quite  firmly  and  yet  allows  it 
to  shake  about  in  the  remains  of  the  socket.  This  condition  is  quite 
uniformly  ab.scnt  in  phagedenic  pericementitis  ;  so  that  the  tooth  drops 
from  its  socket,  often  almost  without  effort,  though  it  has  not  seemed 
very  loose — that  is,  did  not  shake  about  much  in  the  remains  of  the 
socket.     This  difference  is  quite  characteristic. 

If  the  disease  is  phagedenic  pericementitis,  we  Mill,  on  the  other  hand, 
when  the  calculus  is  cleared  away,  find  that  the  peridental  membrane  is 
destroyed  at  particular  points  much  farther  than  the  calculus  has  extended 
on  the  root  of  the  tooth,  forming  the  pockets  I  have  described,  and  the 
wall  of  the  alveolus,  instead  of  being  destroyed  as  a  whole,  is  destroyed 
somewhat  in  the  form  of  Assures  extending  toward  the  apex  of  the  root ; 
or  it  is  only  over  a  portion  of  one  of  the  surfaces  of  the  root,  leaving 
angidar  prominences  of  the  bone  that  are  often  unduly  thickened,  as 
though  the  margin  of  the  bone  was  everted.  In  the  final  loosening  of 
the  tooth  it  will  usually  be  found  that  it  is  at  last  held  by  a  portion  of 
the  membrane  of  one  of  its  sides,  the  membrane  over  the  apex  of  the 
root  having  been  destroyed.  These  differences,  as  they  are  closely 
studied  from  day  to  day  in  the  examination  of  the  cases  that  present 
themselves  for  treatment,  become  quite  characteristic  and  afford  a  jn-etty 
reliable  ground  of  diagnosis.  I  have  given  these  points  at  some  length 
for  the  reason  that  they  have  been  so  generally  overlooked  by  the 
profession. 


ETIOLOGY  OF  PHAGEDENIC  PERICEMENTITIS.  977 

It  may  here  be  said  that  cases  occur  in  which  the  usual  types  are 
variously  combined,  and  Avhich  cannot  very  certainly  be  assigned  to 
either  one  or  the  other  class.  These  will  generally  be  old  chronic 
cases  of  calcic  inflammation  which  have  been  in  progress  for  many 
years,  and  in  which  the  gum  tissues  have  been  brought  to  so  low  a 
state  of  vitality  that  they  no  longer  resist  the  encroachments  of  the 
ordinary  micro-organisms  of  the  mouth  and  are  continually  invaded 
by  them.  In  these  cases  some  wide  pockets  may  be  seen  by  the  side 
of  the  roots  of  the  teeth,  but  there  is  a  more  general  Avasting  of  the 
tissues  and  a  more  dilapidated  appearance  of  the  whole  apparatus  of 
mastication.  In  this  class  of  cases  it  is  common  to  see  nearly  all  of  the 
teeth  loose — perhaps  very  loose — at  one  time,  none,  or  very  few,  having 
been  lost,  all  being  held  by  the  thickening  of  the  tissues  of  the  apical 
space.  This  state  of  things  is  characteristic  of  the  last  stages  of  general 
calcic  inflammation  of  the  peridental  membrane  and  gums,  and  is  sel- 
dom or  never  seen  in  the  phagedenic  variety. 

Another  point  should  not  be  overlooked.  It  sometimes  happens  that 
a  case  of  alveolar  abscess  simulates  the  form  of  phagedenic  pericemen- 
titis so  closely  as  to  cause  a  mistake  in  diagnosis.  In  this  case  an 
abscess  occurs  at  the  root  of  a  tooth  from  the  previous  death  of  the 
pulp  and  consequent  apical  pericementitis,  and  the  pus,  instead  of  being 
discharged  by  any  of  the  more  usual  routes,  eats  its  way  along  the  side 
of  the  root  and  is  discharged  at  the  margin  of  the  gum.  In  this  process 
the  peridental  membrane  is  destroyed  over  one  side,  or  a  portion  of  the 
side,  of  the  root,  forming  a  narrow  pocket  in  some  cases  very  much 
resembling  the  very  deep  pockets  of  phagedenic  pericementitis.  If  in 
such  cases  it  is  remembered  that  when  pockets  of  such  magnitude  are 
formed  by  the  disease  in  question  there  are  very  sure  to  be  other  points 
of  attack  in  the  neighborhood,  it  will  do  much  to  clear  up  the  diagnosis. 
The  absence  of  these  should  always  rouse  a  suspicion  that  the  case  may 
be  one  of  alveolar  abscess  and  lead  the  inquiry  in  that  direction. 

Of  the  ETIOLOGY  of  phagedenic  pericementitis  we  have  no  very  defi- 
nite information.  It  seems  most  probable  that  the  disease  is  caused  and 
maintained  by  the  presence  of  some  peculiar  fungus  or  form  of  micro- 
organism and  that  it  is  infectious.  Some  years  ago  I  thought  I  had 
detected  a  form  of  fungus  that  stood  in  a  causative  relation  to  it,  but 
further  study  has  placed  the  matter  in  such  doubt  that  I  prefer  to  con- 
sider it  as  not  proven.  Others  have  also  pointed  out  a  seeming  causa- 
tive connection  of  certain  forms  of  micro-organisms  with  the  disease. 

Dr.  Arkoevy  of  Buda-Pesth  says  :  ^  *'  There  constantly  occurs  a  cer- 
tain fungus-formation  which  I  find  in  close  connection  with  the  wasting 
of  the  alveoli  and  gingival  margin,  as  well  as  the  subsequent  loosening 
of  the  teeth ;  it  is  quite  different  from  leptothrix  buccalis,  although  it  is 
in  developmental  relation  with  it."  Dr.  Arkoevy  seems  to  think  that 
the  fungus  stands  in  causative  relation  to  the  disease.  Dr.  Joseph  Islai, 
of  the  same  place,  has  also  studied  this  fungus,  and  expressed  a  similar 
conviction.  Dr.  Adolf  Witzel  of  Essen,  Germany,  describes  the  disease 
as  "  infectious  alveolitis  "  and  considers  it  to  be  primarily  of  the  alveolar 
borders.    He  says  :  ^  "  We  have,  in  fact,  to  deal  neither  with  an  ulceration 

'International  Medical  Congress,  London.  '^British  Journal,  1882. 

Vol.  I.— 62 


978  DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 

of  the  gum  nor  with  a  primary  inflammation  of  the  periosteum,  but  with 
a  molecular  necrosis  of  the  alveoli,  or  caries  of  the  dental  sockets,  pro- 
duced by  septic  irritation  of  the  medulla  of  the  bone."  Again,  Dr. 
Witzel  says :  "  Should  you  ever  chance  to  extract  a  tooth  at  the  early 
stage  of  the  disease,  you  will  find  the  soft  disorganization  of  the  dental 
periosteum  confined  to  the  neck  of  the  tooth.  The  remaining  portions 
of  it  are  velvet-like  and  loosened,  and  present  a  brilliant  vascular 
injection  increasing  toward  the  root  and  associated  with  small  nodules 
and  lobular  granulations.  I  have  not  yet  examined  these  growths  for 
nests  of  micrococci,  but  I  have  no  doubt  that  they  are  to  be  found  not 
only  in  the  granulations,  but  also  in  the  infected  medullary  tissue  of  the 
interalveolar  partition.  In  the  pus  which  may  be  obtained  from  the 
aifected  alveoli  by  pressing  the  gum  we  observe  under  the  microscope  a 
countless  number  of  micrococci  and  bacteria,  which  doubtless  find  in  the 
pockets  of  the  gum  tissue  the  most  favorable  condition  for  their  contin- 
uous develo}>ment." 

I  have  with  some  care  repeated  the  observations  here  alluded  to  and 
made  many  others  of  a  like  nature,  and  there  can  be  no  doubt  as  to  the 
facts  of  the  presence  of  micro-organisms  in  these  situations.  All  these 
observations  are  very  suggestive  and  show  conclusively  that  these  par- 
ticular tissues  are  invaded  by  micro-organisms.  My  own  observa- 
tions, however,  are  not  explicit  in  determining  a  single  variety  in  these 
positions,  and  are  therefore  not  sufficiently  definite.  There  is  such  a  pro- 
fusion of  micro-organisms  constantly  found  in  the  mouth,  especially  in 
conditions  of  disease,  that  it  is  a  work  of  the  utmost  difficulty  to  sepa- 
rate them  and  single  out  that  particular  form  which  produces  the  mis- 
chief and  obtain  experimental  evidence  of  the  fact  that  will  bear  the 
test  of  adverse  criticism.  Until  this  is  done  in  a  way  to  satisfy  the 
critical  demands  of  science  it  cannot  be  positively  affirmed  that  this  is 
a  disease  that  owes  its  origin  to  the  life  and  growth  of  micro-organisms. 
There  are,  however,  other  forms  of  evidence,  which,  while  not  so  posi- 
tive in  their  nature,  may  be  of  use  in  the  absence  of  better  testimony; 
these  also  point  to  micro-organisms  as  the  cause  of  the  disease.  They 
may  briefly  be  stated  as  follows :  Those  remedies  that  are  known  to 
destroy  micro-organisms  influence  the  disease  most  favorably  ;  indeed, 
no  other  form  of  medication  has  been  known  to  produce  decidedly 
favorable  results.  The  complete  removal  of  the  diseased  tissue  will 
often  be  sufficient  to  produce  a  cure.  The  presence  of  the  disease  in 
one  part  of  the  mouth  is  generally  followed  by  its  appearance  in  the 
neighborhood.  It  is  observed  that  the  disease  will  not  flourish  except 
in  situations  in  Avhich  a  fungus-growth  would  have  some  form  of  ])ro- 
tection  against  the  free  flow  of  the  buccal  fluids  such  as  the  pockets 
formed  by  rather  deeji  free  margins  of  the  gum  will  give ;  hence  the 
cure  of  the  disease  l)y  the  removal  of  all  free  margins  of  the  gums. 
Besides  this,  I  have  observations  which,  though  they  are  not  of  such  a 
nature  that  I  can  make  a  scientific  use  of  them,  fully  convince  me  that 
the  disease  may  be  transplanted  from  person  to  person — that  it  is  inocu- 
lable ;  hence  it  may  be  transplanted  to  the  cleanest  mouths,  and  the 
greatest  care  should  be  given  to  the  instruments  used  in  the  treatment 
of  these  cases,  to  prevent  its  being  conveyed  to  others.     This  point  is 


ETIOLOGY  OF  PHAGEDENIC  PERICEMEXTITIS.  979 

certainly  true  whether  the  disease  is  due  to  a  fungus  or  not.  The  facts 
I  have  given  show  conclusively  that  it  is  purely  a  local  disease,  and  not 
dependent  upon  any  poison  circulating  in  the  blood  of  the  patient  or 
upon  any  systemic  disorder.  I  have  also  become  satisfied  that  it  is 
in  no  wise  hereditary,  as  is  the  disposition  to  the  deposit  of  calculus ; 
yet  it  seems  likely  that  deposits  of  calculus  do  predispose  the  patient 
to  this  disease  by  placing  the  free  margins  of  the  gums  in  a  more 
favorable  condition  for  its  propagation.  Farther  than  this  I  do  not 
think  the  deposits  of  calculus  favor  its  development. 

In  making  these  statements  I  have  not  overlooked  the  fact  that  many 
who  have  written  on  this  subject  have  regarded  the  disease  as  due  to 
constitutional  causes,  and  that  in  our  journal  literature  we  have  reports 
of  many  cases  in  which  such  causes  have  been  assigned.  Among  these 
may  be  found  in  turn  nearly  all  those  diatheses  that  are  obnoxious.  In 
these  reports  it  is  seldom  that  we  find  descriptions  that  will  enable  us  to 
identify  with  certainty  a  specific  form  of  disease  of  the  peridental  mem- 
brane ;  indeed,  in  most  of  the  cases  reported,  tlje  descriptions  are  so 
vague  that  we  are  unable  to  say  whether  the  particular  case  was  a  gin- 
givitis from  constitutional  causes,  a  simple  calcic  inflammation,  or  an 
inflammation  of  the  phagedenic  variety.  For  this  reason  the  value  of 
most  of  the  reports  that  have  been  made  is  essentially  limited. 

That  cases  of  inflamed  gingivae  with  extension  to  the  peridental 
membrane  occur  from  constitutional  causes  I  have  conclusively  shown. 
Such  disease  may  be  produced  at  will  by  the  use  of  mercury  and  other 
known  substances,  and  we  have  every  reason  to  conclude  that  such  dis- 
ease may  be  produced  by  agents  that  are  entirely  unknown  to  us  circu- 
lating in  the  blood.  Until  w'e  can  differentiate  these  forms  from  the 
calcic  and  phagedenic  varieties  in  the  reports  given  us  it  is  difficult, 
however,  to  estimate  the  true  value  of  the  observations. 

The  gouty  and  rheumatic  diatheses  have  been  regarded  as  contribut- 
ing to  inflammations  of  the  peridental  membrane ;  this  opinion  seems 
to  be  quite  generally  entertained  by  English  practitioners  Avhose  oppor- 
tunities for  the  observation  of  such  cases,  especially  of  the  gouty  dia- 
thesis, are  very  abundant.  In  my  locality  this  disease  is  rare,  but 
among  the  few  families  subject  to  it  who  have  come  under  my  obser- 
vation disease  of  the  peridental  membrane  has  not  appeared  except  in 
a  few  cases  which  w^ere  clearly  calcic,  and  which  promptly  returned  to 
a  state  of  health  without  other  treatment  than  the  removal  of  the  local 
cause.  As  to  the  rheumatic  diathesis,  my  opportunities  seem  to  have 
been  sufficient ;  but  an  analysis  of  my  cases  of  disease  of  the  peridental 
membrane  of  all  sorts  fails  to  connect  this  diathesis  with  them  as  a 
cause. 

The  scrofulous  diathesis  seems  to  favor  the  development  of  any  of 
this  group  of  diseases.  From  my  personal  observations  I  should  say  that 
this  influence  is  to  be  regarded  purely  as  a  predisposing  cause — a  con- 
dition in  which  the  tissues  of  the  individual  have  less  power  of  resist- 
ance, and  therefore  more  readily  succumb.  Anaemia  and  various  other 
disorders  or  conditions  serve  much  in  the  same  way  as  predisposing 
causes. 

The  TREATMENT  of  phagedenic  pericementitis  calls  for  certain  opera- 


980  DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 

tions  in  common  with  the  treatment  of  calcic  inflammations.  In  all 
cases  the  first  thing  to  be  done  is  to  discover  and  remove  any  and  all 
deposits  that  may  be  on  or  about  the  necks  of  the  teeth  or  their  roots. 
In  the  phagedenic  form  of  inflammation  this  presents  greater  difficulties 
than  in  the  calcic  form,  for  the  reason  that  the  deposits  are  often  situ- 
ated farther  up  on  the  roots  and  are  more  covered  in  by  the  soft  tissues. 
It  also  happens  more  frequently  that  lying  close  against  the  sides  of  the 
roots  of  the  teeth  there  will  be  found  very  thin  scales,  these  being  so 
smooth  that  their  outlines  are  with  the  greatest  difficulty  detected  by  the 
touch  ;  for  this  reason  much  care  and  patience  is  required  for  their  com- 
plete removal.  This  operation,  however,  must  be  absolutely  complete  in 
order  to  effect  a  cure.  This  calculus,  wdiich  is  usually  of  the  serumal 
variety,  is  an  irritant,  no  matter  how  small  the  amount,  and  any  parts 
left  will  serve  to  keep  up  the  irritation. 

As  I  have  described  the  process  and  the  instruments  for  the  removal 
of  the  scales  in  treating  of  calcic  inflammations,  repetition  is  unneces- 
sary. I  would  only  urge  the  necessity  for  absolute  perfection  in  this 
operation.  With  the  removal  of  all  deposits  from  the  teeth  the  simi- 
larity in  the  treatment  in  the  two  diseases  ends,  for  in  calcic  inflamma- 
tion the  tendency  is  to  spontaneous  cure  when  all  calcic  deposits  are 
removed,  but  in  the  phagedenic  forms  there  is  no  such  tendency. 

The  further  treatment  is  best  considered  under  two  heads — Surgical 
and  Medicinal.  In  a  large  proportion  of  the  cases  the  surgical  treatment 
may  end  with  the  removal  of  the  deposits  from  the  necks  of  the  teeth. 
This  applies  to  all  those  cases  in  which  there  has  as  yet  been  but  little 
destruction  of  the  pericementum  and  alveolar  walls  and  not  much 
thickening  or  eversion  of  the  alveolar  margins,  and  will  presently 
be  considered. 

In  the  graver  cases  surgical  operations  sometimes  seem  necessary — not 
but  that  we  may  effect  a  cure  without  them,  but  the  cure  will  be  accom- 
plished much  more  readily  with  them.  When  there  is  rapid  destruction 
of  the  tissue  and  a  considerable  portion  of  the  alveolar  wall  has  been 
destroyed  and  much  of  the  peridental  membrane  detached  from  the  root 
of  the  tooth,  it  is  found  better  to  cut  away  some  parts  of  this  with 
instruments.  The  pericementum  is  in  a  state  of  molecular  disintegra- 
tion and  the  alveolar  wall  is  undergoing  active  absorption.  Experience 
seems  to  demonstrate  that  the  direct  removal  of  a  portion  of  these 
with  instruments  will  expedite  the  cure.  The  means  of  doing  this 
will  vary  greatly  with  the  case.  In  cases  in  which  the  destructive 
process  has  not  been  very  great  and  the  diseased  parts  can  be  readily 
reached  with  an  instrument  passed  up  between  the  tooth  and  the 
gingival  margin,  a  hoe-shaped  excavator  with  a  broad  cutting  edge 
or  a  chisel  bent  at  an  angle  of  twenty-five  to  fifty  degrees  may  be 
introduced  and  the  margin  of  the  alveolar  wall  cut  away  as  far  as 
the  judgment  of  the  o])erator  may  dictate.  This  should  usually  be 
carried  to  such  an  extent  that  the  bone  may  be  felt  to  become  firm  and 
resistant  to  the  cutting  edge  of  the  instrument.  In  this  operation  the 
greatest  care  should  be  taken  not  to  wound  or  injure  the  gingival  mar- 
gin. This  remark  applies,  however,  only  to  that  margin.  The  soft 
tissue  farther  up  toward  the  apex  of  the  root  may  be  lacerated  con- 


TREATMENT  OF  PHAGEDENIC  PERICEMENTITIS. 


981 


siderably  without  evil  result ;  but  if  the  gingival  margin  be  broken 
clown  or  so  injured  as  to  cause  a  slough,  this  margin  will  be  lost,  and 
will  defeat  our  efforts  to  obtain  a  reformation  of  the  peridental  *mem- 
brane  in  its  completeness.  The  stretching  of  the  gingival  margin  by 
an  instrument  passed  through  for  cutting  away  the  process  or  the 
removal  of  the  calculus  is  sometimes  a  serious  evil.  After  the  opera- 
tion is  completed  the  gingivae  should  close  around  the  neck  of  the  tooth 
as  well  as,  or  better  than,  before  it  was  begun.  The  closing  of  the 
gingival  aperture  in  such  a  manner  that  irritating  substances,  and  even 
tiie  saliva,  may — in  the  main,  at  least — be  kept  out  will  diminish  the 
growth  of  micro-organisms  to  the  minimum  and  expedite  the  cure.  In 
cases  still  more  grave,  in  which  the  cutting  away  of  the  diseased  bor- 
ders of  the  bone  cannot,  without  injury,  be  well  done  through  the  gingi- 
val aperture,  other  modes  of  operating  should  take  its  place.  The  gums 
should  be  cut  through  directly  over  those  portions  of  the  alveolar  wall 
to  be  removed  or  in  such  position  that  they  Mill  be  readily  reached  with 
the  instrument.  This  may  b^  in  the  form  of  a  puncture  through  which 
an  instrument  may  be  passed  in  several  directions,  or  a  flap  of  the  soft 
tissue  may  be  raised  as  represented  in  Figs.  527,  528,  and  the  tissues 


Fro. 527 


Fig.  528. 


Illustration  of  the  Position  and  Form  of  Incision 
through  the  (ium  for  exposing  the  Root  of  the 
Tooth  and  injured  Alveolar  Process:  «,  incis- 
ions.   (Compare  with  Figs.  520  and  521.) 


Incision  for  the  Treatment  of  the  Root 
and  Alveobir  Process  in  a  Case  of  Phage- 
denic Pericementitis.  (Compare  with 
Fig.  524.) 


beneath  exposed  to  view.  In  this  way  the  gingival  margin  may  be 
saved  from  injury,  and  the  denuded  root  of  the  tooth  may  be  closely 
examined  for  any  traces  of  calculus  or  other  deposits  and  mo.st  thor- 
otighly  cleaned,  while  the  trimming  of  the  alveolar  wall  may  be  more 
perfectly  done.  After  all  is  satisfactory  and  the  wound  properly 
washed  as  presently,  described  the  flaps  should  be  replaced  and 
stitched  down.  In  all  cases  the  cutting  of  the  alveolar  walls  should 
be  done  in  such  a  way  that  the  soft  tissues  will  lie  clo.sely  against  the 
roots  of  the  tooth.  No  spaces  should  be  left  intervening,  for  all  such 
become  pockets  for  the  growth  of  micro-organisms  and  the  formation 
of  pus,  which  invariably  retards  the  cure;  therefore  it  is  especially 
necessary  that  all  jagged  points  of  the  bone  be  removed,  all  thick  edges 
be  trimmed  down  or  broken  away.  All  eversions  of  the  alveolar  wall 
should  be  cut  off  or  their  form  so  modified  that  no  intervening  space 
shall  be  left  between  them  and  the  root  of  the  tooth.  In  cases  of  ever- 
sion  of  the  alveolar  wall  or  thickening  of  its  borders  without  consider- 
able destruction  of  the  peridental  membrane,  this  may  be  cut  away  by  a 
few  well-directed  blows  of  a  chisel  passed  directly  through  the  gum,  and 
the  bone  so  broken  down  that  it  will  lie  close  in  against  the  root  of  the 


982  DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 

tooth.  Tlic  pieces  may  be  left  in  this  position  rather  than  mutilate  the 
gingival  margin  in  the  effort  to  remove  them.  If  they  become  necrosed, 
they  nill  be  tlirown  out  witliin  a  few  days,  or  will,  if  they  retain  their 
vitality,  become  united  with,  and  assist  in  the  rebuilding  of,  the  alveolar 
wall.  In  those  cases  in  which  very  deep  pockets  have  formed  extend- 
ing lengthwise  of  the  root  of  the  tooth,  with  thickened  borders  of  the 
alveolar  wall  on  either  side,  I  have  found  it  best  to  raise  a  semicircular 
flap  of  the  gum  in  order  that  I  may  reach  both  sides  with  the  chisel  and 
pare  them  down  in  such  a  way  that  the  soft  tissues  may  lie  in  smoothly 
against  the  root  of  the  tooth.  I  regard  the  chisel  as  much  better  for 
this  purpose  than  the  burr.  The  burr  driven  by  the  engine  produces 
unnecessary  injury  of  the  soft  tissues  in  very  many  instances,  and  the 
trimming  of  the  alveolar  process  is  usually  not  so  evenly  and  per- 
fectly done  as  with  the  excavator  or  the  chisel  and  the  injured  tissues 
are  left  in  a  much  worse  condition.  Besides^,  there  is  more  danger  of 
injury  to  the  gingival  border.  The  object  of  this  operation  is  twofold : 
first,  the  removal  of  tissues  sunk  so  low  in  the  scale  of  vitality  as  to  be 
unable  to  recuperate,  and  with  them  the  removal  of  the  micro-organisms 
by  which  they  are  invaded  ;  in  this  way  the  operation  acts  as  a  power- 
ful antiseptic.  A  reasonable  degree  of  mutilation  of  the  subjacent  tis- 
sues acts  as  a  stimulant  and  invites  the  formation  of  granulations  for  the 
restoration  of  the  lost  parts  ;  if,  however,  the  mutilation  of  the  tissues 
be  carried  too  far,  the  injury  will  overbalance  the  good  results.  Second, 
the  placing  of  the  tissues  in  such  position  as  to  obliterate  all  interspaces, 
so  that  granulations  may  be  the  more  effective  in  forming  reattachments 
and  repairing  the  injured  parts. 

It  is  important  that  all  blood-clots  be  removed.  This  is  true  of  all 
surgical  wounds,  and  here  it  is  doubly  so,  for  the  reason  that  the  clot 
will  so  generally  become  septic.  A  bloot-clot,  as  such,  is  perhaps  not 
an  irritant,  yet  it  is  always  a  hindrance  to  the  process  of  repair.  It 
never  becomes  organized,  as  was  held  by  the  older  pathologists,  but  is 
removed  by  a  process  of  absorption.  Granulations  grow  out  into  its 
mass,  and  the  clot  disappears  as  they  advance ;  therefore,  even  when  the 
clot  does  not  decompose,  considerable  vital  energy  is  expended  in  its 
removal  and  the  granulations  are  diverted  from  the  immediate  work  of 
connecting  the  diiferent  parts  of  the  lesion.  In  this  particular  instance 
the  clot  is  almost  always  decomposed  by  the  micro-organisms  present 
in  the  tissues  or  entering  from  without ;  therefore  the  parts  should  be 
washed  with  a  peroxide-of-hydrogen  solution  of  bichloride  of  mercury 
(1  grain  to  the  ounce)  in  orcler  to  remove  all  blood-clots,  and  for  the 
furtlier  purpose  of  rendering  the  parts  as  nearly  aseptic  as  possible. 
Then,  if  a  flap  has  been  raised,  it  should  be  stitched  in  place.  It  is  only 
in  a  few  of  the  more  acute  cases  that  we  may  expect  the  parts  to  unite 
with  the  root  of  the  tooth  by  first  intention,  biit  it  is  often  desirable  that 
the  wound  through  the  gum  tissue  should  unite  at  once  ;  this  it  will  very 
generally  do  if  the  parts  are  placed  Avell  in  apposition.  If  they  are  not 
so  placed,  the  fluids  of  the  mouth  are  liable  to  wash  away  the  granula- 
tions and  considerably  delay  the  union.  In  order  to  prevent  this,  I  am 
in  the  habit  of  first,  after  thoroughly  drying  the  parts,  covering  the 
immediate  wound  Avith  a  bit  of  tissue-paper  and  then  coating  the  whole 


TREATMENT  OF  PHAGEDENIC  PERICEMENTITIS.  983 

surface  with  a  solution  of  gutta-percha  in  chloroform ;  this  completely 
seals  up  the  wound  and  prevents  it  from  becoming  septic,  in  addition  to 
the  protection  to  the  granulations.  This,  if  desired,  may  also  be  used  to 
seal  up  the  gingival  margins  after  operations  through  the  gingival  aper- 
ture, by  first  drying  the  parts  thoroughly  and  packing  the  gutta-percha 
around  the  necks  of  the  teeth.  In  order  to  render  it  more  secure  in  its 
jDOsition,  a  wire  or  thread  may  be  used  to  first  secure  to  the  teeth  a 
small  piece  of  undissolved  gutta-percha,  to  which  the  solution  may  be 
added.  This  means  of  sealing  the  gingival  margins  would  be  very  val- 
uable if  tiie  gutta-percha  would  cling  to  the  gums  with  more  tenacity, 
but  it  will  generally  hold  for  two  days  if  well  applied.  Some  effort  in 
this  direction  has  been  made  in  the  way  of  the  construction  of  plates  to 
fit  over  the  parts,  but  such  an  apparatus  is  likely  to  do  more  harm  by 
the  collection  of  irritating  agents  under  it  than  good  by  preventing  fric- 
tion. The  requirement  of  such  an  appliance  is  that  it  shall  hermetically 
seal  the  parts.  After  these  operative  procedures  the  further  treatment 
is  to  be  conducted  as  recommended  for  the  simpler  cases  that  are  treated 
without  other  surgical  interference  than  the  thorough  cleaning  of  the 
necks  and  roots  of  the  affected  teeth. 

Many  cases  of  this  disease  will  be  met  with  in  which  operative 
procedures  further  than  the  thorough  cleaning  of  the  necks  and  de- 
nuded portions  of  the  roots  of  the  teeth  are  entirely  unnecessary.  If 
there  are  no  thickened  or  roughened  margins  to  interfere  with  the  con- 
tact of  the  parts,  in  many  cases  the  medicinal  treatment  may  be  begun 
at  once,  even  when  considerable  portions  of  the  alveolar  wall  have  been 
lost. 

Some  of  the  cases  will  present  no  calculus  whatever  to  be  removed,, 
but  even  in  these  the  roots  should  be  well  cleaned,  for  a  close  examina- 
tion will  show  them  to  be  coated  with  an  apparent  gummy  material  which, 
clings  quite  closely  and  tenaciously  to  the  root  and  should  generally  be 
loosened  with  an  instrument.  This  is  usually  composed  of  micro-organ- 
isms and  a  kind  of  inspissated  mucus  or  pus.  The  cavity  or  pocket 
should  now  be  thoroughly  washed  with  peroxide  of  hydrogen,  for  the 
removal  of  all  debris.  This  and  all  subsequent  washings  may  be  done 
with  peroxide  of  hydrogen  in  M'hicli  a  grain  of  the  bichloride  of  mercury 
to  the  ounce  has  been  dissolved.  This  combination  has  become  quite  a 
favorite  in  my  hands  for  the  beginning  of  the  treatment,  on  account  of 
its  very  fine  antiseptic  qualities.  This  washing  should  be  done  with  the 
Farrar's  syringe,  or  other  instrument  possessing  its  advantages. 

In  most  cases  we  may  go  directly  forward  with  antiseptic  stimulant 
remedies  presently  to  be  described,  but  in  some  of  the  more  acute  forms 
tlie  gums  and  soft  tissues  will  occasionally  be  found  much  congested 
and  turgid  with  blood.  In  such  cases,  after  thoroughly  cleaning  the^ 
parts  and  washing  with  the  peroxide  of  hydrogen  and  bichloride  of" 
mercury,  it  is  well  to  begin  the  treatment  with  the  application  of  a  30- 
per-cent.  solution  of  chloride  of  zinc;  this  should  be  applied  deep  down 
in  the  pockets.  After  one  or  two  applications  of  this  remedy  others  of 
a  different  character  should  take  its  place,  for  its  principal  use  is  that  of 
aa  astringent  for  the  reduction  of  the  calibre  of  the  blood-vessels,  which 
have  become  abnormally  large.    This  remedy,  however,  possesses  another 


984  DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 

advantage  in  its  antiseptic  quality,  which  in  this  disease  is  very  import- 
ant. In  phagedenic  inflammation,  whether  acute  or  chronic,  the  inflamed 
tissue  is  usually  very  slow  in  the  formation  of  granulations  for  the  reat- 
tachment of  the  peridental  membrane  and  restoration  of  the  lost  parts. 
The  tissue  seems  to  have  lost  tone;  the  character  of  the  irritant  or  cause 
seems  to  be  such  that  the  tissues  are  lowered  in  their  vitality,  and  for 
this  reason  they  require  a  stimulating  course  of  treatment  in  order  to 
induce  them  to  form  granulations.  For  this  purpose  there  is  perhaps 
nothing  yet  discovered  that  acts  better  than  the  oil  of  cinnamon,  but, 
as  the  destruction  of  the  micro-organisms  found  growing  in  the  tissues 
is  an  important  desideratum,  carbolic  acid  may  be  added,  in  the  propor- 
tion of  1  part  of  carbolic  acid  in  crystals  to  2  parts  of  oil  of  cinnamon, 
or  the  mixture  recommended  for  the  treatment  of  alveolar  abscesses  may 
be  used.'  This  should  be  applied  within  the  pockets  regularly  once  in 
four  days. 

The  object  of  this  treatment  is  twofold  :  first,  the  destruction  of  the 
micro-organisms  or  the  removal  of  the  septic  character  of  the  disease ; 
second,  the  stimulation  of  the  tissues,  whose  vitality  is  low.  In  pursu- 
ing this  treatment  it  is  especially  important  that  the  application  be  made 
with  regularity.  I  have  pursued  this  plan  of  treatment,  closely  study- 
ing the  cases  day  after  day  by  aid  of  the  microscope,  and  have  found 
that  the  next  day  after  the  application  of  the  remedy  no  micro-organ- 
isms could  be  found  in  a  mobile  state,  and  all  eflbrts  in  staining  and 
searching  in  this  way  for  micro-organisms  among  the  tissues  have  failed, 
but  on  the  fourth  day  they  will  usually  be  found.  This  plan  of  treat- 
ment is  very  much  like  the  weeding  of  a  foul  garden  :  Ave  may  go  over 
it  to-day  with  a  hoe  and  destroy  all  the  growing  weeds,  but  within  a 
few  days  young  weeds  will  be  found  springing  up  again,  and  it  is  neces- 
sary to  repeat  the  operation.  We  may  destroy  the  growing  Aveeds  Avith 
the  hoe,  but  aa^c  cannot  destroy  the  seeds  that  are  in  the  ground ;  there- 
fore the  hoeing  must  be  re})eated  time  after  time  for  success.  The  seeds 
that  are  in  the  ground  must  sprout  and  the  sprouts  be  destroyed.  Just 
so  Avith  our  treatment  in  this  disease :  we  can  destroy  the  groAving 
micro-organisms  Avith  our  remedy,  but  Ave  cannot  destroy  the  spores 
that  are  in  the  tissues ;  therefore  the  treatment  must  be  followed  up 
Aveek  after  AA^eek  until  the  spores  have  been  eradicated  from  the  tissues. 
Then  Ave  may  expect  the  healing  process  to  go  on  undisturbed  and  the 
tissue  to  recover  its  normal  tone.  This  is  the  theory  of  the  treatment, 
and  is  found  to  succeed.  I  mention  the  particular  remedies  that  are 
favorites  in  my  hands,  but  it  is  not  necessary  that  these  special 
ones  be  used.  Any  other  remedies  that  may  answer  a  similar  pur- 
pose— and  of  these  our  materia  medica  furnishes  many — may  be  used 
instead. 

If  the  operator  understands  the  principles  upon  Avhich  the  treatment 
should  be  conducted,  he  should  have  but  little  difficulty  in  the  selection 
of  suitable  preparations.     In  addition  to  those  Avhich  I  have  mentioned, 

1 1-2-3  Mixture. 
Take  of  Oil  of  cinnamon,  1  part. 

Carbolic  acid  (crystals),  2  parts. 
Oil  of  gaultheria",  3     "         Mix. 


TREATMENT  OF  PHAGEDENIC  PERICEMENTITIS.  985 

Dr.  A.  W,  Harlan  of  Chicago  has  been  instrumental  in  the  introduction 
of  a  number  of  agents  that  are  very  valuable.  Among  these  I  will  men- 
tion the  iodide  of  zinc  in  solutions  of  various  strength  as  an  astringent 
and  stimulant,  combinations  of  iodoform  and  eucalyptus,  iodoform  and 
eugenol,  iodoform  and  oil  of  cinnamon,  weak  solutions  of  chloride  of 
aluminum  in  water,  1  to  3  grains  to  the  ounce,  sanitas  and  eugenol,  3 
parts  of  the  former  to  1  of  the  latter,  as  a  germicide  and  tissue  stimu- 
lant, resorcin  in  solution, from  8  to  24  grains  to  the  ounce  of  water,  as 
an  antiseptic  and  tissue  stimulant.  All  of  these  except  the  iodoform 
combinations  are  to  be  injected  with  Farrar's  syringe  into  the  pockets 
once  in  four  days.  The  iodoform  mixture  may  be  packed  into  the 
pockets. 

Dr.  T.  L.  Gilmer  of  Quincy,  111.,  has  used  phenol  camphor^  success- 
fully in  the  treatment  of  this  affection.  He  regards  it  as  especially  use- 
ful in  obstinate  chronic  cases,  and  has  found  it  succeed  where  other 
remedies  seemed  incapable  of  preventing  the  continuous  discharge  of  pus. 
It  is  certainly  a  good  parasiticide  and  its  stimulant  qualities  seem  very 
excellent.  Its  taste  will  be  very  objectionable  to  some  persons.  It  is 
to  be  injected  into  the  pockets  in  the  same  manner  as  the  other  remedies 
named. 

The  washing  with  the  peroxide  of  hydrogen,  either  with  or  without 
the  addition  of  the  bichloride  of  mercury,  should  generally  be  repeated 
at  each  sitting,  for  the  purpose  of  freeing  the  pockets  from  all  debris 
before  the  application  of  the  other  remedies.  Lately  I  have  successfully 
treated  some  cases  with  this  alone. 

In  the  after-treatment  of  all  cases  the  greatest  care  should  be  taken  to 
prevent  injury  to  the  granulations  in  process  of  growth.  Usually,  after 
a  decided  disposition  to  heal  is  shown,  the  treatment  should  be  limited 
to  keeping  the  parts  well  cleaned.  As  a  wash  for  the  patient  to  use 
with  the  brush  during  the  treatment  the  ordinary  cinnamon-water  of 
the  United  States  Pharmacopoeia  is  very  excellent  and  agreeable.  Most 
of  ray  patients,  however,  have  used  the  1-2-3  mixture  (page  984) 
diluted  to  about  one-half  with  oil  of  anise  or  oil  of  lemon,  or  without 
dilution,  by  placing  half  a  dozen  drops  on  the  brush  once  per  day. 
This  mixture  seems  to  be  in  general  use  among  physicians  of  my 
acquaintance  for  the  treatment  of  catarrhal  affections  of  the  mucous 
membranes,  especially  the  chronic  forms,  and  its  results  are  especially 
good.  Any  disinfectant  stimulant  wash  will  be  beneficial,  though  not 
much  reliance  can  be  placed  on  anything  of  this  kind,  for  the  reason 
that  it  cannot  be  applied  to  the  diseased  parts  (within  the  pockets)  by 
the  patient. 

Just  here  a  word  in  regard  to  the  action  of  antiseptics  may  be  import- 
ant. A  great  majority  of  the  antiseptics  which  are  safe  for  use  in  con- 
nection with  living  tissues  are  depressant  of  the  living  forces  and  act 
directly  to  impair  the  functional  activity  of  the  living  cells.     For  this 

'  Phenol  camphor  is  prepared  as  follows : 

Take  of  Carbolic  acid,  in  crystals,  )        i    - 

Gnm  camphor,        '  ^eacn^ss. 

Mix  and  heat  on  a  sand-bath   until  both  are  melted ;  they  combine  to  form  an  oily 
liquid. 


986  DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 

reason  the  use  of  a  strong  disinfectant  agent  in  this  disease  cannot  be 
recommended,  for,  instead  of  building  up,  theytend  to  further  depress 
the  tissues  ah-eady  lowered  in  tone;  therefore  in 'their  use  it  is  especially 
necessary  that  some  agent  be  combined  with  them  to  counteract  this 
influence.  Yet  this  can  be  only  partially  done,  because  any  agent 
which  will  depress  life  in  the  form  of  micro-organisms  will  also  depress 
life  as  it  exists  in  the  individual  cell  in  the  tissues ;  yet  experimental 
study  of  the  action  of  remedies  shows  us  plainly  that  the  different  anti- 
septics depress  the  life-force  of  the  animal  cells  and  that  of  the  micro- 
organisms in  a  different  ratio.  Hence  there  should  be  discrimination  in 
their  selection.  Carbolic  acid  possesses  this  depressant  power  in  a  very 
marked  degree.  In  the  combination  of  carbolic  acid  with  the  oil  of 
cinnamon  and  the  oil  of  wintergreen  the  depressant  eifect  of  the  car- 
bolic acid  is  reduced  to  the  least  degree  as  to  its  action  on  the  animal 
cells,  while  retaining  its  power  over  the  vegetable  cells.  In  this  way 
we  retain  that  quality  of  the  carbolic  acid  desired,  while  we  remove  its 
undesirable  properties.  In  eugenol  we  have  also  an  antiseptic  possess- 
ing a  minimum  depressing  power  over  the  animal  cells ;  hence  it  is 
valuable  in  the  treatment  of  this  aifection.  In  the  bichloride  of  mer- 
cury we  have  an  agent  seemingly  possessing  very  peculiar  power  over 
the  life  of  micro-organisms — an  agent  which  in  solutions  of  i  to  300  or 
1  to  1000  parts  seems  to  destroy  the  life  of  these  low  organisms  without 
especially  influencing  the  animal  cells  with  which  it  may  come  in  con- 
tact. In  studying  the  effect  of  these  solutions  I  have  been  unable  to 
discover  that  they  produce  any  marked  local  depression  ;  this  would 
indicate  that  their  depressing  power  is  rather  feeble.  Carbolic  acid  used 
in  the  same  Avay  w^ould  cause  marked  local  depression.  This  quality  of 
carbolic  acid  renders  it  inapplicable,  in  its  unmodified  form,  for  use  in 
this  disease. 

In  regard  to  the  reparation  of  the  peridental  membrane  and  the 
alveolar  wall  in  this  disease  it  may  be  said  that  repair  rarely  or  never 
takes  place  after  the  manner  of  healing  by  first  intention,  but  is  always 
by  granulation.  Granulation  may  begin  in  the  tissues  overlying  the 
parts  of  the  root,  but  the  reattachment  creeps  in  from  the  margin  of  the 
injury  where  the  peridental  membrane  is  intact,  or  from  the  extremity 
of  the  pocket  above,  and  slowly  covers  over  the  denuded  portion  of  the 
root  of  the  tooth.  This  is  usually  a  slow  process,  but  varies  greatly  in 
different  cases.  In  explanation  of  this  three  theories  may  be  entertained  : 
First,  in  those  cases  in  M'hicli  the  destruction  of  the  membrane  is  trau- 
matic or  very  recent  it  may  be  supposed  that  the  ceraentum  covering 
the  root  has  not  lost  its  vitality,  and  that  its  cells  may  grow,  subdivide, 
and  throw  out  processes  beyond  the  surface  of  the  cementum  which  may 
join  with  the  granulations  from  the  soft  parts.  In  this  way  we  can  sup- 
pose the  peridental  membrane  to  be  reformed,  or  rather  reattached  to 
the  root  of  the  tooth  by  first  intention.  As  a  fact,  we  see  this  occur  in 
case  of  incision.  Observation  shows  that  this  does  not  occur  in  the 
healing  process  following  this  disease.  Second,  we  may  suppose  that, 
the  cells  of  the  cementum  having  lost  their  vitality,  the  granulaticms 
from  the  soft  tissues  grow  into  the  old  canaliculi  or  lacun?e  of  the 
cementum  and  reinhabit  them,  and  in  this  way  the  reattachment  is 


SPONGE-GRAFTING.  987 

formed  witli  the  root  of  tlie  tooth.  Third,  we  may  suppose  that  the 
cells  or  granulations  from  the  soft  parts  grow  into  the  root  of  the  tooth 
and  remove  a  portion  of  the  old  tissue  of  the  cementum  by  absorption 
and  reform  so  much  of  it  as  may  be  necessary,  and  in  this  way  reattach- 
ment occurs.  However  it  may  be,  it  is  certain  that  the  peridental 
membrane  will  attach  itself  to  the  root  of  a  dead  tooth,  for  otherwise 
Hunter  Mould  not  have  succeeded  in  any  case  in  obtaining  the  attach- 
ment of  the  peridental  membrane  to  the  root  after  boiling  the  tooth, 
and  yet  this  mode  of  preparing  teeth  for  the  purpose  of  replanting  was 
recommended  by  him  in  1778.  In  this  case  we  must  assume  the  reat- 
tachment of  the  peridental  membrane  to  be  that  of  the  second  or  third 
of  the  supposititious  forms  above  mentioned.  In  a  large  proportion  of 
the  chronic  cases,  at  least,  of  this  disease,  the  reattachment  must  be  in 
the  same  Avay. 

In  the  treatment  of  phagedenic  pericementitis  the  complete  reforma- 
tion of  the  peridental  membrane  should  be  expected  in  all  cases  if  the 
gingival  margin  has  remained  intact.  Just  so  far  as  the  margin  of  the 
gum  may  have  receded  from  its  normal  position,  just  so  far  will  we  fail 
of  regaining  the  reformation  of  the  peridental  membrane — that  is  to 
say,  if  a  portion  of  the  root  of  the  tooth  is  uncovered,  we  cannot  expect 
a  reformation  of  its  peridental  membrane  at  that  point. 

The  renewal  or  reformation  of  the  alveolar  wall  is  far  more  uncer- 
tain, yet  in  most  cases  this  will  also  be  reformed.  I  have  examined  my 
cases  very  carefully  on  this  point,  and  have  found  that  in  most  of  them 
the  alveolar  wall  has  been  slowly  reproduced,  yet  in  some  in  which  the 
reformation  of  the  peridental  membrane  has  been  complete  the  alveolar 
wall  has  not  reformed  during  the  two  or  three  years  the  cases  have  been 
under  observation. 

These,  so  far  as  I  have  yet  observed,  are  all  cases  in  which  there  was 
much  eversion  of  the  alveolar  wall,  which  was  not  cut  away  at  the  time 
of  the  treatment.  These  observations  have  determined  m€  hereafter  to 
cut  away  much  more  freely. 

Sponge-grafting  suggests  itself  as  a  means  of  renewing  the  gingivae 
and  lower  border  of  the  peridental  membrane  when  lost  from  this  dis- 
ease. Soon  after  the  introduction  of  this  operation  in  general  surgery, 
a  few  years  ago,  I  made  trials  of  it  in  the  mouth  with  the  view  of  test- 
ing its  efficiency  in  the  restoration  of  lost  parts.  For  this  purpose  very 
fine  sponge  thoroughly  freed  of  sand  is  prepared  by  macerating  it  in 
dilute  hydrochloric  acid,  to  remove  any  calcareous  material  it  may  con- 
tain. It  should  then  be  rendered  aseptic  by  maceration  in  some  one  of 
the  antiseptic  solutions — preferably,  one  that  will  be  the  most  nearly 
non-irritant  to  the  granulations  to  which  it  may  be  applied.  Thus  pre- 
pared, the  sponge  is  cut  to  a  suitable  size  and  applied  to  the  granulating 
sore  in  such  position,  form,  and  quantity  that  it  will  represent  the  lost 
part,  due  allowance  being  made  for  after-shrinkage  of  the  newly-formed 
tissue.  The  granulations  will  quickly  grow  into  all  of  the  meshes  of  the 
sponge  and  completely  fill  every  space.  The  growth  of  the  granulations 
seems  to  be  stimulated  and  greatly  accelerated  by  the  presence  of  the 
sponge,  while  its  meshes  seem  to  act  as  a  ladder  on  which  they  climb, 
so  that  the  form  of  the  sponge  directs  the  form  of  the  growth.     The 


988  DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 

sponge,  wlien  enclosed  by  the  granulations,  is  absorbed ;  in  other  words, 
it  is  digested  or  dissolved  in  a  material  elaborated  by  the  granulations 
in  contact  with  it,  and  in  this  form  taken  into  the  circulation.  It  is 
thus  removed  completely,  leaving  newly-formed  tissue  in  its  place. 
This  new  tissue  is,  of  course,  scar  or  cicatricial  tissue,  and  shrinks  very 
much  after  the  absorption  of  the  sponge ;  it  is  therefore  necessary  that 
the  sponge  should  be  abundantly  large  when  first  applied. 

Under  favorable  conditions  the  granulations  grow  into  the  sponge 
with  such  flicility  and  so  rapidly  that  it  seems  to  offer  a  wonderful 
opportunity  for  the  restoration  of  lost  parts.  The  sponge  can  be 
trinnned  to  any  form  desired,  so  that  the  space  left  by  the  sloughing 
of  the  j)art  or  tissue  destroyed  by  accident  can  be  very  perfectly  refilled. 
In  practice,  however,  some  serious  objections  to  its  use  have  been  de- 
veloped, which,  as  they  have  come  to  be  understood,  have  very  much 
modified  the  opinion  of  surgeons  as  to  its  general  usefulness.  In  the 
first  place,  in  those  cases  in  which  the  sponge-graft  seems  to  have  done 
well,  the  new  tissue  that  has  grown  is  often  very  poor  in  quality  and 
liable  to  excessive  shrinkage.  The  second,  and  worst,  objection  to  its 
use  is  that  the  sponge-graft  is  especially  liable  to  become  septic.  It 
seems  to  offer  a  remarkably  favorable  harbor  for  septic  micro-organ- 
isms, and  not  unfrequently  non-pathogenic  forms  will  fill  the  sponge 
in  such  numbers  as  to  do  great  mischief.  When  these  pests  have  once 
gained  a  foothold  in  the  sponge,  it  is  next  to  impossible  to  dislodge 
them  with  any  antiseptics  that  can  be  applied  with  safety  to  the  granu- 
lations. All  this  is  true  in  any  case  in  which  the  sponge-graft  can  be 
applied,  and  has  caused  its  abandonment  by  the  careful  surgeon  in  all 
but  the  most  necessary,  and  at  the  same  time  most  promising,  cases. 
These  are  cases  of  loss  of  tissue  on  exposed  parts  where  antiseptics  can 
readily  be  applied,  and  where  the  wound  is  not  subject  to  irrigation  by 
any  of  the  secretions  but  its  own.  AYounds  of  the  hands  or  feet  in 
which  the  parts,  wound,  sponge-graft,  and  all,  can  be  frequently  im- 
mersed in  an  antiseptic  lotion  or  can  be  perfectly  sealed  by  dressings 
impervious  to  micro-organisms,  offer  the  most  favorable  conditions  for 
the  sponge-graft,  while,  on  the  other  hand,  the  natural  cavities  of  the 
body,  ii:i  which  these  precautions  are  impossible,  are  the  most  unfavor- 
able positions  for  this  procedure. 

In  my  efforts  at  sponge-grafting  for  the  renewal  of  the  peridental 
membrane  and  gingival  margin  I  have  proceeded  in  this  wise :  After 
determining  by  examination  the  size  and  form  of  the  space,  a  suit- 
able piece  of  prepared  sponge  is  cut  as  near  the  required  form  as 
practicable  and  placed  well  up  into  the  pocket,  between  the  remaining 
])ortion  of  the  gum  and  the  root  of  the  tooth.  It  should  be  of  such 
form  and  size  that  when  thus  placed  it  will  cover  the  exposed  portion 
of  the  cementum  and  extend  farther  down  on  the  crown  of  the  tooth 
than  the  gum  should  do,  so  that  it  may  be  secured  in  position  by  a  liga- 
ture passed  about  the  tooth.  The  space  for  the  reception  of  the  graft 
can  often  be  improved  and  its  form  more  accm'ately  determined  by  tent- 
ing with  antiseptic  cotton  for  a  few  hours  before  the  application  of  the 
sponge.  If  the  case  progresses  favorably,  the  granulations  will  within 
twenty-four  hours  have  grown  into  the  meshes  of  the  sponge  to  such  an 


SPONGE-GRAFTING.  989 

extent  as  to  secure  it  in  its  position,  and  the  ligature  is  no  longer  needed 
except  to  retain  the  sponge  in  immovable  contact  with  the  cenientum 
of  the  root  of  the  tooth,  and  thus  favor  the  attachment  of  the  tissue.  In 
a  few  cases  this  has  been  accomplished,  but  even  in  these  but  little  good 
has  resulted,  seemingly  because  of  the  poor  quality  of  the  nfew  tissue, 
while  a  large  proportion  of  the  cases  failed  utterly  on  account  of  inflam- 
mation and  suppuration,  induced,  apparently,  by  the  foul  condition  of 
the  sponge. 

In  the  mouth  antiseptic  precautions  are  next  to  impossible  on  account 
of  the  flow  of  saliva  and  its  constant  contamination  with  micro-organ- 
isnis.  Indeed,  in  this  position  the  sponge  cannot  be  kept  in  good  con- 
dition for  a  day  by  any  precautions  thus  far  known  to  us.  I  have 
thought  to  accomplish  this  by  applying  antiseptics  very  frequently,  but 
have  uniformly  failed.  In  many  instances  the  contamination  is  only 
with  non-pathogenic  organisms,  and  the  constant  ingrowth  of  the  gran- 
ulations will  succeed  in  expelling  the  intruders  even  from  a  foul,  stink- 
ing sponge,  but  in  my  own  hands  the  contamination  has  so  often  been 
with  septic  organisms,  as  evinced  by  the  occurrence  of  fever,  that  I 
must  regard  it  as  in  some  degree  an  unsafe,  as  well  as  a  very  uncertain, 
procedure.  The  more  extended  the  grafts,  the  more  care  is  required  in 
their  management,  especially  as  the  danger  from  sepsis  is  in  some 
degree  in  proportion  to  the  surface  from  which  absorjstion  may  take 
place. 

In  one  case — a  woman  of  about  fitly — a  sponge-graft  was  applied 
for  the  purpose  of  filling  in  the  upper  jaw  a  gap  about  as  large  as  the 
last  joint  of  the  finger,  the  opening  having  been  caused  by  exfoliation 
of  bone.  For  the  first  two  days  it  seemed  to  do  well,  and  the  granula- 
tions were  rapidly  filling  the  sponge.  On  the  third  day  the  patient  had 
some  fever,  and  on  the  fourth  day  it  was  found  necessary  to  her  safety 
to  remove  the  sponge  and  adjacent  tissues  with  the  knife.  Septicaemia 
was  very  pronounced,  but  after  the  removal  of  the  cause  the  effect  read- 
ily passed  away,  and  no  great  harm  was  done  farther  than  a  slight  in- 
crease of  the  gap  which  it  was  intended  to  fill. 

The  application  of  the  sponge-graft  for  the  rebuilding  of  the  peri- 
dental membrane  and  gum  about  one  or  two  teeth  cannot  be  regarded 
as  especially  dangerous  to  the  patient,  but  the  occurrence  of  fever  in 
several  cases  under  my  observation  shows  plainly  that  it  is  not  entirely 
devoid  of  danger,  and  that  the  extended  application  of  these  grafts  in 
the  mouth  would  not  be  justifiable  even  if  the  results  were  more  uni- 
formly successful  than  they  have  proved  in  my  hands. 

Before  closing  this  paper  I  wish  to  say  a  word  in  regard  to  the 
habit  of  the  profession  in  the  management  of  this  group  of  diseases. 
It  seems  as  yet  to  be  the  universal  custom  to  consider  them  as  constitut- 
ing one  disease,  and  therefore  there  has  been  no  division  of  treatment. 
The  treatment  which  has  been  most  strongly  urged  is  in  its  surgical 
aspects  similar  to  that  which  I  have  here  recommended  for  the  phage- 
denic variety,  and  it  has  been  applied  to  all  of  the  forms,  the  calcic  as 
well  as  the  phagedenic.  This  treatment,  especially  in  the  calcic  forms 
of  the  disease,  is  entirely  unnecessary,  and  even  hurtful ;  for  if  the  peri- 
dental membrane  and  the  alveolar  wall  are  largely  cut  away,  the  injury 


990 


DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 


is  unnecessarily  increased.  Clinical  experience  demonstrates  that  in  the 
calcic  variety  of  the  disease  the  tendency  is  toward  a  return  to  health, 
and  that  the  mutilation  of  the  parts  is  not  only  unnecessary  to  that 
end,  but  results  in  a  much  greater  shrinkage  of  the  gum-tissue  and 
increased  exposure  of  the  root  of  the  tooth,  the  great  evil  which  we 
should  labor  to  avoid ;  therefore  I  urge  a  close  discrimination  between 
these  two  forms  of  disease. 


Amputation  op  the  Roots  of  Teeth. 

In  practice  a  considerable  number  of  cases  occur  in  which  a  valuable 
tooth  can  be  retained  by  the  amputation  and  removal  of  one  of  its  roots. 
These  are  cases  in  which  one  root  of  a  molar  has  lost  its  socket  from 
any  cause,  such  as  alveolar  abscess  neglected  until  the  membrane  is 
destroyed  and  the  gum  shrunken  away,  or  from  localized  calcic  inflam- 
mation, but  perhaps  oftenest  fi-om  phagedenic  pericementitis.  In  any 
of  these  cases,  if  the  tooth  be  a  first  molar,  or  a  second  molar  with  the 
roots  well  separated  and  the  other  roots  in  a  fairly  good  condition  or 
capable  of  being  rendered  so  by  appropriate  treatment,  the  root  which 
has  lost  its  socket  may  be  cut  away  and  the  tooth  will  be  ftiirly  well 
supported  on  the  root  or  roots  that  remain.  The  greater  number  of  my 
amputations  have  been  of  the  palatine  root  of  the  upper  first  molar, 
although  I  have  frequently  removed  one  or  the  other  of  the  roots  of 
the  first  molar  of  the  lower  jaw.  The  amputation  of  the  palatine  root 
of  the  first  molar  of  the  upper  jaw  is  the  easiest  of  performance,  and 
leaves  the  tooth  on  its  remaining  roots  in  a  better  condition  than  any 
other  tooth  after  a  similar  operation.  The  amputation  is  usually  easily 
performed  with  the  fissure-burr  driven  by  the  engine,  or  a  common  drill 
may  be  used  to  drill  a  row  of  holes  through  the  root  very  close  together, 
after  which  they  may  be  connected  by  cutting  out  the  interspaces  with 

the  fissure-burr.  It  is  a  work  of  but 
a  few  moments  by  either  plan.  The 
root  should  be  cut  as  close  to  its  bifur- 
cation as  possible ;  and  if,  after  its 
removal,  it  is  found  not  to  be  cut  low 
enough,  the  remaining  part  should  be 
burred  away,  so  that  no  point  shall 
be  left.  Finally,  the  whole  surface 
should  be  made  thoroughly  smooth. 
Figs.  529  and  530  will  give  a  good 
idea  of  this.  The  operation  involves,  of 
course,  the  filling  of  the  jndp-canals 
of  the  healthy  roots,  as  is  usual  in 
]>ulp-cases,  and  it  is  usually  best  to  fill 
the  root  to  be  amputated  solidly  with 
gold  before  the  operation  of  removal, 
as  it  IS  then  more  easily  done.  If  from 
any  cause  this  is  inconvenient,  with  a  fissure-burr  a  fissure  may  be  cut 
which  will  include  the  pulp-canal  as  it  emerges  from  the  pulp-chamber, 


Fig.  529. 


Chronic  Case  of  Phagedenic  Pericementitis 
in  wliicli  tlu!  whole  of  the  Palatine  Hoot 
of  an  Upper  Molar  is  denuded  of  its  Mem- 
brane.   (Compare  with  Kig.  530.) 


AMPUTATION  OF  THE  ROOTS  OF  TEETH. 


991 


and  which  may  be  filled  at  any  convenient  time  after  the  removal  of  the 
root. 

The  amputation  of  one  of  the  roots  of  the  first  molar  of  the  lower 
jaw  is  perhaps  called  for  oftenest  from  neglected  alveolar  abscess  of  the 
posterior  root — at  least,  this  has  been  the  case  in  my  practice.  The  ope- 
ration is  performed  by  the  same  means  as  that  described  for  the  removal 
of  the  palatine  root  of  the  upper  molar.  The  operation,  however,  is  rather 
more  difficult,  for  the  reason  that  it  is  not  so  easy  of  aj)proach  in  the 
process  of  cutting,  nor  is  the  root  so  readily  removed  after  it  has  been 
severed  from  the  crown.  Generally,  the  root  should  be  cut  as  close  to 
the  bifurcation  of  the  roots  as  possible  and  sloped  down  toward  the  prox- 
imal surface  in  such  a  manner  that  when  the  gum  is  well  and  shrunken 
as  wide  a  space  as  practicable  shall  be  left  between  the  cut  surface  and 
the  gum,  so  that  it  may  the  more  easily  be  kept  clean.     (See  Fig.  531.) 

Fig.  530. 


Case  represented  in  Fig.  529  after  Treatment  by 
Amputation  of  the  alfected  Root  and  filling 
of  the  Pulp-cavitv  and  Canals.  (Compare  with 
Fig.  529.) 


Amputation  of  the  Posterior  Root  of  the 
first  Lower  JNIolar  (the  roots  of  the  teeth 
are  shown  by  dotted  lines):  a,  root  re- 
moved; h,  line  of  g"um  after  shrinkage 
has  occurred. 


Usually  this  is  most  readily  accomplished  by  passing  a  long  fissure- 
burr  through  between  the  I'oots  and  cutting  backward,  or,  if  it  is  the 
anterior  root  that  is  being  severed,  forward.  In  most  cases  the  lips 
can  be  held  sufficiently  out  of  the  way  to  permit  of  this  without  diffi- 
culty. In  some  cases  the  incision  wnll  open  into  the  j)ulp-chamber ;  but 
if  this  has  been  solidly  filled  before  the  operation,  it  will  occasion  no 
difficulty. 

The  removal  of  the  root  after  it  is  severed  from  the  crown  is  occa- 
sionally a  little  perplexing,  yet  in  most  cases  in  which  this  operation  is 
advisal)le  the  alveolus  of  the  root  is  so  much  destroyed  that  it  comes 
away  easily  and  may  be  pushed  through  to  the  lingual  side  with  any 
appropriate  instrument.  Occasionally  it  will  be  found  necessary  to 
burr  away  some  of  the  buccal  side  of  the  root  to  allow  it  to  clear  the 
crown  as  it  is  turned  toward  the  inside  of  the  mouth.  These  two  posi- 
tions are  those  in  Avhich  the  amputation  of  an  entire  root  will  oftenest 
be  found  available,  but  occasionally  other  teeth  will  be  found  on  which 
the  operation  may  be  performed  with  advantage.  These  operations 
have  uniformly  been  very  satisfactory.  A  tooth  that  has  long  been  a 
source  of  continuous  annoyance  is  rendered  comfortable  and  serviceable. 

The  amputation  of  the  apex  of  the  root  of  any  of  the  teeth  is  occa- 
sionally required  in  case  of  long-neglected  abscess.     This  is  generally 


992  DISEASES  OF  THE  PERIDENTAL  MEMBRANE. 

made  necessary  by  the  collection  of  serumal  calculus  on  the  apex  of  the 
root  or  by  the  cementum  of  the  apex  l>ecoming  so  infiltrated  with  the 
products  of  putrefactive  processes  that  it  becomes  an  irritant.  In  the 
first  case  it  is  generally  best  to  remove  the  serumal  calculus  if  this  can 
be  done  without  too  much  mutilation  of  the  parts,  but  I  have  sometimes 
felt  that  to  cut  oif  the  end  of  the  root  was  the  least  objectionable  of  the 
two.  In  the  second  case  the  amputation  of  the  apex  of  the  root  seems 
to  be  the  only  remedy.  The  operation  is  usually  easy  of  performance 
with  the  fissure-burr.  In  any  case  in  which  this  is  justifiable  there  is 
usually  no  difficulty  in  reaching  the  root,  for  the  bone  covering  it  is 
generally  destroyed  by  disease,  so  that  only  the  soft  tissues  are  in  the 
way ;  but  any  margins  of  bone  may  readily  be  removed  with  the  burr 
or  chisel. 

This  operation  has  been  recommended  by  various  persons  within  the 
last  two  decades,  but  in  my  hands  the  percentage  of  cures  of  old  chronic 
abscesses  by  this  means  has  not  been  sufficiently  great  for  me  to  recom- 
mend it  with  much  confidence  or  to  affirm  that  it  will  be  found  service- 
able in  any  considerable  number  of  cases ;  it  should  be  used  as  a  last 
resort  only.  The  operation  is  usually  not  very  painful  and  can  be 
done  in  a  few  moments,  and  is  worthy  of  a  trial  before  giving  up 
an  otherwise  valuable  tooth. 


ABRASION  AND  EROSION  OF  THE  TEETH. 

By  G.  V.  BLACK,  M.  D.,  D.  D.  S. 


Abrasion. 

Abrasion  of  the  teeth  is  a  gradual  loss  of  their  substance  from 
mechanical  causes.  It  is  seen  almost  entirely  on  the  grinding  sur- 
faces of  the  molars  and  bicuspids,  the  cusps  of  the  cuspids,  and  the  cut- 
ting edges  of  the  incisors.  From  the  time  that  the  teeth  come  through 
the  gums  they  are  subjected  to  wear  through  the  exercise  of  their  pecu- 
liar function  in  masticating  food.  Unlike  other  organs  of  the  body, 
they  are  incapable  of  repairing  losses  which  they  may  sustain  by  attri- 
tion, and  jjortions  of  their  substance  removed  in  this  way  are  perma- 
nently lost.  If  the  epithelium  of  the  sole  of  the  foot  is  worn  thin  by 
attrition  in  walking  over  a  sandy  way,  it  is  soon  replaced  by  a  groMth 
of  young  cells  from  beneath  and  restored  to  its  usual  thickness.  Except 
the  teeth,  this  is  true  of  any  other  portion  of  the  body  subject  to  attri- 
tion. Even  the  harder  structures,  such  as  the  nails,  are  subject  to  a 
continuous  growth  through  which  the  losses  by  wear  are  replaced.  This 
growth  always  takes  place  at  what  may  be  termed  the  root  of  the  organ 
— not  upon  the  surface  worn  away — and  the  nail  as  a  whole  is  pushed 
forward  to  supjjly  the  portions  lost  by  the  processes  of  attrition.  In  the 
case  of  certain  animals — notably  the  rodents — we  find  the  teeth  con- 
structed on  this  plan  ;  that  is  to  say,  they  are  continuously-groicing 
organs  in  which  the  loss  sustained  by  attrition  upon  the  icorking  end  is 
continually  counterbalanced  by  normal  additions  at  the  groiving  end, 
and  in  this  way  the  Avhole  tooth  is  continuously  moved  forward  to  com- 
pensate for  the  loss. 

This  plan  of  compensating  for  loss  by  attrition  is  not  present  in  the 
Herbivora,  Carnivora,  or  Omnivora.  In  these  the  teeth  have  a  definite 
period  of  formation  and  growth ;  and  when  this  is  completed,  the  size 
and  form  of  the  tooth  are  no  longer  subject  to  change  through  vital 
processes.    Any  loss  by  the  process  of  attrition  is,  therefore,  permanent. 

A  certain  amount  of  wear  is  normal,  and  present  in  each  individual 
as  age  increases.  AVhen  the  incisors  first  present  themselves  through 
the  gums,  they  are  distinctly  tuberculated  on  their  cutting  edges.  These 
tubercles  usually  disappear  by  the  processes  of  abrasion  at  periods  vary- 
ing from  the  twelfth  to  the  eighteenth  vear,  and  the  cutting  eNge  of  the 
tooth  assumes  a  straight  or  slightly-curved  line,  which  it  afterward 
maintains.  At  the  same  time  facets  produced  by  wear  appeaiKon  the 
sidcH  of  the  cusps  of  the  molars  and  bicuspids.  These  facets  are  (deter- 
mined by  the  peculiarities  of  the  antagonism  of  the  particular  deiVure 

Vol.  I.— 63  993  1 


\ 

1 


994  ABRASION  AND  EROSION  OF  THE  TEETH. 

examined,  and  are,  therefore,  inconstant  as  to  position.  They  always 
occur  at  such  points  as  come  in  contact  when  the  jaws  are  closed  nor- 
mally. In  cases  of  fracture  and  disturbance  of  the  relative  positions  of 
the  two  jaws  the  line  of  normal  closure  may  as  early  as  the  fourteenth 
year  be  found  in  reasonably  good  casts  of  the  teeth  by  noting  these  facets 
and  bringing  them  together.  In  several  instances  at  an  earlier  age  I 
have  succeeded  in  doing  this  by  making  use  of  the  facets  \on  the  milk- 
teeth.  In  some  cases  the  occlusion  of  the  teeth  is  very  imperfect,  so  that 
but  few  teeth  touch  when  the  jaws  are  closed,  and  in  this  c^e  there  will 
be  correspondingly  few  facets.  ■, 

The  rapidity  of  wear  seems  to  depend  more  on  the  manner  of  the 
antagonism  than  upon  any  other  circumstance.  Other  conditions  may 
modify  it,  such  as  the  hardness  of  the  teeth,  which  may  hinder,  or  their 
softness,  which  may  hasten,  the  process.  The  habitual ./ use  of  rough, 
coarse  food  requiring  much  trituration  will  naturall}:- produce  more 
wear  than  the  habitual  use  of  very  soft  foods,  etc.  JThese  are  only 
modifying  conditions,  and  not  principal  elements,  in  tpe  predisposition 
to  great  waste  by  wear.  I  am  persuaded  that  the  chieF  causative  agency 
consists  in  the  rubbing  of  the  teeth  one  upon  another.  As  is  plainly  shown 
in  the  disposition  to  the  formation  of  facets  on  the  t^eeth  of  young  per- 
sons. This  wear  is  normal  so  long  as  these  facets /remain  distinct  and 
clear ;  when  these  are  lost,  it  becomes  abnormal.     I 

Two  elements  seem  to  enter  into  abnormal  wear,  or  abrasion.  The 
principal  of  these  is  a  fault  in  the  antagonism  of  the  teeth  which  per- 
mits sliding  movements  wh6n  the  jaws  are  closed.  In  the  perfectly 
normal  antagonism  of  the  human  teeth  sliding:  movements  of  the  teeth 
of  the  one  jaw  upon  those  of  the  other  v»'ithout  parting  them  slightly 
are  impossible,  for  the  reason  that  the  euisps  of  the  upper  teeth  fit  into 
the  sulci  of  the  lower,  and  vice  versa,  in  such  a  way  as  to  prevent  it. 
In  the  normal  use  of  the  teeth  this  a^daptation  is  made  more  perfect  by 
the  formation  of  the  facets  above  alluded  to,  which  are  in  this  case 
always  on  the  slopes  of  the  cusi^^js ;  for  by  this  process  the  points  which 
tend  to  hold  the  teeth  asunder  are  worn  down,  allowing  the  cusjds  to 
become  more  firmly  seated  in  the  sulci  opposite.  In  this  way  an  antag- 
onism naturally  good  becomes  perfected.  If,  on  the  other  hand,  the 
antagonism  is  from  the  beginning  very  imperfect,  so  that  the  cusps  of 
the  teeth  of  the  opposirig  jaws  rest  the  one  upon  the  other,  the  case  is 
altogether  different.  This  involves  the  formation  of  facets  on  the  points 
of  the  cusps  instead  off  on  their  sides,  and  in  this  way  the  cusps  are  short- 
ened and  a  flat  surlfr'ace  is  established.  If  at  first  there  are  but  few  points 
preventing  a  slidi-ng  motion  of  the  jaws,  such  points  are  usually  early 
worn  down  by  'lateral  or  backward-and-forward  motions,  and  all  hin- 
drance to  thescj,  and  even  to  rotary  motions,  is  removed.  These  move- 
ments are  tb,en  liable  to  become  habitual  with  the  person  and  the  teeth 
are  worn  fli?it,  and  in  this  condition  ground  down  with  abnormal  rapidity. 
This  is  eZ-pecially  liable  to  occur  if  at  the  same  time  the  incisors  are  in 
such  a  Tposition  that  their  cutting  edges  come  the  one  upon  the  other. 
In  thi>^  case  all  restraint  uj)on  lateral,  and  even  rotary,  movement  is 
speediily  removed  ;  and  such  movements  are  often  adopted  by  the  indi- 
vid^ial,  with  the  effect  of  rapidly  wearing  away  the  teeth. 


ABRASION.  995 

In  a  considerable  number  of  cases  I  have  noted  an  habitual  disposi- 
tion to  rub  the  teeth  together — to  gritting,  as  it  is  called,  of  the  teeth — 
and  this  seemed  to  be  connected  Avith  abnormal  abrasion.  It  will  read- 
ily be  seen  that  a  habit  of  this  kind,  once  formed,  may  be  maintained 
for  years,  and  by  the  abnormal  wear  which  it  occasions  may  tend  to 
remove  the  cusps  of  the  teeth  quite  rapidly,  and  as  these  are  removed 
the  lateral  and  back-and-forward  movements  take  a  wider  range,  until 
the  cusps  disappear.  Then  the  abrasion  will  proceed  as  if  the  antag- 
onism had  been  faulty  from  the  beginning.  In  this  class  of  cases  it  is 
not  unusual  to  see  the  upper  incisors  worn  from  their  palatine  surfaces 
until  they  become  very  thin,  and  finally  only  the  enamel  of  the  labial 
surface  is  left,  this  breaking  away,  leaving  a  jagged  edge.  As  the  jagged 
portions  are  gradually  removed  a  wider  range  is  given  to  the  forward 
motions  of  the  lower  jaw,  and  the  wear  proceeds  more  rapidly  than 
before.  It  thus  appears  that  as  the  abrasion  progresses  it  becomes 
more  rapid,  and  it  is  not  infrequent  to  find  the  teeth  worn  down  to  the 
gum  within  a  very  few  years  after  they  become  distinctly  flat,  so  as  to 
permit  of  rotary  movement  upon  a  given  plane. 

In  these  cases,  if  a  few  teeth  have  been  lost  in  one  jaw,  the  teeth  in 
the  opposite  jaw,  having  no  antagonists,  are  not  worn  down  ;  and  if  the 
loss  has  occurred  early,  they  will  be  found  to  have  retained  their  cusps, 
serving  to  show  the  original  form  of  the  denture.  In  addition  to  this, 
they  will  have  risen  in  their  sockets  also  ;  so  that  their  crowns  will  pro- 
ject much  beyond  the  plane  of  the  other  teeth.  Occasionally  irregular- 
ities formed  in  this  way  become  very  prominent. 

When  flat  surfaces  have  been  formed  and  wear  has  proceeded  so  far 
as  to  expose  the  dentine,  this,  being  softer  than  the  enamel,  is  hollowed 
out  in  the  form  of  a  cup  by  the  trituration  of  food.  These  cup-shaped 
cavities  are  often  of  considerable  depth,  especially  in  case  the  enamel  is 
very  thick  and  strong.  They  are  apt  to  be  deepest  when  the  teeth  are 
about  one-third  or  one-half  worn,  for  the  reason  that  on  this  part  of  the 
crown  the  enamel  is  thicker  than  it  is  farther  toward  the  neck  of  the 
tooth.  Where  this  cupping  out  is  considerable,  the  enamel  is  liable  to 
be  broken  away  as  the  wear  approaches  those  portions  about  the  neck 
of  the  tooth,  where  it  is  thinner.  In  these  cases  it  is  very  liable  at  such 
points  to  split  away  from  the  dentine  up  to  its  junction  with  the  cemen- 
tum.  Then  the  dentine  wears  in  such  a  way  that  food  slides  away  from 
between  the  teeth  during  the  process  of  trituration,  a  deep  groove  being 
abraded ;  or  if  the  loss  of  enamel  has  extended  over  the  greater  part  of 
one  side,  while  it  remains  intact  on  the  other,  the  tooth  may  be  worn  to 
a  wedge-shape.  By  such  mechanism  as  this  teeth  occasionally  become 
very  much  worn  and  misshapen. 

It  is  therefore  characteristic  of  simple  abrasion  of  the  teeth  that  a 
flat  surface  is  formed  as  the  leading  abnormality.  Tliis  results  from 
the  rubbing  away  of  the  cusps  by  lateral  and  back-and-forward  move- 
ments of  the  jaws,  either  from  a  habit  acquired  or  from  an  original 
imperfection  in  the  antagonism.  As  yet  no  way  of  checking  this,  when 
it  has  once  made  sufficient  progress  to  be  noticeable,  has  been  put  into 
practice.  It  seems  prol table  that  the  judicious  building  of  cusps  at  suit- 
able points,  so  that  they  would  interlock  in  such  a  way  as  to  prevent  the 


996  ABRASION  AND  EROSION  OF  THE  TEETH. 

sliding  movements,  would  in  a  large  measure  prevent  the  disastrous 
results.  AVhile,  in  some  cases  that  have  been  presented,  I  have  thought 
of  doing  this,  I  have  not  had  quite  sufficient  confidence  to  subject  my 
patient  to  the  amount  of  disagreeable  manipulation  required.  Still,  if 
it  were  proven  to  be  eJffectual,  it  would  be  well  worth  doing.  One  great 
difficulty  in  the  way  of  such  an  operation  is  the  uncertainty  of  diag- 
nosis. 

Another  procedure  that  might  be  utilized  in  many  cases  is  the  early 
correction  of  slight  irregularities  in  such  a  way  as  to  seat  the  cusps  in 
the  sulci  of  opposing  teeth.  This  has  the  same  objection  as  that  men- 
tioned above.  Yet  my  own  observations  in  the  correction  of  irregular- 
ities show  conclusively  that  if  the  diagnosis  were  made  sufficiently  early 
and  the  corrections  effected  it  would  save  the  teeth  from  untimely  destruc- 
tion. As  I  write  I  have  before  me  the  cast  from  the  mouth  of  a  boy 
thirteen  years  old,  the  cast  being  made  for  the  purpose  of  correcting  an 
apparently  slight  irregularity  of  the  anterior  teeth,  in  which  the  cusps 
of  the  first  molars  are  so  much  flattened  by  the  antagonism  being  on 
their  points  as  to  render  them  practically  useless  for  the  prevention  of 
sliding  movements.  This  early  wear  will  illustrate  the  extreme  diffi- 
culties of  this  subject. 

It  does  not  seem  to  have  entered  the  minds  of  writers  in  the  past  that 
abrasion  abnormal  in  degree  is  a  thing  calling  for  early  diagnosis  and 
operative  procetlures  for  the  prevention  of  its  ultimate  results;  there- 
fore a  sufficient  mass  of  well-digested  facts  bearing  on  the  subject  have 
not  been  collected  to  enable  even  the  well-informed  operator  to  confi- 
dently recommend  a  tedious  operation,  of  the  utility  of  which  his 
patient  can  have  no  conception,  and  concerning  which  the  operator 
himself  is  in  doubt.  Yet  if  the  cause  of  this  abnormal  M'ear  is  such 
as  I  have  represented  it  to  be,  it  is  capable  of  correction  by  the  early 
adjustment  of  irregularities,  or  by  the  timely  and  judicious  building  of 
cusps  with  gold  or  gold  and  platinum  foil  that  will  prevent  free  slid- 
ing movements  and  save  the  denture  from  untimely  abrasion.  Of 
course  all  dentists  are  acquainted  with  the  capping,  or  building  down, 
of  abraded  teeth,  but  I  now  allude  to  operations  that  will  prevent  abra- 
sion in  its  inception  and  preserve  the  form  of  the  teeth. 

Abrasion  also  occurs  in  portions  of  the  denture  after  the  loss  of  a 
considerable  number  of  the  teeth,  owing  to  the  fact  that  all  the  force 
of  the  muscles  clasing  the  jaws  and  all  the  work  of  mastication  have 
been  thrown  on  a  few  teeth.  In  these  instances,  if  much  sliding  motion 
is  allowed,  abrasion  will  be  very  rapid.  This  I  have  been  in  the  habit 
of  correcting,  and  the  results  have  been  such  as  to  give  me  assurance 
that  by  the  aid  of  the  judicious  registering  and  discussion  of  observa- 
tions we  should,  in  full  dentures,  be  able  to  make  timely  diagnosis  of 
danger  in  this  direction  and  apply  the  remedy  in  time  to  jDrevent  abnor- 
mal abrasion. 

In  abrasion  of  the  teeth  there  are  no  changes  in  the  adjacent  dentine 
except  it  be  a  slight  yellowing  of  the  superficial  portions  of  the  exposed 
surface.  Formerly  it  was  suppjosed  that  consolidation  of  the  dentinal 
fibrils  occurred  as  an  effort  of  vitality  to  erect  a  barrier  to  farther  prog- 
ress (J.  Tomes).     This  view  is  no  longer  tenable.     In  those  cases  in 


EROSION.  997 

Avhich  the  progress  of  wear  has  been  exceedingly  slow,  as  well  as  in  the 
more  rapid  ones,  the  dentinal  tubnles  are  found  to  be  open  at  the  abraded 
surface.  There  is  also  a  popular  notion  that  the  surface  of  the  abraded 
dentine  is  harder  than  normal.  This  is  an  error.  The  assumption  that 
the  dentinal  fibrils  undergo  calcification  probably  has  had  something  to 
do  with  this  opinion,  but  the  principal  circumstance  leading  to  it  is 
doubtless  the  difficulty  experienced  in  penetrating  abraded  surfaces  with 
instruments.  This  difficulty  exists,  and  has  been  noted  by  many  ;  but 
it  is,  however,  not  on  account  of  a  greater  density  of  the  dentine,  but 
is  the  superior  resistance  of  a  polished  surface  over  one  that  is  not 
polished.  Precisely  the  same  differences  are  noted  in  the  penetration 
of  polished  and  unpolished  surfaces  of  marble,  or  any  other  kind 
of  stone. 

Abraded  dentine  is  often  exquisitely  sensitive,  and  certain  changes 
are  found  to  take  place  in  the  dental  pulp  as  a  consequence.  These 
will  be  discussed  after  the  consideration  of  erosion. 

Erosion. 

Erosion  of  the  teeth  is  an  affection  characterized  by  a  loss  of  substance 
of  the  organ  occurring  without  apparent  cause.  It  always  has  its  begin- 
ning on  the  surface  of  the  tooth  over  a  limited  space,  and  very  gradually 
a  pit  or  groove  is  formed  which  steadily  widens  and  deepens,  until  in 
many  cases  a  large  part  of  the  tooth  is  destroyed.  This  happens  most 
frequently  on  the  labial  surface  of  the  crown,  and  is  often  confined  to 
the  anterior  teeth.  It  has  been  noted  by  a  number  who  have  written 
on  kindred  subjects,  and  much  variety  of  opinion  has  been  expressed  in 
regard  to  it.  In  addition  to  the  term  erosion,  it  has  been  termed  chem- 
ical abrasion,  decay  by  denudation,  etc.,  while  others,  as  Salter,  have 
regarded  it  as  being  essentially  a  result  of  friction  applied  by  the  tooth- 
brush or  in  some  manner  not  very  easy  to  comprehend. 

As  most  usually  seen  on  its  first  appearance,  erosion  consists  of  a 
slight  cup-  or  dish-shaped  excavation  in  the  enamel  of  some  one  of  the 
anterior  teeth,  generally  situated  from  a  half  line  to  a  line  below  the 
free  margin  of  the  gum.  It  is,  how'cver,  not  confined  to  this  position, 
and  may  occur  at  any  point  on  the  crowns  of  any  of  the  teeth  ;  but 
perhaps  four-fifths  of  the  cases  that  have  come  under  my  observation 
have  begun  as  far  forward  as  the  first  bicuspid,  and  one-half  or  more 
have  been  on  the  labial  surfaces  of  the  incisors.  Next  to  the  incisors, 
the  cuspids  are  much  the  more  frequent  points  of  attack.  This  applies 
to  both  the  upper  and  the  lower  jaw.  When  this  little  excavation  is 
discovered  on  one  tooth,  if  it  be  closely  watched  it  will  be  seen  in  the 
course  of  a  few  months — possibly  a  few  weeks — that  it  is  gradually 
broadening  and  deepening,  and  as  this  process  goes  on  it  will  be  noticed 
that  little  cups  are  appearing  in  a  similar  position  in  the  teeth  next 
adjacent.  The  erosion  is  rarely  solitary,  though  such  cases  are  known 
to  occur.  It  very  generally  extends  from  tooth  to  tooth  at  either  side 
of  the  one  first  attacked,  but  in  nearly  every  case  there  is  a  preference 
that  is  quite  noticeable  for  one  or  the  other  side.  Although  I  have  seen 
a  number  of  cases  that  seemed  to  have  be^un  on  the  central  incisors  and 


998  ABRASION  AND  EROSION  OF  THE  TEETH. 

in  which  the  invasion  of  these  continued  to  be  about  equal,  I  have  never 
yet  seen  a  case  that  maintained  a  symmetrical  progress  in  respect  to  the 
the  other  teeth.  The  illustrations  on  another  page  will  give  a  good  idea 
of  this.  In  many  cases  there  is  a  marked  tendency  to  the  formation 
of  a  sharp  angle  with  the  surface  of  the  enamel  on  the  lower  (toward 
the  crown)  margin  of  the  erosion.  This  is  particularly  noticeable  in 
Fig.  532.  Occasionally  this  is  seen  to  be  next  the  gum  (Fig.  534),  but 
much  more  rarely,  and  in  some  instances  both  the  upper  and  the  lower 
margins  are  very  square  incuts.  A  few  days  ago  I  was  consulted  in 
regard  to  a  case  in  which  both  of  the  superior  central  incisors  were  cut 
as  if  done  with  a  No.  4  separating  file,  the  cut  extending  considerably 
into  the  dentine.  This  case  is  remarkable  as  being  the  deepest  cut,  in 
proportion  to  its  width,  that  I  have  ever  seen.  Generally  the  incuts 
are  of  considerable  width  ;  and  if  one  margin  is  squarely  cut  in,  or 
nearly  so,  the  other  slopes  much  more  gradually  to  the  surface,  as  will 
be  seen  in  all  the  illustrations  presented.  More  rarely  cases  may  be 
seen  in  which  the  excavations  are  nearly  circular,  with  the  sides  equally 
sloping.  It  will  thus  be  observed  that  there  is  nothing  definite  as 
relates  to  form.  I  have  seen  a  few  cases  in  which  there  was  a  groove 
excavated  lengthwise  of  the  crown  of  the  tooth,  but  these  are  very  rare. 
Dr.  Cushino;  of  Cliicago  has  related  to  me  a  curious  case  that  came 
under  his  care,  in  which  a  groove  was  excavated  in  the  labial  surface 
of  an  incisor  close  to  the  .proximal  border,  extending  from  near  the 
gum  to  the  cutting  edge,  from  which  point  it  passed  backward  across 
the  cutting  edge  and  then  down,  in  the  form  of  a  groove  in  the  palatine 
surface,  nearly  to  tiie  gum.  Such  a  form  as  this  is  certainly  remarkable. 
Another  variety,  of  which  two  cases  have  come  under  my  observation, 
is  the  wasting  of  the  proximal  surfaces  of  the  teeth.  In  each  of  these 
round  holes  were  formed,  passing  through  between  the  teeth  (each 
tooth  being  about  equally  eroded),  as  if  filed  out  with  a  rat-tail  file, 
the  surfaces  remaining  hard  and  finely  polished.  When  one  of  these 
first  came  under  my  observation,  the  crowns  of  the  central  incisors 
were  almost  severed  from  their  roots,  and  similar  openings  were  in  pro- 
cess of  formation  between  the  other  teeth  on  one  side  as  far  back  as  the 
space  between  the  first  and  second  bicuspids,  while  on  the  other  it 
extended  to  the  lateral  incisor  and  cuspid  only.  This  effect  was  con- 
fined to  the  ui)per  jaw.  In  the  other  case  the  teeth  of  both  jaws  were 
similarly  affected. 

In  all  these  cases  the  erosion  makes  the  greatest  progress  in  the  teeth 
first  attacked,  and,  in  whatever  stage  of  progress  the  case  is  seen,  the 
extent  of  the  loss  of  substance  gradually  diminishes  as  it  recedes  from 
this  point  in  either  direction.  The  difference  in  the  extent  of  the  loss 
of  substance  generally  has  a  close  relation  to  the  time  of  beginning. 
Exceptions  to  this  rule  now  and  then  occur,  but  it  holds  good  in  so 
large  a  majority  of  cases  that  after  seeing  the  ]>osition  and  form  of  the 
erosion  in  two  or  three  teeth  we  may  jM'ognosticate  })retty  certainly  the 
form  it  will  take  in  the  adjacent  teeth  if  the  case  progresses  without 
interruption.  This  progress  is  well  marked  in  illustrations  532  and  533. 
So  far  as  my  observation  extends,  the  form  and  direction  of  the  erosion 
are  not  materially  changed — but  rarely,  at  any  rate — after  it  has  once 


EROSION. 


999 


begun.  If  the  teeth  are  regular  in  the  arch,  the  second  tooth  attacked 
Avill  be  eroded  in  ahnost  precisely  the  same  form  as  the  first,  and  so  on 
with  third  and  fourth.  But  it  is  rare  to  see  two  teeth  which  are 
alike  in  the  extent  of  erosion  at  the  same  date,  except  it  be  the  cen- 
tral incisors.  Those  on  which  the  process  begins  later  will  pass 
through  the  same  forms  and  stages  which  the  first  has  gone  through 
before  them. 

Fig.  582  represents  a  cast  made  from  an  impression  of  a  case  in  the 
practice  of  Dr.  E.  D.  Swain  of  Chicago ;  its  principal  peculiarity  is  the 

Fig.  532. 


Case  of  Erosion  of  the  Lower  Anterior  Teeth  (drawn  from  a  cast  prepared  by 
Dr.  E.  D.  Swain  of  Chicago) :  B,  silhouettes  representing  the  loss  of  substance 
ill  five  of  the  atTected  teeth:  1,  right  liitcral  incisor;  J,  right  cmitral ;  3,  left 
central;  4,  left  lateral;  5,  left  cuspid.  The  lines  aaaaii  show  the  position  of 
the  margin  of  the  gum.  A  line  is  drawn  also  to  show  the  original  form  of  the 
tooth. 

uniform  sharpness  of  the  angles  made  by  the  erosive  pro- 
cess. Usually,  when  a  groove  is  formed  in  this  position, 
the  margins  are  more  rounded.  It  will  be  seen  that  at  the 
time  this  impression  was  taken  the  erosion  had  extended 
from  the  right  lateral  incisor  to  the  left  first  bicuspid  of 
the  lower  jaw,  with  the  deepest  point  of  erosion  in  the  left 
central  incisor.  In  this  case  the  left  central  was  doubtless 
the  point  of  beginning,  from  which  it  gradually  extended 
to  the  other  teeth.  In  all  of  these  the  surface  of  the  teeth 
is  cut  into  as  if  done  with  a  square  file,  and  the  particular 
angles  are  maintained  in  all  of  the  teeth  affected.  I  have 
shown  these  angles  in  the  silhouettes  of  the  incisors  and 
cuspid.^ 
The  surface  of  the  exposed  dentine  was  firm  and  hard  and  had  a  per- 
fect polish  everywhere,  and  there  was  no  jutting  of  the  enamel  above 
the  eroded  dentine  at  any  point.     These  tissues,  differing  so  much  in 

1  Tliese  silhouettes  were  made  as  follows :  An  impression  Mas  taken  from  the  cast  in 
modelling!;  compound,  care  being  taken  to  get  it  as  sharp  as  possible.  When  this  was 
thoroughly  cold,  ii  was  oiled  lightly  and  a  cast  made,  also  of  modelling  compound,  by 
]>ressing  the  softened  material  quickly  and  firmly  into  the- impression.  When  cold, 
they  parted  very  readily.  The  cast  was  then  cut  away  from  before  backward,  perpen- 
dicularly, from  its  right-hand  end  until  tlie  right  lateral  incisor  was  reached.  Then 
the  cut  surface  was  dressed  down  carefully  on  a  piece  of  emery-paper  laid  flat  until  the 
centre  of  the  tooth  was'  reached,  ju-oducing  a  perpendicular  section  from  before  back- 
ward of  this  tooth.  The  surface  was  then  smoothly  finished  on  fine  emery-paper,  and 
the  back  part  of  the  cast  was  cut  away  to  something  near  the  shape  of  the  tooth.  (This 
cast  was  only  of  the  labial  surfaces;  therefore  the  lingual  surfaces  as  shown  are 
only  an  approximation  to  correctness.)  This  was  then  inked  on  an  ordinary  rubber- 
stamp  inking-pad  and  the  silhouette  of  this  tooth  jirinted.  The  cast  was  then  trimmed 
to  the  centre  of  the  next  tooth  and  its  siliiouette  printed  in  the  same  way,  and  so  on 
from  tooth  to  tooth.     The.se  accurately  represent  the  angles. 


1000 


ABRASION  AND  EROSION  OF  THE  TEETH. 


density,  were  finished  as  evenly  and  smoothly,  the  one  with  the  other, 
as  if  done  on  the  lapidary's  wheel. 

Fig.  533  was  made  trom  the  cast  of  a  case  in  my  own  practice,  and 
represents  the  teeth  as  I  first  saw  them.  The  patient  was  sufficiently 
intelligent  to  give  what  seemed  to  be  a  very  reliable  account  of  its  prog- 


FiG.  533. 


A  Case  of  Erosion  (drawn  from  tlie  castl:   B,  silhouette  from  a  perpendicular  line  through  the  left 
centrals,  upper  and  lower,  showing  the  loss  of  substance. 

ress.  A  little  more  than  three  years  before,  she  had  noticed  slight  cups, 
which  caused  her  some  solicitude,  appearing  on  the  labial  surfaces  of 
the  upper  central  incisors,  near  the  gums.  These  were  observed  to 
widen  very  slowly,  but  seemingly  very  steadily,  toward  the  cutting  edge 
and  laterally.  About  six  months  later  the  same  condition  was  seen  on 
the  lower  centrals,  and  the  lesion  seemed  to  progress  more  rapidly  than 
the  erosion  of  the  upper  teeth ;  so  that  at  the  end  of  the  first  year  the 
loss  of  substance  appeared  to  be  about  equal  in  depth.  At  about  this 
time  the  erosive  process  was  seen  to  be  making  its  appearance  on  other 
teeth.  Her  dentist  was  then  consulted,  and  she  was  told  that  the 
trouble  resulted  from  the  use  of  a  stiff  toothbrush  which  she  employed. 
Very  much  against  her  will,  she  abandoned  the  brush  for  a  year. 
During  this  time  the  erosion  made  more  rapid  progress  than  before, 
and  the  .sensitiveness  of  the  eroded  surfaces,  already  quite  considerable, 
increased  greatly ;  so  that,  in  addition  to  the  marred  appearance  of  the 
teeth,  the  hvper8e.sthesia  became  a  source  of  great  annoyance,  occasional 
exacerbations  occurring,  during  which  exquisite  suffering  resulted  when- 
ever the  eroded  surface.^}  were  touched.  Finding  that  the  abandonment 
of  the  u.se  of  the  brush  did  not  retard  the  erosion,  she  again  resumed  it ; 
but,  on  account  of  the  great  sensitiveness  of  the  eroded  surfaces,  she  was 
ever  after  compelled  to  avoid  them  in  cleaning  het  teeth.  The  erosion 
continued  steadily,  and  at  the  end  of  the  third  year  was  as  represented 
in  the  illu.stration.  At  this  time  intense  hyperse.sthcsia  of  the  pulps  had 
occurred  in  the  central  incisors  above  and  below.  The  sensitiveness 
was  so  extreme  that  the  patient  could  not  be  induced  to  submit  to  any 
manipulation  whatever.  I  therefore  gave  an  anse.sthetic  and  removed 
the  pulps  of  the  four  centrals,  which  had  the  effect  of  rendering  the 
patient  fairly  comfortable.  Before  cutting  into  the  teeth  the  outline  of 
the  former  pulp-chamber  was  distinctly  seen  in  what  seemed  to  be  the 


EROSION.  1001 

exposure  of  a  secondary  deposit,  and  in  the  removal  of  tlie  pulps  it  was 
found  that  the  chambers  were  abnormally  small,  on  account  of  secon- 
dary deposits.  After  proper  treatment  of  the  root-canals  the  contour 
of  the  four  incisors  Avas  restored  with  gold  and  platinum  foil,  and  has 
stood  perfectly  to  this  date  (two  years).  In  the  mean  time,  the  erosion 
of  the  other  teeth  has  been  progressing,  but  much  more  slowly  than  for- 
merly, and  the  sensitiveness  has  abated  to  such  a  degree  that  thev  are 
fairly  comfortable.  The  indications  now  are  that  the  process  has  come 
to  a  spontaneous  standstill.  I  have  in  several  instances  observed  this 
spontaneous  cessation  of  erosion  after  it  had  made  considerable  progress, 
and  in  this  case  I  do  not  think  that  the  treatment  of  the  central  incisors 
had  any  influence  in  bringing  about  this  result.  The  cessation  did  not 
occur  at  once,  lor  very  decided  advance  was  made  during  the  six  months 
following  the  operation. 

Fig.  534  was  made  from  a  cast  of  a  case  occurring  under  the  obser- 
vation of  Dr.  George  H.  Cashing  of  Chicago,  and  is  here  introduced 
because  of  its  marked  peculiarities. 
The  case  had  not  progressed  very  "^" 

far  when  this  cast  was  made,  but 
I  learn  from  Dr.  Cushing  that  it. 
is  steadily  advancing  without  any 
disposition  to  change  in  the  form 
of  the  eroded  surfaces.  In  this 
case  the  incut  is  sharply  down 
from  the  surface  of  the  enamel — 
slightly   undercut,    indeed — in    a 

circular     line     following     the     free  feetii  (drawn  from  a  cast  prepared  by  i)r.  Geo. 

n     .-i  11,  H.  Cushing  of  Chicago^ 

margin    ot   the   gum    and    about 

half  a  line  from  it,  until  the  proximal  borders  of  the  tooth  are  reached, 
and  then  these  borders  are  followed  toward  the  cutting  edge.  The 
superficial  portions  of  the  tooth  are  smoothly  removed  in  the  included 
area,  being  deepest  in  that  portion  nearest  the  gum,  and  thinning  out 
toward  the  cutting  edge  in  such  a  M'ay  as  to  leave  a  perfectly  flat  sur- 
face. The  surface  thus  eroded  is  perfectly  hard  and  smooth  in  all  its 
parts.  This  is  the  left  lateral  and  central.  In  the  tooth  next  adjacent 
on  either  side  the  erosion  has  begun  in  the  same  way,  only  that  it  has 
not  extended  over  the  crown  of  those  teeth  lying  next  those  first  attacked 
at  the  time  the  cast  was  taken.  It  will  be  observed  that  the  right  cen- 
tral is  a  little  rotated  in  its  socket — a  circumstance  that  Mill  have  the 
effect  of  modifying  the  form  of  the  erosion  occurring  in  it.  I  have 
noted  this  in  enough  cases  to  be  sure  that  it  is  the  position  of  the  tooth 
that  produces  the  modification — a  fact  that  is  of  importance  in  consid- 
ering the  etiology  of  the  affection. 

The  forms  shown  in  these  illustrations  serve  to  give  an  idea  of  the 
variations  that  occur  in  this  process.  Each  case  examined  presents 
characteristics  peculiar  to  it,  and  to  no  other.  There  are  however,  not- 
withstanding their  sharp  differences,  certain  similarities  of  form  run- 
ning through  all  the  cases,  which,  after  one  has  become  accustomed  to 
observing  this  affection,  at  the  first  glance  mark  them  as  cases  of  ero- 
sion.    There  are  some  cases  in  which  the  effect  is  seen  over  a  large  part 


Peculiar  Case  of  Erosion  of  the  Superior  Anterior 


1002  ABRASION  AND  EROSION  OF  THE  TEETH. 

of  the  labial  surfaces  of  the  teeth  without  any  sharp  incuts  at  any  point; 
others  in  which  a  simple  groove  well  rounded  at  its  bottom  occurs  across 
the  crown  of  the  teeth,  near  the  gum,  and  at  the  margins  of  the  enamel. 
I  think  it  a  fact  that  those  cases  which  are  thus  indefinite  as  to  their 
boundaries  are  not  as  rapidly  destructive  as  those  that  show  sharp 
outlines. 

Erosion  sometimes  exists  in  association  with  mechanical  abrasion. 
Where  this  occurs  I  think  it  is  simply  intercurrent,  and  not  because  the 
two  processes  have  anything  in  common  in  their  etiology.  The  only 
cases  that  I  have  seen  in  practice  or  in  the  literature  of  the  subject 
seeming  to  offer  a  suggestion  of  interdependence  of  the  one  upon  the 
other  are  those  which  aifect  the  cutting  ends  of  the  incisors  in  some  rare 
cases  of  mechanical  abrasion.  In  a  few  cases  that  came  under  my  obser- 
vation several  years  ago  all  the  crowns  of  the  teeth,  except  the  usual 
cupping  out  of  the  dentine,  were  worn  flat  and  smooth,  and  the  antag- 
onism was  perfect  in  the  bicuspids  and  molars ;  but  the  incisors  failed, 
in  the  worst  case,  to  come  together,  by  about  three-sixteenths  of  an  inch. 
It  does  not  seem  to  me  possible  that  this  shortening  of  the  incisors 
could  have  been  the  effect  of  simple  abrasion.  They  cannot  possibly 
be  brought  in  contact,  and  they  have  become  almost  useless  in  the  pre- 
hension of  food  ;  so  that,  as  a  matter  of  fact,  they  are  scarcely  used  at 
all.  Yet  they  continue  to  lose  substance  much  faster  than  those  teeth 
that  bear  the  burden  of  mastication  and  the  friction  of  the  one  upon 
the  other.  I  have  sought  to  find  some  explanation  of  this  in  the  struc- 
ture of  the  dentine,  but  without  result ;  the  structure  of  the  teeth  that 
were  rapidly  losing  substance  seemed  as  good  as  that  of  the  others.' 
The  effect  is  certainly  that  of  erosion,  and  is  identical  with  that  process 
as  seen  on  the  labial  surfaces  of  the  teeth  and  occurring  independently 
of  mechanical  abrasion.  This  has  been  noted  by  most  writers  since 
the  time  of  Hunter. 

Etiology. 

The  etiology  of  mechanical  abrasion  has  been  sufficiently  explained  in 
connection  with  its  description. 

The  etiology  of  erosion  is  probably  one  of  the  most  obscure  subjects 
in  pathology ;  with  our  present  knowledge,  it  is  practically  unexplain- 
able.  This  being  the  case,  it  seems  incumbent  upon  every  writer 
w'ho  treats  of  the  subject  to  give  any  facts  in  his  possession  that  may 
seem  to  have  significance,  in  the  hope  that  from  the  accumulation  of 
data  something  tangible  may  be  derived  in  the  future.  In  the  past 
various  suggestions  iiave  been  made,  most  of  which  seem  untenable. 
Tiie  chemical  theory,  notwithstanding  the  many  valid  objections  to  it, 
is  jiorhaps  the  one  more  generally  held.     Some,  Avitli  J.  Tomes  and 

'  One  of  tliese  cases  was  treated  by  restoring  in  gold  tlie  contour  of  the  lost  tissue,  so 
as  to  perfect  the  antagonism.  For  tliis  purpose  pits  were  drilled,  into  which  screws 
were  driven,  and,  without  otherwise  cutting  the  surface,'  the  gold  built  al)Out  these  for 
retention.  The  surface  was  simply  carefully  washed  with  sulphuric  ether,  to  cleanse  it 
of  any  possible  adherent  animal  matter.  I  had  opportunity  occasionally  to  see  the  case 
up  to  the  time  of  the  patient's  death,  ten  years  after  the  operation  ;  the  treatment  was 
successful  in  every  respect.  This  seems  to  argue  that  the  cause  was  not  in  the  tooth 
itself. 


ETIOLOGY.  1003 

Salter,  seem  to  regard  it  as  the  effect  of  the  vigorous  use  of  the  tooth- 
brush, or  some  other  form  of  friction — indeed,  as  a  species  of  abrasion. 
It  is,  however,  difficult  to  believe  that  simple  friction  of  any  kind  can 
produce  the  eliect  seen  in  the  cases  I  have  illustrated,  and  many  other 
tbrms  occur  equally  difficult  of  explanation  by  that  hypothesis.  A 
causative  agency  has  been  sought  for  in  the  structure  of  the  teeth  them- 
selves, but  microscopical  examination  of  the  tissue  undergoing  erosion 
gives  no  results  except  to  demonstrate  that  the  fault  does  not  lie  in  this 
direction,  such  teeth  being  generally  found  perfect  in  their  organization 
and  development.  Again,  faulty  development  has  certain  characteristics 
that  are  well  known.  If  many  teeth  are  faulty  in  a  part  of  their  struc- 
ture, the  faults  are  present  in  those  parts  of  each  of  the  teeth  in  process 
of  development  at  the  same  time ;  therefore,  if  what  I  have  called 
erosion  were  the  washing  out  or  brushing  away  of  such  portions  of  the 
tooth  as  were  soft  from  faulty  development,  the  erosion  should  follow 
the  developmental  lines,  which  it  does  not  do  in  any  case  that  I  have 
seen. 

The  erodent,  whatever  it  may  be,  acts  from  without.  Neither  the 
dentine  nor  the  enamel  immediately  adjacent  to  the  portions  being  re- 
moved, even  up  to  the  immediate  surface,  shows  any  changes  whatever 
except  it  be  a  slight  discoloration  which  is  present  in  only  a  ^lortion  of 
the  cases.  There  is,  indeed,  in  most  of  the  cases  a  very  marked  sen- 
sitiveness of  the  surface  eroded,  and  finally  of  the  pulp  itself — which 
condition  I  shall  discuss  presently — but  this  does  not  seem  to  influence 
the  hard  tissues  in  any  degree.  Sensitive  dentine  is  just  as  hard  as  den- 
tine that  is  not  sensitive. 

As  already  stated,  the  more  generally  accepted  theory  is  that  erosion 
is  in  some  way  effected  by  acids,  and,  all  things  considered,  this  supposi- 
tion is  perhaps  more  tenable  than  any  other  that  has  been  advanced ; 
still,  there  are  great  difficulties  in  the  way  of  its  adoption.  It  is  gen- 
erally admitted  that  if  it  be  an  acid  that  acts  as  the  agent  the  action 
must  be  different  from  anything  now  known  to  us.  On  this  point  I 
can  throw  some  light,  though  I  will  fall  far  short  of  clearing  up  the 
mystery.  Teeth  may,  by  the  action  of  acids,  be  eroded  artificially  so 
nearly  like  some  of  the  forms  seen  in  the  human  mouth  that  the  dif- 
ference cannot  well  be  demonstrated.  It  is  difficult  to  conceive,  how- 
ever, that  the  same  conditions  should  occur  in  the  mouth.  But  the 
experiment  shows  that  it  is  not  impossible  that  erosion  may  be  the  action 
of  acids. 

In  1870,  while  studying  experimentally  the  condensation  of  gases  on 
the  metals  (surface  attraction)  and  the  corrosion  of  mi?tals  with  weak 
solutions  of  acids  in  the  still  condition  as  compared  with  the  effects 
when  the  solutions  were  ke])t  in  motion,  it  occurred  to  me  to  try  the 
effects  on  the  teeth.  From  the  results  of  my  experiments  on  metals  I 
supposed  that  the  parts  of  a  tooth  exposed  to  a  brisk  current  would  not 
be  softened  in  a  given  solution  so  rapidly  as  in  the  still  condition.  The 
apparatus  I  was  using  at  the  time  was  a  train  of  wheels  like  those  of  a 
common  clock,  only  heavier,  run  by  a  weight  and  made  to  revolve  a 
glass  paddle  in  a  glass  jar.  This  aj^paratus  when  in  motion  caused  the 
liquid  to  spin  around  in  the  vessel  continuously.     It  was  capable  of 


1004  ABBASION  AND  EROSION  OF  THE  TEETH. 

regulation,  so  that  it  would  give  a  current  of  any  number  of  feet  per 
minute  up  to  one  hundred  or  more.  The  jar  was  filled  with  a  solution 
of  hydrochloric  acid  of  the  strength  of  1  part  of  acid  to  400  parts  of 
water,  and  the  apparatus  was  arranged  to  run  at  about  forty  revolutions 
per  minute. 

Two  bicuspids  fresh  from  the  mouth  and  perfect,  with  fairly  long 

cusps  (removed  to  obtain  room  for  the  correction  of  iregularity),  were 

placed  with  their  proximal  surfaces  together,  to  repre- 

FiG.  535.  ggj^|.  .^  2iatural  position,  and  their  roots  were  enveloped 

in  gutta-percha,  to  represent  the  gum  and  alveolus, 

leaving  the  crowns  exposed.     These  were  fixed  in  the 

current  in  such  a  way  that  it  would  strike  against 

their  buccal  surfaces  not  quite  squarely,  but  at  an 

angle  that  would  cause  tlie  current  that  passed  between 

the  teeth  to  be  deflected  slightly  from  its  course.    The 

Artificial  Erosion,     effect  ou  thcsc  tcctli  was  quitc  remarkable  and  entire- 

Ihe  ZlfhV^i^lrl     h  at  variance  with  anything  that  I   had    expected. 

sented  at  a.     At  b     Metals  corrodc  much  less  in  a  current  than  in  the 

the    same    tooth     is  .,,  ,..  .  .  ,.  „         .  ■,  t     ,^ 

represented      after       stlU    COUdltlOn    lU    a    glVCD    SOlutlOU    ot    aCld,    aucl    the 

ed7o  a 'cun'ent  ^of  a     difference  is  quite  marked  on  any  surfaces  that  are 
chiori^°acW  for'five'     ^ell  sheltered  from  the  current,  and  I  naturally  ex- 
days,    strength  of     pectcd  that  something  similar  would  occur  in  case  of 
the  teeth.     The  result,  however,  was  the  removal  of 
the  cusps  and  the  formation  of  a  round  opening  between  the  two  teeth. 
The  effect  on  the  cusps  was  noted  on  the  second  day,  and  the  opening 
between  the  teeth  on  the  third.     On  the  fifth  day  the  condition  of  the 
teeth  was  such  as  shown  in  the  illustration  (Fig.  535),  in  which  a  shows 
the  condition  of  the  tooth  at  the  beginning  as  well  as  I  could  do  it  after 
witnessing  tiie  results,  and  6  represents  the  condition   on  the  fifth  day 
of  the  experiment.^ 

The  effect  of  the  acid  was  to  cut  away  the  teeth  at  the  points  where 
the  current  broke  around  the  sharper  angles,  especially  over  the  points 
of  the  cusps.  At  the  point  where  the  solution  ran  between  the  teeth, 
that  tooth  against  which  the  current  bore  while  being  deflected  from  its 
course  was  cut  in  the  form  of  a  deep  groove,  which  corresponded  in 
width  with  the  space  between  the  contact  of  the  two  teeth  and  the  gutta- 
percha that  represented  the  gum.  The  other  tooth  was  grooved  also, 
but  not  so  deeply.  At  these  points  the  eroded  surface  was  left  fairly 
hard  and  smooth,  as  in  erosion  as  it  occurs  naturally  in  the  mouth. 
The  groove  betNveen  the  teeth  reminded  me  strongly  of  a  case  T  had 
seen  some  time  before,  in  which  round  openings  were  cut  between 
several  teeth,  while  the  effect  on  the  grinding  surface  was  more  like 
abrasion. 

These  experiments  were  repeated  a  number  of  times  with  results  that 
were  somewhat  variable.  Three  months'  trial  with  a  solution  of  1  of 
acid  to  1 500  of  water  gave  no  appreciable  result.  Very  strong  solu- 
tions produced  general  softening. 

These  experiments  show  that  an  acid  may  possess  an  action  under  a 

'  These  figures  are  made  from  the  drawinsrs  that  aecompany  my  notes  of  the  experi- 
ments made  at  the  time.     I  have  represented  only  the  tooth  inost  eroded. 


ETIOLOGY.  1005 

change  of  circumstances  very  different  from  that  seen  when  the  action 
takes  place  in  the  ordinary  still  condition,  and  leads  us  to  suspect  that 
there  may  be  circumstances  modifying  its  erosive  power  which  are  not 
yet  known  or  recognized.  When  we  come  to  analyze  the  results  of 
these  experiments,  this  is  all  that  can  be  said  of  it,  so  far  as  the  expla- 
nation of  erosion  is  concerned  ;  for  if  an  acid  were  present  in  the  mouth 
in  the  strength  of  solution  that  is  required  to  produce  this  peculiar  effect 
out  of  the  mouth,  tlie  teeth  would  be  quickly  destroyed.  Were  this  not 
the  case,  it  is  difficult  to  conceive  of  a  current  being  maintained  in  the 
mouth  sufficient  to  effect  the  erosions  met  with  in  practice.  Indeed, 
some  of  the  forms  of  erosion  are  such  that  a  current  could  not  possibly 
be  the  cause — such  forms,  for  instance,  as  are  given  in  Fig.  534,  where 
there  is  a  perpendicular  incut  in  a  half  circle,  or  in  Fig.  535,  where  the 
teeth  were  eroded  in  the  form  of  cups,  or  in  many  other  cases  that  might 
be  given. 

The  possibility  that  erosion  might  be  effected  by  something  like  the 
absorptive  processes  occurred  to  me  some  years  ago.  Certainly  a  num- 
ber of  cases  that  have  come  under  my  observation  have  shown  a  peculiar 
congested  condition  of  the  lip  that  came  against  the  portion  of  the  labial 
surface  being  eroded,  and  it  seemed  probable  that  an  acid  secretion 
abnormal  in  character  was  being  produced  at  this  immediate  point, 
Avhich,  together  with  the  motions  occasioned  by  the  lip,  might  effect 
the  solution  of  the  substance  of  the  tooth.  In  a  few  instances  I  have 
seen  clearly  the  impression  of  the  eroded  surface  in  the  lip,  showing 
that  it  fitted  into  it  very  exactly.  At  the  same  time,  litmus-paper 
applied  to  the  lip  showed  that  the  secretions  at  that  point  were  decidedly 
acid.  This  seems  very  near  a  demonstration  of  the  cause,  but  I  have  met 
with  cases  in  which  no  such  agency  could  be  proven — cases  in  which 
there  is  no  tissue  in  habitual  contact  with  the  surface. 

Dr.  E.  D.  Swain  of  Chicago,  who  has  taken  much  interest  in  this 
subject,  has  made  a  close  study  of  the  theory  of  electrolysis,  especially 
of  the  ideas  advanced  by  Mr.  Bridgeman,  whose  experiments  he  has 
repeated  and  varied,  using  a  large  number  of  acids,  different  strengths 
of  solution,  etc.,  becoming  finally  convinced,  however,  that  the  explana- 
tion is  not  to  be  found  in  this  direction.^ 

While  pursuing  these  experiments  Dr.  S.  has  made  some  important 
discoveries  in  the  diffusibility  of  acids,  a  table  of  which  I  have  the  priv- 
ilege of  giving.  This  table  represents  the  percentage  of  each  of  the  acids 
named  (dissolved  in  distilled  water)  that  can  clearly  be  detected  as  giv- 
ing an  acid  reaction  with  litmus-paper  : 

Oxalic  acid 1-260  of  1 

Citric  acid 1-160  of  1 

Phosphoric  acid 1-130  of  1 

Acetic  acid 1-65  of  1 

Butyric  acid 1-30  of  1 

Tannic  acid 1-30  of  1 

Tartaric  acid 1-260  of  1 

Sulphuric  acid .  1-130  of  1 

Nitric  acid 1-130  of  1 

Hydrochloric  acid 1-140  of  1 

1  T  am  indebted  to  Dr.  Swain  for  the  privilege  of  the  perusal  of  several  unpublished 
manuscripts  on  this  subject. 


1006  ABRASION  AND  EROSION  OF  THE  TEETH. 

Dr.  Swain's  results  agree  with  my  own  conviction  as  to  the  possible 
influence  of  electrolysis  in  the  causation  of  this  affection.  Even  if  it 
were  shown  that  the  teeth  could  be  eroded  successfully  by  this  method, 
the  matter  of  the  peculiar  localization  would  present  to  its  adoption  as 
a  theory  (as  it  does  to  every  other  yet  advanced)  an  obstacle  that  seems 
insurmountable. 

The  theory  that  it  is  caused  by  acid  mucus  is  supported  by  several 
who  have  written  on  the  subject,  and  our  present  knowledge  affords  no 
alternative  but  the  acceptance  of  the  general  idea  that  it  is  the  action  of 
an  acid  under  some  peculiar  modifying  influences  as  yet  unknown  to  us. 
While  this  is  unsatisfactory  in  the  extreme,  there  seems  to  be  nothing 
better  to  offer.  The  influence  of  micro-organisms  appears  to  be  out  of 
the  question.  These  enemies  are  accustomed  to  seek  foul  places,  and 
eroded  surfaces  are  habitually  clean  surfaces.  If  by  a  change  of  con- 
ditions the  surface  eroded  becomes  habitually  foul,  caries  takes  the  place 
of  erosion.     This  occurrence  is  very  rare,  but  is  not  unknown. 


Sensitiveness  of  the  Dentine. 

The  extreme  sensitiveness  of  the  eroded  surfaces,  not  unfrequently 
occurring,  has  been  alluded  to.  In  a  number  of  cases  I  have  seen  this 
so  extreme  that  only  the  destruction  of  the  pulp  of  the  tooth  afforded 
relief.  Indeed,  experience  has  taught  me  •  that  this  result  is  sooner  or 
later  likely  to  follow  spontaneously,  notwithstanding  the  large  amount 
of  secondary  dentine  usually  found  over  the  pulp  in  this  disease.  I 
have  seen  the  death  of  the  pulp  occur  when  there  was  seemingly  an 
abundance  of  dentine  between  it  and  the  eroded  surface  for  its  protec- 
tion. On  the  other  hand,  while  I  have  seen  the  pulp-chamber  cut 
through  eitlier  after  being  closed  with  a  secondary  deposit  or  after  the 
death  of  the  pulp,  I  have  never  seen  a  case  in  which  the  living  pulp 
became  exposed.'  There  seems  to  be  something  in  the  cause  of  this 
affection  peculiarly  irritating  to  the  dentinal  fibrils,  and  the  results  of 
that  irritation  are  shown  by  pathological  changes  in  the  pulp  of  the 
tooth.  This  naturally  leads  to  an  examination  of  the  anatomical  and 
physiological  conditions  that  produce  these  peculiar  results. 

The  dentine  has  no  demonstrable  nerves,  and  with  our  present  facil- 
ities for  microscopic  examination  it  is  reasonable  to  suppose  that  if  they 
were  present  we  -would  bo  able  to  demonstrate  them.  It  seems  to  have 
been  the  thought  of  pathologists  that  in  the  production  of  the  sensation 
which  we  call  'pain  some  nerve  or  nerve-ending  has  received  the  initial 
lesion  which  has  produced  this  effect.  It  has  long  been  recognized  that 
in  the  strict  adherence  to  this  doctrine  we  would  be  unable  to  account 
for  even  the  normal  sensitiveness  of  dentine,  much  less  the  occurrence 
of  hypersesthesia.  Yet  the  hyperaesthesia  does  occur,  and  in  the  most 
excruciating  forms,  and  especially  in  the  disease  we  are  considering.  It 
seems,  therefore,  fitting  that  we  should  study  this  condition  in  connec- 
tion with  this  disease,  especially  as  there  is  here  absolutely  no  discover- 

'  Dr.  E.  D.  Swain  of  Chicago  gives  a  case  in  which  the  pulp  was  fully  exposed  from 
erosion. 


SENSrTIVE^'ESS  OF  THE  DENTINE. 


1007 


able  pathological  change  in  the  dentine  itself  which  presents  this  hvper- 
aesthesia,  except  a  waste  of  its  surface. 

Fig.  536  is  a  sectional  view  of  a  central  incisor  with  an  erosion  at  a 


At  6  the  layer  of  odontoblasts  are 


Fig.  536. 


which  exposes  the  dentinal  fibrils 
shown — these  line  the  pulp-cham- 
ber— and  at  c  a  nerve-branch  the 
finer  filaments  of  which  are  found 
ramifying  in  close  conjunction  with 
the  odontoblasts.  The  processes 
from  these  odontoblasts  form  the 
dentinal  fibrils  which  pass  by  way 
of  the  dentinal  tubules  to  the  per- 
iphery of  the  dentine.  The  odon- 
toblast and  its  process,  the  denti- 
nal fibril,  constitute  one  cell ;  the 
protoplasm  is  united  in  one  life ; 
and  whatever  markedly  affects 
the  protoplasm  of  the  fibril  affects 
the  protoplasm  of  the  w^hole  cell. 
For  this  reason  any  pathological 
changes  that  may  be  set  in  mo- 
tion in  consequence  of  irritation 
of  the  dentinal  fibrils  are  found 
in  the  odontoblasts  and  the  tissues 
in  intimate  association  with  them 
— in  that  portion  of  the  pulp 
marked  e  in  the  figure.  Along 
the  course  of  the  fibril  itself  no 

pathological  changes  whatever  can  be  discovered,  seemingly  for  the 
reason  that  the  hard  substance  of  the  dentine — the  basis-substance  and 
the  lime  salts — is  incapable  of  manifesting  vital  phenomena,  is  not  liv- 
ing protoplasm.  This  portion  of  the  dentine  is  essentially  fixed  mate- 
rial. It  may  be  acted  upon,  but  does  not  in  itself  act.  It  is  passive. 
The  changes  which  occur  in  the  tissues  of  the  pulp  in  consequence 
of  distal  irritation  of  the  dentinal  fibrils  are  sufficiently  discussed  in  the 
paper  on  Pathology  of  the  Dental  Pulp,  and  will  not  be  repeated  here 
except  for  the  purpose  of  illustration.  The  effect  of  slight  but  continu- 
ous irritation  of  the  ends  of  the  fibrils  is  seen  in  the  production  of  sec- 
ondary deposits  of  dentine,  which  in  those  cases  in  which  the  area  of 
irritation  is  small  are  not  unfrequently  confined  to  the  area  represented 
by  the  pulpal  ends  of  the  fibrils  irritated.  If  the  area  of  irritation  is 
large,  as  in  most  cases  of  mechanical  abrasion,  the  area  of  secondary 
deposits  includes  the  whole  internal  surface'of  the  pulp-chamber.  If  the 
intensity  of  the  irritation  of  the  fibrils  be  more  considerable,  the  result 
will  be  irritation  of  the  pulp,  instead  of  secondary  deposits,  or  possibly 
both,  the  secondary  dentine  proper  giving  place  to  irregular  deposits. 
In  case  the  irritation  becomes  excessive,  well-marked  hyperemia  of  the 
pulp  will  occur,  which  occasionally  results  in  the  destruction  of  that 
organ  before  it  is  exposed  to  external  influences  other  than  through 
the  medium  of  the  fibrils. 


Section  of  the  Crown  of  an  Incisor:  n,  an  erosion 
exposing  the  dentine;  b,  the  layer  of  odonto- 
blasts liiiing  the  pulp-chamber;  c,  a  nerve- 
branch  the  delicate  filaments  of  which  are  dis- 
trilnited  about  the  layer  of  odontoblasts;  d,  (I, 
gingival  margin  ;  E,  point  at  which  pathological 
changes  first  occur  as  the  result  of  irritatiou  of 
the  dentinal  fibrils  at  a. 


1008  ABRASION  AND  EROSION  OF  THE  TEETH. 

Here  we  find  that  the  pathological  changes  pass  from  the  external  to 
the  internal  structures  by  M'ay  of  the  protoplasmic  lines,  the  dentinal 
fibrils.     Having  injured  the  process  of  a  cell,  the  cell  itself  is  injured. 

Protoplasm  is  sensitive ;  this  is  exhibited  in  the  amoeba,  the  leuco- 
cyte, and  the  young  connective-tissue  cells  generally.  All  of  these 
respond  to  stimulants,  both  mechanical  and  chemical,  and  exhibit  their 
sensitive  properties  by  certain  motions,  by  ceasing  from  the  perform- 
ance of  motions,  and  by  various  forms  of  contraction.  They  exhibit 
sensitiveness  to  thermal  changes.  Cold  tends  to  slow  their  motions, 
and  if  its  degree  is  increased  will  stop  them  entirely.  Heat  renders 
their  motions  more  active  for  a  time ;  but  if  the  increase  of  the  temper- 
ature is  continued,  it  causes  them  to  take  on  a  state  of  tetanic  con- 
traction and  assume  the  spherical  form.  If  the  heat  is  discontinued, 
the  movements  will  be  resumed.  Among  the  chemical  irritants  many 
affect  them  in  a  marked  degree.  Common  salt  in  very  small  quantity 
(a  drop  of  a  1-per-cent.  solution  added  very  slowly)  first  quickens 
their  motions,  and  then  causes  sudden  tetanic  contractions,  and  in 
amoeba  the  expulsion  of  any  food  they  may  contain  at  the  moment 
(Brunton).  The  acids  and  alkalies  affect  them  prominently.  Hydro- 
chloric acid  causes  the  amoeba  to  contract  and  form  a  ball  with  a  sharp 
double  contour.  In  it  occur  twitching  motions  which  expel  any  food  it 
may  contain  in  its  substance. 

These  are  a  few  of  the  many  well-known  examples  of  the  effects  of 
reagents  upon  protoplasm  by  wdiich  its  sensitiveness  is  shown.  The 
leucocyte  exhibits  the  same  phenomena,  with  some  variations,  as  do  also 
the  young  connective-tissue  cells.  Leucocytes  from  different  animals 
show  some  differences  in  their  response  to  different  stimulants. 

These  cells  contain  no  nerves,  and  we  cannot  say  that  they  exhibit 
pain  ;  but  when  protoplasmic  bodies — cells — come  to  be  built  into  tis- 
sue and  enter  into  physiological  relations  with  nerves,  may  not  this  sen- 
sitiveness— which  in  the  simple  cell,  when  standing  alone,  is  exhibited 
in  motion,  or  tetanic  contraction — be  communicated  to  the  sensoriura 
and  translated  into  the  sensation  which  we  know  as  pain?  There 
seems  to  be  no  reasonable  objection  to  this  view.  Mobile  there  are  some 
difficulties  that  are  more  readily  explained  by  this  than  by  the  hypothe- 
sis that  in  the  production  of  pain  the  initial  lesion  must  be  of  soma 
nerve  or  nerve-ending. 

Fig.  537  represents  diagramatically  a  group  of  odontoblasts  w'ith 
their  processes,  the  dentinal  fibrils,  with  a  nerve-branch  in  close  con- 
junction with  the  odontoblasts.  In  case  of  the  irritation  of  the  distal 
ends  of  the  processes  of  these  cells  pain  is  produced,  yet  no  nerve  or 
nerve-ending  is  touched,  there  being  no  nerves  in  the  dentine.  Every- 
where in  the  periphery  of  the  pulp  fine  nerve-filaments  may  be  demon- 
strated in  close  conjunction  with  the  odontoblasts,  and  it  seems  evident 
that  they  communicate  to  the  sensorium  the  impression  made  on  the 
protoplasm  of  these  cells  through  the  injury  to  the  fibrils.  In  this  as 
in  most  other  cases  sensation  follows  the  lines  of  pathological  changes. 
According  to  present  theories,  hypersemia  is  induced  through  the  agency 
of  the  nervous  system  by  a  reflex  action,  and  must  be  induced  by  the 
same  manner  of  reflex  action  as  pain  itself. 


SENSITIVENESS  OF  THE  DENTINE. 


1009 


Pathologists  have  generally  regarded  the  nerve-endings  as  receiving 
the  initial  impression  or  injury  in  the  production  of  pain  on  touch.  It 
is  a  subject,  however,  that  has  always  been  veiy  obscure — in  fact,  unde- 
nionstrable.  Nerve-tissue  is  certainly  itself  sensitive,  for  pain  may  be 
produced  by  the  injury  of  sensory  nerves  ;  but  pain  so  induced  is  referred 
to  the  tissue  to  which  the  nerve  is  distributed,  not  to  the  nerve  itself. 
Indeed,  so  far  as  consciousness  goes,  we  would  never  know  that  we  had 
nerves.  In  most  positions  in  the  body  nerve-endings  and  the  cellular 
elements  are  in  such  close  relation  that  it  is  impossible  to  injure  one 


\~d 


Group  of  Odontoblasts  with  their  Processes  (dentinal  fibrils):  a,  odontoblasts;  b,  fibrils;  c,  nerve- 
supply.     Irritation  at  the  point  d  produces  pain. 

without  injuring  the  other.  The  experimental  isolation  of  a  tissue- 
injury  from  injury  to  the  nerves  (these  being  intact)  for  the  purpose  of 
determining  which  receives  the  initial  lesion  causing  pain  does  not  seem 
to  have  been  thought  of  or  to  have  been  possible  to  other  positions  than 
the  one  under  discussion,  and  the  general  fact  that  without  nerves  there 
is  no  pain  seems  to  have  led  physiologists  to  adopt  the  supposition  that 
the  nerves  or  their  endings  received  the  initial  lesion  giving  the  sensa- 
tion of  pain. 

A  close  study  of  the  literature  of  the  subject  of  sensory  nerve-endings 
and  their  relation  to  the  various  sensations  will  serve  to  demonstrate  the 
obscurity  of  the  subject  and  show  how  inaccurate  is  our  knowledge  of  it. 
In  practice  the  cases  in  which  pain  is  developed — that  is,  demonstrably 
due  to  the  direct  wounding  of  nerves  or  nerve-endings — are  very  few 
indeed.  In  this  statement  I  have  not  reference  to  pain  or  perturbations 
of  functions  that  may  result  from  disease  of  the  nerve-centres ;  in  this 
case  we  would  deal  with  the  nerve-cells  (ganglion-cells)  individually, 
and  their  processes.  These  are  protoplasmic  bodies  in  which  specialized 
function  is  developed  to  such  a  w^onderful  degree  that  their  injury  pro- 
duces exceedingly  complex  results. 

The  striped  or  voluntary  muscles  furnish  an  example  of  the  propaga- 
tion of  impulse  along  proto])lasmic  bodies  which  is  like  that  I  have  sug- 
gested in  case  of  dentinal  fibrils,  except  that  it  is  an  eiferent  instead  of 
an  afferent  impulse.  There  is  but  one  motor  nerve-ending  in  conjunc- 
tion with  a  single  muscular  fibre,  no  matter  what  its  length  (Krause, 
Koelliker) ;  this  is  sufficient  to  communicate  the  impulse  to  contraction 
to  the  whole  fibre,  though  it  may  be  much  longer  than  the  dentinal 
fibril.     Here  it  will  be  seen  that  the  passage  of  an  impulse  along  a 

Vol.  T.— 64 


lUlO  ABEASION  AND  EROSION  OF  THE  TEETH. 

protoplasmic  bocly//'o»i  a  nerve-ending  seems  demonstrated.  In  the 
explanation  offered  of  the  sensitiveness  of  dentine  the  impulse  passes 
along  a  protoplasmic  body  to  a  nerve-ending.  The  conduction  in  the 
two  instances  is  the  same,  but  the  impulse  travels  in  the  opposite 
direction. 

By  this  consideration  of  the  facts  at  hand  it  seems  clear  that  this  is 
the  mode  of  transmission  of  sensation  from  the  dentine.  The  dentine 
has  no  nerves,  and,  with  the  peculiar  arrangement  of  the  odontoblasts 
and  their  processes,  nerves  are  not  needed.  The  dentinal  fibrils  being 
processes  of  the  odontoblasts,  and  these  cells  being  in  physiological  rela- 
tion to  the  sensory  nerve-endings,  the  conditions  for  the  translation  of 
injury  to  protoplasm  into  the  sensation  of  pain  are  complete. 

These  considerations  also  render  sufficiently  clear  the  reasons  for 
hypernesthesia  of  dentine  and  injury  to  the  dental  pulp  by  irritation  of 
the  dentinal  fibrils. 


\. 


-.y 


INDEX  TO  VOLUME   I. 


A. 

Abdominal  plates  of  embryo,  543 

Abducent  nerve,  282 
Abrasion  and  erosion  of  teeth,  993 
of  teeth,  prevention  of,  996 
secondary  dentine  resulting  from,  867 
Abscess,  701 
alveolar,  929 
blind,  936 

of  dental  pulp,  855-857 
septic,  treatment  of,  950 
Absorption  of  bone,  47 
of  ligatures,  922 
of  roots  in  phagedenic   pericementitis, 

973 
of  roots  of  teeth,  921 
Absorptive  processes  in  caries,  777 
Accessory  palatine  canals,  91 

parotid  gland,  208 
Acliatina,  teeth  of,  349 
Acid  causing  caries,  analysis  of,  798,  799 
mucus  in  caries,  776 

produced  by  fungi  of  human  mouth,  824- 
826 
Action  of  muscles  of  mastication,  182 
Acute  apical  pericementitis,  diagnosis  of, 
924 
symptoms  of,  924 
^luropus,  teeth  of,  464 
African  elephant,  teeth  of,  489 

tusks  of,  489 
Ailurodon,  teeth  of,  453 
Air-cells,  openings  of,  137 
Alligator,  dentition  of,  385 
Alveolar  abscess,  929 
chronic,  935 

constitutional  treatment  in,  946 
diagnosis  of,  943 
discharge  of,  at  gingival  margin,  934 

on  face,  933 
discharging  into  antrum,  941 
into  nose,  940 
on  neck,  943 
evacuation  of  pus  in,  945 
opening  pulp-chamber  in,  948 
pointing  in  hard  palate,  934 
treatment  of,  944 
margin,  thickening  of,  971 
or  superior  maxillary  artery,  234 
process,  necrosis  of,  951 
of  inferior  maxilla,  103 


Alveolar  process  of  superior  maxilla,  86 
maxillary  bone,  86 
removal  of,  980 

septum,  destruction  of,  972 

wall,  destruction  of,  971 
development  of,  107,  632 
eversion  of,  971 
Alveoli  of  inferior  maxilhv,  103 

of  superior  maxillary  bone,  87 
Alveolitis,  infectious,  968 
Alveolo-dental  nerve,  290 
anterior  superior,  291 
branches  of,  291 
Amalgam  in  caries,  811 
Amblypoda,  teeth  of,  492 
Amelification,  595 
Ameloblasts,  641 

contact  of  capillaries  with,  633 
Amphicyon,  teetii  of,  452 
Amoeboid  cells,  692 
Amputation  of  dental  pulp,  905 

of  roots  of  teeth,  990 
Amynodon,  teeth  of,  479 
Ansemia,  687 

Analysis  of  acid  causing  caries,  798,  799 
Anatomy,  Dental,  351 

Regional,  35 
Anchitherium,  teeth  of,  481 
Angular  artery,  226 

vein,  249 
Annelids,  teeth  of,  338 
Anomodontia,  teeth  of,  384 
Anterior  auricular  arteries,  229 
vein,  253 

cerebral  artery,  242 

condyloid  foramina,  53,  124,  128 

communicating  artery,  242 

dental  foramen,  101,  133 

ethmoid  artery,  240 

ethmoidal  foramina,  75,  134 

fossa  of  brain-case,  120 

jugular  vein,  255 

lacerated  foramen,  66,  122 

median  fontanelle,  119 

nasal  openings,  132 

occipital  or  transverse  sinus,  261 

palatine  canal,  86 
meatus,  86 

superior  dental  nerve,  291 

temporal  artery,  230 
Anthracotheridfie,  genera  of,  485 

molars  of,  486 

1011 


1012 


INDEX   TO    VOLUME  I. 


Anthroidial  articulation  of  Gray,  112 
Aiitliropoid  apes,  teeth  of,  436 
Antiseptic  filling  materials,  influence  of,  on 
fungi  of  dental  caries,  806 
power  of  filling  materials,  810 
wash  in  calcic  inflammation,  967 
Antiseptics  in  alveolar  abscess,  948 
in  phagedenic  pericementitis,  984 
power  of,  808 

uses  of,  on  gangrenous  pulps,  907 
Antrum  of  Highmore,  89 
Aortic  obstruction,  pulse  in,  671 

i-egurgitation,  671 
Ai^ical  foramen,  355 
pericementitis,  923 
cause  of,  925 
chronic,  925 

constitutional  treatment  of,  928 
treatment  of,  926 
space,  918 

painless  penetration  of,  928 
Aponeurosis,  occipito-frontalis,  167 

supra-hyoid,  188 
Aponeurotic  fascia,  155 
Apophyses  of  bones,  35 
Appendages  of  skin,  147 
Appendix  to  paper  on  dental  caries  (Mil- 
ler), 791 
Aqueduct  of  Fallopius,  59,  305 
Aqueductus  cochlea,  60 

vestibuli,  59 
Archajlurus,  teeth  of,  459 
Arctoidea,  teeth  of,  463 
Areolar  tissue,  154 
Arion,  jaw  of,  349 
Aristotle,  lantern  of,  339 
Arrow-tooth  (Toxoglossate)  dentition,  346 
Arsenious  acid,  action  of,  on  dental  pulp, 
901 
and  morphia  pastes,  900 
method  of  application  to  dental  pulp, 

902 
use  of,  on  dental  pulp,  899 
Arteries,  215 

alveolar  or  superior  maxillary,  234 
angular,  226 
anterior  cerebral,  242 
communicatinji",  242 
ethmoid,  240 
temporal,  230 
ascending  cervical,  246 
pJKiryngeal,  228 

meningeal  branches  of,  229 
auricular,  228 
basilar,  243,  246 
buccal,  234 
central  retinal,  239 
cerebral,  241 
ciliary,  239 
circle  of  Willis,  242 
crico-lhyroid,  220 
deep  ain-icular,  232 

teni])(U'al,  233 
descending  cervical,  227 

p:ilatine,  234 
dorsalis  lingual,  221 


Arteries,  external  nasal,  241 

facial  or  external  maxillary,  222 

frontal,  241 

glandular,  224 

incisive,  233 

inferio?*  coronary,  225 

dental,  233 

labial,  225 

laryngeal,  247 

palatine,  224 

thyroid,  246 
infraorbital,  234 
internal  carotid,  235 

maxillarv,  or  deep  facial,  230 
lachrymal,"'238 
lateral  communicating,  243 

nasal,  225 
left  common  carotid,  216 
lingual,  221 
masseteric,  234 
mental,  233 
middle  cerebral,  242 

or  great  meningeal,  232 

temporal,  229 
muscular,  of  the  orbit,  240 
mylo-hyoid,  233 
nasal  or  spheno-palatine,  235 
occipital,  226 
ophthalmic,  238 
palpebral,  241 
posterior  auricular,  227 

cerebral,  242 

communicating,  243 

ethmoid,  240 

temporal,  230 
pterygoid,  234 
pterygo-jDalatine,  235 
ramus  cervicularis  princeps,  227 
ranine,  222 

right  common  carotid,  216 
small  meningeal,  233 
stylo-mastoid,  228 
subclavian,  243 
sublingual,  222 
submental,  225 
superficial  temporal,  229 
superior  coronary,  225 

laryngeal,  220 
suprascapular,  247 
thyroid  axis,  246 
tonsillar,  224 
tracheal,  247 
transversalis  colli,  247 
transverse  facial,  229 
tymjianic,  232 
vertebral,  245 
Vidian,  235 
Articular  veins,  253 
Articidating  arteries,  229 
Articulation,  diarthroses,  112 

temporo-maxillary,  112 
Articuhuions,  111 

of  l)ase  ol'  ))rain-case,  117 

of  occi])ut,  117 

of  .skull  at  difierent  periods,  118 

syncliondroses,  112 


INDEX  TO    VOLUME  I. 


1013 


Artiodactyla,  divisions  of,  484 
Atrophy  of  odontoblasts,  884 
Attolens  aurem  muscle,  175 
Attrahens  aurem  muscle,  175 
Ascending  cervical  artery,  246 

nasal  nerve,  291 

or  orbital  nerve,  301 

pharyngeal  artery,  228 

meningeal  branches  of,  229 
Auditory  nerve,  310 
Auricular  artery,  228 
Auriculo-teniporal  nerve,  294 
Axis-cylinder,  266 
Aye-aye,  teeth  of,  432 
Azygos  uvula  muscle,  198 

B. 

Balistes  vetulus,  teeth  of,  377 
Baleen  plates  of  cetacea,  413 
Band  of  embryo,  618 
Bartholin,  duct  of,  211 

gland  of,  210 
Base  of  brain-case,  124 
Basement-membrane,  145 
Basilar  artery,  243,  246 
branches  of,  246 
process  of  occipital  bone,  51,  54. 
Batrachia,  teeth  of,  379 
Bats,  classification  of,  465 
dentition  of,  465 
probable  derivation  of,  465 
Bears,  evolution  of,  464 

teeth  of,  463 
Beginnings  of  caries,  779 
Bel  a,  teeth  of,  346 
Bell  on  caries,  732 

Bichloride  of  mercury  in  phagedenic  peri- 
cementitis, 986 
Bicuspids,  human,  442 
Biological  studies,  cultures  for,  822 
methods  in,  821 
on  fungi  of  human  mouth,  819 
Black  on  formation  of  poisons  by  micro- 
organisms, 757 
Blarina,  teeth  of,  426 
Blastoderm,  142,  543 

development  of,  554 
Blind  abscess,  936 
Blood,  absorption  of,  686 
-clot,  granulations  in,  710 
how  formed,  680 
organization  of,  709 
-corpuscles,  531 

development  of,  566 
physiology  of,  533 
-pressure,  increase  of  677 
-supply  of  peridental  membrane,  919 
variations  in,  and  in  its  distribution,  671 
-vessels,  development  of,  566,  706 
of  dental  pulp,  831 
of  muscles,  164 
of  skin,  145 
system  of,  215 
thrombi  in,  681 
Bloodletting,  local,  927 


Bodies,  stellate,  624 

Body  of  inferior  maxillary  bone,  101 

Bone-cells,  41,  575 

canaliculi  of,  41 

formation,  subperiosteal,  47,  585 
Bones,  35 

apophyses  of,  35 

arrangement  of,  48 

articulations  of,  118 

cancellated,  36 

chemical  analysis  of,  37 

cranial,  50 

dentigerous,  of  dog,  403 

development  of,  45 

diaphyses  of,  35 

epiphyses  of,  35 

ethmoid,  76 

facial,  131 

frontal,  72 

Haversian  canals  of,  39 

hyoid,  108 

inferior  maxillary,  100 
turbinated,  94 

inflammation  of,  43 

intracartilaginous,  45 

lachrymal,  95 

lacunae  of,  41 

lamellae  of,  39 

malar.  97 

maxillary,  inferior,  100 
superior,  81 

minute  structure  of,  38 

nasal,  96 

occipital,  52 

palate,  90 

parietal,  69 

perforating  fibres  of,  40 

periosteum  of,  42 

softening  of,  37 

sphenoid,  62 

spongy,  36 

subperiosteal,  47 

temporal,  55 

turbinated,  inferior,  79 
superior,  79 

vomer,  80 

weight  of,  37 

Wormian,  118 
Bourrelet,  617 
Brachio-cephalic  veins,  248 
Bradypus  tridactylus,  teeth  of,  411 
Brain-case,  anterior  fossa  of,  120 

articulations  of  base  of,  117 

floor  of,  120 

middle  fossa  of,  122 

posterior  fossa  of,  123 

walls  of,  120 
Briditeman  on  caries,  744 
Broken  striae  of  Eetzius,  656 
Buccal  and  labial  surfaces,  caries  in,  781 

artery,  234 

cavitv,  development  of,  550 

glands,  206 

nerve,  293,  309 
Buccinator  muscle,  173 
Bulbous  cord,  invagination  of,  624 


1014 


INDEX  TO   VOLUME  I. 


Bunodontia,  teeth  of,  484 
Bunotheria,  classification  of,  416 

c. 

Calcic  inflammation  of  the  peridental  mem- 
brane and  gums,  957 
prognosis  in,  968 
treatment  of,  963 
Calcification,  570 

and  decalcification  of  teeth,  chart  of,  647 

cylindrical,  878 

of  bone,  46 

of  dental  pulp,  914 

of  dentine,  644 

of  permanent  teeth,  Pierce  on,  645 

of  pulp,  symptoms  of,  914 
treatment  of,  915 

of  teeth,  363 

of  tissues  of  dental  pulp,  874 

Tomes  on.  573 
Calcoglobulin,  575 

deposits  of,  in  inflamed  pulp,  860 
Calcospherules,  575 
Calculus,  removal  of,  963 
Camphor  phenol,  985 
Canal,  anterior  palatine,  86 

Haversian,  39,  576 

inferior  dental,  104 

infraorbital,  82,  134 

lachrymal,  134,  136,  212 

naso-palatine,  81 

posterior  palatine,  84,  91 

Vidian,  65 
Canaliculi  of  bone,  41,  576 
Canals,  accessory  palatine,  130 

dentinal,  594 
Cancellated  portion  of  bone,  36 
Canine  eminence,  84 

fossa,  84,  133 
Canines,  definition  of,  399 

human,  441 
Cape  anteater,  teeth  of,  412 
Capillaries,  lymph,  326 
Capping  materials,  894 

of  exposed  dental  pulp,  886,  894 
Capsular  ligament,  1 14 
Capsule  of  Tenon,  178 
Capybara,  teeth  of,  469 
Carbolic  acid  in  capping,  897 

in  superficial  pulpitis,  905 
Carbonate  of  sodium  as  an  antiseptic,  909 
Cariacus,  teeth  of,  488 
Caries,  absorptive  processes  in,  777 

acid  nuicus  in,  776 

action  of  tobacco  on,  808 

agency  of  micro-organisms  in,  750 

beginnings  of,  779 

characteristics  of,  786 

clinical  history  of,  779 

commencement  of,  in  enamel,  765 

dental,  729 

producing  secondary  formations,  913 

discoloration  in,  769 

diseases  causative  of,  778 

etiology  of,  731 


Caries,  experiments  on,  797 

fungi  causing,  801,  802 

fungi  of,  814,  815 

growths  in,  767 

hereditary  influences  causing,  772 

infectious  nature  of,  789 

inflammatory,  theory  of,  734 

in  necks  of  teeth,  786 

in  pits  and  grooves  of  the  enamel,  779 

in  proximal  surfaces,  779 

lactic  acid  in,  798 

penetration  of  dentine  in,  765 
of  enamel  in,  768 

phenomena  of,  764 

predisposing  causes  of,  770 

pulp-exposure  in,  767 
Carious  dentine,  lactic  acid  in,  800 

surfaces,  classes  of,  779  • 

Carnivora,  classification  of,  448 

teeth  of,  448 
Carotid  arteiy,  external,  218 
internal,  235 

canal,  59,  122,  127 

sheath,  157,  216 

superior  triangle,  188 
Cartilage,  138 

-cells,  140 

connective  tissue,  35 

elasticity  of,  138 

fibre,  140 

fibro-elastic,  140 

hyaline,  139 

interarticulating  disc  of,  114 

lacuna,  140 

Meckel's,  105 

nasal,  77 
Cartilago  dentalis,  617 
Caruncula  lachrymalis,  212 
Cats,  dental  evolution  of,  460 
Cause  of  apical  pericementitis,  925 

of  fever,  715 

of  shock,  719 
Cavernous  sinus,  259 
Cavity  of  the  mouth,  137 
Cebida>,  teeth  of  435 

Cell-movements  in  inflammation  of  dental 
pulp,  850 

-proliferation,  Ziegler  on,  526 
Cells,  amoeboid,  692 

bone-,  41 

cartilage-,  140 

embryonal,  of  mucous  membrane,  201 

epithelial,  535 

granulation-,  704 

medullary  or  true  marrow,  44 

morpliological  appearance  of,  531 

multipolar  giant-,  44 

nucleated  red  blood-,  44 

physiological  consideration  of,  524 

stellate,  624 

structure  of,  523 

wandering,  214,  692 
Cementification,  590 
Cementoblasts,  569,  591 
Cement  organ,  364 

development  of,  364 


INDEX  TO    VOLUME  I. 


1015 


Cementum,  858 

canaliculi  of,  358 

lacunae  of,  358 
Central  retinal  artery,  239 
Centrifugal  nerves,  274 
Centripetal  nerves,  275 
Ceratodus,  dentition  of,  375 
Cerebral  arteries,  241 

fossa,  124 

nasal  slit,  80 
Ceruminous  glands,  152 
Cervical  fascia,  156 

ganglion,  313 

nerve,  309 
Cervico-facial  nerve,  309 
Cervicularis  princeps  artery,  227 
Cetacea,  baleen  of,  353 

teeth  of,  413 
Change  in  the  maxillary  bones  after  birth, 

107 
Characteristics  of  caries,  786 
Chart  of  calcification  and   decalcification 

of  teeth,  647 
Charts,  782-785 
Cheiroptera,  teeth  of,  465 
Chemical  analysis  of  bone,  37 
Chill  in  fever,  713 
Chimsera  plumbea,  dentition  of,  375 
Chiromvs,  teeth  of,  432 
Ciiitin,  337,  342 
Chloride  of  zinc  in  calcic  inflammation, 

966 
Chlorosis,  689 

Choloepus  didactylus,  teeth  of,  411 
Chorda  tynipani  nerve,  307 
Chronic  alveolar  abscess,  935 
discharging  on  face,  940 
pus  burrowing  in,  937 

apical  pericementitis,  925 
Ciliary  arteries,  239 

ganglion,  298 

nerves,  299 
long,  289 
Cingulum  of  premolar  of  dog,  355 
Circle  of  Willis,  242 
Circular  sinus,  260 
Civets,  teeth  of,  457 
Classes  of  carious  surfaces,  779 
Classification  of  bone,  48 

of  fishes,  365 

of  Mammalia,  393 
Clinical  history  of  caries,  779 
Clinoid  processes,  anterior,  62 
middle,  62,  63 
posterior,  62 
Cocci  in  caries,  801 
Collateral  circulation  of  carotid  arteries, 

218 
Collodion  in  capping,  897 
Coloring  matter  produced  by  fungi,  825 
Color  of  bones,  37 

of  muscle,  160 
Common  carotid  arteries,  215 
artery,  left,  216 
line  of,  216 


Common  carotid  artery,  right,  216 
sheath  of,  216 
variations  of,  218 

temporal  vein,  252 
Compact  portion  of  bone,  36 
Comparative  chronologv  of  dental  follicle, 

651 
Composition  of  enamel,  608 
Compound  tubular  salivary  glands,  204 
mucous  glands,  202 

nerves,  277 
Compressible  pulse,  666 
Compressor  nasi  muscle,  170 
Condyle  of  bones,  49 
Condyles  of  occipital  bone,  52,  128 
Condyloid  fossa,  53 

processes  of  inferior  maxilla,  104 
Congestion,  local,  674 
Connective  tissue,  135 
embryonic,  564 
envelope,  630 
fibrillar,  565 
Constitutional   treatment  in  alveolar  ab- 
scess, 946 
of  apical  pericementitis,  928 
Contractile  substance,  162 
Conus,  teeth  of,  346 

Cord  for  permanent  teeth,  development  of, 
634 

of  enamel  organ,  620 
Cornea,  irritation  of,  697,  698 
Cornua  of  hyoid  bone,  109 
Coronal  suture,  112 
Coronary  artery,  inferior,  225 

superior,  225 
Coronoid  process,  104 
Corpuscles,  lymph,  325 

osseous,  41 

Pacinian,  146 

tactile,  142,  146 

white,  325,  532 
Cortical  layer  of  enamel,  608 
Corrugator  supercilii  muscle,  169 
Counter-irritation,  927 
Cranial  bones,  50 

nerves,  223 

region  supplied  by,  277 
Crest,  infratemporal,  65 

of  nasal  bones,  97 
Cribriform  plate,  79 
Crico-thyroid  artery,  220 
Crista  galli,  77 
Crocodilia,  teeth  of,  385 
Crustacea,  masticatory  apparatus  of,  339 
Crusta  petrosa,  355 
Cryptoproctidae,  classification  of,  458 

teeth  of,  457 
Culture  materials,  792,  793 
Cultures  for  biological  studies,  822 

gelatin,  814 
Cup-shaped  abrasions,  995 
Cusps  of  teeth,  facets  on,  993 
Cushing's  scalers,  964 
Cuticula  dentis,  606 
Cylindrical  calcification,  878 


1016 


INDEX  TO    VOLUME  I. 


D. 

Death  of  dental  pulp,  852 
Deculeilication  of  temporary  teetli,  Pierce 

on,  645 
Deciduous  dentition  of  man,  446 
Decoiajwyition  of  the  dental  pulp,  892 
Deep  auricular  branch  of  internal  maxil- 
lary arteiy,  232 
cervical  fascia,  156 

facial    or   anterior    internal    maxillary 
vein,  251 
artery,  230 

vein,  tributaries  of,  251 
fascia,  155 
of  face,  158 
of  head,  158 
temporal  artery,  233 
Deep-seated  pulpitis,  treatment  of,  906 
Degeneration  of  structure  of  dental  jaulp, 

859 
Deinotheriuni,  dentition  of,  491 
Delphinidse,  teeth  of,  414 
Dendrohyrax,  teeth  of,  475 
Density  of  dentine,  causes  increasing,  912 
Dental  anatomy,  351 
caries,  729 

gi-owths  of  secondary  dentine  excited 
by,  868 
erosion,  hyperaesthesia  in,  1006 
follicle,  comparative  chronology  of,  651 
formula,  403 
groove,  616 
ligament,  919,  955 
nerves,  middle  superior  set,  291 
neui'algia,  837 
operations,  shock  from,  725 
papilla,  641 
pulp,  592-636 

abscess  of,  855-857 
blood-vessels  of,  831 
calcification  of,  914 
of  tissues  of,  874 
causes  of  inflannnation  in,  849 

producing  devitalization  of,  892 
cells  of,  830 

chronic  inflammation  of,  857-859 
death  of,  852 
decomposition  of,  892 
degeneration  of  structure  of,  859 
differential  diagnosis  between  diseases 

of,  837 
dilated  vessels  of,  846 
diseases  and  treatment  of,  888 
exposure  of,  853 
function  of,  832 
gangrene  of,  892 
hyperffimia  of,  840-843 
inflammation  of,  848-853 
irritation  of.  844,  889 
microscopic  study  of,  840-842 
nerves  of,  831 
pathology  of,  829 
removal  of,  903,  926 
sensitiveness  to   thermal   changes  in, 
848 


Dental  pulp,  sensory  functions  and  symp- 
tomatology of,  832 
simple  exposure  of,  890 
suppuration  of,  853-855 
swelling  of,  839 

symptoms  of  inflammation  of,  852 
fissure  of,  829 
ridge,  616 
sacculus,  361,  364 
tissues,  356 
tubes,  356 
Dentajy  bone  of  fishes,   development   of, 

378 
Dentate  sutures,  111 
Dentinal  canals,  594 
fibrils,  357 

secondary  dentine  resulting  from  irri- 
tation of,  870 
papilla,  568,  622 
processes,  357,  594 
sheath,  357 

tubules,  softening  of,  768 
Dentine,  356 
analysis  of,  356 
calcification  of,  644 
deposit  of,  592 
development  of,  593 
discoloration  of,  852 
granular  layer  of,  357 
increase  of  density  of,  911 
nodular,  911 
organ,  361 

development  of,  361 
secondary,  911 

resulting  from  irritation  of  dentinal 
fibrils,  870 
sensitiveness  of,  1006 
structure  of,  356 
Dentinification,  591 
Dentition  of  alligator,  385 
Deposition  of  fat,  565 
Deposit  of  dentine,  592 
Deposits  of  calcoglobulin  in  inflamed  pulp, 
860 
secondary  causes  of,  913 
Depressor  alse  nasi  nuiscle,  171 
anguli  oris  muscle,  173 
labii  superioris  nniscle,  172 
Dermal  denticles,  353 
development  of  354 
structure  of,  353 
spines,  354 
Descendens  noni  nerve,  323 
Descending  cervical  artery,  227 
or  dental  nerve,  291 
palatine  artery,  234 
nerves,  301 
Desiccation  of  enamel,  609 
Desirabode  on  caries,  736 
Desmatotherium,  teeth  of,  478 
Development,  embryonic,  542 
of  alveolar  wall,  632 
of  blood-corpuscles,  566 
of  blood-vessels,  566,  706 
of  bone,  45 

intercartilaginous,  587 


INDEX  TO    VOLUME  I. 


1017 


Development   of  bone,  intraiuenil)r:inous, 
48 
subperiosteal,  47 

of  bones  of  the  face,  110 

of  buccal  cavity,  550 

of  cord  for  permanent  teeth,  634 

of  dentine,  593 

of  dermal  denticles,  354 

of  enamel,  643 

of  enamel  organ,  562 

of  epiblast,  555 

of  ethmoid  bone,  80 

of  fat,  565 

of  frontal  bone,  76 

of  glands,  560 

of  hair,  558 

of  head,  109 

of  hyoid  bone,.  109 

of  inferior  maxilla,  105 

of  interior  turbinated  bone,  95 

of  jaws,  110,  550 

of  lachrymal  bone,  96 

of  malar  bones,  100 

of  maxillfe,  551 

of  mesoblast,  555 

of  nails,  556 

of  nasal  bone,  97 

of  occipital  bone,  54 

of  parietal  bone,  71 

of  palate,  551 

of  palate  bone,  93 

of  jiharyngeal  teeth  of  fishes,  361 

of  sphenoid  bone.  67 

of  superior  maxillary  bone,  88 

of  the  teeth.  360,  609 

of  teeth  of  fishes,  378 

of  temporal  bone,  61 

of  vomer,  81 
Devitalization  and  removal  of  dental  pulp, 
898 

of  dental  pulp,  causes  producing,  892 
Devitalized  pulps,  removal  of,  907 
Diadectes,  teeth  of,  384 
Diagnosis  of  alveolar  absces's,  943 

of  exposed  dental  pulp,  891 
Diapedesis  of  red  blood-globules,  679 

of  white  blood-globules,  692 
Diaphyses  of  bones,  35 
Diarthrosis,  articulation,  112 
Diclonius,  teeth  of,  387 
Dicrotous  pulse,  670 
Didelphis  Virginianus,  teeth  of,  495 
Didymictis,  teeth  of,  430 
Difierentiai  diagnosis  between  diseases  of 

the  dental  pulp,  837 
Digastric  fossa,  60,  102 

groove,  60,  127 

muscle,  187 

nerve,  308 
Dilated  vessels  of  dental  pulp,  846 
Dilophodon,  teeth  of,  478 
Dimetrodon,  teeth  of,  383 
Dinictis,  teeth  of,  460 
Diodon,  teeth  of,  378 
Diphyodont  dentition,  396 
Diploe,  120 


Diploic  veins,  261 
Dipi'otodontia,  teeth  of,  496 
Discoloration  in  <-aries,  769 

of   dentine    following   death    of    dental 
pulp,  852 
Disease,  definition  of,  661 
Diseases  causative  of  caries,  778 

of  dental  pulp  and  their  treatment,  888 

of  peridental  membrane,  918,  921 

having  their  beginning  at  margin 
of  gum,  953 
Dissacus,  teeth  of,  420 
Distal  end  of  bones,  49 
Division  of  nerve  fibres,  268 
Divisions  of  mannnalian  dentition,  396 
Dicoglossata,  348 
Dog,  teeth  of,  397 
Dolphin,  teeth  of,  414 
Dome  or  vertex  of  the  skull,  120 
Domestic  cat,  teeth  of,  4(>1 
Dorsal  plates  of  embryo,  543 
Dorsalis  lingual  artery,  221 
Dorsum  sella,  62 
Dry  gangrene,  893,  910 
Duct,  lachrymal,  212 

lachrymo-nasal,  213 

of  Bartholini,  211 

of  Steno,  208 

of  Wharton,  210 

parotid,  208 

submaxillary,  210 

thoracic,  330 
Ducts  of  Eivinus,  211 

sublingual,  211 

E. 

Ear,  muscles  of  the,  174 

Echinidffi,  food  of,  341 

Echinus  (sea-urchin ),  dental  system  of,  340 

oral  apparatus  of,  339 
Ectocium,  molars  of,  480 
Ectoconus,  teeth  of,  471 
Edentata,  teeth  of,  408 
Egg,  ovarian,  540 
Eggs,  mammalian,  542 
Eighth  nerve,  310 
Elasmobranchii,  definition  of,  365 

teeth  of,  370 
Elasticity  of  cartilage,  138 
Elei)hants,  teeth  of,  488 
Eleventh  nerve,  320 
Embryo,  dorsal,  plates  of,  543 

neural,  groove  of,  543 

plates  of  abdominal,  543 
Embryology,  539 

and  histology,  dental,  519 
Embryonal  cells  of  mucous  Inembrane,  201 

mucous  membrane  of  the  mouth,  611 
Embryonic  connective  tissue,  564 

development,  542 
Embolism,  683 

Eminence  of  parietal  bone,  69 
Emissary  veins,  262 
Emenentia  articularis,  56 
Empedocles  molaris,  teeth  of,  383 


1018 


INDEX  TO    VOLUME  I. 


Enamel,  359 

analysis  of,  359 

cells'  362 

composition  of,  608 

cortical  layer  of,  608 

cuticle,  358 

desiccation  of,  609 

development  of,  643 

fixed  material  in,  600 

formed  material  in,  600 

membrane,  606 

nacreous  layer  of,  60S 

organ  and  papilla,  connection  between, 
628 
cord  of,  620 
inner  tunic  of,  626 
development  of,  361,  562 

organic,  layer  of,  608 

prisms,  359,  601 

structure  of,  359 

variations  in  hardness  of,  602 
Endochondral  bone,  45 
Endomysium  of  muscles,  161 
Endosteum  of  bone,  43 
Envelope,  connective  tissue  of,  630 
Epiblast,  142,  543 

development  of,  555 

products  of,  556 
Epicranial  or  occipito-frontal  aponeurosis, 

167 
Epidermis,  143 
Epiphyses  of  bones,  35 
Epithelial  cells,  535 
Epithelium  of  mucous  membrane,  199 

of  oi'al  cavity,  199 

reproduction  of,  708 

of  tiie  skin,  614 

transplantation  of,  708 
Erosion  and  abrasion  of  teeth,  993 

etiology,  1002 
Erosions  of  teeth,  position  and  form  of, 

997-1002 
Esthonyx,  teeth  of,  425 
Ethmoid  bone,  76 

process  of  turbinated  bone,  94 
Ethmoidal  cells,  posterior,  79 

foramina,  75,  78,  134 

notch,  75 

sj^ine.  62 

wings,  77 
Etiology  of  caries,  731 

of  erosion,  1002 

of  mechanical  abrasion,  994 

of  pliagedenic  pericementitis,  977 
Eustachian  sulcus,  127 
Evacuation  of  pus  in  alveolar  abscess,  945 
P>olution,  theory  of,  520 
P^xainination  of  pulse,  663 
Exciting  cause  of  inilannnation,  700 
Exostosis,  causes  producing,  913 
Experiments  on  caries,  797 

with  acids  on  teeth,  1003-1006 
Exposed  dental  pulp,  capping  of,  886 

diagnosis  of,  891 

Exposure  of  dental  pulp,  853 

treatment  of,  893 


Exposure   of  dental   pulp,  secondary  de- 
posit in,  886 
fJxternal  auditory  meatus,  60,  127 
angular  process,  73 
carotid  artery,  218 

branches  of,  219 
jugular  vein,  255 

and  tributaries,  255 
lateral  ligament,  114 
maxillaiy  artery,  222 
nasal  artery,  241 

oblique  line  of  inferior  maxilla,  101 
occipital  protuberance,  53 
palatine  nerve,  301 
pterygoid  muscle,  182 
nerve,  293 
plate,  67 
rectus  muscle,  176 
surface  of  brain-case,  124 
tendo-palpebrarum  muscle,  169 
Exudate,  fibrinous,  694 
Exudates  in  inflammation,  694 

F. 

Face,  swelling  of,  in  acute  alveolar  abscess, 

931 
Facets  in  cusps  of  teeth,  993 
Facial  artery,  222 
branches  of,  224 

bones,  131 

muscles,  166 

nerve,  304 

communicating  branches,  305-307 

origin  of,  305 

table  of  its  branches,  305 

notch  of  inferior  maxilla,  103 

or  anterior  region  of  skull,  131 

or  terminal  nerves  of  superior   maxil- 
lary, 291 

region  of  skull,  131 

vein,  224,  249 
Farrar's  syringe,  967 
Fascia,  154 

aponeurotic,  155 

deep,  155 

cervical,  156 

of  face,  156 

of  head,  156 

of  neck,  156 

of  orbit,  178 

of  Tenon,  178 

omo-hvoid,  157 

parotid,  209 

prevertebral,  157 

subcutaneous,  155 

submaxillary,  157 

superficial,  155 

temporal,  179 
Fasciculi  of  muscles,  161 
Fat,  deposition  of  665 

development  of,  565 

-vesicles  or  adipose  tissue,  44 
Faulty    antagonism    of    teeth    producing 
'  wear,  994 

formation  of  the  teeth,  770 


INDEX  TO    VOLUME  I. 


1019 


Fermentation  a  cause  of  caries,  738 

in  human  mouth,  experiments  on,  793- 
795 
its  relation  to  caries  of  teeth,  791 

in  mouth,  apparatus  for  experiments  on, 
792 
Fever,  711 

cause  of,  715 

chill  in,  713 

heat-production  in,  714 

results  of,  717 

surgical,  713 

temperature  in,  711 
Fibres,  muscular,  162 
Fibrillar  connective  tissue,  565 
Fibrils,  dental,  357 
Fibrinous  exudate,  694 
Fibro-cartilage,  140 

-connective  tissue,  35 

-elastic  cartilage,  140 
Fifth  nerve,  2S2 

origin  of,  284 

pair  of  nerves,  sympathetic  ganglia  of, 
297 

table  showing  distribution  of,  287 
Filling  materials,  antiseptic  power  of,  810 

for  pulp-canals,  909 

pulp-canals,  899 
time  for,  903 

used  in  capping,  898 
Fishes,  classification  of,  365 

teeth  of,  364 
Fissure,  pterygo-maxillary,  130 

glenoid,  56,  57,  127 

sphenoid,  66 

spheno-maxillary,  65,  99,  130,  134 
Fistula  discharging  under  the  chin,  942 

passing  through  lower  maxilla,  942 
Fixed  material  in  enamel,  600 
Flagg,  Foster,  formula  for  nerve-paste,  900 
Flat  bones,  36 
Floor  of  nasal  fossa,  135 

of  the  mouth,  137 
Fluids  of  the  mouth,  morbid  conditions  of, 

774 
Flying  foxes,  teeth  of,  465 
Foetal  septum,  551 

Fomentations  in  alveolar  abscess,  947 
Fontanelle,  anterior  median,  119 

posterior  median,  119 
Fontanelles,  119 

lateral,  119 
Foramen,  anterior  condyloid,  124 
dental,  101,  133 
lacerated,  66,  134 

caecum,  74 

incisive,  86,  136 

infraorbital,  84,  132 

jugular  or  posterior  lacerated,  62 

lacerum  medius,  122 
posterius,  123 

magnum,  54,  124 

malar,  97,  134 

mental,  101 

middle  lacerated,  58,  127 

of  Scarpa,  136 


Foramen  of  Stetson,  86,  136 

optic,  133 

ovale,  65,  122,  126 

parietal,  70 

posterior  dental,  103 
lacerated,  127 

ptery  go-palatine,  130 

rotundum,  65,  122 

spheno-palatine,  92,  130,  136,  127 

spinosum,  65,  122 

stylo-mastoid,  60,  122 

supraorbital,  73,  132 

Vesali,  122 
Foramina,  anterior  condyloid,  53 
ethmoidal,  75,  78,  134 
lacerated,  122,  134 

infraorbital,  132 

malar,  97,  134 

mastoid,  124 

naso-palatine,  86 

of  Scarpa,  86 

optic,  62,  67 

parietal,  117 

posterior  condyloid,  53,  124 
ethmoidal,  75,  78,  134 
Formation  of  bone,  interstitial,  580 
intramembranous,  48,  583 

of  ducts  in  grain,  707 

of  poisons    by  micro-organisms.    Black 
on,  757 
Formed  materials  in  enamel,  600 
Formula,  dental,  403 
Fossa,  anterior,  of  the  brain-case,  120 

canine,  84,  133  , 

cerebral,  124 

condyloid,  53 

digastric,  of  inferior  maxilla,  102,  127 

incisive,  101 

lachrymal,  75,  133 

middle,  of  the  brain-case,  122 

nasal,  134 

parietal,  70 

pituitary,  62 

posterior,  of  brain-case,  123 

pterygoid,  67,  104 

scaphoid,  67 

vspheno-maxillary,  130 

sublingual,  102 

temporal,  128 

trochlear,  75 

zygomatic,  129 
Fox  squirrel,  teeth  of,  467 
Frsenum  of  lower  lip,  173 

of  upper  lip,  172 
Frontal  artery,  241 

bone,  72 

eminence,  74 

nerve,  286 

notch,  73 

processes  of  malar  bones,  98 

sinuses,  73 

vein,  250 
Fronto-ethmoidal  cells,  75 

-malar  suture,  117 

-parietal  suture,  117 

-sphenoidal  suture,  117 


1020 


INDEX  TO    VOLUME  I. 


Function  of  peridental  membrane,  920 
Fungi  causing  caries,  801,  802 
coloring  matter  produced  by,  825 
of  caries,  814,  815 
action  of  sugar,  805 
evolution  of  carbonic  acid  by,  805 
of  dental  caries,  their  pure  cultivation 
and  efiect  upon  lower  animals,  813 
of  human  mouth,  acid  produced  bv,  824- 
826 
biological  studies  on,  819 
morphology  of,  823 
relation  to  oxygen,  824 
peptonizing  action  of,  824 
oxygen  in  relation  to,  805 
production  of  gas  by,  825 
Fungus  growths  in  caries,  767 

G. 

Galeopithecus,  teeth  of,  428 
Ganglion,  cervical,  313 

-cells  of  nerves,  264 

ciliary,  298 

Gasseriari,  284 

geniculate,  306 

jugular,  313 

inferior  or  petrous,  311 

lenticular,  798 

of  Andersch,  31 1 

of  Ehrenritter,  311 

of  Meckel,  299,  301 

ophthalmic,  598 

optic„302 

otic,  302 

semilunar,  284 

spheno-palatine,  299,  301 

submaxillary,  303 

superficial  jugular,  311 

sympatlietic,  of  fifth  pair  of  nerves,  297 
Gangrene,  dry,  893,  91(3 

of  dental  pulp,  892 
Gangrenous  pulps,  causes  of,  906 

treatment  of,  907 
Gasserian  ganglion,  284 
Gastro-pneumonic  system  of  mucous  mem- 
branes, 199 
Gelatin  cultures,  814 
(xeneral  development  of  the  head,  109 

pathology,  661 
Generation,  spontaneous,  521 
Genial  tubercles,  102 
Cieniculate  ganglion,  306 
tienio-glossus  muscle,  190 

hyoid  muscle,  190 
Genito-urinary  system   of   mucous   mem- 
brane, 199 
Geomalacus,  jaw  of,  349 
Gila  monster,  teeth  of,  386 
Gingival  organ,  955 
Gingivitis,  955 

(jinglymus,  or  hinge-joint  of  Allen,  112 
Glands,  laclirvmal.  21 1 

of  Bartholin,  210 

parotid,  207 

sublingual,  210 


Glands,  submaxillarv,  209 

buccal,  206 

ceruminous,  152 

compound  tubular  mucus,  202 
saliva,  204 

development  of.  560 

labial.  206 

lingual,  207 

lympliatic,  328 

Meibomian,  153 

molar,  206 

muco-salivarv,  206 

mucus,  198,  204 

of  mucous  membrane,  198 

palatine,  207 

racemose,  203 

sebaceous,  152,  560 

secretory,  of  mucous  membrane,  201 

simple  mucous,  tubular,  202 

sudoriferous,  151 

sweat,  151 

true  salivary,  205 
Glandular  arteries,  224 
Glandula  socia  jjarotidis,  208 
Glasserian  fissure,  56 
Glenoid  fissure,  56,  57,  127 

fossa,  56,  127 
Glosso-pharyngeal  nerve,  310 

communicating  branches  of,  312 
lingual  branches  of,  312 
muscular  branches  of,  312 
pharyngeal  branches  of,  312 
table  of  branches,  311 
Glyptodon,  teeth  of,  410 
Glyptostoma,  jaw  of,  349 
Gold  in  caries,  811 
Gouty   inflammations    of    the    peridental 

membrane,  979 
Grain,  formation  of  ducts  in,  707 
Granulation-cells,  704 
Granulations  in  blood-clot,  710 
Great  superficial  petrosal  nerve,  306 

wings  of  siihenoid  bone,  64 
Groove,  dental,  616 

digastric,  127 

medullary,  548 

mylo-hyoid,  102 
Grooves  for  olfactory  nerves,  77 
Growth  of  bone,  47 
Gum,  structure  of,  955 
Gutta-percha  for  filling  pulp-canals,  909 

H. 

Hair,  147 

bull)  of,  147 

cuticle  of,  148 

development  of,  558 

fibrous  or  cortical  portion  of,  148 

follicles  of,  147-149 

medulla  of,  149 

papilla  of,  150 

root  of,  147 
health  of,  149 

shaft  of,  1 47 
Halmaturus,  teeth  of,  496 


INDEX  TO    VOLUME  I. 


1021 


Hamular  process,  67 
Hanover,  stratum,  interraediura  of,  625 
Ha  pale,  teetli  of,  435 
Ilariuonic  sutures.  111 
Haversian  canal,  576 
canals  of  bone,  39 
Heads  of  bones,  4!J 
Health,  definition  of,  661 
Heart  lesions,  pulse  in,  670 
Heat-production  in  fever,  714 
Hedgehog,  teeth  of,  429 
Helodernia  suspectum,  teeth  of,  386 
Hemorrhage,  685 
Hemorrhagic  infarction,  683 
Plereditary  influences  causing  caries,  772 
Herpestes,  teeth  of,  456 
Heterodont  dentition,  396 
Hiatus  Fallopii,  58,  123 
Highmore,  antrum  of,  89 
Hippotherium,  teeth  of,  481 
Hirudinse  (leeches),  teeth  of,  338 
Histologv,  dental,  519 

of  teeth,  356 
Hog,  teeth  of,  484 
Homodont  dentition,  396 
Horse,  canines  of,  483 
digits  of,  482 
incisors  of,  482 
molars  of,  483 
Human  dentition,  437 
Hunter  on  caries,  731 
Hysena,  teeth  of,  455 
Plysenidie,  evolution  of,  453 
Hysenarctos,  teeth  of  464 
Hysenictis,  teeth  of,  456 
Hysenodontidie,  teeth  of,  420 
H3'aline  cartilage,  139 
Hyo-branchial  skeleton,  369 

bones  of,  369 
«Hvo-glossus  muscle,  191 
Hyoid  artery,  220 
bone,  108 

development  of,  109 
Hyo-mandibular  arch  of  codfish,  367 
Hyperaemia,  676 
local,  674 
of  dental  pulp,  840,  843,  847,  848 

])ain  in,  844 
passive,  677 

results  of,  678 
tissue,  change  in,  845 
Hypersesthesia  in  dental  erosion,  1006 
Hypoblast,  142,  543 
Hyracoidea,  ancestry  of,  476 
Hyracotherium,  teeth  of,  477 
Hyrax,  teeth  of,  475 
Hypoglossal  nerve,  322 

communicating  branches  of,  323 

lingual  branches  of,  324 

table  of,  323 


I. 


Ictitherium,  teeth  of,  453 
Iguanidse,  teeth  of,  386 
Ignanodon,  teeth  of,  387 


Incisive  artery,  233 
crest,  86 

foramen,  86,  136 
fossa  of  inferior  maxilla,  101 
of  superior  maxilla,  84 
Incisors,  definition  of,  398 
human,  43S 
lower,  human,  440 
upper  central,  luiman,  440 
lateral,  human,  440 
Indian  elephant,  molars  of,  490 

tusks  of,  489 
Infant  layer  of  epithelium,  618 
Infarction,  hemorrhagic,  683 
Infection  bv  micro-organisms  of  the  mouth, 

816' 
Infectious  alveolitis,  968 

nature  of  caries,  789 
Inferior  constrictor  muscle,  194 
coronary  artery,  225 
curved  lines  of  occipital  bone,  53 
dental  artery,  233 
canal,  104 
foramen,  103 
nerve,  296 

branches  of,  296,  297 
communicating  branch,  296 
incisive,  branches  of,  297 
lesser,  297 

mental  or  labial  branch,  297 
labial  artery,  225 
laryngeal  arteiy,  247 
longitudinal  sinus,  258 
maxilla,  at  birth,  105 
development  of,  105 
movement  of,  105 
maxillary  bone,  100 
nerve,  292 

deep  temporal  branches  of,  292 
posterior  temporal  branch  of,  293 
meatus,  85,  136 
oblique  muscle,  177 
ophthalmic  vein,  261 
or  palatine  artery,  224 
or  recurrent  laryngeal  nerve,  318 
palatine  vein,  251 
palpebral  veins,  251 
pedicle  of  sphenoid  bone,  67 
petrosal  sinus,  261 
petrous  ganglion,  311 
rectus  muscle,  176 
thyroid  artery,  246 

veins,  248 
turbinated  bone,  94 
crest,  92 
Inflammation,  690 

chronic,  of  dental  pulp,  857-859 

exciting  cause  of,  700 

exudates  in,  694 

in  dental  pulp,  causes  of,  949 

of  bone,  43 

of  dental  pulp,  848-853 

cell,  movements  in,  850 
lymph-deposits  in,  852 
recovery  from,  853 
symptoms  of,  852 


1022 


INDEX  TO    VOLUME  I. 


Inflammation  of  dental  pulp,  tissue-changes 
in,  849 

of  peridental  membrane,  cause  of,  893 

pain  in,  693 

subperiosteal,  944 

swelling  in,  693 

temperature  in,  693 

tissue-changes  in,  695 

white  blood-corpuscles  in,  695 
Influence  of  disease  on  bones,  49,  135 
Infraorbital  arteiy,  234 

canal,  82,  134 

foramen,  84 

foramina,  132 

nerve,  290 

plexus,  292 

ridge,  84 
Infratonsillar  or  pliarvngeal  tonsils,  214 
Infratemporal  crest,  65,  129 
Infratrochlear  nerve,  289 
Infundibulum  of  ethmoid  bone,  79 

of  nasal  chamber,  137 
Inner  tunic,  640 

of  enamel  organ,  626 
Innominate  veins,  248 
right  and  left,  248 
Insectivora,  teeth  of,  417 
Inter-articulating   disc   or   fibro-cartilage, 
114 

-cartilaginous  development  of  bone,  587 

-globular  spaces,  357,  595,  766 

-maxillary  bone,  88 

-parietal  bone,  54 
suture,  116 
Intermfttent  pulse,  670 
Internal  angular  process,  73 

auiiitory  meatus,  59,  123 

carotid  artery,  235 

frontal  crest,  74 

jugular  vein  and  tributaries,  256 

laryngeal  nerve,  318 

lateral  ligament,  115 

mammary  artery,  247 

maxillary  artery,  230 

dee) )  temporal,  branches  of,  233 
vein,  253 

nasal  nerves,  289 

oblique  ridge,  101 

occipital  crest,  53 
protuberance,  53 

ptervgoid  muscle,  181 
nerve,  293 
lilate,  67,  68 

rectus  nniscle,  176 

tendo-palpebrarum  muscle,  169 
Interstitial  formation  of  bone,  580 
Intra-cartilaginous  bone,  45 
Intra-membranous  bone,  48 

formation  of  bone,  48,  583 
Invagination  of  bulbous  cord,  624 
Invertebrates,  teeth  of,  337 
Involuntary,  smooth,  or  unstriated   mus- 
cles, i64 
Iodine,  uses  of,  on  gangrenous  pulps,  908 
Iodoform  in  capping,  898 

in  superficial  pulpitis,  905 


Irregularities  of  pulse,  669 

of  teeth  caused  by  inflammation  of  the 
throat,  135 
Irritation  causing  secondary  dentine,  913 

of  cornea,  697,  698 

of  dental  pulp,  844,  889 
Ivory,  nature  of,  489 

J. 

Jaw,  development  of,  550,  629 
Jelly  of  Wharton,  566 
Jugular  foramen,  52 

ganglion,  313 

notch,  52 

process  of  occipital  bone,  51 

K. 

Kangaroo,  teeth  of,  496 
Koecker  on  cai-ies,  733 

L. 

Labial  and  buccal  surfaces,  caries  in,  781 

glands,  206 

or  descending  nerves,  292 
Labyrinthodonts,  teeth  of,  381 
Laciarymal  artery,  238 

bone,  95 

canal,  134,  136,  212 

crest,  95 

duct,  212 

fossa,  75,  133 

gland, 211 

groove,  84 

nasal  duct,  213 
passage,  213 

nerve,  288 

process,  94 

sac,  213 

tubercle,  84 
Lactic  acid  in  caries,  798 

in  carious  dentine,  800 
Lacto-phosphate  of  lime  in  capping,  897 
Lacuna-cartilage,  140 
Lacunae  of  bone,  41,  576 
Lagomorpha,  teeth  of,  469 
Lambdoid  suture,  117 
Lambdotherium,  molars  of,  480 
Lamella  of  bone,  39 
Lamina  cribrosa,  59 

of  embryo,  618 
Lantern  of  Aristotle,  339 
Laryngeal  artery,  220 
Lateral  communicating  arteries,  243 

fontanel  les,  119 

masses  of  ethmoid  bone,  78 

nasal  artery,  225 

processes  of  pulp,  358 

region  of  the  skull,  128 

sinuses,  259 
Layer,  odontoblastic,  640 
Leber  and  Rottenstein  on  caries,  751 
Leeching  in  apical  pericementitis,  928 
Leeches  (Ilirudinse),  teeth  of,  338 


IXDEX  TO    VOLUME  I. 


1023 


Left  common  carotid  artery,  216 
Leimirs,  teeth  of,  431 
Lenticular  gantjlion,  298 
Leptictis,  teetii  of,  424 
Leptocardii,  definition  of,  365 
Leptotluix  biiccalis,  751, 795 

gigantea.  795 
Lesser  superficial  petrosal  nerve,  306 

wings  of  sphenoid  bone,  66 
Leucocytes,  325,  692 
Levator  anguii  oris  muscle,  172 
labii  inferioris  muscle,  173 

superioris  alseque  nasi  muscle,  171 
proprius  muscle,  171 
palati  muscle,  197 
palpebral  muscle,  176 
Life,  nature  of,  519 
Ligament,  capsular,  114 
dental,  919,  955 
internal  lateral,  115 
stylo-hyoid,  189 
-maxillary,  115 
Ligaments  of  the  temporo-maxillary  artic- 
ulation, 113 
Ligatures,  absorption  of,  922 
Limnsea,  teeth  of,  349 
Line  ridge  or  crest,  49 
Lingual  artery,  221 
glands,  207 
nerve,  295 

branches  of  communication,  295 
vein  and  tributaries,  254 
Lingualis  muscle,  191 
Lister,  method  of,  755 
Lizard,  teeth  of,  386 
Local  congestion,  674 

hypersemia,  674 
Longitudinal  sinus,  75 
Lophiodontidsej  digital  formula  of,  477 

teeth  of,  477 
Loxodon  Africanus,  dentition  of,  489 
Lutrictis,  teeth  of,  4(54 
Lymph-capillaries,  326 
Lymph,  composition  of,  325 
-corpuscles,  325 
deposits  in  inflammation  of  dental  pulp, 

852 
-sinus,  329 
-spaces,  326 
of  bone,  41 
Lvniphatic  duct,  330 
"glands;  328 
vessels,  325 

of  head  and  neck,  330 
structure  of,  327 
valves  of,  327 
Lymphatics,  deep,  330 
of  muscles,  164 
of  skin,  145 
origin  of,  326 
superficial,  330 
Lyrifera,  definition  of,  365 

M. 

Magitot  on  caries,  747 


Magnum  foramen,  124 
Malar  bones,  97 
foramina,  97,  134 
process,  85 
Malpighi  stratum,  144 
Malpighian  layer  of  the  skin,  615 
Mammalia,  classification  of,  393 
origin  of,  391 
teeth  of,  390 
Mammalian  dentition,  divisions  of,  396 

eggs,  542 
Marmosets,  dentition  of,  434 
Marrow-fat,  vesicles  of,  44 
of  bone,  43 
red,  43 

red  cells  of,  45 
yellow^,  43 
Marsipobranchii,  definition  of,  365 
JSIarsupials,  distinctions  of,  493 

teeth  of,  493 
Masseter  muscle,  179 
Masseteric  artery,  234 

nerve,  293 
Mastication,  action  of  muscles  of,  182 

muscles  of,  178,  406 
Mastodon,  teeth  of,  491 
Mastoid  artery,  227 
foramen,  124 

portion  of  temporal  bone,  60 
Materials  for  capping,  894 
Matrix  of  osseous  substance,  571 
Maxillae,  development  of,  551 
Maxillary  bone,  inferior,  100 
superior,  81 
bones  of  codfish,  368 
process  of  turbinated  bone,  94 

of  malar  bones,  99 
sinus,  89 
Meatus,  anterior  palatine,  86 
external  auditory,  60,  127 
inferior,  85,  136 
internal  auditory,  59,  123 
middle,  136 

of  superior  maxillary  bone,  85 
superior,  136 

of  ethmoid  bone,  79 
of  superior  maxillary  bone,  85 
Mechanical  abrasion,  etiology  of,  994 
Meckel's  cartilage,  57,  105 
development  of,  552 
ossification  of,  105,  554 
ganglion,  299 
Medullary  groove,  548 
or  true  marrow-cells,  44 
plates,  548 
sheath,  266 
Megalonyx,  teeth  of,  411 
Megalotidaj,  teeth  of,  453 
Megatherium,  teeth  of,  410 
Meibomian  glands,  153 
Membrana  eboris,  358 
destruction  of,  885 
Membrane,  basement,  145 
corium  of  mucous,  200 
epithelium  of  mucous,  199 
mucous,  198 


1024 


INDEX  TO    VOLUME  I. 


Membrane  of  enamel,  606 

of  Nasmyth,  358 
Meningeal  arteries,  229 
Meniscotherium,  teeth  of,  474 
Menopomea,  dentition  of,  381 
Mental  artery,  233 

foramen,  101,  133 

process,  101 
Mento-hyoid  mnscle,  189 
Mesoblast,  142,  543 

development  of,  555 

products  of,  556 
Mesonyx,  teeth  of,  418 
Miacis,  teeth  of,  430 

Micro-organisms    in    phagedenic    perice- 
mentitis, 977 

of  the  moutli,  infection  by,  816 
Microscopic  study  of  dental  pulp,  840-842 
Microscopical  examination,  preparation  of 

bone  for,  38 
Midas,  teeth  of,  434 
Middle  cerebral  artery,  242 

clinoid  process,  63 

constrictor  mnscle,  193 

deep  temporal  nerve,  293 

fossffi  of  brain-case,  122 

lacerated  foramen,  58,  122,  127 

meatus,  85,  136 

or  great  meningeal  artery,  232 

superior  dental  nerve,  291 

temporal  artery,  229 
vein,  253 

turbinated  bone,  79 
Migrating  lymph-corpuscles  of  tonsils,  214 
Milk  dentition,  498 
Miller,  experiments  of,  759 

on  fermentation  in  the  human  mouth, 
its  relation  to  caries  of  the  teeth, 
791 
Mills  and  Underwood  on  caries,  752 
Minute  structure  of  bone,  38 
Molar  glands,  206 
Molars,  definition  of,  401 

liuman,  443 

of  elephant,  shedding  of,  490 
wear  of,  490 
Molecular  disturbances  in  shock,  722 
Mollusca,  dental  apparatus  of,  341,  349 
Molluscan  animals,  functions  of  teeth,  350 

radidar  apparatus,  342 
Mollusks,  cliitinous  armature  of,  342 

radular  of,  instructions  for  examining, 
344,  345 
Monkeys,  teeth  of,  434 
Monodon,  teeth  of,  414 
Monophyodont  dentition,  396 
Morbid  conditions  of  fluids  of  the  mouth, 

774 
Morphia  and  arsenious-acid  pastes,  900 
Morfjhological  appearance  of  cells,  531 
Morplioldgv  of  fungi  of  the  human  mouth, 

823  ■ 
Motion,  nerves  of,  274 
Motor   nerves,    peripheral   end-organs  of, 

272 
Mouth,  cavity  of,  137 


Mouth,  embryonal  mucous  membrane  of, 
201,  611 
floor  of,  137 
roof  of,  137 
Movements  of  inferior  maxilla,  115 
Muco-periosteum,  200 
salivarv  glands,  206 
Mucous  glands,  198,  204 
membrane,  198 

embryonal  cells  of,  201 

epithelium  of,  199 

gastro-pne\mionic  system  of,  199 

genito-urinarv  svstem  of,  199 

glands  of,  198 

secretory  glands  of,  201 
Multipolar  giant-cells,  44 
Mummified  condition  of  the  pulp,  893 

pulps,  910 
Muscles,  action  of  orbital,  177 
attolens  aurem,  175 
attrahens  aurem,  175 
azygos  uvulje,  198 
blood-vessels  of,  164 
buccinator,  173 
contractile  substance  of,  162 
corrugator  supercilii,  169 
depressor  anguli  oris,  173 

labii  inferioris,  173 

labii  superioris,  172 
endomysium  of,  161 
external  pterygoid,  182 
facial,  166 
fasciculi  of,  161 

size  of,  162 
fibres  of,  164 
genio-glossns,  190 

-hyoid,  190 
Honer's,  169 
hyo-glossus,  191 
inferior  oblique,  177 

constrictor,  194 
internal  pterygoid,  181 
involuntar)',  164 
levator  anguli  oris,  172 

labii  superioris  alseque  nasi,  171 
proprius,  171 

palati,  197 

palpebrse,  176 
lingualis,  191 
lymphatics  of,  164 
of  mastication,  action  of,  182 
mento-hyoid  (Macalister),  189 
of  ear,  174 
of  mastication,  406 
oral  group,  171 
middle  constrictor,  193 
niylo-hyoid,  189 
nasal  set,  170 
neck,  183 

action  of,  183,  185 
nerves  of,  164 
number  of,  166 
occijiito-lrontalis,  166 
of  orbit,  175 
of  the  j)harynx,  192 
omo-hyoid,  186 


INDEX  TO    VOLUME  I. 


1025 


Muscles,  oral,  action  of,  174 
orbicularis  oris,  171 
palpebrarum,  168 
orbital,  action  of,  177 
palato-Eustachian,  197 
-glossus,  196 
-pharyngeus,  195 
perimysium  of,  161 
pterygoideus  proprius  (Henle),  182 
pyramidales  nasi,  168 
recti  or  straight  of  the  orbit,  176 
retrahens  aurem,  175 
risorus,  173 
soft  palate,  192 
sterno-cleido-mastoideus,  184 
-hyoid,  185 
-thyroid,  186 
stylo-glossus,  191 
'-hyoid,  189 
-pharyngeus,  194 
superior  constrictor,  192 

oblique,  177 
supra-hyoid  space,  187 
temporal,  180 
tensor  palati,  197 

tarsi,  169 
thyro-hyoid,  186 
trochlearis,  177 
unstriped,  164 
varieties,  165 
voluntary,  fibres  of,  160 
zygomaticus  major,  172 
minor,  172 
Muscular  arteries  of  the  orbit,  240 
fibres,  162 
tissue,  159 
Muskrat,  teeth  of,  467 
Mustilidse,  teeth  of,  464 
Myeloplaxes  of  bone,  43 
Mylo-hyoid  artery,  233 
groove,  102 
muscle,  189 
nerve,  296 
ridge,  101 
Myolemma,  162 
Myrmecobius,  dentition  of,  493 
Myrtiform  fossa,  84 

N". 

Nacreous  layer  of  enamel,  608 
Kails,  development  of,  556 
Narwhal,  teeth  of,  414 
Nasal  angle,  97 

aperture,  posterior,  136 

arch,  132,  136 

artery,  lateral,  225 

bones,  96 

cartilage,  77 

chamber,  infundibulum  of,  137 

crest,  86 

eminence,  73 

fossa,  134 

muscles,  170 

nerve,  branches  of,  288 

notch,  73 

Vol.  I. — 65 


Nasal  openings,  anterior,  132,  136 

or  internal  set  of  nerves,  292 

or  spheno-palatine  arteiy,  235 

process  of  superior  maxillary  bone,  85 

septum,  135 

abnormality  of,  135 

spine  of  frontal  bone,  73 
of  superior  maxilla,  86 

of  superior  maxillary  bone,  86 
Nasmytli's  membrane,  office  of,  608 

origin  of,  608 
Naso-  or  oculo-nasal  nerve,  288 

-palatine  canal,  81,  136 
foramina,  86 
nerve,  302 
Neck,  muscles  of,  183 

of  bones,  49 

veins  of,  254 
Necks  of  the  teeth,  caries  in,  786 
Necrosis  of  alveolar  process,  951 

of  bone,  cause  of,  in  alveolar  abscess,  934 
Nervse  vasorum,  327 
Nerve,  axis-cylinder  of,  266 

-centres,  263 

eighth,  310 

eleventh,  320 

endings  in  gland-cells,  271 

fibres,  264,  268 

fifth,  282 

table  showing  distribution  of,  287 

medullary,  sheath  of,  266 

ninth,  310 

non-medullary  or  pale  fibres,  268 

posterior  superior  dental,  290 

seventh,  304 

sixth,  282 

supply  of  the  peridental  membrane,  919 

tenth,"  313 

trifacial,  282 

trigeminus,  282 

twelfth,  322 
Nerves,  abdominal  or  terminal,  branches 
of  pneumogastric,  320 

abducens,  282 

alveolar  dental,  290 

anterior  palatine,  301 
superior  dental,  291 

articular,  294 

ascending  or  orbital,  301 

auditory,  310 

auriculo-temporal,  294 

buccal,  293,  309 

cardiac  branches  of  the  pneumogastric, 
319 

centrifugal,  274 

centripetal,  275 

cervical  or  intramaxillary,  309 

cervico-facial,  309 

chorda  tympani,  301 

communicating  branches  of  the  facial, 
306 

compound,  277  , 

cranial.  273 

descending  or  descendens  noni,  323 
palatine,  301 

digastric,  308 


1026 


INDEX  TO    VOLUME  I. 


Nerves,  division  of  fibres,  268 
end-plates  of  Kiihne,  272 
external  pterygoid,  293 
facial,  304 
first  pair  of,  277 
fourth  pair  of,  281 
frontal,  28G 
ganglion-cells  of,  264 
glosso-pharyngeal,  310 
hj'poglossal,  322 
incisor,  297 
inferior  dental,  296,  297 

maxillary,  292 

or  recurrent  laryngeal,  318 
infraorbital,  290 
intratrochlear,  289 
internal  laryngeal,  318 

nasal,  289 

pterygoid,  293 
lachrymal,  288 
lelt  pneimiogastric,  315 
lesser  inferior  dental  (Sapolini),  297 

superficial  petrosal,  306 
lingual,  295  , 

long  ciliary,  289 
masseteric,  293 
mental  or  labial,  297 
middle  deep  temporal,  292 

superior  dental,  291 
motor  oculi,  280 

peripheral  end-organs,  272 
mylo-liyoid,  290 
nasal  or  oculo-nasal,  288 
naso- palatine,  302 
neurilenmia  of,  267 
nodes  and  internodes  of  Kanvier,  267 
occipital,  308 
oesophageal,  320 

branch  of  tlie  pneumogastric,  320 
of  external  auditory  meatus,  295 
of  motion,  274 
of  pulp,  655 
of  muscles,  164 
of  sensation,  275 
of  skin,  145 
of  special  sense,  275 
olfactory,  277 
ophthalmic,  286 
optic,  278 

orbital  or  temporal  malar,  290 
parotid,  295 
pathetic,  281 

pharyngeal  or  pterygopalatine,  302 
pneumogastric,  313 

accessory  portion  of,  313 

cervical  or  inferior  ganglion  of,  313 

communicating  of,  312 

jugular  or  superior  ganglion,  313 

lingual  or  terminal  branches  of,  312 
posterior  auricular,  308 

superior  dental,  290 

temjioral,  293 
pulmonarv  branches  of  the  pneumogas- 
tric, 319 
recurrent  branch,  hypoglossus,  323 
right  pneumogastric,  315 


Nerves,  second  pair  of,  278 

sensoi-y  peripheral  end-organs,  271 
spheno-ethmoidal,  289 

palatine,  290 
spheroidal  end-bulbs  of  Krouse,  272 
spinal  accessory,  320 
stvlo-glossal,  308 

'-hyoid,  308_ 
superior  maxillary,  290 
supramaxillary,  309 
supraorbital,  286 
supratroclilear,  286 
table  of  the  branches  of  the  fifth,  287 
of  the  hypoglossal,  323 
of  the  spinal  accessory,  320 
temporal,  308 
third  pair  of,  280 
thyro-hyoid,  324 
tonsillar,  312 

branches  of,  312 
trochlear,  281 
tympanic,  branches  of,  312 
o'f  Wrisberg,  305,  310 
Nervous  system,  263 

nerve-endings  in  gland-cells,  271 
peripheral     end  -  organs     of     motor 
nerves,  272 
of  sensory  nerves,  271 
Neural  groove  of  embryo,  543 
Neuralgia,  dental,  837 
Neurilemma,  or  sheath  of  Schwann,  267 
Ninth  nerve,  310 

Nitric-acid  treatment  in  capping,  896 
Nodes  of  Ranvier,  267 
Nodular  dentine,  911 

deposits  in  pulp,  862 
Nodules  in  pulp-tissue,  914 
Non-medullary  or  i>ale  nerve-fibres,  268 
Notidanus,  teeth  of,  372 
Notochord  or  chorda  dorsalis,  109 
Nucleated  red' blood-cells,  44 
Number  of  muscles,  1 66 

O. 

Obtundents,  use  of,  890 
Occipital  artery,  226 
branches  of,  226 

posterior  meningeal,  branches  of,  227 
bone,  51 

basilar  process,  51,  54 
[)haryngeal,  spine  of,  51 
crest,  53 
groove,  60 
nerve,  308 
vein,  254 
Occipito-frontalis  aponeurosis,  167 
nuiscle,  166,  167 
mastoid  suture,  51 
parietal  sutui'e,  117 
Oculo-motor  nerve,  280 
Odontoblastic  laver,  640 
Odontoblasts,  357,  569,  592,  641 
atrophy  of,  884 

of  dental  pulp,  pathological   condition 
of,  882 


INDEX  TO    VOLUME  I. 


1027 


Odontoclasts,  922 
Oli'actoiy  apertures,  136 

nerves,  277 
Olivary  process,  62 
Omo-hyoid  fascia,  157 

muscle,  186 
Ornithorhynchus,  horny  teeth  of,  352 
Operation  for  diseased  alveolar  process,  980 

for  scar  on  the  face,  952 
Opercular  bones  of  codfish,  368 
Ophidia,  classification  of,  388 
Ophthalmic  artery,  2'38 

muscular  branches  of,  240 

ganglion,  298 

nerve,  286 
Optic  chiasm  or  commissure,  278 

foramen,  133 

foramina,  62,  67,  133 

groove  of  sphenoid  bone,  62 

nerve,  278 

tract,  278 
Oral  arraatui'e,  353 

cavity,  epithelium  of,  199 

muscles,  171 
actions  of,  174 
Orl)icularis  oris  muscle,  171 

palpebrarum  muscle,  168 
Orbit,  fascia  of  the,  178 

muscles  of  the,  175 

veins  of,  261 
Orbital  cavity,  132,  133 

plates,  75 

process  of  malar  bones,  99 
of  palate  bone,  93 
Organic  layer  of  enamel,  608 
Organization  of  blood-clot,  709 
Origin  of  osteoblasts,  589 
Orthocynodon,  teeth  of,  479 
Orycteropus  capensis,  teeth  of,  412 
Ossa  triquetra,  118 
Osseous  corpuscles,  41 
Os  lingua,  108 

planum,  79 
Ossein,  571 

Osseous  substance  of  matrix,  571 
Ossification,  574 

classification  of,  577 

of  bone,  46 
Osteoblasts,  42,  45,  575 

origin  of,  589 
Osteoclasts,  43,  44,  922 
Osteo-dentine,  880 
Osteo- porosis,  47 
Os  unguis,  95 
Otic  ganglion,  302 
Ovale,  foramen,  65,  122 
Ovarian  egg,  540 
Ovum,  segmentation  of,  543 
Oxychloride  of  zinc  for  filling  pulp-canals, 
909 
use  of,  in  capping,  895 
Oxychlorides  in  caries,  811 
Oxygen  in  relation  to  fungi,  805 

relation  of  fungi  to,  824 
Oxyphosphates  in  caries,  811 

of  zinc  for  filling  pulp-canals,  909 


P. 

Pacchionian  fossae,  71 

Pacinian  corpuscles.  146 

Pain  in  hyperajmia  of  dental  pulp,  844 

in  inflammation,  693 
Painless  penetration  of  apical  space,  928 
Palatal  process,  86 
Palate,  development  of,  88,  551 

bone,  90 
Palatine  glands,  207 

spine,  91 

vein,  inferior,  251 
Palato-Eustachian  muscle,  197 

-glossus  muscle,  196 

-pharyngeus  muscle,  195 

-quadrate  arch  of  codfish,  368 
Palpebral  arteries,  241 
Panniculus  carnosum,  183 
Papilla    and    enamel    organ,    connection 
between,  628 

dental,  641 

dentinal,  568,  622 

of  skin,  144 
Parietal  bone,  69 

eminence  69 

foramen,  70 

foramina,  70,  117  ^ 

'    fossa,  70 
Parieto-mastoid  suture,  117 

-sphenoid  suture,  117 

-squamous  suture,  119 
Parotid  arteries,  229 

duct,  208 

fascia,  209 

gland,  207 

glandula  socia,  208 

space,  208 

veins,  253 
Par  vagus  nerve,  313 
Passive  hypersemia,  677 
Pasteur,  experiments  of,  755 
Pathological  condition  of  odontoblasts  of 

dental  pulp.  882 
Pathology,  general,  661 

of  the  dental  pulp,  829 
Peccary,  teeth  of,  485 
Penetration  of  enamel  in  caries,  768 
Pepper  bags,  927 
Peptonizing  action  of  fungi,  824 
Pei'forating  fibres,  40 
Pericementitis,  ajjical,  923 

phagedenic,  954,  968 
Pericementum,  formation  of,  631 
Pericliondrinni.  141 

Peridental  membrane,  blood-supply  of,  919 
diseases  of,  918,  921 
function  of,  920 
nerve-supply  of,  919 
structure  of,  918 
Perimysium  of  muscles,  161 
Periosteum,  42 
Peripheral  end-organs  of  nerves,  271 

of  Jaw,  development  of,  629 

separation  of,  in  alveolar  abscess,  932 
Periptychus,  teeth  of,  470 


1028 


INDEX  TO    VOLUME  I. 


Peroxide  of  hydrogen  in  alveolar  abscess, 

94S 
Perpendicular  plate  of  ethmoid  bone,  77 
Petro-basilar  groove,  127 

suture,  51 
Petrous  portion  of  temporal  bone,  55,  57 
Phacochcerus,  teeth  of,  485 
Phagedenic  pericementitis,  954,  968 

complicated  with    serumal    calculus, 
975 

treatment  of,  979 
Pharyngeal  arteries,  228 

or  pterygo-palatine  nerve,  302 
spine  of  occipital  bone,  51,  127 
teeth  of  fishes,  development  of,  361 
vein,  254 
Pharynx,  muscles  of  the,  192 
Plilebitis,  252 

Physiological  consideration  of  cells,  524 
Physiology  of  the  blood,  533 
Phenacodus,  teeth  of,  472 
Phenol  camphor,  985 
Phenomena  of  caries,  764 
Pierce  on  calcification  and  decalcification 

of  teeth,  645 
Pigment  of  skin,  146 
Pine  marten,  teeth  of,  464 
Pinna,  shell  of,  596 
Pisces,  definition  of,  365 
Pituitary  fossa,  62 
Placoid  scales,  354 
Plagiaulax,  teeth  of,  494 
Plates,  medullary,  548 
Plethora,  673 
Pleurodont  dentition,  381 
Plexus,  infraorbital,  292 
Pliolophus,  teeth  of,  477 
Pneumogastric  nerve,  313 

abdominal  bi'anches,  320 

anastomotic  branches,  316 

auiicular  branch,  316 

cardiac  branches,  319 

communicating  branches,  313 

ini'erior  laryngeal  branch,  318 

left,  315 

meningeal  branch,  316 

oesophageal  branches,  319 

pharyngeal  branches,  316 

pulmonary  branches,  319 

right,  315 

superior  laryngeal  brancli,  316 

table  of,  315 
Porcupine,  teeth  of,  468 
Polyprotodoutia,  teeth  of,  494 
Polypus  of  ))ulp,  915 

structure  of,  915 

ti-eatment  of,  916 
Port  Jackson  shark,  teeth  of,  372 
Portio  dura,  304 

mollis,  310 
Posterior  auricular  artery,  227 

nerve,  308 

vein,  253 
basal  tubercle,  355 
cerebral  artery,  242 
cliuoid  foramen,  124 


Posterior  commimicating  arteries,  243 

condyloid  foramina,  53 

dental  foramen,  103 

ethmoid  artery,  240 

ethmoidal  cells,  79 
foramina,  75,  134 

facial  vein,  253 

fossa  of  brain-case,  1 23 

lacerated  foramen,  52,  123,  127 

median  fontanelle,  119 

nasal  aperture,  131 

occipital  sinus,  258 

palatine  canal,  84,  91 

region  of  the  skull,  128 

superior  dental  nerve,  290 

temporal  artery,  230 
nerve,  293 
Poultices  in  alveolar  abscess,  947 
Predisposing  causes  of  caries,  770 
Prefrontal  bone  of  catfishes,  368 

of  codfish,  368 
Premaxillary,  88 

bones  of  codfish,  368 
Premolar  of  dog,  354 
cingulum  of,  355 
crown  of,  354 
fangs  of,  354 
neck  of,  354 
parts  of,  354 
Premolars,  definition  of,  399 
Prevention  of  abrasion  of  teeth,  996 
Prevertebral  arteries,  228 

fascia,  157 
Primates,  teeth  of,  434 
Primitive  dentition,  characters  of,  392 

streak,  547 

trace,  543 
Priodon,  teeth  of,  410 
Prisms,  enamel,  601 
Proselurus,  teeth  of,  458 
Proboscidea,  teeth  of,  488 
Process,  alveolar,  of  inferior  maxilla,  103 
of  superior  maxillary  bone,  86 

anterior  clinoid,  62 

condyloid,  104 

coronoid,  104 

ethmoid,  94 

external  angular,  73 

frontal,  98 

hamular,  67 

internal  angular,  73 

jugular,  of  occipital  bone,  51 

laciirymal,  94 

malar,  85 

maxillary,  94 

ol'  malar  bones,  99 

mental,  101 

middle  clinoid,  63 

nasal,  of  superior  maxillary  bone,  85 

of  bones,  49 

olivary,  62 

orbital,  93 

of  malar  bones,  99 

palatal,  86,  91 

posterior  clinoid,  62 

pyramidal,  92 


INDEX  TO    VOLUME  I. 


1029 


Process,  sphenoidal,  93 

spinous,  49 

styloid,  60 

uncinate,  78 

vaginal,  67 

zygomatic,  99 
Processes,  condyloid,  128 

dentinal,  594 

pterygoid,  67 
Products  of  the   epiblast   and   mesoblast, 

556 
Prognosis  in  calcic  inflammation,  968 
Prosimiie,  teeth  of,  431 
Protopterus,  teeth  of,  377 
Proximal  end  of  bones,  49 

surfaces,  caries  in,  779 
manner  of  contact  of,  772 
Pseudeelurus,  teeth  of,  458 
Ptenoglossate  teeth,  347 
Pterygoid  artery,  234 

bones  of  codfish,  368 

fossa,  67,  104 

notch,  67 

processes,  67 

spinosus  muscle,  182 
Pterygoideus  proprius  muscle,  182 
Pterygo-maxillary  fissure,  130 

-palatine  artery,  235 
foramen,  130 
Pulmonary  veins,  247 
Pulmonates,  jaws  of,  349 

teeth  of,  349 
Pulp  calcification,  symptoms  of,  914 
treatment  of,  915 

-canals,  method  of  filling,  910 

-chamber,  dentinal  tumors  within,  872 

hard  formations  within,  864 

dental,  592,  636 

exposure  in  caries,  767 

irritation  in  dental  erosion,  1007 

mummified  condition  of,  893 

nerves  of,  655 

-nodules,  862 

polypus  of,  915 

-tissue,  nodules  in,  914 
Pulpitis,  origin  of,  889 

superficial,  891 
Pulps,  mummified,  910 
Pulse,  compressible,  666 

dicrotous,  670 

different  characters  of,  668 

examination  of,  653 

frequency  of,  664 

how  produced,  662 

in  aortic  obstruction,  671 

in  lesions  of  the  heart,  670 

intermittent,  670 

irregularities  of,  669 

qualities  of,  665 
Pus,  burrowing  of,  930 

of  chronic  alveolar  abscess,  937 
through  lower  maxilla,  942 

formation  of,  in  apical  space,  930 
Putrefactive  gases,  generation  of,  907 
Putrescent  pulp,  causes  of,  906 
treatment  of,  907 


Pyramidal  process,  92 
Pyramidales  nasi  muscle,  168 
Pyorrhoea  alveolaris,  954 

Q. 

Quadratus  menti,  173 
Quiuia  as  a  germicide,  909 

R. 

Rabbit,  deciduous  teeth  of,  469 

teeth  of,  469 
Racemose  glands,  203 
Rachiglossate  teeth,  346 
Rachiodon,  teeth  of,  388 
Radular  apparatus,  molluscan,  342 

of  mollusks,  instructions  for  examining, 
344 
Rami  of  inferior  maxilla,  103 
Rannis  cervicularis  princeps,  227 
Ranvier,  nodes  of,  267 
Ranine  artery,  222 
Rat,  teeth  o{,  466 
Raffish,  teeth  of,  375 
Rattlesnake,  fangs  of,  389 
Rays,  teeth  of,  373 
Red  blood-globules,  diapedesis  of,  679 

cells  of  marrow,  45 

marrow,  43 
Region  supplied  by  cranial  nerves,  277 
Regional  Anatomy,  35 
Regnard  on  caries,  735 
Regurgitation,  aortic,  671 
Removal  of  calculus,  963 

of  dental  pulp,  926 
Reproduction  of  epithelium,  708 

of  tissue,  702 
Reptilia,  teeth  of,  382 
Resorption  of  the  roots  of  temporary  teeth, 
922 

of  tLssue,  Ziegler  on,  529 

of  tissues,  530 
Results  of  fever,  717 
Rete  Malpighii,  617 
Reticular  laver  of  skin,  145 
Reticulum  stellate,  626,  640,  641 
Retrahens  aurem  muscle,  175 
Retzius,  broken  striae  of,  656 
Rheumatic  diathesis,  979 
Rhinoceros,  dental  evolution  of,  478 

teeth  of,  478 
Rhiphidoglossate  teeth,  347 
Ridge,  dental,  616 

infraorbital,  84 
Riggs's  disease,  954 
Right  common  carotid  artery,  216 
Risorus  muscle,  173 
Kivinus,  duct  of,  211 
Robertson  on  caries,  735 
Rodentia,  teeth  of,  466 
Roof  of  mouth,  137 

of  nasal  fossa,  135 
Root-fillings  after  alveolar  abscess,  952 

obtrusion  of,  into  apical  space,  923 
Roots  of  teeth,  absorption  of,  921 


1030 


INDEX  TO    VOLUME  I. 


Koots   of  temporary   teeth,  resorption  of, 

922 
Eostriiin  of  sphenoid  bone,  64 
Round  foramen,  65,  122 

S. 

Sacculns,  dental,  361 
Sagittal  suture,  116 
Salicylized  cotton,  965 
Salivary  calculus,  960,  961 

glands,  compound  tubular,  204 
increased  supply  to,  672 
muco-,  206 
true,  205 
Sanguinary  calculus,  958 
Sarcolemma,  162 
Scalers,  Cushing's,  964 
Scaphoid  fossa,  67,  126 
Scar  on  the  face,  operation  for,  952 
Scarpa,  foramina  of,  86,  136 
Schlenker  on  new  formations,  914 
Schroeder,  experiments  of,  754 
Scrofulous  diathesis,  979 
Sea-urchin  (Echinus),  dental  system  of,  340 

oral  apparatus  of,  339 
Seal,  teeth  of,  449 
Sealing  gingival  margins,  983 
Sebaceous  glands,  152,  560 
Secondai-y  dentine,  865-872,  911 
causes  producing,  912 
formation  of,  890 

deposit  in  exposure  of  dental  pulp,  886 

deposits  in  dental  erosion,  1007 

formations  resulting  from  metallic  fill- 
ings, 913 
resulting  from  wear  of  clasps,  913 
Secretory  glands  of  mucous  membrane,  201 
Sectorials,  characters  of,  402 
Segmentation  of  ovum,  543 
Sella  turcica,  62,  68 
Selenodontia,  teeth  of,  486 
Semilunar  ganglion,  284 
Semnopithecidffi,  teeth  of,  436 
Sensation,  nerves  of,  275 
Sensitive  dentine,  treatment  of  890 
Sensitiveness  of  the  dentine,  1006 

to  thermal  changes  in  dental  pulp,  843 
Sensory  functions  of  dental  pulp,  832 

nerves,  peripheral  end-organs  of,  271 

tract  in  teeth,  1009 
Septic  abscess,  treatment  of,  950 
Septum,  foetal,  551 

nasal,  135 
Serrated  sutures,  111 
Serumal  calculus,  958 
Seventh  nerve,  304 
Sharks,  teeth  of,  370 
Sharpey's  fibre,  40,  47 
Sheath  of  common  carotid  artery,  216 

of  Schwann,  or  neurolemma,  267 
Shock,  cause  of,  719 

from  dental  operations,  725-728 

liability  to,  724 

molecular  disturbances  in,  722 
symptoms  of,  723 


Shoulder-girdle  of  codfish,  365 
Sigmoid  groove,  61 

of  sphenoid  bone,  63 

notch,  104 
Simiidse,  teeth  of,  436 
Simple  exposure  of  dental  pulp,  890 

mucous  tubular  glands,  202 
Sinus,  anterior,  occipital  or  transverse,  261 

cavernous,  259 

circular,  260 

inferior  longitudinal,  258 
petrosal,  261 

longitudinal,  75 

lymph,  329 

maxillary,  89 

posterior  occipital,  258 

superior  longitudinal,  258 

sphenoidal,  63 

spheno-palatal,  259 

straight,  258 

superior  petrosal,  260 
Sinuses,  frontal,  73 

lateral,  259 

of  brain-case,  123,  257,  259 

venous,  of  the  cranium,  257 
Siphonaria,  teeth  of,  349 
Sirenia,  palatal  plates  of,  352 
Sixth  nerve,  282 
Skin,  141 

appendages  of,  147 

blood-vessels  of,  145 

derm,  corium,  or  cutis  vera  of,  144 

epidermis  of,  143 

epithelium  of,  614 

lymphatics  of,  145 

nerves  of,  145 

reticular  layer  of,  145 

papilla  of,  144 

pigment  of,  146 

stratum  corneum  of,  144 
granulosum  of,  144 
lucidum  of,  144 
Malpighii  of,  144 

tactile  corpuscles  of,  142,  146 

true,  144 
Skull,  50 

and  its  articulations  at  different  periods, 
118 

as  a  whole,  109 

facial  or  anterior  region  of,  131 

general  development  of,  109 

lateral  region  of,  1 28 

posterior  region  of  128 
Sloth,  three-toed,  teeth  of,  411 
Small  meningeal  artery,  233 
Smilodon,  teeth  of,  463 
Snakes,  poison-glands  of,  389 

teeth  of  388 
Sodium  carbonate  as  an  antiseptic,  909 
Soft  palate,  muscles  of  the,  192 
Softening  of  bone,  37 
Space,  apical,  918 
Spaces,  interglobular,  595,  766 
Special  sense,  nerves  of,  275 
Species,  transmutation  of,  520 
Sperm  whale,  teeth  of,  414 


INDEX  TO    VOLUME  I. 


1031 


Spheno-ethmoidal  nerves,  289 

-malar  suture,  117 

-maxillary  fissure,  65,  99,  130,  134 
fossa,  130 

-palatal  sinus,  259 

-palatine  foramen,  130,  136 
ganglion,  299 
nerve,  290 
notch,  92 
Sphenoid  bone,  62 

ethmoidal  spine,  62 

bone,  optic  gx-oove  of,  62 
spinous  process,  65 
Sphenoidal  fissures,  66 

process  of  palate  bone,  93 

sinuses,  63 

turbinated  bones,  64 
Sphygmographic  tracings,  667,  668 
Spinal  accessory  nerve,  320 

table  of, '320 
Sjiinosum,  foramen,  122 
Spinous  process  of  sphenoid  bone,  65,  127 
Sponge-grafting,  987 
Spongy  portion  of  bone,  35 
Spontaneous  generation,  521 
Squamo-tympanic  suture,  56 
Squamous  portion  of  temporal  bone,  56 

sutures.  111 
Stellate  bodies,  624 

cells,  624 

reticulum,  626,  640,  641 
Stapedius  or  tympanic  nerve,  307 
•Stellwagen  on  caries,  764 
Steno's  duct,  2()8 
Sterno-cleido-mastoid  muscle,  184 

-hyoid  muscle,  185 

-mastoid  artery,  220 

-thyroid  muscle,  186 
Stetson,  foramen  of,  86,  136 
Stoppings  used  in  capping,  898 
Straight  sinus.  258 
Stratum  corneum,  144 

granulosum,  144 

intermedium,  362,  642 
of  Hanover,  625 

lucidum,  144 

Malpighii,  144 
Strieker  on  inflammation,  699 
Structure  of  cells,  523 

of  dermal  denticles,  353 

of  enamel,  359 

of  gum,  955 

of  occipital  bone,  54 

of  parietal  bone,  71 

of  peridental  membrane,  918 
Styloid  process  of  temporal  bone,  60,  127 
Stylo-glossus  muscle,  191 
nerve,  308 

-hyoid  ligament,  189 
muscle,  189 
nerve,  308 

-mastoid  artery,  228 
foramen,  60,  127 

-maxillary  ligament,  115 

-pharyngeus  muscle,  194 
Stypolophus,  teeth  of,  422 


Subclavian  arteries,  243 
Sublingual  artery,  222 
fossa,  102 
gland,  210 
Submaxillary  duct,  210 
fascia,  157 
fossa,  102 
ganglion,  304 
gland,  209 
triangle,  188 
Submental  artery,  225 

vein,  251 
Subperiosteal  bone  formation,  47,  585 

inflammation,  944 
Succinea,  teeth  of,  349 
Sudoriferous  glands,  151 
Sulphui-etted  hydrogen,  generation  of,  in 
pulp,  907 
in  pulp-chamber,  893 
Superciliary  ridges,  73 
Superficial  fascia,  155 
jugular  ganglion,  311 
or  cranial  arteries,  227 
pulpitis,  891 

treatment  of,  904 
temporal  artery,  229 
branches  of,  229 
muscular  branches  of,  229 
vein,  252 
Superior  carotid  triangle,  188 
constrictor  muscle,  192 
coronary  artery,  225 
curved  lines  of  occipital  bone,  53 
hyoid  artery,  221 
labial  veins,  251 
laryngeal  artery,  220 
longitudinal  groove,  120 

sinus,  258 
maxillary  bone,  81 
bone,  alveoli  of,  87 
nerve,  290 

malar,  branch  of,  290 

orbital  or  temporo-malar  branch  of, 

290 
spheno-palatine  branch  of,  290 
temporal  branch  of,  290 
meatus  of  nasal  chamber,  79,  85,  136 
oblique  muscle,  177 
ophthalmic  vein,  261 
pedicle  of  sphenoid  bone,  67 
petrosal  sinus,  260 
rectus  muscle,  176 
thyroid  artery,  219 
turbinated  bone,  79 

crest,  92 
vena  cava,  248 
Suppuration  of  dental  pulp,  853-855 
Suprahyoid  aponeurosis,  188 

space,  muscles  of,  187 
Supramastoid  ridge,  56 
Supramaxillary  nerve,  309 
Supraorbital  arches,  73 
artery,  240 
nerve,  286 

notch  or  foi'amen,  73 
vein,  251 


1032 


INDEX  TO    VOLUME  I. 


Suprascapular  artery,  247 
Supratrochlear  nerve,  286 
Surgical  anatomy  of  the  basilar  process, 
55 

fever,  713 
Sutura,  111-115 
Suture,  coronal,  117 

fronto-nialar,  117 
-parietal,  117 
-sphenoidal,  117 

inter-parietal,  116 

lambdoid,  117 

occipito-mastoid,  51 
-parietal,  117 

parieto-inastoid,  1 17 
-sphenoid,  117 
-squamous,  117 

petro-basilar,  51 

sagittal,  116 

spheno-malar,  117 

squamo-tynipanic,  56 

temporo-parietal,  56 
Sutures  dentata,  111 

harmonic,  111 

of  cranial  vault,  116 

of  face,  117 

of  skull,  111,  115 

serrata.  111 

squamosa,  111 
Sweat-glands,  151 
Swelling  in  inflammation,  693 

of  dental  pulp,  839 
Sympathetic  ganglia  of  fifth  pair  of  nerves, 

297 
Symphysis  menti,  132 
Symptomatology  of  dental  pulp,  832 
Symptoms  of  shock,  723 
Synchondrosis  articulation,  112 
Synostosis,  118 
Synovial  sac,  114 
Systemic  veins,  247 

T. 

Table  of  the  branches  of  the  facial  nerve, 
305 
of  the  glosso-pharyngeal  nerve,  311 
of  the  pneumogastric  nerve,  315 

of  the  cranial  sympathetic  ganglia,  297 

showing  distribution  of  fifth  nerve,  287 
Tactile  corpuscles,  142,  146 
Tieniodonta,  teeth  of,  434 
Tfenioglossate  teeth,  347 
Tapiridte,  teeth  of,  478 
Tarsius  spectrum,  teeth  of,  431 
Tatusia  hybridus,  teeth  of,  409 
Taxeopoda,  teeth  of,  470 
Tebennophorus,  jaw  of,  349 
Teeth,  calcification  of,  303 

development  of,  360,  609 

ecderonic,  origin  of,  352 

enderonic,  origin  of,  353 

epiblastic,  derivation  of,  353 

faulty  formation  of,  770 

general  definition  of,  352 

histology  of,  356 


Teeth,  hypoblastic  derivation  of,  353 

occlusion  of,  in  man,  445 

origin  of,  in  invertebrata,  352 
of,  in  vertebrata,  352 
Temnocyon,  teeth  of,  453 
Temperature  in  fever,  711 

in  inflammation,  693 
Temporo-facial  nerve,  308 

-maxillary  articulation,  112 
interarticulating  disc  of,  114 
ligaments  of,  113 
synovial  sac  of,  114 
vein,  252 
Temporal  bone,  55 

fascia,  179 

fossa,  128 

muscle,  180 
Tendo-oculi  muscle,  169 
Tendons,  158 
Tenon,  capsule  of,  178 

fascia  of,  178 
Tensor-palati  muscle,  197 

-tarsi  muscle,  169 
Tenth  nerve,  313 

Terms  used  in  describing  bones,  49 
Thermal    changes,   sensibilitv    of   dental 
pulp  to,  832-834 

influences  afiecting  the  dental  pulp,  888 
Thoracic  duct,  330 
Three-toed  sloth,  teeth  of,  411 
Thrombosis,  679 
Thrombus,  formation  of,  681 
Thylocoleo,  teeth  of,  497 
Thyro-hyoid  muscle,  186 

nerve,  324 
Thyroid  artery,  superior,  219 

axis,  246 
Tillodonta,  teeth"  of,  433 
Tin  in  caries,  811 
Tissue,  areolar,  154 

cartilage,  35 

changes  in  hypersemia,  845 
in  inflammation,  695 
of  dental  pulp,  849 

connective,  35_ 

fibre,  connective,  35 

granulations,  704 

muscular,  159 

reproduction  of,  702 

resorption  of,  530 
Tobacco,  action  of,  on  caries,  808 

smoke,  action  of,  on  caries  fungi,  809 
Tomes  on  calcification,  573 

on  caries,  741 

processes,  642 
Tonsillar  artery,  224 

nerves,  312 

space,  213 
Tonsils,  213 

infra-  or  pharyngeal,  214 
Toothbrush,  mode  of  using,  966 
Tooth-cartilage,  356 

-germ,  361 

-pulp,  357,  592,  636 
arteries  of,  358 
lateral  processes  of,  358 


INDEX  TO    VOLUME  I. 


1033 


Torcular  Heropliili,  124,  258 

Toxodontia,  teeth  of,  476 

Toxoglossa,  teeth  of,  343 

Toxoglossate  (arrow-toothed)  dentition,  346 

Trabecule  cranii,  109 

Tracheal  ai'tery,  247 

Tracings,  sphygniographic,  667,  668 

Transplantation  of  epitheliuin,  708 

Transverse  artery,  220 

facial  artery,  229 
vein,  253 
Transversalis  colli  artery,  247 
Treatment  of  alveolar  abscess,  944 

of  apical  [)ericementitis,  926 

of  calcic  inflammation,  963 

of  chronic  alveolar  abscess,  947 

of  phagedenic  pericementitis,  979 
Triangle,  submaxillary,  188 

supra-carotid,  188 
Trifacial  nerve,  282 
Trigeminus  nerve,  282 
Triisodon,  teeth  of,  424 
Tritonium  (trumpet  conch),  jaw  of,  334 
Trochlear  nerve,  281 

fossa  or  tubercles,  75 
Trochlearis  muscle,  177 
True  salivary  glands,  205 

skin,  144 
Trumpet  conch  (Tritonium),  jaw  of,  343 
Tubercle  of  temporal  bone,  56 

posterior  basal,  355 
Tubercle  or  tuberosity,  49 
Tubercles,  genial,  102 
Tuberosity  of  superior  maxillary  bone,  85 
Tubes,  dental,  356 
Tumors,   dentinal,   within   pulp-chamber, 

872 
Tunic,  inner,  640 
Turbinated  bone,  inferior,  79 
middle,  79 
superior,  79 

crest,  inferior,  92 
superior.  92 
Twelfth  nerve,  322 
Tympanic  artery,  232 

nerve,  311 

portion  of  temporal  bone,  60 

U. 

Ulceration,  702 
Uncinate  process,  78 
Unguiculate  series,  teeth  of,  416 
Ungulata,  teeth  of,  476 
Ungulate  series,  classification  of,  470 
teeth  of,  469 

V. 

Vaginal  process  of  sphenoid  bone,  67 

of  temporal  bone,  60 
Vampires,  teeth  of  465 
Variations  in  hardness  of  enamel,  602 

of  common  carotid  artery,  218 
Variet}'  of  muscles,  165 
Vasa  aflerentia,  328 


Vasa  efferentia,  328 

vasorum,  327 
Vaso-motor  nerves,  influence  on  the  circu- 
lation, 673 
Veins,  247 

angular,  249 

anterior  jugular,  255 

common  temporal,  252 

deep  facial,  251 

diploic,  261 

emissary,  262 

external  jugulai',  255 

facial  or  anterior  facial,  249 

frontal,  250 

inferior  ophthalmic,  261 
palpebral,  251 
thyroid,  248 

innominate  or  brachio-cephalic,  248 

internal  jugular.  256 
maxillary,  253 

left  innominate,  248 

lingual,  254 

middle  temporal,  253 

occipital,  254 

of  head  and  neck,  281 

of  neck,  254 

of  orbit,  261 

pharyngeal,  254 

posterior  auricular,  253 
facial,  253 

pulmonary,  247 

right  innominate,  248 

submaxillary,  251 

submental,  251 

superficial  temporal,  252 

superior  labial,  251 
ophthalmic,  261 
or  descending  vena  cava,  248 

supraorbital,  251 

systemic,  247 

temporo-maxillary,  252 

transverse  facial,  253 
Vena  cava  superior,  248 
Venous  sinuses  of  cranium,  257 
Vents  for  putrefied  pulp-canals,  910 
Vertebral  artery,  245 
Vertebrata,  teeth  of,  351 
Vertical  crest  of  nasal  bones,  97 

plate  of  palate  bone,  92 
Vesali,  foramen  of,  122 
Vessels,  lymphatic,  325 
Vidian  arterv,  235 

canal,  65,  123 
Virginia  deer,  teeth  of,  488 

opossum,  teeth  of,  495 
Voluntary  muscles,  160 
Vomer,  SO 

development  of,  81 

W. 

Walls  of  the  brain-case,  120 
Walrus,  teeth  of,  451 
Wandering  cells,  692 
Wai-t-hog,  teeth  of  485 
Watt  on  caries,  745 


1034 


INDEX  TO    VOLUME  I. 


Weasels,  teeth  of,  464 

Wedl  on  polypus  of  the  pulp,  916 

Weight  of  bone,  37 

Westcot,  experiments  of,  743 

Wharton,  jelly  of  566 

Wharton's  duct,  210 

White  blood-corpuscles   in   inflammation, 

695 
globules,  diapedesis  of,  692 
corpuscles,  532 
White,   J.    D.,    formula    for   nerve-paste, 

900 
Willis,  circle  of,  242 
Wormian  bones,  118 
Wrisbei'g,  nerve  of,  310 


Y. 


Yellow  marrow,  43 

Z. 

Zeuglodon,  teeth  of,  415 
Ziegler  on  cell-proliferation,  526 

on  resorption  of  tissue,  529 
Zona  pelhicida,  547 
Zonites,  jaw  of,  349 
Zygomatic  fossa,  129 

process  of  malar  bone,  99 

of  temporal  bone,  56 

Zygomaticus  major  muscle,  172 

minor  muscle,  172 


END    OF    VOLUME    I. 


V'  JAN 


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